Boron toxicity impacts on photosystem II photochemical efficiency of sage (Salvia officinalis)

Abstract

Although boron (B) is an essential element for plants, it becomes toxic in high concentrations. This study was conducted to determine the effects of B toxicity on the photosynthetic performance of sage (Salvia officinalis). Twenty-day old cuttings were exposed to toxic B concentrations (2.5, 5, 7.5, and 10 mM) for 20 days. Chlorophyll fluorescence measurements were determined and analysed by the JIP test. The toxic B content led to a gradual decrease in the efficiency of electron transport, the quantum yields, the photosynthetic performances, and the driving force in sage, while causing an increase in the K-band, L-band, and specific and phenomenological energy fluxes. Membrane damage and water loss gradually increased in response to the severity of toxicity levels (-4.3 fold and 19.5% at 10 mM B, respectively). The reductions in the amounts of photosynthetic pigment and photosynthetic activity showed that sage was highly affected by B toxicity, and even increased anthocyanin and flavonoid amounts were unable to alleviate this effect. Exposure to increased B concentrations was associated with the amount of B accumulation in the sage leaves. This dramatic B accumulation in the sage leaves, which are used in herbal teas and food flavourings, can pose a threat to human health depending on the characteristics of the soil in which the sage grows. An evaluation of PSII photochemical efficiency may serve to determine the effects of B toxicity in sage.