The Effects of Compatible Solutes on the Heat Stability of Glutamine Synthetase from Chickpeas Grown under Different Nitrogen and Temperature Regimes

Abstract

The activity of glutamine synthetase (GS) extracted from chickpeas grown under different nitrogen and temperature regimes was examined. Cytosolic GS (GS₁) was much less temperature sensitive than chloroplastic GS (GS₂). There was no change in the ratio of the two isoforms from plants with different growth temperatures. Specific activity of GS appeared to be independent of growth temperature and was little affected by nitrogen supply. In vitro studies were performed on the heat stability of GS₂ in the presence of glycine betaine, proline, and myoinositol. The latter was most effective in preventing loss of enzyme activity at high temperatures. Glycine betaine was also effective as a heat protectant but enzyme activity in the presence of proline was lower than the control at temperatures above 30 °C. The importance of myo-inositol protection of metabolism is discussed in relation to the accumulation in chickpeas of another cyclitol, pinitol.