Morpho-physiological and Biochemical Effects of Palm Pollen Extract in Alleviation of Cadmium and Cobalt Toxicity in Beans (Phaseolus vulgaris L.)

Abstract

Palm pollen extract (PPE) is a viable source of osmoregulators, phytohormones, vitamins, minerals, enzymes, and cofactors supporting plant growth in normal and challenging environments. In this study, we explored the competency of methanolic-aqueous PPE to amend cadmium (Cd) and cobalt (Co) toxicity in beans (Phaseolus vulgaris L.). Bean seeds were germinated in clay-sandy soil containing plastic containers, thinned, and then administered 50 mM CdCl2, CoCl2, or a combination of both. Treated seedlings were foliar sprayed with PPE or distilled water (10 ml PPE pot-1). To assess their response, seedlings were harvested at 21 days old. Cd and Co, individually or combined, impaired beans growth, chlorophyll content, soluble sugars, amino acids, ascorbate peroxidase (APX), peroxidase (POD), glutathione reductase (GR) activities, flavonoids, macronutrients (N, P, and K), and yield components, particularly when combined. Metal treatments, however, upraised electrolyte leakage and catalase (CAT), superoxide dismutase (SOD), and glutathione S-transferase (GST) activities, beside increasing carotenoids, proline, hydrogen peroxide (H2O2), malondialdehyde (MDA), and phenolic levels. However, PPE contributed to lessening Cd and Co toxicity by restoring the growth, chlorophyll concentration, membrane stability, metabolic activity, and redox and ionic equilibrium. Moreover, PPE restored the metal-induced declines in carotenoids, flavonoids, antioxidant potential, and grain yield. PPE played a valuable role in metal-stressed beans by increasing proteins, amino acids, and phenols; improving APX, POD, and GST activities; and decreasing Cd and Co uptake. Overall, PPE could be employed as a feasible approach to support Cd- and Co-stressed bean growth, photosynthetic activity, osmotic and ionic homeostasis, and yield performance.