Comparative physiological analysis of lotus (Nelumbo nucifera) cultivars in response to salt stress and cloning of NnCIPK genes

Saline or salt water in the ocean accounts for 96.5% of total fresh water resource in the planet. Salinity is a global social and economic problem which severely inhibited plant growth and development. Utilization of marginal salt affected land and/or water resource becomes increasingly important because of the explosion of world population and climate change. In this study, salt stress resistance of fifteen N. nucifera cultivars was firstly evaluated. The results showed that Welcoming Guests was the most resistant cultivar, while Hunan Lotus was the most sensitive one. Resistant cultivar Welcoming Guests accumulated significant higher amount MDA and proline than Hunan Lotus prior to salt stress treatment, indicating Welcoming Guests was pre-conditioned to salt stress. Salt sensitive lotus cultivar exhibited relative lower antioxidant enzyme activities and higher reactive oxygen species accumulation than resistant one after salt treatment. Since calcineurin B-like protein interaction protein kinase (CIPK)/SALT OVERLY SENSITIVE2 gene family played essential roles during plant salt stress response, three NnCIPK genes were successfully cloned in this study. Phylogenetic analysis showed that these genes were high homologous to Arabidopsis and grape CIPK genes. Expression level analysis indicated that NnCIPK6 was highly induced by NaCl treatment in resistant cultivar, while expression levels of NnCIPK14s showed fluctuation in susceptible cultivar after salt treatment. These results partially characterized mechanisms of lotus salt stress resistance and provided useful information for utilization of lotus cultivars in salt water.