Effects of auxins and chemically related non-auxins on photosynthesis and chloroplast ultrastructure in Alaria esculenta (Laminariales)

Abstract

Blade meristems of Alaria esculenta (L.) Grev. (Laminariales, Phaeophyta) were treated with growth-inhibiting concentrations (10−3 M) of auxins and chemically related non-auxins, e.g., 2,4- and 3,5-dichlorophenoxyacetic acids, respectively. Photosynthesis was inhibited with increasing effectiveness by both auxins and non-auxins in the following classes: naphthaleneacetic < naphthoxyacetic <phenoxyacetic acids. Inhibition was reversed by transferring sections to fresh seawater from naphthaleneacetic and naphthoxyacetic acids. Chloroplast swelling, observed in electron micrographs of lateral portions of Alaria blade meristems, was positively correlated with the degree of inhibition of photosynthesis. The ratio of 14C incorporation into mannitol and amino acid fractions of alcohol-soluble organic matter was also modified by the inhibitors, especially phenoxyacetic acids.A 50% increase in photosynthetic rate of the blade meristem occurs within 24 h of its excision from the Alaria frond.