Acclimation by suboptimal growth temperature diminishes photooxidative damage in maize leaves

Leaves of Zea mays L. seedlings which developed at optimal (25 degrees C) or suboptimal (15 degrees C) temperature were exposed to high irradiance (1000 mu mol m(-2) s(-1)) and a severe chilling temperature (5 degrees C) for up to 24 h to investigate their ability to withstand photooxidative stress. During this stress, the degradation of the endogenous antioxidants ascorbate, glutathione and alpha-tocopherol was delayed and less pronounced in 15 degrees C leaves. Similarly, the decline in chlorophyll a, chlorophyll b, beta-carotene and lutein was slower throughout the stress period. Faster development and a higher level of non-photochemical quenching (NPQ) of chlorophyll fluorescence, related to a stronger de-epoxidation of the larger xanthophyll cycle pool in 15 degrees C leaves, could act as a defence mechanism to reduce the formation of reactive oxygen species during severe chilling. Furthermore, plants grown at suboptimal temperature exhibited a higher amount of the antioxidants glutathione and alpha-tocopherol. The higher alpha-tocopherol content in leaves (double based on leaf area; 4-fold higher based on chlorophyll content) which developed at suboptimal temperature may play an especially important role in the stabilization of the thylakoid membrane and thus prevent lipid peroxidation.