The Effect of Gamma Amino Butyric Acid on Improving Dehydration Stress Tolerance in Portulaca oleracea

 Portulaca oleraceae is used in many countries for a variety of purposes, including human nutrition and the conversion and pharmaceutical industries. The edible parts of Portulaca oleracea are the young organs, especially the brittle leaves and stems. Over time, this medicinal herb has been forgotten. Drought, on the other hand, is a factor in the decline of crops and horticulture around the world. Given the vastness of arid and semi-arid regions in Iran and also the reduction of access to water resources, appropriate arrangements should be made for the optimal use of water in the agricultural sector. Changing the planting pattern and using useful and resistant alternative species such as drought-tolerant medicinal plants can enable the optimal use of limited water resources. GABA is an important non-protein amino acid that plays a positive role in increasing plant resistance to stress.
 This experiment was carried out in 2020 as a factorial based on a completely randomized design with three replications in the vegetable research greenhouse of the Faculty of Agriculture, Shahid Bahonar University of Kerman. Experimental treatments included different levels of GABA (0, 20, and 40 mM). Treatment with different concentrations of GABA was done in two stages of 6 and 12 leaves of portulaca oleracea and foliar application and application of dehydration stress in three levels of control, medium and severe at irrigation intervals of 7, 14, and 21 days from 6 leaf stage of plants to the end.
 According to the analysis of variance, the effect of GABA at different concentrations and dehydration stress on plant height was significant at the level of 5% probability. Based on the mean comparison test, the highest plant height was obtained in GABA treatment of 40 mM and irrigation intervals of 7 days (control), and the lowest of this trait was obtained in GABA zero treatment and irrigation intervals of 21 days (highest stress level). The results of analysis of variance showed that the effect of GABA at different concentrations and dehydration stress on vegetative yield was significant, the interaction between irrigation intervals and GABA was significant at 5% level. Based on the mean comparison test, the highest vegetative yield was obtained in GABA treatment of 40 mM and irrigation intervals of 7 days and the lowest in control treatment and irrigation intervals of 21 days. According to the results of the analysis of variance table, the effect of GABA at different concentrations and dehydration stress on the amount of malondialdehyde was significant at the level of 1% probability. Based on the means comparison test, the highest amount of this trait was obtained in the control treatment. Comparison of the mean of the data showed that the effect of GABA at different concentrations and dehydration stress caused a significant difference in the probability level of 1% in the proline content of the data. Based on the mean comparison test, the highest amount of proline was observed in GABA treatment of 40 mM and irrigation intervals of 21 days and the lowest amount was observed in control treatment and irrigation intervals of 7 days. As can be seen in the comparison table of means, the highest activity of superoxide dismutase enzyme was obtained in GABA treatment at 40 mM and irrigation intervals of 14 days and the lowest in control treatment and irrigation intervals was 7 days (Table 2). The results of this study showed that the effect of GABA at different concentrations and dehydration stress on the activity of catalase was significant at the level of 1% probability. As can be seen in the comparison table of means, the highest level of catalase activity was 40 mM in GABA treatment and 21 days irrigation intervals and the lowest in GABA treatment was 40 mM and irrigation intervals were 7 days.
 The results of this study indicate that GABA is able to greatly alleviate the oxidative stress caused by dehydration in Portulaca oleracea. This effect is quite evident in oxidative parameters, especially the activity of antioxidant enzymes. The concentration of 40 mM GABA was the most effective treatment in mitigating the effects of irrigation. The results show that the use of GABA makes Portulaca oleracea tolerant to dehydration stress.