Growth Temperature and Irradiance Modulate Trans-Δ3-Hexadecenoic Acid Content and Photosynthetic Light-Harvesting Complex Organization

Photosynthetic acclimation is an essential physiological process allowing plants to tolerate environmental stress conditions, such as low temperature [5]. Chloroplast thylakoid membranes represent a unique combination of pigments, proteins, and lipids whose organization allows for light harvesting, electron transport, and ultimately, the fixation of carbon. The major chlorophyll (Chi) a/b-binding protein associated with photosystem II (PSII), light-harvesting complex II (LHCII), is thought to be a trimer composed of Lhcbl and Lhcb2 polypeptides and plays a fundamental role in photosynthetic light-harvesting [6]. In addition, phosphatidylglycerol (PG) is the major phospholipid present in thylakoid membranes and characterized by the presence of a novel fatty acid, trans-Δ3-hexadecenoic acid (trans-16:1)[3]. Previously, it has been established that growth at cold-hardening temperatures (5°C) modulates LHCII organization such that the oligomeric form (LHCII 1) predominates at 20°C and monomeric (LHCII 3) and/or intermediate forms (LHCII 2) predominate at 5°C [3, 4, 7, 8, 9]. However, low temperature also results in a specific decrease in trans-16:1 content associated with PG, both in vivo and in situ,with minimal changes in lipid and pigment profiles [3, 4, 7]. Thus, the modulation of the supramolecular organization of LHCII may be achieved by specifically decreasing the trans-16:1 content associated with thylakoid PG, which has been shown to be important for the stabilization of oligomeric LHCII [3, 4, 7, 8, 9].