Biochemical models of photosynthesis use the temperature dependency of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) kinetics and mesophyll conductance to CO 2 (g m). However, the in vivo ...temperature response of Rubisco kinetics and g m has only been measured in the warm adapted Nicotiana tabacum; therefore, we determined these parameters in the cool-adapted Arabidopsis thaliana to see how species-dependent differences impact modeled rates of photosynthesis. While the individual Rubisco kinetic parameters in N. tabacum and A. thaliana were similar across temperatures, they collectively resulted in significantly different modeled rates of photosynthesis. Additionally, g m increased with temperature in N. tabacum but not in A. thaliana. Commentary: New challenges in modeling photosynthesis: temperature dependencies of Rubisco kinetics Biochemical models are used to predict and understand the response of photosynthesis to rising temperatures and CO2 partial pressures. These models require the temperature dependency of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) kinetics and mesophyll conductance to CO2 (gm). However, it is not known how the temperature response of Rubisco kinetics differs between species, and comprehensive in vivo Rubisco kinetics that include gm have only been determined in the warm-adapted Nicotiana tabacum. Here, we measured the temperature response of Rubisco kinetics and gm in N.tabacum and the cold-adapted Arabidopsis thaliana using gas exchange and 13CO2 isotopic discrimination on plants with genetically reduced levels of Rubisco. While the individual Rubisco kinetic parameters in N.tabacum and A.thaliana were similar across temperatures, they collectively resulted in significantly different modelled rates of photosynthesis. Additionally, gm increased with temperature in N.tabacum but not in A.thaliana. These findings highlight the importance of considering species-dependent differences in Rubisco kinetics and gm when modelling the temperature response of photosynthesis. PUBLICATION ABSTRACT
Dark CO.sub.2 fixation by bacteria is believed to be particularly important in oligotrophic ecosystems. However, only a few studies have characterized the role of bacterial dissolved inorganic carbon ...(DIC) fixation in global carbon dynamics. Therefore, this study quantified the primary production (PP), total bacteria dark CO.sub.2 fixation (TB.sub.DIC fixation), and heterotrophic bacterial production (HBP) in the warm and oligotrophic Red Sea using stable-isotope labeling and cavity ring-down spectroscopy (.sup.13 C-CRDS). Additionally, we assessed the contribution of bacterial DIC fixation (TB.sub.DIC %) relative to the total DIC fixation (total.sub.DIC fixation). Our study demonstrated that TB.sub.DIC fixation increased the total.sub.DIC fixation from 2.03 to 60.45 µg C L.sup.-1 d.sup.-1 within the photic zone, contributing 13.18 % to 71.68 % with an average value of 33.95 ± 0.02 % of the photic layer total.sub.DIC fixation. The highest TB.sub.DIC fixation values were measured at the surface and deep (400 m) water with an average value of 5.23 ± 0.45 and 4.95 ± 1.33 µg C L.sup.-1 d.sup.-1, respectively. These findings suggest that the non-photosynthetic processes such as anaplerotic DIC reactions and chemoautotrophic CO.sub.2 fixation extended to the entire oxygenated water column. On the other hand, the percent of TB.sub.DIC contribution to total.sub.DIC fixation increased as primary production decreased (R.sup.2 =0.45, p<0.0001), suggesting the relevance of increased dark DIC fixation when photosynthetic production was low or absent, as observed in other systems. Therefore, when estimating the total carbon dioxide production in the ocean, dark DIC fixation must also be accounted for as a crucial component of the carbon dioxide flux in addition to photosynthesis.
Arthrospira platensis, known as spirulina, is a cyanobacterium with multiple nutritional benefits, as it contains substantial amounts of proteins, fatty acids, and pigments. However, the production ...of this microalga has faced significant challenges, primarily related to the cost and composition of the required culture medium for its optimal growth. This study focused on optimizing two nitrogen sources (urea and potassium nitrate) to maximize the growth of A. platensis and the production of phycocyanin, a photosynthetic pigment of significant commercial value. Optimization was performed using the response surface methodology (RSM) with a central composite design (CCD). Analysis of variance (ANOVA) was employed to validate the model, which revealed that the different concentrations of urea were statistically significant (p < 0.05) for biomass and phycocyanin production. However, potassium nitrate (KNOsub.3) showed no significant influence (p > 0.05) on the response variables. The RSM analysis indicated that the optimal concentrations of KNOsub.3 and urea to maximize the response variables were 3.5 g Lsup.−1 and 0.098 g Lsup.−1, respectively. This study offers valuable perspectives for the efficient production of A. platensis while reducing production costs for its cultivation on a larger scale.
Csub.4 photosynthesis has evolved independently multiple times in grass lineages with nine anatomical and three biochemical subtypes. Chloridoideae represents one of the separate events and contains ...species of two biochemical subtypes, NAD-ME and PEP-CK. Assessment of Csub.4 photosynthesis diversification is limited by species sampling. In this study, the biochemical subtypes together with anatomical leaf traits were analyzed in 19 species to reveal the evolutionary scenario for diversification of Csub.4 photosynthesis in tribe Zoysieae (Chloridoideae). The effect of habitat on anatomical and biochemical diversification was also evaluated. The results for the 19 species studied indicate that 11 species have only NAD-ME as a decarboxylating enzyme, while eight species belong to the PEP-CK subtype. Leaf anatomy corresponds to the biochemical subtype. Analysis of Zoysieae phylogeny indicates multiple switches between PEP-CK and NAD-ME photosynthetic subtypes, with PEP-CK most likely as the ancestral subtype, and with multiple independent PEP-CK decarboxylase losses and its secondary acquisition. A strong correlation was detected between Csub.4 biochemical subtypes studied and habitat annual precipitation wherein NAD-ME species are confined to drier habitats, while PEP-CK species prefer humid areas. Structural adaptations to arid climate include increases in leaf thickness and interveinal distance. Our analysis suggests that multiple loss of PEP-CK decarboxylase could have been driven by climate aridization followed by continued adaptive changes in leaf anatomy.
Rhodopseudomonas palustris is a species of purple photosynthetic bacteria that has a multigene family of puc genes that encode the alpha and beta apoproteins, which form the LH2 complexes. A genetic ...dissection strategy has been adopted in order to try and understand which spectroscopic form of LH2 these different genes produce. This paper presents a characterisation of one of the deletion mutants generated in this program, the pucBA.sub.d only mutant. This mutant produces an unusual spectroscopic form of LH2 that only has a single large NIR absorption band at 800 nm. Spectroscopic and pigment analyses on this complex suggest that it has basically a similar overall structure as that of the wild-type HL LH2 complex. The mutant has the unique phenotype where the mutant LH2 complex is only produced when cells are grown at LL. At HL the mutant only produces the LH1-RC core complex.
Since it was established that the early hominins of the Cradle of Humankind in South Africa ate sup.13C-enriched foods that may have included sedges with Csub.4 photosynthetic pathways, much work has ...focused on the reconstruction of hominin dietary ecologies in both southern and eastern Africa. Through the years emphasis was placed on Cyperus papyrus as a possible source, even inspiring an 'aquatic diet' hypothesis for all hominins. Baboon feeding habits and sedge regimes observed in South Africa's 'Lowveld' have provided a proxy for the dietary ecology of the southern 'Highveld' hominins, and from the Cradle of Humankind sedges, amongst other plants, have been collected for nutritional studies. To date, however, there has been no attempt to compile an inventory of the sedge species currently growing in the demarcated area of the Cradle of Humankind. Here I list 29 Cyperaceae taxa currently recorded as growing in the Cradle of Humankind. I show that, contrary to previous inference, most of them have Csub.4 photosynthetic pathways and do not need aquatic ecologies or permanent wetland settings. I discuss and provide photographic records for the six species identified as current baboon and human foodplants, and highlight Cyperus esculentus as a possible nutritious and prolific Csub.4-sedge-USO food source for southern African hominins based on its energy, protein and fat/lipid profile. Keywords: Cyperaceae, hominin diet, wetland hypothesis, nutrition, yellow nutsedge, patrysuintjies
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
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