Chlorophyll content and peroxidase activity as biomarkers in screening rice varieties against iron (Fe²⁺) toxicity

Abstract

Iron toxicity is one of the widely distributed nutritional disorders that affect rice production negatively. Therefore, the identification of efficient biomarkers for screening rice varieties with tolerance to excess Fe²⁺ is important. However, leaf bronzing has been widely used as a phenotypic biomarker in screening rice varieties against Fe²⁺ toxicity. Hence, this study aimed to investigate the applicability of chlorophyll content and peroxidase activity (POD) as biomarkers for screening rice varieties against iron (Fe²⁺) toxicity. Two rice varieties recommended for the low-country Wet Zone (LCWZ) of Sri Lanka were identified as iron tolerant (Ld408) and susceptible (Ld365) by the initial study before being used in the experiments. Seven-day old seedlings of both varieties were exposed to different levels of Fe²⁺ [150 mg L⁻¹ (Control), 450 mg L⁻¹ , 650 mg L⁻¹ , 850 mg L⁻¹ , 1,050 mg L⁻¹ and 1,250 mg L⁻¹ ] at pH 5.5 for seven days. A randomized block design (RBD) was employed with three replicates per treatment and control, and the experiment was carried out in a modified flood and drain hydroponic system. At the end, the total chlorophyll content and POD activity were measured. All data were analyzed through two-way ANOVA followed by Tukey’s posthoc test using the statistical software MINITAB 17. Ld408 showed Fe²⁺ level-dependent significant (p < 0.050) increase in the total chlorophyll content and POD activity with the increase in Fe²⁺ concentration. In contrast, Ld365 indicated a significant reduction (p < 0.050) in the total chlorophyll content and POD in the treatments with the Fe²⁺ concentration higher than 450 mg L⁻¹ and 650 mg L⁻¹ , respectively. Further POD activity of Ld408 showed a lower rate in all treatments compared to Ld365. The observed decreases in the chlorophyll content and increasing POD activity of Ld365 infer that the exposed plants to Fe²⁺ treatments are under the stressful condition compared with plants of Ld408 under the same treatments. The overall results indicate the variety-specific sensitivity of both chlorophyll content and POD towards Fe²⁺ concentration, highlighting higher tolerance of Ld408 than Ld365 for the excess Fe²⁺ . According to our preliminary data, it may be possible to apply total chlorophyll content and peroxidase (POD) activity as biomarkers for screening tolerant rice varieties to Fe²⁺ toxicity at the early growth stage.