| Salt stress is one of the most important abiotic stresses that limit crop production. It reduces quantity and quality of fruit trees production especially apple tree. Many studies have been applied in different crops to reduce the negative effects of salt stress. Application of some iron (Fe) compound like Fe-EDDHA improved salt stress responses, and this are probably due to its effects on ionic stress or oxidative stress in plant cells. However, effect of iron through molecular mechanism of resistance to salt stress is a little in higher plant especially fruit trees. Therefore, this study was evaluated and investigated the contribution of iron in salt stress responses through physiological, biochemical and molecular mechanisms of plant resistance in two genotypes of apple, Malus xiaojinensis and Malus baccata, exhibiting different sensitivities to salt and iron stresses. One-month old apple seedlings were subjected to0or75mM NaCl with100μM Ferrozine (-Fe),40(+Fe) or160μM FeNaEDTA (++Fe). Roots, young and old leaves were sampled after0,1,3,6and9days of treatments. After which, differences in genes expression, ions concentration in leaves and roots, rhizosphere pH, electrolyte leakage (EL), reactive oxygen species (ROS) and hydrogen peroxide (H2O2) content in roots were analyzed.In M. xiaojinensis salt stress increased the expression of MdSOS1gene at iron-deficient; the expression was higher in roots compared to young and old leaves and was more abundant than in M. baccata. Under salt stress MdAPXl gene was highly expressed in roots and young leaves of M. xiaojinensis than in M. baccata, and under deficient or excess iron than sufficient one. In M. baccata MdAPX1expression was more at sufficient and excess iron. Transcripts from old leaves of the two genotypes showed expression of gene under all iron conditions with abundant expression under excess iron. Moreover, salt stress reduced expression of MxFIT, MxIRT and MxHA2in roots of M. xiaojinensis under iron deficiency but no change was observed in M. baccata with increased in the rhizosphere pH in two genotypes. On the other hand, Na+concentration was less under salt stress at iron deficiency in M. xiaojinensi and exhibited more increased in M. baccata, and the concentration was more in old and young leaves than in roots. Contrasting results for K+concentration were observed, where any increase in Na+was associated with decrease in K+and vice versa. Additionally, Ca2+and Mg2+concentrations were decreased under salt stress at different iron. However the reduction was less in M. xiaojinensis than in M. baccata and under deficient iron than that under sufficient one. Under both iron conditions, salt stress reduced Fe2+concentrations and the reduction was clearly in M. baccata tissues than in M. xiaojinensis. Under salt stress at iron deficiency, Fe2+concentration was more in M. xiaojinensis than in M. baccata. Furthermore, iron supply significantly affected Mn2+concentrations in roots and young leaves of both genotypes but no differences between two iron conditions. While Zn2+concentration was unaffected except in roots of M. baccata. A significant accumulation of ROS and H2O2was observed in both genotypes roots after exposed to treatments with a greater extent in M. baccata. In M. xiaojinensis the levels of H2O2decreased under deficient iron compared with those under sufficient and excess ones. Also electrolyte leakage (EL) was significantly increased under treatments, but decreased in M. xiaojinensis under iron deficiency while was increased in M. baccata regardless iron availability.The findings indicated that under low iron (Fe) treatments M. xiaojinensis is more tolerant to salt stress than under high iron treatment. Under salt and iron stresses M. xiaojinensis tends to absorb more Fe2+compared to M. baccata. Iron deficiency has a positive influence on M. xiaojinensis and could be used to minimize the negative impact of salt stress and thus contribute into enhancing salt stress tolerance. |
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