Polyamines in Solanum tuberosum in vitro: Free and Conjugated Polyamines in Hormone-Induced Tuberization

Abstract

Summary The putative role of polyamines (PAs) in in vitro tuberization in single leaved cuttings of Solanum tuberosum was investigated by comparing the pattern of distribution of acid-soluble free and bound PAs (putrescine (PUT), spermidine (SPD), spermine (SPM)) in shoots grown on non-tuber-inducing, hormone- free and tuber-inducing hormone-augmented medium. 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 hormone-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 wider margin, free SPM. The profile of conjugated PAs was dominated by conjugated SPD. Conjugated PUT was the least abundant. Distinct modifications of the profile of both free and conjugated endogenous PAs were found to be associated with the process of tuberization. On tuber induction by cytokinin (benzylaminopurine 2 mg/L) and auxin (indol-3-ylacetic acid 1 mg/L) free SPD became the main PA relegating free PUT to second place. The overall content of conjugated PAs increased. The distribution of the individual conjugated PAs shifted: conjugated SPD decreased and conjugated SPM increased with tuberization. In the system used, tuberizing conditions can be characterized by ratios between the individual PAs: free PUT/SPD below 1, conjugated PUT/SPD above 1 and conjugated SPD/SPM at least below 0.5.