INCREASED LEVEL OF CYTOKININ RIBOSIDES IN JASMONIC ACID-TREATED POTATO (SOLANUM-TUBEROSUM) STEM NODE CULTURES

Cytokinin free bases, ribosides and 9-glucosides were measured in stem node cultures of potato (Solanum tuberosum L. cv. Ulster Sceptre) in the presence or absence of 1 mu M jasmonic acid (JA) to examine whethe r or not their changed levels were part of the JA-induced growth respo nse. The enhanced growth response in JA-treated plantlets included: ex panded root systems, extended leaf areas, increased number of nodes, a nd enlarged stem diameters. The protein analysis revealed a substantia l decrease in a 62-kDa polypeptide. On a dry weight basis, the levels of ribulose-1,5-biphosphate carboxylase/oxygenase (RuBP carboxylase, E C 4.1.1.39) and chlorophylls a and b were constant. The total concentr ation of endogenous cytokinins remained virtually the same in control and treated plantlets; but in JA-treated plantlets the amount of cytok inin free bases and cytokinin 9-glucosides decreased. In addition, the level of cytokinin ribosides was elevated. The ratio between active a nd inactive cytokinins increased from 1.2 to 2.1, which correlates wit h the enhanced growth of potato plantlets grown on 1 mu M JA. Thus the observed growth and developmental changes may be a consequence of the measured altered cytokinin level. However, significant morphological alterations of the potato plantlets treated with JA may also be a resu lt of the changed critical cytokinin concentration or critical ratios of cytokinins to auxins and JA, rather than their absolute concentrati ons.