Search

Summary: Leaf structure plays an important role in photosynthesis. However, the causal relationship and the quantitative importance of any single structural parameter to the overall photosynthetic performance of a leaf remains open to debate. In this paper, we report on a mechanistic model, eLeaf, which successfully captures rice leaf photosynthetic performance under varying environmental conditions of light and CO2.We developed a 3D reaction‐diffusion model for leaf photosynthesis parameterised using a range of imaging data and biochemical measurements from plants grown under ambient and elevated CO2 and then interrogated the model to quantify the importance of these elements.The model successfully captured leaf‐level photosynthetic performance in rice. Photosynthetic metabolism underpinned the majority of the increased carbon assimilation rate observed under elevated CO2 levels, with a range of structural elements making positive and negative contributions. Mesophyll porosity could be varied without any major outcome on photosynthetic performance, providing a theoretical underpinning for experimental data.eLeaf allows quantitative analysis of the influence of morphological and biochemical properties on leaf photosynthesis. The analysis highlights a degree of leaf structural plasticity with respect to photosynthesis of significance in the context of attempts to improve crop photosynthesis. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented which discusses the use of photosynthetic parameter estimation in determining the approximated rate of maximum potential electron transport.

Keywords: chlorophyll fluorescence; coordination; development; function; photosynthesis; plant water-use-efficiency; stomata EN chlorophyll fluorescence coordination development function photosynthesis plant water-use-efficiency stomata 350 352 3 03/22/22 20220415 NES 220415 What inspired your interest in plant science? I have a number of favourite plants, the top spot being shared between I Gingko i and I Dicksonia i tree ferns, possibly for similar reasons, i.e. the fact that they are "ancient plants", having first evolved many millions of years ago, and therefore provide us with a glimpse of the past. Chlorophyll fluorescence, coordination, development, function, photosynthesis, plant water-use-efficiency, stomata. [Extracted from the article]

Summary: The wild relatives of modern wheat represent an underutilized source of genetic and phenotypic diversity and are of interest in breeding owing to their wide adaptation to diverse environments. Leaf photosynthetic traits underpin the rate of production of biomass and yield and have not been systematically explored in the wheat relatives.This paper identifies and quantifies the phenotypic variation in photosynthetic, stomatal, and morphological traits in up to 88 wheat wild relative accessions across five genera. Both steady‐state measurements and dynamic responses to step changes in light intensity are assessed.A 2.3‐fold variation for flag leaf light and CO2‐saturated rates of photosynthesis Amax was observed. Many accessions showing higher and more variable Amax, maximum rates of carboxylation, electron transport, and Rubisco activity when compared with modern genotypes. Variation in dynamic traits was also significant; with distinct genus‐specific trends in rates of induction of nonphotochemical quenching and rate of stomatal opening.We conclude that utilization of wild relatives for improvement of photosynthesis is supported by the existence of a high degree of natural variation in key traits and should consider not only genus‐level properties but variation between individual accessions. [ABSTRACT FROM AUTHOR]

Seedlings of Pseudotsuga menziesii (Mirb.) Franco were grown for six-16 months in untrenched and trenched treatments in three 90-120-yr-old mixed forests dominated by Betula papyrifera Marsh. and P. menziesii in the southern interior of British Columbia. Each forest was characterized by mesic conditions and low light intensity (PAR ≤ 200 μmol m-2 s-1) in the understorey. The objective of the study was to evaluate the influence of overstorey tree roots on (i) ectomycorrhizal fungal composition, richness and diversity, and (ii) photosynthesis and growth of understorey P. menziesii seedlings. Seventeen ectomycorrhizal morphotypes were recognized on seedlings in the untrenched treatment, and nine in the trenched treatment over the three sites. Six types occurred in both treatments, of which on average Rhizopogon vinicolor Smith type was 20 times more abundant and Thelephora type six times less abundant in the untrenched as in the trenched treatment. Of types that formed strands or rhizomorphs, eight occurred in the untrenched treatment, where they occupied on average 23% of root tips, and only four occurred in the trenched treatment over 4% of the root tips. Mean richness, diversity, and evenness of ectomycorrhizal associates per seedling were approx. twice as great in the untrenched as in the trenched treatment. Net photosynthetic rate of P. menziesii seedlings was greater in the untrenched than in the trenched treatment in July and August, but not in September 1994. Height, diameter and biomass of seedlings did not differ between treatments, but height: diameter ratio was greater in the untrenched treatment at time of harvest. The effect of trenching on seedling performance was attributed mainly to differences in ectomycorrhizal colonization patterns because trenching had no significant effect on soil nutrient concentrations (total C, total N, NH4-N, available N, exchangeable Ca, exchangeable Mg, exchangeable K) C:N ratio, soil pH or light availability. Nor was there a significant difference in soil water in August, when seedlings in untrenched plots had higher net photosynthetic rates than those in trenched plots. Results suggest that influence of overstorey trees and pattern of ectomycorrhizal formation are important to P. menziesii seedling performance in deeply shaded forest environments. [ABSTRACT FROM AUTHOR]

Widely different rates of carbon dioxide assimilation by apple leaves have been reported. Data from forty-nine papers are examined and likely reasons for their variation are deduced. Many studies were made on glasshouse-grown plants, the leaves of which can have a very different structure and photosynthetic capacity from those grown outdoors. Other biological aspects including the influence of fruits are discussed. Leaf temperatures have rarely been measured but there is evidence that excessive temperatures occurred in some studies and many other assimilation rates were probably decreased by less obviously extreme conditions. The rates of air flow employed have often been inadequate for true assimilation rates to be obtained. However, many rates higher than those normally quoted have been obtained by several workers including the author and it is concluded that the maximum photosynthetic rate of apple leaves in normal air is at least 35 mg CO[SUB2] dm[SUP-2] h[SUP-1]. [ABSTRACT FROM AUTHOR]

Quantitative results of an earlier paper by Wuenscher (1970) are corrected, and the implications for the adaptive significance of mullein leaf hairs discussed. Wuenscher's paper seemed to show that the leaf hairs thickened the leaf boundary layer by a distance equal to the thickness of the hair layer, causing boundary layer resistance to increase by a factor of 90. The corrections indicate that the hairs increase boundary layer resistance by a factor of about 2. The results imply that measured differences in total transpiration resistance were due to higher stomatal (or cuticular) resistance of normal hairy leaves compared with shaved leaves. Such higher epidermal resistances would tend to reduce photosynthesis. The hypothesis is made that plant species having dense leaf hairs and growing in full sunlight are likely to have high temperature optima for photosynthesis. A related hypothesis is that such species are likely to use the C[sub4] pathway for carbon assimilation, as mullein apparently does. Finally, it is pointed out that dense leaf hairs increase boundary layer resistance to a value equivalent to that of larger glabrous leaves. Thus, the hypotheses suggested should also apply to plants having large leaves and growing in full sunlight. [ABSTRACT FROM AUTHOR]

Summary: Leaves with stomata on both upper and lower surfaces, termed amphistomatous, are relatively rare compared with hypostomatous leaves with stomata only on the lower surface. Amphistomaty occurs predominantly in fast‐growing herbaceous annuals and in slow‐growing perennial shrubs and trees. In this paper, we present the current understanding and hypotheses on the costs and benefits of amphistomaty related to water and CO2 transport in contrasting leaf morphologies. First, there is no evidence that amphistomatous species achieve higher stomatal densities on a projected leaf area basis than hypostomatous species, but two‐sided gas exchange is less limited by boundary layer effects. Second, amphistomaty may provide a specific advantage in thick leaves by shortening the pathway for CO2 transport between the atmosphere and the chloroplasts. In thin leaves of fast‐growing herbaceous annuals, in which both the adaxial and abaxial pathways are already short, amphistomaty enhances leaf–atmosphere gas‐exchange capacity. Third, amphistomaty may help to optimise the leaf‐interior water status for CO2 transport by reducing temperature gradients and so preventing the condensation of water that could limit CO2 diffusion. Fourth, a potential cost of amphistomaty is the need for additional investments in leaf water transport tissue to balance the water loss through the adaxial surface. [ABSTRACT FROM AUTHOR]

Kok effect, day respiration, mitochondria, photorespiration, photosynthesis Keywords: day respiration; Kok effect; mitochondria; photorespiration; photosynthesis EN day respiration Kok effect mitochondria photorespiration photosynthesis 5 10 6 03/04/21 20210401 NES 210401 Leaf respiration plays a key role in plant primary production due to its roles in determining rates of daily net carbon gain, nutrient acquisition, and growth. (2017) did not reveal a close relationship between I R i SB light sb and I R i SB dark sb , with I R i SB light sb < I R i SB dark sb in 84% of cases and I R i SB light sb > I R i SB dark sb in 16% of cases. [Extracted from the article]

Ventilated Solardomes (hemispherical glasshouses) have been used for 20 yr for studying the effects of gaseous pollutants on plants. This paper describes a computer-operated facility for studying the effects of CO2 × temperature regimes on plants. The eight chambers were set up for factorial design experiments - with two levels of CO2 (ambient and ambient+ 340 ppmv), two levels of temperature (ambient and 3 °C tracked continuously above ambient) and two replicates of each CO2 × temperature treatment. Monitoring of environmental conditions within the chambers over a 2 yr period has shown highly effective control of CO2 and temperature regimes. Even with high-quality and u.v.-B transmitting glass, the irradiance in the PAR region was reduced by 18% within the domes. Variation in temperature across the radii of the domes increased with higher photosynthetic photon flux density (PPFD). Vapour pressure deficits (VPDs) in the ambient temperature domes compared well with outside conditions but were higher in the elevated temperature domes. The watering regime within the domes affected intermittently the relationship between 'dome' and 'outside' VPDs. The Solardome facility has been used extensively for studies of the impacts of climate change within the UK Programme on Terrestrial Initiative on Global Environmental Research (TIGER). [ABSTRACT FROM AUTHOR]

• This paper presents the results of 2 yr of CO2 flux measurements on grassland communities of varying species richness, exposed to either the current or a warmer climate. • We grew experimental plant communities containing one, three or nine grassland species in 12 sunlit, climate-controlled chambers. Half of these chambers were exposed to ambient air temperatures, while the other half were warmed by 3°C. Equal amounts of water were added to heated and unheated communities, implying drier soils if warming increased evapotranspiration. Three main CO2 fluxes (gross photosynthesis, above-ground and below-ground respiration) were measured multiple times per year and reconstructed hourly or half-hourly by relating them to their most important environmental driver. • While CO2 outputs through respiration were largely unchanged under warming, CO2 inputs through photosynthesis were lowered, especially in summer, when heat and drought stress were higher. Above-ground CO2 fluxes were significantly increased in multispecies communities, as more complementary resource use stimulated productivity. Finally, effects of warming appeared to be smallest in monocultures. • This study shows that in a future warmer climate the CO2 sink capacity of temperate grasslands could decline, and that such adverse effects are not likely to be mitigated by efforts to maintain or increase species richness. [ABSTRACT FROM AUTHOR]

• This study establishes a topographical framework for functional investigations on the regulation of lipid biosynthesis and its interaction with embryo photosynthesis in developing soybean seed. • Structural observations, combined with molecular and functional parameters, revealed the gradual transformation of chloroplasts into storage organelles, starting from inner regions going outwards. This is evidenced by electron microscopy, confocal laser scanning microscopy, in situ hybridization and histochemical/biochemical data. • As a consequence of plastid differentiation, photosynthesis becomes distributed along a gradient within the developing embryo. Electron transport rate, effective quantum yield and O2 production rate are maximal in the embryo periphery, as documented by imaging pulse-amplitude-modulated fluorescence and O2 release via microsensors. The gradual loss of photosynthetic capacity was accompanied by a similarly gradual accumulation of starch and lipids. Noninvasive nuclear magnetic resonance spectroscopy of mature seeds revealed steep gradients in lipid deposition, with the highest concentrations in inner regions. • The inverse relationship between photosynthesis and lipid biosynthesis argues against a direct metabolic involvement of photosynthesis in lipid biosynthesis during the late storage stage, but points to a role for photosynthetic oxygen release. This hypothesis is verified in a companion paper. New Phytologist (2005) doi: 10.1111/j.1469-8137.2005.01474.x© New Phytologist (2005) [ABSTRACT FROM AUTHOR]

• Based on the topographical analysis of photosynthesis and oil storage, we propose in a companion paper that photosynthetic oxygen release plays a key role in the local energy state, storage metabolism and flux toward lipid biosynthesis in developing soybean seeds. To test this hypothesis, we combined topographical analysis of ATP gradients across tissues, microsensor quantifications of internal O2 levels, assays of energy balance, metabolite profiles and isotope-labelling studies. • Seeds show a marked degree of oxygen starvation in vivo (minimum O2 levels 0.1 kPa, ≈ 1.3 µ m), affecting ATP gradients, overall energy state, metabolite pools and storage activity. • Despite the low light availability, photosynthesis supplies significant amounts of oxygen to the hypoxic seed tissue. This is followed by an increase in local ATP levels, most prominently within the lipid-synthesizing (inner) regions of the embryo. Concomitantly, partitioning of 14C-sucrose to lipids is increased, suggesting higher rates of lipid biosynthesis. • It is concluded that both respiratory and biosynthetic fluxes are dynamically adjusted to photosynthetic oxygen supply. New Phytologist (2005) doi: 10.1111/j.1469-8137.2005.01473.x© New Phytologist (2005) [ABSTRACT FROM AUTHOR]

Sun and shade environments place markedly different constraints on the photosynthetic performance of plants. Leaf-level photosynthetic responses to sun and shade have been extensively investigated, whereas there has been much less research on the functional role of crown architecture in these environments. This paper focuses on the role of architecture in maximizing light capture and photosynthesis in shaded understories and in minimizing exposure to excess radiation in open high light environments. Understanding these contrasting roles of architecture is facilitated by application of a three-dimensional structural–functional model, Y-plant. Surveys of understory plants reveal a diversity of architectures but a strong convergence at only modest light-capture efficiencies because of significant self-shading. Simulations withPsychotriaspecies revealed that increasing internode lengths would increase light-capture efficiencies and whole plant carbon gain. However, the costs of the additional required biomechanical support was high, which, in terms of relative growth rates, would override the advantage provided by higher light-capture efficiencies. In high light environments, leaf angles and self-shading provide structural photoprotection, minimizing potential damage from photoinhbition. Simulations reveal that without these structural protections photoinhibition of photosynthesis is likely to be much greater with daily carbon gain significantly reduced.New Phytologist(2005)doi: 10.1111/j.1469-8137.2005.01328.x© New Phytologist(2005) [ABSTRACT FROM AUTHOR]

This paper reports the effects of nutrient magnesium (Mg) concentrations on the growth and photosynthetic physiology of clonal Pinus radiata from four female parents (families) known to differ in their tolerance to Mg deficiency and in their needle Mg concentrations. Plants were grown in flowing nutrient solutions with 2 mg l-1 (control) and 0.8 mg l-1 (low) Mg. Plant growth, needle Mg concentration, photosynthesis, chlorophyll fluorescence and carotenoid pigment content were measured. At low Mg, needle Mg concentration was about half that of control plants, height growth was reduced 15-25%, and the needles showed strong visual characteristics of Mg deficiency. Photosynthesis was also halved, and was associated with closure of the stomata under low Mg and with reductions in the residual conductance. In needles from plants grown at low Mg, photochemical yield was reduced both in the light and in the dark, and was strongly dependent on needle Mg concentrations below a threshold concentration of 0.02-0.025% (d. wt basis). The electron transport rate (ETR) at saturating photon flux density in low-Mg-grown needles was reduced to about half that of their Mg controls, but the photon efficiency of ETR was unaffected by the Mg concentration the plants were grown in. Photosynthetic quenching was markedly reduced and non-photosynthetic quenching was increased following growth in low Mg. Growth under low Mg also increased levels of zeaxanthin. Although family differences in growth and photosynthetic physiology were present, few family × Mg interactions were significant. We conclude that Mg deficiency probably affects growth through severe reductions in photosynthesis. [ABSTRACT FROM AUTHOR]

Summary: Although leaves are considered the main site for photosynthesis, other green nonfoliar tissues can carry out considerable amounts of photosynthetic carbon assimilation. With photosynthesis, a potential target for improving crop productivity, physiology and contribution of nonfoliar tissues to overall plant carbon acquisition is gaining increasing attention. This review will provide an overview of nonfoliar photosynthesis, the role of stomata in these tissues and methodologies for quantification and the contribution to overall carbon gain. [ABSTRACT FROM AUTHOR]

Changes in carotenoid profile can influence the content of important molecules such as xanthophylls (photoprotection), apocarotenoid growth regulators, and signaling molecules and plant hormones. Keywords: apocarotenoids; carotenoids; metabolic engineering; photosynthesis; phytohormones; stress tolerance; yield EN apocarotenoids carotenoids metabolic engineering photosynthesis phytohormones stress tolerance yield 1946 1950 5 02/21/23 20230315 NES 230315 Carotenoids are isoprenoid compounds synthesized by all photosynthetic organisms and several heterotrophic microorganisms. Therefore, enhancing carotenoid content, in particular provitamin A carotenoids, has been one of the preferred targets of plant genetic engineering, resulting in biofortified cereals, fruits, and tubers, including rice, tomato, and potato. [Extracted from the article]

Keywords: carbon cycling; chilling tolerance; field phenotyping; global change; photosynthesis; Spartina; water-use efficiency EN carbon cycling chilling tolerance field phenotyping global change photosynthesis Spartina water-use efficiency 1034 1036 3 07/16/20 20200815 NES 200815 What inspired your interest in plant science? At that time, C SB 4 sb photosynthesis was considered exclusive to warm climates, but from my classes at Reading, it appeared to me that some plants of the northern European flora should be C SB 4 sb , based on evolutionary relationships. What was more significant was that not only was this a C SB 4 sb plant existing in a cool climate, but against all prior knowledge of C SB 4 sb photosynthesis, it was thriving in the British climate. [Extracted from the article]

Branch bags were used to expose branches on mature Sitka spruce trees to either ambient [CO2] (A) or elevated [CO2] (E) for 4 yr. This paper reports the effects of this treatment on the growth, development and phenology of the branches, including shoot expansion, shoot numbers, needle dimensions, needle numbers and stomatal density. The effect of elevated [CO2] on the relationship between leaf area and sapwood area was investigated Exposure to elevated [CO2] doubled photosynthetic rates in current-year shoots and, despite sonic down- regulation, 1-yr-old E shoots also had higher rates of photosynthesis than their A counterpart. Thus the amount of assimilate fixed by E branches was substantially more than that fixed by A branches: however, this increase in the local production of assimilate did not lead to an increase in non -structural carbohydrate or stimulate growth or meristematic activity within the E branches. There was a very consistent relationship between leaf area and stem cross-sectional area that was not influenced by [CO2]. However, unbagged branches had thicker stems than bagged branches, resulting in a slightly lower ratio of leaf area to cross-sectional area. The implications of the results tot the modelling of growth and allocation and the potential utility of the branch bag technique are discussed. [ABSTRACT FROM AUTHOR]

The function of a leaf is photosynthesis, which requires the interception of light and access to atmospheric CO2 while controlling water loss. This paper examines the influence of leaf anatomy on both light capture and CO2 diffusion. As photosynthetic metabolism is spread between many chloroplasts, a leaf faces the challenge of matching light capture by a given chloroplast with the metabolic capacity of that chloroplast. Chloroplasts nearest the leaf surface receive the greatest irradiance and therefore absorb more light per unit chlorophyll than chloroplasts in the centre of a leaf. Electron transport and carbon fixation capacities per unit of chlorophyll decline with increasing depth in the leaf, to complexes in chloroplasts have nuclear encoded genetic information. Consequently, all chloroplasts within a given cell have a similar metabolic complement, which limits the potential gradient of photosynthetic capacity per unit chlorophyll across the leaf. A simple model couples light absorption through the leaf (based on the Beer-Lambert law) with the profile of chlorophyll through a leaf and the gradient in photosynthetic capacity. It is validated by comparison with 14CO2 fixation profiles through spinach leaves obtained in various studies. The model can account for published 14C fixation profiles obtained with blue, red and green light of different irradiances and white light applied in different combinations to the adaxial and abaxial surfaces of spinach leaves. The model confirms that spongy mesophyll increases the apparent extinction coefficient of chlorophyll compared to palisade tissue. The palisade tissue nearest the surface which received light facilitates the penetration of light to a greater depth, while spongy mesophyll promotes scattering to enhance light absorption, thus reducing the gradient in light absorbed per unit chlorophyll through a leaf CO2 fixation faces a diffusional limitation, which necessitates Rubisco to be spread evenly across the cell walls exposed to intercellular airspace. Mesophyll cell structure reflects the need to have a large cell surface per unit volume exposed to airspaces, The regular array of columnar cells in palisade tissue, or cell lobing in monocot leaves, results in greater exposed surface per unit tissue volume than spongy mesophyll. The exposed surface area per unit leaf area scales with photosynthetic capacity such that the difference in CO2 partial pressure surface area per unit leaf area scales with photosynthetic capacity such that the difference in CO2 partial pressure between substomatal cavities and the sites of carboxylation within chloroplasts is, on average, independent of photosynthetic capacity of the leaf. However, Rubisco specific activity declines as the Rubisco content per unit leaf area increases due to grater internal diffusional limitations. [ABSTRACT FROM AUTHOR]