Abstract
In arid and semiarid regions, low precipitation rates lead to soil salinity problems, which may limit plant establishment, growth, and survival. Herein, we investigated the NaCl stress effect on chlorophyll fluorescence, photosynthetic-pigments, movement and chloroplasts ultrastructure in chlorenchyma cells of Opuntia streptacantha cladodes. Cladodes segments were exposed to salt stress at 0, 100, 200, and 300 mM NaCl for 8, 16, and 24 h. The results showed that salt stress reduced chlorophyll content, Fv/Fm, ΦPSII, and qP values. Under the highest salt stress treatments, the chloroplasts were densely clumped toward the cell center and thylakoid membranes were notably affected. We analyzed the effect of exogenous catalase in salt-stressed cladode segments during 8, 16, and 24 h. The catalase application to salt-stressed cladodes counteracted the NaCl adverse effects, increasing the chlorophyll fluorescence parameters, photosynthetic-pigments, and avoided chloroplast clustering. Our results indicate that salt stress triggered the chloroplast clumping and affected the photosynthesis in O. streptacantha chlorenchyma cells. The exogenous catalase reverted the H2O2 accumulation and clustering of chloroplast, which led to an improvement of the photosynthetic efficiency. These data suggest that H2O2 detoxification by catalase is important to protect the chloroplast, thus conserving the photosynthetic activity in O. streptacantha under stress.
Highlights
To ensure their survival, plants have evolved to optimize the capture of energy and nutrients[1]
We performed chlorophyll fluorescence measurements in O. streptacantha to evaluate the effect of salinity on photosynthesis, by using cladode segments exposed to salt treatments at 0, 100, 200, and 300 mM NaCl for 8, 16, and 24 h
We found that the photosynthetic electron transport rate (ETR) was significantly reduced at 200 and 300 mM NaCl compared to the control (Supplementary Fig. S1)
Summary
Plants have evolved to optimize the capture of energy and nutrients[1]. The chloroplast movement in response to light (photo-relocation) is essential for the survival of plants under extreme light conditions[5, 6]. Our research group reported that the Opuntia streptacantha chloroplasts were grouped together within the cells under combined light and water stress, which probably maintain its photosynthetic process active in CAM plants[9]. Opuntia streptacantha is an endemic cactus from Mexico, which is distributed along the southern Chihuahuan Desert[14] It performs a CAM type photosynthesis, which permits a successful establishment of intracellular levels www.nature.com/scientificreports/. ROS are important signaling molecules involved in the control of plant growth, development, photosynthetic functions, and responses to biotic and abiotic stress[19,20,21]. The balance between ROS generation and ROS-scavenging during exposure to stressful environments is essential to regulate the mechanisms of ROS signaling in plants[26, 27]
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