Patterns of pinitol accumulation in soybean plants and relationships to drought tolerance

Previous studies indicate that methylated cyclitols are potentially importa nt osmolytes in plants. In a search for genetic diversity for pinitol (D-3- O-methyl-chiro-inositol) accumulation in soybean (Glycine max (L,) Merr,), two- to three-fold differences in pinitol accumulation in leaf blades were found among Chinese plant introductions, Furthermore, it was found that gen otypes that accumulated high concentrations of pinitol, when grown under we ll-watered conditions, had been selected for performance in regions of Chin a having low rainfall. Among the carbohydrates analysed, pinitol accumulati on was uniquely associated with adaptation to dry areas of China. A detaile d study of pinitol accumulation in the soybean plant showed two- to three-f old gradients in pinitol concentration from the bottom to the top of the pl ant. The gradient shifted during plant development, with consistently highe r concentrations of pinitol in the uppermost leaves. Pinitol accumulation w as not correlated with activity of the key biosynthetic enzyme, inositol me thyl transferase. This result and other lines of evidence indicated that sh ifting patterns of pinitol accumulation were due to translocation of the cy clitol from lower to upper nodes, Pinitol, proline, and sugars accumulated in leaf blades on soybean plants subjected to drought, but the molar concen tration of pinitol in stressed plants was greater than the concentrations o f proline or sugars, Although the mechanism by which pinitol participates i n drought tolerance is not fully known, our results provide additional corr elative evidence linking pinitol and drought tolerance in soybean.