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.

In vivo qualitative changes of 31P NMR in stressed maize roots vis-à-vis carbon substrate determining the degree of stress.

High resolution 31P nuclear magnetic resonance spectroscopy was used to investigate the changes in phosphate metabolism and intracellular pH in intact maize (Zea mays L) root segments to hyper osmotic shock. The results were compared with the happenings under field conditions, when the stress was given gradually. Effect of sugar substrate on adaptation of tissue to both kinds of situations was also studied. The hyper osmotic shock resulted in large vacuolar alkalinization and a decrease in pH across tonoplast membrane. There was gradual build up of phosphocholine and decrease in glucose 6P and UPDG levels. In gradual stress, the root segments were able to adapt to the stress and maintained pH gradient across tonoplast, with marginal alkalinization of vacuoles. The presence of sugar substrate reduced the impact of stress significantly, commensurate with the increased activity of plasmalemma H(+)-ATPase. The latter providing the driving force for uptake of organic molecules and ions required for osmoregulation.