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Byline: Osamu Ueno (1), Masataka Wakayama (1,2) Keywords: Amphibious plant; C.sub.3 and C.sub.4 photosynthetic enzymes; C.sub.4 pathway; Eleocharis retroflexa ssp. chaetaria; Immunogold localization; Kranz anatomy Abstract: The amphibious leafless sedge Eleocharis retroflexa ssp. chaetaria expresses C.sub.4-like biochemical characteristics in both the terrestrial and submerged forms. Culms of the terrestrial form have Kranz anatomy, whereas those of the submerged form have Kranz-like anatomy combined with anatomical features of aquatic plant leaves. We examined the immunolocalization of C.sub.3 and C.sub.4 enzymes in culms of the two forms. In both forms, phosphoenolpyruvate carboxylase pyruvate, Pi dikinase and NAD-malic enzyme were compartmentalized between the mesophyll (M) and Kranz cells, but their levels were somewhat reduced in the submerged form. In the terrestrial form, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) occurred mainly in the Kranz cells, and weakly in the M chloroplasts. In the submerged form, the rubisco occurred at higher levels in the M cells than in the terrestrial form. In both forms, the C.sub.4 pattern of enzyme expression was clearer in the M cells adjacent to Kranz cells than in distant M cells. During the transition from terrestrial to submerged conditions, the enzyme expression pattern changed in submerged mature culms that had been formed in air before submergence, and matched that in culms newly developed underwater. It seems that effects of both environmental and developmental factors overlap in the C.sub.4 pattern expression in this plant. Author Affiliation: (1) Plant Physiology Department, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan (2) Department of Biochemistry and Molecular Biology, Faculty of Science, Saitama University, Saitama 338-8570, Japan Article History: Registration Date: 25/08/2004 Received Date: 01/06/2004 Accepted Date: 18/08/2004 Online Date: 05/10/2004

The purpose of our research was to determine why seeds of Schoenoplectus hallii germinate only in some wet years. Seeds mature in autumn, at which time they are dormant. Seeds come out of dormancy during winter, if buried in nonflooded, moist soil, but they remain dormant if buried in flooded soil. Nondormant seeds require flooding, light, and exposure to ethylene to germinate. One piece of apple in water (1/12 of an apple in 125 mL of water in a glass jar for a depth of 5 cm) or a 1-[micro]mol/L solution of ethephon elicited very similar (high) germination percentages and vigor of seedlings. Apple, which was shown to produce ethylene in the air space of the jar, was used in a series of experiments to better understand germination. Seeds germinated to 72% if apple was removed from the water after 1 d of incubation, and they germinated to 97% if seeds were washed and placed in fresh water after 3 d of exposure to apple. No seeds germinated in control with no apple. Seeds incubated in apple leachate for 5 d and then transferred to filter paper moistened with distilled water germinated to 90%. Minimum depth of flooding in apple leachate (no soil in jars) for optimum germination was [greater than or equal] 3 cm. Buried seeds of S. hallii exhibited an annual conditional dormancy/nondormancy cycle. Regardless of the month in which seeds were exhumed, they germinated to 59-100% in light in water with apple at daily alternating temperature regimes of 25[degrees]/15[degrees], 30[degrees]/15[degrees], and 35[degrees]/20[degrees]C, but germination at 20[degrees]/10[degrees]C (and to some extent at 15[degrees]/6[degrees]C) tended to peak in autumn to spring. Thus, seeds can germinate throughout the summer if flooded (ethylenc production) and exposed to light. An ethylene cue for germination serves as a 'flood-detecting' mechanism and may serve as an indirect signal that water is available for completion of the life cycle and competing species are absent. Key words: Cyperaceae; ethylene; flooding requirement; germination cue; light requirement; Schoenopleetus hallii; seed dormancy-breaking requirements; seed germination requirements.