Text by Lauri Laanisto
First of all a quote from Ülo: “Isoprenoids constitute a versatile pathway of compounds that play major roles as integral components of foliage photosynthetic apparatus..”. It´s from a previous blog post about the hybrid aspen´s isoprenoid-related pathways and mechanisms (link to blog post). This should explain why this topic is being studied in our lab, mainly by Bahtijor, who is our leading specialist in this research area. This paper covers the results of another intricate and detailed lab experiment uncovering mechanisms of one of the most crucial planetary processes – photosynthesis.
Full citation: Rasulov, B., Bichele, I., Hüve, K., Vislap, V., & Niinemets, Ü. (2015). Acclimation of isoprene emission and photosynthesis to growth temperature in hybrid aspen: resolving structural and physiological controls. Plant, Cell & Environment, 38(4), 751-766. (link to full text)
Acclimation of foliage to growth temperature involves both structural and physiological modifications, but the relative importance of these two mechanisms of acclimation is poorly known, especially for isoprene emission responses. We grew hybrid aspen (Populus tremula x P. tremuloides) under control (day/night temperature of 25/20 °C) and high temperature conditions (35/27 °C) to gain insight into the structural and physiological acclimation controls. Growth at high temperature resulted in larger and thinner leaves with smaller and more densely packed chloroplasts and with lower leaf dry mass per area (MA). High growth temperature also led to lower photosynthetic and respiration rates, isoprene emission rate and leaf pigment content and isoprene substrate dimethylallyl diphosphate pool size per unit area, but to greater stomatal conductance. However, all physiological characteristics were similar when expressed per unit dry mass, indicating that the area-based differences were primarily driven by MA. Acclimation to high temperature further increased heat stability of photosynthesis and increased activation energies for isoprene emission and isoprene synthase rate constant. This study demonstrates that temperature acclimation of photosynthetic and isoprene emission characteristics per unit leaf area were primarily driven by structural modifications, and we argue that future studies investigating acclimation to growth temperature must consider structural modifications.