The maryland mammoth allele and rooting both perturb the fate of florally determined apices in Nicotiana tabacum.

The stability of the florally determined state in terminal and axillary buds of two tobacco cultivars was studied. We used Hicks and Hicks Maryland Mammoth, near-isogenic cultivars of Nicotiana tabacum differing at the recessive maryland mammoth locus which confers short-day behavior. The experimental design consisted of growing plants in short-day conditions and subjecting them to three bioassays in long-day conditions: in vitro culture of apices consisting of meristems and three to four leaf primordia; rooting of buds consisting of meristems and 8 to 12 leaves, leaf primordia, and internodes; and release from apical dominance of axillary buds in situ. Cultured terminal and axillary apices expressed floral determination, indicating that meristems can be florally determined. Two lines of evidence indicate that rooting destabilizes an already acquired florally determined state: cultured apices from both axillary and terminal buds produced fewer nodes after excision than homologous buds which were rooted; and a lower percentage of rooted axillary buds from Hicks Maryland Mammoth plants expressed floral determination than did homologous axillary buds grown out in situ in noninductive conditions. Rooted buds from the two genotypes expressed floral determination at different frequencies, but produced abnormal inflorescences at similar frequencies, indicating that roots and the maryland mammoth allele influence common as well as unique processes associated with floral determination.