Lipids are the major form of carbon storage in arbuscular-mycorrhizal fungi. We studied fatty acid synthesis by Glomus intraradices and Gigaspora rosea. Our data strongly suggest that the fatty acid synthase activity of arbuscular-mycorrhizal fungi is expressed exclusively in the intraradical mycelium and indicate that fatty acid metabolism may play a major role in the obligate biotrophism of arbuscular-mycorrhizal fungi.

A 2-year experiment with Prunus ×cistena sp. was conducted in pots using seven substrates composed of various proportions of primarily peat, compost and bark. Peat substrates significantly affected root and shoot dry weight. Water desorption characteristics and saturated hydraulic conductivity were measured in situ to estimate the pore tortuosity factor and the relative gas diffusion coefficient. The pH, electrical conductivity, C/N ratio, total and hydrolyzable N, as well as NO3--N and NH4+-N in solution were also measured. Estimates of the physical properties suggest that a lack of aeration limited plant growth. Plant growth was significantly correlated with both the gas relative diffusivity and the pore tortuosity factor. Among the chemical factors, pH and soil nitrate level were also correlated with plant growth. No significant correlation was found between plant growth and air-filled porosity or any other measured chemical properties. This study indicates that an index of gas-exchange dynamics could be a useful complementary diagnostic tool to guide substrate manufacturing.

Pour la première fois, toutes les étapes de la micropropagation de l'érable à sucre (Acer saccharum Marsh.) ont été complétées avec succès. Les bourgeons de plus de 200 plants d'érable à sucre âgés de 2 ans ont été débarrassés de leurs écailles et mis en culture sur un milieu contenant les sels de Murashige et Skoog ainsi que les éléments organiques de Bourgin et Nitsch, tous dilués au tiers, avec ou sans régulateur de croissance. Le taux de survie des explants en fin d'induction a été supérieur sur un milieu sans régulateur de croissance. La formation de tigelles et la multiplication ont été accomplies sur les mêmes milieux additionnés de 0,01 ou 0,025 mg·L -1 de thidiazuron ainsi que du 6-(γ γ , -diméthylallylamino)purine, du 6-(γ γ , -diméthylallylamino)purine riboside ou de l'acide phénylacétique (APA). Les tigelles se sont allongées sur des milieux contenant 0,3 mg·L -1 d'APA et l'induction racinaire a été réalisée sur des milieux contenant 0,3 mg·L -1 d'APA en présence d'acide naphtalène-acétique. Quelques tigelles se sont enracinées lorsque transférées dans de la vermiculite. Bien que le taux de réussite soit faible, des tiges enracinées ont été produites par la multiplication de bourgeons.Abstract: For the first time, all stages required for the micropropagation of sugar maple (Acer saccharum Marsh.) have been successfully completed. Buds of more than 200 seedlings of two-year-old sugar maple trees were stripped of their scales and cultured on media containing Murashige and Skoog salts with Bourgin and Nitsch organic elements, all diluted to 33%, with or without growth regulator. Survival rate after induction was higher in media without growth regulator. Stem formation and multiplication succeeded in media of the same composition but containing 0.01 or 0.025 mg·L -1 thidiazuron, as well as 6-(γ γ , -dimethylallylamino)purine, 6-(γ γ , -dimethylallylamino)purine riboside, or phenylacetic acid (PAA). Stem elongation took place in media with 0.3 mg·L -1 PAA. Root induction was achieved in media containing 0.3 mg·L -1 PAA with naphthaleneacetic acid. A few shoots rooted when transferred into vermiculite. Although the overall rate of success is still low, rooted shoots were produced by bud multiplication.Brassard et al. 690

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