PINITOL OCCURRENCE IN SOYBEAN PLANTS AS AFFECTED BY TEMPERATURE AND PLANT-GROWTH REGULATORS

Unsuitable temperatures are frequently encountered by soybean (Glycine max L. Merr.) plants grown in the field. Certain polyols have been reported to protect plants from high temperature or frost damage. Controlled environment studies were conducted to investigate the effect of stressful temperature regimes on the content of pinitol (3-O-methyl-D-chiro-inositol) in soybean plants. Hydroponically-grown soybean plants were subjected to high (35/30 degrees C) or low (15/10 degrees C) day/night temperature stresses, and pinitol content in different plant parts was determined using high performance liquid chromatography (HPLC). A synthetic plant growth regulator, PGR-IV, was foliarly applied to the plants to evaluate its effect on pinitol content in different plant components. Uniformly-labelled C-14-glucose was fed into the leaves via the transpiration stream, and the effects of high temperature and EXP-S1089, another synthetic plant growth regulator, on the incorporation of C-14-glucose into pinitol was evaluated using HPLC separation and scintillation spectrometry. High-temperature stress significantly increased plant pinitol content and the incorporation of C-14-glucose into pinitol, but decreased the content of sucrose, glucose and fructose. Under low-temperature stress, there was hardly any change in pinitol content, but a drastic increase in soluble sugars. PGR-IV enhanced pinitol translocation from leaves to stems and roots, while EXP-S1089 increased pinitol/sucrose ratio. Accumulation of pinitol may be an adjustment mechanism of the plant to reduce high-temperature damage, but not low-temperature injuries.