| Genotypic differences in RuP2carboxylase
activities during ontogeny of x Triticosecale Witt.
A. RAMACHANDRA REDDY, A. NITYAGOPAL and G.M. REDDY Department of Genetics, Osmania University, Hyderabad-500 007 India RuP2 carboxylase (EC 4.1.1.39) is the fundamental carboxylating enzyme in C3 photosynthesis and the correlation of RuP2Case activity with photosynthetic rates were reported (BJORKMAN 1968 ; FREY & Moss 1976 ; TREHARNE 1972). Photosynthetic CO2 fixation is the ultimate source of plant dry matter and the role of RuP2Case in this process has gained much importance in recent times. However little is known about the regulatory role of RuP2Case as a rate limiting enzyme for crop improvement pogrammes. It would be of great interest to screen genotypes of economically important crops for genetic diversity in RuP2Case activity for selection of plants to improve photosyntictic productivity. The objective of present investigation was to screen genotypes of triticale for variations in RuP2Case activity to understand the genetic diverisity of this enzyme during different developmental stages. Materials and Methods Six American triticale lines-6A 1092 (Rosner+ +), 6A 1093 (Rosner- -) 6A 845, 6A 854, 801/1208, 801/1210 and a Poland line 'Salvo' were used in the present study. Plants were grown in 30 cm clay pots under natural photoperiod during September-December, 1983. The day/night temperature regime was 30/20C with the average photosynthetic photon flux density of 1,300 microE m-2 sec-1. Evalutations were made by random selection of leaves from the plants of individual pots. The excised leaves of each genotype were washed and cut into small pieces and the crude enzyme extract was prepared by rinding the leaf bits in a pre-chilled mortor with a pinch of sand in 50 mM tris-HCl buffer (pH 7.8) containing 5 mM dithiothreitol (DTT), 5 mM MgCl2 and 1% PVP. The homogenate was filtered through cheese cloth and the filtrate was centrifuged at 10,000 rpm for 10 minutes. The enzyme was pre-activated in 5 mM NaHCO3 and then assayed by measuring the fixation of 14C-bicarbonate. The reaction mixture contained 50 mM tris-HCl buffer (pH 8.0), 5 mM DTT, 10mM MgCl2, 5 mM NaHCO3(14C), 0.5 mM RuP2 and the enzyme extract. The reaction was initiated by adding RuP2 and terminated with the addition of 3N HCl. The incorporated radioactivity was determined with liquid scintillation system. Chlorpophyll was estimated according to ARNON (1949). |
| * Present address : Dept. of Botany, School of Biol. & Earth Sciences, Sri Venkateswara University, Tirupati, India. |
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