Developmental changes of plant in the regulation of photosynthate distribution of leaves were studied in hydroponically cultivated rice by the 14CO2 tracer technique and analysis of the activity of the regulatory enzymes, sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), and pyruvate kinase (PK). The distribution of primary photosynthates into sugars, amino acids, organic acids, sugar phosphates, proteins, and polysaccharides was determined by column chromatography. The relative primary photosynthate distribution to the sugar phosphate fraction was significantly larger in the 5th leaf than in the 6th one. Correspondingly, the Vmax of PEPC was significantly higher in the 5th than in the 6th leaf, while no significant differences between leaves were detected in the other enzymes. As a consequence, the ratio of the Vmax of SPS and PEPC was lower in the 5th than in the 6th leaf. As the 5th leaf develops before panicle initiation in rice, it predominantly supports vegetative growth, while the 6th leaf develops after panicle initiation and thus contributes mainly to reproductive growth. We conclude that the physiological properties of each leaf are regulated developmentally. When the 6th leaf became fully expanded (corresponding to the panicle initiation stage of plant), the distribution pattern of 14C was transiently changed in the 5th leaf, indicating that individual organs that are mainly involved in vegetative development are affected to some extent by the whole-plant-level physiological transformation that occurs at the transition from the vegetative to the reproductive stage. and T. Shinano ... [et al.].
mRNA expression patterns of genes for metabolic key enzymes sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), pyruvate kinase, ribulose 1,5-bisphosphate carboxylase/oxygenase, glutamine synthetase 1, and glutamine synthetase 2 were investigated in leaves of rice plants grown at two nitrogen (N) supplies (N0.5, N3.0). The relative gene expression patterns were similar in all leaves except for 9th leaf, in which mRNA levels were generally depressed. Though increased N supply prolonged the expression period of each mRNA, it did not affect the relative expression intensity of any mRNA in a given leaf. SPS Vmax, SPS limiting and PEPC activities, and carbon flow were examined. The ratio between PEPC activity and SPS Vmax was higher in leaves developed at the vegetative growth stage (vegetative leaves: 5th and 7th leaves) than in leaves developed after the ear primordia formation stage (reproductive leaves: 9th and flag leaves). PEPC activity and SPS Vmax decreased with declining leaf N content. After using 14CO2 the 14C photosynthate distribution in the amino acid fraction was higher in vegetative than in reproductive leaves when compared for the same leaf N status. Thus, at high PEPC/SPS activities ratio, more 14C photosynthate was distributed to the amino acid pool, whereas at higher SPS activity more 14C was channelled into the saccharide fraction. Thus, leaf ontogeny was an important factor controlling photosynthate distribution to the N- or C-pool, respectively, regardless of the leaf N status. and T. Shinano ... [et al.].
Activities of crucial enzymes involved in the Calvin cycle, glycolysis, and oxidative pentose phosphate cycle (PPC) were investigated in green calli of sugar beet {Beta vulgaris L.) during the transitíon from photoheterotrophic to photoautotrophic growth. The actívities of the Calvin cycle enzymes were increased by lowering the sucrose concentration of the medium, whereas the actívities of dissimilatíon related enzymes were either decreased or not inftuenced. The photoautotrophic culture cultívated on sucrose-free medium and 2 % CO2 grew at a rate six tímes slower than the photoheterotrophic one. Its growth continued on polyurethane pads soaked with agar-free medium and was fully inhibited by 0.5 pM DCMU.
Incorporation of labelled CO2, 3-phosphoglycerate (PGA), phosphoenolpyruvate (PEP) and pyruvate into hexane extractable rabber ffactions in the cut shoots of guayule {Parthenium argentatum Gray) was determined in order to evaluate the role of photosynthesis in providing precursors for rubber biosynthesis. DCMU inhibited the incorporation of labelled CO2 and PGA into rubber. The incorporation of i'*C02 into rubber depended on irradiance. Enzymatic activities of phosphoglyceromutase, enolase, pyruvate kinase and pyruvate dehydrogenase complex found in purified chloroplasts from the leaves indicated the chloroplast autonomy for intraplastid acetyl coenzyme A formation. The enzymes related to the biosynthesis of isopentenyl pyrophosphate (IPP) were associated with both leaf and stem extracts. Rubber producing enzyme activities, námely IPP isomerase and rubber transferase, were abundantly localized in roots and stems of guayule while the leaves exhibited low activities of these enzymes. Hence the leaves of guayule play a major role in providing precursors for rubber formation in stems and roots.