Photoinhibition in chilling stressed wheat and maize

At chilling stress. the contents of photosynthetic pigments decreased significantly in maize, but in wheat the contents of chlorophyll (Chi) remained unchanged whereas the contents of total carotenoids (Car) increased. In both species the contents of alpha+beta carotene and lutein + lutein-5,6-epoxide remained unaffected, but the de-epoxidation state involving the components of the xanthophyll cycle increased. Under chilling stress the photosynthetic electron transport also displayed a general failure in maize but in wheat only photosystem (PS) 2 coupled to the water oxidation complex was inhibited. Moreover, in stressed maize the quinone pool decreased, while the low and high potential forms of cytochrome b(559) increased. In wheat only the contents of cytochrome b(559LP) decreased. Peroxidation of acyl lipids in the chloroplast lamellae became more distinct in chilling stressed maize but could also be detected in wheat. Thus in chilling stressed maize prevails an impairment of the acceptor site of PS2 while in wheat photodamage is restricted to the electron donation pathway from water to P680 or to the oxygen evolving complex.