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Variability between individuals can cause error in plant physiology studies when measurements or treatments occur on a chronological basis. Thus, plant growth indices such as the Quercus morphological index (QMI) were developed, enabling distinctions between exogenous treatment effects and endogenous ontological effects. Few studies have examined posttransplant northern red oak (Quercus rubra L.) seedling physiology in relation to the QMI. We used [sup.14]C[O.sub.2] to label current photosynthate of post-transplant northern red oak seedlings during the first flush to assess endogenous patterns of current photosynthate translocation. Carbon translocation patterns relative to QMI growth stages of post-transplant seedlings resembled those described in pre-transplant seedlings, with expanding leaves and shoots retaining the majority of current photosynthate early in the flush, followed by increases in downward translocation to both new and old roots during the lag stage, when active aboveground growth ceased for the flush. Early post-transplant growth of new shoots relied heavily on stored carbohydrates, and old shoots demonstrated negligible sink strength for current photosynthate throughout the experiment. Our findings emphasize the importance of stored carbohydrates for early post-transplant growth and suggest that QMI-based observations regarding carbohydrate translocation patterns of pre-transplant seedlings in this species remain largely valid for post-transplant seedlings. Key words: carbon translocation, growth index, episodic growth, ontogeny, Quercus morphological index. La variabilite entre les individus peut entrainer des erreurs dans les etudes en physiologie vegetale lorsque les mesures et les traitements sont effectues sur une base chronologique. Par consequent, les indices de croissance vegetale, tels que l'indice morphologique des chenes (QMI), ont ete elabores pour permettre de distinguer entre les effets exogenes des traitements et les effets endogenes d'origine ontologique. Peu d'etudes ont examine la physiologie des semis de chene rouge (Quercus rubra L.) apres transplantation en relation avec le QMI. Nous avons utilise le [sup.14]C[O.sub.2] pour marquer le photosynthetate courant apres la transplantation de semis de chene rouge, durant la premiere poussee de croissance, pour evaluer le profil endogene de translocation du photosynthetate. Les profils de translocation du carbone en lien avec le QMI des stades de croissance des semis apres transplantation ressemblent a ceux qui ont ete decrits chez les semis avant transplantation. Les feuilles et les pousses en expansion retiennent alors la majorite du photosynthetate courant au debut de la poussee de croissance. Par la suite, on observe des augmentations de la translocation vers le bas, vers les nouvelles et vieilles racines durant le stade de ralentissement, lorsque la croissance aerienne active cesse. La croissance initiale apres transplantation des nouvelles pousses dependait largement des hydrates de carbone emmagasines et l'activite des vieilles pousses en tant que puits pour le photosynthetate courant a ete negligeable tout au long de l'experience. Nos resultats font ressortir l'importance des reserves d'hydrates de carbone pour la croissance initiale apres transplantation et indiquent que les observations fondees sur le QMI au sujet des profils de translocation des hydrates de carbone avant transplantation demeurent largement valides apres transplantation chez les semis de cette espece. [Traduit par la Redaction] Mots-cles : translocation du carbone, indice de croissance, croissance episodique, ontogenie, indice morphologique des chenes., Introduction A source of error in plant biology studies occurs when individuals are measured on a strictly chronological basis (Erickson and Michelini 1957; Hanson et al. 1986; Coleman and McConnaughay [...]

Giant clams Tridacna crocea harbor symbiotic zooxanthellae in tubular systems and display high growth rate when exposed to light. Light/dark alternation plays an important role in growth performance and physiological change of giant clam-zooxanthellae symbiosis in natural ecosystems. In this study, photosynthetic performance, antioxidant enzymes, transcriptome, and expression of eight illumination-related genes were investigated in the mantle of giant clam at different treatment times of 12-h light/12-h dark (15,000 lx). (1) The effective photochemical quantum yield of PSII (Y(II)) was high in the early morning, but significantly decreased to a low level at 6 h of light treatment (P < 0.05), and recovered slightly thereafter during light, then dropped at night; (2) Superoxide dismutase (SOD) and catalase (CAT) activity in the clam mantle increased slightly, and peaked at 6 h of light treatment (201.23 U/mg protein and 20.95 U/mg protein, respectively). This was significantly different (P < 0.05) to the results of SOD and CAT activities, exposed to 12 h of dark treatment; (3) Six paired-end libraries were sequenced in 3 h of light and 12 h of dark treatments. Through the assembling of 310,548,208 of clean reads with lengths of 150 bp, a total of 463,645 unigenes were obtained, which mostly derived from giant clam. Bioinformatics analysis revealed that 14,036 genes were up-regulated and 44,361 genes were down-regulated in 3 h of light treatment; (4) The results of quantitative real-time PCR demonstrated that the expression related to circadian rhythm (Bmal1 and NFIL3), antioxidant enzymes (SOD and CAT) and sodium- and chloride-dependent taurine transporters (SLC6A6) of giant clam, as well as photosynthesis (psbA and rbcl) of symbiotic zooxanthellae peaked at ~ 6 h of light phase, except of psbA at 1 h of light treatment. This study provides information on the light-adaptive mechanisms of giant clam-zooxanthellae symbiosis during daily light and dark cycles., Author(s): Chunsheng Liu [sup.1] [sup.2] [sup.3] , Xiaoyu Yang [sup.2] [sup.3] , Yun Sun [sup.1] [sup.2] [sup.3] , Yumei Yang [sup.2] [sup.3] , Aimin Wang [sup.1] [sup.2] [sup.3] , Linwen [...]

Resting cysts represent the dormant life stage produced by sexual reproduction of dinoflagellates; it generally maintain a limited level of metabolic activities. In the present study, changes in the photosynthetic apparatus of Akashiwo sanguinea during the encystment process in different nitrogen (N) conditions were characterized, and the transcriptional responses of nine photosynthesis genes were further evaluated. The photochemical efficiency decreased with elevation of N deprivation and growth of algae, and the resting cysts maintained limited photosynthetic activity. Meanwhile, the transcription of photosystem II genes (psbA and psbD) were down-regulated, especially the levels of the psbA gene, suggesting the inactivation of photosystem II under N limitation. Moreover, genes involved in cytochrome f (petA) and ATP synthase (atpA, atpB) were also transcribed at low levels in N-deprivation cultures. In contrast, the transcription of the RubisCO large subunit gene (rbcL) was up-regulated, indicating the maintenance of carbon fixation in N-limited conditions. The transcription levels of photosystem I genes (psaA and psaB) showed no significant correlation with the N condition. Further, most of the photosynthesis genes were down-regulated in the resting cysts, which was coincided with the inactive physiological status of the dormant stage. The results demonstrated that photosynthesis genes are differentially regulated in response to varying N conditions and life cycles. The findings will provide fundamental knowledge for better understanding the physiological characteristics and molecular regulation mechanisms in the developmental life cycle of marine dinoflagellates., Author(s): Yun Liu [sup.1] [sup.2] [sup.3], Tiantian Chen [sup.1] [sup.2] [sup.3], Xiaoting Wang [sup.4], Shuqun Song [sup.1] [sup.2] [sup.3], Caiwen Li [sup.1] [sup.2] [sup.3] [sup.5] Author Affiliations: (1) grid.9227.e, 0000000119573309, [...]

Some species of planktic foraminifera inhabiting oligotrophic surface water environments are in an obligate symbiotic relationship with dinoflagellate microalgae, which can assimilate carbon (C) through photosynthesis. However, the mechanism and dynamics of C photosynthate translocation to the foraminiferal host, and related benefits for the dinoflagellates in this symbiotic association, are poorly constrained. As a consequence, the role of planktic foraminifera as autotroph organisms in ocean surface ecosystems is not well understood. Here, we performed pulse-chase experiments with .sup.13C-enriched dissolved inorganic carbon, followed by TEM and quantitative NanoSIMS isotopic imaging to visualize photosynthetic C assimilation by individual symbiotic dinoflagellates and subsequent translocation to their Orbulina universa host. Although most of the dinoflagellate population migrates out of the host endoplasm onto external spines during the day, our observations show that a small fraction remains inside the host cell during daytime. All symbionts, whether outside or inside the foraminifera cell, effectively assimilate C into starch nodules during daytime photosynthesis. At the onset of night, all dinoflagellates from the exterior spine-ectoplasm region migrate back into the foraminiferal cell. During the night, respiration by dinoflagellates and carbon translocation to the host, likely in the form of lipids, greatly reduces the abundance of starch in dinoflagellates. Dinoflagellate mitosis is only observed at night, with a substantial contribution of carbon fixed during the previous day contributing to the production of new biomass., Author(s): Charlotte LeKieffre [sup.1] [sup.2] , Howard J. Spero [sup.3] , Ann D. Russell [sup.3] , Jennifer S. Fehrenbacher [sup.3] [sup.4] , Emmanuelle Geslin [sup.2] , Anders Meibom [sup.1] [sup.5] [...]

The SCHIC domain of the [B.sub.12]-binding domain family present in the Rhodobacter sphaeroides AppA protein binds heme and senses oxygen. Here we show that the predicted SCHIC domain PpaA/AerR regulators also bind heme and respond to oxygen in vitro, despite their low sequence identity with AppA. doi: 10.1128/JB.00736-10

Light is the source of energy for photosynthetic organisms; when in excess, however, it also drives the formation of reactive oxygen species and, consequently, photoinhibition. Plants and algae have evolved mechanisms to regulate light harvesting efficiency in response to variable light intensity so as to avoid oxidative damage. Nonphotochemical quenching (NPQ) consists of the rapid dissipation of excess excitation energy as heat. Although widespread among oxygenic photosynthetic organisms, NPQ shows important differences in its machinery. In land plants, such as Arabidopsis thaliana, NPQ depends on the presence of PSBS, whereas in the green alga Chlamydomonas reinhardtii it requires a different protein called LHCSR. In this work, we show that both proteins are present in the moss Physcomitrella patens. By generating KO mutants lacking PSBS and/or LHCSR, we also demonstrate that both gene products are active in NPQ. Plants lacking both proteins are more susceptible to high light stress than WT, implying that they are active in photoprotection. These results suggest that NPQ is a fundamental mechanism for survival in excess light and that upon land colonization, photosynthetic organisms evolved a unique mechanism for excess energy dissipation before losing the ancestral one found in algae. LHCSR | nonphotochemical quenching | photosystem | plants evolution | PSBS doi/ 10.1073/pnas.1002873107

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2009.01491.x Byline: Peter J. Vermeulen (1), Josef F. Stuefer (2), Niels P. R. Anten (1), Heinjo J. During (1) Keywords: canopy; coexistence; clonal; competition; exclusion; height; light; model; photosynthesis; resource acquisition Abstract: Summary Different views exist as to what traits will lead to dominance when plants compete for light. One view is that taller plants with better relative positions in the canopy will exclude shorter plants because they intercept almost all light and thus can achieve a higher carbon gain. Alternatively, resource competition models predict that plants that are capable of positive net photosynthesis at the lowest light level will win. In a 5-year-old dense competition experiment with 10 genotypes of the clonal plant Potentilla reptans, both these views were tested to see if either of them could explain the dominance of one of the genotypes, or the possible coexistence of several others. Using a combination of measured morphological and physiological traits, a canopy model was constructed to calculate whole-shoot daily photosynthetic rates of the genotypes in the different layers of the canopy in relation to the invested mass. Results show that the dominant genotype exhibited characteristics of relative shade tolerance: low rates of light-saturated photosynthesis and respiration. This resulted in a calculated daily carbon gain at the bottom of the canopy, where other genotypes could not achieve that. However, the dominant genotype did not have the highest photosynthetic rates throughout the whole canopy. Some genotypes that persisted in the stand in coexistence with the dominant one achieved greater daily carbon gain at the top of the canopy. Synthesis. The dominant genotype had characteristics similar to those predicted by resource competition models such as the ability to have positive growth at lower light levels. The persistence of several other genotypes, in contrast, may be explained by traits that allowed them to achieve higher carbon gains at the top of the canopy. This suggests that the light gradient formed by the plants themselves creates enough heterogeneity for strategies for dealing with different light requirements to coexist, even within a single species. Author Affiliation: (1)Department of Plant Ecology and Biodiversity, Institute of Environmental Biology, Utrecht University, PO Box 80084, 3508 TB Utrecht, The Netherlands (2)Experimental Plant Ecology, Institute for Water and Wetland Research, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands Article History: Received 3 September 2008; accepted 11 February 2009Handling Editor: Stephen Bonser Article note: (*) Correspondence author. E-mail: peterjvermeulen@gmail.com

Photosynthetic and respiratory exchanges of C[O.sub.2] by plants with the atmosphere are significantly larger than anthropogenic C[O.sub.2] emissions, and these fluxes will change as growing conditions are altered by climate change. Understanding feedbacks in C[O.sub.2] exchange is important to predicting future atmospheric [C[O.sub.2]] and climate change. At the tissue and plant scale, respiration is a key determinant of growth and yield. Although the stimulation of [C.sub.3] photosynthesis by growth at elevated [C[O.sub.2]] can be predicted with confidence, the nature of changes in respiration is less certain. This is largely because the mechanism of the respiratory response is insufficiently understood. Molecular, biochemical and physiological changes in the carbon metabolism of soybean in a free-air C[O.sub.2] enrichment experiment were investigated over 2 growing seasons. Growth of soybean at elevated [C[O.sub.2]] (550 [micro]mol x [mol.sup.-1]) under field conditions stimulated the rate of nighttime respiration by 37%. Greater respiratory capacity was driven by greater abundance of transcripts encoding enzymes throughout the respiratory pathway, which would be needed for the greater number of mitochondria that have been observed in the leaves of plants grown at elevated [C[O.sub.2]]. Greater respiratory quotient and leaf carbohydrate content at elevated [C[O.sub.2]] indicate that stimulated respiration was supported by the additional carbohydrate available from enhanced photosynthesis at elevated [C[O.sub.2]]. If this response is consistent across many species, the future stimulation of net primary productivity could be reduced significantly. Greater foliar respiration at elevated [C[O.sub.2]] will reduce plant carbon balance, but could facilitate greater yields through enhanced photoassimilate export to sink tissues. climate change | elevated C[O.sub.2] | free air C[O.sub.2] enrichment | metabolic | soybean

We studied the robustness of photosynthetic metabolism in the chloroplasts of [C.sub.3] plants under drought stress and at high C[O.sub.2] concentration conditions by using a method called Minimization of Metabolic Adjustment Dynamic Flux Balance Analysis (M_DFBA). Photosynthetic metabolism in the chloroplasts of [C.sub.3] plants applies highly cooperative regulation to minimize the fluctuation of metabolite concentration profiles in the face of transient perturbations. Our work suggests that highly cooperative regulation assures the robustness of the biological system and that there is closer cooperation under perturbation conditions than under normal conditions. This results in minimizing fluctuations in the profiles of metabolite concentrations, which is the key to maintaining a system's function. Our methods help in understanding such phenomena and the mechanisms of robustness for complex metabolic networks in dynamic processes. climate extremes | environmental stress | flux balance | metabolic control | metabolomics

The recent sequence analysis of the photosynthetic and plant-symbiotic Bradyrhizobium sp. strain BTAi1 revealed the unexpected presence of a pucBA operon encoding the apoproteins of peripheral light-harvesting (LH) complexes. This pucBA operon is found close to a bacteriophytochrome gene ([BphP3.sub.B BTAi1]) and a two-component transcriptional regulator gene ([TF.sub.BTAi1] gene). In this study, we show that [BphP3.sub.B BTAi1] acts as a bona fide bacteriophytochrome and controls, according to light conditions, the expression of the pucBA operon found in its vicinity. This light regulatory pathway is very similar to the one previously described for chromo-[BphP4.sub.RP] in Rhodopseudomonas palustris and conducts the synthesis of a peripheral LH complex. This LH complex presents a single absorption band at low temperature, centered at 803 nm. Fluorescence emission analysis of intact cells indicates that this peripheral LH complex does not act as an efficient light antenna. One putative function of this LH complex could be to evacuate excess light energy in order to protect Bradyrhizobium strain BTAi1, an aerobic anoxygenic photosynthetic bacterium, against photooxidative damage during photosynthesis.

Acaryochloris marina is a unique cyanobacterium that is able to produce chlorophyll d as its primary photosynthetic pigment and thus efficiently use far-red light for photosynthesis. Acaryochloris species have been isolated from marine environments in association with other oxygenic phototrophs, which may have driven the niche-filling introduction of chlorophyll d. To investigate these unique adaptations, we have sequenced the complete genome of A. marina. The DNA content of A. marina is composed of 8.3 million base pairs, which is among the largest bacterial genomes sequenced thus far. This large array of genomic data is distributed into nine single-copy plasmids that code for >25% of the putative ORFs. Heavy duplication of genes related to DNA repair and recombination (primarily recA) and transposable elements could account for genetic mobility and genome expansion. We discuss points of interest for the biosynthesis of the unusual pigments chlorophyll d and s-carotene and genes responsible for previously studied phycobilin aggregates. Our analysis also reveals that A. marina carries a unique complement of genes for these phycobiliproteins in relation to those coding for antenna proteins related to those in Prochlorococcus species. The global replacement of major photosynthetic pigments appears to have incurred only minimal specializations in reaction center proteins to accommodate these alternate pigments. These features clearly show that the genus Acaryochloris is a fitting candidate for understanding genome expansion, gene acquisition, ecological adaptation, and photosystem modification in the cyanobacteria. comparative microbial genomics | photosynthesis | oxygenic phototrophs | evolution

The lability of Rubisco activase function is thought to have a major role in the decline of leaf photosynthesis under moderate heat ( Key words: heat stress; photosynthesis; red maple; Rubisco activase; Rubisco large subunit; warming.

Research shows that the ccoNOQP operon and the rdxBHIS gene cluster are functionally and positionally related in Rhodobacter sphaeroides 2.4.1. The transcriptional activities of this DNA region suggest that the ccoNOQP- rdxBHIS cluster is transcribed in various forms, whose stoichiometry and their products play a role in controlling photosynthetic gene expression.

A proton-sucrose symporter mediates the key step in carbon export from leaves of most plants. Sucrose transport activity and steady-state mRNA levels of BvSUT1, a sugar beet leaf sucrose symporter, are negatively regulated specifically by sucrose. Results reported here show that BvSUT1 mRNA was localized to companion cells of the leaf's vascular system, which supports its role in the systemic distribution of photoassimilate. Immunoblot analysis showed that decreased transport activity was caused by a reduction in the abundance of symporter protein. RNA gel blot analysis of the leaf symporter revealed that message levels also declined, and nuclear run-on experiments demonstrated that this was the result of decreased transcription. Further analysis showed that symporter protein and message are both degraded rapidly. Taken together, these data show that phloem loading is regulated by means of sucrose-mediated changes in transcription of a phloem-specific sucrose symporter gene in a regulatory system that may play a pivotal role in balancing photosynthetic activity with resource utilization.