Three-year-old plants of Parthenium argentatum Gray cv. 11591 grown under natural photoperiod were exposed for 60 d to low night temperature (LNT) of 15 °C (daily from 18:00 to 06:00). Effects of the treatment on net photosynthetic rates (PN), rubber accumulation, and associated biochemical traits were examined. LNT initially reduced PN with a parallel decline in the activities of ribulose-1,5-bisphosphate carboxylase, fructose bisphosphatase, and sucrose phosphate synthase for 20-30 d. Later, LNT enhanced PN and the activities of photosynthetic enzymes. Associated with high PN in LNT-treated guayule plants was a two-fold increase in rubber content and rubber transferase activity per unit of protein. The initial decrease in PN in LNT-treated guayule was associated with low content of chlorophyll (a+b), large starch accumulation, and higher ratio of glucose-6-phosphate/fructose-6-phosphate. Photosystem 2 activity in isolated chloroplasts was initially decreased, but increased after 30 d. There was a significant increase in the leaf soluble protein content in LNT-treated plants. Hence the photosynthetic performance of plants grown at 15 °C night temperature for 50 d was superior to those grown under natural photoperiod in all parameters studied. The high photosynthetic capacity may contribute to superior rubber yields under LNT. and D. Sundar, A. Ramachandra Reddy.
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.
Among four mulberry (Morus alba L.) cultivars (K-2, MR-2, BC2-59, and S-13), highest net photosynthetic rate (PN) was observed in BC2-59 while the lowest rates were recorded with K-2. Significant differences among the four cultivars were found in leaf area, biomass production, activities of ribulose-1,5-bisphosphate carboxylase and sucrose phosphate synthase, and glucose and sucrose contents. The PN and the activities of photosynthetic enzymes in the four cultivars were significantly correlated with the growth and biomass production measured as leaf yield, total shoot mass, and aerial plant biomass. and K. V. Chaitanya ... [et al.].