Physiological and Biochemical Regulation of Dormancy and Sprouting in Potato Tubers (Solanum tuberosum L.)

At harvest, potato (Solanum tuberosum L.) tubers are in a dormant state and do not have the ability to sprout. After harvesting, tuber dormancy is released progressively. This release is accompanied by numerous physiological and biochemical changes, such as carbohydrate hydrolysis and the accumulation of saccharides, which are detrimental to the nutritional and processing qualities of potatoes. Endogenous hormones are thought to play a significant role in the regulation of tuber dormancy and in the onset of sprouting. This review aims to describe the involvement of all major classes of endogenous hormones in tuber dormancy, as well as the physiological and biochemical changes during these steps. Based on current scientific evidence, both abscisic acid (ABA) and ethylene are required for the induction of dormancy, however, only ABA plays a role in maintaining bud dormancy. Moreover, an increase in cytokinin sensitivity and content appear to be the principal factor leading to the release of dormancy. Changes in endogenous indole-3-acetic acid (IAA) and gibberellin (GA) content appear to be more closely related to the regulation of subsequent sprout growth. Physiological and biochemical changes during tuber dormancy and the termination of dormancy centre on carbohydrate levels and the activity of enzymes involved in carbohydrate metabolism. In particular, starch breakdown, accompanied by an increase in the concentration of sucrose and reducing sugars, appears to play an important role in the onset of sprouting of tuber buds. Many of these changes are initially observed in tissues in the region of the buds, but subsequent growth of the sprout significantly affects the metabolism of tissues in other regions of the tuber. The application of dormancy-breaking chemicals, such as bromoethane, or phytohormones (GA3), to potato tubers induces metabolic changes that lead to dormancy breakage. These changes differ between treatments and also from those occurring when dormancy is broken naturally. _____________________________________________________________________________________________________________