During the growth cycle of micropropagated Juglans regia plantlets, phosphoenolpyruvate carboxylase (PEPC) activity was aiways higher than initial ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity. The ratio of PEPC/RuBPCO activities was higher during the first part of the exponential phase of growth and lower during the second part. The variations of PEPC activity were parallel to the soluble protein content and the variations of initial and total RuBPCO activities were parallel to the chlorophyll accumulation.
Two cultivars of bean, Tacarigua and VUL 73-401 were subjected to two levels of water stress followed by rewatering. During the water deficit period, water potential (Ψ№), osmotic potential (Ψ5) and relative water content (rwc) decreased with an associated decrease of ribulose-l,5-bisphosphate carboxylase activity (RuBPC), protein and chlorophyll (Chi) contents. In cv. Tacarigua, the % decrease of RuBPC was less marked than that of protein content. There was a significant correlation among the components of leaf water status and the measured photosynthetic parameters. Groups of water stressed plants were rewatered, when reached -1.25 to -1.60 MPa. During the recovering period all components of leaf water status increased and reached the control values on the 6th day after rewatering. Chi content increased above the control values. Protein content and RuBPC activity also increased during the rewatering period, but the % increases in protein content and RuBPCase activity were not parallel.
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.
Intact chloroplasts were isolated from dark-senescing primary barley (Hordeum vulgare L.) leaves in order to study selective ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) degradation by the stromal and membrane fractions. RuBPCO specific degradation was estimated and characterised applying sensitive avidin-biotin ELISA method with non-modified or oxidatively modified biotinylated RuBPCO (BR) as substrates. Distinct proteolytic activities were detected. They differed in ATP and divalent metal ion dependence, protease inhibitory profile, and dynamics in the time-course of dark-induced senescence. The results supported involvement of ATP- and metal ion-dependent serine type proteolytic activity against non-modified BR early in induced senescence and appearance of ATP-independent activity at later stage. Active oxygen-modified BR was degraded by ATP-independent serine-type protease probably containing essential SH-groups and requiring divalent metal ions. and L. Simova-Stoilova, K. Demirevska-Kepova, Z. Stoyanova.
In the field, supplemental application of N fertilizer to rice (Oryza sativa) shortly before the beginning of heading stage increases leaf N content and enhances photosynthesis during the grain-filling period. In search of varietal differences in leaf gas exchange in response to supplemental N application, we examined 13 rice varieties grown in the field during two successive years. The varieties included japonica and indica varieties, both of which are widely grown in Japan. The response to supplemental N application could not be separated clearly between variety groups; some of the japonica varieties, but none of the indica varieties, exhibited significant increase in stomatal conductance (gs) after supplemental N application. Supplemental N was more effective to increase stomatal aperture in the varieties with inherently lower gs. Varieties that showed greater response of g s to supplemental N application might be able to adjust their stomatal aperture with appropriate N control. Although the internal-to-ambient CO2 mole fraction ratio and the leaf carbon isotopic composition (δ13C) differed among varieties as a result of variations in stomatal aperture and the CO2 requirement of mesophyll, supplemental N application barely influenced these parameters, because it only moderately affected stomatal aperture. Since δ13C tended to increase with increasing number of days from transplantation to heading stage in japonica varieties, δ13C values were more sensitive to differences in growth rate between years than to N application., S. Shimoda, A. Maruyama., and Obsahuje bibliografii
RNA editing is post-transcriptional modification to RNA molecules. In plants, RNA editing primarily occurs to two energy-producing organelles: plastids and mitochondria. Organelle RNA editing is often viewed as a mechanism of correction to compensate for defects or mutations in haploid organelle genomes. A common type of organelle RNA editing is deamination from cytidine to uridine. Cytidine-to-uridine plastid RNA editing is carried out by the RNA editing complex which consists of at least four types of proteins: pentatricopeptide repeat proteins, RNA editing interacting proteins/multiple organellar RNA editing factors, organelle RNA recognition motif proteins, and organelle zinc-finger proteins. The four types of RNA editing factors work together to carry out RNA editing site recognition, zinc cofactor binding, and cytidine-to-uridine deamination. In addition, three other types of proteins have been found to be important for plastid RNA editing. These additional proteins may play a regulatory or stabilizing role in the RNA editing complex., Y. Lu., and Obsahuje bibliografické odkazy
Personal recollections of Robin Hill as a friend, teacher, farmer, neighbour, botanist, meteorologist and photographer, and of Cambridge University and town atmosphere during the World War II and after it are combined with the author's experience with Hill´s "fish-eye" lens used for hemispherical photography and analysis of plant stand structure