The Temperature Response of Photosynthesis and Metabolites in Anti-RbcS Tobacco

Abstract

The reasons for the decline in net CO2 assimilation (A) at high temperatures are controversial, and there is conflicting evidence about the changes to photosynthetic metabolites above the thermal optimum of A. We tested the hypothesis that increasing the ratio of Rubisco activase to Rubisco catalytic sites would alter the relationship between the consumption and regeneration of RuBP, using wild-type (WT) and two transgenic (anti-RbcS) Nicotiana tabacum genotypes with reduced amounts of Rubisco. We measured photosynthetic gas-exchange from 15–42°C at 38 Pa CO2, and the pools of RuBP and PGA from 25–42°C. Transgenic plants had lower A than WT at all measurement temperatures, but had a similar thermal optimum for photosynthesis. Photosynthesis declined 20–30% between 35°C and 42°C in all three genotypes, a decline that was reversible by a 20-min exposure to 35°C. The ratio of RuBP to PGA was insensitive to temperature in WT tobacco, but declined slightly in the two transgenic lines. Our data indicate that the light harvesting and light utilising reactions remain balanced across a broad range of temperatures in tobacco.