Stress Metabolism. VI.* Temperature Stress and the Accumulation of Proline in Barley and Radish

Abstract

Barley (cv.Prior) and radish (cv.White Icicle) plants were subjected to heat stress (39°C) for 1–5 days when growing in either a high (90–95 %) or low (50%) relative humidity environment. Although the plants were watered daily, leaf water potential (ψw) in heat-stressed plants at low relative humidity fell to a low level (– 30 bars, day 5) whereas there was no such decrease in the leaves of those maintained at a high humidity (– 4.6 bars). Growth in height was inhibited and leaf chlorophyll concentration decreased by high temperature, these effects being accentuated by accompanying water-stress in the leaves. On the other hand, proline only accumulated in the leaves when (ψw) fell, there being apparently no direct response to elevated temperature. These effects were confirmed for a range of temperatures extending to a maximum of 41°C. Proline accumulated rapidly, after an initial lag phase, in both barley and radish plants exposed to a low temperature (4°C). This accumulation was unrelated to any changes in the leaf water relationships. Neither leaf water potential, osmotic potential nor turgor demonstrated changes with low temperature sufficient to account for the accumulation of proline. The characteristics of this cold- induced accumulation of proline are compared with those of water stress-induced accumulation. * Part V, Aust. J. Biol. Sci., 1973, 26, 319–27.