Influence of L-Ascorbic Acid on Post-anoxic Growth and Survival of Chickpea Seedlings (Cicer arietinum L.)

Chickpea seedlings show diminished survival and reduction ingrowth when kept under anoxia for more than 48 h. Treatmentwith L-ascorbic acid before re-exposure to air after varyingperiods of anoxia shows that this anti-oxidant can improve seedlinggrowth and survival during the post-anoxic recovery period.Comparisons of growth during the recovery period with and withoutascorbic acid treatments, as well as observing the effects ofascorbic acid on K⁺ leakage from roots, suggest that post-anoxicinjury is a significant component of the damage that is causedto chickpea seedlings as a result of prolonged anaerobic incubation. Key words: L-ascorbic acid, anoxia, post-anoxia, growth     

Effects of chronic chlorine exposure on litter processing in outdoor experimental streams

SUMMARY 1. The effects of chlorine on litter ( Potamogeton crispus L.) processing were examined using six outdoor experimental streams. Downstream portions of two streams were dosed at c . 10 μg l⁻¹ Total Residual Chlorine (TRC), one stream at 64 μgl¹, and one stream at 230μg l⁻¹. Two control streams were not dosed; upstream riffles of each stream served as instream controls.
2. Two 35 day litter breakdown (per cent AFDW remaining) experiments indicated significantly lower decay rates in the high dose riffle. No other concentration of chlorine significantly affected decay rate.
3. A third experiment, conducted in medium and high dose streams, indicated that high dose chlorine exposure reduced litter decomposition rates significantly, and reduced microbial colonization, microbial electron transport system activity, and microbial litter decomposition after 4 days but not after 11 days of exposure. The number of amphipod shredders colonizing litter bags was also reduced significantly with high chlorine dose.
4. A fourth experiment, after dosing was terminated, provided direct evidence that amphipod shredders were important in facilitating litter decomposition: litter bags stocked with amphipods had significantly higher decomposition rates than bags which excluded shredders.
5. Overall results indicate that the high dose (c. 230 μgl⁻¹ TRC) of chlorine reduced litter processing rates partly by reducing initial microbial conditioning, but primarily by reducing the colonization of amphipod shredders.     

Mating system and genetic diversity of a rare desert legume Ammopiptanthus nanus (Leguminosae)

Ammopiptanthus nanus is an endangered evergreen shrub endemic to the deserts of central Asia and plays an important role in delaying further desertification. We examined allozyme variation and AFLP diversity in A. Nanus populations and investigated the mating system of this species using progeny arrays assayed for poly-morphic allozyme loci. Mating system analysis in the Keyi'eryongke'er population showed low levels of out-crossing, and strong inbreeding depression. Low levels of genetic variation were detected at both population (allozyme, Pp=14.0%,A=1.14, He=0.031; AFLP, Pp=14.5%, Shannon's information index I=0.063) and species (allozyme, Pp=21.1%,A=1.21, He=0.040; AFLP, Pp=20.9%, I=0.083) levels; while moderate genetic differentia-tion existed among populations, as indicated by allozymes (GST=0.081) and AFLP (GST=0.151-0.193). Founder effect, bottlenecks in evolutionary history, the mixed mating system and co-ancestry may have influenced the level of genetic diversity in A. Nanus. Markers of both types provide new insights for conservation management, indicating that the Biao'ertuokuoyi and Keyi'eryongke'er populations should be given priority for in situ conser-vation and regarded as seed sources for ex situ conservation.     

Evolutionary Physiology of Closely Related Taxa: Analyses of Enzyme Expression

Comparative biochemistry and physiology offer the advantageof specifically defining the functional parameters or traitsthat affect an organism's performance (e.g., amino acids thataffect K_m, enzymes that affect metabolism). By combining thesefunctional determinations with both intraspecific and phylogeneticallyappropriate analyses, comparative biologists can indicate thata trait is biologically important by demonstrating that it isevolving by natural selection. An evolutionary approach maybenefit from the analysis of variation within and among closelyrelated species. The advantages of analyzing closely relatedspecies are that they allow one to identify more definitivelythe derived conditions and suggest why differences arose. Importantly,there is substantial variation in physiological and biochemicaltraits within and among closely related species. For example,among species within a single genus of teleost, Fundulus, thevariation in enzyme expression is similar to the variation seenamong most superorders of teleost. However, most of the variationwithin the genus Fundulus is most readily explained by evolutionarydistance, and thus there is no compelling reason for furtheradaptive hypotheses. Extending this observation, the greaterthe phylogenetic distance between taxa in a comparative study,the more likely there will be a statistically significant differencethat may only represent evolutionary time. The molecular mechanismsaffecting adaptive variation in enzyme expression appear tobe readily altered and may vary within a species or betweenacclimation conditions. Thus, studies among closely relatedorganisms are more likely to identify the specific molecularor biochemical changes responsible for adaptive variation.