Limitations of Gas Exchanges in Intact Leaves during Ontogeny of Field-grown Chickpeas

Abstract

The ontogenic changes in several component processes of photosynthesis were measured in chickpeas. Gas exchange characteristics of intact leaves were studied to analyse the effects of ambient conditions under which chickpeas are usually grown. The C02 assimilation rate per unit leaf area remained fairly high during the vegetative stage, reaching a peak at early pod-fill and declining subsequently throughout pod development. The intercellular C02 partial pressure (Ci) remained more or less constant (~ 195 /?bar) during vegetative growth and the early stages of seed-filling. With falling RWC and PAR interception, the stomatal conductance declined more rapidly than the C02 assimilation rate resulting in a value of C, less than that normally existing under ambient conditions. From the ^/?i-analysis, C02 assimilation during pod-filling appears to be limited by the RuBP-regeneration capacity because the carboxylation efficiency and in vitro RuBPCase activity were initially unaffected. However, as leaves aged, the carboxylation efficiency and in vitro RuBPCase activity decreased abruptly with increasing leaf temperatures above 30 °C, and the Ci was greater than normally existing values (~ 195 /?bar), suggesting an increased mesophyll limitation of photosynthesis. It is suggested that a decline in the C02 assimilation rate of leaves during pod development and an accelerated senescence are induced by adverse ambient conditions, particularly plant water stress and high leaf temperature.