植物生理与分子生物学学报最新文献

Plant cell wall-plasma membrane-cytoskeleton (CW-PM-CSK) continuum plays important roles in the regulation of plant responses to environmental cues. It has been found in our previous study that an integrin-like protein identified in Arabidopsis and Zea mays plasma membrane mediates the interactions between cell wall and plasma membrane and cell responses to osmotic stress. In the present study, the co-localization of integrin-like protein and alpha-tubulin and their possible interactions were investigated in the root cells of maize using an indirect immunofluorescence technique combined with pharmacological approach. As compared with the control, after treatment with GRGDS, a synthetic peptide contained the RGD domain which binds specifically to integrin-like protein, the integrin-like protein was distributed more evenly over the plasma membrane and the density of alpha-tubulin array became lower. However, treatment with SDGRG, a GRGDS analog which does not contain the RGD domain, had no influences on them. Microtubule-depolymering or -stabilizing reagents exerted their effects either on the distribution over the plasma membrane or on the expression of integrin-like protein. The above results showed that the distribution of integrin-like protein on plasma membrane was closely linked to the alignment of microtubule arrays. Integrin-like protein mediates the interaction between cell wall and plasma membrane, and this interaction in return affected the alignment of microtubule arrays. Changes in cytoskeleton dynamics had significant effect on the distribution of integrin-like protein on the plasma membrane. These results strongly suggest that there are interactions between integrin-like protein and cytoskeleton in plant cells which are very complicated. It is worthy of extensive study to work out the mechanisms of plant responses to intracellular and extracellular signals.

With electron spin resonance and chemical assay, the production of superoxide anion in the Xanthomonas oryzae pv. oryzae strain OS-14 suspension is extracellularly localized. It was found that superoxide anion produced in the filtrate. It was confirmed that peptide or enzyme did not contribute to the production of superoxide anion in the filtrate of OS-14. Organic acids were shown to be the primary source of superoxide anion produced in the filtrate of OS-14. These results indicated that non-enzymic molecules might be another source of superoxide anion produced by Xanthomonas oryzae pv. oryzae, in addition to enzymes, which suggested the multiform generation of superoxide anion.

Amylose, amylopectin and starch dynamic accumulation and key enzymes activities in the grains of 4 maize inbred lines (two high-starch ones and two low-starch ones) were studied. The amounts of amylose, amylopectin and starch in the grains of 4 maize inbred lines increased as sigmoid curves during grain filling period. The changes in amylose, amylopectin and starch accumulation rates followed single-peaked curves, and reached their peaks in the 25-30 days after pollination (DAP). Changes in activities of adenosine diphosphoglucose pyrophosphorylase (ADPG-PPase, EC 2.7.7.27), soluble starch synthase (SSS, EC 2.4.1.21) and starch granule-bound synthase (GBSS, EC 2.4.1.21) in the grains of 4 inbred lines appeared single-peaked curves with the peaks appearing 20-30 DAP. Changes in activities of starch-branching enzyme (Q-enzyme, EC 2.4.1.18) in the grains of high-starch inbred lines appeared single-peaked curves with the peak values at 20 DAP, while the two low-starch inbred lines showed double-peaked curves with the peak values in the 15-20 DAP and 30-35 DAP. There was significant correlation between ADPG-PPase, SSS and GBSS activities. The results indicated that the Q-enzyme had different expression in high- and low-starch maize inbred lines, and verified that ADPG-PPase, SSS and GBSS activities were significantly and positively correlated with amylose, amylopectin and starch accumulation rates.

Arabinose is one of the most dynamic cell wall glycosyl residues released during fruit ripening, alpha-L-arabinofuranosidase (alpha-Arab) are major glycosidases that may remove arabinose units from fruit cell wall polysaccharides. To find out whether alpha-Arab plays important roles in banana fruit softening, the enzyme activities in peel and pulp, fruit firmness, respiration rate and ethylene release rate were assayed during banana softening. The results showed that alpha-Arab activities in banana pulp and peel increased slightly at the beginning of storage and reached their maxima when the fruit firmness decreased drastically, alpha-Arab activity increased by more than ten folds in both pulp and peel during ripening and alpha-Arab activities were higher in pulp than in peel. Treatment of banana fruits with ethylene absorbent postponed the time of reaching of its maxima of respiration and ethylene, enhanced the firmness of pup and decreased alpha-Arab activity in the peel and pulp. These results suggest that alpha-Arab induced the decrease of fruit firmness and played an important role in banana fruit softening, and its activity was regulated by ethylene.

Yeast complementation experiments were carried out to define the possible function of PeNhaD1, a Na(+)/H(+) antiporter gene from Populus euphratica Oliv., a salt resistant tree. PeNhaD1 was introduced to the Saccharomyces cerevisiae mutant strain ANT3 (Deltaena1-4::HIS3 Deltanha1::LEU2), which lacks the plasma membrane Na(+)/H(+) antiporter gene ScNHA1 or GX1 (Deltanhx1::TRP1), which lacks tonoplast Na(+)/H(+) antiporter gene ScNHX1. Our results showed that PeNhaD1 rescued the normal growth of ANT3 in the presence of high salt (80 mmol/L NaCl on solid medium or 400 mmol/L in liquid medium, pH 6.0), but not that of GX1, suggesting that PeNhaD1 may play a role in salt tolerance of Populus euphratica by maintaining the capacity for salt exclusion under saline condition.

TaLEA1, a gene encoding a late-embryogenesis-abundant protein, was cloned from wheat and was transformed into Salvia Miltiorrhiza Bunge by Agrobacterium-mediated leaf-disk transformation method. Seven transgenic lines were obtained after kanamycin (50 mg/L) screening. Six positive lines were obtained by PCR amplification, and after four additional generations, one stable line was obtained by Southern hybridization. Transgenic plants had better growth states than control plants on mediums containing 1% NaCl and 8% PEG6000, which demonstrated that TaLEA1 played an important role in increasing the salt and drought tolerance of S. miltiorrhiza.

Some desiccation-tolerant plants can survive the loss of water even when the water content becomes as low as 0.3 g H2O/g dry weight, and can still repair quickly their cellular structures and function damages by desiccation when they get access to enough moisture again. While moderate dehydration, the tissue could accumulate some special proteins, small molecules, carbohydrate etc. which can protect the original structure and function of macromolecule and membrane through themselves' natural characteristics. Mean-while, water loss results in increased activities of reactive-oxygen-scavenging enzymes (SOD, CAT, APX and GR). For the acquisition of desiccation tolerance, water in the plants or seeds must be induced to enter the glassy state, a change which can be induced by many compounds. The crucial protective means also include the increased formation of endogenous antioxidants and the partitioning of amphiphilic substances in the lipid phase to protect the membrane. The resurrection plants and seeds are good materials for desiccation tolerance research.

The relationships between the rates of starch synthesis and the activities of enzymes responsible for starch biosynthesis in developing grains of normal, pop, sweet and waxy corns were investigated and compared throughout the grain filling period. The results indicated that the rates of starch synthesis and the activities of sucrose synthase (SS), soluble starch synthase (SSS), granule-bound starch synthase (GBSS), starch-branching enzyme (SBE) and starch-debranching enzyme (DBE) each exhibited a single peak during grain filling period. Normal corn showed significantly higher SS activity than other genotypes between 30 and 40 DAP. The mean and maximum activities of SSS were in the following order: normal corn>waxy corn>pop corn>sweet corn. GBSS activities were significantly higher in normal corn, and significantly lower in waxy corn at late filling period. SBE activity of waxy corn was significantly higher than other lines after 10 DAP. DBE activity of sweet corn was extremely low and completely lost at 40 DAP. The rates of starch synthesis had some correlation with the activities of SS, SSS, GBSS and SBE during the grain filling process. No correlation was found between the rates of starch synthesis and the activities of ADP-glucose pyrophosphorylase (AGPase) and DBE. SS activity appears to play a major role in starch biosynthesis in maize. GBSS is responsible for amylose synthesis especially in the later period. SSS and SBE are associated with amylopectin biosynthesis.

'Bright Yellow 2' ('BY-2') tobacco (Nicotiana tabacum L.) suspension cells could not proliferate even with proper 2, 4-D concentration (0.6 mg/L) in the medium, when the initial cell density is low. However, the cells could divide and grow normally if conditioned medium (CM) was added to the medium, and the rate of proliferation of cells was proportional to the quantities of CM supplied. The same results were obtained, when the CM was replaced by synthesized phytosulfokine-alpha (PSK-alpha), a sulfated pentapeptide, PSK-alpha was found in CM of 'BY-2' cells by MS identification. From the significant linear relationship between rate of cell proliferation (measured by OD600 value) and concentrations (0.05 nmol/L-10 micromol/L) of PSK-alpha, it can be seen that the 'BY-2' suspended cells are the ideal plant material for bioassay of PSK-alpha. This result suggests that the PSK-alpha might be involved in promoting the proliferation of 'BY-2' suspension cells.

Gas exchange and chlorophyll a fluorescence in soybean plants were investigated to explore the effects of iron deficiency on photosynthesis and photosystem II function in vivo. Iron deficiency induced a drastic decrease in net photosynthesis (Pn). Compared with normal plants, the maximal quantum yield of PSII photochemistry (psipo) in iron-deficient plants was only slightly lower; whereas, the efficiency with which a trapped exciton can move an electron into the electron transport chain further than QA-(Psio) and quantum yield of electron transport beyond QA (psiEo) were significantly depressed. Iron deficiency also caused a clear enhancement of the relative variable fluorescence at K step (VK). When exposed to light, iron-deficient plants had considerably lower efficiency of excitation energy capture by open PSII reaction centers (Fv'/Fm'), quantum yield of PSII electron transport (PhiPSII), and photochemical quenching coefficient (qP), but markedly higher non-photochemical quenching (NPQ). In addition, post-illumination transient increase in chlorophyll fluorescence was clearly enhanced in iron-deficient plants. Basing on these data, we suggest that both the donor and the acceptor sides of PSII complex were damaged by iron deficiency; cyclic electron transport around PSI in iron-deficient soybean plants might play an important role in inducing the excitation energy dissipation and meeting the demand for extra ATP as a compensation for the loss of phosphorylation capability.