dentified among the known flowering genes. Among the genes downstream of FT, the expression of the APETALA1 homolog correlated well with the flowering response, but the expression of the FD homolog was not detected (Yamada, unpublished data).

5. Interaction between SA and PnFT2 in the Regulation of Stress-Induced Flowering

We hypothesized that stress-induced flowering is regulated by PnFT, which is induced by SA. Accordingly, we examined the influences of both a PAL inhibitor and SA on PnFT expression in pharbitis. AOA inhibited flowering and PnFT2 expression induced by poor nutrition, and SA eliminated the inhibitory effects of AOA [15]. SA enhanced PnFT2 expression under poor nutrition but not under non-stressful conditions. These results suggest that SA induces PnFT2 expression, which in turn induces flowering. This conclusion is consistent with the results observed in A. thaliana and sunflower, in which SA induced the expression of FT and HAFT, a sunflower ortholog of FT [12,37]. However, SA did not induce PnFT2 expression and flowering under non-stressful conditions in pharbitis, suggesting that SA alone may not be sufficient to induce PnFT2 expression. Stress may induce the production of SA and other unknown factor(s), which may work in combination to induce PnFT2 expression and flowering.

6. Conclusion

Pharbitis is typically induced to flower under SD conditions and can be induced to flower under unfavorable photoperiodic conditions when exposed to stress. Stress activates PAL and enhances SA levels, promoting PnFT2 expression to induce flowering. However, SA alone cannot induce flowering, and other factors are necessary. The regulation of stress-induced flowering by SA may be common, at least in L. paucicostata and A. thaliana.


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