Abstract
Iron plays a pivotal role in the redox reactions of photosynthesis and metabolic processes such as chlorophyll synthesis. Iron availability in waterlogged soils can reach toxic levels and promote oxidative stress. Fe toxicity is the most concerning of stresses for rice in many lowland environments around the world and may cause severe impairments in rice photosynthesis. This study aimed to investigate the extension of oxidative stress after excess Fe exposure and its effects on the photosynthesis of rice cultivars with differential sensitivity. Three Brazilian rice cultivars (EPAGRI 107, BRSMG SELETA and BR IRGA 409) were grown in Hoagland nutrient solution (pH 4.0) with two Fe-EDTA doses corresponding to excess Fe (7 mM) and control (0.009 mM) treatments. After just three days of excess Fe exposure, there was a significant increase in iron concentration in the shoots. The BR IRGA 409 cultivar exhibited higher Fe accumulation in its shoots, and the EPAGRI 107 cultivar recorded the lowest values, which were below the critical toxicity level, as a resistance strategy. Impairment in light energy partitioning and oxidative damage became evident before changes in stomatal resistance, chlorophyll content, maximal PSII quantum yield or visual symptoms for the most sensitive cultivar (BR IRGA 409). The photosynthesis limitations, in addition to the impairment of excess energy dissipation in rice from iron toxicity, are the results of oxidative damage.
Highlights
Iron (Fe) is a micronutrient that plays important physiological roles in plants as a component of enzyme cofactors that catalyze redox reactions in fundamental metabolic processes
The reduction in shoot and root lengths caused by excess Fe-EDTA treatments (Fe) occurred differently between cultivars because these variables were not affected in the EPAGRI 107 cultivar
The data are presented as the means ± standard errors of four replicates
Summary
Iron (Fe) is a micronutrient that plays important physiological roles in plants as a component of enzyme cofactors that catalyze redox reactions in fundamental metabolic processes. Fe is a cofactor in both photosystems (PSII and PSI) and in the cytochrome (Cyt) b6/f complex. It is required for chlorophyll biosynthesis and to promote the structural integrity of photosynthetic reaction centers and light-harvesting complex (LHC) subunits (Guerinot and Yi, 1994; Msilini et al, 2011; Yadavalli et al, 2012). In addition to its abundance in the earth’s crust, iron in aerobic soils is found mostly in the form of insoluble Fe3+ oxides or hydroxides, which decrease Fe bioavailability to plants (Stein et al, 2014). Fe toxicity is the most widespread nutritional disorder that affects wetland rice production (Dobermann and Fairhurst, 2000)
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