Abstract:

Soil salinity is becoming a serious threat to global agriculture including cotton. Although cotton has been classified as a salt-tolerant crop, it is also seriously attacked by salinity especially during emergence and seedling growth. Levels of glycine betaine, an osmoprotectant accumulated in plants during abotic stresses, vary among cotton genotypes, and positively correlated with the degree of salt tolerance. Therefore, enhancing glycine betaine synthesis is one of the most promising ways to improve salt tolerance in cotton. Choline monooxygenase (CMO) catalyzes the committed step in the synthesis of glycine betaine. AhCMO, a gene cloned from Atriplex hortensis, was introduced into the cotton (Gossypium hirsutium L.) hypocotyl explants of SM3 via Agrobacterium mediation, and the transformed plants were regenerated through somatic embryogenesis in tissue culture. After selection with 0.5% kanamycin, the kanamycin-resistant regenerated plants were confirmed to be electropositive by polymerase chain reaction (PCR). Southern and Northern blotting analyses further indicated the introduction and the expression of AhCMO gene in transgenic cotton plants, respectively. At the two true-leaf stage, transgenic cotton seedlings were treated with 0.5% NaCl for 15 days under greenhouse conditions, plant height, fresh weight per plant and net photosynthetic rate were determined. The results showed that NaCl stress decreased plant height, fresh weight per plant and net photosynthetic rate by 37.3%, 54.6%, and 47.9% for transgenic plants, and by 57.6%, 65.6%, and 69.9% for non-transgenic SM3, compared with their corresponding NaCl-free controls, respectively. The fact that less injury of NaCl to transgenic plants than to non-transgenic plants, suggested that induction and expression of AhCMO considerably enhanced salinity tolerance of transgenic cotton plants. Transgenic cotton with improved tolerance against salt stress is of great agronomic value. However, it should be noted that the improvement in salt tolerance of the transgenic lines is still limited. An integration of the transgenic technology and the traditional breeding technique may further improve both salt-tolerance and other agronomic properties of cotton.

Key words: Cotton, Choline monooxygenase, Genetic transformation, Salinity tolerance