(American Journal of Botany. ;90:0.)
© Botanical Society of America, Inc.
Down regulation
Liu and Baird explore the problem of the regulation of plant ribosomal proteins. The authors discovered the ribosomal S28 protein in a salinity experiment and proceeded to observe down regulation of the gene under drought and [chsalinity stress and after abscisic acid application. The gene, Ha-RPS28,is expressed preferentially in metabolically active mature organs, especially leaves. This is the first report on the effects of environmental stimuli on S28, and the description of regulation in mature tissue, rather than actively dividing tissue, is novel.
(see p. 526)
Shaw et al. present a bryological test of the Madrean-Tethyan plant distribution pattern proposed and championed by Daniel Axelrod and others largely on the basis of paleobotanical data. In combined morphological/molecular studies of three mosses that exhibit disjunct distributions, their study is the first attempt by bryologists to evaluate the hypothesis from a mostly independent perspective and they offer some new results to think about. They favor recent long-distance dispersal rather than ancient vicariance, postulated by the Madrean-Tethyan hypothesis, as the best explanation for disjunct distributions.
(see p. 540)
There are very few cases of functional androdioecy in plants, and current theoretical models have difficulty offering explanations for the phenomenon. Lopez-Almansa et al. examine a new candidate, the riparian European field elm (Ulmus minor), in which female-sterile individuals act as males and cosexual individuals act as both females and males; there is considerable potential for asexual reproduction as well. The authors propose a model for the double reproductive system, such that sexual reproduction occurs during flooding events and asexual reproduction (sprouting) under other environmental conditions.
(see p. 603)
Irish et al. have isolated and describe an unusual mutation in maize, wandering carpel(wcr[cf1]), located on chromosome 2L, which has several striking phenotypic effects: it promotes a shift from zygomorphy to radial symmetry (there are no other mutations known in any plant that can, in effect, turn a flower upside down), and it allows the development of a second seed inside a kernel. The authors use this mutation to elucidate the nature of polarity in flowers and spikelets and propose that WCR;plis required for normal maize spikelet polarity and that wcrmay have played a role in the evolution of the caryopsis.
(see p. 551)
