Physiological Studies on the Head Formation in Cabbage

III. Role of Terminal Bud in the Head Formation Posture

Abstract

1. At the beginning of head formation the effect of removal of small head including the terminal bud followed by application of 0.1% hormone paste to the stem stump on the nasty movement of wrapper leaves was investigated with cabbage grown in vinyl house.
When the terminal bud was removed, inner wrapper leaves assumed an elevated position, but outer ones did not.
The application of both NAA and BA to the stem of decapitated plants induced a downward movement of inner wrapper leaves, while the application of both GA and ABA induced an upward movement more remarkable than that in the lanolin paste control.
2. The effect of hormone application as a foliar spray before head formation on the nasty movement of wrapper leaves in relation to the head formation posture was investigated. Both NAA and BA induced a downward movement, while both GA and TIBA induced an upward movement. Especially the head formation posture was promoted by GA application showing the embrace posture due to both hyponasty of leaf petiole and cupping of leaf blade.
Nasty movement was not affected by BCB as in the control.
3. NAA spray induced the inhibition of leaf growth, followed by a decrease in leaf area, and also showed the increase of leaf shape index due to the inhibition of width growth more than length growth. On the contrary, TIBA, one of antiauxins, increased leaf area of inner leaves due to the promotion of length and width growth.
GA spray inhibited the width growth more than length growth in inner wrapper leaves, while promoted both the length and width growth in inner leaves, which resulted in an increase in leaf area.
BCB, an antigibberellin, showed no significant effect on the growth of length and width.
The growth of length and width, and especially of the latter was promoted by BA spray. Consequently both an increase in leaf area and a decrease in leaf shape index were found.
4. The effects of root pruning, decapitation and hormone treatment on the nasty movement were ascertained with seedlings having a pair of leaves roughly opposite to each other and grown in light and dark conditions.
(1) The heavier the root pruning, the more a pair of leaves curved upward. And the hyponasty movement was accelerated by the addition of decapitation both in the light and in the dark.
(2) NAA, BA, and Ethrel spray after decapitation promoted the downward movement in contrast to the upward movement by GA spray. TIBA and BCB showed little or no effect on nasty movement.
(3) When applied to the stem stump as 0.5% lanolin paste, NAA, BA, and Ethrel induced a downward movement, but on the contrary GA and ABA induced an upward movement.
5. The foregoing results suggested that the leaf petiolar epinasty was controlled by the hormone balance in apical region of the stem and the leaf shape might be controlled by the ratio of GA to BA.