Differential heat-induced changes in the CO2 assimilation rate and electron transport in tomato (Lycopersicon esculentum Mill.)

Measurements of leaf stomatal conductance, leaf CO2 assimilation rate, leaf chlorophyll fluorescence, and a previously published biochemical model have been used to evaluate the thermo-tolerance of the photosynthetic apparatus in two tomato genotypes ('Amalia' and 'Nagcarlang'). The study was carried as two experiments. In Experiment 1, a brief (20 min) increase in leaf temperature to 35 degrees C reduced the photosynthetic rate of Amalia' leaves grown at 25 degrees C, but stimulated photosynthesis in `Nagcarlang', due to an increase in the maximum rate of carboxylation of ribulose-1,5-bisphosphate-carboxylase/oxygenase (VCmax). The heat-sensitive step in Amalia' seemed to be the maximum rate of electron transport (Jmax). However, in Experiment 2, there was no significant difference between Jmax at 25 degrees C and 35 degrees C when plants had been acclimatised to these temperatures.