In this study, changes in plant growth, photosynthetic pigments, nutritional activity, polyamine content and certain metabolic parameters (soluble sugars, proline, polyphenols) were investigated for interspecific hybrid almond rootstock GF677 exposure to various external K+, Ca2+ and Na+. Plants were either grown with a full nutrient solution containing, without or with 75 mM NaCl and 75 mM NaCl alone, 10 mM K+ and Ca2+. Development, exchange of gases, leaf pigments, free polyamine, proline, total sugar, total polyphenols, and total antioxidant activity were calculated. In response to additional KCl and CaCl2 in the culture medium, a major biomass reduction was observed in GF677. Nevertheless, in response to the combined Ca2+ + NaCl or K+ + NaCl treatment, the best results were obtained in terms of photosynthetic rate, photosynthetic pigment concentrations and mineral nutrition (limitation of Na+ accumulation and conservation of Ca2+ and K+ leaf content). The most importantly, however, was the fact that the addition of K+ under salinity increased the content of chlorophyll, the ratio of Chla and Cha/Chlb. This rise was more pronounced compared to that caused in the saline medium by the addition of Ca2+. In addition, our findings have shown that the exogenous supply of K+ under saline conditions increases the leaf content of petunidin-3-glucoside. This component’s high accumulation is known to be a more significant source of antioxidants than the other components. Interestingly, the findings showed that Putriscine, proline and sugar accumulated significantly under K++ NaCl treatment in GF677. Compared to unstressed plants, the addition of Ca2+ or K+ alone or with NaCl increased the polyphenol accumulations in GF677 leaves. The results also suggested that by enhancing the antioxidant activity of Petudinin, polyphenols and Putrescine, the combination of K and Na+ could play a synergetic role in regulating several properties that condition plant salt resistance. Moreover, the supply of K+ under salinity appeared to be more successful than the supply of Ca2+ in improving osmoregulation through proline aggregation and soluble sugars.
Ahlem Zrig Research Unit of Biodiversity and Valorization of Bioresources in Arid Zones, Faculty of Sciences of Gabès- City Erriadh, Zrig, Gabes 6072, Tunisia.