Zn deficiency induced increases in epicuticular wax deposits, lamina thickness, degree of succulence, water saturation deficit, diffusive resistance, and proline accumulation and decreases in carbonic anhydrase activity, water potential, stomatal aperture, and transpiration in the leaves of cauliflower (Brassica oleracea L. var botrytis cv Pusa) plants. Restoration of Zn supply to the deficient plants increased stomatal aperture, transpiration, and carbonic anhydrase activity significantly within 2 h. However, leaf water potential in the Zn-deficient plants did not recover within 24 h after resupply of Zn. The guard cells in epidermal peels from the Zndeficient leaves had less K+ than those from the controls. Stomatal aperture in the epidermal peels from Zn-deficient leaves was 64% less than in the controls when the epidermal strips were floated on 125 mM KCI. Supplementing the ambient medium 25 mM KCI with ZnCI, enhanced stomatal aperture in both control and Zn-deficient peels, and the effect was significant in the latter. The observations indicate involvement of Zn in stomatal opening, possibly as a constituent of carbonic anhydrase needed for maintaining adequate [HCO;] in the guard cells, and also as a factor affecting K+ uptake by the guard cells.Previous studies have shown that Zn deficiency stress decreased ij, stomatal aperture, and E and increased WSD in cabbage (Brassica oleracea capitata) (Sharma et al., 1982(Sharma et al., , 1984 and cauliflower (Brassica oleracea botrytis) (Sharma and Sharma, 1987). Hu and Sparks (1991) reported a significant decrease in stomatal conductance in Zn-deficient Stuart pecan leaves. According to Sharma et al. (1982) and Sharma and Sharma (1987), decrease in stomatal opening and transpirational water loss from Zn-deficient cabbage leaves can be attributed to decreased water potential.

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