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.