Studies on the floral regulatory mechanism in a non-flowering cabbage mutant that spontaneously reacquires flowering ability

概要

‘nfc’ (non-flowering cabbage) was discovered as a non-flowering natural
mutant among the open-pollinated cabbage line ‘T15’ (Brassica oleracea L. var. capitata
L.) in 1978. ‘nfc’ has been propagated vegetatively by cutting for over 40 years. Cabbage
is a plant-vernalization-type plant, which can sense low temperatures only after
developing to a certain size, and also requires long-term low-temperature exposure for
flowering. ‘nfc’ hardy flowers under floral inductive conditions where ‘T15’ and other
cabbage cultivars flower at 100%. Meanwhile, another phenomenon in which lateral
shoots generated near the base of the main stem of ‘nfc’ flowered in spring has been
occasionally observed. Elucidation of the mechanism controlling the unique flowering
characteristics of ‘nfc’ is expected to provide new insights into the physiology of plant
flowering. The main objective of this study was to elucidate the non-flowering
mechanisms and the causes of spontaneous flowering in ‘nfc’.
In Chapter 1, to confirm the reproducibility of the flowering characteristics of
‘nfc’, I cultivated ‘nfc’ and the parental line ‘T15’ in the open field for three years.
Throughout the 3-year cultivation period, all ‘T15’ plants flowered, while the flowering
rates of ‘nfc’ were 0, 32, and 4%, in the first, the second, and the third years, respectively.
Consistent with previous observations, only the lateral shoots of ‘nfc’ flowered, while the
terminal bud of ‘nfc’ continued to grow vegetatively. The flowering dates of the flowering
‘nfc’ plants were later than those of ‘T15’, and the average numbers of flowering shoots
per plant of the flowering ‘nfc’ were lower than those of ‘T15’.
I hypothesized that ‘nfc’ is a chimeric plant composed of wild type and mutant
cells with and without flowering ability, respectively. ...