Influence of molecular resolution on sequence-based discovery of ecological diversity among Synechococcus populations in an alkaline siliceous hot spring microbial mat

Previous research has shown that sequences of 16S rRNA genes and 16S-23S rRNA internal transcribed spacer regions may not have enough genetic resolution to define all ecologically distinct Synechococcus populations (ecotypes) inhabiting alkaline, siliceous hot spring microbial mats. To achieve higher molecular resolution, we studied sequence variation in three protein-encoding loci sampled by PCR from 60°C and 65°C sites in the Mushroom Spring mat (Yellowstone National Park, WY). Sequences were analyzed using the ecotype simulation (ES) and AdaptML algorithms to identify putative ecotypes. Between 4 and 14 times more putative ecotypes were predicted from variation in protein-encoding locus sequences than from variation in 16S rRNA and 16S-23S rRNA internal transcribed spacer sequences. The number of putative ecotypes predicted depended on the number of sequences sampled and the molecular resolution of the locus. Chao estimates of diversity indicated that few rare ecotypes were missed. Many ecotypes hypothesized by sequence analyses were different in their habitat specificities, suggesting different adaptations to temperature or other parameters that vary along the flow channel.     

Cyanobacterial Ecotypes in Different Optical Microenvironments of a 68°C Hot Spring Mat Community Revealed by 16S-23S rRNA Internal Transcribed Spacer Region Variation

We examined the population of unicellular cyanobacteria (Synechococcus) in the upper 3-mm vertical interval of a 68°C region of a microbial mat in a hot spring effluent channel (Yellowstone National Park, Wyoming). Fluorescence microscopy and microsensor measurements of O₂ and oxygenic photosynthesis demonstrated the existence of physiologically distinct Synechococcus populations at different depths along a light gradient quantified by scalar irradiance microprobes. Molecular methods were used to evaluate whether physiologically distinct populations could be correlated with genetically distinct populations over the vertical interval. We were unable to identify patterns in genetic variation in Synechococcus 16S rRNA sequences that correlate with different vertically distributed populations. However, patterns of variation at the internal transcribed spacer locus separating 16S and 23S rRNA genes suggested the existence of closely related but genetically distinct populations corresponding to different functional populations occurring at different depths.     

Allozyme variation of populations of Castanopsis carlesii (Fagaceae) revealing the diversity centres and areas of the greatest divergence in Taiwan

• Background and Aims The genetic variation and divergence estimated by allozyme analysis were used to reveal the evolutionary history of Castanopsis carlesii in Taiwan. Two major questions were discussed concerning evolutionary issues: where are the diversity centres, and where are the most genetically divergent sites in Taiwan?• Methods Twenty-two populations of C. carlesii were sampled throughout Taiwan. Starch gel electrophoresis was used to assay allozyme variation. Genetic parameters and mean F_ST values of each population were analysed using the BIOSYS-2 program. Mean F_ST values of each population against the remaining populations, considered as genetic divergence, were estimated using the FSTAT program.• Key Results Average values of genetic parameters describing the within-population variation, the average number of alleles per locus (A = 2·5), the effective number of alleles per locus (A_e = 1·38), the allelic richness (A_r = 2·38), the percentage of polymorphic loci (P = 69 %), and the expected heterozygosity (H_e = 0·270) were estimated. High levels of genetic diversity were found for C. carlesii compared with other local plant species. Genetic differentiation between populations was generally low.• Conclusions From the data of expected heterozygosity, one major diversity centre was situated in central Taiwan corroborating previous reports for other plant species. According to the mean F_ST value of each population, the most divergent populations were situated in two places. One includes populations located in north central Taiwan between 24·80°N and 24·20°N. The other is located in south-eastern Taiwan between 22·40°N and 23·10°N. These two regions are approximately convergent with the most divergent locations determined for several other plant species using chloroplast DNA markers published previously. An important finding obtained from this study is that unordered markers like allozymes can be used to infer past population histories as well as chloroplast DNA markers do.     

Temperature sensitivity of the low-moisture-content limit to negative seed longevity--moisture content relationships in hermetic storage

• Background and Aims The negative logarithmic relationship between orthodox seed longevity and moisture content in hermetic storage is subject to a low-moisture-content limit (m_c), but is m_c affected by temperature?• Methods Red clover (Trifolium pratense) and alfalfa (Medicago sativa) seeds were stored hermetically at 12 moisture contents (2–15 %) and five temperatures (–20, 30, 40, 50 and 65 °C) for up to 14·5 years, and loss in viability was estimated.• Key Results Viability did not change during 14·5 years hermetic storage at −20 °C with moisture contents from 2·2 to 14·9 % for red clover, or 2·0 to 12·0 % for alfalfa. Negative logarithmic relationships between longevity and moisture contents >m_c were detected at 30–65 °C, with discontinuities at low moisture contents; m_c varied between 4·0 and 5·4 % (red clover) or 4·2 and 5·5 % (alfalfa), depending upon storage temperature. Within the ranges investigated, a reduction in moisture content below m_c at any one temperature had no effect on longevity. Estimates of m_c were greater the cooler the temperature, the relationship (P < 0·01) being curvilinear. Above m_c, the estimates of C_H and C_Q (i.e. the temperature term of the seed viability equation) did not differ (P > 0·10) between species, whereas those of K_E and C_W did (P < 0·001).• Conclusions The low-moisture-content limit to negative logarithmic relationships between seed longevity and moisture content in hermetic storage increased the cooler the storage temperature, by approx. 1·5 % over 35 °C (4·0–4·2 % at 65 °C to 5·4–5·5 % at 30–40 °C) in these species. Further reduction in moisture content was not damaging. The variation in m_c implies greater sensitivity of longevity to temperature above, compared with below, m_c. This was confirmed (P < 0·005).     

Isolation and characterization of EstC, a new cold-active esterase from Streptomyces coelicolor A3(2)

The genome sequence of Streptomyces coelicolor A3(2) contains more than 50 genes coding for putative lipolytic enzymes. Many studies have shown the capacity of this actinomycete to store important reserves of intracellular triacylglycerols in nutrient depletion situations. In the present study, we used genome mining of S. coelicolor to identify genes coding for putative, non-secreted esterases/lipases. Two genes were cloned and successfully overexpressed in E. coli as His-tagged fusion proteins. One of the recombinant enzymes, EstC, showed interesting cold-active esterase activity with a strong potential for the production of valuable esters. The purified enzyme displayed optimal activity at 35°C and was cold-active with retention of 25% relative activity at 10°C. Its optimal pH was 8.5–9 but the enzyme kept more than 75% of its maximal activity between pH 7.5 and 10. EstC also showed remarkable tolerance over a wide range of pH values, retaining almost full residual activity between pH 6–11. The enzyme was active toward short-chain p-nitrophenyl esters (C2–C12), displaying optimal activity with the valerate (C5) ester (k _cat/K _m = 737±77 s⁻¹ mM⁻¹). The enzyme was also very active toward short chain triglycerides such as triacetin (C2:0) and tributyrin (C4:0), in addition to showing good primary alcohol and organic solvent tolerance, suggesting it could function as an interesting candidate for organic synthesis of short-chain esters such as flavors.     

Resolution of Prochlorococcus and Synechococcus Ecotypes by Using 16S-23S Ribosomal DNA Internal Transcribed Spacer Sequences

Cultured isolates of the marine cyanobacteria Prochlorococcus and Synechococcus vary widely in their pigment compositions and growth responses to light and nutrients, yet show greater than 96% identity in their 16S ribosomal DNA (rDNA) sequences. In order to better define the genetic variation that accompanies their physiological diversity, sequences for the 16S-23S rDNA internal transcribed spacer (ITS) region were determined in 32 Prochlorococcus isolates and 25 Synechococcus isolates from around the globe. Each strain examined yielded one ITS sequence that contained two tRNA genes. Dramatic variations in the length and G+C content of the spacer were observed among the strains, particularly among Prochlorococcus strains. Secondary-structure models of the ITS were predicted in order to facilitate alignment of the sequences for phylogenetic analyses. The previously observed division of Prochlorococcus into two ecotypes (called high and low-B/A after their differences in chlorophyll content) were supported, as was the subdivision of the high-B/A ecotype into four genetically distinct clades. ITS-based phylogenies partitioned marine cluster A Synechococcus into six clades, three of which can be associated with a particular phenotype (motility, chromatic adaptation, and lack of phycourobilin). The pattern of sequence divergence within and between clades is suggestive of a mode of evolution driven by adaptive sweeps and implies that each clade represents an ecologically distinct population. Furthermore, many of the clades consist of strains isolated from disparate regions of the world's oceans, implying that they are geographically widely distributed. These results provide further evidence that natural populations of Prochlorococcus and Synechococcus consist of multiple coexisting ecotypes, genetically closely related but physiologically distinct, which may vary in relative abundance with changing environmental conditions.     

In vitro propagation of female Ephedra foliata Boiss. & Kotschy ex Boiss.: an endemic and threatened Gymnosperm of the Thar Desert

Ephedra foliata Boiss. & Kotschy ex Boiss., (family – Ephedraceae), is an ecologically and economically important threatened Gymnosperm of the Indian Thar Desert. A method for micropropagation of E. foliata using nodal explant of mature female plant has been developed. Maximum bud-break (90 %) of the explant was obtained on MS medium supplemented with 1.5 mg l⁻¹ of benzyl adenine (BA) + additives. Explant produces 5.3 ± 0.40 shoots from single node with 3.25 ± 0.29 cm length. The multiplication of shoots in culture was affected by salt composition of media, types and concentrations of plant growth regulators (PGR’s) and their interactions, time of transfer of the cultures. Maximum number of shoots (26.3 ± 0.82 per culture vessel) were regenerated on MS medium modified by reducing the concentration of nitrates to half supplemented with 200 mg l⁻¹ ammonium sulphate {(NH₄) ₂SO₄} (MMS3) + BA (0.25 mg l⁻¹), Kinetin (Kin; 0.25 mg l⁻¹), Indole-3-acetic acid (IAA; 0.1 mg l⁻¹) and additives. The in vitro produced shoots rooted under ex vitro on soilrite moistened with one-fourth strength of MS macro salts in screw cap bottles by treating the shoot base (s) with 500 mg l⁻¹ of Indole-3-butyric acid (IBA) for 5 min. The micropropagated plants were hardened in the green house. The described protocol can be applicable for (i) large scale plant production (ii) establishment of plants in natural habitat and (iii) germplasm conservation of this endemic Gymnosperm of arid regions.     

Oxygen-binding characteristics of three extra-cellular haemoglobins of Artemia salina

The oxygen-binding characteristics of the three extracellular haemoglobins of brine shrimp (Artemia salina) were studied in vitro by using highly purified preparations. Haemoglobin I is induced last in the development of brine shrimps when functional gills are formed. It has the lowest oxygen affinity (p₅₀ 5.34mmHg), an intermediate Bohr effect (ø −0.09 at 20°C) above pH8 and a temperature-sensitivity (ΔH −44.8 to −45.6kJ/mol at pH8–9) comparable with those observed with other invertebrate haemoglobins [Weber & Heidemann (1977) Comp. Biochem. Physiol. A 57, 151–155]. Haemoglobin II, which is the first to be induced, soon after hatching of nauplius larvae, persists generally throughout the whole adult life. It has an intermediate oxygen affinity (p₅₀ 3.7mmHg), the highest Bohr effect (ø −0.21 at 20°C) above pH8 and a similar temperature-sensitivity (ΔH −46.0 to −54.8kJ/mol at pH8–9) as haemoglobin I. However, haemoglobin III, which is induced second several hours after the induction of haemoglobin II but disappearing from the haemolymph in the middle of adult life, has the highest oxygen affinity (p₅₀ 1.8mmHg), the lowest Bohr effect (ø −0.03 at 20°C) above pH8.5 and a high resistance against temperature variation between 10 and 25°C at pH8.5–9 (ΔH −22.6 to −23.0kJ/mol). At pH7.5–8, haemoglobin III exhibits a similar temperature-sensitivity under 30°C as do other haemoglobins. All three haemoglobins have a rather low co-operativity, with Hill coefficients (h 1.6–1.9 at pH8.5), which are dependent on both pH and temperature. The highest co-operativity was observed at 20°C and pH9 for haemoglobins I and II, whereas it was at 27°C and pH8.5 for haemoglobin III. Thus the oxygen-binding behaviour of haemoglobin III in vitro is significantly different from those of haemoglobins I and II and indicates possibly its specific physiological role in vivo in the adaptive process in the natural environment.     

Pushed to the limit: consequences of climate change for the Araucariaceae: a relictual rain forest family

Background and Aims

Under predicted climate change scenarios, increased temperatures are likely to predispose trees to leaf and other tissue damage, resulting in plant death and contraction of already narrow distribution ranges in many relictual species. The effects of predicted upward temperatures may be further exacerbated by changes in rainfall patterns and damage caused by frosts on trees that have been insufficiently cold-hardened. The Araucariaceae is a relictual family and the seven species found in Australia have limited natural distributions characterized by low frost intensity and frequency, and warm summer temperatures. The temperature limits for these species were determined in order to help understand how such species will fare in a changing climate.

Methods

Experiments were conducted using samples from representative trees of the Araucariaceae species occurring in Australia, Agathis (A. atropurpurea, A. microstachya and A. robusta), Arauacaria (A. bidwilli, A. cunninghamii and A. heterophylla) and Wollemia nobilis. Samples were collected from plants grown in a common garden environment. Lower and higher temperature limits were determined by subjecting detached winter-hardened leaves to temperatures from 0 to –17 °C and summer-exposed leaves to 25 to 63 °C, then measuring the efficiency of photosystem II (F_v/F_m) and visually rating leaf damage. The exotherm, a sharp rise in temperature indicating the point of ice nucleation within the cells of the leaf, was measured on detached leaves of winter-hardened and summer temperature-exposed leaves.

Key Results

Lower temperature limits (indicated by FT₅₀, the temperature at which PSII efficiency is 50 %, and LT₅₀ the temperature at which 50 % visual leaf damage occurred) were approx. –5·5 to –7·5 °C for A. atropurpurea, A. microstachya and A. heterophylla, approx. –7 to –9 °C for A. robusta, A. bidwillii and A. cunninghamii, and –10·5 to –11 °C for W. nobilis. High temperature damage began at 47·5 °C for W. nobilis, and occurred in the range 48·5–52 °C for A. bidwillii and A. cunninghamii, and in the range 50·5–53·5 °C for A. robusta, A. microstachya and A. heterophylla. Winter-hardened leaves had ice nucleation temperatures of –5·5 °C or lower, with W. nobilis the lowest at –6·8 °C. All species had significantly higher ice nucleation temperatures in summer, with A. atropurpurea and A. heterophylla forming ice in the leaf at temperatures >3 °C higher in summer than in winter. Wollemia nobilis had lower FT₅₀ and LT₅₀ values than its ice nucleation temperature, indicating that the species has a degree of ice tolerance.

Conclusions

While lower temperature limits in the Australian Araucariaceae are generally unlikely to affect their survival in wild populations during normal winters, unseasonal frosts may have devastating effects on tree survival. Extreme high temperatures are not common in the areas of natural occurrence, but upward temperature shifts, in combination with localized radiant heating, may increase the heat experienced within a canopy by at least 10 °C and impact on tree survival, and may contribute to range contraction. Heat stress may explain why many landscape plantings of W. nobilis have failed in hotter areas of Australia.     

Germination responses to temperature and water potential in Jatropha curcas seeds: a hydrotime model explains the difference between dormancy expression and dormancy induction at different incubation temperatures

Background and Aims

Jatropha curcas is a drought-resistant tree whose seeds are a good source of oil that can be used for producing biodiesel. A successful crop establishment depends on a rapid and uniform germination of the seed. In this work we aimed to characterize the responses of J. curcas seeds to temperature and water availability, using thermal time and hydrotime analysis,

Methods

Thermal and hydrotime analysis was performed on germination data obtained from the incubation of seeds at different temperatures and at different water potentials.

Key Results

Base and optimum temperatures were 14·4 and 30 °C, respectively. Approximately 20 % of the seed population displayed absolute dormancy and part of it displayed relative dormancy which was progressively expressed in further fractions when incubation temperatures departed from 25 °C. The thermal time model, but not the hydrotime model, failed to describe adequately final germination percentages at temperatures other than 25 °C. The hydrotime constant, θ_H, was reduced when the incubation temperature was increased up to 30 °C, the base water potential for 50 % germination,Ψ_b(50), was less negative at 20 and 30 °C than at 25 °C, indicating either expression or induction of dormancy. At 20 °C this less negative Ψ_b(50) explained satisfactorily the germination curves obtained at all water potentials, while at 30 °C it had to be corrected towards even less negative values to match observed curves at water potentials below 0. Hence, Ψ_b(50) appeared to have been further displaced to less negative values as exposure to 30 °C was prolonged by osmoticum. These results suggest expression of dormancy at 20 °C and induction of secondary dormancy above 25 °C. This was confirmed by an experiment showing that inhibition of germination imposed by temperatures higher than 30 °C, but not that imposed at 20 °C, is a permanent effect.

Conclusions

This study revealed (a) the extremely narrow thermal range within which dormancy problems (either through expression or induction of dormancy) may not be encountered; and (b) the high sensitivity displayed by these seeds to water shortage. In addition, this work is the first one in which temperature effects on dormancy expression could be discriminated from those on dormancy induction using a hydrotime analysis.     

Saturating light and not increased carbon dioxide under ocean acidification drives photosynthesis and growth in Ulva rigida (Chlorophyta)

Carbon physiology of a genetically identified Ulva rigida was investigated under different CO_2(aq) and light levels. The study was designed to answer whether (1) light or exogenous inorganic carbon (Ci) pool is driving growth; and (2) elevated CO_2(aq) concentration under ocean acidification (OA) will downregulate CA_ext-mediated dehydration and alter the stable carbon isotope (δ¹³C) signatures toward more CO₂ use to support higher growth rate. At pH_T 9.0 where CO_2(aq) is <1 μmol L⁻¹, inhibition of the known use mechanisms, that is, direct uptake through the AE port and CA_ext-mediated dehydration decreased net photosynthesis (NPS) by only 56–83%, leaving the carbon uptake mechanism for the remaining 17–44% of the NPS unaccounted. An in silico search for carbon-concentrating mechanism elements in expressed sequence tag libraries of Ulva found putative light-dependent transporters to which the remaining NPS can be attributed. The shift in δ¹³C signatures from –22‰ toward –10‰ under saturating light but not under elevated CO_2(aq) suggest preference and substantial use to support photosynthesis and growth. U. rigida is Ci saturated, and growth was primarily controlled by light. Therefore, increased levels of CO_2(aq) predicted for the future will not, in isolation, stimulate Ulva blooms.     

Sensitivity of Altitudinal Ecotypes of the Wild Tomato Lycopersicon hirsutum to Chilling Injury

The transition temperature of the leaf polar lipids and the critical temperature for chill-induced inhibition of photosynthesis was determined for three altitudinal ecotypes of the wild tomato Lycopersicon hirsutum. Photosynthesis was measured as CO₂-dependent O₂ evolution at 25°C after leaf slices were exposed to chilling temperatures for 2 hours at a moderate photon flux density of 450 micromoles per square meter per second. The transition temperature of the leaf polar lipids was detected from the change in the temperature coefficient of the fluorescence intensity of trans-parinaric acid. Chill-induced photoinhibition was evident in the three tomato ecotypes when they were chilled below a critical temperature of 10°, 11°, and 13°C, respectively, for the high (LA1777), mid (LA1625), and low (LA1361) altitudinal ecotypes. The temperature differential, below the critical temperature, required to produce a 50% inhibition was also similar for the three ecotypes. A transition was detected in the leaf polar lipids of these plants at a temperature similar to that of the critical temperature for photoinhibition. The results show that the three tomato ecotypes are similar with respect to their critical temperature for chilling-induced photoinhibition and the rate of their response to the chilling stress. They are, thus, similarly sensitive to chilling.     

Extracellular Hsp72 concentration relates to a minimum endogenous criteria during acute exercise-heat exposure

Extracellular heat shock protein 72 (eHsp72) concentration increases during exercise-heat stress when conditions elicit physiological strain. Differences in severity of environmental and exercise stimuli have elicited varied response to stress. The present study aimed to quantify the extent of increased eHsp72 with increased exogenous heat stress, and determine related endogenous markers of strain in an exercise-heat model. Ten males cycled for 90 min at 50 % in three conditions (TEMP, 20 °C/63 % RH; HOT, 30.2 °C/51%RH; VHOT, 40.0 °C/37%RH). Plasma was analysed for eHsp72 pre, immediately post and 24-h post each trial utilising a commercially available ELISA. Increased eHsp72 concentration was observed post VHOT trial (+172.4 %) (p < 0.05), but not TEMP (−1.9 %) or HOT (+25.7 %) conditions. eHsp72 returned to baseline values within 24 h in all conditions. Changes were observed in rectal temperature (T_rec), rate of T_rec increase, area under the curve for T_rec of 38.5 and 39.0 °C, duration T_rec ≥ 38.5 and ≥39.0 °C, and change in muscle temperature, between VHOT, and TEMP and HOT, but not between TEMP and HOT. Each condition also elicited significantly increasing physiological strain, described by sweat rate, heart rate, physiological strain index, rating of perceived exertion and thermal sensation. Stepwise multiple regression reported rate of T_rec increase and change in T_rec to be predictors of increased eHsp72 concentration. Data suggests eHsp72 concentration increases once systemic temperature and sympathetic activity exceeds a minimum endogenous criteria elicited during VHOT conditions and is likely to be modulated by large, rapid changes in core temperature.     

Can Tropical Insects Stand the Heat? A Case Study with the Brown Planthopper Nilaparvata lugens (St?l)

The brown planthopper Nilaparvata lugens (Stål) is the most serious pest of rice across the world, especially in tropical climates. N. lugens nymphs and adults were exposed to high temperatures to determine their critical thermal maximum (CT_max), heat coma temperature (HCT) and upper lethal temperature (ULT). Thermal tolerance values differed between developmental stages: nymphs were consistently less heat tolerant than adults. The mean (± SE) CT_max of nymphs and adult females and males were 34.9±0.3, 37.0±0.2 and 37.4±0.2°C respectively, and for the HCT were 37.7±0.3, 43.5±0.4 and 42.0±0.4°C. The ULT₅₀ values (± SE) for nymphs and adults were 41.8±0.1 and 42.5±0.1°C respectively. The results indicate that nymphs of N. lugens are currently living at temperatures close to their upper thermal limits. Climate warming in tropical regions and occasional extreme high temperature events are likely to become important limiting factors affecting the survival and distribution of N. lugens.     

Community ecology of hot spring cyanobacterial mats: predominant populations and their functional potential

Phototrophic microbial mat communities from 60 °C and 65 °C regions in the effluent channels of Mushroom and Octopus Springs (Yellowstone National Park, WY, USA) were investigated by shotgun metagenomic sequencing. Analyses of assembled metagenomic sequences resolved six dominant chlorophototrophic populations and permitted the discovery and characterization of undescribed but predominant community members and their physiological potential. Linkage of phylogenetic marker genes and functional genes showed novel chlorophototrophic bacteria belonging to uncharacterized lineages within the order Chlorobiales and within the Kingdom Chloroflexi. The latter is the first chlorophototrophic member of Kingdom Chloroflexi that lies outside the monophyletic group of chlorophototrophs of the Order Chloroflexales. Direct comparison of unassembled metagenomic sequences to genomes of representative isolates showed extensive genetic diversity, genomic rearrangements and novel physiological potential in native populations as compared with genomic references. Synechococcus spp. metagenomic sequences showed a high degree of synteny with the reference genomes of Synechococcus spp. strains A and B′, but synteny declined with decreasing sequence relatedness to these references. There was evidence of horizontal gene transfer among native populations, but the frequency of these events was inversely proportional to phylogenetic relatedness.     

Variation in the functioning of autonomous self-pollination, pollinator services and floral traits in three Centaurium species

Background and Aims

Reproductive assurance through autonomous selfing is thought to be one of the main advantages of self-fertilization in plants. Floral mechanisms that ensure autonomous seed set are therefore more likely to occur in species that grow in habitats where pollination is scarce and/or unpredictable.

Methods

Emasculation and pollen supplementation experiments were conducted under laboratory conditions to investigate the capacity for, and timing of autonomous selfing in three closely related Centaurium species (Centaurium erythraea, C. littorale and C. pulchellum). In addition, observations of flower visitors were combined with emasculation and pollen addition experiments in natural populations to investigate the degree of pollinator limitation and pollination failure and to assess the extent to which autonomous selfing conferred reproductive assurance.

Results

All three species were capable of autonomous selfing, although this capacity differed significantly between species (index of autonomous selfing 0·55 ± 0·06, 0·68 ± 0·09 and 0·92 ± 0·03 for C. erythraea, C. littorale and C. pulchellum, respectively). The efficiency and timing of autogamous selfing was primarily associated with differences in the degree of herkogamy and dichogamy. The number of floral visitors showed significant interspecific differences, with 1·6 ± 0·6, 5·4 ± 0·6 and 14·5 ± 2·1 floral visitors within a 2 × 2 m² plot per 20-min observation period, for C. pulchellum, C. littorale and C. erythraea, respectively. Concomitantly, pollinator failure was highest in C. pulchellum and lowest in C. erythraea. Nonetheless, all three study species showed very low levels of pollen limitation (index of pollen limitation 0·14 ± 0·03, 0·11 ± 0·03 and 0·09 ± 0·02 for C. erythraea, C. littorale and C. pulchellum, respectively), indicating that autonomous selfing may guarantee reproductive assurance.

Conclusions

These findings show that limited availability of pollinators may select for floral traits and plant mating strategies that lead to a system of reproductive assurance via autonomous selfing.     

Simulating the influence of vernalization, photoperiod and optimum temperature on wheat developmental rates

Background and Aims

Accurately representing development is essential for applying crop simulations to investigate the effects of climate, genotypes or crop management. Development in wheat (Triticum aestivum, T. durum) is primarily driven by temperature, but affected by vernalization and photoperiod, and is often simulated by reducing thermal-time accumulation using vernalization or photoperiod factors or limiting accumulation when a lower optimum temperature (T_optl) is exceeded. In this study T_optl and methods for representing effects of vernalization and photoperiod on anthesis were examined using a range of planting dates and genotypes.

Methods

An examination was made of T_optl values of 15, 20, 25 and 50 °C, and either the most limiting or the multiplicative value of the vernalization and photoperiod development rate factors for simulating anthesis. Field data were from replicated trials at Ludhiana, Punjab, India with July through to December planting dates and seven cultivars varying in vernalization response.

Key Results

Simulations of anthesis were similar for T_optl values of 20, 25 and 50 °C, but a T_optl of 15 °C resulted in a consistent bias towards predicting anthesis late for early planting dates. Results for T_optl above 15 °C may have occurred because mean temperatures rarely exceeded 20 °C before anthesis for many planting dates. For cultivars having a strong vernalization response, anthesis was more accurately simulated when vernalization and photoperiod factors were multiplied rather than using the most limiting of the two factors.

Conclusions

Setting T_optl to a high value (30 °C) and multiplying the vernalization and photoperiod factors resulted in accurately simulating anthesis for a wide range of planting dates and genotypes. However, for environments where average temperatures exceed 20 °C for much of the pre-anthesis period, a lower T_optl (23 °C) might be appropriate. These results highlight the value of testing a model over a wide range of environments.Key words: Wheat, Triticum aestivum, T. durum, air temperature, thermal time, shoot apex, phenology, growth stages, anthesis, flowering     

Photosynthetic responses to heat treatments at different temperatures and following recovery in grapevine (Vitis amurensis L.) leaves

Background

The electron transport chain, Rubisco and stomatal conductance are important in photosynthesis. Little is known about their combined responses to heat treatment at different temperatures and following recovery in grapevines (Vitis spp.) which are often grown in climates with high temperatures.

Methodology/Findings

The electron transport function of photosystem II, the activation state of Rubisco and the influence of stomatal behavior were investigated in grapevine leaves during heat treatments and following recovery. High temperature treatments included 35, 40 and 45°C, with 25°C as the control and recovery temperature. Heat treatment at 35°C did not significantly (P>0.05) inhibit net photosynthetic rate (P _n). However, with treatments at 40 and 45°C, P _n was decreased, accompanied by an increase in substomatal CO₂ concentration (C _i), decreases in stomatal conductance (g _s) and the activation state of Rubisco, and inhibition of the donor side and the reaction center of PSII. The acceptor side of PSII was inhibited at 45°C but not at 40°C. When grape leaves recovered following heat treatment, P _n, g_s and the activation state of Rubisco also increased, and the donor side and the reaction center of PSII recovered. The increase in P _n during the recovery period following the second 45°C stress was slower than that following the 40°C stress, and these increases corresponded to the donor side of PSII and the activation state of Rubisco.

Conclusions

Heat treatment at 35°C did not significantly (P>0.05) influence photosynthesis. The decrease of P _n in grape leaves exposed to more severe heat stress (40 or 45°C) was mainly attributed to three factors: the activation state of Rubisco, the donor side and the reaction center of PSII. However, the increase of P _n in grape leaves following heat stress was also associated with a stomatal response. The acceptor side of PSII in grape leaves was responsive but less sensitive to heat stress.