Inhibition of proline oxidation by water stress.

The conversion of proline to glutamic acid and hence to other soluble compounds (proline oxidation) proceeds readily in turgid barley (Hordeum vulgare) leaves and is stimulated by higher concentrations of proline. This suggests that proline oxidation could function as a control mechanism for maintaining low cellular levels of proline in turgid tissue. In water-stressed tissue, however, proline oxidation is reduced to negligible rates. These results are consistent with the idea that proline accumulation results from inactivation by water stress of normal control mechanisms. It seems likely that inhibition of proline oxidation is necessary in maintaining the high levels of proline found in stressed barley leaves.