The influence of plant water deficit on photosynthesis and translocation of 14C-labeled assimilates in cacao seedlings


R. J. Joly (corresponding author)


The effect of plant status on net assimilation and translocation of “C-labeled assimilates in cacao (Theobroma cacao L.) was evaluated. As plant water potential (ψ) decreased from −0.5 to −1.0 MPa, neither net assimilation nor the rate of label translocation out of the l4CO,-fed leaf were affected, but as iji fell between −1.0 and −1.5 MPa, net assimilation decreased sharply and label retention increased greatly. Translocation out of source leaves was strongly correlated with net assimilation (r =−0.93). Translocation velocity, assessed by detection of labeled assimilates in sink leaves, was sensitive to plant water deficit, and it declined linearly (r = 0.97) throughout the range of leaf water potentials observed. The results may be explained by reduction in the velocity of assimilate movement within the sieve elements, reduction in supply of labeled assimilates from source leaves, reduction in sink strength or diversion of assimilates to sites of storage or utilization.