Rapid heating of intact leaves reveals initial effects of stromal oxidation on photosynthesis.

Heat stress in leaves under natural conditions is characterized by rapid fluctuations in temperature. These fluctuations can be on the order of 10 degrees C in 7 s. By using a specially modified gas-exchange chamber, these conditions were mimicked in the laboratory to analyse the biochemical response to heat spikes.

High temperature enhances inhibitor production but reduces fallover in tobacco Rubisco.

High temperature inhibits photosynthesis by several mechanisms including reduction in Rubisco activity. While the initial reaction velocity of purified, fully carbamylated, inhibitor-free Rubisco increases with temperature in vitro, over time, the reaction velocity slowly declines (fallover) because of the enzymatic and non-enzymatic production of inhibitors from the substrate ribulose-1,5-bisphosphate. We tested whether fallover could contribute to the decline in Rubisco activity observed in leaf extracts at high temperature.

Carbon balance and circadian regulation of hydrolytic and phosphorolytic breakdown of transitory starch.

Transitory starch is formed in chloroplasts during the day and broken down at night. Transitory starch degradation could be regulated by light, circadian rhythms, or carbon balance. To test the role of these potential regulators, starch breakdown rates and metabolites were measured in bean (Phaseolus vulgaris) and Arabidopsis (Arabidopsis thaliana) plants.