Photosynthetic Carbon Assimilation Research Articles

Increasing photosynthetic carbon assimilation in C3 plants to improve crop yield: current and future strategies.

The realization that crop yields are reaching a plateau, while population increases continue at pace, has placed manipulation of photosynthesis in a central position to achieve increases in yield. Increasing flux through the C3 cycle will be a major focus of this effort. Through application of new

Assessing vineyard water status using the reflectance based Water Index

In the Mediterranean arc, vines for wine production are mainly grown without the support of irrigation. Under such conditions, site variables affecting the extent and seasonal timing of water deficits are the dominant environmental constraints for grape production. Moreover, water availability and vine water status are the factors most comprehensively determining fruit composition and, thus, wine quality. Therefore, monitoring the extent of water stress in vines might be a valuable tool for the optimisation of grape yield and quality. The objective of this study was to evaluate the feasibility of using the reflectance based Water Index (WI) to estimate vine water status at the leaf and canopy levels. The study was conducted on Vitis vinifera cv. Chardonnay potted plants submitted to contrasting water availability and in ten commercial vineyards in the D.O. Penedès region (Catalonia, Spain) over two consecutive years (2007–2008). In potted plants, differences in water supply were translated into differences in net photosynthetic carbon assimilation, stomatal conductance (gs) and WI, despite similar predawn water potentials (Ψp). There was a negative close correlation between WI and gs, although the relationship was treatment dependent (r2=0.81 and r2=0.95, for control and deficit plants, respectively). Similarly the leaf to air temperature difference was inversely related to gs (r2=0.51). In the field study there were significant differences in Ψp among vineyards and between years and indicated that vines experienced moderate to severe water stress. Water availability determined vine canopy development as indicated by the close relationship between the Normalized Difference Vegetation Index and in Ψp (r2=0.57). The canopy to air temperature difference (determined with an infrared thermometer at midday) was inversely correlated with WI with r2=0.45 and r2=0.56 in 2007 and 2008, respectively. Thus, the reflectance based Water Index effectively tracked variation in both leaf stomatal conductance and canopy transpiration under a range of moderate to severe water stress. The results are discussed in relation to the potential application of WI to irrigation scheduling and to monitoring vineyard performance.

Stable isotopes reveal limitations in C and N assimilation in the Caribbean reef corals Madracis auretenra, M. carmabi and M. formosa

We used tissue δ 15 N and δ 13 C to elucidate nitrogen and carbon utilization in 3 branching coral species of the genus Madracis. Coral branches were sampled between 5 and 47 m water depth, and tissue was sub-sampled from the tips and sides of branches. Photosynthetically active radiation (PAR) ranged between 1 and 71% of surface PAR. There was a good correlation between δ 15 N and δ 13 C, and these had similar ranges of 5.6 and 5.2‰, respectively, suggesting that light-driven photo- synthesis is a strong factor in isotope fractionation. However, at shallow depths, δ 13 C decreased more strongly while δ 15 N remained constant, while at deeper depths δ 15 N decreased while δ 13 C remained constant. Comparisons of δ 13 C in polyps and zooxanthellae revealed that prey capture at the tips of branches was more pronounced than at the corresponding sideward-facing positions and that corals at deeper depths did not increase their food uptake to compensate for a decrease in photosynthetic carbon assimilation. This indicates that foraging in branching Madracis depends on current regimes and prey encounter rather than selective food capture. The systematic analysis of tissue δ 15 N along a steep depth gradient revealed that the shallow-water coral M. auretenra was nitrogen limited throughout its entire depth range.

Relationship of Photosynthetic Carbon Assimilation Related Traits of Flag Leaves with Yield Heterosis in a Wheat Diallel Cross

In spite of commercial use of heterosis in agriculture,the physiological basis of heterosis is poorly understood.Photosynthetic carbon assimilation related traits of flag leaves,including photosynthetic capacity,stomatal conductance,intercellular CO2 concentration,transpiration rate,water use efficiency and efficiency of primary conversion of light energy,were measured at early,middle,and post grain-filling stages in a wheat(Triticum aestivum L.) diallel cross involving 20 hybrids and nine parents,with the purpose of determining the relationship of yield heterosis with these traits.The magnitude of heterosis varied subject to cross combination,trait,and developmental stage.Further analysis indicated that heterosis of photosynthetic carbon assimilation related traits was not correlated with that of spike length and spike number per plant,but significantly correlated with that of other yield components.Moreover,at middle grain-filling stage,the heterosis of photosynthetic rate,intercellular CO2 concentration,water use efficiency and efficiency of primary conversion of light energy were significantly and positively correlated with those of grain number per spikes,thousand-grain weight,yield per plant and yield of main stem,suggesting that higher photosynthetic capacity and water use efficiency could be one of the important physiological basis of wheat hybrid vigor.

Spectral reflectance from a soybean canopy exposed to elevated CO2 and O3.

By affecting the physiology and structure of plant canopies, increasing atmospheric CO2 and O3 influence the capacity of agroecosystems to capture light and convert that light energy into biomass, ultimately affecting productivity and yield. The objective of this study was to determine if established remote sensing indices could detect the direct and interactive effects of elevated CO2 and elevated O3 on the leaf area, chlorophyll content, and photosynthetic capacity of a soybean canopy growing under field conditions. Large plots of soybean (Glycine max) were exposed to ambient air (∼380 μmol CO2 mol−1), elevated CO2 (∼550 μmol mol−1), elevated O3 (1.2× ambient), and combined elevated CO2 plus elevated O3 at the soybean free air gas concentration enrichment (SoyFACE) experiment. Canopy reflectance was measured weekly and the following indices were calculated from reflectance data: near infrared/red (NIR/red), normalized difference vegetation index (NDVI), canopy chlorophyll content index (chl. index), and photochemical reflectance index (PRI). Leaf area index (LAI) also was measured weekly. NIR/red and LAI were linearly correlated throughout the growing season; however, NDVI and LAI were correlated only up to LAI values of ∼3. Season-wide analysis demonstrated that elevated CO2 significantly increased NIR/red, PRI, and chl. index, indicating a stimulation of LAI and photosynthetic carbon assimilation, as well as delayed senescence; however, analysis of individual dates resolved fewer statistically significant effects of elevated CO2. Exposure to elevated O3 decreased LAI throughout the growing season. Although NIR/red showed the same trend, the effect of O3 on NIR/red was not statistically significant. Season-wide analysis showed significant effects of O3 on PRI; however, analysis of individual dates revealed that this effect was only statistically significant on two dates. Elevated O3 had minimal effects on the total canopy chlorophyll index. PRI appeared to be more sensitive to decreased photosynthetic capacity of the canopy as a whole compared with previously published single leaf gas exchange measurements at SoyFACE, possibly because PRI integrates the reflectance signal of older leaves with accumulated O3 damage and healthy young, upper canopy leaves, enabling detection of significant decreases in photosynthetic carbon assimilation which have not been detected in previous studies which measured gas exchange of upper canopy leaves. When the canopy was exposed to elevated CO2 and O3 simultaneously, the deleterious effects of elevated O3 were diminished. Reflectance data, while less sensitive than direct measurements of physiological/structural parameters, corroborate direct measurements of LAI and photosynthetic gas exchange made during the same season, as well as results from previous years at SoyFACE, demonstrating that these indices accurately represent structural and physiological effects of changing tropospheric chemistry on soybean growing in a field setting.

식물의 탄소대사공학 연구동향

Yield productivity of staple crops must be increased at least 50% by 2050, in order to feed the world population which is expected to reach 90 billions. Photosynthetic carbon assimilation and carbohydrate metabolism leading to the production of starch would be the final frontier to quest for new sources of technology enabling such a drastic increase of crop productivity. In this review, attempts to genetically engineer plant photosynthetic carbon reduction cycle and metabolic pathways to increase starch production are introduced.

Relationship of Photosynthetic Carbon Assimilation Related Traits of Flag Leaves with Yield Heterosis in a Wheat Diallel Cross

In spite of commercial use of heterosis in agriculture, the physiological basis of heterosis is poorly understood. Photosynthetic carbon assimilation related traits of flag leaves, including photosynthetic capacity, stomatal conductance, intercellular CO 2 concentration, transpiration rate, water use efficiency, and efficiency of primary conversion of light energy, were measured at early, middle, and post grain-filling stages in a wheat ( Triticum aestivum L.) diallel cross containing 20 hybrids and 9 parents. The purpose of this study was to determine the relationship between yield heterosis and these traits. The magnitude of heterosis varied subject to cross combination, trait, and developmental stage. Further analysis indicated that heterosis of photosynthetic carbon assimilation related traits was not correlated with that of spike length and spike number per plant, but significantly correlated with that of other yield components. At middle grain-filling stage, the heterosis of photosynthetic rate, intercellular CO 2 concentration, water use efficiency, and efficiency of primary conversion of light energy were significantly and positively correlated with those of fertile spikelets per plant, thousand-grain weight, yield per plant, and yield of main stem. These results suggested that higher photosynthetic capacity and water use efficiency could be one of the important physiological bases of wheat hybrid vigor.

Mechanism of photosynthetic response in Microcystis aeruginosa PCC7806 to low inorganic phosphorus

Photosynthetic response of Microcystis aeruginosa PCC7806 to different concentrations of phosphorus supply was studied so as to elucidate if the declining process of Microcystis bloom under freshwater ecosystem is related to soluble reactive phosphorus (SRP) decrease in water volume. Growth rate of M. aeruginosa PCC7806 was significantly reduced under P-deficient conditions, and its photosynthetic activity in terms of rETR max (maximum electron transport rate) decreased significantly after 48 h growth, while it kept elevating and reached to a relative stable value when supplied with rich phosphorus of 0.6 mg/L. With the increasing actinic irradiance along the rapid light curves of M. aeruginosa PCC7806 cultured under low-phosphorus level, qP (photochemical quenching) and rETR (relative electron transport rate) decreased greatly, and the increase in qN (non-photochemical quenching) and Φ PS (actual photochemical efficiency of PSII) was obviously inhibited. The affinity of M. aeruginosa PCC7806 to inorganic carbon was reduced evidently in 0.02 mg/L P compared with in 0.6 mg/L P. When P was reduced from 0.6 to 0.02 mg/L, the decreasing rate of rETR max (77%) was significantly greater than that of photosynthetic carbon assimilation (22%), which indicated that down-regulation of CO 2 affinity caused by P-deficiency was, but not the only reason that resulted in the decline of photosynthetic efficiency. Instantaneous low-temperature significantly limited rETR max under rich-P condition but had no effect on it when P was insufficient, and 1% ethanol could enhance rETR max at low-P level but did not influence it at rich-P level. These two results proved that the decrease in thylakoid membrane fluidity caused by P-deficiency was another important reason that results in the decline of photosynthetic efficiency of M. aruginosa PCC7806.

Dependence of tree ring stable isotope abundances and ring width on climate in Finnish oak

We measured ring widths and isotopic abundances of carbon, oxygen and hydrogen (delta(13)C, delta(18)O and delta(2)H) from the latewood of tree rings of pedunculate oak (Quercus robur L.) in its distributional northern limit in Southern Finland. Ring width was observed to be related to precipitation and relative humidity but not significantly to temperature. delta(13)C and delta(18)O were significantly related to all studied climatic variables, most strongly to cloud cover. Variations in delta(2)H were discovered to be complex combinations of signals from biochemical and physical processes. The results suggest that oaks in Finland can be used as a source of climate information. delta(18)O was discovered to be especially promising as it showed the strongest climate signal and highest common signal between trees. The relationship between climate and ring width indicates that water availability is the main control of ring radial growth. This is supported by the isotope data. High correlation between delta(13)C and delta(18)O time series indicates that photosynthetic carbon assimilation is limited by stomatal control. Therefore, in contrast to the expected temperature limitation, our data indicate that drought limits oak growth more than cold temperatures on the border of its northernmost distribution range.

Systemic Signaling and Local Sensing of Phosphate in Common Bean: Cross-Talk between Photosynthate and MicroRNA399

Shoot-to-root communication is crucial for plant acclimation to phosphorus (P)-deficiency. Both sugars and miRNAs have been implicated as potential signal molecules transported through phloem from shoot to root for the regulation of gene expression and Pi uptake in the root. By studying the expression patterns of both a serine/threonine phosphatase gene (PvHAD1) and microRNA399 (miR399) in common bean (Phaseolus vulgaris L.), we provide evidence for the interaction between light, phloem transport, and miR399 in the systemic regulation of gene expression under P-deficiency. Especially, miR399 expression in both the shoot and the root requires photosynthetic carbon assimilation during the onset of P-deficiency. In contrast to systemic signaling, local sensing was the primary causal factor for rapid down-regulation of PvHAD1 by Pi prior to the reduction of miR399 level in P-deficient roots. Furthermore, this initial response to Pi in P-deficient root was also mimicked by the Pi analog, phosphonate (Phi). Our current findings suggest that plants have developed a highly coordinated dual regulatory pathway, namely long-distance signaling of P-deficiency from shoot to root versus local sensing of Pi in the root.

Importance of AOX pathway in optimizing photosynthesis under high light stress: role of pyruvate and malate in activating AOX.

The present study shows the importance of alternative oxidase (AOX) pathway in optimizing photosynthesis under high light (HL). The responses of photosynthesis and respiration were monitored as O(2) evolution and O(2) uptake in mesophyll protoplasts of pea pre-incubated under different light intensities. Under HL (3000 micromol m(-2) s(-1)), mesophyll protoplasts showed remarkable decrease in the rates of NaHCO(3)-dependent O(2) evolution (indicator of photosynthetic carbon assimilation), while decrease in the rates of respiratory O(2) uptake were marginal. While the capacity of AOX pathway increased significantly by two fold under HL, the capacity of cytochrome oxidase (COX) pathway decreased by >50% compared with capacities under darkness and normal light (NL). Further, the total cellular levels of pyruvate and malate, which are assimilatory products of active photosynthesis and stimulators of AOX activity, were increased remarkably parallel to the increase in AOX protein under HL. Upon restriction of AOX pathway using salicylhydroxamic acid (SHAM), the observed decrease in NaHCO(3)-dependent O(2) evolution or p-benzoquinone (BQ)-dependent O(2) evolution [indicator of photosystem II (PSII) activity] and the increase in total cellular levels of pyruvate and malate were further aggravated/promoted under HL. The significance of raised malate and pyruvate levels in activation of AOX protein/AOX pathway, which in turn play an important role in dissipating excess chloroplastic reducing equivalents and sustenance of photosynthetic carbon assimilation to balance the effects of HL stress on photosynthesis, was depicted as a model.

Plant Biochemistry by Caroline Bowsher, Martin Steer, Alyson Tobin

BOOK REVIEW Cite as follows: Fricke,W. 2010 Book review: Plant Biochemistry. Biology and Environment: Proceedings of the RoyalIrish Academy 110B, 163-164. DOI: 10.3318/ BIOE.2010.110.2.163. Plant Biochemistry Caroline Bowsher, Martin Steer and Alyson Tobin Garland Science 2008; 500 pp; 49.00; ISBN-13 9780815341215 Plant Biochemistryby Bowsher, Steer and Tobin, is a comprehensive treatment of the biochemis tryof plants. The book is an excellent resource not only to thosewho are interested in the actual biochemical reactions and metabolic pathways, but also to thosewho want to link aspects of the physiology and ecology of plants to their bio chemistry. Throughout the book, the authors take a holistic approach to the topic and express theirown fascination forplants.One can tell that the authors have a vast teaching experience and try to approach topics from a student's point of view. The result isbiochemistry packaged into an easily 'digestible' form for the non-specialist (in particular concerning chemistry!). By providing ample examples ofhow the structureofmolecules is linked to everyday experiences, such as starch biochemistry or alkaloid occurrence tofood prop erties and toxicity, the authors render the topic attractive to first- and second-year undergraduate students. In-depth treatment of the regulation of metabolic processes and of the chemical reactions involved also make thebook a valuable resource for students atmore advanced undergraduate level and postgraduate level. Those of us who teach on related aspects of plant biology and who are not experts in thebiochemistry of plantswill find the book very useful to complement teaching contents through biochemical information. As for any book, the choice and in-depth treatment of topics reflects the research background of authors. Energy metabolism, photosynthetic reactions and nitrogen assimilation are covered in great detail. In comparison, topics such as the biochemistry ofwalls or thebiochemistry of plant hormones are treated in far less detail. Chapter 1 and 2 provide a concise introduction to the topic and nice selection ofmethodological approaches to study plant biochemistry. Personally, I would have liked to see included a section on the ionic environment in plants cells, and how this can impact on protein structureand activity,together with a method section detailing electrophysio logical approaches, and a separate section (orbox) on redox potentials, being crucial to the under standing of energymetabolism. Chapter 3 gives a comprehensive overview of the structure of plant cells. There are some great electron micrographs included. Unfortunately, although most pictures refer to the same reference, there is an almost complete lack of scales, labelling and details about plants species (and, often, cell type). Chapters 4 and 5, about photosynthetic light reactions and carbon assimilation, are an excellent up-to-date and in-depth summary of the topic.Box 5.5 on page 107 is a must?as are sections on the evolu tionofC4-plants orC4 in single cells.This chapter would have benefited, aswould most of the fol lowing chapters, from a simple scheme inwhich the location of reactions is shown at the plant, tissue,cell and organelle level (e.g. as a box). The not-so-experienced reader my find it difficult to follow 'where' 'what' ishappening and should refer to basic first-yeartextbooks in biology. Chapter 6 on respiration again provides a nice synthesisof biochemical reactions and their regulation.This is followed by a chapter on storage and structural carbohydrates. The cellwall comes a bit short,but this ismore than compensated forby an excellent treatment of sucrose and starch biochemistry and applied aspects in food industry and agriculture. Chapter 8 focuses on thoseplantmineral nutrients (nitrogen, sulphur) that involve themost of bio chemical reactions as compared to other mineral nutrients that are required at large quantities (e.g. potassium, calcium). The topic, in particular regu lation of nitrogen assimilation, is treated in great detail; again a simple scheme outlining the subcel lular location of reactions would have been great. The last chapter, on what is considered bymany as 'primary metabolism', addresses lipids.The bio chemical detail is excellent. Electronmicrographs of cuticle structure and waxes would have been good tovisually linkbiochemistry to anatomy and physiology and to render this chapter less abstract. In the final three chapters, the authors cover the biochemistry of three largergroups of plant...

Wood 13C, 18O and radial growth responses of residual red pine to variable retention harvesting

Variable retention harvests are used to enhance the development of structural complexity in managed forests by retaining living trees and other structural legacies from the pre-harvest ecosystem. While harvesting should increase resource availability to residual trees, greater crown exposure may also increase environmental stress, which makes it difficult to predict growth in different structural environments. We used stable carbon isotope ratios (delta(13)C) of annual rings from red pine trees (Pinus resinosa Ait.) as an index of intrinsic water use efficiency (iWUE), the ratio of photosynthetic carbon assimilation (A) to stomatal conductance (g(s)), to better understand how differences in physiological performance relate to growth responses following harvests that left residuals dispersed, aggregated between small (0.1 ha) gaps or aggregated between large (0.3 ha) gaps. Stable oxygen isotope ratios (delta(18)O) were used as an index of g(s) to investigate the drivers behind changes in iWUE. Retention harvesting did not appear to affect delta(13)C or delta(18)O at the stand scale when compared to unharvested control stands, but there was a significant, negative correlation between residual tree delta(13)C and plot basal area in the second and third years after harvesting that suggests declining iWUE as overstory competition increases. Residual tree delta(18)O was similar across treatments and basal areas. Trees in variable retention harvests showed small but positive increases in radial growth from the pre-treatment to post-treatment measurement periods, while radial growth declined in unharvested control stands. There were no significant differences in radial growth among retention treatments. Our results suggest residual red pine in relatively open environments benefit from greater A but do not show evidence of changes in g(s) that would indicate altered water relations.

Importance of ROS and antioxidant system during the beneficial interactions of mitochondrial metabolism with photosynthetic carbon assimilation.

The present study suggests the importance of reactive oxygen species (ROS) and antioxidant metabolites as biochemical signals during the beneficial interactions of mitochondrial metabolism with photosynthetic carbon assimilation at saturating light and optimal CO2. Changes in steady-state photosynthesis of pea mesophyll protoplasts monitored in the presence of antimycin A [AA, inhibitor of cytochrome oxidase (COX) pathway] and salicylhydroxamic acid [SHAM, inhibitor of alternative oxidase (AOX) pathway] were correlated with total cellular ROS and its scavenging system. Along with superoxide dismutase (SOD) and catalase (CAT), responses of enzymatic components--ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), glutathione reductase (GR) and non-enzymatic redox components of ascorbate-glutathione (Asc-GSH) cycle, which play a significant role in scavenging cellular ROS, were examined in the presence of mitochondrial inhibitors. Both AA and SHAM caused marked reduction in photosynthetic carbon assimilation with concomitant rise in total cellular ROS. Restriction of electron transport through COX or AOX pathway had differential effect on ROS generating (SOD), ROS scavenging (CAT and APX) and antioxidant (Asc and GSH) regenerating (MDAR and GR) enzymes. Further, restriction of mitochondrial electron transport decreased redox ratios of both Asc and GSH. However, while decrease in redox ratio of Asc was more prominent in the presence of SHAM in light compared with dark, decrease in redox ratio of GSH was similar in both dark and light. These results suggest that the maintenance of cellular ROS at optimal levels is a prerequisite to sustain high photosynthetic rates which in turn is regulated by respiratory capacities of COX and AOX pathways.

Diurnal patterns of photosynthesis, chlorophyll fluorescence, and PRI to evaluate water stress in the invasive species, Elaeagnus umbellata Thunb.

Photosynthesis, chlorophyll fluorescence, and hyperspectral reflectance were used to evaluate diurnal changes of Elaeagnus umbellata to quantify physiological responses of the invasive species during times of stress. Field measurements showed that E. umbellata is able to maintain higher levels of photosynthesis relative to nearby Quercus alba plants, with less water loss. Plants subjected to progressive drought were able to recover photosynthesis one day following re-watering. Laboratory and field measurements revealed decreasing ΔF/F′m values in response to drought stress, with little corresponding decrease in photochemical reflectance index values. This research supports the view that xanthophyll cycle dissipation is not the photoprotective mechanism at work for Elaeagnus species under water stress. Elaeagnus umbellata maintains photosynthetic carbon assimilation even under drought conditions, in part, due to chemical dissipation of excess light, and in part because of morphological features that limit excess radiation while maximizing photosynthetic carbon gain. These characteristics may contribute to the invasive success of E. umbellata.

Label-free Quantitative Proteomics Analysis of Etiolated Maize Seedling Leaves during Greening

To better understand light regulation of C(4) plant maize development, we investigated dynamic proteomic differences between green seedlings (control), etiolated seedlings, and etiolated seedlings illuminated for 6 or 12 h using a label-free quantitative proteomics approach based on nanoscale ultraperformance liquid chromatography-ESI-MS(E). Among more than 400 proteins identified, 73 were significantly altered during etiolated maize seedling greening. Of these 73 proteins, 25 were identified as membrane proteins that seldom had been identified with two-dimensional electrophoresis methods, indicating the power of our label-free method for membrane protein identification; 31 were related to light reactions of chlorophyll biosynthesis, photosynthesis, and photosynthetic carbon assimilation. The expression of photosystem II subunits was highly sensitive to light; most of them were not identified in etiolated maize seedlings but drastically increased upon light exposure, indicating that the complex process of biogenesis of the photosynthetic apparatus correlates with the transition from a dark-grown to a light-grown morphology. However, transcriptional analysis indicated that most transcripts encoding these proteins were not regulated by light. In contrast, the levels of mRNAs and proteins for enzymes involved in carbon assimilation were tightly regulated by light. Additionally phosphoenolpyruvate carboxykinase, the key enzyme of the phosphoenolpyruvate carboxykinase C(4) pathway, was more tightly regulated by light than the key enzymes of the NADP-malic enzyme C(4) pathway. Furthermore phosphoenolpyruvate carboxylase 1C, which was originally reported to be specifically expressed in roots, was also identified in this study; expression of this enzyme was more sensitive to light than its isoforms. Taken together, these results represent a comprehensive dynamic protein profile and light-regulated network of C(4) plants for etiolated seedling greening and provide a basis for further study of the mechanism of gene function and regulation in light-induced development of C(4) plants.

Photosynthetic acclimation to different light levels in the brown marine macroalga, Hizikia fusiformis (Sargassaceae, Phaeophyta)

Hizikia fusiformis thalli experience dynamic incident light conditions during the period of growth. The present study was designed to examine how changing photon irradiance affects the photosynthesis both in the short and long terms by culturing H. fusiformis under three different light levels: 35 μmol photons m-2 s-1 (low light, LL), 85 μmol photons m-2 s-1 (intermediate light, IL), and 165 μmol photons m-2 s-1 (high light, HL). A similar relative growth rate was observed between IL- and HL-grown algae, but the growth rate was significantly reduced in LL-grown algae. The photosynthetic rates (Pn) measured at their respective growth light levels were found to be lowest in the thalli grown at LL and highest at HL. However, LL-grown algae exhibited much higher Pn in comparison with IL- and the HL-grown thalli at the same measuring photosynthetic photon flux density, indicating the photosynthetic acclimation to low growth light in H. fusiformis. The photosynthesis–light curves showed that LL-grown algae had a highest light-saturating maximum Pn (Pmax) in comparison with IL- or HL-grown algae when the photosynthetic rates were expressed on the biomass basis. However, Pmax was highest in HL-grown algae compared to IL- or LL-grown algae when the rates were normalized to chlorophyll a. The photosynthesis–inorganic carbon (Ci) response curves were also significantly affected by the growth light conditions. The highest value of apparent photosynthetic conductance occurred in LL-grown algae while the lowest value in HL-grown algae. Additionally, the activity of external carbonic anhydrase (CA) tended to increase while the total CA activity inclined to decrease in H. fusiformis thalli when the growth light level altered from 35 to 165 μmol photons per square meter per second. The external CA inhibitors showed a higher inhibition in HL-grown algae compared with LL-grown algae. It was proposed that photosynthetic acclimation to low light condition in H. fusiformis was achieved through an increase in the number of reaction centers and increased capacities of electron transport and of Ci transport within cells. The ability of photosynthetic acclimation to low light confers H. fusiformis thalli to overcome the environmental low light condition as a result of the attenuation of seawater or self-shading through enhancing its photosynthetic performance and carbon assimilation necessary for growth.

The ‘Mother of Thousands’ (Kalanchoë daigremontiana): A Plant Model for Asexual Reproduction and CAM Studies

The genus Kalanchoë plays an important role in the investigation of biochemical, physiological and phylogenetic aspects of Crassulacean acid metabolism (CAM) in plants, which is an important evolutionary adaptation of the photosynthetic carbon assimilation pathway to arid environments. In addition, natural compounds extracted from tissues of Kalanchoë have potential applicability in treating tumors and inflammatory and allergic diseases, and have been shown to have insecticidal properties. Kalanchoë daigremontiana (Hamet & Perrier) originated in Madagascar and reproduces asexually by spontaneously forming whole plantlets on leaves. Plantlets develop symmetrically along the leaf margins on leaf notches, closely resembling zygotic embryos in development, and once the root system is formed, they detach from the mother-leaf, fall to the ground, and grow into new plants. This phenomenon is also found in other species from this same genus; however, the formation of leaf-plantlets is variable among species. Nevertheless, all species illustrate the remarkable ability of plant somatic cells to regenerate an entire organism, which has fascinated the scientific community for many years. It was only recently that the morphogenic process involved in the origin of K. daigremontiana plantlets was determined using molecular and genetic tools: K. daigremontiana forms plantlets by co-opting both organogenesis and embryogenesis programs into leaves. The ability of K. daigremontiana species to form somatic embryos outside of a seed environment provides an attractive model system to study somatic embryogenesis in nature, particularly the molecular mechanism involved in the acquisition of competence by vegetative cells to make embryos without fertilization.

Responses to precipitation treatment for Haloxylon ammodendron growing on contrasting textured soils

AbstractThe responses to precipitation of Haloxylon ammodendron (C.A. Mey.) Bunge (Chenopodiaceae), a small xerophilous tree growing on contrasting textured soils, were evaluated under no, natural, and double precipitation treatments during the entire growing season of 2006. The contrasting textured soils are sandy and heavy textured, and both are the original habitat of H. ammodendron at the south edge of Gubantonggute Desert, Central Asia. Photosynthesis, leaf water potential, transpiration, water use efficiency and leaf biomass production were monitored throughout the growing season. Root distribution of H. ammodendron was evaluated at the end of the experiment. Overall, this small tree did not show significant response to a large summer precipitation pulse or precipitation treatments, in terms of photosynthetic carbon assimilation on either soil. The leaf water potential, transpiration, and water use efficiency appeared to be highly sensitive to a large precipitation pulse and precipitation treatments in sandy soil; and leaf biomass production was also much higher for plants in sandy than that of heavy‐textured soil. In sandy soil, defoliation occurred when pre‐dawn leaf water potential dropped below −3.0 MPa, while in heavy‐textured soil, defoliation occurred when pre‐dawn leaf water potential dropped below −3.75 MPa. For similar above‐ground parts, the small trees at the sandy site developed much deeper root systems and had nearly double the surface area of feeder roots compared to those at the heavy‐textured site. Partially owning to the deeper and larger root system, H. ammodendron growing at coarse‐textured site was in better water conditions than those at heavy‐textured site under the same climatic conditions.

Photoacclimation processes in phytoplankton: mechanisms, consequences, and applications

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 56:163-176 (2009) - DOI: https://doi.org/10.3354/ame01345 AME Special: 'Progress and perspectives in aquatic primary productivity: highlights of the GAP VIII workshop, Eilat, Israel, 2008' REVIEW Photoacclimation processes in phytoplankton: mechanisms, consequences, and applications Zvy Dubinsky*, Noga Stambler The Mina & Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel *Email: dubinz@mail.biu.ac.il ABSTRACT: In nature and in the laboratory, phytoplankton cells are exposed to fast and extreme fluctuations in light intensity. These include diel and seasonal changes in irradiance, and changes stemming from vertical mixing over the light field. In algal mass cultures and photobioreactors, similar changes take place as cultures grow denser and as cells are mixed rapidly in the system. To survive supraoptimal, free-radical-generating irradiance levels as well as prolonged exposure to dim light, phytoplankton species are capable of photoacclimation. Under low light, light-harvesting pigments such as phycobilins, chlorophylls, fucoxanthin and peridinin increase all the way to optically becoming black cells. The same pigments decrease under high light, resulting in cells being rather transparent. The opposite takes place with the photoprotective pigments β-carotene and astaxanthin and the elements of the xanthophyll cycle, all of which increase whenever cells are exposed to high irradiance levels, concomitant with enhanced activity of the antioxidant enzymes catalase, superoxydismutase, and peroxidase. These processes are complemented by up to 5–fold changes in RUBISCO per photosystem unit (PSU) levels, and parallel changes in light-saturated photosynthetic rates. Thus, light-harvesting and utilization efficiencies are maximized under low light, whereas photosynthetic carbon assimilation and throughput rates reach their peak values whenever light is sufficiently high. Maximal photosynthesis and growth rates have to be matched by correspondingly high respiration rates. Photoacclimation can be used to optimize biomass and target product yields in biotechnological applications. KEY WORDS: Photoacclimation · Photoadaptation · Pigments · Xanthophyll cycle · Photosynthesis · Phytoplankton · Algae Full text in pdf format PreviousNextCite this article as: Dubinsky Z, Stambler N (2009) Photoacclimation processes in phytoplankton: mechanisms, consequences, and applications. Aquat Microb Ecol 56:163-176. https://doi.org/10.3354/ame01345 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 56, No. 2-3. Online publication date: September 03, 2009 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2009 Inter-Research.