A role for spermidine in the bolting and flowering of Arabidopsis

Several lines of experimental evidence indicate a close connection between polyamines (PAs) and reproductive development in Arabidopsis thaliana. (I) Measurement of the titers of endogenous spermidine (SPD) and putrescine (PUT), extracted from various organs of two ecotypes and a genetic line of Arabidopsis, revealed that flowers had the highest titers of both PAs, with SPD predominating. (2) In aseptic cultures of whole plants of the ecotype Columbia, the application of appropriate enzyme inhibitors lowered SPD titer while almost completely preventing bolting and flowering. When the plants were removed to an inhibitor-free medium, bolting and flowering resumed. (3) SPD added to the medium of aseptically cultured plants of Columbia growing under short-day (SD) conditions, where flowering is naturally delayed, increased the SPD titer and augmented the rate and extent of flowering. Under long-day (LD) conditions, where flowering is already rapid and abundant, it did not promote flowering any further. (4) Enzyme inhibitors of SPD synthesis given shortly before the transition from SD conditions to LD conditions prevented flowering. (5) In a delayed-flowering mutant (CS 3123), the addition of SPD significantly accelerated flowering.