POLYAMINES IN SOLANUM-TUBEROSUM IN-VITRO - FREE AND CONJUGATED POLYAMINES IN HORMONE-INDUCED TUBERIZATION

The putative role of polyamines (PAs) in in vitro tuberization in sing le leaved cuttings of Solanum tuberosum was investigated by comparing the pattern of distribution of acid-soluble free and bound PAs (putres cine (PUT), spermidine (SPD), spermine (SPM)) in shoots grown on non-t uber-inducing, hormone-free and tuber-inducing hormone-augmented mediu m. Exogenous free PAs (PUT, SPD, SPM each at 10(-4) M) and/or phenolic acids (t-cinnamic, caffeic, chlorogenic, p-coumaric and ferulic acid, each at 10(-5) M) had no tuber-inducing effect when supplied in hormo ne-free medium, and growth, morphology and endogenous distribution of PAs were largely unaffected. Under non-tuberizing conditions, PUT was the main free PA followed more or less closely by free SPD and, by a w ider margin, free SPM. The profile of conjugated PAs was dominated by conjugated SPD. Conjugated PUT was the least abundant. Distinct modifi cations of the profile of both free and conjugated endogenous PAs were found to be associated with the process of tuberization. On tuber ind uction by cytokinin (benzylaminopurine 2 mg/L) and auxin (indol-3-ylac etic acid 1 mg/L) free SPD became the main PA relegating free PUT to s econd place. The overall content of conjugated PAs increased. The dist ribution of the individual conjugated PAs shifted: conjugated SPD decr eased and conjugated SPM increased with tuberization. In the system us ed, tuberizing conditions can be characterized by ratios between the i ndividual PAs: free PUT/SPD below 1, conjugated PUT/SPD above 1 and co njugated SPD/SPM at least below 0.5.