Growth and energy status of arrowhead tubers, pondweed turions and rice seedlings under anoxic conditions

Abstract

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...

Anoxia-enhanced expression of genes isolated by suppression subtractive hybridization from pondweed (Potamogeton distinctus A. Benn.) turions

“…The increase in the activities of ADH and SuSy after anoxic treatment was reported by Ishizawa et al (1999) and Harada et al (2005), respectively. In Table 3, the changes of three additional enzymes are shown.…”

“…Stems were placed on moist Wlter paper and preincubated at 25°C in the dark for 1 day and then stood in a small vial (10 mm in diameter) containing 500 l of distilled water. The vials were placed in a 100-ml glass vessel that was connected to a continuous supply of water-saturated air or pure N 2 gas (Ishizawa et al 1999). After incubation in aerobic or anaerobic conditions at 25°C in the dark, stems were plunged into liquid nitrogen for extraction of RNA.…”

“…Homeostasis of turion cells is consistently maintained highenergy charge of anoxic turion tissues for more than one week under anoxic conditions (Ishizawa et al 1999). We previously reported that alcoholic fermentation is the main pathway for energy production of pondweed turions under anoxic conditions (Ishizawa et al 1999;Sato et al 2002). Turions have many amyloplasts in the cells.…”

“…Some aquatic plant species show extremely high tolerance to oxygen deprivation (Ishizawa et al 1999;Dixon et al 2006). Pondweed (Potamogeton distinctus A.…”

“…and arrowhead (Sagittaria pygmaea Miq. ) are typical examples of anoxiatolerant species (Ishizawa et al 1999). Their overwintering buds can survive and grow under strict anoxia.…”