The rate of transport through a phosphate translocator affects delayed luminescence induction: an experiment and a theoretical model

Delayed luminescence (DL) induction curves were studied in leaves from a mu tant pea line containing mutations at both the r and rb loci, compared with leaves from wild type plants. Genes at the r and rb loci encode starch bra nching enzyme and ADP - glucose pyrophosphorylase, respectively. The presen ce of mutations at both loci, previously known to reduce the starch content in the dry mature seed by 75%, have been shown to lower the starch level i n leaves by at least 20%. During induction, the half-time for the DL intens ity decrease from maximum to steady state in the mutant was 1.5 +/- 0.2 tim es longer than for the wild type. It is proposed that the prolongation of t he induction period in leaves from the mutant plants is caused by a lack of inorganic phosphate (P-i) restricting the rate of ATP synthesis at the beg inning of induction. The reduced P-i would be compensated by triose flow fr om the chloroplast, via the triose phosphate translocator, being exchanged for P-i from the cytosol. Analysis of our theoretical photosynthesis model confirmed that a decrease in the rate of P-i released from the Calvin cycle could lead to a prolongation of the induction period.