Lower Rates Of Photosynthesis Research Articles

Differences in photosynthesis and terpene content in leaves and roots of wild-type and transgenic Arabidopsis thaliana plants

We investigated the hypotheses that two different varieties of Arabidopsis thaliana show differences in physiology and terpene production. The two varieties of A. thaliana used in this study were wild-type (WT) and transgenic line (CoxIV-FaNES I) genetically modified to emit nerolidol with linalool/nerolidol synthase (COX). Photosynthetic rate, electron transport rate, fluorescence, leaf volatile terpene contents and root volatile terpene contents were analyzed. For both types, we found co-eluting α-pinene+β-ocimene, limonene, and humulene in leaves; and in the roots we found co-eluting α-pinene+β-ocimene, sabinene+β-pinene, β-myrcene, limonene, and humulene. At the end of the growing cycle, COX plants tended to have lower pools of terpene compounds in their leaves, with 78.6% lower photosynthesis rates and 30.8% lower electron transport rates, compared with WT plants at that time. The maximal photochemical efficiency F v/F m was also significantly lower (25.5%) in COX plants, indicating that these varieties were more stressed than WT plants. However, COX plants had higher (239%) root terpene contents compared to WT plants. COX plants appear to favor root production of volatile terpenes rather than leaf production. Thus we conclude that there were significant differences between COX and WT plants in terms of terpenoid pools, stress status and physiology.

Photosynthesis-dependent/independent control of stomatal responses to CO2 in mutant barley with surplus electron transport capacity and reduced SLAH3 anion channel transcript

The mechanisms of stomatal sensitivity to CO2 are yet to be fully understood. The role of photosynthetic and non-photosynthetic factors in stomatal responses to CO2 was investigated in wild-type barley (Hordeum vulgare var. Graphic) and in a mutant (G132) with decreased photochemical and Rubisco capacities. The CO2 and DCMU responses of stomatal conductance (gs), gas exchange, chlorophyll fluorescence and levels of ATP, with a putative transcript for stomatal opening were analysed. G132 had greater gs than the wild-type, despite lower photosynthesis rates and higher intercellular CO2 concentrations (Ci). The mutant had Rubisco-limited photosynthesis at very high CO2 levels, and higher ATP contents than the wild-type. Stomatal sensitivity to CO2 under red light was lower in G132 than in the wild-type, both in photosynthesizing and DCMU-inhibited leaves. Under constant Ci and red light, stomatal sensitivity to DCMU inhibition was higher in G132. The levels of a SLAH3-like slow anion channel transcript, involved in stomatal closure, decreased sharply in G132. The results suggest that stomatal responses to CO2 depend partly on the balance of photosynthetic electron transport to carbon assimilation capacities, but are partially regulated by the CO2 signalling network. High gs can improve the adaptation to climate change in well-watered conditions.

Disruption of both chloroplastic and cytosolic FBPase genes results in a dwarf phenotype and important starch and metabolite changes in Arabidopsis thaliana.

In this study, evidence is provided for the role of fructose-1,6-bisphosphatases (FBPases) in plant development and carbohydrate synthesis and distribution by analysing two Arabidopsis thaliana T-DNA knockout mutant lines, cyfbp and cfbp1, and one double mutant cyfbp cfbp1 which affect each FBPase isoform, cytosolic and chloroplastic, respectively. cyFBP is involved in sucrose synthesis, whilst cFBP1 is a key enzyme in the Calvin-Benson cycle. In addition to the smaller rosette size and lower rate of photosynthesis, the lack of cFBP1 in the mutants cfbp1 and cyfbp cfbp1 leads to a lower content of soluble sugars, less starch accumulation, and a greater superoxide dismutase (SOD) activity. The mutants also had some developmental alterations, including stomatal opening defects and increased numbers of root vascular layers. Complementation also confirmed that the mutant phenotypes were caused by disruption of the cFBP1 gene. cyfbp mutant plants without cyFBP showed a higher starch content in the chloroplasts, but this did not greatly affect the phenotype. Notably, the sucrose content in cyfbp was close to that found in the wild type. The cyfbp cfbp1 double mutant displayed features of both parental lines but had the cfbp1 phenotype. All the mutants accumulated fructose-1,6-bisphosphate and triose-phosphate during the light period. These results prove that while the lack of cFBP1 induces important changes in a wide range of metabolites such as amino acids, sugars, and organic acids, the lack of cyFBP activity in Arabidopsis essentially provokes a carbon metabolism imbalance which does not compromise the viability of the double mutant cyfbp cfbp1.

Stable carbon and nitrogen isotope compositions change with leaf age in two mangrove ferns

After assimilation, plants often fractionate stable carbon and nitrogen isotopes among different organs depending on synthesis and transport of metabolites. We investigated stable carbon and nitrogen isotope compositions among leaves of different age (0 to 6 months) in two mangrove fern species (Acrostichum danaeifolium Langsd. & Fisch. and Acrostichum aureum L.) from Mexico. Leaves of all ages were analysed for δ13C, δ15N, carbon and nitrogen concentrations and gas exchange parameters. In both species, δ13C slightly decreased with leaf age. Leaf salt concentration increased with leaf age, and thus did not decrease 13C discrimination markedly. Enrichment in 13C in younger versus older leaves can be explained by stage of development: Carbon is assimilated and incorporated into autotrophic leaves, but also transported as 13C-enriched carbohydrates into still expanding and more heterotrophic younger leaves—indicated by lower rates of photosynthesis. Depletion in 13C in old autotrophic leaves, which export photosynthetic assimilates, could mainly be explained by respiratory fractionation releasing 13C-enriched CO2. In contrast, δ15N values in A. danaeifolium increased with leaf age. This pattern could be related to the transport of 15N-depleted amino acids into younger leaves, and leaf construction with these compounds. In conclusion, 13C depletion and 15N enrichment with leaf age were described for other plant species earlier and were explained by different mechanisms of carbon and nitrogen assimilation and the export of these assimilates from older to younger leaves. These stable isotope patterns were approved for two mangrove fern species in this study.

Physiological and NPK Studies for Developing Agrotechniques for SRHD Energy Plantations in the North-Western Himalayas

The study was undertaken to develop agrotechniques for raising short-rotation, high-density (SRHD) energy plantations as a renewable energy source by using planting densities of 10,000 and 14,000 plants/ha. Under Species × Spacing × Fertilizers (N:P:K), the effect of fertilizers was more evident on plant height than on stem diameter. The species as Grevillea robusta, Bauhinia variegata, and Eucalyptus showed the most statistically significant vertical and radial growth in both of the spacings. The N:P:K::50:25:25 kg/ha produced statistically significant growth. The photosynthesis rate, as recorded, showed that Salix tetrasperma had high rates of CO2 assimilation but poor aerial growth.The photosynthetic rate under varying fertilizer treatments remained unchanged, but the biomass improved significantly. In G. robusta, excellent aerial growth was observed despite a low rate of photosynthesis (even at low water potential). The dry weight of Eucalyptus was recorded (60 and 233 t/ha; spacing 1 m × 1 m and 1 m × 0.71 m) after 3 yr. After 10 yr, the highest dry weight was recorded again in Eucalyptus at 1,471.44 t/ha. The lowest moisture content (36–38%) was recorded in Morus alba, while the highest moisture content was recorded in Eucalyptus (66–70%). In all tested species, G. robusta (26%) showed the maximum calorific value.

Variations in leaf respiration and photosynthesis ratio in response to air temperature and water availability among Mediterranean evergreen species

Net photosynthesis (PN) and leaf respiration (RL) of the evergreen species co-occurring in the Mediterranean maquis in response to water availability and air temperature variations were analyzed. The results underlined that the ratio RL/PN of the considered species ranged from 0.15 ± 0.08 (in winter) to 1.32 ± 0.80 (in summer). Variations of RL and PN during the year were attested by the PCA which was carried out using leaf physiological and morphological traits of the considered species. In particular, Cistus incanus having the highest mean yearly PN and RL rates and low leaf mass area (LMA) and leaf tissue density (LTD), was furthest from the other species emphasizing its drought semi-deciduous habitus, the highest photosynthetic capability in favorable conditions (spring), but low tolerance to drought. Erica multiflora and Rosmarinus officinalis were characterized by the highest LMA and LTD, low PN rates in drought and the lowest PN ones in spring. Erica arborea, Pistacia lentiscus, Phillyrea latifolia and Quercus ilex had the highest drought tolerance. Arbutus unedo and Smilax aspera were close to this group despite lower RL rates during the year. The xeromorphic leaves of the considered evergreen species (i.e. high LMA and LTD) favor carbon gain profits over transpiration losses during drought, nevertheless, the high construction cost of these leaf type justifies the relatively high RL rates.

Microscale measurements reveal contrasting effects of photosynthesis and epiphytes on frictional drag on the surfaces of filamentous algae

SUMMARY 1. Filamentous algae are widespread in freshwater ecosystems worldwide with a significant presence in streams, rivers and lakes with sufficient light and nutrients. Although typically not a preferred food source for grazers, dense filamentous mats provide surfaces for epiphytic microorganisms that are more palatable, thus adding to stream productivity. 2. We tested the hypothesis that epiphytes change velocity gradients, and consequently shear stress and skin friction drag, near the surface of algal filaments. Using both digital holography and particle image velocimetry to measure micrometre-scale velocity fields, we found that the surface shear stress on filamentous algae was much greater when the algae were actively photosynthesising. The presence of attached diatoms significantly reduced surface shear stress, while those filaments were photosynthesising, compared with bare filaments. 3. A nutrient flux model, based on boundary layer thickness and surface shear stress, predicts that nutrient flux to the surface of a photosynthesising filament under measured flow conditions will be 1.5 times greater than for a preserved (i.e. dead) filament. Modelled nutrient flux to filaments with epiphytic assemblages dominated by diatoms is 75% of the flux to bare filaments under similar flow conditions. 4. The proposed positive feedback between photosynthesis, surface shear stress and nutrient flux could be an important biophysical mechanism that overcomes diffusion limited nutrient supply within dense algal mats, enhancing algal survival through increased nutrient flux to actively photosynthesising filaments and decreased sloughing risk for filaments with lower rates of photosynthesis (due to epiphyte coverage or other light-limiting factors).

Integrating Transient Heterogeneity of Non-Photochemical Quenching in Shade-Grown Heterobaric Leaves of Avocado (Persea americana L.): Responses to CO2 Concentration, Stomatal Occlusion, Dehydration and Relative Humidity

Long-lived shade leaves of avocado had extremely low rates of photosynthesis. Gas exchange measurements of photosynthesis were of limited use, so we resorted to Chl fluorescence imaging (CFI) and spot measurements to evaluate photosynthetic electron transport rates (ETRs) and non-photochemical quenching (NPQ). Imaging revealed a remarkable transient heterogeneity of NPQ during photosynthetic induction in these hypostomatous, heterobaric leaves, but was adequately integrated by spot measurements, despite long-lasting artifacts from repeated saturating flashes during assays. Major veins (mid-vein, first- and second-order veins) defined areas of more static large-scale heterogeneous NPQ, with more dynamic small-scale heterogeneity most strongly expressed in mesophyll cells between third- and fourth-order veins. Both responded to external CO2 concentration ([CO2]), occlusion of stomata with Vaseline™, leaf dehydration and relative humidity (RH). We interpreted these responses in terms of independent behavior of stomata in adjacent areoles that was largely expressed through CO2-limited photosynthesis. Heterogeneity was most pronounced and prolonged in the absence of net CO2 fixation in 100 p.p.m. [CO2] when respiratory and photorespiratory CO2 cycling constrained the inferred ETR to ~75% of values in 400 or 700 p.p.m. [CO2]. Likewise, sustained higher NPQ under Vaseline™, after dehydration or at low RH, also restricted ETR to ~75% of control values. Low NPQ in chloroplast-containing cells adjacent to major veins but remote from stomata suggested internal sources of high [CO2] in these tissues.

Alleviation of salt stress in citrus seedlings inoculated with arbuscular mycorrhizal fungi depends on the rootstock salt tolerance

Seedlings of Cleopatra mandarin (Citrus reshni Hort. ex Tan.) and Alemow (Citrus macrophylla Wester) were inoculated with a mixture of AM fungi (Rhizophagus irregularis and Funneliformis mosseae) (+AM), or left non-inoculated (−AM). From forty-five days after fungal inoculation onwards, half of +AM or −AM plants were irrigated with nutrient solution containing 50mM NaCl. Three months later, AM significantly increased plant growth in both Cleopatra mandarin and Alemow rootstocks. Plant growth was higher in salinized +AM plants than in non-salinized −AM plants, demonstrating that AM compensates the growth limitations imposed by salinity. Whereas AM-inoculated Cleopatra mandarin seedlings had a very good response under saline treatment, inoculation in Alemow did not alleviate the negative effect of salinity. The beneficial effect of mycorrhization is unrelated with protection against the uptake of Na or Cl and the effect of AM on these ions did not explain the different response of rootstocks. This response was related with the nutritional status since our findings confirm that AM fungi can alter host responses to salinity stress, improving more the P, K, Fe and Cu plant nutrition in Cleopatra mandarin than in Alemow plants. AM inoculation under saline treatments also increased root Mg concentration but it was higher in Cleopatra mandarin than in Alemow. This could explain why AM fungus did not completely recovered chlorophyll concentrations in Alemow and consequently it had lower photosynthesis rate than control plants. AM fungi play an essential role in citrus rootstock growth and biomass production although the intensity of this response depends on the rootstock salinity tolerance.

High temperature stress monitoring and detection using chlorophyll a fluorescence and infrared thermography in chrysanthemum (Dendranthema grandiflora)

Modern highly insulated greenhouses are more energy efficient than conventional types. Furthermore applying dynamic greenhouse climate control regimes will increase energy efficiency relatively more in modern structures. However, this combination may result in higher air and crop temperatures. Too high temperature affects the plant photosynthetic responses, resulting in a lower rate of photosynthesis. To predict and analyse physiological responses as stress indicators, two independent experiments were conducted, to detect the effect of high temperature on photosynthesis: analysing photosystem II (PSII) and stomatal conductance (gs). A combination of chlorophyll a fluorescence, gas exchange measurements and infrared thermography was applied using Chrysanthemum (Dendranthema grandiflora Tzvelev) 'Coral Charm' as a model species. Increasing temperature had a highly significant effect on PSII when the temperature exceeded 38°C for a period of 7 (±1.8) days. High temperature decreased the maximum photochemical efficiency of PSII (Fv/Fm), the conformation term for primary photochemistry (Fv/Fo) and performance index (PI), as well as increased minimal fluorescence (Fo). However, at elevated CO2 of 1000μmolmol(-1) and with a photosynthetic photon flux density (PPFD) of 800μmolm(-2)s(-1), net photosynthesis (Pn) reached its maximum at 35°C. The thermal index (IG), calculated from the leaf temperature and the temperature of a dry and wet reference leaf, showed a strong correlation with gs. We conclude that 1) chlorophyll a fluorescence and a combination of fluorescence parameters can be used as early stress indicators as well as to detect the temperature limit of PSII damage, and 2) the strong relation between gs and IG enables gs to be estimated non-invasively, which is an important first step in modelling leaf temperature to predict unfavourable growing conditions in a (dynamic) semi closed greenhouse.

Leaf Gas Exchange Characteristics of Jatropha as Affected by Nitrogen Supply, Leaf Age and Atmospheric Vapour Pressure Deficit

AbstractFacing a steadily increasing world energy demand, jatropha, among other energy crops, has been reported to potentially contribute to biofuel production. A basic characterisation of plant responses to abiotic environmental factors is important for assessing the model‐assisted potential of this plant in view of the many agro‐ecological zones in which jatropha is presently cultivated. Two pot experiments and two field studies were used to record gas exchange parameters in response to light, nitrogen supply, atmospheric vapour pressure deficit (VPD), leaf age and time of measurements. Variation of N supply from 0 to 16 mm resulted in lower rates of photosynthesis (A) and stomatal conductance (gs) of treatment 0 mm N compared with other N levels, whereas the light compensation point (IC), quantum yield (QY) and dark respiration rates (Rd) were similar in all treatments. In the field, diurnal effects were evident with higher light‐saturated photosynthetic rate (Amax) and QY and lower IC and Rd in the morning than in the afternoon. Considering leaf age effects, fully expanded leaves had a lower Amax compared with expanding leaves and this variation in leaf gas exchange was not related to changes in the chlorophyll index value (SPAD) which steadily increased with leaf age. QY of field and greenhouse plants varied from 0.023 to 0.037 and was substantially lower than in C3 plants. A was positively correlated with gs in a hyperbolic function. A varied from 0.64 to 21.13 μmol m−2 s−1 and gs varied from 12 to 469 mmol m−2 s−1. With increasing VPD, gs decreased, but this response differed between the field experiments and the two pot experiments which contrasted each other distinctively. Applying the inverse logistic function of Webb (Ecological Modeling, 56 (1991), 81), the maximal stomatal conductance of jatropha was in the range of 382 mmol m−2 s−1 and gs is predicted to be close to zero at 5 kPa. These data altogether indicate that light absorption characteristics of single leaves and carbohydrate status parameters should be investigated further to explain the low QY and the pronounced diurnal variation.

The Tonoplast-Localized Sucrose Transporter in Populus (PtaSUT4) Regulates Whole-Plant Water Relations, Responses to Water Stress, and Photosynthesis

The Populus sucrose (Suc) transporter 4 (PtaSUT4), like its orthologs in other plant taxa, is tonoplast localized and thought to mediate Suc export from the vacuole into the cytosol. In source leaves of Populus, SUT4 is the predominantly expressed gene family member, with transcript levels several times higher than those of plasma membrane SUTs. A hypothesis is advanced that SUT4-mediated tonoplast sucrose fluxes contribute to the regulation of osmotic gradients between cellular compartments, with the potential to mediate both sink provisioning and drought tolerance in Populus. Here, we describe the effects of PtaSUT4-RNA interference (RNAi) on sucrose levels and raffinose family oligosaccharides (RFO) induction, photosynthesis, and water uptake, retention and loss during acute and chronic drought stresses. Under normal water-replete growing conditions, SUT4-RNAi plants had generally higher shoot water contents than wild-type plants. In response to soil drying during a short-term, acute drought, RNAi plants exhibited reduced rates of water uptake and delayed wilting relative to wild-type plants. SUT4-RNAi plants had larger leaf areas and lower photosynthesis rates than wild-type plants under well-watered, but not under chronic water-limiting conditions. Moreover, the magnitude of shoot water content, height growth, and photosynthesis responses to contrasting soil moisture regimes was greater in RNAi than wild-type plants. The concentrations of stress-responsive RFOs increased in wild-type plants but were unaffected in SUT4-RNAi plants under chronically dry conditions. We discuss a model in which the subcellular compartmentalization of sucrose mediated by PtaSUT4 is regulated in response to both sink demand and plant water status in Populus.

Plant trait–environment relationships in salt marshes: Deviations from predictions by ecological concepts

Abstract Salt marshes are exposed to high groundwater levels and salinity due to periodical inundation and are under constant influence of physical disturbance. Plants inhabiting salt marshes need to pursue different strategies to colonize this environment and hence, trait expressions should vary along the elevation gradient from pioneer zone to upper salt marsh. We verified various trait–environment concepts for their applicability to different salt marshes zones, and found some are opposite to that of other terrestrial plants. We used RLQ to analyse the joint structure between environmental conditions (R-table) and species traits (Q-table) by use of a species abundance table (L-table). RLQ analyses the inertia of scores of R- and Q-table linked by species scores of L-table. Then we clustered species according to their position along the RLQ axes to form functional groups. The ‘physiological–ecological–amplitude’ concept could not be confirmed from the trait perspective, as the species of the ‘stressful’ lower marsh show trait values indicating higher competitive ability (canopy height and stem mass fraction) than those of the ‘benign’ upper parts. Also, specific leaf area (SLA) and leaf dry matter content (LDMC) of salt marsh plants were more constrained by a salt–waterlogging gradient than by a nutrient gradient. This is opposite to the leaf economics spectrum, which describes a trade-off from fast growing species with the potential of quick return of investments of nutrients to species with long leaf lifetime and low rates of photosynthesis. Our results are consistent with the theory of functional equilibrium and Tilman's allocation model, which is a shift in allocation to plant organs responsible for capturing limiting resources resulting in higher fractions of that organ relative to the whole plant body.

Seasonal variation in concentrations of carbohydrates and lipids in two epiphytic lichens with contrasting, snow-depth related distribution on subarctic birch trees

The lichens Parmelia olivacea and Parmeliopsis ambigua are common epiphytes in subarctic forests in Europe. They differ in abundance and vertical distribution particularly on birch trees, and these differences relate to the level and duration of the winter snow cover. Parmeliopsis ambigua is covered much of the cold season on the lower trunk whereas P. olivacea occurs well above the snow surface. Periods over 6 months under snow have no apparent effect on P. ambigua thalli while much shorter snow cover has been demonstrated to kill P. olivacea. It was hypothesized that the contrasting distributions are due to differences in growth rates and in size and quality of non-structural carbon stores in their tissues affecting their endurance to extended periods of dark respiration. To test these hypotheses, growth measurements were performed on both species and their thalli were sampled for chemical analyses. The results show that the mean annual margin extension growth of P. olivacea thalli was significantly higher than that of P. ambigua, i.e. 1.1 mm and 0.5 mm, respectively. The average non-structural carbohydrate concentration in the two species did not differ, but the annual concentration of storage lipids (triacylglycerol) in P. ambigua was four times higher than that in P. olivacea, despite a shorter growing season and lower rate of photosynthesis. The proportion of polyunsaturated fatty acids in structural (polar) lipids was high in both species, i.e. 77% in P. olivacea and 64% in P. ambigua, which appears to enable both species to withstand low ambient thallus temperatures. The higher concentration of storage lipids in P. ambigua allows survival in environments where P. olivacea would respire to death, e.g. under a prolonged snow cover. Parmeliopsis ambigua avoids competition by establishing toward the base of the tree trunk, where P. olivacea would not survive.

Effects of nutrient addition on leaf chemistry, morphology, and photosynthetic capacity of three bog shrubs

Plants in nutrient-poor environments typically have low foliar nitrogen (N) concentrations, long-lived tissues with leaf traits designed to use nutrients efficiently, and low rates of photosynthesis. We postulated that increasing N availability due to atmospheric deposition would increase photosynthetic capacity, foliar N, and specific leaf area (SLA) of bog shrubs. We measured photosynthesis, foliar chemistry and leaf morphology in three ericaceous shrubs (Vaccinium myrtilloides, Ledum groenlandicum and Chamaedaphne calyculata) in a long-term fertilization experiment at Mer Bleue bog, Ontario, Canada, with a background deposition of 0.8 g N m(-2) a(-1). While biomass and chlorophyll concentrations increased in the highest nutrient treatment for C. calyculata, we found no change in the rates of light-saturated photosynthesis (A(max)), carboxylation (V(cmax)), or SLA with nutrient (N with and without PK) addition, with the exception of a weak positive correlation between foliar N and A(max) for C. calyculata, and higher V(cmax) in L. groenlandicum with low nutrient addition. We found negative correlations between photosynthetic N use efficiency (PNUE) and foliar N, accompanied by a species-specific increase in one or more amino acids, which may be a sign of excess N availability and/or a mechanism to reduce ammonium (NH(4)) toxicity. We also observed a decrease in foliar soluble Ca and Mg concentrations, essential minerals for plant growth, but no change in polyamines, indicators of physiological stress under conditions of high N accumulation. These results suggest that plants adapted to low-nutrient environments do not shift their resource allocation to photosynthetic processes, even after reaching N sufficiency, but instead store the excess N in organic compounds for future use. In the long term, bog species may not be able to take advantage of elevated nutrients, resulting in them being replaced by species that are better adapted to a higher nutrient environment.

Effects of leaf age and tree size on stomatal and mesophyll limitations to photosynthesis in mountain beech (Nothofagus solandrii var. cliffortiodes)

Mesophyll conductance, g(m), was estimated from measurements of stomatal conductance to carbon dioxide transfer, g(s), photosynthesis, A, and chlorophyll fluorescence for Year 0 (current-year) and Year 1 (1-year-old) fully sunlit leaves from short (2 m tall, 10-year-old) and tall (15 m tall, 120-year-old) Nothofagus solandrii var. cliffortiodes trees growing in adjacent stands. Rates of photosynthesis at saturating irradiance and ambient CO(2) partial pressure, A(satQ), were 25% lower and maximum rates of carboxylation, V(cmax), were 44% lower in Year 1 leaves compared with Year 0 leaves across both tree sizes. Although g(s) and g(m) were not significantly different between Year 0 and Year 1 leaves and g(s) was not significantly different between tree heights, g(m) was significantly (19%) lower for leaves on tall trees compared with leaves on short trees. Overall, V(cmax) was 60% higher when expressed on the basis of CO(2) partial pressure at the chloroplasts, C(c), compared with V(cmax) on the basis of intercellular CO(2) partial pressure, C(i), but this varied with leaf age and tree size. To interpret the relative stomatal and mesophyll limitations to photosynthesis, we used a model of carbon isotopic composition for whole leaves incorporating g(m) effects to generate a surface of 'operating values' of A over the growing season for all leaf classes. Our analysis showed that A was slightly higher for leaves on short compared with tall trees, but lower g(m) apparently reduced actual A substantially compared with A(satQ). Our findings showed that lower rates of photosynthesis in Year 1 leaves compared with Year 0 leaves were attributable more to increased biochemical limitation to photosynthesis in Year 1 leaves than differences in g(m). However, lower A in leaves on tall trees compared with those on short trees could be attributed in part to lower g(m) and higher stomatal, L(s), and mesophyll, L(m), limitations to photosynthesis, consistent with steeper hydraulic gradients in tall trees.

Lutein from deepoxidation of lutein epoxide replaces zeaxanthin to sustain an enhanced capacity for nonphotochemical chlorophyll fluorescence quenching in avocado shade leaves in the dark.

Leaves of avocado (Persea americana) that develop and persist in deep shade canopies have very low rates of photosynthesis but contain high concentrations of lutein epoxide (Lx) that are partially deepoxidized to lutein (L) after 1 h of exposure to 120 to 350 μmol photons m(-2) s(-1), increasing the total L pool by 5% to 10% (ΔL). Deepoxidation of Lx to L was near stoichiometric and similar in kinetics to deepoxidation of violaxanthin (V) to antheraxanthin (A) and zeaxanthin (Z). Although the V pool was restored by epoxidation of A and Z overnight, the Lx pool was not. Depending on leaf age and pretreatment, the pool of ΔL persisted for up to 72 h in the dark. Metabolism of ΔL did not involve epoxidation to Lx. These contrasting kinetics enabled us to differentiate three states of the capacity for nonphotochemical chlorophyll fluorescence quenching (NPQ) in attached and detached leaves: ΔpH dependent (NPQ(ΔpH)) before deepoxidation; after deepoxidation in the presence of ΔL, A, and Z (NPQ(ΔLAZ)); and after epoxidation of A+Z but with residual ΔL (NPQ(ΔL)). The capacity of both NPQ(ΔLAZ) and NPQ(ΔL) was similar and 45% larger than NPQ(ΔpH), but dark relaxation of NPQ(ΔLAZ) was slower. The enhanced capacity for NPQ was lost after metabolism of ΔL. The near equivalence of NPQ(ΔLAZ) and NPQ(ΔL) provides compelling evidence that the small dynamic pool ΔL replaces A+Z in avocado to "lock in" enhanced NPQ. The results are discussed in relation to data obtained with other Lx-rich species and in mutants of Arabidopsis (Arabidopsis thaliana) with increased L pools.

Hybrid Rubisco of tomato large subunits and tobacco small subunits is functional in tobacco plants

Biogenesis of functional ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in plants requires specific assembly in the chloroplast of the imported, cytosol-synthesized small subunits (SS) with the chloroplast-made large subunits (LS). Accumulating evidence indicates that chloroplasts (plastids) generally have a low tolerance for assembling foreign or modified Rubisco. To explore Rubisco engineering, we created two lines of transplastomic tobacco plants whose rbcL gene was replaced by tomato-derived rbcL: plant LLS2 with Rubisco composed of tobacco SS and Q437R LS and plant LLS4 with a hybrid Rubisco of tobacco SS and tomato LS (representing four substitutions of Y226F, A230T, S279T and Q437R from tobacco LS). Plant LLS2 exhibited similar phenotypes as the wild type. Plant LLS4 showed lower chlorophyll and Rubisco levels particularly in young emerging leaves, lower photosynthesis rates and biomass during early stages of development, but was able to reach reproductive maturity and somewhat wild type-like phenotype under ambient CO2 condition. In vitro assays detected similar carboxylase activity and RuBP affinity in LLS2 and LLS4 plants as in wild type. Our studies demonstrated that tomato LS was sufficiently assembled with tobacco SS into functional Rubisco. The hybrid Rubisco of tomato LS and tobacco SS can drive photosynthesis that supports photoautotrophic growth and reproduction of tobacco plants under ambient CO2 and light conditions. We discuss the effect of these residue substitutions on Rubisco activity and the possible attribution of chlorophyll deficiency to the in planta photosynthesis performance in the hybrid Rubisco plants.

Zooxanthellar symbiosis in planula larvae of the coral Pocillopora damicornis

We characterized the planular-zooxanthellae symbiosis of the coral Pocillopora damicornis using criteria that are familiar in studies on corals. Similar to adult corals, planulae exhibited photoacclimation, as changes in symbiont chlorophyll a (chl a); changes in the light-saturation constant for photosynthesis ( I k); and, at insufficient light, fewer zooxanthellae, decreased respiration, increased weight loss, and increased sensitivity to photoinhibition. Numbers of zooxanthellae in newly-released planulae varied by at least three-fold within broods. Planulae with low versus high numbers of zooxanthellae (termed pale versus dark planulae, respectively) did not differ in symbiont chl a content, I k, or biomass-specific rate of dark respiration. Pale planulae had lower rates of photosynthesis, but this difference vanished after three weeks, when zooxanthellar numbers increased by 225% in pale planulae and by 31% in dark planulae. Numbers of zooxanthellae also increased significantly in planulae cultured in ammonium-enriched seawater; ammonium also apparently prevented weight loss and induced settlement. Approximately 70% of photosynthetically-fixed carbon (labeled using 14C) apparently was translocated from the zooxanthellae to their host. A comparison of planulae cultured at 0.3% versus 11% sunlight suggested that photosynthesis provided ∼ 31% of the energy utilized by the latter. Overall, we conclude that the physiology of symbiosis in planulae of P. damicornis is broadly similar to symbiosis physiology in adult corals.

Effects of hydrology on the growth and physiology of an invasive exotic, Lygodium microphyllum (Old World climbing fern)

SummaryWe conducted a glasshouse study to examine effects of hydrology on the growth and physiology of Lygodium microphyllum (Old World climbing fern), an invasive exotic that is rapidly colonising forested wetlands in Florida, USA. We assessed the fern’s growth and physiological responses to three hydrological treatments – flood, drought and field capacity. To further explore the physiology of the treatment responses of L. microphyllum, we also sprayed each plant with gibberellic acid, paclobutrazol (gibberellin inhibitor) or a water control solution (at a rate of 5 mL three times per week) using a 3 × 3 factorial design. Flooding reduced relative growth rate by 55%, whereas periodic exposure of ferns to a soil water potential of −1 MPa did not affect growth or physiology. Flooding led to substantial decreases in specific leaf area and area‐based rates of pinna photosynthesis, resulting in a 64% lower rate of photosynthesis per unit pinna mass. Application of growth regulators had no effect on fern growth, morphology or physiology. Even though flooding substantially reduced growth, L. microphyllum still showed a positive relative growth rate after >2 months of inundated soils. This apparent hydrological plasticity is likely a contributing factor to the introduced fern’s widespread establishment across a range of plant communities within the Florida Everglades ecosystem. Short‐term manipulation of site hydrology does not appear to be an effective management option. Consequently, this has considerable implications for the Everglades, which is undergoing a 30‐year system‐wide hydrological restoration.