Effect of growth conditions on isoprene emission and other thermotolerance-enhancing compounds

Isoprene is emitted from the leaves of many plants in a light-dependent and temperature-sensitive manner. Plants lose a large fraction of photo-assimilated carbon as isoprene but may benefit from improved recovery of photosynthesis following high-temperature episodes. The capacity for isoprene emission of plants in natural conditions (assessed as the rate of isoprene emission under standard conditions) varies with weather. Temperature-controlled greenhouses were used to study the role of temperature and light in influencing the capacity of oak leaves for isoprene synthesis. A comparison was made between the capacity for isoprene emission and the accumulation of other compounds suggested to increase thermotolerance of photosynthesis under two growth temperatures and two growth light intensities. It was found that the capacity for isoprene emission was increased by high temperature or high light. Xanthophyll cycle intermediates increased in high light, but not in high temperature, and the chloroplast small heat-shock protein was not expressed in any of the growth conditions. Thus, of the three thermotolerance-enhancing compounds studied, isoprene was the only one induced by the temperature used in this study.