Physiological Changes in Mesembryanthemum crystallinum During the C3 to CAM Transition Induced by Salt Stress

Abstract

Salt stress impedes plant growth and development, and leads to yield loss. Recently, a halophyte species <i>Mesembryanthemum crystallinum</i> has become a model to study plant photosynthetic responses to salt stress. It has an adaptive mechanism of shifting from C₃ photosynthesis to crassulacean acid metabolism (CAM) photosynthesis under stresses, which greatly enhances water usage efficiency and stress tolerance. In this study, we focused on investigating the morphological and physiological changes [e.g., leaf area, stomatal movement behavior, gas exchange, leaf succulence, and relative water content (RWC)] of <i>M. crystallinum</i> during the C₃ to CAM photosynthetic transition under salt stress. Our results showed that in <i>M. crystallinum</i> seedlings, CAM photosynthesis was initiated after 6 days of salt treatment, the transition takes place within a 3-day period, and plants became mostly CAM in 2 weeks. This result defined the transition period of a facultative CAM plant, laid a foundation for future studies on identifying the molecular switches responsible for the transition from C₃ to CAM, and contributed to the ultimate goal of engineering CAM characteristics into C₃ crops.