Role of Osmotic Potential Gradients during Water Stress and Leaf Senescence in Fragaria virginiana

The physiological basis underlying differences in sensitivity of different aged leaves to water stress was investigated in Fragaria virginiana Duchesne. Differential susceptibility of only older leaves to water stress in the field during summer months appeared related to gradients in leaf osmotic potential within the plant and by an age dependency in the ability of leaves to adjust osmotically when challenged by periodic water deficits. Under greenhouse conditions, older leaves senesced invariably during an imposed water stress while control leaves of comparable age and stressed younger leaves remained green. Osmotic potentials of intermediate aged and younger leaves became approximately 1 to 2 bars lower after a single cycle of imposed stress and up to 10 bars lower after two cycles of stress. Pronounced gradients in leaf osmotic potential within individual whole plants were observed following two cycles of water stress that were significantly different from control values. Osmotic adjustment was dependent on leaf age with the greatest capacity for adjustment in the intermediate aged leaves. Loss of osmotic adjustment was rapid upon rewatering with a half-life of 4 days. An irreversible component of adjustment was observed, amounting to about 10% (or 2 bars) of the maximally adjusted state. This irreversible component could be accounted for in part by significant changes in cell size and other anatomical alterations in the leaf that affect cellular osmotic volume, and, hence, cellular water relations.     

Effects of Light and Nutrients on Leaf Size, CO(2) Exchange, and Anatomy in Wild Strawberry (Fragaria virginiana)

Plants of a single genotype of wild strawberry, Fragaria virginiana Duchesne, were grown with or without fertilizer in high (406 microeinsteins per square meter per second) and low (80 microeinsteins per square meter per second) light. High-light leaves were thicker than low-light leaves and had greater development of the mesophyll. Within a light level, high-nutrient leaves were thicker, but the proportions of leaf tissues did not change with nutrient level. Maximum net CO₂ exchange rate and leaf size were greatest in high-light, high-nutrient leaves and lowest in high-light, low-nutrient leaves. Changes in mesophyll cell volume largely accounted for differences in CO₂ exchange rate in low-light leaves, but not in high-light leaves.

Leaf size in these experiments was apparently determined by nutrient and carbon supply. This may explain the observation that the largest leaves produced by wild strawberries in the field occur in high-light, mesic habitats, rather than in shady habitats.

     

Elevated CO2and Temperature have Different Effects on Leaf Anatomy of Perennial Ryegrass in Spring and Summer

Mature second leaves of Lolium perenne L. cv. Vigor, were sampledin a spring and summer regrowth period. Effects of CO₂enrichmentand increased air temperature on stomatal density, stomatalindex, guard cell length, epidermal cell density, epidermalcell length and mesophyll cell area were examined for differentpositions on the leaf and seasons of growth. Leaf stomatal density was smaller in spring but greater in summerin elevated CO₂and higher in both seasons in elevated temperatureand in elevated CO₂xtemperature relative to the respective controls.In spring, leaf stomatal index was reduced in elevated CO₂butin summer it varied with position on the leaf. In elevated temperature,stomatal index in both seasons was lower at the tip/middle ofthe leaf but slightly higher at the base. In elevated CO₂xtemperature,stomatal index varied with position on the leaf and betweenseasons. Leaf epidermal cell density was higher in all treatmentsrelative to controls except in elevated CO₂(spring) and elevatedCO₂xtemperature (summer), it was reduced at the leaf base. Inall treatments, stomatal density and epidermal cell densitydeclined from leaf tip to base, whilst guard cell length showedan inverse relationship, increasing towards the base. Leaf epidermalcell length and mesophyll cell area increased in elevated CO₂inspring and decreased in summer. In elevated CO₂xtemperatureleaf epidermal cell length remained unaltered in spring comparedto the control but decreased in summer. Stomatal conductancewas lower in all treatments except in summer in elevated CO₂itwas higher than in the ambient CO₂. These contrasting responses in anatomy to elevated CO₂and temperatureprovide information that might account for differences in seasonalleaf area development observed in L. perenne under the sameconditions. Lolium perenne ; perennial ryegrass; elevated CO₂and temperature; stomatal density; stomatal index; cell size     

Osmotic Adjustment and the Development of Freezing Resistance in Fragaria virginiana

Cold temperature acclimation in strawberry (Fragaria virginiana) leaves apparently involves the alteration of cellular osmotic properties. Alterations in leaf osmotic potential were closely correlated with alterations in soluble carbohydrate content of the leaf tissue and changing temperatures. Leaf starch content was inversely related to soluble carbohydrate levels, suggesting that starch is a partial source of osmoticum during osmotic adjustment associated with cold temperature stress. Free amino acid changes were more closely linked to senescence and growth processes while changes in ion content suggested a rapid mobilization of solutes at the onset of freezing temperatures. This was supported by changes in whole plant gradients in leaf osmotic potential before and after exposure to freezing temperatures. In terms of freezing resistance and the role of osmotic adjustment in the development of resistance, it was found that of all leaves undergoing osmotic adjustment only the younger leaves survived, suggesting an age-dependent component to freezing resistance in leaves. Freezing resistance appears to involve alterations in several cellular properties that act in concert to confer a hardy state of the tissue. Although osmotic adjustment may be an important component of the final combination of cellular properties, this study indicates that solute accumulation does not function alone to confer freezing resistance.     

Genetic mapping of sex determination in a wild strawberry, Fragaria virginiana, reveals earliest form of sex chromosome

The evolution of separate sexes (dioecy) from hermaphroditism is one of the major evolutionary transitions in plants, and this transition can be accompanied by the development of sex chromosomes. Studies in species with intermediate sexual systems are providing unprecedented insight into the initial stages of sex chromosome evolution. Here, we describe the genetic mechanism of sex determination in the octoploid, subdioecious wild strawberry, Fragaria virginiana Mill., based on a whole-genome simple sequence repeat (SSR)-based genetic map and on mapping sex determination as two qualitative traits, male and female function. The resultant total map length is 2373 cM and includes 212 markers on 42 linkage groups (mean marker spacing: 14 cM). We estimated that approximately 70 and 90% of the total F. virginiana genetic map resides within 10 and 20 cM of a marker on this map, respectively. Both sex expression traits mapped to the same linkage group, separated by approximately 6 cM, along with two SSR markers. Together, our phenotypic and genetic mapping results support a model of gender determination in subdioecious F. virginiana with at least two linked loci (or gene regions) with major effects. Reconstruction of parental genotypes at these loci reveals that both female and hermaphrodite heterogamety exist in this species. Evidence of recombination between the sex-determining loci, an important hallmark of incipient sex chromosomes, suggest that F. virginiana is an example of the youngest sex chromosome in plants and thus a novel model system for the study of sex chromosome evolution.     

叶片生长进程中气孔发育对叶温调节的影响

鉴于气孔发育影响气孔导度和蒸腾速率,推测气孔发育可能影响叶温调节。为验证这一假设并阐述相关规律,在控光和控温条件下研究了冬青卫矛和华北紫丁香气孔发育、气孔导度、蒸腾速率及其与叶温的关系。结果表明,伴随冬青卫矛、华北紫丁香叶片生长气孔逐渐增大,但气孔密度下降;在此过程中,气孔导度和蒸腾速率逐步提高,而叶片温度降低;尽管冬青卫矛和华北紫丁香叶片的气孔密度和大小差异很小,但华北紫丁香近轴侧和远轴侧均有气孔分布,而冬青卫矛则只有远轴侧分布气孔,且相同条件下华北紫丁香的气孔导度和蒸腾速率高、叶温低。因此,气孔发育能够促进气孔导度和蒸腾速率提高,有助于降低叶温;近轴侧气孔可能更有利于蒸腾降温。     

The Initiation, Growth, and Emergence of Leaf Primordia in Fragaria

The leaf initiation rate in Fragaria vesca (var. ‘RoyalSovereign’) has been compared with the elongation rateof the leaf primordia at different seasons. Certain conceptionsof growth correlation within the bud are presented. Experimentson the nature of elongation and emergence of primordia are described,and the causes of emergence are discussed.     

Dissecting the causes of variation in intra-inflorescence allocation in a sexually polymorphic species, Fragaria virginiana (Rosaceae)

In this study we dissect the causes of variation in intra-inflorescence allocation in a sexually polymorphic species, Fragaria virginiana. We separated out the effects of resource competition during flowering from those of inflorescence architecture, as well as identified the effects of sex morph and genotype. We found position-based variation in petal length, ovule, pollen, and flower number to be influenced more by architecture than by our resource manipulations during flowering. We also found both genotype- and sex-specific intra-inflorescence patterns. Furthermore, our data indicate that the sex morph-specific intra-inflorescence patterns result from architectural modifications of the basic pattern. In fact, sex-differential intra-inflorescence patterns suggest that fitness through male and female function may be maximized by different resource distribution patterns within the inflorescence and may have been modified by past selection. Specifically, females invested heavily in ovules at positions where fruit set was most likely (primary and secondary), at the expense of flower number and allocation per flower at more distal positions. Whereas functional males invested minimally in ovules at all flower positions and produced the most abundantly flowered inflorescences, hermaphrodites, on the other hand, showed intermediate patterns, implying a compromise between sex functions. We suggest that consideration of intra-inflorescence allocation and inflorescence architecture may reveal the mechanism underlying sexual dimorphism in flower allocation and number.     

Hydrostatic Pressure and Temperature Effects on the Membranes of a Seasonally Migrating Marine Copepod

Marine planktonic copepods of the order Calanoida are central to the ecology and productivity of high latitude ecosystems, representing the interface between primary producers and fish. These animals typically undertake a seasonal vertical migration into the deep sea, where they remain dormant for periods of between three and nine months. Descending copepods are subject to low temperatures and increased hydrostatic pressures. Nothing is known about how these organisms adapt their membranes to these environmental stressors. We collected copepods (Calanoides acutus) from the Southern Ocean at depth horizons ranging from surface waters down to 1000 m. Temperature and/or pressure both had significant, additive effects on the overall composition of the membrane phospholipid fatty acids (PLFAs) in C. acutus. The most prominent constituent of the PLFAs, the polyunsaturated fatty acid docosahexanoic acid [DHA – 22:6(n-3)], was affected by a significant interaction between temperature and pressure. This moiety increased with pressure, with the rate of increase being greater at colder temperatures. We suggest that DHA is key to the physiological adaptations of vertically migrating zooplankton, most likely because the biophysical properties of this compound are suited to maintaining membrane order in the cold, high pressure conditions that persist in the deep sea. As copepods cannot synthesise DHA and do not feed during dormancy, sufficient DHA must be accumulated through ingestion before migration is initiated. Climate-driven changes in the timing and abundance of the flagellated microplankton that supply DHA to copepods have major implications for the capacity of these animals to undertake their seasonal life cycle successfully.     

Sex ratio and subdioecy in Fragaria virginiana: the roles of plasticity and gene flow examined

Here we examined the roles of sex-differential plasticity (SDP) and gene flow in sex ratio evolution of subdioecious Fragaria virginiana. We assessed whether female frequency varied with resource availability in 17 natural populations and then characterized plasticity and mean investment in allocation to female function at flower and plant levels in the sex morphs in the glasshouse. We estimated patterns of population divergence using five microsatellite markers. We reveal SDP in fruit production substantial enough to translate into a higher equilibrium female frequency at low resources. Thus SDP can account, in part, for the strong negative relationship between female frequency and resources found in the field. Pollen-bearing morphs varied in plasticity across populations, and the degree of plasticity in fruit number was positively correlated with in situ variation in nitrogen (N) availability, suggesting an adaptive component to sex-allocation plasticity. Low neutral genetic differentiation, indicating high gene flow or recent divergence, may contribute to the absence of population differentiation in fruit-setting ability of pollen-bearing morphs despite considerable sex ratio variation. We consider how these processes, in addition to other features of this system, may work in concert to influence sex ratios and to hinder the evolution of dioecy in F. virginiana.     

The Effects of Temperature on Leaf Growth in Cyperus longus, a Temperate C4 Species

Plants of the C₄ sedge Cyperus longus L. were grown at 10, 20and 30 °C. An asymptotic growth curve, the Richards function,was fitted to growth data for successive leaves. The mean rateof leaf appearance was a linear function of temperature with0.014 leaves appearing per day for every 1 °C increase intemperature. The instantaneous relative rate of leaf extensionshowed a marked ontogenetic drift which was most rapid at 30°C and slowest at 10 °C. The mean absolute extensionrate for foliage had a temperature coefficient of 0.16 cm d^–1° C^–1 in the range from 10 to 30 °C. The durationof leaf growth was independent of leaf number at 10 and 20 °Cbut increased linearly with leaf number at 30 °C. The smalldifferences in relative growth rate at the three temperaturesresulted in large differences in foliage area produced at theend of a 30 d growth period. The final foliage areas at 20 and10 °C were 51 and 9% respectively of that at 30 °C. Cyperus longus, temperature, leaf growth, Richards function, growth analysis     

High variability and disomic segregation of microsatellites in the octoploid Fragaria virginiana Mill. (Rosaceae)

The objectives of the present study were to develop microsatellite markers for the wild strawberry, Fragaria virginiana, to evaluate segregation patterns of microsatellite alleles in this octoploid species, and assess genetic variability at microsatellite loci in a wild population. A genomic library was screened for microsatellite repeats and several PCR primers were designed and tested. We also tested the use of heterologous primers and found that F. virginiana primers amplified products in cultivated strawberry, Fragaria × ananassa Duch. and Fragaria chiloensis. Similarly, microsatellite loci developed from cultivated strawberry also successfully amplified F. virginiana loci. We investigated four microsatellite loci in detail, three developed from F. virginiana and one from cultivated strawberry. A survey of 100 individuals from a population of F. virginiana in Pennsylvania demonstrated high heterozygosities (H_e or gene diversity ranged from 0.80 to 0.88 per locus) and allelic diversity (12–17 alleles per locus), but individual plants had no more than two alleles per locus. Segregation patterns in parents and progeny of two controlled crosses at these four loci were consistent with disomic Mendelian inheritance. Together these findings suggest that the genome of F. virginiana is "highly diploidized" and at least a subset of microsatellite loci can be treated as codominant, diploid markers. Significant heterozygote deficiencies were found at three of the four loci for hermaphroditic individuals but for only one locus among females in this gynodioecious species.Communicated by J. Dvorak     

Temperature and Leaf Wetness Effects on Infection of Sugarcane by Puccinia melanocephala

Brown rust epidemics in sugarcane, caused by Puccinia melanocephala, vary in severity between seasons. To improve the understanding of disease epidemiology, the effects of leaf wetness, temperature and their interaction on infection of sugarcane by the pathogen were studied under controlled conditions. Disease severity was low at 15 and 31°C regardless of leaf wetness duration. No infection occurred with a 4‐h leaf wetness period. Increasing leaf wetness duration from 7 to 13 h lowered the temperature required for disease onset from 21 to 17°C. More infection occurred with 13 compared to 10 h of leaf wetness at 17°C, and severity decreased for all leaf wetness periods at 29 compared to 27°C. Postinfection suboptimal low and high temperatures increased the time required for lesion development and high temperatures decreased maximum disease severity. The observed effects of leaf wetness and temperature on infection by P. melanocephala could help explain the initiation, rate of increase and decline of brown rust epidemics in the field.     

Interactions Between Temperature and Sugars in the Regulation of Leaf Senescence in the Perennial Herb Arabis alpina L.

Annual plants usually flower and set seed once before senescence results in the death of the whole plant (monocarpic senescence). Leaf senescence also occurs in polycarpic perennials; even in "evergreen" species individual leaves senesce. In the annual model Arabidopsis thaliana sugars accumulate in the senescent leaves and senescence is accelerated by high sugar availability. Similar to A. thaliana, sugar contents increased with leaf age in the perennial Arabis alpina grown under warm conditions (22 C day/18 night). At 5 C, sugar contents in non-senescent leaves were higher than at a warm temperature, but dependent on the accession, either sugars did not accumulate or their contents decreased in old leaves. In A. alpina plants grown in their natural habitat in the Alps, sugar contents declined with leaf age. Growth at a cold temperature slightly delayed senescence in A. alpina. In both warm and cold conditions, an external glucose supply accelerated senescence, but natural variation was found in this response. In conclusion, sugar accumulation under warm conditions could accelerate leaf senescence in A. alpina plants, but genotype-specific responses and interactions with growth temperature are likely to influence senescence under natural conditions.     

Growth Analysis of Sumatran Monophyllaea, Possessing Only One Leaf Throughout Perennial Life

Abstract Growth and allometry were analyzed for populations of Monophyllaea hirtella Miq and M. horsfieldii R. Br. (Gesneriaceae), forest floor herbs that have only one cotyledonous leaf throughout life, in an equatorial rain forest in West Sumatra. Monophyllaea populations consisted of individuals of various sizes up to 30 g dry weight and 50x70 cm in leaf width and length. The relative growth rate (RGR) declined with size to an asymptotic value of 0.015–0.018 gg^-1 week^-1 for large individuals at sexual maturity (>2 g dry weight). The size-RGR relation did not differ among observations at three differen times of year and between two species in different habitals, indicating that it takes 4.6 years for seedlings to attain sexual maturity and 6.4 years to reach 10 g dry weight. Irrespective of embryonic organization of Monophyllaea , clear allometry existed among organs. Net assimilation rate was constant for juveniles and increased with size for adults. Decline of both the specific leaf area and the ratio of assimilate allocation to leaf caused the decrease of RGR with size. Reproductive allocation was 31% to reproductive organs and at most 5% to seeds in net production in a large individual of 20 g dry weight.     

An experimental test of the effects of resources and sex ratio on maternal fitness and phenotypic selection in gynodioecious Fragaria virginiana

Resources, sex ratio, and seed production by hermaphrodites covary among natural populations of many gynodioecious plant species, such that they are functionally "more dioecious" as resources become more limiting. Strong correlations among these three factors confound our understanding of their relative roles in maintaining polymorphic sexual systems. We manipulated resource availability and sex ratio and measured their effects on relative fertility and phenotypic selection through the maternal fitness of females and hermaphrodites of Fragaria virginiana. Two results were particularly surprising. First, hermaphrodites showed little variability in fecundity across resource treatments and showed strong positive and context-dependent selection for fruit set. This suggests that variation in hermaphrodite seed production along resource gradients in nature may result from adaptation rather than plasticity. Second, although females increased their fecundity with higher resources, their fertility was unaffected by sex ratio, which is predicted to mediate pollen limitation of females in natural populations where they are common. Selection on petal size of females was also weak, indicating a minimal effect of pollinator attraction on variation in the fertility of female plants. Hence, we found no mechanistic explanation for the complete absence of high-resource high female populations in nature. Despite strong selection for increased fruit set of hermaphrodites, both the strength of selection and its contribution to the maintenance of gynodioecy are severely reduced under conditions where females have high relative fecundity (i.e., low resources and high-female sex ratios). High relative fertility plus high female frequency means that the evolution of phenotypic traits in hermaphrodites (i.e., response to selection via seed function) should be manifested through females because most hermaphrodites will have female mothers. Fruit set was never under strong selection in females; hence, selection to increase fruit set hermaphrodites will be less effective in maintaining their fruiting ability in natural populations with low resources and high female frequency. In sum, both sex ratio and resource availability influence trait evolution indirectly-through their effects on relative fertility of the sexes and patterns of selection. Sex ratio did not impose strong pollen limitation on females but did directly moderate the outcome of natural selection by biasing the maternal sex of the next generation. This direct effect of sex ratio on the manifestation of natural selection is expected to have far greater impact on the evolution of traits, such as seed-producing ability in hermaphrodites and the maintenance of sexual polymorphisms in nature, compared to indirect effects of sex ratio on relative fertility of the sexes.     

Rates of Leaf and Tiller Production in Young Spaced Perennial Ryegrass Plants in Relation to Soil Temperature and Solar Radiation

In an experiment designed to investigate the rate of leaf appearanceand tiller production in young spaced plants of three clonesof perennial ryegrass grown in the field, it was found thatthe rate of leaf appearance per tiller increased linearly withmean soil temperature up to approx. 14 °C. The rate of productionof tillers in relation to the rate of leaf appearance (sitefilling) appeared to be virtually independent of weather conditions.In plants which were adequately established, but still relativelysmall, site filling was equal to or exceeded the theoreticalsteady state; all the tiller buds which were being formed weredeveloping into visible tillers. Thus the relative rate of tillerproduction was controlled by the rate of leaf appearance. Inlarger plants site filling was less complete, and site redundancieswere probably caused by within-plant competition for light atthe tiller bases. Lolium perenne L., perennial ryegrass, tillering, leaf production, solar radiation, soil temperature     

Effects of Fermentation Conditions and Aging Temperature on Volatile Ester Contents in Wine

In these present experiments, rats were fed a low casein, vitamin E and selenium deficient diet and were killed at various time intervals up to the occurrence of massive liver necrosis. Liver malondialdehyde, and liver and serum vitamin E levels were analyzed simultaneously with a pathological investigation of the features of the liver and measurement of serum GOT and GPT activities. These investigations were also performed on control rats given a high casein, vitamin E defincient diet or a low casein, vitamin E supplemented diet.

The results show that the liver malondialdehyde level was not increased concomitant with the decrease in liver and serum vitamin E level nor with the occurrence of massive liver necrosis. Liver cells of the rats fed on the low casein, vitamin E deficient diet showed swelling of the cytoplasm at the initial stage, and progressive centrilobular lipid deposition was observed by Sudan III stain.