Canadian Science Publishing

The composition of a medium is described that proved useful to culture callus of a variety of monocotyledonous and dicotyledonous plants. Growth on the medium was often better than on some other excellent media. In addition to supporting rapid cell growth, a soft, friable type of colony growth was often obtained. This type of loose, friable cell growth facilitated work with single cells and the enzymatic removal of cell walls in related studies. A high level of auxin-type growth-regulating substances (AGRS) generally favored cell cultures of monocotyledonous plants, while low levels of cytokinin were essential for most dicotyledonous cell cultures. Some cultures of dicotyledonous plant cells adapted to a cytokinin-free medium containing a high level of 2,4-dichlorophenoxyacetic acid (2,4-D) or p-chlorophenoxyacetic acid (pCPA). The preferred AGRS were 2,4-D and pCPA. Citrate, succinate, and 2(N-morpholino) ethane sulfonic acid (MES) were effective medium buffers, but phosphate alone seemed adequate to buffer the medium at pH 5.8–5.9.

We examined the species diversity of an ectomycorrhizal community in natural stands of bishop pine (Pinus muricata D. Don) to determine the correspondence between above- and below-ground views of species composition, spatial frequency, and abundance. We addressed this question by simultaneously sampling fruit bodies and ectomycorrhizae over a 4-year period. By using molecular methods based on polymerase chain reaction, we were able to identify the fungal symbionts directly from mycorrhizae in nearly all of the mycorrhizal morphotypes we found. Most species were either rare or low in abundance. Among the common species we observed three patterns: (i) some species, such as Russula xerampelina s.l. and Amanita francheti were well represented both above- and below-ground; (ii) some common fruiting species such as Suillus pungens were rare components belowground; (iii) some species that were common as mycorrhizae were represented poorly or unrepresented in the aboveground fruiting record. The latter was the case for Russula amoenolens, thelephoroid types (i.e., Tomentella sublilacina and thelephoroid-2), and a boletoid type. These results show that (i) the pattern of resource allocation to production of fruit bodies versus ectomycorrhizae varied among species, and (ii) the correspondence between above- and below-ground is imprecise at best at the community level. Keywords: mycorrhizal types, basidiocarps, sporocarps, fungal community, ecology of fungi, PCR, molecular ecology.

More than 80 disease biocontrol products are on the market worldwide, but none of these contain mycor rhizal fungi. This is despite ample evidence that both arbuscular mycorrhizal fungi and ectomycorrhizal fungi can control a number of plant diseases. A procedure for successful development of disease biocontrol agents in general is used as a background to examine the potential for achieving commercial mycorrhizal biocontrol agents. This includes (i) selection and screening; (ii) characterization involving identification, studies of modes of action and ecophysiology, as well as inoculum production, formulation, application and shelf life; (iii) registration. The last stage is problematic for mycorrhizal fungi, as currently they can be sold as plant growth promoters without any form of costly registration, even though in some instances they may actually function to some extent through biocontrol activity. The significance of this approach is discussed, and some possible ways of enhancing biocontrol by mycorrhizas are considered.Key words: arbuscular mycorrhizas, ectomycorrhizas, biological disease control, soilborne pathogens, modes of action, ecology.

Suberin is a term used to define a specific cell wall component that occurs, for example, in phellem (cork) endodermal and exodermal cells and is characterized by the deposition of both poly(phenolic) and poly(aliphatic) domains. Historically, the poly(phenolic) domain has been likened to lignin, and while there is an element of truth to this comparison, recent evidence supports an alternative view in which the poly(phenolic) domain contains a significant amount of nonlignin precursors (principally hydroxycinnamic acids and their derivatives) that are covalently linked to each other in a manner analogous to the monolignols in lignin. Similarly, the conceptual model in which the poly(aliphatic) domain of suberized tissues is represented as a random network of polyesterified, modified fatty acids and alcohols has been replaced with one comprising a three-dimensional, glycerol-bridged network. Taken together, a new model for suberin is emerging in which a hydroxycinnamic acid – monolignol poly(phenolic) domain, embedded in the primary cell wall, is covalently linked to a glycerol-based poly(aliphatic) domain located between the primary cell wall and the plasma membrane. The structural and biochemical evidence supporting this new suberin paradigm are examined in this minireview, along with the presentation of a new structural model encompassing a current view of the structure of suberin.Key words: suberin, lignin, hydroxycinnamic acid, monolignol, poly(aliphatic) domain, poly(phenolic) domain, glycerol polyester.

Plants of rape, safflower, sunflower, flax, and castor bean were grown at temperatures of 10, 16, 21, and 26.5 °C for the period of seed development. Oil content of sunflower, safflower, and castor bean was not affected by temperature. Highest oil content in rape and flax was found at the lowest temperature and a continual decrease was observed with increases in temperature. Fatty acid composition of the oil from safflower and castor bean was not affected by a change in temperature. In the other three species the amount of the more highly unsaturated fatty acids decreased as the temperature was increased. This decrease was accompanied by an increase in oleic acid. The levels of saturated fatty acids in all of the species were not affected by changes in temperature.

Substantial progress has been made towards the development of systems for in vitro embryogenesis in conifers. Since the first report of somatic embryogenesis from zygotic embryos of Picea abies in 1985, cultured explants of at least 18 different coniferous species have been induced to produce somatic embryos. Somatic embryos have been cryopreserved, grown in liquid suspensions, and matured into plants. In addition, plantlets have been regenerated from protoplasts isolated from embryogenic suspensions of Picea glauca and Larix ×eurolepis, permitting studies into direct gene transfer and somatic hybridization. Currently however, it is only possible to obtain somatic embryogenesis from embryonic and juvenile explants. Furthermore, for most species the efficiency of plantlet production from somatic embryos is poor and remains a problem for the commercial utilization of this technology. Biochemical, cytological, and physiological studies of conifer somatic embryogenesis have resulted in improved knowledge concerning the origin of somatic embryos, storage product accumulation during embryo development, and similarities with zygotic embryos. Furthermore, the technique of indirect immunofluorescence microscopy has permitted investigations of the cytoskeleton in conifer cells and protoplasts, providing insights into cell division and morphogenesis. In this review, emphasis is placed on the more fundamental aspects of conifer somatic embryogenesis. Where possible, comparisons between zygotic and somatic embryogenesis are made. Key words: somatic embryogenesis, zygotic embryogenesis, conifers, review.

The decomposition dynamics of four types of needle litter and three types of leaf litter were followed for 4 years. Mass losses and certain chemical changes were studied. Most of the nutrient-rich litters appeared to decompose relatively quickly during the first 12–18 months. After 3–4 years, however, their accumulated mass losses were lower compared with litter types that intially had lower rates. Thus the more nutrient-rich litters had considerably lower mass-loss rates in the later stages. This pattern was even more pronouced for extract-free lignocellulose: its mass-loss rate was negatively related to the lignin concentration, which increased progressively as litter decomposition proceeded. During late stages in litter with a high nitrogen content, there was also a clear negative relation between nitrogen concentration and lignin mass-loss rate, as well as between nitrogen concentration and litter mass-loss rate. By extrapolation of measured mass-loss values, maximum values for accumulated litter–mass loss were estimated. A nonlinear statistical model predicted that the proportion of mass lost through decomposition should be 50% for grey alder leaves, 54% for green leaves of white birch, and 57% for brown leaves of white birch. For Scots pine the predicted maximums for accumulated mass loss were 68% for green needles and 89% for brown needles, whereas corresponding values for lodgepole pine needles were 81% (green) and 100% (brown). Lodgepole pine is an introduced species in this system. Key words: litter, decomposition, lignin, nitrogen, maxium mass loss.

The structure of an ectomycorrhizal community was assessed on a 100-m² plot in a 100-year-old, oligotrophic Norway spruce, Picea abies (L.) Karst., forest in southern Sweden. During the 6-year study (1986–1992) sporocarps were identified and their biomass determined. Late in the fall of 1993, we identified mycorrhizas and estimated their abundance. Forty-eight epigeous, ectomycorrhizal taxa were identified based on the examination of sporocarps. Hygrophorus olivaceoalbus (Fr.:Fr.) Fr. and six species of Cortinarius, i.e., C. acutus (Pers.:Fr.) Fr., C. brunneus (Pers.:Fr.) Fr., C. evernius (Fr.:Fr.) Fr., C. obtusus (Fr.) Fr., C. paleaceus Fr., and C. strobilaceus Moser, were found every year. For the period as a whole, they accounted for 32% of the annual sporocarp biomass. Twenty-one species were observed during 1 year only. Cenococcum geophilum Fr. and Piloderma croceum Erikss. & Hjortst. accounted for 18 and 19%, respectively, of the mycorrhizal abundance of the mycorrhizal root tips examined. Using polymerase chain reaction (PCR) based molecular methods, we were able to distinguish 25 taxa forming mycorrhiza from soil cores covering a total of 22.5 cm² of the forest floor. Twelve of these taxa were identified using a sporocarp or mycelial culture based reference data base containing 25 of the sporocarp-producing species. These 12 species accounted for an average of 74% of the sporocarp biomass. In contrast, their share of the estimated mycorrhizal abundance and biomass was about 30%. At least half of the abundance of the belowground ectomycorrhizal community was accounted for by species that did not produce conspicuous epigeous sporocarps. Ascomycetes accounted for about 20% of the mycorrhizal abundance. Calculations showed that on a per hectare basis there was 8.8 kg of fungal biomass in the form of sporocarps (average annual cumulative production), an estimated 250–400 kg as mycorrhiza (standing crop) and 440 kg in the form of sclerotia of Cenococcum geophilum (standing crop). Key words: ectomycorrhizal community structure, ITS–RFLP, Picea abies.

Three cycles of successive trap cultures were utilized to determine the taxonomic structure of arbuscular fungi associated with mesquite (Prosopis spp.) from three locations in the Sonoran desertscrub biotic community and one location in the Chihuahuan desertscrub biotic community. Unlike the low species richness found in previous studies of some arid habitats, seven to nine species were recovered from each sampling site. This number is comparable to that found in many other plant communities. Seventy-five percent of the species found after three culture cycles were not detected in the first trap cultures, suggesting that a high proportion of arbuscular fungi in arid habitats may be nonsporulating in the field. Low colonization levels may account for the absence of sporulation, but ecological factors such as moisture limitations also may be involved. Although a total of 10 different species was detected, generic richness was limited, with 9 of these species in Glomus and 1 in Entrophospora. As long as measurement of species richness is based on occurrence of sporulation, successive trap cultures provide a means of detecting nonsporulating mycorrhizal colonizers in arid and other habitats. Keywords: vesicular – arbuscular mycorrhizae, ecology, desert, Glomales.

We used long-term litter decomposition data to estimate final decomposition levels using an asymptotic function. The estimated final limit values for decomposition were compared with available chemical data for the different litter types. A total of 41 limit values were estimated from as many different decomposition studies, and 20 different litter types were incubated in eight different forest systems. The limit values estimated varied with litter type. They ranged from about 35 to about 100% decomposition and were linearly related to the initial litter concentrations of N, Mn, and Ca in the newly shed litter. For these three nutrients, there are causal relationships to lignin degradation and to the lignin-degrading microbial community. Using all available data, we made simple and multiple linear regressions and obtained a negative linear relationship between limit value and initial N concentration ([Formula: see text]; n = 41; p < 0.001). For needle litter alone, we obtained a better relationship ([Formula: see text]; n = 23; p < 0.001). Manganese concentrations in litter gave a positive relationship ([Formula: see text]; n = 25; p < 0.001), with a clear improvement when needle litter was tested for alone ([Formula: see text]; n = 16; p < 0.001). Calcium alone gave a barely significant relationship. When combining nutrients in multiple linear relationships we obtained high R² values, indicating that the models were good. Thus for all sites and litter types, N, Mn, and Ca combined gave an [Formula: see text] value of 0.640 with n = 25 (p < 0.001). All needle litters combined gave an [Formula: see text] of 0.745 (n = 16; p < 0.001). The significance of this finding is discussed. Keywords: litter decomposition, limit values, maximum decomposition, nitrogen, manganese, calcium.