Soluble Acid Invertase (SAI) Activity and Gene Expression Controlling Sugar Composition in Sugarcane

Abstract

Enhancing cane and sugar productivity is the major concern of sugarcane growing countries. The present study was aimed to monitor the expression of SAI gene related to the sugar content during elongation phase and its modulation at the onset of cane ripening using an early maturing, high-sugar genotype (CoJ 64) and a mid-late maturing, low-sugar genotype (BO 91). The results indicated comparatively higher concentrations of non-reducing, total sugars and non-reducing/reducing sugar ratio (NRS/RS ratio) in CoJ 64 in all plant tissues (root, stalk and leaf); the highest was in stalk tissue. Similar to sugar content, Brix value (a field indicator of sucrose content) was also higher in CoJ 64. In contrast to this, reducing sugars content, SAI enzyme activity and gene expression level were relatively higher in BO 91. Root tissues showed higher SAI gene expression in BO 91 as compare to CoJ 64, indicating its utility as a molecular tool for characterizing high- and low-sugar genotypes at an early growth stage. Correlation data indicated a negative association of SAI activity and gene expression with non-reducing sugars and NRS/RS ratio, but positive with reducing sugars contents. Differential SAI expression in low- and high-sugar genotypes at the stage of crop elongation may help to manipulate sucrose accumulation process in low-sugar genotypes. In this domain, an effort was also made to improve sucrose content in cane stalk of BO 91 during inclined phase using enzyme effectors (Mg, Mn, B, Mg + Mn, ethrel and a mixture of Mg + Mn + ethrel as a chemical formulation). Chemical formulation was found to be more effective for increasing sucrose content with reduced SAI activity. Findings thus suggest downregulation of SAI activity in response to foliar application of chemical formulation vis-a-vis improvement in sucrose content might be due to significant negative association of SAI gene with non-reducing sugars (sucrose) in both low- and high-sugar genotypes.