Zinc-induced changes in chlorophyll fluorescence, pigment profile and antioxidant machinery in cowpea under controlled conditions

Abstract

A sand culture experiment was conducted to investigate the effects of zinc (Zn) deficiency on oxidative status and antioxidant defense mechanisms in cowpea (Vigna unguiculata L. Walp., cv. Pusa Komal). Plants were grown under greenhouse conditions with varying Zn concentrations ranging from 0.01 to 10 µM. Optimal growth and dry matter accumulation were observed at 1 µM Zn supply, indicating adequate Zn nutrition.  In contrast, Zn deficiency significantly suppressed plant growth, reduced root development, and led to the formation of thin lateral roots. Zn-deficient plants exhibited pronounced oxidative stress, as evidenced by elevated malondialdehyde (MDA) content, a marker of lipid peroxidation. The lowest lipid peroxide levels were recorded in the leaves of Zn-sufficient plants, highlighting the protective role of Zn against oxidative damage. Suboptimal Zn supply resulted in reduced chlorophyll and carotenoid contents, along with decreased activities of key antioxidant enzymes, including ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), and superoxide dismutase (SOD), while malondialdehyde (MDA) accumulation increased. These findings highlight the crucial role of adequate Zn nutrition in maintaining an efficient antioxidant defense system. Zinc deficiency downregulation of the antioxidant defense system, making plants more vulnerable to oxidative damage induced by reactive oxygen species. These findings emphasize the critical role of Zn in maintaining cellular redox balance and ensuring efficient antioxidant defense. Adequate Zn nutrition is therefore essential for sustaining normal growth, physiological functioning, and protection against oxidative stress in cowpea plants.