Study of the Biochemical Responses and Enzymatic Activity of GF677 (Peach and Almond Hybrid) Rootstock to In Vitro Salinity Stress

Salinity is the most significant abiotic factor limiting crop productivity and several physiological responses, including modification of ion balance, water status, mineral nutrition, stomatal behavior, photosynthetic efficiency and so on. The GF677 (Prunuspersica×Prunusamygdalus) is widelyusedas rootstock for peach and almond. It is mainly used as a rootstock because of its resistance to drought, calcic soil and Fe deficiency. Nowadays, using tissue culture techniques is very popular for the selection of plant resistant to abiotic stress (in vitro salinity); because in vitro conditions are more controllable than in vivo conditions and the large number of genotypes can be evaluated in a limited space. For example, in the field, plants are exposed to variable biological and climatic conditions which result in some interaction effects. In other words, the nutrition and climatic effects are easily controllable in the in vitro conditions all over the year. The objective of this study is to identify biochemical markers of salinity stress of GF677 rootstock under in vitro conditions. Plantlets of GF677 rootstock were subcultured into the Murashige and Skoog (MS) proliferation medium containing1 mg/l BA (6-Benzyladenine)and 0.1 mg/l NAA (naphthaline acetic acid) with different concentrations (0, 40, 80 and 120 mM) of sodium chloride (NaCl) with four replicates. Cultures were transferred to the growth chamber with temperature of 25±2°C, relative humidity of 70%, under a 16/8 h (day/night) photoperiod. Data were collected at the end of the experiment (6th weeks). Antioxidant enzymes activity (catalase and peroxidase),total protein content, proline content, soluble sugars, and Na and Cl were measured. The experiments were set up in a completely randomized design (CRD) with four replicates (a vessel in each replicate) and statistical analysis was performed using MSTAT-C program. Means were separated according to the Duncan’s multiple range test (DNMRT) at 0.05 level of probability. After six weeks, the results showed that by increasing salinity levelsin the culture medium, antioxidant enzymes activity (catalase and peroxidase),total protein content, proline content and soluble sugars increased significantly. The antioxidant enzyme activities (catalase and peroxidase) were increased significantly in the GF677 rootstock by increasing salinity levels. Catalase activity increased with increasing salinity levels, such that the maximum value (0.61 [abs/min /mg protein (f.m)]) was observed in 80 mM sodium chloride treatment. The lowest catalase activity (0.11 mg [abs/min /mg protein (f.m)]) was observed in 120 mM. The highest of peroxidase enzyme activity (0.109 and 0.105 [abs/min /mg protein (f.m)]), was obtained in 80 and 40 mM, respectively. Also, by increasing the salinity level, total protein content increased significantly in GF677 plantlets. The highest total protein was observed in 80 mM sodium chloride. By increasing salinity levels, proline content increased compared to the control at the GF677 rootstock, but no significant difference was observed between salinity levels. The highest accumulation of proline was obtained in 80 and 120 mM, respectively, while the lowest proline was obtained in control. By increasing salinity levels, soluble sugars increased in GF677 rootstock. The highest accumulation of soluble sugars was obtained in 80 mM. By increasing salinity levels in the cultural medium, the uptakeof sodium (Na+) and chlorine (Cl-) significantly increased in GF677 rootstocks over the six-week culture period. The highest uptake of Na and Cl ions in plant tissue was observed in 4th week. The results showed that with increasing salinity levels 80 to 120 mM), leaf chlorophyll index (SPAD unit) decreased in GF677 rootstock. The lowest chlorophyll index was observed in 120 mM treatment, while the highest leaf chlorophyll index was obtained in the control treatment. According to the results and analysis of biochemical and enzymatic responses,it can be concluded that GF677 is a concentration tolerant to salinity up to 120 mM. The highest amount of biochemical responses and enzymatic activity was observed at 80 mM, where the continued growth of the plant was in terms of salinity. The rootstock was due to antioxidant defense mechanisms such as antioxidant systems, osmotic adjustment by proline and soluble sugars and increasing protein synthesis can sustain growth even under salinity conditions, as a tolerant rootstock was used for peach and almond cultivars.