Role of polyamines in gibberellin-induced internode growth in peas.

To determine the requirement for polyamines in gibberellin (GA) induced internode growth polyamine content was measured in internodes of peas of various internode phenotypes (slender, tall, dwarf, nana) with and without applied gibberellin (GA(3)) and polyamine synthesis inhibitors. Polyamines were assayed as dansyl derivatives which were separated by reverse phase high performance liquid chromatography and detected by fluorescence spectrophotometry. The amounts of polyamines in the different genetic lines of peas, which differed in internode lengths and extractable GA content, correlated with the extent of internode elongation. High polyamine concentrations were associated with young internodes and decreased with internode expansion. Extremely short internodes of nana plants without GA exhibited equal or higher amine concentrations relative to internodes of other lines of peas and GA-stimulated nana seedlings. The polyamine synthesis inhibitors, alpha-difluoromethylornithine and alpha-difluoromethylarginine, independently or in combination, inhibited polyamine accumulation and internode elongation of tall peas and GA-stimulated nana plants. Agmatine and putrescine restored growth and endogenous polyamine content to variable degrees. However, exogenous polyamines were not effective in promoting growth unless intracellular amines were partially depleted.These results suggest that polyamines do not have a role in cell elongation, but may be required to support cell proliferation. Polyamines do not mediate the entire action of GA in internode growth of peas since GA induction of growth involves both cell division and cell elongation, whereas polyamines appear to affect cell division only.