Iodine enhances the nutritional value but not the tolerance of lettuce to NaCl

Positive stress or essential and non-essential elements can improve nutritive values (bio- 14 fortification) of edible plants. In the present study we evaluate i) the effect of moderate salinity on 15 lettuce biofortification evaluated as nutritional bioactive compounds accumulation and ii) the role 16 of iodine in enhancing the salt tolerance also by increasing photorespiration and the content of an- 17 tioxidants in lettuce. Physiological (gas exchange and chlorophyll fluorescence emission) and bio- 18 chemical (photosynthetic pigment and bioactive compound) analyses were performed on lettuce 19 plants grown under moderate salinity (50 mM NaCl alone or 50 mM NaCl in combination with 20 iodine, KIO3). Our results show that the treatment NaCl + iodine improves nutritional value of let- 21 tuce in terms of bioactive compounds acting as antioxidants. More specifically iodine enhances the 22 accumulation of photosynthetic pigments and polyphenols such as anthocyanins under salt but 23 does not improve the salt tolerance. Our findings indicate that iodine application under moderate 24 salinity could be a valid strategy in plant biofortification by improving nutritional bioactive com- 25 pound accumulation exercising functional effects on human health