Isolation and characterization of a symbiosis-regulated ras from the ectomycorrhizal fungus Laccaria bicolor.

Ectomycorrhizae formed by the symbiotic interaction between ectomycorrhizal fungi and plant roots play a key role in maintaining and improving the health of a wide range of plants. Mycorrhizal initiation, development, and functional maintenance involve morphological changes that are mediated by activation and suppression of several fungal and plant genes. We identified a gene, Lbras, in the ectomycorrhizal fungus Laccaria bicolor that belongs to the ras family of genes, which has been shown in other systems to be associated with signaling pathways controlling cell growth and proliferation. The Lbras cDNA complemented ras2 function in Saccharomyces cerevisiae and had the ability to transform mammalian cells. Expression of Lbras, present as a single copy in the genome, was dependent upon interaction with host roots. Northern analysis showed that expression was detectable in L bicolor 48 h after interaction as well as in the established mycorrhizal tissue. Phylogenetic analysis with other Ras proteins showed that Lbras is related most closely to Aras of Aspergillus nidulans.

Visible and microscopic injury in leaves of five deciduous tree species related to current critical ozone levels.

Because the current critical level of ozone (O(3)) for forest trees is based only on one species, the responses of five deciduous tree species were differentiated in a climate chamber experiment. The number of symptomatic leaves per tree was significantly increased, and stomatal conductance was decreased under 50% ambient+30 nl l(-1) O(3) as compared to 'normal' senescence at 50% ambient [O(3)]. Species with a high stomatal conductance did not show earlier or more leaf injury symptoms. The additional 30 nl l(-1) O(3) induced specific pectinaceous cell wall protrusions, phenolic cell wall incrustations, tonoplast vesicles, and inhomogeneous, condensed/precipitated phenolic material in the vacuoles. Due to added O(3), cell senescence was accelerated with increased electron-density of the cytoplasm, and initial chloroplast degeneration. The slow degeneration process started in mesophyll cells, and expanded into epidermal and finally guard cells. Because of the large variance in biomass between individuals and species, the current critical level is supported by the assessment of visible leaf symptoms rather than growth reduction.

Effects of ozone and acidic fog on red spruce needle epicuticular wax production, chemical composition, cuticular membrane ultrastructure and needle wettability.

One-year-old red spruce (Picea rubens Sarg.) seedlings were exposed, from bud break, to ozone (O3 ) and acidic fog for 14, 42 or 77 days. Ozone was more damaging than acidic fog to epicuticular wax. Wax quantity on needles exposed to charcoal-filtered air (CFA) and pH 4.2 fog (control) increased from 14 to 42 days, but decreased by 77 days. Exposure of elongating needles to 70 ppb O3 and pH 4.2 fog reduced the rate of de novo wax synthesis. Red spruce wax is composed of secondary alcohols (50%), nonacosane diols (25%), alkyl esters (12%), primary alcohols (6 %), estolides (2 %), fatty acids (3 %), and hydroxy-fatty acids (2 %). Wax chemical composition varied temporally. Needles exposed to O3 had significantly less secondary alcohols, diols, alkyl esters, fatty acids, and hydroxy-fatty acids than needles exposed to CFA. Production of secondary alcohols was significantly reduced following needle exposure to fog at pH 3.0. Cuticular membrane thickness increased significantly following needle exposure to O3 . The increase in thickness at 250 ppb O3 was due to a new amorphous layer which appeared above the reticulate layer. Contact angles on needles exposed to CFA and pH 4.2 fog increased from 92° after 14 days to 96° after 42 days, then declined to 77° after 77 days. Needle exposure to O3 for 42 or 77 days significantly decreased contact angles.