Mulberry leaf metabolism under high temperature stress

Effects of high temperature on the activity of photosynthetic enzymes and l eaf proteins were studied in mulberry (Morus alba L. cv. BC2-59). A series of experiments were conducted at regular intervals (120, 240 and 360 min) t o characterize changes in activities of ribulose-1,5-bisphosphate carboxyla se (RuBPC) and sucrose phosphate synthase (SPS), photosystem 2 (PS 2) activ ity, chlorophyll (Chl), carotenoid (Car), starch, sucrose (Suc), amino acid , free proline, protein and nucleic acid contents in leaves under high temp erature (40 degreesC) treatments. High temperature markedly reduced the act ivities of RuBPC and SPS in leaf extracts. Chl content and PS 2 activity in isolated chloroplasts were also affected by high temperature, particularly over 360 min treatment. Increased leaf temperature affected sugar metaboli sm through reductions in leaf starch content and sucrose-starch balance. Wh ile total soluble protein content decreased under heat, total amino acid co ntent increased. Proline accumulation (1.5-fold) was noticed in high temper ature-stressed leaves. A reduction in the contents of foliar nitrogen and n ucleic acids (DNA and RNA) was also noticed. SDS-PAGE protein profile showe d few additional proteins (68 and 85 kDa) in mulberry plants under heat str ess compared to control plants. Our results clearly suggest that mulberry p lants are very sensitive to high temperature with particular reference to t he photosynthetic carbon metabolism.