Characteristics Of Arabidopsis

In Arabidopsis thaliana and all flowering plants, one of the most characteristic features of development is axial development. There is a gradient in terms of age along the axial structure, as there are active meristematic tissues at the apices of the shoot and root. These apical meristems divide continuously to establish the basic patterns of new organs and tissues. There are also lateral primordia, which start to develop when environmental conditions become favourable for the growth of lateral tissues. The main axial structure of a plant is its shoot system, which is a stack of unit segments, each composed of an internode with a leaf and a bud. The unit segment is called a phytomer(Evans, 1940). The ontogeny and morphology of shoots represent

Genetic analysis of species which are polymorphic for flowering time has been useful in revealing the action of some of the genes involved in the control of flower initiation (Murfet IC et al., 1967). However, theinterpretation of the effects of these genes has been complicated by the lack of isogenic lines and the lack of a method for identifying the genes or the gene products affected by the mutations. In these respects, Arabidopsis is an attractive model species for a genetic analysis of flowering because the rapid development of the molecular genetics of Arabidopsis (Chang C et al., 1988; Finkelstein et al., 1988) may allow the cloning of genes which are otherwise evident only on the basis of a mutant phenotype. Arabidopsis thaliana is a quantitative long day plant. Long photoperiods promote flowering in all Arabidopsis ecotypes. However, this is not an absolute requirement and plants of all ecotypes will flower in short days. Similarly, exposure to cold temperatures accelerates flowering of many geographical races of Arabidopsis. This requirement is also not

Theoretical investigations of the evolutionary consequencesof mutation have addressed its role in numerous biological phenomena, including the maintenance of genetic variation (Zhang et al., 2004), the evolution of mating systems (Charlesworth et al., 1990), population extinction (Lynch et al., 1995), and ecological specialization (Kawecki et al., 1997),among others. These studies have shown that predictions about the evolutionary implications of spontaneousmutation depend primarily on three of its properties, the rate of occurrence throughout the genome of mutations affecting fitness, the distribution of the effects of new mutations on fitness, and the gene action of new mutations. Recent empirical studies of spontaneous mutation employing the mutation-accumulation (MA) approach have largely focused on quantifying the genomewide mutation rate, U (Drake et al., 1998). Mutational properties have been studied in haploid organisms, as well as in diploids; we consider here studies of diploids. In studies where mutations are accumulated over generations in lines advanced by close inbreeding, phenotypic assays of the lines evaluate traits of highly inbred individuals (Keightley and Caballero 1997). Such studies yield information about the effects of new mutations on traits; given the extreme inbreeding of the lines, resulting