Studies on the regulation of Chrysanthemum flowering with special reference to plant regulators. II

Inhibitor in non-induced leaves

Abstract

The previous experiments with Chrysanthemum (var. Ginpa), a short-day plant, showed that LD leaves exert an inhibition on the action of floral stimulus produced in SD leaves. The present experiment suggests that LD leaves would produce some floral inhibitors, acropetally transmissible like floral stimulus.
The plants of Ginpa chrysanthemum with some 22 leaves fully expanded were subjected to localized SD treatments.
1. Seven or three upper leaves were exposed to SD, while the remaining leaves to LD. When seven leaves were given SD, initial stem elongation and the rate of leaf differentiation were slightly less, while the number of days to bud appearance was almost the same, as compared with the results when the entire plant was given SD. When three leaves were given SD, lower LD leaves exerted inhibition on stem elongation and less pronounced inhibition on the rate of leaf differentiation, the plants thus showing growth of rosette-type. No flower bud was observed during the 82 days of experiment, while some of the plants wilthout lower LD leaves produced the flower buds.
These results seem to support the idea that floral inhibition of lower LD leaves results from the effects of some transmissible inhibitor produced in LD leaves.
2. Three or 7 upper leaves were exposed to LD and all of the others to SD. When three leaves were given LD initial stem elongation and the rate of leaf differentiation were slightly less, but afterwards more, as compared with the results when the entire plant was given SD. Flower bud initiation was delayed. When seven leaves were given LD, stem elongation was much reduced, while the rate of leaf differentiation was slightly lower only in the initial stage of treatments. The upper LD leaves grew larger than those of the former and plants showed a rosette-type growth. No flower bud was observed during the experimental period.
Floral inhibition by upper LD leaves seems to be caused by an inhibitor produced in the LD leaves through its effect on the action of floral stimulus at the apex, since the promotion or inhibition of growth is unlikely to be due to mere dilution effects of LD leaves on floral stimulus.
3. It is suggested that the ratio-floral stimulus/inhibitor at the apex may play a significant role in the process leading to flower bud formation and in plant growth.