The effect of Calcium and Potassium on Physiological and Biochemical Aspects on Salt Stressed Almond Rootstock

Changes in plant growth, photosynthetic pigments, nutritional behavior, polyamine content and some
metabolic parameters (soluble sugars, proline, polyphenols) of interspecific hybrid almond rootstock
GF677 exposure to different external K+, Ca2+ and Na+ were investigated in this study. Plants were
grown either with a complete nutrient solution containing 10 mM K+ and Ca2+ without or with 75 mM
NaCl and 75 mM NaCl alone. Growth, gas exchange, leaf pigments, free polyamine, proline, total
sugar contents, total polyphenols as well as total antioxidant activities were determined. A significant
reduction of biomass was detected in GF677 in response to additional KCl and CaCl2 in the culture
medium. Nevertheless, the best results in terms of photosynthetic rate, photosynthetic pigment
concentrations and mineral nutrition (limitation of Na+ accumulation and maintenance of Ca2+ and K+
leaf content) were obtained in response to the combined Ca2+ + NaCl or K+ + NaCl treatment.
However, the most important was the fact that the addition of K+ under salinity increased the
chlorophyll content, the Chla and Cha/Chlb ratio. Such increment was more pronounced compared to
that induced by Ca2+ addition in saline medium. Furthermore, our results showed that the exogenous
supply of K+ under saline conditions increase the petunidin-3-glucoside leaf content. The high
accumulation of this component is considered as a more important source of antioxidants than others
components. Interestingly, the results showed a significant accumulation of Putriscine, proline and
sugar under K++ NaCl treatment in GF677. The addition of Ca2+ or K+ alone or with NaCl enhanced
the polyphenols accumulations in leaves of GF677 compared to unstressed plants. The findings also
indicated that combination of K and Na+ could play a synergetic role in regulating several properties
conditioning plant salt resistance by enhancing the antioxidant activity of Petudinin, polyphenols and
Putrescine. Besides, it appeared that the supply of K+ under salinity was more effective than Ca2+
supply to improve the osmoregulation by accumulation of proline and soluble sugars.