Impact of varying shade on CO2 assimilation, carboxylation efficiency, thylakoid electron transport and water use efficiency in Sesamum indicum L.

Abstract

Importantphotosynthetic traits of sesame (Sesamum indicumL.)werestudied under different regimes of shad~ (33%,50%, and75%of incident sunlight) with control (open sunlight)S. ignificantreductions were observed in the rates of CO2assimilation, Carboxylation efficiency, Thylakoid electrontransportand Water Use Efficiency with increase in shade intensity. Maximum reductions in the photosynthetic traits were noted in 75% shade, followed by50%shade,while a moderate reduction was recorded in33%shadeincomparisonto open grown plants. Shadeinducedadaptationsto low light environment have been reflectedin the functioning of photosynthetic apparatus throughchangingtheir light requirement to saturate the rateof CO2assimilation. Light saturated rate of CO2 assimilation(Amaxw)as obtained at photosynthetic photon fluxdensity(PPFD) of about 1400 1-1mol m-2s-1in both openand33%shade grown plants, wh8reas, these were about8001.1molm-2s.1for the plants grown in 50% or 75% shade. Shade-induced reductions in rate of CO2 assimilationhas been corroborated with the reduction in thecarboxylationefficiency, photosystem-2 (PS2) activity andefficiencyof photochemical reactions. The results wouldbeusefulin developing or selecting shade-tolerant cropsfor semi-arid climate with rc~ource utilization efficiency