Reproductive efficiency and growth of Emex australis in relation to stress

The reaction of Emex australis to different degrees of stress was examined in a pot experiment by varying pot size and in a field experiment by varying density. In pots, the proportion of energy in seeds was more stable to the imposition of stress than in roots and stems; that in roots increasing with increasing stress and that in stems declining. Similarly in the field, there was little difference between densities of 1–32 plants m^?2 in the proportion of seeds in biomass. There were no significant differences in mean individual seed weights in either experiment and all plants set seed. Again in both experiments, high stress plants were more precocious than low stress ones. In pots, this took the form of earlier attainment of maxima in calorific values, ‘reproductive effort’, root, stem and seed weights and in the field, a shorter life cycle and earlier senescence. In pots, estimates of the overall mean reproductive effort were 62% for the low and medium stress plants and 36% for the high stress plants. The results are discussed in terms of the high values for reproductive effort, the plasticity and precocity of E. australis under stress and the implications for weed control.     

The Emergence of Culture: The Evolution of a Uniquely Human Way of Life

The Emergence of Culture: The Evolution of. Uniquely Human Way of Life . Philip G. Chase. New York: Springer Press, 2006. 227 pp.     

The Arabidopsis GIBBERELLIN METHYL TRANSFERASE 1 suppresses gibberellin activity,reduces whole‐plant transpiration and promotes drought tolerance in transgenic tomato

Previous studies have shown that reduced gibberellin (GA) level or signal promotes plant tolerance to environmental stresses, including drought, but the underlying mechanism is not yet clear. Here we studied the effects of reduced levels of active GAs on tomato (Solanum lycopersicum) plant tolerance to drought as well as the mechanism responsible for these effects. To reduce the levels of active GAs, we generated transgenic tomato overexpressing the Arabidopsis thaliana GA METHYL TRANSFERASE 1 (AtGAMT1) gene. AtGAMT1 encodes an enzyme that catalyses the methylation of active GAs to generate inactive GA methyl esters. Tomato plants overexpressing AtGAMT1 exhibited typical GA‐deficiency phenotypes and increased tolerance to drought stress. GA application to the transgenic plants restored normal growth and sensitivity to drought. The transgenic plants maintained high leaf water status under drought conditions, because of reduced whole‐plant transpiration. The reduced transpiration can be attributed to reduced stomatal conductance. GAMT1 overexpression inhibited the expansion of leaf‐epidermal cells, leading to the formation of smaller stomata with reduced stomatal pores. It is possible that under drought conditions, plants with reduced GA activity and therefore, reduced transpiration, will suffer less from leaf desiccation, thereby maintaining higher capabilities and recovery rates.     

Reticulate evolution: ancient introgression of the Adriatic brown trout mtDNA in softmouth trout Salmo obtusirostris (Teleostei: Salmonidae)

Two populations of softmouth trout ( Salmo obtusirostris ) from the rivers Neretva (Bosnia and Herzegovina) and Jadro (Croatia), along with two neighbouring populations of brown trout ( Salmo trutta ) were analysed with a suite of genetic markers (two mtDNA genes, two nuclear genes, and nine microsatellites) as well as morphological characters. The Jadro softmouth trout were fixed for a brown trout mtDNA haplotype of the Adriatic lineage, which is 1.7% divergent from a previously described haplotype characteristic for the Neretva softmouth trout. All other genetic markers, as well as morphological analysis, supported the clear distinction of softmouth trout from the rivers Neretva and Jadro from brown trout in neighbouring populations, and thus a mtDNA capture event is assumed. Population specific microsatellite allele profiles, as well as a high number of private alleles for both populations of softmouth trout, support the hybridization between brown trout and the Jadro softmouth trout most likely being of ancient origin, thus leading to a reticulate evolutionary pattern of mtDNA in this taxon.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 139–152.