The responses of two aquatic plants, arrowhead (Sagittaria pygmaea Miq.) and pondweed (Potamogeton distinctus A. Benn), to anoxia were compared with those of rice (Oryza sativa L.). Shoot elongation of arrowhead tubers was enhanced at around 1 kPa O 2 , whereas that of pondweed turions was slight in air and reached a maximum in the absence of O 2 . Anaerobic enhancement of alcohol dehydrogenase (ADH) activity took place in rice coleoptiles but not in arrowhead and pondweed shoots. Shoots of both arrowhead and pondweed maintained a more stable energy status than did the rice coleoptile under anaerobic conditions. Total adenylate nucleotide contents of arrowhead and pondweed shoots were constant under anaerobic conditions. Adenylate energy charge in both shoots remained at a high and stable level of more than 0·8 for at least 8 d. Three forms of ADH from arrowhead shoots were separated by starch gel electrophoresis, showing that the activity of each ADH form was different under aerobic and anaerobic conditions. The incorporation of 35 S-labelled Cys and Met into soluble proteins in arrowhead shoots showed active protein biosynthesis and an involvement of a special set of polypeptides in the anaerobiosis.Key-words: Oryza sativa; Potamogeton; Sagittaria; adenylate energy charge; alcohol dehydrogenase; alcoholic fermentation; anaerobiosis; aquatic plants; growth in an anoxic state; protein synthesis in an anoxic state. INTRODUCTIONStudies on the responses of plants to anaerobic conditions are important to improve the productivity of cultivated plants in fields that are in danger of flooding. Therefore, many studies have been made on major crops such as tomato, barley, corn, soybean (Perata & Alpi 1993;Sachs, Subbaiah & Saab 1996;Vartapetian & Jackson 1997). These crops only survive a few days under anaerobic conditions because of lethal damage to their roots from exposure to anoxia. Studies of early events occurring in the cells of plants exposed to anaerobic conditions have focused on adenosine 5'-triphosphate (ATP) production, fermentation, protein synthesis, gene expression, and acidosis.It has been shown, on the other hand, that several aquatic plants exposed to anoxia have the ability not only to survive but even to elongate their shoots for a certain period (Crawford 1989;Kennedy, Rumpho & Fox 1992;Crawford & Braendle 1996;Vartapetian & Jackson 1997). This does not mean that all aquatic plants can tolerate an anaerobic environment. Instead most aquatic plants avoid anaerobiosis by developing a system to ventilate tissues under water (Armstrong 1979). Some aquatic plants, however, have been known to be tolerators of anoxia. The most extreme example of this is the overwintering shoots of Potamogeton pectinatus L., which can elongate under anaerobic conditions (Summers & Jackson 1994). In this study, we found that the shoots of arrowhead (Sagittaria pygmaea Miq.) tubers and pondweed (Potamogeton distinctus A. Benn.) turions can also grow under anaerobic conditions.Arrowheads are an emergent plant and a per...
Temporal variations of net Kuroshio transport are examined for 1972–2018 based on a repeated hydrographic section along 137°E, which is maintained by the Japan Meteorological Agency. The net Kuroshio transport obtained by integration of geostrophic current velocity relative to 1000 dbar depth fluctuates on inter-annual and decadal timescales. The predominant timescale of the net Kuroshio transport changes with time; the inter-annual variation is pronounced in 1972–1990 and 2000–2018, and the decadal variation is detected only before 2000. We find that a winter wind stress curl variation in the central North Pacific which reflects meridional movements of the Aleutian Low and intensity fluctuations of the North Pacific subtropical high on an inter-annual timescale and intensity fluctuations of the Aleutian Low on a decadal timescale, causes the net Kuroshio transport variation. In addition to the inter-annual and decadal variations, we further pointed out a bi-decadal-scale variation of the net Kuroshio transport and its possible link to the Aleutian Low intensity fluctuation. Moreover, our results indicate that during large net Kuroshio transport, sea surface temperature around the Kuroshio and Kuroshio Extension region tends to increase, resulting in vigorous upward sensible and latent heat release.
Typhoons decrease sea surface temperature (SST) along their wakes through upwelling of subsurface water, vertical mixing in the upper ocean, and heat release from the sea surface, and these cold wakes can influence subsequent typhoons. In this study, we investigated interactions between the upper ocean and typhoons in the North Pacific subtropical gyre with focuses on Kuroshio's response and feedback using atmosphere–ocean coupled model simulations. In late August and early September 2018, typhoons SOULIK, CIMARON, and JEBI passed through the northwestern subtropical gyre. During the passages of SOULIK and CIMARON, SST decreased along their paths due to vertical mixing except in the Kuroshio region. We quantitatively revealed that the Kuroshio stayed warm because the deep mixed layer along its path and small vertical temperature gradient around the mixed layer base, which are unfavorable conditions for cooling by vertical mixing, limited the cooling effects. After SOULIK and CIMARON had passed, SST recovered through horizontal Kuroshio heat transport and radiative heating. The possibility that the SST field after SOULIK and CIMARON passages influences JEBI was also discussed. Although impacts on JEBI intensity were not identified, it is implied that the turbulent heat flux (THF; sum of the sensible and latent heat fluxes) around JEBI was modulated by the SST field: heat release from the ocean was reduced in the region with decreased SST and enhanced over the sustained high SST of the Kuroshio. Furthermore, the large THF over the Kuroshio may have caused an increase of JEBI‐associated precipitation around Japan.
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