Info

f*ft§

Fig 5.4. Zinc deficiency effect on leaf micro morphology of faba bean (Vtcia faba L. cv. VH 130). in contrast to Zn-sutlident leaves (A), leaves of Zn-deficient plants IB) show thick epicuticular wax, flaccid guard cells and closed stomata Removal of the wax coating with chloroform shows that stomata of Zn-sufficient leaves (C) are wide open but those of Zn-deficient leaves (D) are sunken and closed, with their guard and accessory cells having concentric wrinkles. (After Sharma et al. IWic).

Fig 5.4. Zinc deficiency effect on leaf micro morphology of faba bean (Vtcia faba L. cv. VH 130). in contrast to Zn-sutlident leaves (A), leaves of Zn-deficient plants IB) show thick epicuticular wax, flaccid guard cells and closed stomata Removal of the wax coating with chloroform shows that stomata of Zn-sufficient leaves (C) are wide open but those of Zn-deficient leaves (D) are sunken and closed, with their guard and accessory cells having concentric wrinkles. (After Sharma et al. IWic).

Increased accumulation of proline, a characteristic feature of water-stressed plants, is also a common feature of zinc-deficient plants (Childiyal et al. 1977; Sharma et al. 1982, 1984a, 1995c; Sharma and Sharma, 1987). Induction of changes, characteristic of water deficit, in zinc deficient but well-watered plants, suggests development of physiological water stress, possibly involving a common target or signaling mechanism under zinc deficiency, and water deficit.

5.4.9 Oxidative Stress

Zinc deficiency accelerates oxidative stress both by overproduction of free oxygen radicles and restricted detoxification of the reactive oxygen species (Cakmak, 2000; Obata et al. 2001). Zinc deficiency causes activation of the membrane bound NADH-oxidase leading to enhanced production of superoxide ions (Cakmak and Marschner, 1988b). It also decreases the activities of superoxide dismutase (Cu-Zn SOD), a key enzyme of the antioxidant defence system (Cakmak et al. 1997c; Yu and Rengel, 1999; Obata et al. 1999; Pandey et al. 2002b, c). Decrease in Cu-Zn SOD activity not only leads to toxic build up of superoxide ions (02") but also their conversion to even more toxic OH" radicles involving Fen ton chemistry. The hydroxyl radicles thus generated cause oxidative damage to different cellular constituents, more particularly the membrane lipids. Figure 5.5 shows some Zn-deficiency induced changes in antioxidant defense system of maize resulting in enhanced lipid peroxidation (Pandey et al. 2002c). Plants that are inadequately supplied with zinc show enhanced damage from oxidative stress imposed by photoinhibitory conditions or ozone injury (Wenzel and Mehlorn, 1994).

Was this article helpful?

0 0

Post a comment