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 Mesembryanthemum crystallinum has become a model to study plant photosynthetic responses to salt stress. It has an adaptive mechanism of shifting from C 3 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 M. crystallinum during the C 3 to CAM photosynthetic transition under salt stress. Our results showed that in M. crystallinum 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 C 3 to CAM, and contributed to the ultimate goal of engineering CAM characteristics into C 3 crops.

Salinity and Salt-Priming Impact on Growth, Photosynthetic Performance, and Nutritional Quality of Edible Mesembryanthemum crystallinum L.

“…CAM acidity of salt-primed M. crystallinum L., which were gradually transferred from 10% ASW to 100% ASW was 4 to 8-fold higher than those grown in the other salinity conditions ( Figure 5 B). This result agrees with the recent study by Guan et al [ 41 ], which indicates that when M. crystallinum L. is under high salt stress, it has an adaptive mechanism of switching its photosynthetic mode from C 3 photosynthesis to CAM to enhance water use efficiency. When plants use CAM photosynthesis, photorespiration is reduced as they only open their stomata in the night to prevent water loss.…”

At the Edges of Photosynthetic Metabolic Plasticity—On the Rapidity and Extent of Changes Accompanying Salinity Stress-Induced CAM Photosynthesis Withdrawal

“…This is often recognised as a key factor allowing normal growth and development under water-related stresses. A recent study regarding the symptoms of stress-related CAM induction in the common ice plant confirmed the occurrence of β-carboxylation after 6 days of salt treatment [5]. The reorganisation of the CO 2 metabolism is accompanied by substantial modifications at the chloroplast ultrastructure, photosystem reactive centre organisation and photochemical efficiency levels [6].…”

“…An earlier study on the functionality of the photosynthetic apparatus in M. crystallinum showed higher and similar quantum efficiencies of PSII and PSI, respectively, in salt-stressed (CAM) plants than in control (C 3 ) plants [5]. Our analysis revealed quite a different picture of PSII and PSI functionality during a similar salt treatment, with lower PSII and PSI quantum efficiencies, elevated nonphotochemical quenching (NPQ), decreased photochemical quenching (qL) and elevated acceptor side limitation (Y ND ) of PSI detected at midday in salt-stressed plants.…”

Low Salinity Improves Photosynthetic Performance in Panicum antidotale Under Drought Stress

“…Salinity can even stimulate their growth by the accumulation of Na + and Cl − , i.e., cheap osmotica (Cheeseman, 2015). Such physiological mechanisms are well established in the literature (Muchate et al, 2016). In contrast, there exist a few studies on the combined effect of salinity and drought, and that, too, are on glycophytes, the plants of a non-saline environment, where reduction in plant biomass is a common finding (Ahmed et al, 2013).…”