SciCombinator

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Concept: Chlorophyll

161

While photosystem II (PSII) of plants utilizes light for photosynthesis, part of the absorbed energy may be reverted back and dissipated as long-term fluorescence (delayed fluorescence or DF). Because the generation of DF is coupled with the processes of forward photosynthetic activities, DF contains the information about plant physiological states and plant-environment interactions. This makes DF a potentially powerful biosensing mechanism to measure plant photosynthetic activities and environmental conditions. While DF has attracted the interest of many researchers, some aspects of it are still unknown because of the complexity of photosynthetic system. In order to provide a holistic picture about the usefulness of DF, it is meaningful to summarize the research on DF applications. In this short review, available literature on applications of DF from PSII is summarized.

Concepts: Photosynthesis, Oxygen, Plant, Photosystem, Chlorophyll, Photosystem II, Oxygen evolution, Light-dependent reactions

119

The value of a leaf to a plant depends on the fate of its exported assimilates. When these are translocated and used in the growth of new leaves they contribute to further carbon assimilation. The result is that their value to the plant is greatest while they are young. In contrast, when assimilates are translocated to storage, assimilates produced early and late in the life of a leaf are of equal value. This arguments is developed in relation to the optimal distribution of mineral resources and defenses during the life of leaves.

Concepts: Photosynthesis, Water, Fern, Epidermis, Leaf, Plant morphology, Chlorophyll, Gymnosperm

34

Global estimates of terrestrial gross primary production (GPP) remain highly uncertain, despite decades of satellite measurements and intensive in situ monitoring. We report a new approach for quantifying the near-infrared reflectance of terrestrial vegetation (NIRV). NIRV provides a foundation for a new approach to estimate GPP that consistently untangles the confounding effects of background brightness, leaf area, and the distribution of photosynthetic capacity with depth in canopies using existing moderate spatial and spectral resolution satellite sensors. NIRV is strongly correlated with solar-induced chlorophyll fluorescence, a direct index of photons intercepted by chlorophyll, and with site-level and globally gridded estimates of GPP. NIRV makes it possible to use existing and future reflectance data as a starting point for accurately estimating GPP.

Concepts: Photosynthesis, Carbon dioxide, Plant, Photosystem, Leaf, Chlorophyll, Primary production, Chemosynthesis

30

Plants cannot change location to escape stressful environments. Therefore, plants evolved to respond and acclimate to diverse stimuli, including the seemingly innocuous touch stimulus [1-4]. Although some species, such as Venus flytrap, have fast touch responses, most plants display more gradual touch-induced morphological alterations, called thigmomorphogenesis [2, 3, 5, 6]. Thigmomorphogenesis may be adaptive; trees subjected to winds develop less elongated and thicker trunks and thus are less likely damaged by powerful wind gusts [7]. Despite the widespread relevance of thigmomorphogenesis, the regulation that underlies plant mechanostimulus-induced morphological responses remains largely unknown. Furthermore, whether thigmomorphogenesis confers additional advantage is not fully understood. Although aspects of thigmomorphogenesis resemble ethylene effects [8], and touch can induce ethylene synthesis [9, 10], Arabidopsis ethylene response mutants show touch-induced thigmomorphogenesis [11]; thus, ethylene response is nonessential for thigmomorphogenesis. Here we show that jasmonate (JA) phytohormone both is required for and promotes the salient characteristics of thigmomorphogenesis in Arabidopsis, including a touch-induced delay in flowering and rosette diameter reduction. Furthermore, we find that repetitive mechanostimulation enhances Arabidopsis pest resistance in a JA-dependent manner. These results highlight an important role for JA in mediating mechanostimulus-induced plant developmental responses and resultant cross-protection against biotic stress.

Concepts: Organism, Plant, Chlorophyll, Ethylene, Wind, Perennial plant, Rapid plant movement, Venus Flytrap

29

The machinery that conducts the light-driven reactions of oxygenic photosynthesis is hosted within specialized paired membranes called thylakoids. In higher plants, the thylakoids are segregated into two morphological and functional domains called grana and stroma lamellae. A large fraction of the luminal volume of the granal thylakoids is occupied by the oxygen-evolving complex of photosystem II. Electron microscopy data we obtained on dark- and light-adapted Arabidopsis thylakoids indicate that the granal thylakoid lumen significantly expands in the light. Models generated for the organization of the oxygen-evolving complex within the granal lumen predict that the light-induced expansion greatly alleviates restrictions imposed on protein diffusion in this compartment in the dark. Experiments monitoring the redox kinetics of the luminal electron carrier plastocyanin support this prediction. The impact of the increase in protein mobility within the granal luminal compartment in the light on photosynthetic electron transport rates and processes associated with the repair of photodamaged photosystem II complexes is discussed.

Concepts: Cyanobacteria, Photosynthesis, Chloroplast, Plastocyanin, Chlorophyll, Thylakoid, Light-dependent reactions, ATP synthase

28

Terrestrial laser scanning (TLS) data allow spatially explicit (x, y, z) laser return intensities to be recorded throughout a plant canopy, which could considerably improve our understanding of how physiological processes vary in three-dimensional space. However, the utility of TLS data for the quantification of plant physiological properties remains largely unexplored. Here, we test whether the laser return intensity of green (532-nm) TLS correlates with changes in the de-epoxidation state of the xanthophyll cycle and photoprotective non-photochemical quenching (NPQ), and compare the ability of TLS to quantify these parameters with the passively measured photochemical reflectance index (PRI). We exposed leaves from five plant species to increasing light intensities to induce NPQ and de-epoxidation of violaxanthin (V) to antheraxanthin (A) and zeaxanthin (Z). At each light intensity, the green laser return intensity (GLRI), narrowband spectral reflectance, chlorophyll fluorescence emission and xanthophyll cycle pigment composition were recorded. Strong relationships between both predictor variables (GLRI, PRI) and both explanatory variables (NPQ, xanthophyll cycle de-epoxidation) were observed. GLRI holds promise to provide detailed (mm) information about plant physiological status to improve our understanding of the patterns and mechanisms driving foliar photoprotection. We discuss the potential for scaling these laboratory data to three-dimensional canopy space.

Concepts: Photosynthesis, Fluorescence, Light, Dimension, Leaf, Chlorophyll, LIDAR

27

Traditionally, it was believed that C4 photosynthesis required two types of chlorenchyma cells to concentrate CO2 within the leaf. However, several species have been identified that perform C4 photosynthesis using dimorphic chloroplasts within an individual cell. The goal of this research was to determine how growth under limited light affects leaf structure, biochemistry and efficiency of the single-cell CO2 -concentrating mechanism in Bienertia sinuspersici. Measurements of rates of CO2 assimilation and CO2 isotope exchange in response to light intensity and O2 were used to determine the efficiency of the CO2 -concentrating mechanism in plants grown under moderate and low light. In addition, enzyme assays, chlorophyll content and light microscopy of leaves were used to characterize acclimation to light-limited growth conditions. There was acclimation to growth under low light with a decrease in capacity for photosynthesis when exposed to high light. This was associated with a decreased investment in biochemistry for carbon assimilation with only subtle changes in leaf structure and anatomy. The capture and assimilation of CO2 delivered by the C4 cycle was lower in low-light-grown plants. Low-light-grown plants were able to acclimate to maintain structural and functional features for the performance of efficient single-cell C4 photosynthesis.

Concepts: Photosynthesis, Carbon dioxide, Plant, Calvin cycle, Leaf, Chlorophyll, C3 carbon fixation, Crassulacean acid metabolism

27

Nitrogen use efficiency (NUE) is relatively low in oilseed rape (Brassica napus L.) due to weak nitrogen remobilization during leaf senescence. Monitoring the kinetics of water distribution associated with the re-organization of cell structures would therefore be valuable to improve characterization of nutrient recycling in leaf tissues and the associated senescence processes. In this study, NMR Relaxometry was used to describe water distribution and status at the cellular level in different leaf ranks of well-watered plants. It was shown to be able to detect slight variations in the evolution of senescence. The NMR results were linked to physiological characterization of the leaves and to light and electron micrographs. A relationship between cell hydration and leaf senescence was revealed and associated with changes in the NMR signal. The relative intensities and the transverse relaxation times of the NMR signal components associated with vacuole water were positively correlated with senescence, describing water uptake and vacuole and cell enlargement. Moreover, the relative intensity of the NMR signal that we assigned to the chloroplast water decreased during the senescence process, in agreement with the decrease in relative chloroplast volume estimated from micrographs. The results are discussed on the basis of water flux occurring at the cellular level during senescence. One of the main applications of this study would be for plant phenotyping, especially for plants under environmental stress such as nitrogen starvation.

Concepts: Photosynthesis, Plant, Rapeseed, Brassica, Chlorophyll

27

The thylakoid-transfer signal is required for energy-dependent translocation of preproteins into the thylakoid lumen and is removed by the thylakoidal processing peptidase (TPP). PGRL1 is an essential component of antimycin A-sensitive photosynthetic cyclic electron flow in chloroplasts. Here we report that one of the TPP isoforms, Plsp1, forms a stable complex with PGRL1. Genetic data demonstrate that PGRL1 is not essential for Plsp1 activity in vivo, leading to a possibility that PGRL1 may act as a regulator of TPP. STRUCTURED SUMMARY OF PROTEIN INTERACTIONS:: PLSP1physically interactswithPGRL1Bbypull down(View interaction) PLSP1physically interactswithPGRL1B,PGRL1AandCASbypull down(View interaction).

Concepts: DNA, Cyanobacteria, Photosynthesis, Chloroplast, Emergence, Chlorophyll, Thylakoid, Light-dependent reactions

27

The embryos of some angiosperm taxa contain chlorophyll and this chlorophyllous stage is persisting until the embryo matures (further referred as chloroembryos). Besides being chlorophyllous, these embryos seem to have the ability to photosynthesize. This suggests that the chlorophyllous state of the embryo has an important role in seed development. The photosynthesis of chloroembryos is highly shade adaptive in nature as it is embedded within the supporting tissues (several layers of pod wall, seed coat and endosperm). Moreover, these chloroembryos are developing in a highly osmotic environment, and contain various components of the photosynthetic machinery. Detailed studies were performed in these chloroembryos in order to elucidate the structure of the chloroplasts, pigment composition, the photochemical activities, the rate of carbon assimilation and also the shade adaptive features. It has been shown that the respired CO2 within these chloroembryos is recycled by the efficient photosynthetic components of the chloroembryos and thus potentially influences the seed’s carbon economy. Thus, the major role of embryonic photosynthesis is to produce both energy-rich molecules and oxygen, of which the former can be directly used for biosynthesis. During embryogenesis oxygen production is especially important, in a situation wherein the oxygen is limited within the enclosed seed. As these chloroembryos grow in an environment of a sugar rich endosperm, it requires some adaptive mechanisms in this high osmotic environment. The additional polypeptides found in the thylakoids of chloroembryo chloroplasts in comparison to the thylakoids of leaf chloroplast have been suggested to have a role in protecting the photosynthetic components in the chloroembryos in an environment of high osmotic strength. An attempt to understand osmotic stress tolerance existing in these chloroembryos may lead to a better understanding of tolerance of photosynthesis to osmotic stress.

Concepts: Cyanobacteria, Photosynthesis, Oxygen, Carbon dioxide, Chloroplast, Plant, Chlorophyll, Thylakoid