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 re ported to protect plants from high temperature or frost damage. Contro lled environment studies were conducted to investigate the effect of s tressful temperature regimes on the content of pinitol (3-O-methyl-D-c hiro-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 par ts was determined using high performance liquid chromatography (HPLC). A synthetic plant growth regulator, PGR-IV, was foliarly applied to t he plants to evaluate its effect on pinitol content in different plant components. Uniformly-labelled C-14-glucose was fed into the leaves v ia the transpiration stream, and the effects of high temperature and E XP-S1089, another synthetic plant growth regulator, on the incorporati on of C-14-glucose into pinitol was evaluated using HPLC separation an d scintillation spectrometry. High-temperature stress significantly in creased plant pinitol content and the incorporation of C-14-glucose in to 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 pi nitol translocation from leaves to stems and roots, while EXP-S1089 in creased pinitol/sucrose ratio. Accumulation of pinitol may be an adjus tment mechanism of the plant to reduce high-temperature damage, but no t low-temperature injuries.