Drought is a major abiotic stress, limiting the survival and growth of young plants. However, little is known about sex-dependent responses to drought at the proteome level. In this study, we carried out investigations on comparative proteomics, combined with physiological and organelle structure analyses, in males and females of Populus cathayana Rehd. Three-month-old poplar cuttings were treated at 30% of field capacity and at 100% field capacity as a control in a greenhouse for 40 days. Drought greatly inhibited plant growth, damaged the photosynthetic system and destructed the structures of chloroplasts, mitochondria and cellular membranes. However, males suffered less from the adverse effects of drought than did females. Using 2-DE, 563 spots were detected, of which 64 spots displayed significant drought effect and 44 spots displayed a significant sex by drought interaction effect. The results suggest that the different responses to drought stress detected between the sexes have a close relationship to the changes in the expression of sex-dependent proteins, including, e.g. photosynthesis-related proteins, homeostasis-related proteins and stress response proteins. These proteins could contribute to a physiological advantage under drought, giving potential clues for understanding sexual differences in the performance of plants in different environments.

Responses of males and females to salinity were studied in order to reveal sex-specific adaptation and evolution in Populus cathayana Rehd cuttings. This dioecious tree species plays an important role in maintaining ecological stability and providing commercial raw material in southwest China. Female and male cuttings of P. cathayana were treated for about 1 month with 0, 75 and 150 mM NaCl. Plant growth traits, gas exchange parameters, chlorophyll pigments, intrinsic water use efficiency (WUEi), membrane system injuries, ion transport and ultrastructural morphology were assessed and compared between sexes. Salt stress caused less negative effects on the dry matter accumulation, growth rate of height, growth rate of stem base diameter, total number of leaves and photosynthetic abilities in males than in females. Relative electrolyte leakage increased more in females than in males under salinity stress. Soil salinity reduced the amounts of leaf chlorophyll a, chlorophyll b and total chlorophyll, and the chlorophyll a/b ratio more in females than in males. WUEi decreased in both sexes under salinity. Regarding the ultrastructural morphology, thylakoid swelling in chloroplasts and degrading structures in mitochondria were more frequent in females than in males. Moreover, females exhibited significantly higher Na + and Cl − concentrations in leaves and stems, but lower concentrations in roots than did males under salinity. In all, female cuttings of P. cathayana are more sensitive to salinity stress than males, which could be partially due to males having a better ability to restrain Na + transport from roots to shoots than do females.

Male and female poplar ( Populus cathayana Rehd.) cuttings respond differently to salinity stress. To understand these differences better, comparative morphological, physiological, and proteomics analyses were performed. Treatments with different concentrations of NaCl applied to male and female poplar cuttings for 4 weeks showed that females reacted more negatively at the morphological and physiological levels than did males, visible as shriveled leaves, decreased growth, lowered photosynthetic capacities, and greater Na(+) accumulation. The proteome analysis identified 73 proteins from 82 sexually related salt-responsive spots. They were involved in photosynthesis, protein folding and assembly, synthesis and degradation, carbon, energy and steroid metabolism, plant stress and defense, redox homeostasis, signal transduction, and so forth. The sex-related changes of these proteins were consistent with the different morphological and physiological responses in males and females. In conclusion, the higher salt resistance of male P. cathayana cuttings is related to higher expression and lower degradation of proteins in the photosynthetic apparatus, more effective metabolic mechanism and protective system, and greater capacity of hydrogen peroxide scavenging. This research allows us to further understand the possible different management strategies of cellular activities in male and female Populus when confronted by salt stress.