Deciphering the possible mechanism of exogenous NO alleviating alkali stress on cucumber leaves by transcriptomic analysis

Alkali stress is a major factor that limits crop yield, and nitric oxide (NO) is involved in the regulation of plants tolerant to abiotic stress. In the present study, sodium nitroprusside (SNP), a NO donor, reversed the chlorosis of cucumber leaves caused by alkali stress. Physiological analysis indicated that application of SNP protected mesophyll cell ultrastructure from damage by alkali stress. SNP increased nutrient element utilization, pigment content, photosynthetic capacity and accumulation of organic acids. In this study, Solexa sequencing was used to investigate the effect of SNP on expression of genes involved in cucumber response to alkali stress. About 5.9 million (M) and 5.8 M 21-nt cDNA tags were sequenced from the cDNA library of the alkali treatment and SNP treatment, respectively. When annotated, a total of 10,271 genes for the alkali stress treatment from the Solexa sequencing tags and 10,288 genes for SNP treatment were identified. We detected 901 differentially expressed genes in two samples, of which 437 and 464 of them were up- or down-regulated by SNP under alkali stress, respectively. The expression levels of 11 differentially expressed genes were confirmed by real-time RT-PCR. The trends observed agreed well with the Solexa expression profiles, although the degree of change was diverse in amplitude. Gene ontology analysis revealed that differentially expressed genes were mainly involved in response to abiotic stress, cellular metabolic process, photosynthesis, transmembrane transportation and organelle development, which were in accordance with physiological results.

► Exogenous NO reversed the chlorosis of cucumber leaves induced by alkali stress.
► Decipher the mechanism of NO alleviating alkali stress from global gene expression.
► Organic acid accumulation could be partly responsible for NO alleviating alkali stress.
► Exogenous NO protected membrane system from alkali stress damage.