Salicylic acid and the flowering gene FLOWERING LOCUS T homolog are involved in poor-nutrition stress-induced flowering of Pharbitis nil

The short-day plants Pharbitis nil (synonym Ipomoea nil), var. Violet and Tendan were grown in a diluted nutrient solution or tap water for 20 days under long-day conditions. Violet plants were induced to flower and vegetative growth was inhibited, whereas Tendan plants were not induced to flower, although vegetative growth was inhibited under these conditions. The Violet plants induced to flower by poor-nutrition stress produced fertile seeds and their progeny developed normally. Defoliated Violet scions grafted onto the rootstocks of Violet or Tendan were induced to flower under poor-nutrition stress conditions, but Tendan scions grafted onto the Violet rootstocks were not induced to flower. These results indicate that a transmissible flowering stimulus is involved in the induction of flowering by poor-nutrition stress. The poor-nutrition stress-induced flowering was inhibited by aminooxyacetic acid, a phenylalanine ammonia-lyase inhibitor, and this inhibition was almost completely reversed by salicylic acid (SA). However, exogenously applied SA did not induce flowering under non-stress conditions, suggesting that SA may be necessary but not sufficient to induce flowering. PnFT2, a P. nil ortholog of the flowering gene FLOWERING LOCUS T ( FT) of Arabidopsis thaliana, was expressed when the Violet plants were induced to flower by growing in tap water, but expression of PnFT1, another ortholog of FT, was not induced, suggesting the specific involvement of PnFT2 in stress-induced flowering.