Keywords: Sugarcane, sink strength, gibberellins, sucrose, semi qRT-PCR
In sugarcane, stem sinks store photosynthates as soluble disaccharide, sucrose, and share a closely co-ordinated relationship with source leaves. Phytohormones like gibberellins (GA) have long been known to promote rapid elongation and division of cells. The current study has ascertained the effects of gibberellins on sucrose metabolism and consequently sucrose accumulation in the sugarcane culm. Since brix%, pol%, sucrose% and reducing sugar% are basic and mandatory parameters in assessing the sugar content of cane, these have been closely observed, and their pattern tracked and analysed. The effect of GA3 was clearly visible, 30 days after spraying (30 DAS), with a drastic increase in reducing sugar (RS) level, especially in the upper internodes, pointing to increase in sink potential. Even as the GA effect waned 60 DAS, the GA3 sprayed canes still showed prominently higher RS% values and complementarily, lesser sucrose%, brix%, pol% values, as compared to control canes. Also, 120 DAS, notably higher sucrose levels were observed in the GA3 sprayed culms. These biochemical findings have been further explored and correlated with end-point and qRT-PCR based data exhibiting differential expression of various sucrose metabolizing genes viz. the three invertases: soluble acid invertase (SAI), cell wall invertase (CWI), neutral invertase (NI) and also sucrose synthase (SuSy). Visibly higher expression of SAI and modified expression of other genes in GA3 treated plants, can perhaps be interpreted as a consequence of increase in sink strength caused by gibberellin treatment. This in turn, extrapolates to better assimilate uptake and hence, the obtained results affirm the role of GA3 in facilitating better sucrose accumulation.
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