Use of the Pressure Chamber in Membrane Damage Studies

The ability to detect membrane damage in plant leaves by thepressure chamber technique was evaluated. Membrane damage wasinduced by freezing and thawing, absorption of the host-specifictoxin victorin, ozonation, inoculation with Helminthosporiummaydis, and spraying with the phytotoxin, fusicoccin. The pressure-volumerelationships, i.e. the volume of sap expressed from a leafwith incremental increases in pressure, were compared in leaveswith intact or damaged membranes. Where membrane damage waswidespread throughout the leaf, sap was expressed at pressuresas low as one tenth of those needed in leaves with intact membranesand at low pressures the amount of water expressed from leaveswith damaged membranes was up to 10 times that from leaves withintact membranes. Further, the pressure-volume curves of healthyleaves became linear when the leaf turgor potential was reducedto zero, but were non-linear in leaves with damaged membranes.Ozone treatment, inoculation with H. maydis, or spraying withfusicoccin damaged only a proportion of the leaf cells, andpressure-volume relationships more nearly resembled those obtainedwith healthy leaves rather than those obtained with freezingand thawing and absorption of victorin. It is concluded that the pressure chamber can be used to observemembrane integrity, but its ability to detect damage may belimited to conditions in which the majority of cells in theleaf are damaged.     

Effects of Pressure Increase and Release on Temperature within a Pressure Chamber Used to Estimate Plant Water Potential

During a water-potential measurement sequence, temperature changewithin the pressure chamber exhibits certain distinct phases.At the introduction of gas into the chamber there is a rapidincrease in temperature, normally in excess of 8 ?C above ambient,which is directly related to the rate of pressure increase.After reaching a maximum, temperature begins to decline graduallyduring continued pressure increase, and subsequently falls toambient after gas entry coases. When pressure is rapidly releasedfrom the chamber at the end of a measurement, temperature instantlyfalls to subzero values. The causes of these temperature changes are explained in termsof simple thermodynamics, and ways of reducing them are described.     

Physiological and isotopic (δ13C and δ18O) responses of three tropical tree species to water and nutrient availability

Water-use efficiency and stable isotope composition were studied in three tropical tree species. Seedlings of Tectona grandis , Swietenia macrophylla and Platymiscium pinnatum were grown at either high or low water supply, and with or without added fertilizer. These three species previously exhibited low, intermediate and high whole-plant water-use efficiency ( TE ) when grown at high water supply in unfertilized soil. Responses of TE to water and nutrient availability varied among species. The TE was calculated as experiment-long dry matter production divided by cumulative water use. Species-specific offsets were observed in relationships between TE and whole-plant ¹³C discrimination (Δ¹³C_p). These offsets could be attributed to a breakdown in the relationship between Δ¹³C_p and the ratio of intercellular to ambient CO₂ partial pressures ( c _i/ c _a) in P. pinnatum , and to variation among species in the leaf-to-air vapour pressure difference ( v ). Thus, a plot of v · TE against c _i/ c _a showed a general relationship among species. Relationships between δ ¹⁸O of stem dry matter and stomatal conductance ranged from strongly negative for S. macrophylla to no relationship for T. grandis . Results suggest inter-specific variation among tropical tree species in relationships between stable isotope ratios ( δ ¹³C and δ ¹⁸O) and the gas exchange processes thought to affect them.     

Genomic islands of speciation or genomic islands and speciation?

Populations of the malaria mosquito, Anopheles gambiae, are comprised of at least two reproductively isolated, sympatric populations. In this issue, White et al. (2010) use extensive sampling, high‐density tiling microarrays, and an updated reference genome to clarify and expand our knowledge of genomic differentiation between these populations. It is now clear that DNA near the centromeres of all three chromosomes are in near‐perfect disequilibrium with each other. This is in stark contrast to the remaining 97% of the assembled genome, where fixed differences between populations have not been found, and many polymorphisms are shared. This pattern, coupled with direct evidence of hybridization in nature, supports models of “mosaic” speciation, where ongoing hybridization homogenizes variation in most of the genome while loci under strong selection remain in disequilibrium with each other. However, unambiguously demonstrating that selection maintains the association of these pericentric “speciation islands” in the face of gene flow is difficult. Low recombination at all three loci complicates the issue, and increases the probability that selection unrelated to the speciation process alters patterns of variation in these loci. Here, we discuss these different scenarios in light of this new data.     

Isolation and characterization of polymorphic microsatellite markers for peacock wrasse (Symphodus tinca)

Eight polymorphic microsatellite loci were isolated and characterized for the peacock wrasse (Symphodus tinca), a labrid fish inhabiting the Mediterranean and Black seas. Characterization of 35 individuals from the western Mediterranean indicated a relatively high allelic diversity (mean = 12.4, range 9–17), and observed heterozygosity ranging from 0.65 to 0.91. We found no evidence of linkage disequilibrium between pairs of loci. Two loci showed significant departure from Hardy–Weinberg equilibrium. These polymorphic markers can be useful in most basic population genetic applications.     

The Role of the Pineal Body in Ectotherm Thermoregulation

The pineal complex may be a part of the sensory and centralneural system controlling thermoregulatory behavior. The pinealand parapineal organs of some ectotherms appear to functionas radiation dosimeters, regulating exposure to sunlight. Physiologicalthermoregulation may be influenced by the pineal complex throughcardiovascular adjustments or metabolic rates. Additionally,the pineal organ may exert thermoregulatory effects throughthe control of brain electrolytes. While the precise mechanismsof action remain to be defined, it is clear that pineal-parapinealorgans participate in thermoregulatory adjustments by actingupon the central nervous system.