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.
Excess supply of the heavy metals Mn, Cu, Zn, Co, and Ni to barley caused their accumulation in shoots and specially in roots and induced symptoms characteristic of the particular heavy metal involved, the syndrome of which varied with the different treatments. The effectiveness of the heavy metals in inducing visual symptoms was in the order of Ni2+ > Co2+ > Cu2+ > Mn2+ > Zn2+. These treatments caused a decrease in dry matter yield of plants in the order Ni2+ > Co2+ > Zn2+ > Mn2+ > Cu2+.Studies using 59Fe indicated that an excess supply of each of the heavy metals reduced iron absorption by plants and affected its distribution in roots and shoots. Excess of Co2+, Cu2+, Mn2+, and Zn2+ reduced iron translocation to shoots, induced chlorosis, and decreased catalase activity of young leaves. Excess nickel, which was most active in producing toxic effects, did not inhibit translocation of iron to young leaves. Unlike iron deficiency, an excess of Ni2+ did not decrease the activity of catalase and stimulated the activity of peroxidase. Excess supply of each of the heavy metals increased the concentration of non-reducing sugars. Observations suggest that toxicity to heavy metals does not necessarily involve induction of iron deficiency, their redox potentials, or the stability of their organometal complexes.
Deficiencies of each of the micronutrients, iron, zinc, copper, and manganese, decreased the activity of FDP-aldolase (D-fructose-1,6-biphosphate D-glyceraldehyde-3-phosphate-lyase (EC 4.1.2.13)) in leaves of radish (Raphanus sativus L. var. All Season). The depression in the enzyme activity was overcome when deficient plants were supplied normal levels of the micronutrient in short supply. The depression in the enzyme activity could not be attributed to decreased protein levels in the deficient plants. Polyacrylamide gel electrophoresis revealed only one form of FDP-aldolase in All Season radish leaves. Deficiencies of iron, zinc, copper, or manganese resulted in the appearance of two forms of aldolase.
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