Effects of water deficit on gas-exchange parameters and ribulose 1,5-bisphosphate carboxylase activation in wheat

Abstract

Two spring wheat ( Triticum aestivum L.) genotypes, Anza, drought resistant, and Chenab 70, drought susceptible, were used to study the effects of a slowly developing water stress on gas-exchange parameters and ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBPCase; EC 4.1.1.39) activities. By day 7 of the experiment, the two genotypes exhibited similar declines in stomatal conductance ( g) (by 77%) and photosynthetic CO 2 assimilation rate ( A) (by 33%). However, their leaf relative water content ( RWC) was still 90% and total (CO 2/Mg 2+ activated) RuBPCase activities had declined only by 12%. By day 12, RWC decreased to 67% for Chenab 70 and 58% for Anza plants, while g was reduced by more than 95%, and A was reduced by 71% for both genotypes. Thus, Anza plants maintained the same A as Chenab 70 plants even though their RWC was less. Total soluble protein decreased by 30% for Chenab 70 and 43% for Anza plants, while a 12% average reduction in chlorophyll occurred. Over the 12-day experiment, an average 31% reduction in RuBPCase activity occurred for both genotypes. However, the proportion of RuBPCase in the activated state did not change (for Anza) or declined by only 9% (for Chenab 70) over the course of the experiment. These data suggest that changes in in vivo RuBPCase activities are not a major consequence of moderate to severe water deficits in spring wheat.