Ultrastructure and functional activity of chloroplasts in wheat leaves under root chilling

The effects of root chilling (2 A degrees C; during 1, 5 h, 1, 2, 4 and 7 days) on the ultrastructure, functional activity of chloroplasts and cold tolerance of leaf cells of wheat (Triticum aestivum L.) were studied. Results indicated that the area of the chloroplasts increased and the number of grana in the chloroplast decreased already within first hours of the experiment. On the 2nd-7th day of the cold treatment, the length of photosynthetic membranes in the chloroplasts increased owing to the membranes of thylakoids in grana. The number of chloroplasts per cell was increased by the end of the experiment. Reduction of electron transport rate and intensification of non-photochemical quenching of chlorophyll fluorescence were observed in the first hours of root chilling. The growth of the leaves slowed in the first day of the treatment and resumed on the second day. Leaf area in the root-chilled plants by the end of the experiment exceeded the initial values by 60 %. The significant rise in cold tolerance of leaf cells was detected after 24 h of root chilling. After 48 h of the treatment, the cold tolerance reached a maximum, and did not change thereafter. It is assumed that most of the observed structural and functional changes are adaptive, and meant to support the photosynthetic function and promote the cold tolerance of the plants.