The Hormonal Regulation of Protonema Development in Mosses III. Auxin-Resistant Mutants of the Moss Funaria hygrometrica Hedw.

Abstract

Summary Mutants altered in their response to auxins were isolated from the moss Funaria hygrometrica by screening the mutagenized spores for growth on high concentrations of naphthaleneacetic acid. These mutants differ in the extent of their inability to form caulonema on Knop's medium (minimal medium without auxin), a behaviour also exhibited by wild type protonema grown in dim light. Of the four auxin-resistant mutants initially chosen, NAR-2 is the most distinct from the wild type by remaining totally in chloronema state on minimal medium. It exhibits caulonema differentiation only when subjected to exogenous auxins or the precursors of IAA. The sensitivity to IAA is not changed in comparison to the wild type. The auxin deficiency of the mutant NAR-2 seems neither to be due to a block of the auxin biosynthetic pathway nor to a block in its uptake/transport mechanism. However a 3 times higher activity of IAA oxidase has been found in the mutant as compared to the wild type. Auxin treatment stimulates the auxin oxidase activity in soluble and particulate fractions. In contrast, peroxidase activity is reduced in the mutant. The results support the hypothesis that the morphogenetic step of caulonema formation is regulated by the internal auxin level.