Influence of temperature on root water and ion transport and the subsequent effect on shoot water status and growth of barley and sorghum seedlings.

Abstract

Short term root temperature treatments between 15 to 40°C at a constant air temperature produced a differential response in shoot growth of barley and sorghum seedlings. Maximum growth rate occurred at 25°C in barley and 35°C in sorghum. The stimulation of growth in barley in the suboptimal temperature ranges (15 to 25°C) was associated with both enhanced L(p) and Jᵢ whereas growth inhibition at elevated temperatures (>25°C) was associated with no changes in L(p), but was accompanied by a severe inhibition of solute fluxes suggesting that supraoptimal temperature inhibition of growth in barley is caused by limited ion and not water supply to the leaves. In sorghum, the enhanced shoot growth in the 15 to 25°C range coincided with stimulated L(p) and Jᵢ. Between 25 to 35° temperature induced enhancement of growth was mainly caused by enhanced L(p). In both plants even when root L(p) appeared to cause temperature induced changes in growth, the bulk leaf water, osmotic and turgor potential remained unaffected. It is suggested that when reduced water supply limits growth, undetectable changes in xylem water potential may mediate temperature response in root L(p) and growth. Temperature effects on ion transport across the root were found to be regulated at the site of ion release into the xylem (Φ(cx)) rather than the site of ion entry into the root (Φ(oc)). When ABA was added to the external solution, L(p) was enhanced but qualitative responses of Jᵢ and L(p) to changes in root temperature remained unchanged in barley. However, addition of ABA to the medium with sorghum roots caused a severe inhibition of solute fluxes at temperatures above 25°C which happened only when the temperature was raised above 35°C in the absence of ABA. The ABA study suggested that temperature induced changes in root transport properties of both plants were not mediated by ABA.