Abstract
Both environmental factors and manipulative treatments (such as fruit excision or stem cincturing) were found to alter gaseous diffusion resistances in grape vine foliage. These responses have been analysed in terms of the hormonal physiology of Vitis vinifera L. leaf tissue. Environmental factors such as moisture stress or photoperiod alterations which contributed towards an increase in stomatal resistance (rs) were correlated with increased levels of endogenous abscisic acid (ABA) and phaseic acid (PA) in mature foliage. Conversely, treatments which elicited a decrease in rs were associated with lower levels of both ABA and PA. For example, rs had increased from 1.41 to 7.14 s cm-1 7 days after fruit removal and stem cincturing, while ABA and PA levels rose by 50 and 370 % respectively. This increase in endogenous ABA was not a consequence of decreased leaf water potential; moisture status was actually improved after treatment. It is proposed that changes in endogenous levels of ABA, and possibly PA, constitute a mechanism for regulating gas exchange in these perennial plants.
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