Sugarcane, Sugar Metabolism and Some Abiotic Stresses

Sugarcane (Saccharum officinarum L.) is a multipurpose and commercial crop of Pakistan. Sugar for food remains the most important product of sugarcane, by-products of the crop, many of them from fiber, are a significant part of its economic production. Sucrose serves as the major form of carbohydrate storage in sugarcane. Metabolism of sucrose, a mobile source of energy and carbon, is an absolute requirement for the survival of heterotrophic plant organs. In these organs, different isoforms of invertase with discrete subcellular locations hydrolyze the disaccharide into hexoses and thereby, feed sucrose into various biochemical pathways. Different invertase isoforms exist in the vacuole, cytoplasm and apoplasm of plant cells. The acid isoforms, having activity optima at pH 4.5-5.5, are present in the vacuole and apoplast. The isoforms with activity optima near neutral pH and alkaline isoforms with activity optima at pH 8.0 are in the cytoplasm. In storage sinks, invertase activity is proposed to be important for creating a sucrose concentration gradient from the phloem to sink tissue and then maintaing the storage sink for promoting phloem unloading. Since sugarcane is the prime source of sugar production in Pakistan, it is imperative to investigate the physiological and biochemical basis of yield reduction under various abiotic stresses.