In photosynthetic electron transport, large multiprotein complexes are connected by small diffusible electron carriers, the mobility of which is challenged by macromolecular crowding. For thylakoid membranes of higher plants, a long-standing question has been which of the two mobile electron carriers, plastoquinone or plastocyanin, mediates electron transport from stacked grana thylakoids where photosystem II (PSII) is localized to distant unstacked regions of the thylakoids that harbor PSI. Here, we confirm that plastocyanin is the long-range electron carrier by employing mutants with different grana diameters. Furthermore, our results explain why higher plants have a narrow range of grana diameters since a larger diffusion distance for plastocyanin would jeopardize the efficiency of electron transport. In the light of recent findings that the lumen of thylakoids, which forms the diffusion space of plastocyanin, undergoes dynamic swelling/shrinkage, this study demonstrates that plastocyanin diffusion is a crucial regulatory element of plant photosynthetic electron transport.

During photosynthesis, electrons travel from light-excited chlorophyll molecules along the electron transport chain to the final electron acceptor nicotinamide adenine dinucleotide phosphate (NADP) to form NADPH, which fuels the Calvin–Benson–Bassham cycle (CBBC). To allow photosynthetic reactions to occur flawlessly, a constant resupply of the acceptor NADP is mandatory. Several known stromal mechanisms aid in balancing the redox poise, but none of them utilizes the structurally highly similar coenzyme NAD(H). Using Arabidopsis (Arabidopsis thaliana) as a C3-model, we describe a pathway that employs the stromal enzyme PHOSPHOGLYCERATE DEHYDROGENASE 3 (PGDH3). We showed that PGDH3 exerts high NAD(H)-specificity and is active in photosynthesizing chloroplasts. PGDH3 withdrew its substrate 3-PGA directly from the CBBC. As a result, electrons diverted from NADPH via the CBBC into the separate NADH redox pool. pgdh3 loss-of-function mutants revealed an overreduced NADP(H) redox pool but a more oxidized plastid NAD(H) pool compared to wild-type plants. As a result, photosystem I acceptor side limitation increased in pgdh3. Furthermore, pgdh3 plants displayed delayed CBBC activation, changes in nonphotochemical quenching, and altered proton motive force partitioning. Our fluctuating light-stress phenotyping data showed progressing photosystem II damage in pgdh3 mutants, emphasizing the significance of PGDH3 for plant performance under natural light environments. In summary, this study reveals an NAD(H)-specific mechanism in the stroma that aid in balancing the chloroplast redox poise. Consequently, the stromal NAD(H) pool may provide a promising target to manipulate plant photosynthesis.

Number of brooded eggs and wet and dry brood weights were measured in the estuarine crab, Chasmagnathus granulatus. Best correlations for all reproductive variables were found with respect to female wet body weight, but while the best fitted model was logarithmic for broods having uneyed embryos (UE), a linear model corresponded to eyed embryo (EE) broods. For UE, larger females invested in each brooded egg 8.4% more of dry biomass than smaller females, in accordance with the logarithmic model adjusted. Overall fecundity was estimated in 26790±9936 eggs/brood/female. Biomass investment in reproduction was estimated in 7.1 % (dry weight basis) and 9.3% (wet weigh basis). Egg dry weight decreased throughout embryonic development, in accordance with metabolic requirements of embryos, while a higher water content was noted in EE, probably related to tissue solvation during development and/or increase of the osmotic pressure needed for hatching.

The photosynthetic machinery of plants can acclimate to changes in light conditions by balancing light-harvesting between the two photosystems (PS). This acclimation response is induced by the change in the redox state of the plastoquinone pool, which triggers state transitions through activation of the STN7 kinase and subsequent phosphorylation of light-harvesting complex II (LHCII) proteins. Phosphorylation of LHCII results in its association with PSI (state 2), whereas dephosphorylation restores energy allocation to PSII (state 1). In addition to state transition regulation by phosphorylation, we have recently discovered that plants lacking the chloroplast acetyltransferase NSI are also locked in state 1, even though they possess normal LHCII phosphorylation. This defect may result from decreased lysine acetylation of several chloroplast proteins. Here, we compared the composition of wild type (wt), stn7 and nsi thylakoid protein complexes involved in state transitions separated by Blue Native gel electrophoresis. Protein complex composition and relative protein abundances were determined by LC-MS/MS analyses using iBAQ quantification. We show that despite obvious mechanistic differences leading to defects in state transitions, no major differences were detected in the composition of PSI and LHCII between the mutants. Moreover, both stn7 and nsi plants show retarded growth and decreased PSII capacity under fluctuating light as compared to wt, while the induction of non-photochemical quenching under fluctuating light was much lower in both nsi mutants than in stn7.

Male and female juvenile crabs of the species Chasmagnathus granulata were collected in Samborombón Bay (Argentina), on October 1994 and February 1995; these dates correspond to the beginning and end of the reproductive period of the species, respectively. No differences in the initial size (measured as carapace width, CW) existed between both clutches. Each clutch of juveniles was observed during a 1-year period, recording the percentage of molted crabs, intermolt period and percentual increment of size after each molting. At the end of the observation period, males and females from the October clutch reached the size of sexual maturity, while crabs of the remaining clutch did not. This difference was due to the higher increment in size of the October crabs at the third and fourth molts, compared to the February ones. Such difference seems to be related to an increase in reproductive effort during the breeding season, once the sexual maturity was attained.