Abstract
Tetraploid black locust (Robinia pseudoacacia L.) is adaptable to salt stress. Here, we compared morphological, physiological, ultrastructural, and proteomic traits of leaves in tetraploid black locust and its diploid relatives under salt stress. The results showed that diploid (2×) plants suffered from greater negative effects than those of tetraploid (4×) plants. After salt treatment, plant growth was inhibited, photosynthesis was reduced, reactive oxygen species, malondialdehyde content, and relative electrolyte leakage increased, and defense-related enzyme activities decreased in 2× compared to those in 4×. In addition, salt stress resulted in distorted chloroplasts, swollen thylakoid membranes, accumulation of plastoglobules, and increased starch grains in 2× compared to those in 4×. However, 4× developed diverse responses under salt stress. A comparative proteomic analysis revealed that 41 and 37 proteins were differentially expressed in 2× and 4×, respectively. These proteins were mainly involved in photosynthesis, stress and defense, energy, metabolism, transcription/translation, and transportation. Distinct patterns of protein changes between 2× and 4× were analyzed. Collectively, our results suggest that the plants showed significantly different responses to salt stress based on ploidy level of the plant. The 4× possessed a better salt protection mechanism than that of 2×, suggesting salt tolerance in the polyploid plant.
Highlights
Soil salinity is a major environmental stressor that severely limits crop growth and harvest worldwide [1]
Little was known about the implications of ploidy level in black locust on the physiological and proteomic responses under salt stress
The physiological and proteomic responses of 2× and 4× black locust were detected under salt stress during different times
Summary
Soil salinity is a major environmental stressor that severely limits crop growth and harvest worldwide [1]. Plants have evolved complex mechanisms to adapt to salt stress based on modifications in metabolites, gene expression and proteins. Many genes responding to salt stress in plants have been identified [4]. These genes do not offer insight into the quantity and quality of the final gene products, i.e., the proteins that are regulated at the translational level [5]. Earlier reports based on proteomics have mainly focused on the responses of diploid (2×) plants, and the proteomic knowledge of the response to salt stress by polyploids is very limited
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