Abstract
Introduction
Drought stress is one of the most important environmental factors, which limit the growth of plants. By the end of the 21^st century, the incidence of drought stress is expected to increase because of the global warming phenomenon. As a consequence, trees growth and viability in the forests and urban greenspace will reduce. Thus, selection of plants that are more tolerant to severe drought stress and are able to cope with such environmental conditions needs to be considered in future silvicultural strategies. This study was carried out to identify candidate drought-tolerance proteins in Maclura pomifera. Therefore, we aimed to explore the performance of Maclura pomifera under a severe drought stress and analyse the proteome changes of Maclura pomifera leaf in response to drought.
 
Materials and Methods
The experiment was carried out on 4-year-old Maclura pomifera saplings genotypes cultivated on a flat field in the Botanical Garden of University of Tehran. Saplings were exposed to irrigation regimes of 100% and 25% field capacity in a completely randomized design. Leaf samples were collected and were frozen immediately in liquid nitrogen and then stored at −80^◦C to be used for further analyses. Experiments were performed using the gradient pH 3-10 NL IPG strips for the isoelectric focusing. IEF was carried out using the PROTEAN IEF. Strips were then equilibrated first for 15 min in reducing solution and then 15 min in alkylating solution. Equilibrated IPG strips were then placed and fixed using hot agarose on the top of home-made 12 % SDS- polyacrylamide gels. Separation of proteins in the second dimension was carried out in Protean XL cell. The protein spots were visualized by staining with BioSafe Coomassie gel stains following manufacturer’s instructions.
 
Results and Discussion
After doing two-dimensional gel electrophoresis, 25 protein spots that had displayed significant protein level changes were identified. Differentially expressed, proteins were divided in three groups. The first group included stress and defense proteins such as lipoxygenase, two types of heat shock protein, Allergen, Convicilin and legumin A2 precursorm; the second group included oxidative stress proteins such as Catalase, Chloroplast stromal ascorbate Peroxidase, Cytosolic ascorbate peroxidase, Iron superoxide dismutase and Manganese superoxide dismutase. The
third group included energy and metabolism proteins such as Ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit, Ribulose -1,5- bisphosphate carboxylase /oxygenase small subuni, Translation elongation factor, Aldolase, Hydroxy-acid oxidase, Isopentenyl diphosphate isomerase, Dihydrolipoamide dehydrogenase and glyoxalase. The present results indicate that most proteins have been identified and their changes caused an increase in tolerance and adaptation of Maclura pomifera to drought stress. Also, our data suggest that drought tolerance of M. pomifera might be correlated with diminishing oxidative damage by activation of the antioxidant systems.
 
Conclusion
The present results indicate that most proteins have been identified and their changes caused an increase in tolerance and adaptation of Maclura pomifera to drought stress. Also, our data suggest that drought tolerance of M. pomifera might be correlated with diminishing oxidative damage by activation of the antioxidant systems.