| Results and Discussion Table 1 reveals a vast array of variation of RuP2carboxylase activty both between genotypes and different developmental stages. RuP2Case levels at the onset of grain filling were at the highest followed by maturity stage. 6A-1093 recorded the highest activity of the enzyme followed by 801/1208 and the lowest was in cultivar 6A-854. In all four stages studied, 6A-1093 exhibited maximal activity. The range of variation among the seven genotypes was not significant at seedling stage but the maximum was observed at grain filling stage. All the genotypes exhibited a unique performance of a gradual increase in RuP2Case activity in the first three developmental stages and a steady decline from grain filling to maturity. The present observations suggest that RuP2Case activity in triticale was found to be associated with developmental stages. The enzyme activity in young seedlings was relatively constant in the seven genotypes and this may be due to beginning of leaf blade expansion prior to reaching the maximum polyribosome content associated with the synthesis of fraction-1 protein. The maximal activities of RuP2Case observed at the grain filing stage indicate greater stimulation of photosynthetic rates, probably due to greater demand for photosynthates to reproductive structures and grains. The decline in maximum activity during the late seedset indicates low photosynthetic CO2 assimilation rates and high partitioning of photosynthates during grain filling period (PEET et al. 1977). The sampling dates in each developmental stage did not vary greatly in light, temperature or moisture and hence the ontogenetic changes in RuP2Case activity was probably not due to the environmental changes. Thus the enzyme activity during grain filling stage may be useful screening tool for improving photosynthetic productivity in triticale. The developmental profile of RuP2Case activity was significantly affected by genotype reflecting the differences in the proportion of carboxylase protein. Screening of genotypes for high RuP2Case activity may be of great advantage in selection of varieties for carboxylation efficiency. Acknowledgements The authors are grateful to Dr. J.P. GUSTAFSON, USDA-SEA-AR, University of Missouri, Columbia, U.S.A., and Dr. T. WOLSKI, Triticale Breeding Station, Warsaw, Poland for the supply of genetic stocks. We gratefully acknowledge the financial support through a grant by USDA, authorised by Public Law 480, New Delhi, India and University Grants Commission, New Delhi. References ARNON, D.I. (1949) Copper enzymes in isolated chloroplasts : Polyphenol oxidase in Beta vulgaris. Plant Physiol. 24 : 1-15. BJORKMAN, O. (1968) Further studies on differentiation of photosynthetic properties in sun and shade ecotypes of Solidago virgauria. Physiol. Plant. 21: 84-89. FREY, N.M. & Moss, D.N. (1976) Variation in RuDPCase in barley. Crop Sci. 16 : 209-213. PEET, M.M., BRAVO, A., WALLACE, D.H. & OZBUN, J.L. (1977) Photosynthesis, stomatal resistance and enzyme and activities in relation to yield of field grown dry bean varieties. Crop Sci. 17: 287- 293. TREHARNE, K. J. (1972) Biochemical limitations to photosynthesis rates. In A.R. Rees ed. Crop Processes in Controlled Environments, Academic Press, New York. |
| <-- Back |