Local adaptation optimizes photoprotection strategies in a Neotropical legume tree under drought stress

Photoprotection is a plant functional mechanism to prevent photooxidative damage by excess light. This is most important when carbon assimilation is limited by drought, and as such, it entails a trade-off between carbon assimilation vs stress avoidance. The ecological adaptation of plants to local water availability can lead to different photoprotective strategies. To test this, we used different provenances of Caesalpinia spinosa (Mol.) Kuntze (commonly known as 'tara') along a precipitation gradient. Tara is a Neotropical legume tree with high ecological and commercial value, found in dry tropical forests, which are increasingly threatened by climate change. Morphological and physiological responses of tara provenances were analysed under three different treatments of drought and leaflet immobilization, i.e., light stress, in a common garden greenhouse experiment. Tara quickly responded to drought by reducing stomatal conductance, evapotranspiration, photochemical efficiency, carbon assimilation and growth, while increasing structural and chemical photoprotection (leaflet angle and pigments for thermal dissipation). Leaflet closure was an efficient photoprotection strategy with overall physiological benefits for seedlings as it diminished the evaporative demand and avoided photodamage, but also entailed costs by reducing net carbon assimilation opportunities. These responses depended on seed origin, with seedlings from the most xeric locations showing the highest dehydration tolerance, suggesting local adaptation and highlighting the value of different strategies under distinct environments. This plasticity in its response to environmental stress allows tara to thrive in locations with contrasting water availability. Our findings increase the understanding of the factors controlling the functional ecology of tara in response to drought, which can be leveraged to improve forecasts of changes in its distribution range, and for planning restoration projects with this keystone tree species.

Local plant responses to global problems: Dactylis glomerata responses to different traffic pollutants on roadsides

The growing number of road vehicles is a major source of regional and global atmospheric pollution increasing concentrations of CO₂ in the air, and levels of metals in air and soil. Nevertheless, the effects of these pollutants on plants growing at roadsides are poorly documented. We carried out an observational study of unmanipulated plants growing by the road, to identify the morpho-physiological responses in a perennial grass Dactylis glomerata. Firstly, we wanted to know the general effect of traffic intensity and ambient CO₂ and its interactions on different plant traits. Accordingly, we analyzed the photosynthetic response by field A/Ci Response Curves, SLA, pigment pools, foliar nitrogen, carbohydrates and morphological traits in plants at three distances to the road. Secondly, we wanted to know if Dactylis glomerata plants can accumulate metals present on the roadside (Pb, Zn, Cu, and Sr) in their tissues and rhizosphere, and the effect of these metals on morphological traits. The MANCOVA whole model results shown: 1) a significant effect of road ambient CO₂ concentration on morphological traits (not affected by traffic intensity, P _{interaction CO2 x traffic intensity}>0.05), that was mainly driven by a significant negative relationship between the inflorescence number and ambient CO₂; 2) a positive and significant relationship between ambient CO₂ and the starch content in leaves (unaffected by traffic intensity); 3) a reduction in J_max (electron transport rate) at high traffic intensity. These lines of evidences suggest a decreased photosynthetic capacity due to high traffic intensity and high levels of ambient CO₂. In addition, Pb, Cu, Zn and Sr were detected in Dactylis glomerata tissues, and Cu accumulated in roots. Finally, we observed that Dactylis glomerata individuals growing at the roadside under high levels of CO₂ and in the presence of metal pollutants, reduced their production of inflorescences.

Unusual positional effects on flower sex in an andromonoecious tree: Resource competition, architectural constraints, or inhibition by the apical flower?

PREMISE OF THE STUDY

Two, nonmutually exclusive, mechanisms-competition for resources and architectural constraints-have been proposed to explain the proximal to distal decline in flower size, mass, and/or femaleness in indeterminate, elongate inflorescences. Whether these mechanisms also explain unusual positional effects such as distal to proximal declines of floral performance in determinate inflorescences, is understudied.

METHODS

We tested the relative influence of these mechanisms in the andromonoecious wild olive tree, where hermaphroditic flowers occur mainly on apical and the most proximal positions in determinate inflorescences. We experimentally increased the availability of resources for the inflorescences by removing half of the inflorescences per twig or reduced resource availability by removing leaves. We also removed the apical flower to test its inhibitory effect on subapical flowers.

KEY RESULTS

The apical flower had the highest probability of being hermaphroditic. Further down, however, the probability of finding a hermaphroditic flower decreased from the base to the tip of the inflorescences. An experimental increase of resources increased the probability of finding hermaphroditic flowers at each position, and vice versa. Removal of the apical flower increased the probability of producing hermaphroditic flowers in proximal positions but not in subapical positions.

CONCLUSIONS

These results indicate an interaction between resource competition and architectural constraints in influencing the arrangement of the hermaphroditic and male flowers within the inflorescences of the wild olive tree. Subapical flowers did not seem to be hormonally suppressed by apical flowers. The study of these unusual positional effects is needed for a general understanding about the functional implications of inflorescence architecture.

The expression of light-related leaf functional traits depends on the location of individual leaves within the crown of isolated Olea europaea trees

BACKGROUND

The spatial arrangement and expression of foliar syndromes within tree crowns can reflect the coupling between crown form and function in a given environment. Isolated trees subjected to high irradiance and concomitant stress may adjust leaf phenotypes to cope with environmental gradients that are heterogeneous in space and time within the tree crown. The distinct expression of leaf phenotypes among crown positions could lead to complementary patterns in light interception at the crown scale.

METHODS

We quantified eight light-related leaf traits across 12 crown positions of ten isolated Olea europaea trees in the field. Specifically, we investigated whether the phenotypic expression of foliar traits differed among crown sectors and layers and five periods of the day from sunrise to sunset. We investigated the consequences in terms of the exposed area of the leaves at the tree scale during a single day.

KEY RESULTS

All traits differed among crown positions except the length-to-width ratio of the leaves. We found a strong complementarity in the patterns of the potential exposed area of the leaves among day periods as a result of a non-random distribution of leaf angles across the crown. Leaf exposure at the outer layer was below 60 % of the displayed surface, reaching maximum interception during morning periods. Daily interception increased towards the inner layer, achieving consecutive maximization from east to west positions within the crown, matching the sun's trajectory.

CONCLUSIONS

The expression of leaf traits within isolated trees of O. europaea varies continuously through the crown in a gradient of leaf morphotypes and leaf angles depending on the exposure and location of individual leaves. The distribution of light-related traits within the crown and the complementarity in the potential exposure patterns of the leaves during the day challenges the assumption of low trait variability within individuals.

The effects of phenotypic plasticity and local adaptation on forecasts of species range shifts under climate change

Species are the unit of analysis in many global change and conservation biology studies; however, species are not uniform entities but are composed of different, sometimes locally adapted, populations differing in plasticity. We examined how intraspecific variation in thermal niches and phenotypic plasticity will affect species distributions in a warming climate. We first developed a conceptual model linking plasticity and niche breadth, providing five alternative intraspecific scenarios that are consistent with existing literature. Secondly, we used ecological niche-modeling techniques to quantify the impact of each intraspecific scenario on the distribution of a virtual species across a geographically realistic setting. Finally, we performed an analogous modeling exercise using real data on the climatic niches of different tree provenances. We show that when population differentiation is accounted for and dispersal is restricted, forecasts of species range shifts under climate change are even more pessimistic than those using the conventional assumption of homogeneously high plasticity across a species' range. Suitable population-level data are not available for most species so identifying general patterns of population differentiation could fill this gap. However, the literature review revealed contrasting patterns among species, urging greater levels of integration among empirical, modeling and theoretical research on intraspecific phenotypic variation.

Leaf-trait responses to irrigation of the endemic fog-oasis tree Myrcianthes ferreyrae: can a fog specialist benefit from regular watering?

Myrcianthes ferreyrae is an endemic, endangered species, with a small number of individuals located only in hyperarid, fog-oases known as lomas along the Peruvian desert in southern Peru, where fog is the main source of water. Following centuries of severe deforestation, reforestation with this native species was conducted in the Atiquipa lomas, Arequipa-Perú. On five slopes, five 2-year-old seedlings were irrigated monthly with water trapped by raschel-mesh fog collectors, supplementing natural rainfall with 0, 20, 40, 60 and 80 mm month(-1) from February to August 2008. We measured plant growth, increment in basal diameter, height and five leaf traits: leaf mass area (LMA), leaf carbon isotope composition (δ(13)C), nitrogen per leaf area, total leaf carbon and stomatal density; which are indicative of the physiological changes resulting from increased water supply. Plant growth rates, estimated from the variation of either shoot basal diameter or maximum height, were highly correlated with total biomass. Only LMA and δ(13)C were higher in irrigated than in control plants, but we found no further differences among irrigation treatments. This threshold response suggests an on-off strategy fitted to exploit pulses of fog water, which are always limited in magnitude in comparison with natural rain. The absence of a differential response to increased water supply is in agreement with the low phenotypic plasticity expected in plants from very stressful environments. Our results have practical implications for reforestation projects, since irrigating with 20 mm per month is sufficient to achieve the full growth capacity of this species.

Temporal matching among diurnal photosynthetic patterns within the crown of the evergreen sclerophyll Olea europaea L

Trees are modular organisms that adjust their within-crown morphology and physiology in response to within-crown light gradients. However, whether within-plant variation represents a strategy for optimizing light absorption has not been formally tested. We investigated the arrangement of the photosynthetic surface throughout one day and its effects on the photosynthetic process, at the most exposed and most sheltered crown layers of a wild olive tree (Olea europaea L.). Similar measurements were made for cuttings taken from this individual and grown in a greenhouse at contrasted irradiance-levels (100 and 20% full sunlight). Diurnal variations in light interception, carbon fixation and carbohydrate accumulation in sun leaves were negatively correlated with those in shade leaves under field conditions when light intensity was not limiting. Despite genetic identity, these complementary patterns were not found in plants grown in the greenhouse. The temporal disparity among crown positions derived from specialization of the photosynthetic behaviour at different functional and spatial scales: architectural structure (crown level) and carbon budget (leaf level). Our results suggest that the profitability of producing a new module may not only respond to construction costs or light availability, but also rely on its spatio-temporal integration within the productive processes at the whole-crown level.

Dark induction of the photoprotective xanthophyll cycle in response to dehydration

Some plants tolerate tissue dehydration. Dehydration conditions suppress photosynthesis, exacerbating photooxidative stress. In this study, fern samples were collected from the field, desiccated in darkness, and subsequently re-watered. During dark dehydration, zeaxanthin (Z) was formed and maximal photochemical efficiency of PS II was strongly reduced. Rehydration in the dark reversed these effects. Violaxanthin de-epoxidase was responsible for the dark formation of Z as illustrated by its complete inhibition by DTT. Nonetheless, its activity was not affected by nigericin, indicating that Z formation in the dark could be a process independent of the transmembrane pH-gradient into the thylakoids. Synthesis de novo of Z was rejected after blocking carotenogenesis with norfluorazon. Dark formation of Z was also observed in dehydrating leaves of desiccation-intolerant plants, which seems to indicate that this is a phenomenon scattered among different taxa within the plant kingdom. Plants may trigger this mechanism during dehydration, for chlorophyll protection during desiccation, and for faster acclimation when rehydrating conditions return. Violaxanthin de-epoxidation to form Z is typically a light-dependent process, but the formation induced solely by dehydration might represent an anticipatory mechanism for preventing early morning photodamage in desiccation-tolerant plants such as the fern Ceterach officinarum.

Phenotypic plasticity and integration across the canopy of Olea europaea subsp. guanchica (Oleaceae) in populations with different wind exposures

Woody plants, as sessile and long-lived organisms, are expected to have effective mechanisms for dealing with recurrent environmental stresses. In the present study, we hypothesized that phenotypic plasticity (the ability to express alternative phenotypes) and integration (covariation among functionally related traits) are elicited in plants under stressful wind speed conditions. We investigated the within-crown variation of nine vegetative traits of a tree species (Olea europaea subsp. guanchica) in six populations that represented a gradient of wind speed exposures. Wind-exposed twigs in outer-canopy layers had smaller leaves; thinner, lighter, and shorter internodes; and a larger internode cross-sectional area to leaf area ratio. Comparison between field and greenhouse trials revealed that field differences among populations were mediated by phenotypic plasticity. Outer-canopy twigs expressed plastic responses in populations exposed to high wind speeds, whereas inner-canopy twigs displayed high phenotypic convergence among populations. In addition, phenotypic integration increased with wind exposure (outer canopy > inner canopy > greenhouse) and was consequently affected by canopy openness. We conclude that exposure to wind above a certain speed threshold in this woody species elicits a plastic response that is associated with increased integration among traits and involves mechanical and hydraulic rearrangements in more exposed parts of the trees.

Alternative methods for sampling and preservation of photosynthetic pigments and tocopherols in plant material from remote locations

Current methods for the study of pigments involve freezing in liquid nitrogen and storage at -80 degrees C or lyophilization until HPLC analysis. These requirements greatly restrict ecophysiological research in remote areas where such resources are hardly available. We aimed to overcome such limitations by developing several techniques not requiring freezing or lyophilization. Two species with contrasting foliar characteristics (Olea europaea and Taraxacum officinale) were chosen. Seven preservation methods were designed, optimized and tested in a field trial. These protocols were compared with a control immediately frozen after collection. Pigments and tocopherols were analysed by HPLC. Main artefacts were chlorophyll epimerization or phaeophytinization, carotenoid isomerization, altered de-epoxidation index and tocopherol degradation. Among all methods, sample desiccation in silica gel provides robust samples (pigment composition was unaffected by storage time or temperature) and almost unaltered pigment profiles, except for a shift in epoxidation state. Although liquid nitrogen freezing and subsequent lyophilization or freezer storage were preferred, when these facilities are either not available or not suitable for long-distance transport, desiccation with silica gel, passive extraction in acetone and/or storage of fresh samples in water vapour saturated atmospheres enable a complete pigment characterization. Silica gel is advisable for long-term sample conservation.

Variation in sclerophylly among Iberian populations of Quercus coccifera L. is associated with genetic differentiation across contrasting environments

Evergreen oaks are an emblematic element of the Mediterranean vegetation and have a leaf phenotype that seems to have remained unchanged since the Miocene. We hypothesise that variation of the sclerophyll phenotype among Iberian populations of Quercus coccifera is partly due to an ulterior process of ecotypic differentiation. We analysed the genetic structure of nine Iberian populations using ISSR fingerprints, and their leaf phenotypes using mean and intracanopy plasticity values of eight morphological (leaf angle, area, spinescence, lobation and specific area) and biochemical traits (VAZ pool, chlorophyll and beta-carotene content). Climate and soil were also characterised at the population sites. Significant genetic and phenotypic differences were found among populations and between NE Iberia and the rest of the populations of the peninsula. Mean phenotypes showed a strong and independent correlation with both genetic and geographic distances. Northeastern plants were smaller, less plastic, with smaller, spinier and thicker leaves, a phenotype consistent with the stressful conditions that prevailed in the steppe environments of the refugia within this geographic area during glaciations. These genetic, phenotypic, geographic and environmental patterns are consistent with previously reported palaeoecological and common evidence. Such consistency leads us to conclude that there has been a Quaternary divergence within the sclerophyllous syndrome that was at least partially driven by ecological factors.

A poorly-differentiated squamous cell thymoma in a chicken with lymphoma

Thymic carcinomas are rare in birds. A poorly-differentiated squamous cell thymoma was found in a chicken in association with a lymphoma caused by Marek's disease. Immunohistochemical techniques with different tumour markers were applied in order to determine the histogenesis of the thymic tumour cells. A positive immunoreaction of the tumour cells to cytokeratin, considered a specific marker for epithelial tumours, confirmed the diagnosis of a thymoma.

Genetic diversity and differentiation processes in the ploidy series of Olea europaea L.: a multiscale approach from subspecies to insular populations

Geographical isolation and polyploidization are central concepts in plant evolution. The hierarchical organization of archipelagos in this study provides a framework for testing the evolutionary consequences for polyploid taxa and populations occurring in isolation. Using amplified fragment length polymorphism and simple sequence repeat markers, we determined the genetic diversity and differentiation patterns at three levels of geographical isolation in Olea europaea: mainland-archipelagos, islands within an archipelago, and populations within an island. At the subspecies scale, the hexaploid ssp. maroccana (southwest Morocco) exhibited higher genetic diversity than the insular counterparts. In contrast, the tetraploid ssp. cerasiformis (Madeira) displayed values similar to those obtained for the diploid ssp. guanchica (Canary Islands). Geographical isolation was associated with a high genetic differentiation at this scale. In the Canarian archipelago, the stepping-stone model of differentiation suggested in a previous study was partially supported. Within the western lineage, an east-to-west differentiation pattern was confirmed. Conversely, the easternmost populations were more related to the mainland ssp. europaea than to the western guanchica lineage. Genetic diversity across the Canarian archipelago was significantly correlated with the date of the last volcanic activity in the area/island where each population occurs. At the island scale, this pattern was not confirmed in older islands (Tenerife and Madeira), where populations were genetically homogeneous. In contrast, founder effects resulted in low genetic diversity and marked genetic differentiation among populations of the youngest island, La Palma.

Field patterns of leaf plasticity in adults of the long-lived evergreen Quercus coccifera

BACKGROUND AND AIMS

Quercus coccifera, as a long-lived sprouter, responds plastically to environmental variation. In this study, the role of foliar plasticity as a mechanism of habitat selection and modification within the canopy and across contrasted habitats was characterized. An examination was made of the differential contribution of inner and outer canopy layers to the crown plasticity expressed in the field by adult individuals and its dependence on environmental and genetic factors.

METHODS

Within-crown variation in eight foliar traits was examined in nine populations dominated by Q. coccifera. The difference between mean trait values at the inner and outer canopy layers was used as a proxy for crown plasticity to light. Correlations between geographic distances, environmental differences (climatic and edaphic) and phenotypic divergence (means and plasticities) were assessed by partial Mantel tests. A subset of field measurements was compared with data from a previous common garden experiment.

KEY RESULTS

Phenotypic adjustment of sun leaves contributed significantly to the field variation in crown plasticity. Plasticity in leaf angle, lobation, xanthophyll cycle pigments and beta-carotene content was expressed in sun and shade leaves concurrently and in opposite directions. Phenotypic plasticity was more strongly correlated with environmental variation than mean trait values. Populations of taller plants with larger, thinner (higher specific leaf area) and less spiny leaves exhibited greater plasticity. In these populations, the midday light environment was more uniform at the inner than at the outer canopy layers. Field and common garden data ranked populations in the same order of plasticity.

CONCLUSIONS

The expression of leaf plasticity resulted in a phenotypic differentiation that suggests a mechanism of habitat selection through division of labour across canopy layers. Signs of plasticity-mediated habitat modification were found only in the most plastic populations. Intracanopy plasticity was sensitive to environmental variation but also exhibited a strong genetic component.

Extensive gene flow blurs phylogeographic but not phylogenetic signal in Olea europaea L

Genetic structure and evolutionary patterns of the wild olive tree (Olea europaea L.) were investigated with AFLP fingerprinting data at three geographic levels: (a) phylogenetic relationships of the six currently recognized subspecies in Eurasia and Africa; (b) lineage identification in subsp. europaea of the Mediterranean basin; and (c) phylogeography in the western Mediterranean. Two statistical approaches (Bayesian inference and analysis of molecular variance) were used to analyse the AFLP fingerprints. To determine the congruency and transferability of results across studies previous RAPD and ISSR data were analysed in a similar manner. Comparisons proved that qualitative results were mostly congruent but quantitative values differed, depending on the method of analysis. Neighbour-Joining analysis of AFLP phenotypes supported current classification of subspecies. At a Mediterranean scale no clear cut phylogeographic pattern was recovered, likely due to extensive gene flow between populations of subsp. europaea. Gene flow estimates calculated with conventional F-statistics showed that reproductive barriers separated neither populations nor lineages of O. europaea. Genetic divergence between eastern and western parts of the Mediterranean basin was observed only when geographical and population information were incorporated into the analyses through hierarchical analysis of molecular variance (AMOVA). Within the western Mediterranean, the highest genetic diversity was found in two regions: on both sides of the Strait of Gibraltar and in the Balearic archipelago. Additionally, long-lasting isolation of the northern-most populations of the Iberian Peninsula appeared to be responsible for a significant divergence.

Winter photoinhibition in the field involves different processes in four co-occurring Mediterranean tree species

Photoinhibition was examined in four co-occurring Mediterranean evergreen tree species during two consecutive winters. In response to low temperatures and saturating light, Juniperus phoenicea L., Pinus halepensis Mill., Quercus coccifera L. and Q. ilex ssp. ballota (Desf.) Samp. exhibited marked chronic photoinhibition, indicated by low predawn maximal photochemical efficiency of photosystem II (PSII) (Fv/Fm). Low Fv/Fm values were correlated with high concentrations of xanthophyll cycle components (VAZ) and with the maintenance of high concentrations of zeaxanthin overnight (DPSpd). In all species, however, chronic photoinhibition was enhanced as the winter progressed in the absence of changes in DPSpd, suggesting cumulative damage toward the end of winter. Photoinhibition differed among species: P. halepensis always displayed significantly higher Fv/Fm values; and Q. coccifera had the lowest Fv/Fm values, showing a high sensitivity to the combination of high light and low temperatures. Differences among species were not fully explained by differences in the xanthophyll pool or its de-epoxidation state. Chronic photoinhibition overlapped with a dynamic photoinhibition as shown by the low values of photochemical efficiency of the open reaction centers of PSII at midday. Winter photoprotective strategies differed among species and may involve photoprotective mechanisms in addition to those associated with xanthophylls. The observed species-specific differences matched results obtained for the same species in summer; however, comparison of the two seasons suggests that the higher VAZ concentration observed in winter has an additional structural photoprotective role.

Mechanisms underlying the amelioration of O3-induced damage by elevated atmospheric concentrations of CO2

There is growing evidence that rising atmospheric CO2 concentrations will reduce or prevent reductions in the growth and productivity of C3 crops attributable to ozone (O3) pollution. In this study, the role of pollutant exclusion in mediating this response was investigated through growth chamber-based investigations on leaves 4 and 7 of spring wheat (Triticum aestivum cv. Hanno). In the core experiments, plants were raised at two atmospheric CO2 concentrations (ambient [350 micro l l(-1)] or elevated CO2 [700 micro l l(-1)] under two O3 regimes (charcoal/Purafil-filtered air [<5 nl l(-1) O3] or ozone-enriched air [75 nl l(-1) 7 h d(-1)]). A subsequent experiment used an additional O3 treatment where the goal was to achieve equivalent daily O3 uptake over the life-span of leaves 4 and 7 under ambient and CO2-enriched conditions, through daily adjustment of exposures based on measured shifts in stomatal conductance. Plant growth and net CO2 assimilation were stimulated by CO2-enrichment and reduced by exposure to O3. However, the impacts of O3 decreased with plant age (i.e. leaf 7 was more resistant to O3 injury than leaf 4); a finding consistent with ontogenic shifts in the tolerance of plant tissue and/or acclimation to O3-induced oxidative stress. In the combined treatment, elevated CO2 protected against the adverse effects of O3 and reduced cumulative O3 uptake (calculated from measurements of stomatal conductance) by c. 10% and 35% over the life-span of leaves 4 and 7, respectively. Analysis of the relationship between O3 uptake and the decline in the maximum in vivo rate of Rubisco carboxylation (Vcmax) revealed the protection afforded by CO2-enrichment to be due, to a large extent, to the exclusion of the pollutant from the leaf interior (as a consequence of the decline in stomatal conductance triggered by CO2-enrichment), but there was evidence (especially from flux-response relationships constructed for leaf 4) that CO2-enrichment resulted in additional effects that alleviated the impacts of ozone-induced oxidative stress on photosynthesis.

Plasticity, instability and canalization: is the phenotypic variation in seedlings of sclerophyll oaks consistent with the environmental unpredictability of Mediterranean ecosystems?

•   Evergreen oaks from the Mediterranean basin exhibit a conservative resource-use strategy based on a reduced expression of phenotypic variation (i.e. canalization). We hypothesized that genetic variation across closely related species is more canalized than the response to environmental variation. •   Seedlings of Quercus ilex and Q. coccifera, two important oak species from the Mediterranean basin that belong to the same subgenus and section, were grown in contrasted light and nutrient environments following a factorial design. Phenotypic variation was explored in a total of 75 variables including photosynthetic capacity, nutrient allocation, allometric relationships and crown architecture. •   Path analysis showed that phenotypic variation was not significantly affected by differences between species but by those between and within environments, which are argued to be primarily linked to phenotypic plasticity and developmental instability, respectively. This finding is interpreted as evidence of genetic canalization across species. •   The similar importance of plasticity and instability as sources of phenotypic variation and the high degree of genetic canalization are consistent with the expected role of the environmental unpredictability of Mediterranean ecosystems in shaping the developmental patterns of these two species.

Low leaf-level response to light and nutrients in Mediterranean evergreen oaks: a conservative resource-use strategy?

We have explored leaf-level plastic response to light and nutrients of Quercus ilex and Q. coccifera, two closely related Mediterranean evergreen sclerophylls, in a factorial experiment with seedlings. Leaf phenotypic plasticity, assessed by a relative index (PI = (maximum value - minimum)/maximum) in combination with the significance of the difference among means, was studied in 37 morphological and physiological variables. Light had significant effects on most variables relating to photosynthetic pigments, chlorophyll fluorescence and gas exchange, whereas nutrient treatment had a significant effect in only 10% of the variables. Chlorophyll content was higher in the shade whereas carotenoid content and nonphotochemical quenching increased with light. Nutrient limitations increased the xanthophyll-cycle pool but only at high light intensities, and the same interaction between light and nutrients was observed for lutein. Predawn photochemical efficiency of PSII was not affected by either light or nutrients, although midday photochemical efficiency of PSII was lower at high light intensities. Photosynthetic light compensation point and dark respiration on an area basis decreased with light, but photosynthetic capacity on a dry mass basis and photochemical quenching were higher in low light, which translated into a higher nitrogen use efficiency in the shade. We expected Q. ilex, the species of the widest ecological distribution, to be more plastic than Q. coccifera, but differences were minor: Q. ilex exhibited a significant response to light in 13% more of the variables than Q. coccifera, but mean PI was very similar in the two species. Both species tolerated full sunlight and moderate shade, but exhibited a reduced capacity to enhance photosynthetic utilization of high irradiance. When compared with evergreen shrubs from the tropical rainforest, leaf responsiveness of the two evergreen oaks was low. We suggest that the low leaf-level responsiveness found here is part of a conservative resource use strategy, which seems to be adaptive for evergreen woody plants in Mediterranean-type ecosystems.

Energy dissipation in drought-avoiding and drought-tolerant tree species at midday during the Mediterranean summer

Photosynthetic performance was monitored during two consecutive summers in four co-occurring evergreen Mediterranean tree species growing on a south-facing rocky slope. In response to midday water stress, the drought-avoiding species Pinus halepensis Mill. exhibited marked stomatal closure (g(s)) but no changes in stem water potential (Psi(s)), whereas the drought-tolerant species Quercus coccifera L., Q. ilex ssp. ballota (Desf.) Samp. and Juniperus phoenicea L. displayed declines in midday g(s) and Psi(s). The higher resistance to CO(2) influx in needles of P. halepensis compared with the other species did not result in either a proportional increase in non-radiative dissipation of excess energy or photo-inactivation of photosystem II (PSII). No significant differences were found among species either in the de-epoxidation state of the xanthophyll cycle (DPS) or in the pool of its components on a total chlorophyll basis (VAZ). Despite contrasting midday assimilation rates, the three drought-tolerant species all exhibited a pronounced drop in photochemical efficiency at midday that was characterized by a decrease in the excitation capture efficiency of the open PSII centers. Although photoinhibition was not fully reversed before dawn, it apparently did not result in cumulative photo-damage. Thus, the drought-avoiding and drought-tolerant species employed different mechanisms for coping with excess light during the midday depression in photosynthesis that involved contrasting midday photochemical efficiencies of PSII and different degrees of dynamic photoinhibition as a photo-protective mechanism. These behaviors may be related to the different mechanisms employed by drought-avoiding and drought-tolerant species to withstand water deficit.

Predictability of the combined effects of sulphur dioxide and nitrate on the green-algal lichen Ramalina farinacea

The interactive effects of SO2 and NO3− on the green-algal lichen Ramalina farinacea (L.) Ach. were investigated using the degree of chlorophyll phaeophytinization and ultrastructural damage to the Trebouxia photobiont. Thalli were submitted to several factorial design experiments in which they were exposed to mean SO2 concentrations ranging from 118 to 140 nmol∙mol−1 plus or minus aqueous solutions of NO3− at either 50 or 1000 μmol∙L−1, for 6–14 days. Interactive effects of SO2 and NO3− were synergistic when the effects of each individual pollutant were slight. However, this pattern reverted to additive effects, and sequentially to antagonistic effects as the detrimental impact of SO2 alone became more severe. Despite this transition, neutralization of the damaging impact of SO2 by simultaneous treatment with NO3− was not observed. The results show that interactions between SO2 and NO3− were variable, but predictable on the basis of the expected effects following exposure to each pollutant alone. The coincidence of this empirical pattern with those observed in previous studies suggests involvement of unspecific causes. The wider ecological significance of interactions between SO2 and NO3− is discussed in the light of other findings with respect to the effects of air pollution on lichens in the field. Key words: air pollution, sulphur dioxide, nitrate, interactive effects, lichens, pigments, ultrastructure.

Prevalence and characteristics of enteropathogenic Escherichia coli with the eae gene in diarrhoeic rabbits

A field study was carried out with the objective of investigating the prevalence of enteropathogenic Escherichia coli (EPEC) with the eae gene in diarrhoeic rabbits. EPEC eae+ were isolated from 60 (74%) of 81 diarrhoeic rabbits sampled in 30 industrial fattening farms localized in the four provinces of Galicia (northwestern Spain). Attaching and effacing lesions were found in 44 of 50 animals processed for histology. The 111 E. coli strains identified belonged to 19 different O serogroups and 13 biotypes. However, 53 (48%) of the strains belonged to serogroup O103 and 36 (32%) showed the serobiotype O103:B14. The eae gene was significantly more frequent (100%; 47 of 47) among the highly pathogenic rhamnose-negative strains of serobiotypes O103:B6 and O103:B14 than among the E. coli strains belonging to other serobiotypes (36%; 23 of 64) (P < 0.001). In this first report about the prevalence of EPEC with the eae gene in rabbits, we conclude that the class of E. coli strains observed is a common cause of diarrhoea in Galician rabbit farms, and that highly pathogenic rhamnose-negative strains of serotype O103:K-:H2 and biotype B14 are specially predominant.

O serogroups, biotypes, and eae genes in Escherichia coli strains isolated from diarrheic and healthy rabbits

A total of 305 Escherichia coli strains isolated from diarrheic and healthy rabbits in 10 industrial fattening farms from different areas of Spain were serotyped, biotyped, and tested for the presence of the eae gene and toxin production. The characteristics found in strains isolated from healthy rabbits were generally different from those observed in E. coli strains associated with disease. Thus, strains with the eae gene (74% versus 22%); strains belonging to serogroups O26, O49, O92, O103, and O128 (64% versus 12%); rhamnose-negative strains (51% versus 5%); and rhamnose-negative O103 strains with eae genes present (41% versus 1%) were significantly (P < 0.001 in all cases) more frequently detected in isolates from diarrheic animals than in those from healthy rabbits. Whereas a total of 35 serogroups and 17 biotypes were distinguished, the majority of the strains obtained from diarrheic rabbits belonged to only four serobiotypes, which in order of frequency were O103:B14 (72 strains), O103:B6 (16 strains), O26:B13 (12 strains), and O128:B30 (12 strains). These four serobiotypes accounted for 48% (112 of 231) and 5% (4 of 74) of the E. coli strains isolated from diarrheic and healthy rabbits, respectively. Only six strains were toxigenic (three CNF1+, two CNF2+, and one VT1+). We conclude that enteropathogenic E. coli strains that possess the eae gene are a common cause of diarrhea in Spanish rabbit farms and that the rhamnose-negative highly pathogenic strains of serotype O103:K-:H2 and biotype B14 are especially predominant. Detection of the eae gene is a useful method for the identification of enteropathogenic E. coli strains from rabbits. However, a combination of serogrouping and biotyping may be sufficient to accurately identify the highly pathogenic strains for rabbits.

Potential effects of rising tropospheric concentrations of CO2 and O3 on green-algal lichens

Pormelia sulcata Taylor was used as a model to examine the effects of elevated CO₂ and/or O₃ on green algal lichens. Thalli were exposed for 30 d in duplicate controlled-environment chambers to two atmospheric concentrations of CO₂ ('ambient' [350μmol mol^-1 ] and 'elevated' [700μmol mol^-1 ] 24 h d^-1 ) and two O₃ regimes ('non-polluted' air [CF, < 5 nmol mol^-1 ] and 'polluted' air [15 nmol mol^-1 overnight rising to a midday maximum of 75 nmol mol^-1 ]), in a factorial design. Elevated CO₂ , or elevated O₃ depressed the light saturated rate of CO₂ , assimilation A_sat ) measured at ambient CO₂ , by 30% and 18%, respectively. However, despite this effect ultrastructure) studies revealed increased lipid storage in cells of the photobiont in response to CO₂ -enrichment. Simultaneous exposure to elevated O₃ reduced CO₂ -induced lipid accumulation and reduced A_sat in an additive manner. Gold-antibody labelling revealed that the decline in photosynthetic capacity induced by elevated CO₂ and/or O₃ was accompanied by a parallel decrease in the concentration of Rubiscoa in the algal pyrenoid (r= 0.93). Interestingly, differences in the amount of Rubisco protein were not correlated with changes in pyrenoid volume. Measurements of in vivo chlorophyll-fluorescence induction kinetics showed that the decline in A_sat induced by elevated CO₂ , and/or O₂ , was not associated with significant changes in the photochemical efficiency of photosystem (PS) II. Although the experimental conditions inevitably imposed some stress on the thalli, revealed as a significant decline in the efficiency of PS II photochemistry, and enhanced starch accumulation in the photobiont over the fornication period, the study shows that the green-algal lichen symbiosis might be influenced by future changes in atmospheric composition. Photosynthetic capacity, measured at ambient CO₂ , was found to be reduced after a controlled 30 d exposure to elevated CO₂ , and/or O₃ and this effect was associated with a parallel decline in the amount of Rubisco in the pyrenoid of algal chloroplasts.

The localization of neurons innervating the carotid sinus in the dog

The localization of neurons innervating the carotid sinus of the dog was studied by horseradish peroxidase histochemistry following microinjection of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) under the adventitia of the carotid sinus. Labeled cell bodies were found in the petrosal (198 +/- 108; mean +/- S.D.) and superior cervical ganglia (SCG) (890 +/- 354 mean +/- S.D.) supporting the existence of both a sensory afferent and a sympathetic efferent innervation of the carotid sinus. Labeled neurons in the petrosal ganglion were round pseudounipolar neurons of variable size. Labeled neurons in the SCG were multipolar and appeared distributed over the whole ganglion, but with a higher density toward its caudal half. No labeled perikarya appeared either in the brainstem or in the nodose or jugular ganglia, suggesting that in the dog a vagal pathway for carotid sinus baroreceptor afferents does not exist.

The projections to the medulla of neurons innervating the carotid sinus in the dog

The localization and brain stem projections of neurons innervating the carotid sinus of the dog were studied by horseradish peroxidase histochemistry following microinjection of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) under the adventitia of the carotid sinus. Within the brain stem, labeled afferent fibers and presumptive terminals were found bilaterally in the caudal nucleus tractus solitarius (nTS), the area postrema (AP), and the lateral tegmental field (LTF), reaching the area of the nucleus ambiguus (nA). Sparse labeling was also seen in the ipsilateral spinal trigeminal nucleus (SpV) and lateral cuneatus nucleus (LCn). These findings suggest the existence of multiple pathways by which peripheral baroreceptor inputs may influence central cardiovascular-related neurons. In addition to classically defined relay in the nTS, carotid sinus afferents may also interact more directly with these neurons in other brain stem regions.

Prolactinoma in a sheep

This report describes the incidental finding of an acidophilic adenoma of the pituitary gland in an adult ewe with clinical signs of a nervous disorder. Immunohistochemical examination demonstrated prolactin in the tumour cells, justifying the use of the term "prolactinoma" for the first time in veterinary medicine. This tumour should be considered in the differential diagnosis of nervous diseases of sheep.

Immunoreactivity to chromogranin and to vasoactive intestinal peptide in a canine phaeochromocytoma

A canine phaeochromocytoma was diagnosed by (1) argyrophil methods, (2) immunoreactivity to chromogranin and to vasoactive intestinal peptide (VIP), and (3) the demonstration of typical electron-dense granules by transmission electron microscopy. This is the first report of immunoreactivity to general neuroendocrine markers such as chromogranin, and to VIP, in a phaeochromocytoma in domestic animals. The use of these markers for the differential diagnosis of phaeochromocytoma, and the role of VIP in the severe chronic diarrhoea shown by the dog in this study are discussed.

Coexistence of serotonin and cholecystokinin in paraneurons of the foetal sheep lung

The coexistence of serotonin and cholecystokinin was studied in foetal sheep lungs at pseudoglandular stage of development by light microscopic immunohistochemistry. The coexistence was examined by staining consecutive sections with the different antibodies. Serotonin and cholecystokinin immunoreactivity was found within consecutive sections of most bronchopulmonary neuroepithelial bodies and in consecutive sections of the same intrapulmonary autonomic ganglia.

Localization of serotonin, cholecystokinin and somatostatin immunoreactivity in the lower respiratory tract of embryonic, foetal and postnatal sheep

The lower respiratory tract of the sheep was studied by light-microscopical immunocytochemistry for serotonin, cholecystokinin, somatostatin, bombesin and calcitonin during different periods of lung development; embryonic, foetal and postnatal. At embryonic period only intraepithelial serotonin-containing cells as solitary neuroendocrine cells (NEC) and neuroepithelial bodies (NEB) were found. At foetal stages, immunoreactive cells to serotonin, cholecystokinin and somatostatin were observed in airway epithelium, as solitary NEC and NEBs, and in autonomic intrapulmonary ganglia as single or clusters of small intensely-fluorescent (SIF) cells. In postnatal sheep, serotonin- and cholecystokinin-containing cells were found within airway mucosa as solitary NECs and NEBs. No immunoreactive cells were observed with antiserum to bombesin and calcitonin. Quantitative studies showed that serotonin was the predominant substance, and that solitary neuroendocrine cells were more numerous in distal conducting airways and at foetal stages.

Quantitative assessment of ATPase-positive epidermal dendritic (Langerhans) cells in piglets and adult swine

To assess the distribution pattern of Langerhans cells (LC) in normal porcine skin, epidermal sheets from six anatomical sites from three age-matched groups of male and female pigs were stained for ATPase activity. This histoenzymological technique is considered specific for Langerhans cells in normal epidermis. No statistically significant differences were observed between mean Langerhans cell density per mm2 of epidermis from male and female pigs, nor between different anatomical sites in the same age group. Statistically significant differences (P less than 0.0005) were observed when comparing group A one- to two-week-old piglets (463 to 518 LC mm-2) with group B six month olds (641 to 804 LC mm-2) and group C two years and over sows (741 to 830 LC mm-2). Morphological variations in the skin of young piglets, much thinner and with rudimentary or no epidermal rete pegs, could account for this significant variation.

Serotonin immunoreactivity in the autonomic intrapulmonary ganglia of the fetal sheep

Using light microscopic immunohistochemistry, serotonin immunoreactivity was found in paraganglionic cells within pulmonary autonomic ganglia of fetal sheep at pseudoglandular and canalicular stages of lung development. Serotonin immunoreactive cells appeared individually or in clusters, and were occasionally seen around or in close contact with blood vessels.

Ultrastructural identification of Langerhans cells in normal swine epidermis

Langerhans cells of the epidermis of 6-month-old white crossbred farm pigs were identified by electron microscopy. Ultrastructurally they were similar to those described in other mammals. They were present in basal and suprabasal layers and were characterised by a lobulated nucleus and an electrolucent cytoplasm with occasional dendritic processes, and the absence of tonofilaments and specialised unions with surrounding keratinocytes. They were specifically identified by the presence of characteristic rod or racquet-shaped intracytoplasmic granules. Intraepidermal clear cells without specific granules were present, although no melanocytes were observed. This is the first report of the presence of Birbeck granules in porcine Langerhans cells.

Solitary neuroendocrine cells and neuroepithelial bodies in the lower airways of embryonic, fetal, and postnatal sheep

The sheep pulmonary intraepithelial APUD system was studied by histochemical, immunocytochemical, and electron microscopy techniques during different periods of lung development: embryonic, fetal (pseudoglandular, canalicular, and alveolar), and postnatal. The cells of the ovine pulmonary intraepithelial APUD system were found randomly distributed throughout the conducting and respiratory or undifferentiated airways. They appeared as isolated cells (solitary neuroendocrine cells) or in groups (neuroepithelial bodies). These cells were argyrophilic and immunoreactive for neuron-specific enolase but were not argentaffin. Ultrastructurally they were characterized by a basal position in the respiratory epithelium and by the presence of neurosecretory granules (dense-core vesicles) ranging between 65 and 230 nm of diametre. Quantitative studies showed that single neuroendocrine cells were more numerous in distal conducting airways and at fetal stages. The earliest identifiable argyrophilic and NSE-immunoreactive neuroendocrine cells in sheep airways appeared at gestational week 5, close to the term of the embryonic period.