DEVELOPMENT, GENETICS AND MOLECULAR-BIOLOGY OF MOSSES

The first descriptions of sex chromosomes in plants, of the continuity of chromosomes during the mitotic cycle and of non-Mendelian inherita nce as well as the introduction of UV-mutagenesis to genetic research are landmarks in biological sciences first achieved by scientists work ing on bryophytes. Haploidy of the tissue facilitates mutant isolation and many developmental moss mutants have been isolated. Early moss de velopment is triggered by auxin, by cytokinin and by light, mainly act ing via phytochrome and a blue-light receptor. Due to the simplicity o f the plants, development can be pinpointed to the differentiation of a single cell and be analysed in living tissue, making mosses ideal ca ndidates for the analysis of development in an integrated approach of cell and molecular biology. Molecular genetic techniques have been app lied mainly to Physcomitrella patens (Hedw.) B.S.G., where efficient p rotocols for transformation of nuclear DNA have been established and s everal nuclear, chloroplast and mitochondrial genes have been analysed . These studies reveal that Physcomitrella may be an appropriate model to study plant development in molecular terms. Recently, it has been shown that, in this species, nuclear genes can be targeted very effici ently by homologous recombination, now opening the door to reverse gen etics for plant biologists.