Regulation of some salt defense-related genes in relation to physiological and biochemical changes in three sugarcane genotypes subjected to salt stress

Sugarcane (Saccharum officinale L.; Poaceae) is a sugar-producing plant widely grown in tropic. Being a glycophytic species, it is very sensitive to salt stress, and salinity severely reduces growth rate and cane yield. The studies investigating the regulation of salt defense metabolite-related genes in relation to final biochemical products in both susceptible and tolerant genotypes of sugarcane are largely lacking. We therefore investigated the expression levels of sugarcane shaggy-like kinase (SuSK), sucrose transporter (SUT), proline biosynthesis (pyrolline-5-carboxylate synthetase; P5CS), ion homeostasis (NHX1), and catalase (CAT2) mRNAs, and contents of Na+, soluble sugar, and free proline in three sugarcane genotypes (A19 mutant, K88-92, and K92-80) when subjected to salt stress (200 mM NaCl). The relative expression levels of salt defense-related genes in salt-stressed plantlets of sugarcane cv. K88-92 were upregulated in relation to salt exposure times when compared with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as housekeeping gene. In addition, final biochemical products, i.e., low Na+, sucrose enrichment, and free proline accumulation, were evidently demonstrated in salt-stressed plantlets. Chlorophyll b, total chlorophyll, total carotenoid concentrations, and maximum quantum yield of PSII (F (v)/F (m)) in positive check (K88-92) were maintained under salt stress, leading to high net photosynthetic rate (P (n)) and growth retention (root length, fresh weight, and leaf area). In contrast, photosynthetic abilities in negative check, K92-80, and A19 mutant lines grown under salt stress declined significantly in comparison to control, leading to a reduction in P (n) and an inhibition of overall growth characters. The study concludes that the genetic background of sugarcane cv. K88-92 may further be exploited to play a key role as parental clone for sugarcane breeding program for salt-tolerant purposes.