Influence of potassium nutrition and the nitrate ammonium ratio on the putrescine and spermidine contents in banana vitroplants

Potassium (K) is required in high doses by the banana (Musa sp.) plant and interacts with other nutrient elements in which banana tissues are maintain ed under in vitro condition as a consequence modifications in the plant met abolism take place mainly in nitrogen (N) compounds, such as proteins, amin o acids, and secondary compounds. When K is present in concentrations lower than that required, diamines such as putrescine and poliamines are formed. This metabolic disorder can also be correlated with the presence of differ ent inorganic N forms, such as nitrate (NO3) and ammonium (NH4), and the ra tios between both ions as well. In order to follow the physiological perfor mance of the interrelationships, K/putrescine and of the NO3/NH4 ratio in t he tissue of banana vitroplantlets, shoot apex of two banana cvs. Nanica an d Prata Ana were maintained in modified MS medium in the presence of six di fferent doses of K: 5, 10, 15, 20, 25, and 30 mM. After the period of tissu e proliferation the cultures were transferred to rooting media containing t he same different K doses. Dry matter, K, putrescine, and spermidine conten ts and their accumulation were determined in the shoots and roots of the vi troplantlets and in the shoot apex of the explant donor cultivar as well as the corresponding values for the whole vitroplantlets calculated. The data were statistically analyzed. The contents and accumulations of putrescine and spermidine in banana tissues were enhanced as K concentration decreased in the medium: four times (0.19% of the dry matter) for cv. Nanica and eig ht times (0.25% of the dry matter) for cv. Prata Ana. This behavior was not only related to the K depletion but to the NO3/NH4 ratio as well.