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Wheat Information Service
Number 82: 19-23 (1996)

Genotypic variation in photosynthetic characteristics and kinetic properties of RuBP carboxylase in x Triticosecale Witt.

A. Ramachandra Reddy

School of Life Sciences, Pondicherry University, Pondicherry 605 014, India


Summary

The photosynthetic capacity of single leaves and kinetic properties of RuBP carboxylase were studied among seven genotypes of xTriticosecale Witt. The photosynthetic rates among the genotypes ranged from 15.7 to 25.8 micromole m^-2 s^-1 at an irradiance of 1500 micromole quanta m^-2 s^-1. The cultivar 6A-1093 showed the highest rates of CO₂ fixation while 6A-854 showed the lowest. The photosynthetic rates were significantly correlated with RuBP carboxylase activities in leaf extracts. There was no apparent difference in the chlorophyll content among the genotypes. The Km and Vmax values for RuBP carboxylase in leaf extracts greatly varied among the genotypes. It was concluded that the variation in the rates of CO₂ fixation and kinetic characteristics of RuBP carboxylase among triticale genotypes is important in selection of varieties for improved photosynthetic productivity.


Introduction

Photosynthetic performance of higher plants could be used for prognosis of plant productivity. The photosynthetic rate per unit leaf area depends on the development of the photosynthetic system including energy transducing components and on enzymes of carbon reduction cycle (Evans and Terashima 1988; Geiger and Servaites 1994). Maintenance of active photosynthesis by leaves is a major requirement for production of adequate carbohydrates in crop plants (Lawlor et aL 1989).
Triticale has particular promise as a supplement to current foods, feeds and brewing grains. The crop has recently been known to be one of the most nutritious grains and is used in baking industry. The nutritional superiority of triticale is well known due to its higher protein levels than the other cereal grains (CIMMYT 1985). Much attention has been given to the agronomic and breeding aspects in triticale development programs. It is also important to understand the physiological limitations to the productivity of triticale which could be used in the evaluation and breeding programs for yield improvement. As photosynthesis is one of the most fundamental processes in relation to dry matter production and crop yields, it is necessary to obtain information on the photosynthetic performance among genotypes of this relatively underexploited cereal crop. We have previously reported the genotypic differences in RuBP carboxylase activity during ontogeny of certain triticale genotypes (Ramachandra Reddy et al. 1986). The primary objective of the work reported here is to analyze the relationship between leaf photosynthetic capacity and kinetic properties of RuBP carboxylase among seven genotypes of triticale.

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