Co-regulation of dark and light reactions in three biochemical subtypes of C(4) species.

Regulation of light harvesting in response to changes in light intensity, CO(2) and O(2) concentration was studied in C(4) species representing three different metabolic subtypes: Sorghum bicolor (NADP-malic enzyme), Amaranthus edulis (NAD-malic enzyme), and Panicum texanum (PEP-carboxykinase). Several photosynthetic parameters were measured on the intact leaf level including CO(2) assimilation rates, O(2) evolution, photosystem II activities, thylakoid proton circuit and dissipation of excitation energy. Gross rates of O(2) evolution (J(O)₂'), measured by analysis of chlorophyll fluorescence), net rates of O(2) evolution and CO(2) assimilation responded in parallel to changes in light and CO(2) levels.

Feedback limitation of photosynthesis at high CO acts by modulating the activity of the chloroplast ATP synthase.

It was previously shown that photosynthetic electron transfer is controlled under low CO via regulation of the chloroplast ATP synthase. In the current work, we studied the regulation of photosynthesis under feedback limiting conditions, where photosynthesis is limited by the capacity to utilise triose-phosphate for synthesis of end products (starch or sucrose), in a starch-deficient mutant of Nicotiana sylvestris Speg. & Comes.

Structural, biochemical, and physiological characterization of photosynthesis in two C4 subspecies of Tecticornia indica and the C3 species Tecticornia pergranulata (Chenopodiaceae).

Among dicotyledon families, Chenopodiaceae has the most C(4) species and the greatest diversity in structural forms of C(4). In subfamily Salicornioideae, C(4) photosynthesis has, so far, only been found in the genus Halosarcia which is now included in the broadly circumscribed Tecticornia. Comparative anatomical, cytochemical, and physiological studies on these taxa, which have near-aphyllous photosynthetic shoots, show that T.

Response of mannitol-producing Arabidopsis thaliana to abiotic stress.

In celery, mannitol is a primary photosynthetic product that is associated with celery's exceptional salt tolerance. Arabidopsis plants transformed with celery's mannose-6-phosphate reductase (M6PR) gene produce mannitol and grow normally in the absence of stress. Daily analysis of the increase in growth (fresh and dry weight, leaf number, leaf area per plant and specific leaf weight) over a 12-day period showed less effect of salt (100 mm NaCl) on the M2 transformant than wild type (WT).

Flowers of Bienertia cycloptera and Suaeda aralocaspica (Chenopodiaceae) complete the life cycle performing single-cell C photosynthesis.

Leaves and cotyledons of the terrestrial C plants, Bienertia cycloptera Bunge ex Boiss. and Suaeda aralocaspica (Bunge) Freitag & Schütze (Chenopodiaceae), accomplish C photosynthesis within individual chlorenchyma cells: each species having a unique means of intracellular spatial partitioning of biochemistry and organelles. In this study the chlorenchyma tissue in flowers and stems of these species was investigated.

New Fluorescence Parameters for the Determination of QA Redox State and Excitation Energy Fluxes.

A number of useful photosynthetic parameters are commonly derived from saturation pulse-induced fluorescence analysis. We show, that qP, an estimate of the fraction of open centers, is based on a pure 'puddle' antenna model, where each Photosystem (PS) II center possesses its own independent antenna system. This parameter is incompatible with more realistic models of the photosynthetic unit, where reaction centers are connected by shared antenna, that is, the so-called 'lake' or 'connected units' models.

Development of biochemical specialization and organelle partitioning in the single-cell C4 system in leaves of Borszczowia aralocaspica (Chenopodiaceae).

The terrestrial plant Borszczowia aralocaspica (Chenopodiaceae) has recently been shown to contain the entire C(4) photosynthesis mechanism within individual, structurally and biochemically polarized chlorenchyma cells rather than in a dual cell system, as has been the paradigm for this type of carbon fixation (Nature 414: 543-546, 2001). Analysis of carbon isotope composition and (14)CO(2) fixation shows that photosynthesis and growth of B. aralocaspica occurs through carbon acquired by C(4) photosynthesis.

Interactions of nitrate and CO2 enrichment on growth, carbohydrates, and rubisco in Arabidopsis starch mutants. Significance of starch and hexose.

Wild-type (wt) Arabidopsis plants, the starch-deficient mutant TL46, and the near-starchless mutant TL25 were grown in hydroponics under two levels of nitrate, 0.2 versus 6 mM, and two levels of CO(2), 35 versus 100 Pa. Growth (fresh weight and leaf area basis) was highest in wt plants, lower in TL46, and much lower in TL25 plants under a given treatment.

Bundle sheath diffusive resistance to CO(2) and effectiveness of C(4) photosynthesis and refixation of photorespired CO(2) in a C(4) cycle mutant and wild-type Amaranthus edulis.

A mutant of the NAD-malic enzyme-type C(4) plant, Amaranthus edulis, which lacks phosphoenolpyruvate carboxylase (PEPC) in the mesophyll cells was studied. Analysis of CO(2) response curves of photosynthesis of the mutant, which has normal Kranz anatomy but lacks a functional C(4) cycle, provided a direct means of determining the liquid phase-diffusive resistance of atmospheric CO(2) to sites of ribulose 1,5-bisphosphate carboxylation inside bundle sheath (BS) chloroplasts (r(bs)) within intact plants. Comparisons were made with excised shoots of wild-type plants fed 3,3-dichloro-2-(dihydroxyphosphinoyl-methyl)-propenoate, an inhibitor of PEPC.

Proof of C4 photosynthesis without Kranz anatomy in Bienertia cycloptera (Chenopodiaceae).

Kranz anatomy, with its separation of elements of the C4 pathway between two cells, has been an accepted criterion for function of C4 photosynthesis in terrestrial plants. However, Bienertia cycloptera (Chenopodiaceae), which grows in salty depressions of Central Asian semi-deserts, has unusual chlorenchyma, lacks Kranz anatomy, but has photosynthetic features of C4 plants. Its photosynthetic response to varying CO2 and O2 is typical of C4 plants having Kranz anatomy.

Kranz anatomy is not essential for terrestrial C4 plant photosynthesis.

An important adaptation to CO2-limited photosynthesis in cyanobacteria, algae and some plants was development of CO2-concentrating mechanisms (CCM). Evolution of a CCM occurred many times in flowering plants, beginning at least 15-20 million years ago, in response to atmospheric CO2 reduction, climate change, geological trends, and evolutionary diversification of species. In plants, this is achieved through a biochemical inorganic carbon pump called C4 photosynthesis, discovered 35 years ago.

Analysis of oxygen evolution during photosynthetic induction and in multiple-turnover flashes in sunflower leaves.

Exchange of CO2 and O2 and chlorophyll fluorescence were measured in the presence of 360 μ1 · 1(-1) CO2 in nitrogen in Helianthus annuss L. leaves which had been preconditioned in the dark or at a photon flux density (PFD) of 24 μmol · m(-2) · s(-1) either in 21 or 0% O2. An initial light-dependent O2 outburst of 6 μmol · m(-2) was measured after aerobic dark incubation.

Control of photosynthesis in leaves as revealed by rapid gas exchange and measurements of the assimilatory force FA.

The rapid transients of CO2 gas exchange have been measured in leaves ofHelianthus annuus L. In parallel experiments the assimilatory force FA, which is the product of the phosphorylation potential and the redox ratio NADPH/NADP, has been calculated from measured ratios of dihydroxyacetone phosphate to phosphoglycerate in the chloroplast stroma and in leaves. The following results were obtained: (i) When the light-dependent stroma alkalization was measured under steady-state conditions for photosynthesis in air containing 2000 μl · l(-1) CO2, alkalization increased with photosynthesis as the quantum flux density (irradiance) was increased.

Inhibition of photosynthesis of sunflower leaves by an endogenous solute and interdependence of different photosynthetic reactions.

Photosynthesis of Helianthus annuus L. leaves was transiently inhibited and respiration was stimulated when a leaf was detached from the plant by cutting the petiole under water. These effects were caused by a solute which was released by cutting and was transported by the transpiration stream to the leaf blade.

The state of the photosynthetic apparatus in leaves as analyzed by rapid gas exchange and optical methods: the pH of the chloroplast stroma and activation of enzymes in vivo.

The exchange of CO2 and O2 was measured in leaves using specially constructed equipment capable of responding to rapid transients. Optical measurements provided information on cytochrome f and P 700 oxidation in the light. The following results were obtained: i) The solubilization of CO2 was used to calculate the pH of the chloroplast stroma in darkened leaves.

Assimilatory Power (Postillumination CO(2) Uptake) in Leaves: Measurement, Environmental Dependencies, and Kinetic Properties.

Assimilatory power was measured in ten C(3) species by means of a rapid-response gas exchange device as the total amount of CO(2) fixed in N(2)-CO(2) atmosphere after switching the light off. Different steady-state levels of the assimilatory power were obtained by varying light intensity and O(2) and CO(2) concentrations during the preexposition periods in the leaf chamber.Within the limits of the linear part of the CO(2) curve of photosynthesis in N(2), the assimilatory power is constant, being sufficient for the assimilation of about 20 nanomoles CO(2) per square centimeter leaf.