The unicellular green alga Chlamydomonas reinhardtii acclimates to low-CO.sub.2 (LC) conditions by actively transporting inorganic carbon (Ci) into the cell, resulting in an increase in ...photosynthetic efficiency. This mechanism is called the carbon-concentrating mechanism (CCM), and soluble protein LCIB is essential for the CCM. LCIB is localized in the vicinity of pyrenoid, a prominent structure in the chloroplast, under LC conditions in the light. In contrast, in the dark or in high-CO.sub.2 conditions, where the CCM is inactive, LCIB diffuses away from the pyrenoid. Although the functional importance of LCIB for the CCM has been shown, the significance and mechanism of the change in suborganellar localization of LCIB remain to be elucidated. In this study, we screened 13,000 DNA-tagged mutants and isolated twelve aberrant LCIB localization (abl) mutants under LC conditions. abl-1 and abl-3 with dispersed and speckled localization of LCIB in the chloroplast showed significant decreases in Ci affinity, Ci accumulation, and CO.sub.2 fixation. Ten abl mutants (abl-1, abl-3, abl-4, abl-5, abl6, abl-7, abl-8, abl-9, abl-11, and abl-12) showed not only aberrant LCIB localization but also reduced pyrenoid sizes. Moreover, three abl mutants (abl-10, abl-11, and abl-12) showed the increased numbers of pyrenoids per cell. These results suggested that the specific LCIB localization could be related to pyrenoid development. Keywords Chlamydomonas reinhardtii * Carbonconcentrating mechanism * LCIB * Pyrenoid
For both ecologists and physiologists, foliar physioecology as a function of spatially and temporally variable environmental factors such as sunlight exposure within a tree crown is important for ...understanding whole tree physiology and for predicting ecosystem carbon balance and productivity. Hence, we studied concentrations of nitrogen (N), non-structural carbohydrates (NSC = soluble sugars + starch), and delta.sup.13 C in different-aged needles within Pinus koraiensis tree crowns, to understand the needle age- and crown position-related physiology, in order to test the hypothesis that concentrations of N, NSC, and delta.sup.13 C are needle-age and crown position dependent (more light, more photosynthesis affecting N, NSC, and delta.sup.13 C), and to develop an accurate sampling strategy. The present study indicated that the 1-yr-old needles had significantly higher concentration levels of mobile carbohydrates (both on a mass and an area basis) and N.sub.area (on an area basis), as well as NSC-N ratios, but significantly lower levels of N.sub.mass (on a mass basis) concentration and specific leaf area (SLA), compared to the current-year needles. Azimuthal (south-facing vs. north-facing crown side) effects were found to be significant on starch both on a mass (ST.sub.mass) and an area basis (ST.sub.area ), delta.sup.13 C values, and N.sub.area, with higher levels in needles on the S-facing crown side than the N-facing crown side. Needle N.sub.mass concentrations significantly decreased but needle ST.sub.mass, ST.sub.area, and delta.sup.13 C values significantly increased with increasing vertical crown levels. Our results suggest that the sun-exposed crown position related to photosynthetic activity and water availability affects starch accumulation and carbon isotope discrimination. Needle age associated with physiological activity plays an important role in determining carbon and nitrogen physiology. The present study indicates that across-scale sampling needs to carefully select tissue samples with equal age from a comparable crown position.
In terrestrial plants, strigolactones act as multifunctional endo- and exo-signals. On microalgae, the strigolactones determine akin effects: induce symbiosis formation with fungi and bacteria and ...enhance photosynthesis efficiency and accumulation of biomass. This work aims to synthesize and identify strigolactone mimics that promote photosynthesis and biomass accumulation in microalgae with biotechnological potential. Novel strigolactone mimics easily accessible in significant amounts were prepared and fully characterized. The first two novel compounds contain 3,5-disubstituted aryloxy moieties connected to the bioactive furan-2-one ring. In the second group of compounds, a benzothiazole ring is connected directly through the cyclic nitrogen atom to the bioactive furan-2-one ring. The novel strigolactone mimics were tested on Chlorella sorokiniana NIVA-CHL 176. All tested strigolactones increased the accumulation of chlorophyll b in microalgae biomass. The SL-F3 mimic, 3-(4-methyl-5-oxo-2,5-dihydrofuran-2-yl)-3H-benzothiazol-2-one (7), proved the most efficient. This compound, applied at a concentration of 10sup.−7 M, determined a significant biomass accumulation, higher by more than 15% compared to untreated control, and improved the quantum yield efficiency of photosystem II. SL-F2 mimic, 5-(3,5-dibromophenoxy)-3-methyl-5H-furan-2-one (4), applied at a concentration of 10sup.−9 M, improved protein production and slightly stimulated biomass accumulation. Potential utilization of the new strigolactone mimics as microalgae biostimulants is discussed.
Far‐red photons (701–750 nm) are abundant in sunlight but are considered inactive for photosynthesis and are thus excluded from the definition of photosynthetically active radiation (PAR; 400–700 ...nm). Several recent studies have shown that far‐red photons synergistically interact with shorter wavelength photons to increase leaf photochemical efficiency. The value of far‐red photons in canopy photosynthesis has not been studied. Here, we report the effects of far‐red photons on single leaf and canopy photosynthesis in 14 diverse crop species. Adding far‐red photons (up to 40%) to a background of shorter wavelength photons caused an increase in canopy photosynthesis equal to adding 400–700 nm photons. Far‐red alone minimally increased photosynthesis. This indicates that far‐red photons are equally efficient at driving canopy photosynthesis when acting synergistically with traditionally defined photosynthetic photons. Measurements made using LEDs with peak wavelength of 711, 723, or 746 nm showed that the magnitude of the effect was less at longer wavelengths. The consistent response among diverse species indicates that the mechanism is common in higher plants. These results suggest that far‐red photons (701–750 nm) should be included in the definition of PAR.
Canopy photosynthetic responses of 14 species indicate that far‐red photons (701–750 nm) are equally efficient at driving photosynthesis when acting synergistically with traditionally defined photosynthetic photons (400–700 nm).
Thickness of cotton fiber, referred to as fiber maturity, is a key determinant of fiber quality, lint yield, and textile performance. The cotton immature fiber (im) mutant has been used to study ...fiber maturity since its fiber is thinner than the wild type near isogeneic line (NIL), Texas Marker-1 (TM-1). The im phenotype is caused by a single recessive mutation of a pentatricopeptide repeat (PPR) gene that reduces the activity of mitochondrial complex I and up-regulates stress responsive genes. However, the mechanisms altering the stress responses in im mutant are not well understood. Thus, we characterized growth and gas exchange in im and TM-1 under no stress and also investigated their stress responses by comparing gas exchange and transcriptomic profiles under high temperature. Phenotypic differences were detected between the NILs in non-fiber tissues although less pronounced than the variation in fibers. At near optimum temperature (28±3°C), im maintained the same photosynthetic performance as TM-1 by means of greater stomatal conductance. In contrast, under high temperature stress (>34°C), im leaves reduced photosynthesis by decreasing the stomatal conductance disproportionately more than TM-1. Transcriptomic analyses showed that the genes involved in heat stress responses were differentially expressed between the NIL leaves. These results indicate that the im mutant previously reported to have low activity of mitochondrial complex I displays increased thermosensitivity by impacting stomatal conductance. They also support a notion that mitochondrial complex I activity is required for maintenance of optimal photosynthetic performance and acclimation of plants to high temperature stress. These findings may be useful in the future efforts to understand how physiological mechanisms play a role in determining cotton fiber maturity and may influence stress responses in other crops.
Oxygenic phototrophs have played a fundamental role in Earth’s history by enabling the rise of atmospheric oxygen (O₂) and paving the way for animal evolution. Understanding the origins of oxygenic ...photosynthesis and Cyanobacteria is key when piecing together the events around Earth’s oxygenation. It is likely that photosynthesis evolved within bacterial lineages that are not extant, so it can be challenging when studying the early history of photosynthesis. Recent genomic and molecular evolution studies have transformed our understanding about the evolution of photosynthetic reaction centres and the evolution of Cyanobacteria. The evidence reviewed here highlights some of the most recent advances on the origin of photosynthesis both at the genomic and gene family levels.
Isotope ratios of tree-ring cellulose are a prominent tool to reconstruct paleoclimate and plant responses to environmental variation. Current models for cellulose isotope ratios assume a transfer of ...the environmental signals recorded in bulk leaf water to carbohydrates and ultimately into stem cellulose. However, the isotopic signal of carbohydrates exported from leaf to branch may deviate from mean leaf values if spatial heterogeneity in isotope ratios exists in the leaf. We tested whether the isotopic heterogeneity previously observed along the length of a ponderosa pine (Pinus ponderosa) leaf water was preserved in photosynthetic products. We observed an increase in both sugar and bulk tissue delta.sup.18O values along the needle, but the increase in carbohydrate delta.sup.18O values was dampened relative to the trend observed in leaf water. In contrast, delta.sup.13C values of both sugar and bulk organic matter were invariant along the needle. Phloem-exported sugar measured in the branch below the needles did not match whole-needle values of delta.sup.18O or delta.sup.13C. Instead, there was a near-constant offset observed between the branch and needle sugar delta.sup.13C values, while branch delta.sup.18O values were most similar to delta.sup.18O values observed for sugar at the base of the needle. The observed offset between the branch and needle sugar delta.sup.18O values likely arises from partial isotope oxygen exchange between sugars and water during phloem loading and transport. An improved understanding of the conditions producing differential delta.sup.13C and delta.sup.18O isotope effects between branch phloem and needle sugars could improve tree-ring-based climate reconstructions.
Photosynthetic manipulation provides new opportunities for enhancing crop yield. However, understanding and quantifying the importance of individual and multiple manipulations on the seasonal biomass ...growth and yield performance of target crops across variable production environments is limited. Using a state‐of‐the‐art cross‐scale model in the APSIM platform we predicted the impact of altering photosynthesis on the enzyme‐limited (Ac) and electron transport‐limited (Aj) rates, seasonal dynamics in canopy photosynthesis, biomass growth, and yield formation via large multiyear‐by‐location crop growth simulations. A broad list of promising strategies to improve photosynthesis for C3 wheat and C4 sorghum were simulated. In the top decile of seasonal outcomes, yield gains were predicted to be modest, ranging between 0% and 8%, depending on the manipulation and crop type. We report how photosynthetic enhancement can affect the timing and severity of water and nitrogen stress on the growing crop, resulting in nonintuitive seasonal crop dynamics and yield outcomes. We predicted that strategies enhancing Ac alone generate more consistent but smaller yield gains across all water and nitrogen environments, Aj enhancement alone generates larger gains but is undesirable in more marginal environments. Large increases in both Ac and Aj generate the highest gains across all environments. Yield outcomes of the tested manipulation strategies were predicted and compared for realistic Australian wheat and sorghum production. This study uniquely unpacks complex cross‐scale interactions between photosynthesis and seasonal crop dynamics and improves understanding and quantification of the potential impact of photosynthesis traits (or lack of it) for crop improvement research.
Summary Statement
Grain yield per area information of photosynthetically manipulated crop plants is limited. Cross‐scale modelling predicted how growth dynamics of wheat and sorghum crops can be affected and quantified various manipulation impacts on grain yield in multiple environments for crop improvement research.
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