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...

The present study describes the influence of temperature levels and planting time on the sprouting of rhizome‐buds and the biomass production of torpedograss (Panicum repens L.) in the Okinawa prefecture, Japan. Torpedograss planted in each month (1994–95) was grown for 210 days. Sprouting of the rhizome‐bud of torpedograss was 92–96% at the temperature range of 20–35°C in an incubator, and the sprouting was not observed at the extreme low and high temperature of ≤5 and ≥45°C, respectively. The plant showed 40–72% emergence when grown in pots throughout the year in the ambient temperature range of 17–29°C. The percentage emergence was comparatively higher in March to September, and shoots elongated rapidly in the period from April to October when the temperature range of 22–29°C prevailed. Torpedograss‐rhizome sown in the period from January to June obtained significantly higher biomass because higher temperatures prevailed in the following growth period from May to October, as compared with the torpedograss‐rhizome sown in the period of July to December. The plant required higher temperatures for proper growth and development during the period of moderate (70–110 days after planting (DAP)) and fast growth phases (110 DAP to the last harvest).

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Field and glasshouse experiments were conducted from 1995 through 1996 to evaluate application timing of asulam (methyl sulfanilylcarbamate) for torpedograss (Panicum repens L.) control in relation to plant age in sugarcane. Above-ground shoots of torpedograss were completely controlled with asulam at 2-4 kg active ingredient (a.i.) ha -1 applied 60 or 80 days after planting (DAP) in artificially infested pots. But some newly developed rhizome buds survived after asulam application resulting in 1-25 and 76-100% or more regrowth in 60 and 80 DAP-applied pots, respectively.Whereas the herbicide at 2-4 kg a.i. ha -1 applied within 60 DAP completely controlled above-ground shoots, applied 80 DAP at 2 kg a.i. ha -1 it did not completely control the weed in the artificially infested field. Regrowth levels were 1-25 and 76-100% or more in 60 and 80 DAP-applied plots, respectively. Asulam at 2-3 kg a.i. ha -1 applied 20, 40, 60 or 80 DAP in a naturally infested field completely controlled aboveground shoots and regrowth levels were 76-100 or more, 51-75, 1-25 and 26-50% in these same DAP applied plots, respectively. The herbicide applied at 4 kg a.i. ha -1 caused chlorosis on younger sugarcane leaves (one-leaf stage), but when applied at 2-3 kg a.i. ha -1 , no injury symptoms were shown. The herbicide at 2-4 kg a.i. ha -1 applied within 60 DAP resulted in remarkably higher yield and shoot biomass of sugarcane than that applied 80 DAP.This study suggested that asulam at 2-3 kg a.i. ha -1 should be applied 60 days after planting for the maximum control of torpedograss regrowth and better yield of sugarcane. This study also indicated that torpedograss cannot be completely controlled with a single application of asulam in a naturally infested field because of rhizome fragmentation by cross plowing and distribution of rhizomes into different soil layers that require different times to emerge. The shoots emerging after asulam application could not be controlled. Another study is required to determine the interval between sequential applications of asulam for better control of torpedograss in a naturally infested field.

Three field trials were conducted from 2003-2004 at Utsunomiya University, Japan, to evaluate the safety and herbicidal activity of pyribenzoxim (benzophenone O -[2,6-bis[(4,6-dimethoxy-2-pyrimidinyl)oxybenzoyl]oxime) in turfgrass. Pyribenzoxim showed a high level of safety in bentgrass ( Agrostis palustris Huds.) and zoysiagrass ( Zoysia matrella ) ≤ 300 g ai ha − 1 and it controlled various major grass weeds, including annual bluegrass ( Poa annua L.), large crabgrass ( Digitaria sanguinalis L.), and green foxtail ( Setaria viridis L.), and broadleaf weeds, including common dandelion ( Taraxacum officinale Weber), horseweed ( Erigeron canadensis L.), shepherd's-purse ( Capsella bursa-pastoris (L.) Medic.), common chickweed ( Stellaria media L.), common lambsquarters ( Chenopodium album L.), creeping woodsorrel ( Oxalis corniculata L.), and common dayflower ( Commelina communis L.) by fall or spring application. In comparison with bispyribac-sodium (sodium 2,6-[bis(4,6-dimethoxy-2-pyrimidin-2-yl)oxy]benzoate), pyribenzoxim showed a higher safety level in bentgrass and a stronger herbicidal activity on grass weeds; in particular, annual bluegrass and large crabgrass.