Metabolic response of roots to osmotic stress in sensitive and tolerant cereals--qualitative in vivo [31P] nuclear magnetic resonance study.
High resolution [31P] nuclear magnetic resonance (NMR) spectroscopy was used to investigate the changes in phosphate metabolism and intracellular pH in intact root segments of relatively osmotic stress sensitive species maize (Zea mays L) and insensitive species pearl millet (Pennisetron americanum (L) Leeke) exposed to hyper osmotic shock. The results were used to understand the adaptive mechanism of the two species. The hyper osmotic shock resulted in large build-up of phosphocholine and decrease in glucose 6-phosphate (G-6P) and UDPG levels in both the crops. The osmotic shock produced a large vacuolar alkalinization and decrease in pH across tonoplast membrane in maize roots. However, the roots of pearl millet were able to adapt to the stress and maintained pH gradient across tonoplast with marginal vacuolar alkalinization. This may be attributed to the sustained activity of primary tonoplast pumps and increased activity of H+-ATPase that normally maintain pH gradient across tonoplast.