Light controls bud burst in many plants, which subsequently affects their architecture. Nevertheless, very little is known about this photomorphogenic process. This study ascertains the effects of light on bud burst and on two of its components, i.e. growth of preformed leaves and meristem organogenesis in six cultivars from three Rosa species (R. hybrida L., R. chinensis L., R. wichurana L.). Defoliated plants were severed above the third basal bud and exposed, either to darkness or to different intensities of white light, to blue, red or to FR, at constant temperature. Bud bursting was inhibited in darkness in the six cultivars of Rosa, but not in Arabidopsis, tomato and poplar plants under the same condition. In all Rosa cultivars, bud burst, growth of preformed leaves and meristem organogenesis were triggered by blue and red lights, and extended by increasing light intensities. FR was inhibitory of bud burst. Partial shading experiments demonstrated that bud and not stem was the active site for light perception in bud burst.

SUMMARYAs a preliminary step towards elucidation of the molecular basis of ectomycorrhiza differentiation, polypeptide changes at different stages of mycorrhiza development were analyzed in birch {Betula pendula Roth). Timesequencing of the stages in the infection process of clonal plants inoculated with a compatible isolate of Paxillus involutus Batsch revealed that by 8 d mature ectomycorrhizas were obtained. Total phenol-extracted proteins of roots during the ' mycorrhiza formation stage' (2-8 d post-inoculation) were separated by two-dimensional polyacrylamide gel electrophoresis and the resulting patterns compared with non-mycorrhizal roots and mycelium. Alteration in the concentration of polypeptides from the host plant roots was limited even after 8 d of contact between the symbionts. However, seven novel polypeptides were detected 4 d after inoculation, three of them being already present m 2-d-old ectomycorrhizas. These findings demonstrate that symbiosis-related polypeptides accumulate in ectomycorrhizal roots prior to any of the morphological changes characterizing the symbiotic state.

In birch roots ( Betula pendula Roth), two members of the Bet v 1 gene family which encode PR 10 proteins have previously been characterized. One of these members, named Bet v 1-sc1 , is significantly induced in response to biotic or abiotic factors. We have analysed the expression of Bet v 1-sc1 in birch roots treated either with 1 µ M indole-3-acetic acid (IAA) or 1 µ M kinetin using reverse transcription-polymerase chain reaction (RT-PCR), northern blotting and competitive PCR. High accumulation of the Bet v 1-sc1 transcripts was recorded only after auxin application, while kinetin had no effect. By in situ hybridization, we have investigated the localization of Bet v 1-sc1 mRNA in birch roots after induction of the gene by root treatment with 1 µ M IAA. Using root tip sections, we showed that Bet v 1-sc1 is significantly expressed in the apical meristem and the procambium. In sections taken in the zone producing lateral roots, the presence of Bet v 1-sc1 was found at sites of emerging secondary root primordia. This first report of localization of Bet v 1-sc1 expression suggests that this gene could be involved in the processes leading to lateral root initiation.

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