In Leymus chinensis, mild water stress (soil moisture 60-65 % of field capacity) had no significant effects on nitrogen metabolism, photosynthesis, and chlorophyll fluorescence. Severe water stress (35-40 %) significantly decreased the activities of nitrate reductase, glutamine synthetase, and glutamate dehydrogenase, net photosynthetic rate, stomatal conductance, transpiration rate, maximal efficiency of photosystem 2 photochemistry (Fv/Fm), actual quantum yield, and photochemical quenching, but increased the endopeptidase activity and malondialdehyde contents. The adverse effects on photosynthesis and N metabolism were markedly greater in reproductive shoots than in vegetative shoots. and Z. Z. Xu, G. S. Zhou.
Wheat provides a unique genetic system in which variable sink size is available across the ploidies. We characterized monocarpic senescence in diploid, tetraploid, and hexaploid wheat species in flag leaf from anthesis up to full grain maturity at regular intervals. Triticum tauschii Acc. cv. EC-331751 showed the fastest rate of senescence among the species studied and the rate of loss per day was highest in terms of photosynthesis rate, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) content, and flag leaf N content coupled with a higher rate of gain in grain N content. Cultivars Kundan and HD 4530 maintained high flag leaf N content throughout grain filling as compared to the diploids and showed a slower rate of senescence. RuBPCO content was higher in the diploids as compared to Kundan and HD 4530 at anthesis. However, the rate of decline in RuBPCO content per day was also higher in the diploids. This degradation in RuBPCO was mediated by high endoproteolytic activities in the diploids which in turn supported its higher rate of N mobilization as compared to the tetraploid and hexaploid wheat. Acidic endopeptidases were responsible for the mobilization of flag leaf nitrogen in wheat across ploidy levels (r=-0.582, p<0.01). and B. Srivalli, R. Khanna-Chopra.
Characterisation of proteases degrading ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC: 4.1.1.39) was studied in the cowpea leaf during monocarpic senescence 3 and 9 d after flowering (DAF), representing early and mid pod fill. The stage at 3 DAF coincided with decrease in the metabolic parameters characterising senescence, i.e., contents of total soluble proteins, RuBPCO, and leaf nitrogen. At 9 DAF, there was a decline in total soluble proteins and an appearance of a 48 kDa cysteine protease. Characterisation of the proteases was done using specific inhibitors. Subcellular localisation at 3 DAF was studied by following the degradation of RuBPCO large subunit (LSU) in the vacuole lysates using immunoblot analyses. Cysteine proteases played a predominant role in the degradation of RuBPCO LSU at the crude extract level. At 9 DAF, expression of cysteine protease isoforms was monitored using polyclonal antibodies against papain and two polypeptides of molecular masses 48 and 35 kDa were observed in the vacuole lysates. We confirmed thus the predominance of cysteine proteases in the vacuoles during different stages of pod development in cowpea leaf. and B. Srivalli, Sudhakar Bharti, Renu Khanna-Chopra.