The effects of auxin and antiauxin in an in vitro bioassay of flower regulatory activity in leaf exudate from tobacco plants

An in vitro bioassay system for floral bud formation has been established using Nicotiana tabacum L. cv. MC, explants excised from floral stalks cultured on modified Murashige‐Skoog medium containing excess auxin and antiauxin. Three auxins. indolyl‐3‐acetic acid (IAA), 4‐chloroindolyl‐3‐acetic acid and 5,6‐dichloroindolyl‐3‐acetic acid, were tested for floral bud‐forming activity; IAA was most efficient. Three antiauxins. 5,7‐dichlorindolyl‐3‐isobutyric acid (5,7‐Cl 2 ‐HBA), p ‐chlorophenoxyiso butyric acid and 2,3,5‐triiodobenzoic acid, were tested for the ability to reverse the inhibition of floral bud formation caused by excess IAA. Only 5,7‐Cl 2 ‐HBA was very effective. Leaf exudates from short day‐ and long day‐treated tobacco plants were added to the bioassay system which contained 1 µ M 6‐benzylaminopurine, 5 µ M IAA and 5 µ M 5, 7‐Cl 2 ‐HBA, Interestingly, only the leaf exudate from short day‐treated plants stimulated floral bud formation. Moreover, the buds produced grew into large. well‐developed ones with shapes similar to those of the natural floral buds of intact tobacco plants.