NITROGEN-INDUCED CHANGES IN THE GROWTH AND METABOLISM OF CULTURED POTATO-TUBERS

The effect of N source on 'Kennebec' potato (Solanum tuberosum L.) tuberization was investigated using single-node segments originated from in vitro virus-free plantlets and inoculated on media with two nitrate : ammonia ratios (low, 2:1; high, 5:1). Cell count and size and sugar-use characteristics were measured at intervals of tuber development. Tubers grown on high nitrate-ammonia medium exhibited higher rates of sucrose use and higher dry-matter accumulation than tubers grown on low nitrate-ammonia medium. The median value of tuber fresh weight increased from 0.66 to 1.23 g as a result of increasing nitrate-ammonia. Significant differences in cell size and growth rate were observed between the two N treatments. There was also a high correlation between tuber cell size and dry matter (p = 0.82, P less than or equal to 0.05). These data demonstrate the importance of the nitrate : ammonium ratio in determining C use, tuber cell size, and tuber weight. Chemical names used: alpha-naphtylacetic acid (NAA); 6-benzylaminopurine (BA).