Effects of the developmental state of the tissue on the competence for flower bud regeneration in pedicel explants of tobacco.

The competence of pedicel explants of tobacco (Nicotiana tabacum L. cv Samsun) to regenerate flower buds in response to auxin was manipulated by preincubating excised tissues in the absence of auxin. When exposed to 1 micromolar 1-naphthaleneacetic acid, these tissues formed fewer buds than controls that were not preincubated. The number of buds eventually formed correlated with the 1-naphthaleneacetic acid concentration in the tissue 6 hours after the start of hormone application. The internal concentrations in pretreated explants were lower than in tissues that were not pretreated due to diminished uptake per milligram fresh weight and increased hormone conjugation. The change in the developmental state induced by auxin deprivation had a dual effect on bud regeneration: (a) the pretreatment caused fewer buds to be formed at any 1-naphthaleneacetic acid concentration tested, and (b) a higher auxin concentration in the medium was required to get a maximum bud number on precultured explants. An increase of the 1-naphthaleneacetic acid concentration in the medium led to an elevated hormone level in freshly cut as well as in preincubated tissues. It was concluded that the developmental state of the tissue directly affects the maximum number of buds that can be regenerated. Apart from that there is an indirect effect exerted via modulation of the ratio between external and internal auxin concentration. The change in this ratio can be compensated for by an adjustment of the auxin concentration in the medium.