SUMMARYTransport of dicarboxylates across the chloroplast envelope plays an important role in transferring carbon skeletons to the nitrogen assimilation pathway and exporting reducing equivalent to the cytosol to prevent photo-inhibition (the malate valve). It was previously shown that the Arabidopsis plastidic 2-oxoglutarate/ malate transporter (AtpOMT1) and the general dicarboxylate transporter (AtpDCT1) play crucial roles at the interface between carbon and nitrogen metabolism. However, based on the in vitro transport properties of the recombinant transporters, it was hypothesized that AtpOMT1 might play a dual role, also functioning as an oxaloacetate/malate transporter, which is a crucial but currently unidentified component of the chloroplast malate valve. Here, we test this hypothesis using Arabidopsis T-DNA insertional mutants of AtpOMT1. Transport studies revealed a dramatically reduced rate of oxaloacetate uptake into chloroplasts isolated from the knockout plant. CO 2 -dependent O 2 evolution assays showed that cytosolic oxaloacetate is efficiently transported into chloroplasts mainly by AtpOMT1, and supported the absence of additional oxaloacetate transporters. These findings strongly indicate that the high-affinity oxaloacetate transporter in Arabidopsis chloroplasts is AtpOMT1. Further, the knockout plants showed enhanced photo-inhibition under high light due to greater accumulation of reducing equivalents in the stroma, indicating malfunction of the malate valve in the knockout plants. The knockout mutant showed a phenotype consistent with reductions in 2-oxoglutarate transport, glutamine synthetase/glutamate synthase activity, subsequent amino acid biosynthesis and photorespiration. Our results demonstrate that AtpOMT1 acts bi-functionally as an oxaloacetate/malate transporter in the malate valve and as a 2-oxoglutarate/malate transporter mediating carbon/nitrogen metabolism.

Recent field studies have pointed out that the vulnerability of juvenile fish to predation is higher than anticipated during night-time in vegetated habitats. Effects of abundance, body length, and growth rate on predation were examined in juvenile Japanese black rockfish in 2009–2011 in a macroalgal bed. Juvenile rockfish abundance ranged between 2.5 and 49.0 ind. 100 m–2 and the biomass of potential predators (piscivorous fish >82.5 mm) between 140.0 and 601.3 g 100 m−2. Sebastes inermis was the most dominant predator, compromising more than 50% by wet weight on all sampling days. Comparison of the total length of juveniles surviving (as original population, OP) and that of juveniles ingested (IG) by predators provided the evidence of the size-selective predation on juvenile rockfish on three of seven sampling days. The juvenile predation rate estimated as abundance of IG (N 100 m−2)/(abundance of IG + OP (N 100 m−2)) × 100100 varied between 0.4 and 12.5%. Neither juvenile rockfish abundance nor predator biomass had a significant effect on the juvenile predation rate, whereas the juvenile body length had a significant effect, smaller individuals being more vulnerable to predation. The growth-selective predation was not detected. Macroalgal habitats, although functioning as nurseries during the day, may contribute as feeding grounds for piscivorous fish predators at night leading to enhanced nocturnal predation rates.

The majority of surveys on food webs of aquatic ecosystems have been conducted during the day owning to difficulties in sampling animals at night. In this study, to examine diurnal changes in predator-prey interactions in a temperate seagrass Zostera marina bed, a quantitative day/night survey of fish, the dominant animal community, coupled with acoustic telemetry of their predators, was conducted. The number of species, abundance, and biomass of piscivorous predators and mean trophic level during the night were significantly higher than those in the day in all seasons. Analysis of the stomach contents of 182 piscivorous predators showed that no fish predation occurred during the day whereas predation occurred during the night in winter, spring, and summer. Acoustic telemetry demonstrated nocturnal visits by dominant piscivorous fish species (rockfishes and conger eel) to the seagrass bed. We conclude that the nocturnal visits by piscivorous fishes increased the predation risk and trophic level in the fish nursery. The ecological functions of seagrass beds should be reevaluated accounting for day/night changes in food webs; these areas serve as nurseries for juvenile and small-sized fishes during the day and as foraging grounds for predators during the night.

It is known that double-stranded DNA (dsDNA) turns into a liquid crystalline phase by the addition of a high concentration of polymer with salt. SYBR Green I (SG) is a...

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