TEMPERATURE-SENSITIVE MUTATIONS THAT ARREST ARABIDOPSIS SHOOT DEVELOPMENT

To identify genes involved in meristem function we have designed a scr een for temperature-sensitive mutations that cause a conditional arres t of early shoot development in Arabidopsis. We describe the character ization of three mutations, arrested development (add) 1, 2 and 3. At the restrictive temperature the add1 and add2 mutations disrupt apical meristem function as assayed by leaf initiation. Furthermore, add1 an d add2 plants exhibit defects in leaf morphogenesis following upshift from permissive to restrictive temperature. This result suggests that proximity to a functional meristem is required for the completion of n ormal leaf morphogenesis. The add3 mutation does not have a dramatic e ffect on the production of leaves by the apical meristem; however, add 3 prevents the expansion of leaf blades at high temperature, Thus, in this mutant the temperature-dependent arrest of epicotyl development i s due to a failure of normal leaf development rather than new leaf ini tiation. While all add mutants have a reduced rate of root growth in c omparison to wild-type plants, the mutants do not display a temperatur e-dependent arrest of root development. All add mutants display some d evelopmental defects at low temperature, suggesting that these mutatio ns affect genes involved in inherently temperature-sensitive developme ntal processes.