A Comparative Auxin and Cytokinin Study in Normal and to-2 Mutant Tomato Plants

Torosa-2 (to-2), a tomato mutant with strong apical dominance,was studied in order to determine the mechanism of shoot outgrowthcontrol. In decapitated or defoliated to-2 plants only a fewshoots grew and IAA or morphactin application had little oronly short term effects. No differences were found in auxinand cytokinin activities between normal and mutant plants upto 20 days after sowing. In the period from 40 to 90 days theIAA content increased equally in both genotypes. During thesame period, however, cytokinin increased only in normal plants.The results obtained with the to-2 mutant indicate that budsdo not shoot, probably because bud differentiation does notoccur. The ratio of auxin to cytokinin clearly was affectedby the low level of cytokinin in all tissues of the to-2 plants.This led us to the conclusion that insufficient quantities ofcytokinin for lateral bud differentiation is the cause of thestrong apical dominance in to-2. (Received January 20, 1982; Accepted April 26, 1982)