BRASSINOLIDE AFFECTS THE RATE OF CELL-DIVISION IN ISOLATED LEAF PROTOPLASTS OF PETUNIA-HYBRIDA

Brassinosteroids are known to promote cell elongation in a wide range of plant species but their affect on cell division has not been as ext ensively studied. We examined the effect of brassinolide on the kineti cs and final division frequencies of regenerating leaf mesophyll proto plasts of Petunia hybrida Vilm v. Comanche. Under optimal auxin and cy tokinin conditions, 10-100 nM brassinolide accelerated the time of fir st cell division by 12 h but had little effect on the final division f requencies after 72-120 h of culture. One micromolar brassinolide show ed the same acceleration of first cell division but inhibited the fina l division frequency by approximately 20%. Under sub-optimal auxin con ditions, 10-100 nM brassinolide both accelerated the time of first cel l division and dramatically increased the 72- to 120-h final division frequencies. Isolated protoplasts may provide a useful model system to investigate the molecular mechanisms of brassinosteroid action on cel l proliferation.