Molecular studies on soluble acid invertases in the potato solanum tuberosum l tubers

Abstract

Sucrose is a disaccharide composed of glucose and fructose, i.e. Glc (and#61537;1and#61611;2and#61538;) Fru or Fru (and#61538;2and#61611;1and#61537;) Glc. This nonreducing sugar is a major intermediate product of photosynthesis. Sucrose synthesis occurs exclusively in the cytosol of photosynthetic cells. In many plants sucrose represents the most common form of sugar found in translocation stream where it is transported from leaves (source) to nonphotosynthetic tissues (sink) such as flower, fruit, seed, and root. Sucrose not only plays a vital role in plant growth and development but is also a leading commercial commodity. Sucrose and hexoses also play signaling roles in regulating gene expression and plant development. The cleavage reaction of sucrose is catalyzed by two enzymes in higher plants: Sucrose synthase (Sus, EC 2.4.1.13) or invertase (INV, EC 3.2.1.26). Sus degrades sucrose in the presence of UDP into UDP-glucose and fructose, where as the INV hydrolyses sucrose into glucose and fructose. Based on their solubility, subcellular localization, pH optima and isoelectric point, three different types of invertase isoenzymes can be distinguished: i) vacuolar invertase (VIN)-most plant species contain at least two isoforms of vacuolar invertase; ii) cell wall invertase (CWIN)-several isoforms of extracellular invertase ionically bound to the cell wall; iii) neutral invertases-also known as cytoplasmic invertases (CIN). CWIN is known to play crucial role during flower, seed, and fruit development; whereas VIN as a key modulator for hexose accumulation and cell expansion, but the role of CIN in plants is still unclear. newline Potato is a very important member of the Solanaceae family. Currently, potato is the third most important food crop which comes only after wheat and rice. Storage of potato tubers at low temperatures (~ 40C) for several weeks leads to breakdown of starch into sugars in tubers with consequent accumulation of reducing sugars-a phenomenon known as cold-induced sweetening which negatively affects the quality of potato chips and French fries.