Journal of Experimental Botany, Vol. 45, No. 276, pp. 931-936, July 1994
Journal of Experimental Botany
Stomatal responses to changing irradiance in Phaseolus vulgaris L. Victor L. Barradas1, Hamlyn G. Jones1'3 and Jerry A. Clark2 1
Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK
2
Received 24 January 1994; Accepted 10 March 1994
Abstract The effects of air temperature (TJ, leaf-air vapour pressure differences {VPD) and water deficit on stomatal responses to changing irradiance were studied in Phaseolus vulgaris L. Responses were approximately sigmoidal, with rates of closure being faster than the rates of opening. The mean half-time for closure was 5.4 min and for the opening 9.2 min. Under water deficit, both stomatal opening and closing were faster than in well-watered conditions. Stomata were more sensitive to VPD and water stress than to Tm. The higher the VPD or T, the more rapid was the stomatal response, except in stressed plants where there was no significant effect of T.. Under water stress, stomata were more sensitive to water potential (ifr) in the opening phase than in the closing phase, and the lower the
>0.05). Air temperature and vapour pressure difference
Results
Figure 3 also illustrates the effects of water status, 71, and VPD on opening and closing rates. Increasing temperature from 20 to 26 °C at constant VPD increased the rate of stomatal opening by 17% (P< 0.001) in wellwatered and 35% (/ > 0.05) in either well-watered or stressed plants (Fig. 3a, b). Comparison of Fig. 3a with 3c and Fig. 3b with 3d shows the effect of VPD on the opening and closing rates; this was significant in all cases (P
