Changes in mulberry leaf metabolism in response to water stress

A series of experiments were conducted to characterize the water stress-ind uced changes in the activities of RuBP carboxylase (RuBPCO) and sucrose pho sphate synthase (SPS), photosystem 2 activity, and contents of chlorophylls , carotenoids, starch, sucrose, amino acids, free proline, proteins and nuc leic acids in mulberry (Morus alba L. cv. K-2) leaves. Water stress progres sively reduced the activities of RuBPCO and SPS in the leaf extracts, the c hlorophyll content, and PS2 activity in isolated chloroplasts. Plants expos ed to drought showed lower content of starch and sucrose but higher total s ugar content than control plants. While the soluble protein content decreas ed under water stress, the amino acid content increased. Proline accumulati on (2.5-fold) was noticed in stressed leaves. A reduction in the contents o f DNA and RNA was observed. Reduced nitrogen content was associated with th e reduction in nitrate reductase activity. SDS-PAGE protein profile showed few additional proteins (78 and 92 kDa) in the water stressed plants compar ed to control plants.