Cell wall architecture: normal development and environmental modification of guard cells of the Cyperaceae and related species*

Abstract. The development and cell wall architecture of guard cells in the Cyperaceae were studied with light and electron microscopy. Development occurs along parallel files and results in a stomatal complex that consists of two guard cells each flanked by a subsidiary cell. The developmental pattern and general morphology are thus similar to that in the Gramineae. Several key differences, however, were observed. Wall synthesis in the Cyperaceae, as observed in the polarization and fluorescence microscope, occurs suddenly, within three to four complexes along a file, but is more gradual in the Gramineae. Mature cell walls in the Cyperaceae predominantly contain microfibrils oriented radially relative to the pore, while those in the Gramineae contain axial microfibrils. This difference was demonstrated in numerous species using freshly-collected as well as preserved material. In Cyperus esculentus, however, the alignment of microfibrils appears to be subject to environmental modification. Plants grown in the greenhouse contain guard cells with axial microfibrils, compared to the radial arrangement found in those grown in the field. In the former, wall is deposited gradually, as in the Gramineae. On return to more stressful conditions, radially micellated guard cells again develop. In each case, the cortical cytoplasm adjacent to areas where the wall is to thicken contains microtubules oriented parallel to the microfibril alignment characteristic of that treatment. These results are discussed in terms of the role of varied wall architecture in stomatal mechanics, the regulation of cell wall biosynthesis, and the evolutionary relationship of the Cyperaceae, Gramineae, and other taxa.     

Seedling Blights of Cyperaceae Weeds Caused by Curvularia tuberculata and C. oryzae

Two Curvularia tuberculata isolates (93-020 and 93-022) and one C. oryzae isolate (93-061) were obtained from diseased Cyperus difformis , C. iria , and Fimbristylis miliacea , respectively, in the Philippines in 1993. When inoculated onto their hosts at 1 ×10 8 conidia m -2 , and provided with 24-h dew at 28°C, a severe and rapid blighting of the leaves caused the weed seedlings to die within two weeks. The three Curvularia isolates were cross-pathogenic to C. difformis , C. iria , F. miliacea , and C. rotundus but exhibited varying degrees of virulence depending on the weed species being attacked. C. tuberculata isolates 93-020 and 93-022 effectively controlled C. difformis and C. iria but were less effective on F. miliacea.

C. oryzae was equally virulent on C. difformis , C. iria , and F. miliacea . C. rotundus was not killed by any of the three isolates and exhibited only minor flecking and leaf tip die-back. Sporulation of the three Curvularia isolates on necrotic leaf tissues occurred on the susceptible ( C. difformis , C. iria , and F.miliacea ) but not on the resistant ( C. rotundus ) weed hosts.     

Macrophytic primary production and nutrient concentrations in a deltaic floodplain marsh of the Lower Paraná River

Biomass changes across an annual cycle were followed at two sampling sites in the floodplain marsh of the Lower Paraná River: close to the river-shore and 800 m inside the floodplain marsh, both dominated by Scirpus californicus and Cyperus giganteus. Tidal influence determines a daily exchange of water between the river and the floodplain marsh.Estimated net primary production was higher in the river (2820 against 1770 g m^–2). Contents of nitrogen and phosphorus in plant tissue decreased from the river to the floodplain (0.62 to 0.45% N and 0.18 to 0.14% P). In spite of the important water exchange between the river and the floodplain, a decrease in nitrate, oxygen and suspended matter, and an increase in soluble reactive phosphorus in the water were observed from the river towards the floodplain marsh.A primary production gradient exists from the river to the inner floodplain marsh, where production is nitrogen-limited, sustained mainly on nutrients supplied by the river. Floodplain marshes are nitrate sinks, probably through denitrification losses and macrophyte uptake.