In higher plants and green algae two types of thylakoids are distinguished, granum (stacked) and stroma (unstacked) thylakoids. They form a three-dimensional (3D) network with large lateral heterogeneity: photosystem II (PSII) and the associated main chlorophyll a/b light-harvesting complex (LHCII) are found predominantly in the stacked region, while PSI and LHCI are located mainly in the unstacked region of the membrane. This picture emerged from the discovery of the physical separation of the two photosystems (Boardman and Anderson 1964). Granal chloroplasts possess significant flexibility, which is essential for optimizing the photosynthetic machinery under various environmental conditions. However, our understanding concerning the assembly, structural dynamics and regulatory functions of grana is far from being complete. In this paper we overview the significance of the three-dimensional structure of grana in the absorption properties, ionic equilibrations, and in the diffusion of membrane components between the stacked and unstacked regions. Further, we discuss the role of chiral macrodomains in the grana. Lateral heterogeneity of thylakoid membranes is proposed to be a consequence of the formation of macrodomains constituted of LHCII and PSII; their long range order permits long distance migration of excitation energy, which explains the energetic connectivity of PSII particles. The ability of macrodomains to undergo light-induced reversible structural changes lends structural flexibility to the granum. In purified LHCII, which has also been shown to form stacked lamellar aggregates with long range chiral order, excitation energy migrates for large distances; these macroaggregates are also capable of undergoing light-induced reversible structural changes and fluorescence quenching. Hence, some basic properties of grana appear to originate from its main constituent, the LHCII.
{"title":"Role of LHCII-containing macrodomains in the structure, function and dynamics of grana","authors":"G. Garab, L. Mustárdy","doi":"10.1071/PP99069_C1","DOIUrl":"https://doi.org/10.1071/PP99069_C1","url":null,"abstract":"In higher plants and green algae two types of thylakoids are distinguished, granum (stacked) and stroma (unstacked) thylakoids. They form a three-dimensional (3D) network with large lateral heterogeneity: photosystem II (PSII) and the associated main chlorophyll a/b light-harvesting complex (LHCII) are found predominantly in the stacked region, while PSI and LHCI are located mainly in the unstacked region of the membrane. This picture emerged from the discovery of the physical separation of the two photosystems (Boardman and Anderson 1964). Granal chloroplasts possess significant flexibility, which is essential for optimizing the photosynthetic machinery under various environmental conditions. However, our understanding concerning the assembly, structural dynamics and regulatory functions of grana is far from being complete. In this paper we overview the significance of the three-dimensional structure of grana in the absorption properties, ionic equilibrations, and in the diffusion of membrane components between the stacked and unstacked regions. Further, we discuss the role of chiral macrodomains in the grana. Lateral heterogeneity of thylakoid membranes is proposed to be a consequence of the formation of macrodomains constituted of LHCII and PSII; their long range order permits long distance migration of excitation energy, which explains the energetic connectivity of PSII particles. The ability of macrodomains to undergo light-induced reversible structural changes lends structural flexibility to the granum. In purified LHCII, which has also been shown to form stacked lamellar aggregates with long range chiral order, excitation energy migrates for large distances; these macroaggregates are also capable of undergoing light-induced reversible structural changes and fluorescence quenching. Hence, some basic properties of grana appear to originate from its main constituent, the LHCII.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89140751","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The amelioration of Na toxicity by supplementation of Ca in the growth medium was investigated in wheat with the aims of (1) identifying the Ca-dependent processes that determine the growth responses and (2) defining the limits to Ca effects on these processes. Growth of wheat seedlings was strongly inhibited by 150 mM NaCl but improved as the Ca concentration in the nutrient medium was increased up to 2.34 mM. Further increasing Ca to 10 mM did not increase growth, nor did foliar application of Ca. Even at high concentrations of Ca, the maximum growth was only approximately 50% of the growth at low salinity. We conclude that the main component of improved growth caused by Ca was via its apoplastic effects on the transport of Na and K across the root plasma membrane, rather than by increasing root or shoot Ca concentrations. There was no evidence that high salinity inhibited Ca uptake to the shoot. The limits to improvement of growth by Ca appear to relate to the fact that, although Ca is able to ameliorate the toxicity caused by high intracellular Na, it is not able to overcome the osmotic deficits associated with high salinity.
在小麦中研究了在生长培养基中添加Ca对Na毒性的改善，目的是(1)确定决定生长反应的Ca依赖过程，(2)确定Ca对这些过程的影响限度。150 mM NaCl对小麦幼苗的生长有强烈抑制作用，但当营养介质中Ca浓度增加到2.34 mM时，小麦幼苗的生长得到了改善。进一步增加Ca至10 mM并没有促进生长，叶面施用Ca也没有促进生长。即使在高浓度Ca下，小麦幼苗的最大生长也只有低盐下生长的50%左右。我们得出结论，Ca促进生长的主要成分是通过其对Na和K在根质膜上的运输的外胞效应，而不是通过增加根或茎部Ca浓度。没有证据表明高盐度会抑制茎部对钙的吸收。钙对生长改善的限制似乎与这样一个事实有关，尽管钙能够改善由高细胞内钠引起的毒性，但它不能克服与高盐度相关的渗透缺陷。
{"title":"The limits of sodium/calcium interactions in plant growth","authors":"R. Reid, F. A. Smith","doi":"10.1071/PP00030","DOIUrl":"https://doi.org/10.1071/PP00030","url":null,"abstract":"The amelioration of Na toxicity by supplementation of Ca in the growth medium was investigated in wheat with the aims of (1) identifying the Ca-dependent processes that determine the growth responses and (2) defining the limits to Ca effects on these processes. Growth of wheat seedlings was strongly inhibited by 150 mM NaCl but improved as the Ca concentration in the nutrient medium was increased up to 2.34 mM. Further increasing Ca to 10 mM did not increase growth, nor did foliar application of Ca. Even at high concentrations of Ca, the maximum growth was only approximately 50% of the growth at low salinity. We conclude that the main component of improved growth caused by Ca was via its apoplastic effects on the transport of Na and K across the root plasma membrane, rather than by increasing root or shoot Ca concentrations. There was no evidence that high salinity inhibited Ca uptake to the shoot. The limits to improvement of growth by Ca appear to relate to the fact that, although Ca is able to ameliorate the toxicity caused by high intracellular Na, it is not able to overcome the osmotic deficits associated with high salinity.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77609721","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The influence of water stress on ATP and p-nitrophenyl phosphate (PNPP) hydrolysis by plasma mem-brane ATPases was investigated using plasma membrane vesicles purified from soybean hypocotyls by the sucrose gradient centrifugation method. Results showed that ATPase activity was reduced after 10% polyethylene glycol (PEG) 6000 treatment for 12 h. Water stress also moved the optimal pH from 6.5 to 7.0. A significant decrease in PNPP hydrolysis was observed under PEG treatment. The Km for PNPP hydrolysis was shifted from 2.3042 0.0009 to 2.5048 0.0346 mmol L –1 . Moreover, PNPP hydrolysis was more sensitive to vanadate after PEG treatment, while inhibition of ATP hydrolysis by hydroxylamine was not affected. Our experimental results indicated that water stress changed the catalytic mechanism of the plasma membrane H + -ATPase through affecting the dephosphorylation process catalysed by its phosphatase domain.
{"title":"Water stress inhibits p-nitrophenyl phosphate hydrolysis activity of the plasma membrane H+-ATPase from soybean hypocotyls","authors":"Q. Qiu, Nan Zhang","doi":"10.1071/PP00017","DOIUrl":"https://doi.org/10.1071/PP00017","url":null,"abstract":"The influence of water stress on ATP and p-nitrophenyl phosphate (PNPP) hydrolysis by plasma mem-brane ATPases was investigated using plasma membrane vesicles purified from soybean hypocotyls by the sucrose gradient centrifugation method. Results showed that ATPase activity was reduced after 10% polyethylene glycol (PEG) 6000 treatment for 12 h. Water stress also moved the optimal pH from 6.5 to 7.0. A significant decrease in PNPP hydrolysis was observed under PEG treatment. The Km for PNPP hydrolysis was shifted from 2.3042 0.0009 to 2.5048 0.0346 mmol L –1 . Moreover, PNPP hydrolysis was more sensitive to vanadate after PEG treatment, while inhibition of ATP hydrolysis by hydroxylamine was not affected. Our experimental results indicated that water stress changed the catalytic mechanism of the plasma membrane H + -ATPase through affecting the dephosphorylation process catalysed by its phosphatase domain.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76283546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
U. Jin, B. Jin, Jin-Woo Lee, Young-Su Cho, O. Kwon, Young-Kil Kim, C. Chung
We have cloned and characterised a cDNA (PrLeg) coding for a methionine-rich storage protein, which is reported for the first time in perilla (Perilla frutescens (L.) Britt. var. Japonica) seeds, homologous to the 11S legumin-like storage proteins. The most significant feature of the PrLeg precursor protein is that it has the highest content of methionine residues among the 11S legumin-like storage proteins examined so far. Another feature is that the deduced amino acid sequences of the PrLeg protein are phylogenetically close to the sequence groups derived from evolutionally ancient states of the 11S legumin-like storage proteins, or from gymnospermous seed storage proteins, such as Magnolia, Asarum, Dioscorea, Cryptomeria, Metasequoia and Ginkgo. In contrast, with the exception of sesame, relatively low phylogenetic relationships are determined between the PrLeg sequence group and those derived from crop plants, such as soybean, pea, broad bean, rape, pumpkin, rice, coffee and citrus. Southern blot analysis suggests that there may be several copy numbers of thePrLeg genes and their seed-specific expression patterns at the transcriptional level were confirmed by northern hybridisation analysis.
{"title":"Characterisation of a methionine-rich storage protein cDNA from perilla (Perilla frutescens) seeds","authors":"U. Jin, B. Jin, Jin-Woo Lee, Young-Su Cho, O. Kwon, Young-Kil Kim, C. Chung","doi":"10.1071/PP99159","DOIUrl":"https://doi.org/10.1071/PP99159","url":null,"abstract":"We have cloned and characterised a cDNA (PrLeg) coding for a methionine-rich storage protein, which is reported for the first time in perilla (Perilla frutescens (L.) Britt. var. Japonica) seeds, homologous to the 11S legumin-like storage proteins. The most significant feature of the PrLeg precursor protein is that it has the highest content of methionine residues among the 11S legumin-like storage proteins examined so far. Another feature is that the deduced amino acid sequences of the PrLeg protein are phylogenetically close to the sequence groups derived from evolutionally ancient states of the 11S legumin-like storage proteins, or from gymnospermous seed storage proteins, such as Magnolia, Asarum, Dioscorea, Cryptomeria, Metasequoia and Ginkgo. In contrast, with the exception of sesame, relatively low phylogenetic relationships are determined between the PrLeg sequence group and those derived from crop plants, such as soybean, pea, broad bean, rape, pumpkin, rice, coffee and citrus. Southern blot analysis suggests that there may be several copy numbers of thePrLeg genes and their seed-specific expression patterns at the transcriptional level were confirmed by northern hybridisation analysis.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73288676","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Theory (Craig and Gordon 1965; Dongmann et al. 1974; Sternberg et al. 1986; Farquhar and Lloyd 1993) suggests that the oxygen isotope ratio (d 18 O) of plant material should reflect the evaporative conditions under which the material was formed, so that differences in stomatal conductance should show up in plant d 18 O. To test this theory we measured the oxygen isotope ratio of organic matter from flag leaves at anthesis and grain at harvest from eight cultivars of spring wheat (Triticum aestivum L.) grown under irrigation in each of three seasons in Mexico. The cultivars ranged widely in stomatal conductance and in average grain yield, with which conductance was positively correlated. Supporting theory, the oxygen isotope ratio of flag leaves (d 18 Ol) was found to correlate negatively with stomatal conductance for two of the three seasons. The significant correlations are consistent with high conductance cultivars having lower leaf temperatures and kinetic fractionation factors, and higher vapour pressure fractionation factors and Peclet numbers, all of which combine to result in less enriched d 18 Ol. Yield (grain weight per square meter) was also found to be significantly negatively correlated with d 18Ol in two of the three seasons. d 18 Ol was as good a predictor of yield as stomatal conductance, and significantly better than carbon isotope discrimination. Correlations between grain d 18 O (d 18 Og) and physiological parameters were less clear. Significant negative correlations between d 18 Og and stomatal conductance, leaf temperature and yield were found only during the first season. By measuring the oxygen isotope ratio of cellulose extracted from leaf samples, the difference in fractionation factors (ecp) for cellulose and whole leaf tissue was assessed. ecp was found to be variable, and more negative when d 18 Oc and d 18 Ol were lower. Cultivar means for d 13 C and d 18 O of whole leaf material were found to be significantly positively related, and the factors required to produce such a relationship are discussed.
理论(克雷格和戈登1965;Dongmann et al. 1974;Sternberg et al. 1986;法夸尔和劳埃德1993)表明,氧同位素比值(d 18 O)的植物应该反映材料的蒸发条件下形成,因此,气孔导度的差异应该出现在植物维18 O .来测试这个理论我们测量有机质的氧同位素比率从开花期旗叶和谷物收获从春天的8个品种小麦(小麦l .)在灌溉种植在三个赛季在墨西哥。各品种气孔导度和平均产量差异较大，且与气孔导度呈正相关。旗叶氧同位素比值(d18ol)与气孔导度在3个季节中有2个季节呈负相关。高导品种叶片温度和动力分馏因子较低，蒸气压分馏因子和Peclet数较高，这些因素加在一起导致d - 18 Ol的富集程度较低。产量(每平方米粒重)在3个季节中有2个季节与d 18Ol呈显著负相关。d18ol与气孔导度一样能很好地预测产量，且显著优于碳同位素判别。籽粒d18o (d18og)与生理参数之间的相关性不太清楚。d18og仅在第一季与气孔导度、叶温和产量呈显著负相关。通过测定叶片样品中纤维素的氧同位素比值，评价了纤维素与全叶组织的分馏因子(ecp)差异。ecp是可变的，当d18oc和d18ol较低时，ecp呈负相关。全叶材料的d13c和d18o的品种平均值呈显著正相关，并讨论了产生这种关系所需的因素。
{"title":"Oxygen isotope ratio of leaf and grain material correlates with stomatal conductance and grain yield in irrigated wheat","authors":"M. Barbour, R. Fischer, K. Sayre, G. Farquhar","doi":"10.1071/PP99041","DOIUrl":"https://doi.org/10.1071/PP99041","url":null,"abstract":"Theory (Craig and Gordon 1965; Dongmann et al. 1974; Sternberg et al. 1986; Farquhar and Lloyd 1993) suggests that the oxygen isotope ratio (d 18 O) of plant material should reflect the evaporative conditions under which the material was formed, so that differences in stomatal conductance should show up in plant d 18 O. To test this theory we measured the oxygen isotope ratio of organic matter from flag leaves at anthesis and grain at harvest from eight cultivars of spring wheat (Triticum aestivum L.) grown under irrigation in each of three seasons in Mexico. The cultivars ranged widely in stomatal conductance and in average grain yield, with which conductance was positively correlated. Supporting theory, the oxygen isotope ratio of flag leaves (d 18 Ol) was found to correlate negatively with stomatal conductance for two of the three seasons. The significant correlations are consistent with high conductance cultivars having lower leaf temperatures and kinetic fractionation factors, and higher vapour pressure fractionation factors and Peclet numbers, all of which combine to result in less enriched d 18 Ol. Yield (grain weight per square meter) was also found to be significantly negatively correlated with d 18Ol in two of the three seasons. d 18 Ol was as good a predictor of yield as stomatal conductance, and significantly better than carbon isotope discrimination. Correlations between grain d 18 O (d 18 Og) and physiological parameters were less clear. Significant negative correlations between d 18 Og and stomatal conductance, leaf temperature and yield were found only during the first season. By measuring the oxygen isotope ratio of cellulose extracted from leaf samples, the difference in fractionation factors (ecp) for cellulose and whole leaf tissue was assessed. ecp was found to be variable, and more negative when d 18 Oc and d 18 Ol were lower. Cultivar means for d 13 C and d 18 O of whole leaf material were found to be significantly positively related, and the factors required to produce such a relationship are discussed.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74671788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cyanogenesis is the process by which plantsrelease hydrogen cyanide (HCN) from endogenous cyanide-containing compoundsand is thought to play a role in plant defence against generalist herbivores.Cyanogenesis is poorly understood in natural populations, and has been littlestudied in tree species. In this paper we present the first systematic surveyof cyanogenesis in the economically and ecologically important genusEucalyptus. We document variability in both theconcentration of the cyanogenic glycoside, prunasin, and the accompanyingdegradative b-glucosidase in a woody plant for the first time. Leaves of 96E. cladocalyx F. Muell. trees growing in naturalpopulations on Kangaroo Island, South Australia were analysed. All trees werecyanogenic, containing both cyanogenic glycosides and active b-glucosidase.Cyanogenic glycoside concentration varied by over two orders of magnitude. Theb-glucosidase activity varied widely as well, but plants high in cyanogenicglycosides did not necessarily have higher enzyme activity. A significantproportion of the variation in cyanogenic glycoside concentration can beaccounted for by the variation in leaf nitrogen. Most of the variation,however, appears to be the result of genetic polymorphism, which is inheritedindependently of the level of activity of the degradativeb-glucosidase.
{"title":"Polymorphism in cyanogenic glycoside content and cyanogenic β-glucosidase activity in natural populations of Eucalyptus cladocalyx","authors":"R. Gleadow, I. E. Woodrow","doi":"10.1071/PP00004","DOIUrl":"https://doi.org/10.1071/PP00004","url":null,"abstract":"Cyanogenesis is the process by which plantsrelease hydrogen cyanide (HCN) from endogenous cyanide-containing compoundsand is thought to play a role in plant defence against generalist herbivores.Cyanogenesis is poorly understood in natural populations, and has been littlestudied in tree species. In this paper we present the first systematic surveyof cyanogenesis in the economically and ecologically important genusEucalyptus. We document variability in both theconcentration of the cyanogenic glycoside, prunasin, and the accompanyingdegradative b-glucosidase in a woody plant for the first time. Leaves of 96E. cladocalyx F. Muell. trees growing in naturalpopulations on Kangaroo Island, South Australia were analysed. All trees werecyanogenic, containing both cyanogenic glycosides and active b-glucosidase.Cyanogenic glycoside concentration varied by over two orders of magnitude. Theb-glucosidase activity varied widely as well, but plants high in cyanogenicglycosides did not necessarily have higher enzyme activity. A significantproportion of the variation in cyanogenic glycoside concentration can beaccounted for by the variation in leaf nitrogen. Most of the variation,however, appears to be the result of genetic polymorphism, which is inheritedindependently of the level of activity of the degradativeb-glucosidase.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90960731","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Activities of the soluble and membrane-boundisoforms of Ca 2+ calmodulin (CaCam)-dependent and-independent NAD + kinases, were followed in theembryos during the culture of dormant (D) and after-ripened (AR) seeds ofAvena sativa L. Embryos of D and AR seeds differ mainly in the evolution ofmembrane-bound activities, the majority of which are CaCam-dependent andlinked to mitochondria. The in vivo application ofgibberellic acid, CaCl2 andH2O2, which enhanced germination,induced an enhancement of all CaCam-dependent isoforms. Trifluoperazine (TFP),a calmodulin antagonist, greatly enhanced all CaCam-dependent isoforms andabolished the differences between the NAD + kinaseactivities of the two kinds of embryo. In addition, TFP rendered embryosunable to resume axis growth, probably due to pleiotropic effects. In contrastto H2O2, the reducing agentdithiothreitol diminished the soluble CaCam-dependent enzyme and blocked thegermination of both types of seed, whereas it increased the dependentmembrane-bound activities. The results demonstrate (1) that theCaCam-dependent NAD + kinase isoforms —amongst which is the isoform bound to mitochondrial membranes — play animportant role at the end of sensu stricto germinationand during the following growth of Avena sativa; and (2)that an excess of activity of these isoforms could be markers of stress orlethal conditions.
{"title":"Changes in soluble and membrane-bound isoforms of calcium-calmodulin-dependent and -independent NAD+ kinase, during the culture of after-ripened and dormant seeds of Avena sativa","authors":"S. Gallais, M. P. D. Crescenzo, D. Laval-Martin","doi":"10.1071/PP00010","DOIUrl":"https://doi.org/10.1071/PP00010","url":null,"abstract":"Activities of the soluble and membrane-boundisoforms of Ca 2+ calmodulin (CaCam)-dependent and-independent NAD + kinases, were followed in theembryos during the culture of dormant (D) and after-ripened (AR) seeds ofAvena sativa L. Embryos of D and AR seeds differ mainly in the evolution ofmembrane-bound activities, the majority of which are CaCam-dependent andlinked to mitochondria. The in vivo application ofgibberellic acid, CaCl2 andH2O2, which enhanced germination,induced an enhancement of all CaCam-dependent isoforms. Trifluoperazine (TFP),a calmodulin antagonist, greatly enhanced all CaCam-dependent isoforms andabolished the differences between the NAD + kinaseactivities of the two kinds of embryo. In addition, TFP rendered embryosunable to resume axis growth, probably due to pleiotropic effects. In contrastto H2O2, the reducing agentdithiothreitol diminished the soluble CaCam-dependent enzyme and blocked thegermination of both types of seed, whereas it increased the dependentmembrane-bound activities. The results demonstrate (1) that theCaCam-dependent NAD + kinase isoforms —amongst which is the isoform bound to mitochondrial membranes — play animportant role at the end of sensu stricto germinationand during the following growth of Avena sativa; and (2)that an excess of activity of these isoforms could be markers of stress orlethal conditions.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87124427","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The role of the xanthophyll cycle in the protection against photoinhibition of photosystem II (PSII) induced by chilling in moderate light was investigated in leaves of eight species or varieties of higher plants differing widely in chilling sensitivity. The extent of photoinhibition measured as the increase in the slowly reversible fluorescence quenching (qI) was found not to correlate with the overall amount of zeaxanthin formed during photo-inhibitory treatment. On the other hand, a strong, positive correlation existed between qI and the rate difference between the development of the rapidly relaxing, DpH-dependent quenching component (qf) and the formation of zeaxanthin (DR) across all examined species or varieties. There was also found to be a weaker, negative correlation between qI and the rate of zeaxanthin formation. Ascorbate feeding markedly increased the resistance to chilling-induced photoinhibition mainly by increasing the rate of zeaxanthin formation and therefore by decreasing DR. The possible implications of the present findings in explaining the mechanistic basis for the reversible, sustained photo-inhibition are discussed. It is suggested that the xanthophyll cycle may play a critical role in the protection of the thylakoid lumen against over-acidification and the resulting photoinhibition of PSII reaction centers.
{"title":"Photoprotection in chilling-sensitive and -resistant plants illuminated at a chilling temperature: role of the xanthophyll cycle in the protection against lumen acidification.","authors":"C. Xu, Liangbi Li, T. Kuang","doi":"10.1071/PP00009","DOIUrl":"https://doi.org/10.1071/PP00009","url":null,"abstract":"The role of the xanthophyll cycle in the protection against photoinhibition of photosystem II (PSII) induced by chilling in moderate light was investigated in leaves of eight species or varieties of higher plants differing widely in chilling sensitivity. The extent of photoinhibition measured as the increase in the slowly reversible fluorescence quenching (qI) was found not to correlate with the overall amount of zeaxanthin formed during photo-inhibitory treatment. On the other hand, a strong, positive correlation existed between qI and the rate difference between the development of the rapidly relaxing, DpH-dependent quenching component (qf) and the formation of zeaxanthin (DR) across all examined species or varieties. There was also found to be a weaker, negative correlation between qI and the rate of zeaxanthin formation. Ascorbate feeding markedly increased the resistance to chilling-induced photoinhibition mainly by increasing the rate of zeaxanthin formation and therefore by decreasing DR. The possible implications of the present findings in explaining the mechanistic basis for the reversible, sustained photo-inhibition are discussed. It is suggested that the xanthophyll cycle may play a critical role in the protection of the thylakoid lumen against over-acidification and the resulting photoinhibition of PSII reaction centers.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86584342","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The effect of the herbicidally active compound N-2-(5-chloro-pyridyl)aminomethylene bisphosphonic acid (Cl-pyr-AMBPA), previously found in vitro to inhibit the activity of the first enzyme in the shikimate pathway 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase, was investigated in vivo on suspension cultured cells of Nicotiana plumbaginifolia Viviani. Amino acid pool measurement showed an actual reduction of tyrosine, tryptophan and phenylalanine level following the addition of the compound to the growth medium. However, an even stronger effect was noticed for other amino acids, mainly glutamine. When the activity of the enzymes involved in the glutamate cycle was measured in the presence of Cl-pyr-AMBPA, glutamate synthase was unaffected, while glutamine synthetase was significantly inhibited. Contrary to the herbicide phosphinothricin, the inhibitor bound reversibly to the enzyme. Kinetic analysis accounted for an inhibition of uncompetitive type with respect to ammonium, glutamate and ATP, withKivalues of 113, 97 and 39 M, respectively. Only the exogenous supply of a mixture of glutamine and aromatic amino acids relieved cell growth inhibition, suggesting that the phytotoxic properties of Cl-pyr-AMBPA are due to inhibition of key enzymes in both the corresponding pathways.
{"title":"The herbicidally active compound N-2-(5-chloro-pyridyl) aminomethylene bisphosphonic acid acts by inhibiting both glutamine and aromatic amino acid biosynthesis","authors":"G. Forlani, B. Lejczak, P. Kafarski","doi":"10.1071/PP00011","DOIUrl":"https://doi.org/10.1071/PP00011","url":null,"abstract":"The effect of the herbicidally active compound N-2-(5-chloro-pyridyl)aminomethylene bisphosphonic acid (Cl-pyr-AMBPA), previously found in vitro to inhibit the activity of the first enzyme in the shikimate pathway 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase, was investigated in vivo on suspension cultured cells of Nicotiana plumbaginifolia Viviani. Amino acid pool measurement showed an actual reduction of tyrosine, tryptophan and phenylalanine level following the addition of the compound to the growth medium. However, an even stronger effect was noticed for other amino acids, mainly glutamine. When the activity of the enzymes involved in the glutamate cycle was measured in the presence of Cl-pyr-AMBPA, glutamate synthase was unaffected, while glutamine synthetase was significantly inhibited. Contrary to the herbicide phosphinothricin, the inhibitor bound reversibly to the enzyme. Kinetic analysis accounted for an inhibition of uncompetitive type with respect to ammonium, glutamate and ATP, withKivalues of 113, 97 and 39 M, respectively. Only the exogenous supply of a mixture of glutamine and aromatic amino acids relieved cell growth inhibition, suggesting that the phytotoxic properties of Cl-pyr-AMBPA are due to inhibition of key enzymes in both the corresponding pathways.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82194056","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper the biophysical basis of cell expansion is described, paying particular attention to the waterrelations that underpin the process. The connection of growing root cells to the rest of the plant will be addressed and possible control points in the hardware identified. Examples of environmental modification of root extension, and therefore water and solute import, are given, and the relationship with current accepted theories of solute translocation discussed. The opportunities for delivery of solutes and water to be regulated by the growing root itself will be considered, in particular the dual role of cell wall loosening in decreasing both sink cell turgor and water potential. We conclude that a significant proportion of the water for cell expansion can enter growing root cells through the phloem. The physiological data presented rule out alterations in the turgor pressure difference between sieve element and cell as a modulator of solute flux. The plasmodesmata are identified as the major control point of solute flux along the symplastic pathway.
{"title":"Phloem water relations and root growth","authors":"J. Pritchard, Sam Winch, N. Gould","doi":"10.1071/PP99175","DOIUrl":"https://doi.org/10.1071/PP99175","url":null,"abstract":"In this paper the biophysical basis of cell expansion is described, paying particular attention to the waterrelations that underpin the process. The connection of growing root cells to the rest of the plant will be addressed and possible control points in the hardware identified. Examples of environmental modification of root extension, and therefore water and solute import, are given, and the relationship with current accepted theories of solute translocation discussed. The opportunities for delivery of solutes and water to be regulated by the growing root itself will be considered, in particular the dual role of cell wall loosening in decreasing both sink cell turgor and water potential. We conclude that a significant proportion of the water for cell expansion can enter growing root cells through the phloem. The physiological data presented rule out alterations in the turgor pressure difference between sieve element and cell as a modulator of solute flux. The plasmodesmata are identified as the major control point of solute flux along the symplastic pathway.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77155452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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