Polyamines as Growth Substances in Higher Plants
Aliphatic polyamines, recently recognized as a new class of plant growth substances or plant hormones (Bagni et al., 1982), are present in all the plants examined to date and mainly act on cell division processes. However, as other well-known plant hormones (auxins, cytokinins, gibberellins, but also abscisic acid and ethylene), they display a broad spectrum of effects on plant tissues, but very little is understood of the underlying events and processes. In spite of the wide variety of responses, the tendency is to generalize from observations made on a single type of response. We propose, therefore, to examine some of the characteristics of polyamines especially in relation to their role as plant growth substances. The early studies showed that in a plant tissue, temporarily lacking in polyamines, a positive effect on the induction of cell division was demonstrated by supplying exogenous polyamines (Bertossi et al., 1965), while in plants with a normal polyamine level this positive effect could not be recognized. Anyway a direct correlation between endogenous polyamine levels and growth rate was shown in normal and tumour plant tissues (Bagni and Serafini-Fracassini, 1979 and 1985). In the absence of plant mutants deficient in the enzymes responsible for putrescine synthesis, contrary to those isolated in microorganisms (Tabor and Tabor, 1983; Tabor et al., 1983) and animals (Pohjanpelto et al., 1981; Steglich et al., 1983), the approach used until a few years ago was to study the mechanisms of polyamine-induced plant growth by utilizing different competitive and irreversible inhibitors of polyamine synthesis.
KeywordsExternal Concentration Carrot Cell Polyamine Synthesis Plant Growth Substance Polyamine Transport
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