Abiotic salinity stress: ultrastructural analysis and bioactive compounds detection in Eruca sativa

The salinization of soils is one of the main issue affecting the worldwide agriculture and has been calculated that the arable lands affected by salinity increase by 10% every year. Salinity reduces the crop production and the the quality of cultivated plants leading to harvest losses by 20-50%. In Mediterranean region the 25% of the irrigated cropland is already affected by salinization impairing the plant cultivated in the area as for instance Eruca sativa. This species, commonly known as rocket or arugula is a crop plant belonging to the Brassicaceae family and native of the Mediterranean zone. In this context understand the response of E.sativa to salt stress investigating the plant rsponse to salinity become crucial. Several plant aspects are affected by salt stress ranging from metabolic pathways and physiological processes to morphological and ultrastructural traits. Our study aimed to evaluate changes in salt affected rocket plants under various points mainly regarding anatomy, ultrastructure and the bioactive compounds production. Our first aim was to investigate the E.sativa seedling development under salt stress especially observing the anatomical and ultrastructural adjustment in mesophyll of cotyledons. Our second aim was to understand if rocket plants grown subjected to salinity conditions revealed an increase in glucosinolate production in shoot and evaluate if the resulting vegetable products could be used as source of glucosinolate for madicine or as nutraceutical product. Our third aim was to provide for the first time images of E.sativa leaf anatomy and ultrasctructure as well as observe the anatomical and ultrastructural modification generated by salinity on mesophyll, with a special focus on the detecting of occuring autophagic processes. The last aim was to detect the activation of the unfolding protein response genes in salt affected rocket plants in order to reveal salinity impairments on endoplasmic reticulum activity and provide the sequense of such genes in E.sativa. Our results revealed impairing in rocket seedling developmet under salt stress conditions with limitations observed in lipid reseoirs mobilization in mesophyll cells of cotyledons suggesting a salt negative effect on lypid mobilization phatways. A reduction in intercellular spaces of mesophyll was observed at anatomical level probably as reponse of the plants to reduce water losses by transpiration. Damages on chloroplasts together with activation of autophagic processes at ultrastructural level were recorded, highlighting the detrimental effect of salt especially on chloroplast structure and the plant attempt to recycle damaged organelles or cell components by autophagy. The results on older plants (21 days) shown how salt stress increased the glucosinolates level in rocket plant shoots suggesting a phisiological role, maybe having an osmotic function, of this bioactive compounds in response to salinity. Furthermore, since salt affected Eruca plants had a greater level of glucosinolates their use as bioactive compounds source for medicine or nuctraceutical product was suggested. 21 days old plants shown changes at anatomical level increasing the mesophyll tissues thickness probably in order to reduce the loss of water. At ultrastructural level the results highlighted chloroplasts and plasmamembrane as the most affected cell elements and the revealed of autophagic processes pointed out the crucial role of autophagy as response to salt stress. Moreover a possible new kind of micro-chlorophagy could have been observed. The last results on unfolding protein response allowed to reported the activation of this process in rocket plants grown under salinity conditions and also providing for the first time the sequences of Eruca sativa UBQ10, BIP3 and PDIL genese. In conclusion salt stress affected the anatomy and ultrstructure of E.sativa leaves especially increasing the tissue thicknes and provoking damages on chloroplasts and induction of autophagic processes as well as impair lipid mobilization in seedlings development. Moreover salinity increased the level of glucosinolate in shoot, suggesting a phisiological role of this secondary metabolite, and generated stress to the endoplasmir reticulum leading to the activation of the unfolding protein response related genes.