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Abstract: Prunus persica plants were grown under prolonged exposure to different light treatments to determine the interaction between the blue light (BL) receptor and phytochrome and/or an independent BL response in the photoregulation of shoot and leaf development. Different light conditions were established in growth chambers by changing both the state of phytochrome and the BL photon flux density (PFD) at constant photosynthetically active radiation (PAR). Furthermore, to evaluate the independent action of the BL photoreceptor, increasing amounts of BL photons were added to the light emitted by low-pressure sodium (LPS) lamps without altering irradiance and phytochrome photoequilibrium. Applying the principle of equivalent light action, the observed blue inhibition of shoot elongation, leaf expansion and thickness were clearly related to a specific BL receptor because the state of phytochrome for each treatment was nearly identical. Increasing amounts of blue photons to light emitted from LPS lamps decreased shoot elongation, whereas leaf expansion was negatively affected only at the highest blue level, suggesting a specific fluence dependence response to BL for each organ and tissue. The BL effect was evident in reducing the thickness of all the leaf tissues except for the upper epidermis, which became thicker. This could be the result of an adaptation to protect the underlying photosynthetic apparatus. Other morphological and anatomical responses to the action of the BL receptor were greatly altered when the state of phytochrome changed in the plant tissues.

Six agriculturally important fruit species were screened for emissions of isoprene and other volatile organic compounds (VOCs) at full bloom. The air from a Teflon growth chamber containing the tested plants was collected on carbon absorbents and analyzed by thermal desorption gas chromatography and mass spectrometry (TD-GC-MS). Over 80 individual compounds were identified. All the screened species were isoprene emitters and revealed a unique fingerprint profile determined by monoterpenes. Differences in relative composition of monoterpenes occurred mainly between pome and stone fruit plants. Linalool was emitted exclusively by apple and pear flowers, whereas apricot, cherry and plum showed a pattern dominated by α-pinene and to a less extent by camphene. Limonene appeared to be the most abundant emitted compound from peach flowers. Preliminary quantification of monoterpene emissions indicated that, at full bloom, cherry was the major emitter and peach the minor one.

The effects of an arbuscular mycorrhizal fungus (Glomus sp) on development and carbohydrate metabolism of micropropagated plantlets of a pear clonal rootstock (OH x F 51) were examined during the first vegetative growth and at the beginning of the second growing year. Plant growth was assessed in terms of stem height, leaf number, root length, fresh and dry weight of the whole plant, stem, leaves and root mass at different times following inoculation. The levels of soluble (fructose, glucose, sucrose and sorbitol) and insoluble (starch) sugars were analyzed in stems, leaves and roots using gas-chromatographic techniques. Inoculation with Glomus sp was effective in promoting plant growth causing a strong increase in shoot height, root length and a greater growth rate of dry matter. Colonization of rootstock roots with Glomus sp altered the carbohydrate metabolism and partitioning within the plant. Croissance et ?tat des glucides chez des microplantes de Pyrus communis L inocul?es avec Glomus sp. Les effets d'un champignon mycorhizog?ne ? arbuscule (Glomus sp) sur la croissance et sur le m?tabolisme glucidique d'un porte-greffe micropropag? de poirier (OH x F 51) ont ?t? examin?s pendant les premiers stades et au d?but de la deuxi?me ann?e de d?veloppement. La croissance des plantes a ?t? ?valu?e, ? diff?rentes p?riodes apr?s inoculation, par des mesures de hauteur de tige, de nombre de feuilles, de longueur de racines et de poids de mati?re fra?che et s?che. Le contenu en glucides solubles (fructose, glucose, saccharose et sorbitol) et insolubles (amidon) a ?t? mesur? dans les tiges, les feuilles et les racines par chromatographie gazeuse. L'inoculation avec Glomus sp s'est r?v?l?e efficace pour stimuler la croissance des plantes en induisant une forte augmentation de la hauteur des tiges, de la longueur des racines et du taux de mati?re s?che par rapport aux t?moins. La colonisation des racines de porte-greffes par Glomus sp a provoqu? aussi un changement au niveau du m?tabolisme des glucides et de leur r?partition dans la plante.