Calcium invigorates the cadmium-stressed Brassica napus L. plants by strengthening their photosynthetic system

Abstract

Cadmium (Cd) in plants interrupts numerous metabolic processes and reduces the water and nutrient uptake that cause chlorosis, growth retardation, and ultimately plant death. Response of Brassica napus L. to calcium (Ca) enrichment in growth medium for reducing Cd toxicity stress by strengthening the photosynthesis organelles and their functionality was explored in this study. B. napus seedlings of two cultivars (ZS 758 and ZS 72) were exposed to Cd toxicity at 500 μM in hydroponics, and it was ameliorated with Ca at 2.0 mM. The study included determinations and evaluations pertaining to physiological attributes of plant growth, chlorophyll, and photosynthesis. Cadmium stress significantly depressed the seedling growth and reduced photosynthetic rate (Pn), stomatal conductivity (Gs), and transpiration rate (Tr). Further, Cd toxicity markedly decreased the electron transport rate of PSII, effective quantum yield of photochemical energy conversion in PSII [Y(II)], photosynthetic active radiation, coefficient of photochemical quenching (qP), and chlorophyll fluorescence decrease ratio (R(Fd)). Addition of Ca in Cd-stressed plants antagonized the toxicity effects on all the above-mentioned attributes. Calcium amendment also reversed the Cd stress-induced increase in intercellular CO(2) concentration (Ci) and non-photochemical quenching, and countered the Cd accumulation in seedlings. This study suggests that Ca(2+) in the proximity of plasma membrane is proficient in alleviating Cd toxicity by reducing the cell-surface negativity and competing for Cd(2+) ion influx. Consequently, both the plant growth and activity of diurnal photosynthetic system remain the least altered under Cd-provoked toxicity stress.