Given the fact that plant species with a type 1 (symplasmic) minor vein ultrastructure seem to dominate in the tropics and subtropics, and species with a type 2 (apoplasmic) minor vein ultrastructure in the temperate and boreal climate zones, a cold sensitivity of symplasmic phloem loading was postulated. Electron microscopic observations were taken as support for this proposal. The objective of the present work was to test this postulate by measuring physiological parameters correlated to phloem loading. Carbohydrate levels in the leaf, minor vein loading of 14 CO2-derived assimilates in leaf segments and exudation of sugars and 14 C-labelled compounds in several species from families with known phloem-loading pathways were compared in 10 and 20°C-adapted plants at both 10 and 20°C. No essential differences in response to temperature between symplasmically and apoplasmically phloem-loading species were observed. Carbohydrate availability for export was essentially similar, phloem loading was fully operative at 10°C, and exudation of sugars equally reacted to low temperature in symplasmic and apoplasmic species. Apparently, the geographical distribution of type 1 and 2 species is not explained by a difference in temperature sensitivity of the phloem-loading mode.
{"title":"Temperature effects on symplasmic and apoplasmic phloem loading and loading-associated carbohydrate processing.","authors":"A. A. Schrier, G. Hoffmann-Thoma, A. Bel","doi":"10.1071/PP99166","DOIUrl":"https://doi.org/10.1071/PP99166","url":null,"abstract":"Given the fact that plant species with a type 1 (symplasmic) minor vein ultrastructure seem to dominate in the tropics and subtropics, and species with a type 2 (apoplasmic) minor vein ultrastructure in the temperate and boreal climate zones, a cold sensitivity of symplasmic phloem loading was postulated. Electron microscopic observations were taken as support for this proposal. The objective of the present work was to test this postulate by measuring physiological parameters correlated to phloem loading. Carbohydrate levels in the leaf, minor vein loading of 14 CO2-derived assimilates in leaf segments and exudation of sugars and 14 C-labelled compounds in several species from families with known phloem-loading pathways were compared in 10 and 20°C-adapted plants at both 10 and 20°C. No essential differences in response to temperature between symplasmically and apoplasmically phloem-loading species were observed. Carbohydrate availability for export was essentially similar, phloem loading was fully operative at 10°C, and exudation of sugars equally reacted to low temperature in symplasmic and apoplasmic species. Apparently, the geographical distribution of type 1 and 2 species is not explained by a difference in temperature sensitivity of the phloem-loading mode.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77954796","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 rate of export of recent photoassimilate from source leaves of Pima cotton (Gossypium barbadense L.) is inhibited by ozone (O3). To characterize these effects on export, source leaves of Pima cotton were exposed to pulses (0.75 h) of O3 (0.0, 0.2, 0.5 and 0.8 µL L -1 ) followed by pulses of 14 CO2. Leaves were monitored by gas exchange and with a Geiger-Muller tube, for a sufficient period to characterize carbon assimilation (A) and a rapid and a slower phase of export. Double exponential decay functions (two-compartment model) were fitted and a com- partmental analysis conducted. O3 reduced by half the fast rate constant describing export from a transport pool, without affecting the rate constants for transport from or to a storage compartment. Measured soluble sugar contents increased slightly from control concentrations (1.2 g C m -2 ) by about 5-10% at all O3 concentrations. The calculated soluble sugar content in the transport pool increased from about 200 to 300 mg C m -2 with increasing exposure to O3. The calculated storage pool did not respond to O3 but exceeded measured contents. This discrepancy is attributed to starch deposition and mobilization, which are not considered in the two-compartment model, uncertainties in slower decay parameters, and non-steady-state A induced by O3 exposure. Specific inhibition of rapid efflux sug- gests oxidant damage at the plasmalemma or plasmodesmata of mesophyll or phloem companion cells, and little effect on the tonoplast. A was affected less than export. Future research should target oxidation of components involved in phloem loading.
臭氧(O3)抑制了皮马棉源叶片新近光同化物质的输出速率。为了研究这些对出口的影响，我们将皮马棉源叶片暴露于O3(0.0、0.2、0.5和0.8µL L -1)脉冲(0.75 h)和14co2脉冲(0.75 h)中。通过气体交换和盖革-穆勒管对叶片进行监测，在足够的时间内表征碳同化(a)和快速和较慢的出口阶段。拟合了双指数衰减函数(双室模型)，并进行了共部分析。O3将描述从传输池导出的快速速率常数减少了一半，而不影响从存储隔间传输到存储隔间的速率常数。测定的可溶性糖含量在所有O3浓度下均较对照浓度(1.2 g C m -2)略有增加，增幅约为5-10%。随着O3暴露量的增加，运输池中计算的可溶性糖含量从200 mg C m -2增加到300 mg C m -2。计算的存储池对O3没有响应，但超过了测量的内容。这种差异归因于淀粉沉积和动员，这在双室模型中没有考虑到，缓慢衰变参数的不确定性，以及O3暴露引起的非稳态A。对快速外排的特异性抑制表明，氧化对叶肉或韧皮部伴生细胞的质膜或间连丝造成损伤，对细胞质的影响很小。A受到的影响小于出口。未来的研究应该针对参与韧皮部负荷的成分的氧化。
{"title":"Ozone inhibits phloem loading from a transport pool: compartmental efflux analysis in Pima cotton.","authors":"D. Grantz, J. Farrar","doi":"10.1071/PP99169","DOIUrl":"https://doi.org/10.1071/PP99169","url":null,"abstract":"The rate of export of recent photoassimilate from source leaves of Pima cotton (Gossypium barbadense L.) is inhibited by ozone (O3). To characterize these effects on export, source leaves of Pima cotton were exposed to pulses (0.75 h) of O3 (0.0, 0.2, 0.5 and 0.8 µL L -1 ) followed by pulses of 14 CO2. Leaves were monitored by gas exchange and with a Geiger-Muller tube, for a sufficient period to characterize carbon assimilation (A) and a rapid and a slower phase of export. Double exponential decay functions (two-compartment model) were fitted and a com- partmental analysis conducted. O3 reduced by half the fast rate constant describing export from a transport pool, without affecting the rate constants for transport from or to a storage compartment. Measured soluble sugar contents increased slightly from control concentrations (1.2 g C m -2 ) by about 5-10% at all O3 concentrations. The calculated soluble sugar content in the transport pool increased from about 200 to 300 mg C m -2 with increasing exposure to O3. The calculated storage pool did not respond to O3 but exceeded measured contents. This discrepancy is attributed to starch deposition and mobilization, which are not considered in the two-compartment model, uncertainties in slower decay parameters, and non-steady-state A induced by O3 exposure. Specific inhibition of rapid efflux sug- gests oxidant damage at the plasmalemma or plasmodesmata of mesophyll or phloem companion cells, and little effect on the tonoplast. A was affected less than export. Future research should target oxidation of components involved in phloem loading.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88589424","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}
{"title":"Pathway and control of sucrose import into initiating cotton fibre cells","authors":"Y. Ruan, D. Llewellyn, R. Furbank","doi":"10.1071/PP99154","DOIUrl":"https://doi.org/10.1071/PP99154","url":null,"abstract":"","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89612893","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}
{"title":"Vacuolar chain elongation of raffinose oligosaccharides in Ajuga reptans","authors":"R. Braun, F. Keller","doi":"10.1071/PP99165","DOIUrl":"https://doi.org/10.1071/PP99165","url":null,"abstract":"","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73675336","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}
S. Greiner, U. Köster, K. Lauer, H. Rosenkranz, R. Vogel, T. Rausch
We have recently cloned cDNAs encoding two invertase inhibitors from Nicotiana tabacum, Nt-inh1, an apoplastic isoform, and Nt-inhh, a vacuolar isoform (Greiner et al. (1998) Plant Phys. 116, 733-742; Greiner et al. (1999) Nature/Biotech. 17, 708-711). A database search revealed the presence of related sequences in other dicot families. Here we report the presence of Nt-inh1-related proteins (INH-RPs) in apoplastic fractions from Chenopodium rubrum and Daucus carota suspension-culture cells. Furthermore, we demonstrate that, in Lycopersicon esculentum, the expression of INH-RPs is highly regulated during plant development. In immature tomato fruits two INH-RP isoforms are expressed, whereas in mature fruit a single isoform is detected. Sequential extraction of apoplastic and intracellular fractions from mature fruit pericarp tissue revealed that the major portion of invertase and INH-RP are localized in the vacuole. Recovery of the non-glycosylated INH-RP with the glycosy- lated invertase from the Concanavalin A-bound fraction indicates that INH-RP forms a stable complex with vacuo- lar invertase. As Nt-inh1 and INH-RP from different species contain four conserved cysteine residues, we have compared the inhibitory activity of oxidized and dithiothreitol (DTT)-treated recombinant Nt-inh1 protein. Only the oxidized form is active as an invertase inhibitor. Its higher mobility during sodium dodecyl sulfate-gel electro- phoresis, as compared to DTT-treated Nt-inh1, suggests that disulfide bridge(s) prevent the inhibitor from unfold- ing. A mechanism is proposed for the post-translational inactivation of cell wall and vacuolar invertases via invertase inhibitors during critical stages of plant development.
{"title":"Plant invertase inhibitors: expression in cell culture and during plant development","authors":"S. Greiner, U. Köster, K. Lauer, H. Rosenkranz, R. Vogel, T. Rausch","doi":"10.1071/PP99171","DOIUrl":"https://doi.org/10.1071/PP99171","url":null,"abstract":"We have recently cloned cDNAs encoding two invertase inhibitors from Nicotiana tabacum, Nt-inh1, an apoplastic isoform, and Nt-inhh, a vacuolar isoform (Greiner et al. (1998) Plant Phys. 116, 733-742; Greiner et al. (1999) Nature/Biotech. 17, 708-711). A database search revealed the presence of related sequences in other dicot families. Here we report the presence of Nt-inh1-related proteins (INH-RPs) in apoplastic fractions from Chenopodium rubrum and Daucus carota suspension-culture cells. Furthermore, we demonstrate that, in Lycopersicon esculentum, the expression of INH-RPs is highly regulated during plant development. In immature tomato fruits two INH-RP isoforms are expressed, whereas in mature fruit a single isoform is detected. Sequential extraction of apoplastic and intracellular fractions from mature fruit pericarp tissue revealed that the major portion of invertase and INH-RP are localized in the vacuole. Recovery of the non-glycosylated INH-RP with the glycosy- lated invertase from the Concanavalin A-bound fraction indicates that INH-RP forms a stable complex with vacuo- lar invertase. As Nt-inh1 and INH-RP from different species contain four conserved cysteine residues, we have compared the inhibitory activity of oxidized and dithiothreitol (DTT)-treated recombinant Nt-inh1 protein. Only the oxidized form is active as an invertase inhibitor. Its higher mobility during sodium dodecyl sulfate-gel electro- phoresis, as compared to DTT-treated Nt-inh1, suggests that disulfide bridge(s) prevent the inhibitor from unfold- ing. A mechanism is proposed for the post-translational inactivation of cell wall and vacuolar invertases via invertase inhibitors during critical stages of plant development.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85497507","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}
Previous work has shown different patterns of expression for the three plant sucrose transporters PmSUC1, PmSUC2 and AtSUC1. Each carrier may therefore have different properties appropriate for the transport function at each location in the plant. To test this hypothesis, a detailed characterisation of each carrier was performed by expressing the protein in Xenopus oocytes. All three carriers were functionally active in oocytes and transported both sucrose and maltose with the sugars eliciting inward currents, which increased at more negative membrane voltages. This effect was greater for AtSUC1 and PmSUC1 than for PmSUC2. The affinities of the carriers for each sugar were different, with PmSUC2 having a 10-fold higher Km for sucrose compared to AtSUC1 and PmSUC1. However, these values for all three carriers were dependent on the external pH and membrane voltage. For both PmSUC1 and PmSUC2 the maximal sugar transport was achieved at external pH values of 6.5-7.5, values which do not appear to be consistent with a proton-coupled mechanism of transport. However, the normal saline used for oocyte experiments contains relatively high concentrations of NaCl that could interfere with the function of the carrier protein. To test this idea the sucrose-elicited currents were measured in saline containing lower concentrations of these ions. Sodium, but not chloride, ions modified the sugar transport activities of the carriers and these effects were different for each carrier, inhibiting AtSUC1 and PmSUC1, but stimulating PmSUC2. The properties of each carrier are discussed in relation to their expression in oocytes and what is known about their pattern of expression in planta.
{"title":"Comparison of the transport properties of three plant sucrose carriers expressed in Xenopus oocytes","authors":"Jing-Jiang Zhou, A. Miller","doi":"10.1071/PP99188","DOIUrl":"https://doi.org/10.1071/PP99188","url":null,"abstract":"Previous work has shown different patterns of expression for the three plant sucrose transporters PmSUC1, PmSUC2 and AtSUC1. Each carrier may therefore have different properties appropriate for the transport function at each location in the plant. To test this hypothesis, a detailed characterisation of each carrier was performed by expressing the protein in Xenopus oocytes. All three carriers were functionally active in oocytes and transported both sucrose and maltose with the sugars eliciting inward currents, which increased at more negative membrane voltages. This effect was greater for AtSUC1 and PmSUC1 than for PmSUC2. The affinities of the carriers for each sugar were different, with PmSUC2 having a 10-fold higher Km for sucrose compared to AtSUC1 and PmSUC1. However, these values for all three carriers were dependent on the external pH and membrane voltage. For both PmSUC1 and PmSUC2 the maximal sugar transport was achieved at external pH values of 6.5-7.5, values which do not appear to be consistent with a proton-coupled mechanism of transport. However, the normal saline used for oocyte experiments contains relatively high concentrations of NaCl that could interfere with the function of the carrier protein. To test this idea the sucrose-elicited currents were measured in saline containing lower concentrations of these ions. Sodium, but not chloride, ions modified the sugar transport activities of the carriers and these effects were different for each carrier, inhibiting AtSUC1 and PmSUC1, but stimulating PmSUC2. The properties of each carrier are discussed in relation to their expression in oocytes and what is known about their pattern of expression in planta.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88958286","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}
H. Isopp, M. Frehner, J. Almeida, H. Blum, M. Daepp, U. Hartwig, A. Lüscher, D. Suter, J. Nösberger
Swards of Lolium perenne L. were grown in the field in a long-term free air CO2 enrichment (FACE) facility. The CO2 treatment was combined with two levels of N fertilization and regular defoliation, which resulted in plants with a wide range of source-sink relations. C and N metabolism were investigated to assess the role of carbohydrate and nitrogenous compounds in leaves in indicating source-sink relations. Sucrose exhibited the largest changes in contents during the day-night cycle; therefore, it was identified as the main short-term storage compound for night-time export. Fructan accumulation indicated the degree of surplus C supply in the source compared to C use in sinks. Nitrate content depended mainly on N fertilization, and was reduced under elevated pCO2. Nitrate appeared to indicate a current surplus of available N relative to the need for growth. Amino acid content responded strongly to N fertilization but decreased only slightly under elevated pCO2. Protein content, however, decreased significantly under elevated pCO2. The patterns of diurnal changes of C or N compounds did not differ between CO2 treatments. Down-regulation of photosynthesis appeared to occur when plants were extremely N-limited as under elevated pCO2, low N and at a late regrowth stage.
{"title":"Nitrogen plays a major role in leaves when source-sink relations change: C and N metabolism in Lolium perenne growing under free air CO2 enrichment","authors":"H. Isopp, M. Frehner, J. Almeida, H. Blum, M. Daepp, U. Hartwig, A. Lüscher, D. Suter, J. Nösberger","doi":"10.1071/PP99151","DOIUrl":"https://doi.org/10.1071/PP99151","url":null,"abstract":"Swards of Lolium perenne L. were grown in the field in a long-term free air CO2 enrichment (FACE) facility. The CO2 treatment was combined with two levels of N fertilization and regular defoliation, which resulted in plants with a wide range of source-sink relations. C and N metabolism were investigated to assess the role of carbohydrate and nitrogenous compounds in leaves in indicating source-sink relations. Sucrose exhibited the largest changes in contents during the day-night cycle; therefore, it was identified as the main short-term storage compound for night-time export. Fructan accumulation indicated the degree of surplus C supply in the source compared to C use in sinks. Nitrate content depended mainly on N fertilization, and was reduced under elevated pCO2. Nitrate appeared to indicate a current surplus of available N relative to the need for growth. Amino acid content responded strongly to N fertilization but decreased only slightly under elevated pCO2. Protein content, however, decreased significantly under elevated pCO2. The patterns of diurnal changes of C or N compounds did not differ between CO2 treatments. Down-regulation of photosynthesis appeared to occur when plants were extremely N-limited as under elevated pCO2, low N and at a late regrowth stage.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76023532","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}
An empirical modelling procedure was employed to follow uptake, transport and utilization of photo- assimilated carbon (C) and soil-derived nitrogen (N) over a 19-d period (November 1998) in 2-year-old plantation- grown trees of Eucalyptus globulus Labill. Models utilized data for gains and losses of C and N in dry matter (DM) of tree parts, CO2 exchanges and transpiration of foliage, respiratory losses of stems and roots, C:N weight ratios of xylem and phloem sap collected at different sites within the system, and phloem sap sugar concentration gradients along trunks and branches to indicate directions of assimilate flow. The model for C depicted the fate of exported fixed C from four levels of branches on the shoot system, cycling of 16% of the C supplied from shoot to root back to the shoot in xylem, major involvement of xylem-derived C in nourishment of rapidly growing branches, and a net daily respiratory output per tree equivalent to 39% of its net daytime photosynthetic gain in C by foliage. The model for N showed that upper growing shoot parts gained more N mobilized from lower branches than was being acquired from soil. It also indicated high rates of cycling of N through mature foliage, effective retention of xylem-derived N by growing branches and apices, and feedback of substantial amounts of phloem-exported N from lower branches into xylem moving further up the trunk. Transpiration loss per tree was equivalent to 272 mL g -1 DM accumulated. Data are discussed in relation to similarly executed C:N partitioning studies on herbaceous annual species.
采用经验模型研究了2年树龄的蓝桉人工林在19 d期间(1998年11月)光同化碳(C)和土壤源性氮(N)的吸收、运输和利用。模型利用树木干物质(DM)中C和N的损益、叶片的CO2交换和蒸腾、茎和根的呼吸损失、系统内不同地点收集的木质部和韧皮部汁液的C:N重量比以及韧皮部汁液沿树干和树枝的糖浓度梯度等数据来指示同化物流动的方向。C的模型描述了从茎系统的四个层次上输出的固定C的命运，从茎到根的16%的C在木质部循环到茎，木质部来源的C主要参与快速生长的树枝的营养，每棵树的净每日呼吸输出相当于其白天净光合作用的39%。氮素模型表明，上部生长枝条从下部枝条中吸收的氮素比从土壤中吸收的要多。研究还表明，成熟叶片中氮的循环速率高，生长的分枝和根尖有效地保留了木质部来源的氮，韧皮部输出的大量氮从下部分支反馈到木质部，并向树干上游移动。每棵树蒸腾损失相当于累积272 mL g -1 DM。数据讨论了有关类似执行的C:N分配研究草本一年生物种。
{"title":"Uptake, partitioning and utilization of carbon and nitrogen in the phloem bleeding tree, Tasmanian blue gum (Eucalyptus globulus)","authors":"J. Pate, D. Arthur","doi":"10.1071/PP99149","DOIUrl":"https://doi.org/10.1071/PP99149","url":null,"abstract":"An empirical modelling procedure was employed to follow uptake, transport and utilization of photo- assimilated carbon (C) and soil-derived nitrogen (N) over a 19-d period (November 1998) in 2-year-old plantation- grown trees of Eucalyptus globulus Labill. Models utilized data for gains and losses of C and N in dry matter (DM) of tree parts, CO2 exchanges and transpiration of foliage, respiratory losses of stems and roots, C:N weight ratios of xylem and phloem sap collected at different sites within the system, and phloem sap sugar concentration gradients along trunks and branches to indicate directions of assimilate flow. The model for C depicted the fate of exported fixed C from four levels of branches on the shoot system, cycling of 16% of the C supplied from shoot to root back to the shoot in xylem, major involvement of xylem-derived C in nourishment of rapidly growing branches, and a net daily respiratory output per tree equivalent to 39% of its net daytime photosynthetic gain in C by foliage. The model for N showed that upper growing shoot parts gained more N mobilized from lower branches than was being acquired from soil. It also indicated high rates of cycling of N through mature foliage, effective retention of xylem-derived N by growing branches and apices, and feedback of substantial amounts of phloem-exported N from lower branches into xylem moving further up the trunk. Transpiration loss per tree was equivalent to 272 mL g -1 DM accumulated. Data are discussed in relation to similarly executed C:N partitioning studies on herbaceous annual species.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84508485","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 aryloxyphenoxypropionate herbicide haloxyfop is transported in the phloem to the sink tissue where, in certain species, it disrupts the production of lipids that are essential for the functioning of membranes and organelles involved in the assimilation, partitioning and transport of carbon. Haloxyfop inhibits a key regulatory enzyme of lipid synthesis, acetyl coenzyme A carboxylase (ACCase), in species that lack a herbicide-insensitive multisubunit (MS) form of ACCase found in most plants. The absence of MS-ACCase, and sensitivity to haloxyfop, was considered to be restricted to monocotyledons in the family Gramineae but has recently been demonstrated for the dicotyledon Erodium moschatum (Geraniaceae). Species related to E. moschatum were examined to determine how widespread this phenomenon is among dicotyledons. In the two families most closely related to the Geraniaceae, four species in the Oxalidaceae and one species in the Tropaeolaceae respectively retained MS-ACCase. Within the family Geraniaceae, certain species in the genera Erodium and Pelargonium, but not those in the genus Geranium, have lost MS-ACCase, indicating that this phenomenon may be restricted to Erodium and Pelargonium. When treated with 104 g ai ha–1 haloxyfop-ethoxyethyl, plants of all 15 species retaining MS-ACCase were resistant while 8 out of 13 species lacking MS-ACCase were susceptible. It is noteworthy that five species lacking MS-ACCase were nonetheless resistant. The mechanism(s) of resistance in such species remains to be determined.
芳基苯氧丙酸除草剂haloxyfop在韧皮部运输到汇组织，在某些物种中，它破坏脂质的产生，而脂质对于参与碳的同化、分配和运输的膜和细胞器的功能至关重要。Haloxyfop在大多数植物缺乏对除草剂不敏感的多亚单位(MS)形式的ACCase的物种中抑制脂质合成的关键调节酶乙酰辅酶a羧化酶(ACCase)。MS-ACCase的缺乏和对haloxyfop的敏感性被认为仅限于禾本科的单子叶植物，但最近已证明双子叶植物Erodium moschatum (geranaceae)也存在。我们研究了与紫叶莲有关的物种，以确定这种现象在双子叶植物中有多普遍。在与天竺葵科亲缘关系最密切的两个科中，草木科的4个种和Tropaeolaceae的1个种分别保留了MS-ACCase。在天竺葵科中，黄花属和天竺葵属的某些物种失去了MS-ACCase，而天竺葵属的某些物种没有失去MS-ACCase，这表明这种现象可能仅限于黄花属和天竺葵。当施用104 g ha-1 haloxyfop-ethoxyethyl时，保留MS-ACCase的15种植物全部抗性，而缺乏MS-ACCase的13种植物中有8种敏感。值得注意的是，5个缺乏MS-ACCase的品种仍然具有耐药性。这些物种的耐药机制仍有待确定。
{"title":"Dicotyledons lacking the multisubunit form of the herbicide-target enzyme acetyl coenzyme A carboxylase may be restricted to the family Geraniaceae","authors":"J. Christopher, J. Holtum","doi":"10.1071/PP99160","DOIUrl":"https://doi.org/10.1071/PP99160","url":null,"abstract":"The aryloxyphenoxypropionate herbicide haloxyfop is transported in the phloem to the sink tissue where, in certain species, it disrupts the production of lipids that are essential for the functioning of membranes and organelles involved in the assimilation, partitioning and transport of carbon. Haloxyfop inhibits a key regulatory enzyme of lipid synthesis, acetyl coenzyme A carboxylase (ACCase), in species that lack a herbicide-insensitive multisubunit (MS) form of ACCase found in most plants. The absence of MS-ACCase, and sensitivity to haloxyfop, was considered to be restricted to monocotyledons in the family Gramineae but has recently been demonstrated for the dicotyledon Erodium moschatum (Geraniaceae). Species related to E. moschatum were examined to determine how widespread this phenomenon is among dicotyledons. In the two families most closely related to the Geraniaceae, four species in the Oxalidaceae and one species in the Tropaeolaceae respectively retained MS-ACCase. Within the family Geraniaceae, certain species in the genera Erodium and Pelargonium, but not those in the genus Geranium, have lost MS-ACCase, indicating that this phenomenon may be restricted to Erodium and Pelargonium. When treated with 104 g ai ha–1 haloxyfop-ethoxyethyl, plants of all 15 species retaining MS-ACCase were resistant while 8 out of 13 species lacking MS-ACCase were susceptible. It is noteworthy that five species lacking MS-ACCase were nonetheless resistant. The mechanism(s) of resistance in such species remains to be determined.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81673887","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 deposition of hydrophobic polymers in the xylem of wheat grain floral axes prevents water and solute movement into grains via the xylem (xylem discontinuity). The only pathway for translocation of photo- synthate or externally applied xenobiotics into wheat grains is via the phloem. We have developed a new method based on the xylem discontinuity for rapidly screening phloem mobility of xenobiotics. By quantifying xenobiotic concentration in grains and excised plants after the compounds were applied through the cut stems, the phloem mobility can be estimated quantitatively. The phloem mobility obtained with our new grain-based method was correlated to xenobiotic chemical properties such as log Kow, pKa and electrical charge, and is consistent with pub- lished literature. Phloem mobility values determined by the grain-based assay were correlated to those from the direct phloem sap (aphid stylet exudate) assay of excised and intact plants, indicating that the grain-based assay is as reliable as the direct assay with aphid stylectomy. The new grain-based method is simple, quick, and can be scaled up for rapid screening of xenobiotic phloem mobility in plants. Similar seed (fruit)-based assay could also be developed with wide ranges of plant species that use the phloem as the only pathway for supplying water and nutrients into their seeds or fruits.
{"title":"A new method for rapid screening of xenobiotic phloem mobility in plants","authors":"Ning Wang, Sze-Mei Cindy Lau, G. Rogers, T. Ray","doi":"10.1071/PP99158","DOIUrl":"https://doi.org/10.1071/PP99158","url":null,"abstract":"The deposition of hydrophobic polymers in the xylem of wheat grain floral axes prevents water and solute movement into grains via the xylem (xylem discontinuity). The only pathway for translocation of photo- synthate or externally applied xenobiotics into wheat grains is via the phloem. We have developed a new method based on the xylem discontinuity for rapidly screening phloem mobility of xenobiotics. By quantifying xenobiotic concentration in grains and excised plants after the compounds were applied through the cut stems, the phloem mobility can be estimated quantitatively. The phloem mobility obtained with our new grain-based method was correlated to xenobiotic chemical properties such as log Kow, pKa and electrical charge, and is consistent with pub- lished literature. Phloem mobility values determined by the grain-based assay were correlated to those from the direct phloem sap (aphid stylet exudate) assay of excised and intact plants, indicating that the grain-based assay is as reliable as the direct assay with aphid stylectomy. The new grain-based method is simple, quick, and can be scaled up for rapid screening of xenobiotic phloem mobility in plants. Similar seed (fruit)-based assay could also be developed with wide ranges of plant species that use the phloem as the only pathway for supplying water and nutrients into their seeds or fruits.","PeriodicalId":8650,"journal":{"name":"Australian Journal of Plant Physiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85599822","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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