Studies on the relationship of water balance properties and survival in the Hawaiian drosophilid, D. Mimica

Some aspects of the relationship between water balance characteristics and biological fitness have been explored both for a laboratory-reared stock (K85P1) of Drosophila mimica and for each of four field-caught populations of D. mimica. At low a_v's, there is a clear correlation between water loss rates and survival time, but at saturation, the relationship is less striking. Neither body weight nor sex correlate strongly with water loss rate at 0.70 a_v, but females survive longer than males. Some differences in the response to desiccation between populations from different collection sites are also suggested.     

Physiological aspects of water balance in the Hawaiian drosophilid, Drosophila mimica

The ability to resist desiccation is an important component of biological fitness for terrestrial organisms. Several water balance characteristics have been studied for a strain of laboratory-reared Drosophila mimica and for four populations of D. mimica collected at sites differing in altitude and wetness. In the absence of drinking water, D. mimica are unable to maintain a water balance, even in nearly saturated environments. However, as a_v ($\text{a}{}_{\mathrm{v}}\text{=}\text{r.h.}\text{100}$) decreases, transpiration does not increase as rapidly as expected and absorption remains nearly constant. The size of the fly is not correlated with its water loss characteristics, but some differences in regulation between the sexes are suggested.     

On the water balance ofPhytoseiulus persimilis A.-H. and its ecological significance

The net water vapour exchange ofPhytoseiulus persimilis A.-H. is described. Water loss by transpiration increases progressively with ambient temperature. The transpiration rate is directly proportional to the saturation deficit of the air (15 to 30° C) and at constant temperature linearly dependent on the water vapour activity: m_T=–0.81 a_v+0.91 (for a_v 0.0 to 0.85 at 20°C). Phytoseiulus persimilis is able to absorb water vapour from the unsaturated atmosphere. This occurs above a certain threshold (critical equilibrium activity, CEA), which is a_v=0.9 at 15 to 25°C and increases to a_v=0.935 at 30°C.The environmental humidity conditions influencingP. persimilis on the leaf surface are described. The diurnal water vapour profile within the laminar layer at the leaf surface includes periods with water vapour values high enough for these mites to utilize their water vapour sorption capability and to restore a previously-suffered water deficit. In addition,P. persimilis shows a positive hygrotactic behaviour when in a state of water deficit.The survival time of starvingP. persimilis is at least doubled when a possibility to absorb water vapour is available. The water balance at limited food resources is discussed. With a food supply (one prey mite, containing about 5.5 g water) every 3 days and a water vapour activity of a_v=0.76 (20°C), water balance is achieved and the survival time is maximal (approximately 120 days).     

Gender, mediterranean drought, and seasonality: photosystem II photochemistry in Pistacia lentiscus L.

In this work, photosystem II (PSII) photochemistry, leaf water potential, and pigment contents of male and female Pistacia lentiscus L. were investigated during a seasonal cycle at three different, arid locations: superior semiarid, inferior semiarid, and arid. The results showed that the gender, season, and the site conditions interacted to influence the quantum yield and pigment contents in P. lentiscus. Predawn leaf water status was determined only by the site and season. The annual patterns of PSII maximum quantum efficiency (F_v/F_m) were characterized by a suboptimal activity during the winter, especially, populations with the more negative water potential exhibited a lower chlorophyll (Chl) a content and chronic photoinhibition irrespective of a gender. We also demonstrated that both photochemical or nonphotochemical mechanisms were involved to avoid the photoinhibition and both of them depended on the season. This plasticity of photosynthetic machinery was accompanied by changes in carotenoids and Chl balance. In the spring, the female F_v/F_m ratio was significantly higher than in male individuals, when the sexual dimorphism occurred during the fruiting stage, regardless of site conditions. P. lentiscus sex-ratio in Mediterranean areas, where precipitations exceeded 500 mm, was potentially female-biased. Among the fluorescence parameters investigated, nonphotochemical quenching coefficient appeared as the most useful one and a correlation was found between Chl a content and F_v/F_m. These results suggest that functional ecology studies would be possible on a large scale through light reflectance analysis.     

High resilience to extreme climatic changes in the CAM epiphyte Tillandsia utriculata L. (Bromeliaceae)

Climate change is expected to increase the frequency of extreme climatic events, yet few studies have addressed the capacity of plant species to deal with such events. Species that are widespread are predicted to be highly plastic and able to acclimate to highly changing conditions. To study the plasticity in physiological responses of the widely distributed epiphyte Tillandsia utriculata, we transplanted individuals from a coastal scrub and broadleaf evergreen forest to a similar coastal scrub site and forest. After a 45-day acclimation, the plants were moved to a semi-controlled greenhouse at each site, and then subjected to a 20-day drought. Physiological variables were measured during the acclimation and the drought. The individuals of scrub and forest populations had similar relative water content and carbon assimilation in the contrasting conditions of the two transplantation sites despite the high discrepancy between the environments at their original site. Electron transport rates were higher in individuals from the scrub population. Electron transport rates were also higher than estimated from carbon assimilation, suggesting that photorespiration was present. The individuals of the coastal scrub population had a higher capacity to dissipate excess energy this way. The relative distance index of plasticity was high overall, indicating that some traits are highly plastic (titratable acidity, carbon assimilation) in order to maintain the stability of others (maximum quantum yield F_v/F_m and relative water content). We conclude that T. utriculata is a highly plastic species with a high capacity to tolerate extreme environmental changes over a short time.     

Food and water resources used by the Madagascan hissing-cockroach mite,Gromphadorholaelaps schaeferi

We determined the food source and water balance properties of the hissing-cockroach mite, Gromphadorholaelaps schaeferi. The food source for mites was identified using Evans blue dye by direct injection into a fasting host cockroach, Gromphadorhina portentosa, or by incorporation into cockroach food. No coloration was observed in mites on dye-injected cockroaches, but coloration was present in mites when only the food for the cockroaches had been stained. Thus, the mites are scavengers of cockroach food, and are not parasitic as previously thought. Our results demonstrate that the mites can absorb water from the air anywhere between 0.84 and 0.93 a _v (%RH/100), and wax-block experiments revealed that the mouth is the site of uptake. The mites are normally clumped together on the host, typically in between the cockroach's legs and around the spiracles. Water loss rates for mites in groups (0.16% h^-1) were far lower than for isolated mites (0.30% h^-1), suggesting a group effect with regard to water balance. Above the transition temperature of 30°C rate of water loss was rapid. The sites occupied by mites on the cockroach's body seem to be highly specific for feeding and absorption of water vapour.     

Salmonella spp. are affected by different levels of water activity in closed microcosms

Controlling water activity (a _w) can significantly impact the growth of Salmonella in poultry litter and manure — a phenomenon that was studied quantitatively using two common serotypes of Salmonella. The quantitative effect of changes in levels of a _w on Salmonella populations was determined using inoculated, frosted glass rectangles placed in closed chambers (microcosms). Glass rectangles with known concentrations of Salmonella enteritidis and S. brandenburg were placed in microcosms maintained at an a _w level of 0.893 for 24 h at room temperature (RT) and then transferred to other microcosms maintained at the same temperature but with higher a _w levels (0.932 and 0.987). Salmonella populations on the slides were quantified at 4, 18, 24, and 48 h. Slightly elevated levels of a _w (<0.1, i.e., 10% equilibrium relative humidity) for 24 h resulted in a 100-fold increase in counts of Salmonella. The data also suggested that in vitro adaptation to dry environments may occur when the organisms are exposed to alternating levels of relatively high and low (0.987 and 0.893) levels of a _w. Any increased tolerance of Salmonella to reduced levels of a _w could be the result of physico-chemical changes in the organism due to selective environmental pressure, formation of a protective biofilm, and/or entry into a dormant state. Results from this study are compatible with those from previously reported on-farm surveys, reinforcing the contention that maintaining a _w below 0.85 in and around litter/manure surfaces in poultry or livestock bedding areas may be a critical factor in safe production of food. Journal of Industrial Microbiology & Biotechnology (2001) 26, 222–225. Received 18 May 2000/ Accepted in revised form 24 January 2001     

Growth and Leaf Gas Exchange Characteristics in Dalbergia sissoo Roxb. and D. latifolia Roxb. Under Water Deficit

Forty two-month-old plants of Dalbergia sissoo and D. latifolia were subjected for 56 d to water deficit induced by withholding water. Drought stress caused a significant reduction in plant height, stem diameter, net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s) in both species, but the reduction was greater in D. sissoo than in D. latifolia. Water use efficiency (P _N/E) was adversely affected due to water stress only in D. latifolia, and intrinsic water use efficiency (P _N/g _s) was increased in both species. There was a slight effect of water stress on variable to maximum fluorescence (F_v/F_m) (quantum yield of photosystem 2) in both species, but the species did not differ significantly in this attribute.     

Latitudinal patterns in leaf litter breakdown: is temperature really important?

1. Forest stream food webs depend largely on input of dead riparian zone leaves for their energy, which is converted into living biomass by microbes, macroinvertebrates and fish. 2. Temperature has been invoked as important in controlling breakdown rates, and aquatic biologists have suggested that by normalizing processing rates to degree days rather than days, one can ‘factor out’ the effect of temperature and compare processing rates in streams with different thermal regimes (e.g. different seasons or study sites in different biomes). 3. We examined processing rates (k) along a latitudinal (i.e. thermal) gradient by using reciprocal transplants of leafpacks. We placed leafpacks of ten tree species (representing a large range of leaf litter quality) in streams in Costa Rica, Michigan and Alaska using coarse-mesh (20mm) litter bags. We then examined both the ‘per day’(k_day) and ‘per degree day’ (k_{degree day}) models of leaf litter processing. While processing rates (per day) were fastest at the Costa Rica site (as expected), rates at the Alaska and Michigan sites were similar to each other, which we would not predict if temperature were the principal factor controlling breakdown rate. If using degree days eliminates any effect of differing thermal regimes, rates should be similar across latitudes; however, rates at the Alaska site were much faster (per degree day) than rates at the sites in Costa Rica and Michigan. 4. We compared our data with studies in the North American literature. Regression analysis of k_day and k_{degree day} against latitude of the study site revealed that processing rates (k_day) of leaves (from a wide range of tree species in a wide range of stream types) showed no significant change with increasing latitude. However, when normalized for temperature (k_{Degree day}), a positive correlation was found between processing rates and latitude, causing us to reject the hypothesis that normalizing processing rates to cumulative degree days removes the effect of temperature. 5. We suggest three hypotheses: (i) shredding insect populations have adapted to the local thermal regime, and invertebrate-mediated processing rates are either similar between regions (showing no latitudinal pattern), or increase with latitude; (ii) microbial populations are less active at colder temperatures, and the rate of microbially mediated processing of leaf litter will show a decrease with latitude, and consequently (iii) the relative importance of invertebrate v microbial processing changes on a latitudinal gradient, with invertebrates being more important at high latitudes.     

Biochemical genetics of Fundulus heteroclitus (L.). III. Inheritance of isocitrate dehydrogenase (Idh-A and Idh-B), 6-phosphogluconate dehydrogenase (6-Pgdh-A), and serum esterase (Est-S) polymorphisms

Starch gel electrophoresis has shown that natural populations of Fundulus heteroclitus have variants at four enzyme-coding loci: Idh-A, Idh-B, 6-Pgdh-A, and Est-S. Analysis of the phenotypic distribution of the F₁ generation suggests that each of the variants segregates as autosomally inherited codominant alleles. Tissue specificity and intracellular localization were also determined for the IDH and 6PGDH isozymes.This work was supported by Grants DEB 76-19877 and DEB 79-12216 from the National Science Foundation and by Grant P60-80-04 from the State of Maryland. RVB and REC were supported by NIH Training Grant GM07231 to the Department of Biology.Contribution No. 1103 from the Department of Biology, The Johns Hopkins University.     

Contrasting soil respiration in young and old-growth ponderosa pine forests

Three years of fully automated and manual measurements of soil CO₂ efflux, soil moisture and temperature were used to explore the diel, seasonal and inter‐annual patterns of soil efflux in an old‐growth (250‐year‐old, O site) and recently regenerating (14‐year‐old, Y site) ponderosa pine forest in central Oregon. The data were used in conjunction with empirical models to determine which variables could be used to predict soil efflux in forests of contrasting ages and disturbance histories. Both stands experienced similar meteorological conditions with moderately cold wet winters and hot dry summers. Soil CO₂ efflux at both sites showed large inter‐annual variability that could be attributed to soil moisture availability in the deeper soil horizons (O site) and the quantity of summer rainfall (Y site). Seasonal patterns of soil CO₂ efflux at the O site showed a strong positive correlation between diel mean soil CO₂ efflux and soil temperature at 64 cm depth whereas diel mean soil efflux at the Y site declined before maximum soil temperature occurred during summer drought. The use of diel mean soil temperature and soil water potential inferred from predawn foliage water potential measurements could account for 80% of the variance of diel mean soil efflux across 3 years at both sites, however, the functional shape of the soil water potential constraint was site‐specific. Based on the similarity of the decomposition rates of litter and fine roots between sites, but greater productivity and amount of fine litter detritus available for decomposition at the O site, we would expect higher rates of soil CO₂ efflux at the O site. However, annual rates were only higher at the O site in one of the 3 years (597 ± 45 vs. 427 ± 80 g C m^?2). Seasonal patterns of soil efflux at both sites showed influences of soil water limitations that were also reflected in patterns of canopy stomatal conductance, suggesting strong linkages between above and below ground processes.     

Litter decomposition,soil respiration and soil chemical and biochemical properties at three contrasting sites in karri (Eucalyptus diversicolor F. Muell.) forests of south-western Australia

Litter decomposition, soil respiration and soil chemical and biochemical properties were examined at three contrasting sites in karri (Eucalyptus diversicolor F. Muell.) forest of south-western Australia. The study sites were: a recently clearfelled area (site CF2) which had been subjected to a slash regeneration burn following clearing; a pole-stand regrowth forest about 40 years old which had been regularly burnt by cool, prescribed fires (site RB40); and a pole-stand regrowth forest about 40 years old which had remained unburnt for many years (site UB40). Leaf litter of uniform composition lost 40–54% of its original dry weight after decomposing for 82 weeks on the forest floor. A composite exponential model, with separate decay functions for labile and more resistant litter components, described rate of weight loss better than a simple exponential decay model. Labile components of litter were released at similar rates at the three sites. Decomposition of resistant litter components was slower (half-life = 271 weeks) at the recently clearfelled site than at the two pole-stand sites (half-lives = 119 and 149 weeks). The order in which nutrients were released from decomposing litter, Na > Cl > K > Mg > S > Ca > N > P, was similar at each site. The rate of release of the more mobile elements Na, Cl, K, Mg and S, was also similar at each site. Changes in the amounts of Ca, N and P in decomposing litter differed between the three sites and the differences were related to the amounts of these nutrients in surface soil at each site. Annual soil respiration decreased in the order site CF2 = site UB40 > site RB40. Seasonal variation in respired CO ₂ was partly explained by variation in soil moisture and temperature. Soil carbohydrase activity at the recently clearfelled site was significantly lower than at the two well vegetated pole-stand sites. The differences between sites in enzyme activities were related to differences in the amounts of organic C in surface soils of the three sites. The amount of organic C in surface soil (0–15 cm) was 25–36% lower at the recently clearfelled site than at the two well vegetated pole-Stand sites. Site disturbance during clearing, and combustion of soil organic matter by the subsequent slash regeneration burn, probably account for part of this difference. However, reduced inputs of organic matter in litterfall, slower rates of surface litter breakdown and increased rates of microbial mineralization of soil organic matter on recently clearfelled areas may also contribute substantially to depletion of soil organic C.     

Strategies providing success in a variable habitat: II. Ecophysiology of photosynthesis of Cladophora glomerata

Cladophora glomerata (L.) Kütz. is the dominant filamentous algae of the river Ilm, Thuringia, Germany. For most of the year it can be found at open as well as at shaded sites. Photosynthetic acclimation of C. glomerata to different light intensities was detected by chlorophyll fluorescence measurements and pigment analysis. Cladophora glomerata from highlight sites showed decreased values of efficiency of open photosystem II (F_v/F_m) as compared with C. glomerata from low‐light sites. Winter populations revealed higher F_v/F_m values than summer populations. A light‐induced decrease in efficiency of the closed photosystem II was observed at increasing irradiance intensities. The decrease was higher in C. glomerata from shaded sites compared with plants from open sites. Differences in the photosynthetic electron transport rate of different populations of C. glomerata were shown by photosynthesis–irradiance curves. Summer populations from high‐light sites yielded higher maximum electron transport rates than plants from low‐light sites, whereas winter populations exhibited significantly decreased values compared with the summer populations. Results of the analysis of photosynthetic pigments corresponded with data from chlorophyll fluorescence measurements. In addition to these long‐term acclimation effects, C. glomerata expressed its ability to cope with rapid changes in the light environment by the de‐epoxidation of violaxanthin during exposure to high light intensities.     

Global synthesis of the temperature sensitivity of leaf litter breakdown in streams and rivers

Streams and rivers are important conduits of terrestrially derived carbon (C) to atmospheric and marine reservoirs. Leaf litter breakdown rates are expected to increase as water temperatures rise in response to climate change. The magnitude of increase in breakdown rates is uncertain, given differences in litter quality and microbial and detritivore community responses to temperature, factors that can influence the apparent temperature sensitivity of breakdown and the relative proportion of C lost to the atmosphere vs. stored or transported downstream. Here, we synthesized 1025 records of litter breakdown in streams and rivers to quantify its temperature sensitivity, as measured by the activation energy (E_a, in eV). Temperature sensitivity of litter breakdown varied among twelve plant genera for which E_a could be calculated. Higher values of E_a were correlated with lower‐quality litter, but these correlations were influenced by a single, N‐fixing genus (Alnus). E_a values converged when genera were classified into three breakdown rate categories, potentially due to continual water availability in streams and rivers modulating the influence of leaf chemistry on breakdown. Across all data representing 85 plant genera, the E_a was 0.34 ± 0.04 eV, or approximately half the value (0.65 eV) predicted by metabolic theory. Our results indicate that average breakdown rates may increase by 5–21% with a 1–4 °C rise in water temperature, rather than a 10–45% increase expected, according to metabolic theory. Differential warming of tropical and temperate biomes could result in a similar proportional increase in breakdown rates, despite variation in E_a values for these regions (0.75 ± 0.13 eV and 0.27 ± 0.05 eV, respectively). The relative proportions of gaseous C loss and organic matter transport downstream should not change with rising temperature given that E_a values for breakdown mediated by microbes alone and microbes plus detritivores were similar at the global scale.     

EFFECTS OF UV‐B RADIATION ON THE D1 PROTEIN REPAIR CYCLE OF NATURAL PHYTOPLANKTON COMMUNITIES FROM THREE LATITUDES (CANADA,BRAZIL, AND ARGENTINA)1

Ultraviolet radiation effects were examined in natural phytoplankton communities from Rimouski (Canada), Ubatuba (Brazil), and Ushuaia (Argentina). Outdoor pump‐mixed mesocosms were submitted to ambient solar radiation (NUVB) and ambient with additional UV‐B radiation (UVBR) from lamps (HUVB), corresponding to a local 60% ozone depletion scenario. At all sites, neither algal biomass nor dark‐adapted F_v/F_m were significantly affected by additional UVBR, suggesting the presence of active UV protection or repair mechanisms. To examine the role of D1 protein turnover, essential for PSII repair, short‐term surface incubations were performed in the presence or absence of lincomycin, a chloroplast protein synthesis inhibitor. Effects on PSII were determined using chl a in vivo fluorescence, whereas the D1 protein was detected immunochemically. In the absence of D1 repair, D1 pools and F_v/F_m decreased to a similar extent under both light treatments. In the presence of D1 repair, D1 pools suffered faster net degradation under HUVB compared with NUVB, whereas F_v/F_m was maintained for both light treatments, suggesting that HUVB exposure in field populations had more effect on D1 synthesis and PSII repair than on D1 degradation. The fewer undamaged reaction centers remaining in phytoplankton under HUVB were able to maintain F_v/F_m or actually recovered during the dark acclimation before F_v/F_m measurements. The D1 pools suffered faster net degradation at the tropical site where high irradiance drove faster D1 degradation and high water temperature enabled fast enzymatic activities. This study shows the crucial role of dynamic changes in D1 turnover in the photobiology of natural planktonic communities across a range of latitudes.     

Performance differences among ex situ native-provenance collections of Pinus radiata D. Don. 1: potential for infusion into breeding populations in Australia and New Zealand

Growth and form traits from a series of three provenance trials of Pinus radiata D. Don planted in New Zealand and Australia were analysed at age 9 years from planting. The trials included selections from three mainland California natural populations—A?o Nuevo, Monterey and Cambria. Monterey and Cambria performed better than A?o Nuevo at two New Zealand sites, but Monterey and A?o Nuevo were almost identical in growth, whereas Cambria grew less vigorously at the Australian site. We detected significant provenance differences for diameter at breast height (DBH) growth and stem straightness across countries (p < 0.001). Estimated heritability for DBH ranged from 0.19 to 0.26 within sites, while heritability estimates for stem straightness and branching frequency ranged from 0.10 to 0.24. Estimated type B genetic correlations for DBH were always higher between the two trials in New Zealand trials than between pairs of trials in New Zealand and the Australian site. The genetic coefficient of variation (CV_A) for DBH was around 8–10% compared to ca. 5% for the current breeding population. These results suggested that there is appreciable genetic variation in the native populations, and infusion of these materials would increase the genetic variation in current breeding populations. Ten unrelated parents ranked above control seedlots from the older open-pollinated seed orchard stock for DBH growth and would be potential candidates for infusion. The promising performance of the Cambria material is an important result because the genetic base of the present Australian and New Zealand plantations is principally derived from A?o Nuevo and Monterey.     

Contrasting traits,contrasting environments,and considerations on population dynamics under a changing climate: an ecophysiological field study of two co‐dominant tree species

The increase in light availability resulting from canopy changes or opening is not always beneficial and can inhibit photosynthesis of tree seedlings already under other environmental stress. Tree seedlings' responses to compounded abiotic stress depend on their life‐history traits, and understanding the variations of such responses is important for understanding population dynamics under a changing climate. In this study we investigate how the photosynthesis of juveniles of two canopy tree species with different life‐history traits, Abies sachalinensis and Betula ermanii, differs in two contrasting sites at a sub‐boreal forest in northern Japan—one under a deciduous canopy (Closed site) and the other at a wide canopy opening (Open site). Seedlings at the Open site had low F_v/F_m (quantum yield of photosystem II) for a longer period than those at the Closed site. Abies sachalinensis at the Closed site showed lower F_v/F_m in spring than those at the Open site, but recovered after the canopy's new leaves flushed, indicating its acclimation to the shaded condition. Mean P_max (light‐saturated photosynthetic rate at ambient CO₂ levels) of A. sachalinensis seedlings was affected by site and air temperature, while B. ermanii seedlings were also affected by precipitation. Only B. ermanii's seedlings presented growth in the period studied, in spite of observed mid‐day drops to F_v/F_m attributed to water‐deficit‐related photoprotection. Results suggest that the climate change predicted for the Hokkaido area may increase the competitive advantage of broad‐leaved deciduous species, such as B. ermanii, in relation to evergreen conifers like A. sachalinensis.     

Photosystem II function and herbicide binding sites during photoinhibition of spinach chloroplasts in-vivo and in-vitro

The time courses of some Photosystem II (PS II) parameters have been monitored during in-vivo and in-vitro photoinhibition of spinach chloroplasts, at room temperature and at 10 °C or 0 °C. Exposing leaf discs of low-light grown spinach at 25 °C to high light led to photoinhibition of chloroplasts in-vivo as manifested by a parallel decrease in the number of functional PS II centres, the variable chlorophyll fluorescence at 77K (F _v /F _m ), and the number of atrazine-binding sites. When the photoinhibitory treatment was given at 10 °C, the former two parameters declined in parallel but the loss of atrazine-binding sites occurred more slowly and to a lesser extent. During in-vitro photoinhibition of chloroplast thylakoids at 25 °C, the loss of functional PS II centres proceeded slightly more rapidly than the loss of atrazine-binding sites, and this difference in rate was further increased when the thylakoids were photoinhibited at 0 °C. During the recovery phase of leaf discs (up to 9 h) the increases in F _v /F _m preceded that of the number of functional PS II centres, while only a further decline in the number of atrazine-binding sites was observed. The recovery of variable chlorophyll fluorescence and the concentration of functional PS II centres occurred more rapidly at 25 °C than at 10 °C. These results suggest that the photoinhibition of PS II function is a relatively temperature-independent early photochemical event, whereas the changes in the concentration of herbicide-binding sites appear to be a more complex biochemical process which can occur with a delayed time course.Abbreviations BSA bovine serum albumin - Chl chlorophyll - D1 32kDa herbicide-binding polypeptide in photosystem II and product of the psbA gene - D2 34kDa polypeptide in photosystem II which is the product of the psbD gene - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCPIP 2,6-dichlorophenolin-dophenol - F ₀, F _v , F _m chlorophyll fluorescence with reaction centres open, variable and maximum fluorescence, respectively - LDS lithium dodecyl sulfate - MES 2-(N-morpholino) ethanesulfonic acid - PSII photosystem II - Q_A, Q_B first and second quinone-type PS II acceptor, respectively     

Intraspecific variation in Pinus pinaster PSII photochemical efficiency in response to winter stress and freezing temperatures

As part of a program to select maritime pine (Pinus pinaster Ait.) genotypes for resistance to low winter temperatures, we examined variation in photosystem II activity by chlorophyll fluorescence. Populations and families within populations from contrasting climates were tested during two consecutive winters through two progeny trials, one located at a continental and xeric site and one at a mesic site with Atlantic influence. We also obtained the LT₅₀, or the temperature that causes 50% damage, by controlled freezing and the subsequent analysis of chlorophyll fluorescence in needles and stems that were collected from populations at the continental trial site. P. pinaster showed sensitivity to winter stress at the continental site, during the colder winter. The combination of low temperatures, high solar irradiation and low precipitation caused sustained decreases in maximal photochemical efficiency (F_v/F_m), quantum yield of non-cyclic electron transport (Φ_PSII) and photochemical quenching (qP). The variation in photochemical parameters was larger among families than among populations, and population differences appeared only under the harshest conditions at the continental site. As expected, the environmental effects (winter and site) on the photochemical parameters were much larger than the genotypic effects (population or family). LT₅₀ was closely related to the minimum winter temperatures of the population''s range. The dark-adapted F_v/F_m ratio discriminated clearly between interior and coastal populations.In conclusion, variations in F_v/F_m, Φ_PSII, qP and non-photochemical quenching (NPQ) in response to winter stress were primarily due to the differences between the winter conditions and the sites and secondarily due to the differences among families and their interactions with the environment. Populations from continental climates showed higher frost tolerance (LT₅₀) than coastal populations that typically experience mild winters. Therefore, LT₅₀, as estimated by F_v/F_m, is a reliable indicator of frost tolerance among P. pinaster populations.     

A profile of Drosophila species' enzymes assayed by electrophoresis. I. Number of alleles,heterozygosities, and linkage disequilibrium in glucose-metabolizing systems and some other enzymes

Seven isolated large populations of Drosophila belonging to five different species were examined by starch gel electrophoresis for allozyme variation. Six to eleven enzyme loci in the glucose-metabolizing system (group I) and six to eight enzyme loci (group II) which were not directly involved in the above-mentioned system were assayed. The parameters estimated were the average number of alleles per locus, allele frequencies, proportions of polymorphic loci, and average heterozygosity per population for group I and group II loci. The major finding is that genetic variability measured by allozyme variations is much higher for group II than for group I enzymes in terms of every parameter in all the populations. This is consistent with the earlier findings in D. ananassae by Gillespie and Kojima (1968). Linkage disequilibrium, a measure of genome integration, was computed between an enzyme locus and an inversion segment of the same chromosome. The preliminary analysis of this aspect of the study indicates that no substantial linkage disequilibrium builds up between the chromosomal segments unless the pair of segments is less than 10 centimorgan units apart.This study was supported by USPHS Grant GM-15769 and Atomic Energy Commission Contract AT-(40-1)-3681.NIH Trainee supported by Grant 5 TO 1 GM 00337.