The opportunistic mycopathogen Aspergillus fumigatus expresses both glucosylceramide and galactosylceramide (GlcCer and GalCer), but their functional signi¢cance in Aspergillus species is unknown. We here identi¢ed and characterized a GlcCer from Aspergillus nidulans, a non-pathogenic model fungus. Involvement of GlcCer in fungal development was tested on both species using a family of compounds known to inhibit GlcCer synthase in mammals. Two analogs, D-threo-1-phenyl-2-palmitoyl-3-pyrrolidinopropanol (P4) and D-threo-3P P,4P P-ethylenedioxy-P4, strongly inhibited germination and hyphal growth. Neutral lipids from A. fumigatus cultured in the presence of these inhibitors displayed a signi¢cantly reduced GlcCer/GalCer ratio. These results suggest that synthesis of GlcCer is essential for normal development of A. fumigatus and A. nidulans. ß 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.

SummaryPolygalacturonate 4-α-galacturonosyltransferase (PGAGalAT), the glycosyltransferase that synthesizes the plant cell wall pectic polysaccharide homogalacturonan, has previously been identified and partially characterized in tobacco membranes. Membrane bound PGA-GalAT catalyzes the transfer of galacturonic acid from UDP-galacturonic acid (UDP-GalA) onto an endogenous acceptor to produce polymeric homogalacturonan (Doong et al., (1995

both yeast and mycelium forms). The major components of all species examined differed primarily (and widely) in the level of 2-hydroxy fatty N-acyl D 3 unsaturation, but among the minor components a significant degree of additional structural diversity was observed, based on differences in sphingoid or N-acyl chain length, as well as on the presence or absence of the sphingoid D 8 unsaturation or 9-methyl group. Some variants were isobaric, and were not uniformly present in all species, affirming the need for MS/CID-MS analysis for full characterization of all components in a fungal CMH fraction. The diversity in ceramide distribution observed may reflect significant species-specific differences among fungi with respect to cerebroside biosynthesis and function.

About 95% of swamp tupelo (Nyssa sylvatica var. biflora (Walt.) Sarg.) and sweetgum (Liquidambar styraciflua L.) seedlings survived continuous root flooding for more than two years, whereas none of the swamp chestnut oak (Quercus michauxii Nutt.) and cherrybark oak (Q. falcata var. pagodifolia Ell.) seedlings survived one year of flooding. Death of oak seedlings occurred in phases associated with periods of major vegetative growth, e.g., after bud burst in spring, after summer stem elongation, and during the winter deciduous stage, suggesting that stored reserves and sources were inadequate to maintain the seedlings when vegetative sinks were forming. Additional evidence that flooding induced a source deficiency in oak was that leaves of flooded oak were 65 to 75% smaller than leaves of nonflooded oak. Flooded swamp tupelo seedlings had a normal leaf size and patchy stomatal opening compared with nonflooded seedlings. Flooding caused increases in alcohol dehydrogenase (ADH) specific activity in taproot cambial tissues and increases in starch concentrations of swamp tupelo seedlings that were reversed when seedlings were removed from flooding. Flooding had little effect on soluble sugar concentrations in swamp tupelo or sweetgum. In the long-term flood-dry-flood treatment, in which all species had survivors, upper canopy leaf photosynthetic rates were higher in all species during the dry period than in nonflooded controls, whereas their starch and soluble sugars concentrations were similar to those of nonflooded controls. Based on seedling survival and the sink-source relationships, the order of flood tolerance was: swamp tupelo > sweetgum > swamp chestnut oak > cherrybark oak.

Polygalacturonate 4-a-galacturonosyltransferase (EC 2.4.1.43) activity has been identified in microsomal membranes isolated from tobacco (Nicotiana tabacum L. cv Samsun) cell-suspension cultures. lncubation of UDP-['4C]galacturonic acid with tobacco membranes results i n a time-dependent incorporation of ['4C]galacturonic acid into a chloroform-methanol-precipitable and 65% ethanol-insoluble product. The optimal synthesis of product occurs at a p H of 7.8, of 14C-labeled product into components that co-chromatograph with mono-, di-, and trigalacturonic acid, indicating that a large portion of product contains contiguous 1,4-linked a-D-galactosyluronic acid residues. Optimal EPCase fragmentation of the product requires base treatment prior t o enzymatic digestion, suggesting that 45 to 67% of the galacturonic acid residues i n the synthesized homogalacturonan are esterified. At least 40% of the base-sensitive linkages were shown t o be methyl esters by comparing the sensitivity of base-treated and pectin methylesterase-treated products to fragmentation by EPCase.The wall that surrounds plant cells is a dynamic structure composed largely of carbohydrates and proteins. The wall gives shape to the cell and plays a critical role in plant