Comparison of effects of Iron Excess and Application of Silicon on Fluorescence of Chlorophyll in Shoot and Developmental Changes in Root of Rice seedlings

Induction of soil acidity in the condition of waterlogging in rice fields increases the solubility and uptake of silicon and iron. In this research, the effects of 1.5 mM silicon (in the form of sodium silicate) and extra iron (150 mgL-1 as Fe-EDTA) on physiological parameters of the rice plants were evaluated. After 7 days, in plants treated with 1.5 mM silicon, the minimum and maximum of chlorophyll fluorescence in dark conditions, variable fluorescence and non-photochemical quenching of PSII increased by 27, 20, 19 and 8 percent respectively, but application of silicon in seedling treated with 150 mgL-1 Fe reduced the maximum fluorescence by 23% in light conditions and increased about 55% non-photochemical quenching of PSII. In plants treated with silicon, the amount of root and shoot Si, root and shoot iron and calcium of shoot were increased by 14, 20, 88, 33 and 8 percent, respectively, and the calcium content of root decreased by 11 percent. In the cross section of the root tip of plants treated with 150 mg L-1 iron, the ratio of cortex area to protoxylem area increased significantly compared to the control plants. This study showed that Si induced growth of plants by increasing of photosynthesis capacity and improving relative water content, however, Fe excess decreased growth due to the reduction of quantum yield, decline in water equilibrium and increase of cell wall components in younger parts of roots. Silicon application did not decrease Fe accumulation in plants and could not mitigate effects of iron toxicity on plant growth.