Studies of the Status of Starch Phosphorylation in Developing Tubers from Various Potato Cultivars

Abstract

Potato is one of the most important food crops of the world. It is cultivated for its tubers, which are modified stem structures formed by the enlargement of the tips of underground stems. A crucial feature of the post-harvest physiology of potato tubers is an undesirable process called cold-induced sweetening. A comprehensive biochemical and molecular approach need to be undertaken to overcome such problem in the cultivars suitable to our agroclimatic conditions. Currently, phosphorylation status of starch in potato tubers is believed to play a crucial role in the above process as phosphate groups attached to glucose residues at C-6 and C-3 positions alter overall secondary structure of starch hence its degradability at low temperature. We need to have an insight to find correlation between starch phosphorylarion and cold sweetening process. Keeping in view with the above aim a few basic experiments were done and executed in this dissertation work. The study was done on several potato cultivars namely Kufri Chipsona-1 (CS-1), Kufri Chipsona-2 (CS-2), Kufri Chandramukhi (KCM), Kufri Jyoti (KJ), Kufri Pukhraj (PR), Kufri Ashoka (AS) and Cultivar Desiree (DE), which were routinely micropropagated in our laboratory. After proper hardening and acclimatization, the potato plantlets of the above mentioned varieties were cultivated in the field in the second week of November 2003. Developing mini-tubers were collected time to time through out the entire period of cultivation. Mature tubers from various cultivars were also transferred to 200C for a period of four weeks as required in this study. A rapid and convenient method was adopted during isolation of starch granules from various tuber samples and overall yield was calculated in gm per 100 gm of tuber weight. Starch-bound phosphates were converted to inorganic phosphates by complete ashing procedure. A very sensitive ascorbic acid-ammonium molybdate assay method was adopted for estimation of total phosphorus. The level of free phosphates was also checked in various starch preparations. The purpose was to see the status of starch phosphorylation in the tubers at various stages of development. This study was extended to the several potato cultivars that were routinely micropropagated in our laboratory. With respect to the above biochemical attribute profile was made for each cultivar variety and finally a comparison also made among the cultivars. This type of study could help further to find correlation between starch phosphorylation and cold sweetening phenomenon.