Experimental Studies of the Shoot Apical Meristem of Seed Plants. I. Morphological and Cytochemical Effects of IAA Applied to the Exposed Meristem of Lupinus Albus

Application of 1.5 μg indoleacetic acid (IAA) in a lanolin droplet to the exposed apical meristem of Lupinus albus seedlings caused: (1) axillary buds to form closer to the apex than normal, (2) displacement of primordia formed during the first two plastochrons following treatment, and (3) significant increases in concentration of RNA, protein, and unsaturated lipids in the meristems. Primordial displacement tended to be random relative to the site of the treatment, which may be a feature common to dicotyledonous plants exhibiting spiral phyllotaxis. That IAA conferred initiation site capabilities to all of the peripheral zone for a short time was indicated by (2) and (3) above, and by decreases in concentrations of the observed compounds toward control levels after the second plastochron following treatment. Effects of IAA on RNA suggest that nucleic acid metabolism, and possibly gene action, was involved in the response. Kinetin or gibberellic acid had no apparent morphogenetic effect on Lupinus meristems.