Photosynthetic pathway influences xylem structure and function in Flaveria (Asteraceae)

Higher water use efficiency (WUE) in C(4) plants may allow for greater xylem safety because transpiration rates are reduced. To evaluate this hypothesis, stem hydraulics and anatomy were compared in 16 C(3), C(3)-C(4) intermediate, C(4)-like and C(4) species in the genus Flaveria. The C(3) species had the highest leaf-specific conductivity (K(L)) compared with intermediate and C(4) species, with the perennial C(4) and C(4)-like species having the lowest K(L) values. Xylem-specific conductivity (K(S)) was generally highest in the C(3) species and lower in intermediate and C(4) species. Xylem vessels were shorter, narrower and more frequent in C(3)-C(4) intermediate, C(4)-like and C(4) species compared with C(3) species. WUE values were approximately double in the C(4)-like and C(4) species relative to the C(3)-C(4) and C(3) species. C(4)-like photosynthesis arose independently at least twice in Flaveria, and the trends in WUE and K(L) were consistent in both lineages. These correlated changes in WUE and K(L) indicate WUE increase promoted K(L) decline during C(4) evolution; however, any involvement of WUE comes late in the evolutionary sequence. C(3)-C(4) species exhibited reduced K(L) but little change in WUE compared to C(3) species, indicating that some reduction in hydraulic efficiency preceded increases in WUE.     

Environmental regulation of photosynthetic metabolism in the amphibious sedge Eleocharis baldwinii and comparisons with related species

The amphibious leafless sedge, Eleocharis baldwinii, expresses C₄ characteristics in the terrestrial form and intermediate characteristics between C₃ and C₄ photosynthesis in the submerged form. This study examined the immunocytochemical localization of C₃ and C₄ enzymes in culms of the two forms to elucidate the regulatory mechanism of photosynthetic metabolism and compared the activities and amounts of C₃ and C₄ enzymes with those in other Eleocharis species, E. vivipara and E. retroflexa, which show C₄ characteristics on land but C₃ and C₄ characteristics under water. The terrestrial form of E. baldwinii exhibited a C₄‐like pattern of enzyme localization. The submerged form exhibited a modified anatomy with well‐developed mesophyll cells and small Kranz cells. The C₄ enzyme levels declined conspicuously in outer mesophyll cells adjacent to the epidermis, whereas Rubisco levels increased throughout the mesophyll in the submerged form. These results suggest that intermediate photosynthesis between C₃ and C₄ photosynthesis in the submerged form results from the predominant operation of the C₃ pathway in the outer mesophyll cells and the C₄ pathway in both the inner mesophyll and Kranz cells. Differences in the degree of C₄ expression in terrestrial forms of Eleocharis species may cause the differences in the expression of photosynthetic modes under water.     

C3 photosynthesis in Aristida longifolia: Implication for photosynthetic diversification in Aristidoideae (Poaceae)

Only a small percentage of plant species undergo C(4) photosynthesis. Despite its rarity, the C(4) pathway has evolved numerous times from C(3) ancestors, with as many as 18 independent origins in grasses alone. We report non-Kranz (C(3)) anatomy in Aristida longifolia, a species in a genus of ca. 300 species previously thought to possess only Kranz (C(4)) anatomy. Leaf blade transections of A. longifolia show widely spaced vascular bundles, nonradiate chlorenchyma, and few or no chloroplasts in cells of the sheaths surrounding the vascular bundle, all features indicative of C(3) photosynthesis. Carbon isotope ratios range from -27.68 to -29.71%, likewise indicative of C(3) photosynthesis. We also reconstruct the phylogeny of Aristidoideae, comprising Aristida, Sartidia (C(3)), and Stipagrostis (C(4)), using a sample of 11 species, including A. longifolia, and DNA sequences of the nuclear ribosomal internal transcribed spacer region and the chloroplast rpl16 intron and trnL-trnF region. Sartidia and Stipagrostis resolve as sisters, and sister to this clade is Aristida. Aristida longifolia resolves as sister to the remaining species in the genus. C(3) photosynthesis is hypothesized to be ancestral in Aristidoideae, which means the C(4) pathway evolved twice in the subfamily-in Stipagrostis and early in the diversification of the Aristida clade.     

Shifts from specialised to generalised pollination systems in Miconieae (Melastomataceae) and their relation with anther morphology and seed number

Most species in Melastomataceae have poricidal anthers related to specialised bee buzz‐pollination, while some have anthers with large openings associated to non‐bee pollination systems. We tracked the evolution of anther morphology and seed number on the Miconieae phylogenetic tree to understand the evolutionary shifts in such pollination systems. Anther morphometric data and seed number were recorded for 54 taxa. Pollinators (bees, flies, wasps) were recorded for 20 available species. Ancestral state reconstruction was made using Maximum Likelihood from nrITS sequences. We used phylogenetic eigenvector regressions to estimate phylogenetic signal and the adaptive component for these traits. Species pollinated by bees or bees and wasps tend to have smaller pores and fruits with more seeds. Species pollinated by flies or flies and bees and/or wasps tend to have larger pores and fruits with less seeds. Independent evolution occurred three times for anthers with large pores and twice for fruits with few seeds. We detected a phylogenetic signal in both traits, and negative correlated evolution between them. In actinomorphic small‐flowered Miconieae, changes in anther morphology can be related to generalisation in the pollination system incorporating flies and wasps as pollinators and lessening the importance of buzzing bees in such process. Differences in pollen removal and deposition may explain differences in anther morphology and seed number in Miconieae.     

Crassulacean acid metabolism in the Basellaceae (Caryophyllales)

• C₄ and crassulacean acid metabolism (CAM) have evolved in the order Caryophyllales many times but neither C₄ nor CAM have been recorded for the Basellaceae, a small family in the CAM‐rich sub‐order Portulacineae.
• 24 h gas exchange and day–night changes in titratable acidity were measured in leaves of Anredera baselloides exposed to wet–dry–wet cycles.
• While net CO₂ uptake was restricted to the light period in well‐watered plants, net CO₂ fixation in the dark, accompanied by significant nocturnal increases in leaf acidity, developed in droughted plants. Plants reverted to solely C₃ photosynthesis upon rewatering.
• The reversible induction of nocturnal net CO₂ uptake by drought stress indicates that this species is able to exhibit CAM in a facultative manner. This is the first report of CAM in a member of the Basellaceae.

     

Song and plumage evolution in the New World orioles (Icterus) show similar lability and convergence in patterns

Both song and color patterns in birds are thought to evolve rapidly and exhibit high levels of homoplasy, yet few previous studies have compared the evolution of these traits systematically using the same taxa. Here we reconstruct the evolution of song in the New World orioles (Icterus) and compare patterns of vocal evolution to previously reconstructed patterns of change in plumage evolution in this clade. Individual vocal characters exhibit high levels of homoplasy, reflected in a low overall consistency index (CI = 0.27) and retention index (RI = 0.35). Levels of lability in song are comparable to those found for oriole plumage patterns using the same taxa (CI = 0.31, RI = 0.63), but are strikingly dissimilar to the conservative patterns of change seen in the songs of oropendolas (Psarocolius, Ocyalus; CI = 0.82, RI = 0.87), a group closely related to the orioles. Oriole song is also similar to oriole plumage in exhibiting repeated convergence in overall patterns, with some distantly related taxa sounding remarkably similar. Thus, both song and plumage in orioles show repeated convergence in individual elements and in overall patterns across the clade, suggesting that both of these character classes are highly labile between taxa yet highly conserved within the genus. Our results provide new insights into the tempo and mode of evolution in sexually selected traits within and across clades.     

Diversity, biogeography, and photosynthetic pathways of Argusia and Heliotropium (Boraginaceae) in South-West Asia with an analysis of phytogeographical units

South-West and Central Asia are major centres of diversity in the genus Heliotropium . On the basis of detailed taxonomic studies and information gathered from the literature, a synopsis of 61 known species of Heliotropium and two species of Arguzia in the area is given. Iran, with 32 species and 14 (sub)endemic species, has the highest diversity. The photosynthetic pathways of 42 taxa were determined using the isotope composition method. Except for H. marifolium Retz s.l. and H. rariflorum Stocks, all remaining species analysed showed δ¹³C values characteristic for C₃ photosynthesis. Evidently, by contrast with the families Chenopodiaceae and Polygonaceae, the Irano-Turanian area is not an authochthonous region of developing C₄ species in Heliotropium . The distribution maps of 57 taxa are provided and their biogeographical importance is discussed in order to elucidate the distribution patterns in South-West Asia. In the Irano-Turanian region, the Irano-Anatolian province of Zohary, which extends from central Anatolia to the western Himalaya, is a very large and vaguely defined phytochorion that should be split into smaller units. The consideration of southern Iran and adjacent Pakistan as part of the Sudanian or Saharo-Sindian regions ( sensu either Zohary or Léonard) cannot be accepted, because most endemic species in this area are either typical Irano-Turanian or isolated relicts. Furthermore, it is concluded that the Saharo-Sindian flora is not an autochthonous flora; most species are of transgressive origin from the surrounding phytochoria. Finally, a new species, Heliotropium ziegleri Akhani, is described from Iran.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155 , 401–425.     

Influence of light intensity during growth on photosynthesis and activity of several key photosynthetic enzymes in a C4 plant (Zea mays)

Maize ( Zea mays L. Hybrid Sweet Corn, Royal Crest), a C₄ plant, was grown under different light regimes, after which the rate of photosynthesis and activities of several photosynthetic enzymes (per unit leaf chlorophyll) were measured at different light intensities. Plants were grown outdoors under direct sunlight or 23% of direct sunlight, and in growth chambers at photosynthetic photon flux densities of about 20% and 8% of direct sunlight. The plants grown under direct sunlight had a higher light compensation point than plants grown under lower light. At a light intensity about 25% of direct sunlight, plants from all growth regimes had a similar rate of photosynthesis. Under saturating levels of light the plants grown under direct sunlight had a substantially higher rate of photosynthesis than plants grown under the lower light regimes. The higher photosynthetic capacity in the plants grown under direct sunlight was accompanied by an increased activity of several photosynthetic enzymes and in the amount of the soluble protein in the leaf. Among five photosynthetic enzymes examined, RuBP carboxylase (EC 4.1.1.39) and pyruvate, Pi dikinase (EC 2.7.9.1) were generally just sufficient to account for rates of photosynthesis under saturating light; thus, these may be rate limiting enzymes in C₄ photosynthesis. Pyruvate, Pi dikinase and NADP-malate dehydrogenase (EC 1.1.1.82) were the only enzymes examined which were light activated and increased in activity with increasing light intensity. In the low light grown plants the activity of pyruvate, Pi dikinase closely paralleled the photosynthetic rate measured under different light levels. With the plants grown under direct sunlight, as light intensity was increased the activation of pyruvate, Pi dikinase and NADP⁺-malate dehydrogenase proceeded more rapidly than photosynthesis.     

Variation with age in the photosynthetic carbon fixation pattern by leaves of Amaranthus paniculatus and Oryza sativa: Change in the primary carboxylation but no shift from C4 or C3 pathway

Abstract The pattern of photosynthetic carbon fixation by leaves of Amaranthus paniculatus L. (a C₄ plant) and Oryza sativa L. (a C₃ plant) varied with age. Younger leaves of A. paniculatus incorporated ¹⁴CO₂ into malate and aspartate while senescent leaves fixed predominantly into phosphoglycerate (PGA) and sugar phosphates. Only developing leaves of O. sativa formed malate/aspartate whereas mature and senescent leaves produced PGA/sugar phosphates as the initial labelled products. Correspondingly the ratio of phosphoenolpyruvate/ribulose bisphosphate (RuBP) carboxylase activities was higher in younger leaves of A. paniculatus and developing leaves of O. sativa than in older leaves. However, pulse chase experiments revealed that the main donors of carbon to end products, irrespective of leaf stage, were C₄ acids and PGA in A. paniculatus and O. sativa respectively. The results suggest that although an apparent change from initial β-carboxylation to RuBP carboxylation occurs during leaf ontogeny in both the plants, the overall leaf photosynthesis remains C₄ or C₃. The high rate of ¹⁴CO₂ incorporation into PGA/sugar phosphates by senescent leaves of A. paniculatus is suggested to be partly due to the increased intercellular spaces in their mesophyll, allowing greater access of CO₂ directly to RuBP carboxylase in the bundle sheath.     

Potential distribution of the invasive tree Triadica sebifera (Euphorbiaceae) in the United States: evaluating climex predictions with field trials

Models that project introduced species distributions based on the climates in native and potential introduced ranges can provide valuable insights on the extent of a species' future spread. Yet, the lack of direct field evaluation of these range projections remains a major limitation. We evaluated results from the climex model in conjunction with results from seed and plant field trials in assessing environmental constraints to spread of the invasive tree Triadica sebifera (Chinese tallow tree) in the southeastern USA. climex incorporates key climatic parameters to generate large‐scale projections of potential distributions based on the climate across the species' current distribution. By employing field trials within microhabitats within and beyond the tree's current range, we were able to determine seed and young plants' response to the heterogeneity of the environment at regional scales. Based on projections of the climex model, T. sebifera has the potential to spread 500 km northward beyond its current distribution in the southeastern USA; minimum temperature and limited precipitation are the key climatic constraints in the eastern and western USA, respectively. climex results correlate strongly with seed germination across sites in the southeastern USA. These results do not however correlate with plant growth rates, which were often higher in sites with low projected climatic suitability. Competition and herbivory were not constraints on the growth of T. sebifera in our field trials and were therefore not responsible for the lack of correlation between model results and plant growth rates. If the minimum and maximum temperatures were to rise by 2 °C, the range of T. sebifera could extend northward 700 km beyond its current distribution. While both climex and the field trials indicate that T. sebifera is capable of extensive northward spread in the eastern USA, results of field trials indicate that the patterns of invasion within the region are likely to vary substantially with local site conditions.     

High summer temperatures are associated with poorer performance of underyearling Atlantic salmon (Salmo salar) in upland streams

Future warming scenarios are predicted to result in an increased frequency of high, and potentially stressful, temperatures in aquatic ecosystems. Here we examined whether the performance of wild underyearling Atlantic salmon (Salmo salar) in Scottish streams stocked with identical egg densities was influenced by thermal stress. Biomass and density declined with degree hours exceeding 23°C, indicating apparent mortality or emigration as a possible result of exposure to high temperatures. These results strengthen the need for further action such as riparian tree planting to reduce stream summer temperatures.     

气候变化情景下基于最大熵模型的中国西南地区清香木潜在分布格局模拟

清香木(Pistacia weinmannifolia)是中国西南干旱河谷植被的特征种。本文利用野外调查的165个清香木分布点信息以及22个环境变量数据, 基于最大熵(Maxent)算法构建清香木分布的适宜生境预测模型, 并据此模拟清香木在我国西南地区的适宜分布区, 以及历史和未来不同气候情景下的分布格局变化。结果表明: 清香木生境预测的Maxent模型准确性非常高(AUC = 0.974), 温度季节性变化、极端低温和降水量是限制其分布的主要气候因子。清香木当前的潜在分布区集中在我国西南干旱河谷区, 其适宜生境的气候特征是降水少、温度季节性变化小且无极端低温。对清香木在末次间冰期和末次冰盛期分布的模拟结果表明, 其分布区范围均以诸大江河的河谷为中心, 随气候变化在我国西南地区主要呈现先向东扩张, 然后向西退缩的趋势, 并印证了“冰期走出横断山(glacial out-of-Hengduan Mts.)”的观点。在未来(2061-2080年) 3种典型浓度路径(representative concentration pathway, RCP)的气候情景下, 清香木在我国西南地区的分布都向东扩张, 主要分布在云贵高原与四川盆地结合地带的河谷, 以及云贵高原与广西西部交界地带的河谷中, 这也反映了这些地区河谷地段干旱化的可能, 而当前的潜在分布区趋于消失; 清香木的潜在适宜分布面积在中低浓度路径情景下均将减少约33%, 而在高浓度路径情景下有所增加。     

A comparative anatomical and biochemical analysis in salsola (Chenopodiaceae) species with and without a Kranz type leaf anatomy: a possible reversion of C4 to C3 photosynthesis

Leaf anatomy was studied by light and electron microscopy and the leaf activities of RUBP carboxylase, PEP carboxylase, and malic enzyme were assayed in: Salsola australis and S. oreophila grown on the West Pamirs at 1800 m altitude; in S. australis grown on the East Pamirs at 3860 m; and in S. arbusculiformis grown in the Kisil-Kum desert in Middle Asia near 500 m. Carbon isotope fractionation ratio values also were measured on whole leaf tissue for 18 Salsola species field collected in these and other regions of the former USSR. S. australis leaves are cylindrical and in cross section exhibit a peripheral ring of mesophyll and then an inner ring of bundle sheath type cells; and its biochemical characteristics and deltaC values are typical of a C4 species of the NADP-malic enzyme malate-forming group. These traits were expressed independent of the plant growth altitude up to 4000 m. C4 type deltaC values were obtained in 14 of the Salsola species. Anatomical, structural, and biochemical features typical of the C4 syndrome were absent in S. oreophila and S. arbusculiformis. Four Salsola species, including these two, had C3-type deltaC values. Their cylindrical leaves in cross section exhibited two to three peripheral rings as layers of palisade parenchyma. Although their vascular bundles were surrounded by green bundle sheath cells, their organelle numbers were comparable to those in mesophyll cells. Neither bundle sheath cell wall thickenings nor dimorphic chloroplasts in two leaf cell types were observed. In S. oreophila, there was a high activity of RuBP carboxylase, but a low activity of C4 cycle enzymes. Interpretation of these data lends evidence to the hypothesis that a small group of C3 Salsola species, including S. oreophila, S. arbusculiformis, S. montana, and S. pachyphylla, arose as the result of a reversion of a C4 to a C3 type of photosynthetic CO2 fixation in the cooler climates of Middle Asia.     

Acclimation response of spring wheat in a free-air CO2 enrichment (FACE) atmosphere with variable soil nitrogen regimes. 2. Net assimilation and stomatal conductance of leaves

Atmospheric CO₂ concentration continues to rise. It is important, therefore, to determine what acclimatory changes will occur within the photosynthetic apparatus of wheat (Triticum aestivum L. cv. Yecora Rojo) grown in a future high-CO₂ world at ample and limited soil N contents. Wheat was grown in an open field exposed to the CO₂ concentration of ambient air [370 μmol (CO₂) mol⁻¹; Control] and air enriched to ∼200 μmol (CO₂) mol⁻¹ above ambient using a Free-Air CO₂ Enrichment (FACE) apparatus (main plot). A High (35 g m⁻²) or Low (7 and 1.5 g m⁻² for 1996 and 1997, respectfully) level of N was applied to each half of the main CO₂ treatment plots (split-plot). Under High-N, FACE reduced stomatal conductance (g _s) by 30% at mid-morning (2 h prior to solar noon), 36% at midday (solar noon) and 27% at mid-afternoon (2.5 h after solar noon), whereas under Low-N, g _s was reduced by as much as 31% at mid-morning, 44% at midday and 28% at mid-afternoon compared with Control. But, no significant CO₂ × N interaction effects occurred. Across seasons and growth stages, daily accumulation of carbon (A′) was 27% greater in FACE than Control. High-N increased A′ by 18% compared with Low-N. In contrast to results for g _s, however, significant CO₂ × N interaction effects occurred because FACE increased A′ by 30% at High-N, but by only 23% at Low-N. FACE enhanced the seasonal accumulation of carbon (A′′) by 29% during 1996 (moderate N-stress), but by only 21% during 1997 (severe N-stress). These results support the premise that in a future high-CO₂ world an acclimatory (down-regulation) response in the photosynthetic apparatus of field-grown wheat is anticipated. They also demonstrate, however, that the stimulatory effect of a rise in atmospheric CO₂ on carbon gain in wheat can be maintained if nutrients such as nitrogen are in ample supply. This revised version was published online in June 2006 with corrections to the Cover Date.     

Elevated pyruvate,orthophosphate dikinase (PPDK) activity alters carbon metabolism in C3 transgenic potatoes with a C4 maize PPDK gene

Changes in carbon metabolism and δ¹³C value of transgenic potato plants with a maize pyruvate,orthophosphate dikinase (PPDK; EC 2.7.9.1) gene are reported. PPDK catalyzes the formation of phospho enol pyruvate (PEP), the initial acceptor of CO₂ in the C₄ photosynthetic pathway. PPDK activities in the leases of transgenic potatoes were up to 5.4‐fold higher than those of control potato plants (wild‐type and treated control plants). In the transgenic potato plants, PPDK activity in leaves was negatively correlated with pyruvate content (r²= 0.81), and was positively correlated with malate content (r²= 0.88). A significant increase in the δ¹³C value was observed in the transgenic potato plants, suggesting a certain contribution of PEP carboxylase as the initial acceptor of atmospheric CO₂. These data suggest that elevated PPDK activity may alter carbon metabolism and lead to a partial operation of C₄‐type carbon metabolism. However, since parameters associated with CO₂ gas exchange were not affected, the altered carbon metabolism had only a small effect on the total photosynthetic characteristics of the transgenic plants.     

Changes in levels of phosphoenolpyruvate carboxylase with induction of Crassulacean acid metabolism (CAM)-like behavior in the C4 plant Portulaca oleracea

Changes in levels of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31, orthophosphate: oxaloacetate carboxy-lyase, phosphorylating) were followed in leaves and stems of CAM-expressing and non-expressing Portulaca oleracea L. plants. CAM expression was induced by growing plants under an 8-h photoperiod and water stress conditions (SD-WS). Leaves and stems of these plants (designated CAM) expressed nocturnal acidification with an oscillation pattern and an amplitude characteristic of CAM plants. Generally, PEPC activity increased by ca 3-fold during the period of CAM induction. Over the day/night cycle. PEPC activity oscillated in a pattern typical of CAM plants. Treatment of the other plant group (designated as non-CAM) by growth under a 16-h photoperiod and well-watered conditions (LD-WW) did not induce expression of the tested criteria of CAM in plants. In these plants, nocturnal acidification as well as changes in the magnitude of PEPC, activity and fluctuation pattern were undetectable. SDS-PAGE of leaf extracts of the CAM-expressing plants and the corresponding densitometric scans show progressive increase in the amount of PEPC subunit protein (ca 95 kDa) during the period of CAM induction. These results show that induction of CAM-like characteristics in the C₄ plant Portulaca oleracea is also accompanied by increased PEPC activity, which may be partly due to an increase in enzyme synthesis.     

The genetic differentiation of a cricket (Velarifictorus micado) with two modes of life cycle in East Asia after the middle Pleistocene and the invasion origin of the United States of America

The cricket Velarifictorus micado is widely distributed in East Asia and colonized the United States of America (the USA) in 1959. It has two life cycles: egg and nymph diapause. We aimed to investigate the biogeographic boundary between them and determine when and why V. micado diverged. Mitochondrial fragments including COI and CytB were used for haplotype network, demographic analysis, and divergence time estimation in individuals of East Asia. We selected several samples from the USA to find out the colonization origin. The haplotype network indicated there were three lineages based on COI, NE lineage (the egg diapause and mainly distributed in the northern regions), SE lineage (the egg diapause and mainly distributed in the southern regions), and SN lineage (the nymph diapause and mainly distributed in the southern regions). The molecular chronograms indicated that the first divergence of V. micado into two main lineages, NE and southern lineages (SE and SN), was essentially bounded by the Yangtze River. It occurred around ~0.79 Ma (95% HPD: 1.13–0.46 Ma) in the Middle Pleistocene Transition. This was followed by the divergence of the southern lineage into two sublineages, SE and SN lineage, occurred around ~0.50 Ma (95% HPD: 0.71–0.25 Ma), corresponding to the time of development of glaciers in various parts of the Qinghai–Tibet Plateau (QTP) (0.73–0.46 Ma). SE lineage might originate from southwestern China based on the comparison between the haplotype network based on COI and CytB. Our study suggested that divergences of lineages have twice co‐occurred with tendency of cooling climatic in Asia after the Mid‐Pleistocene, and the life‐history strategy may play an important role in lineage diversification. Additionally, our results indicated that the USA populations were revealed at least twice separate Asian invasions. These both belonged to the egg diapause, which might provide a new perspective for invasion control.