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-assimi lated carbon as isoprene but may benefit from improved recovery of photosyn thesis following high-temperature episodes. The capacity for isoprene emiss ion of plants in natural conditions (assessed as the rate of isoprene emiss ion under standard conditions) varies with weather. Temperature-controlled greenhouses were used to study the role of temperature and light in influen cing the capacity of oak leaves for isoprene synthesis. A comparison was ma de between the capacity for isoprene emission and the accumulation of other compounds suggested to increase thermotolerance of photosynthesis under tw o growth temperatures and two growth light intensities. It was found that t he capacity for isoprene emission was increased by high temperature or high light. Xanthophyll cycle intermediates increased in high fight, but not in high temperature, and the chloroplast small heat-shock protein was not exp ressed in any of the growth conditions. Thus, of the three thermotolerance- enhancing compounds studied, isoprene was the only one induced by the tempe rature used in this study.