Improved Salt Tolerance by Alleviating the Osmotic Stress, Ion Toxicity and Nutrient Imbalance In AhCMO Transgenic Cotton

Cotton is classified as one of the salt-tolerant crop, but it is often adversely affected by excessive salts in soil. Salinity mainly affects plant growth and development by way of osmotic stress, injurious effects of toxic ions and the resulting nutrient imbalance. The objective of this study is to explore the mechanism of improved salt tolerance in AhCOM transgenic cotton. A transgenic AhCOM cotton line (CMO4) and a non-transgenic cultivar (SM3) were sowed in 5 L pots containing substrate (seedling substrate : vermiculite=1:1 in volume) and allowed to grow in the greenhouse. When seedlings reached 2-true-leaf stage, NaCl solution was added in 50 mM increments every 12h, until the final concentration of 150 mM reached, and those irrigated with equal volume of tap water served as the corresponding controls (CK).

The results indicated that salt stress significantly decreased the fresh weight, dry weight, net photosynthetic rate and the K⁺/Na⁺ ratio of SM3 and CMO4, but compared with their respective control, the decrement in CMO4 is smaller than that of SM3, suggesting that AhCMO transgenic cotton was improved in salinity tolerance. Under 150 mM NaCl stress, the levels of glycine betaine, soluble sugar and proline in CMO4 were higher than those in SM3, but the MDA (malondialdehyde) content was lower; Salt stress increased the Na⁺ content in both SM3 and CMO4, much more Na⁺ was accumulated in SM3; Salt stress also reduced nutrient uptake such as N, P, K, and caused nutrient imbalance in both CMO4 and SM3 plants. However, 79.3% more P and 20.4% more K were accumulated in CMO4 than in SM3 plants.

In conclusion,  salt tolerance in AhCMO transgenic cotton (CMO4) was improved relative to wild cotton SM3. Improved salt tolerance was mainly attributed enhanced accumulation of osmoregulation substances, less Na⁺ accumulation in leaves, and improved nutrients uptake.