Photosynthesis and metabolism of sugars from lettuce plants (Lactuca sativa L. var. longifolia) subjected to biofortification with iodine

Iodine, essential to human life, is in part ingested through vegetable consumption, explaining the current application of this element in biofortification programs. Few data are available on the effects of iodine on main plant metabolisms such as carbon metabolism. The objective of this study was to determine the effect of the application of different doses (20, 40 and 80 mu M) and forms of iodine (iodate [IO3 (-)] and iodide [I-]) on photosynthesis and carbohydrate metabolism in lettuce plants. None of these treatments exerted significant effects on the synthesis pathway or on sucrose degradation. Application of 80 mu M of I- reduced the photosynthesis rate, which may be associated with the reduction found in biomass and photosynthetic parameters (stomatic conductance and transpiration). This finding confirms that the application of high doses of I- has a phytotoxic effect on plant physiology. In contrast, all IO3 (-) treatments increased the biomass of the plants which showed an elevated photosynthetic rate, stomatic conductance, and transpiration (vs. controls). The differential crop behavior observed with the two forms of this trace element suggests that IO3 (-) should be selected for future biofortification programs.