Abstract
The short-day plant Pharbitis nil (synonym Ipomoea nil) can flower under long-day conditions when stressed. P. nil, var. Violet was induced to flower by poor-nutrient stress whereas var. Tendan was not. The plants induced to flower by stress produced fertile seeds and the progeny developed normally. The defoliated Violet scions grafted onto rootstocks of Violet or Tendan were induced to flower under the stress conditions, but the Tendan scions grafted onto Violet rootstocks were not. The results indicate that a transmissible flowering stimulus is involved in the stress-induced flowering. Tendan produces the flowering stimulus, but does not respond to it. Anthocyanin was accumulated in the roots of P. nil grown in tap water suggesting that the stress enhanced the activity of phenylalanine ammonia-lyase (PAL). In fact, higher PAL activity was detected in the plants which flowered by stress. The PAL Inhibitor inhibited the stress-induced flowering, and this inhibition was reversed by salicylic acid (SA). The endogenous SA level increased when flowering was induced by stress. PnFT2, a P. nil ortholog of the flowering gene FLOWERING LOCUS T (FT) of Arabidopsis thaliana, was strongly expressed under poor-nutrient stress conditions, but PnFT1, another ortholog of FT, was not. The expression of PnFT2 and a weak expression of PnFT1 were induced by cold stress. PnCO, a P. nil ortholog of CONSTANS (CO) of A. thaliana, was not involved in stress-induced flowering of P. nil.
