Recent advances in the understanding of the molecular hasis of plant response to ozone attack are reviewed. Plants grown in elevated atmospheric ozone are known to undergo several hiochemical changes before any actual damage can be detected. These reactions include increases in the activities of enzymes associated with general plant defence mechanisms. Ozone exposure often causes a surge in the production of the plant hormone ethylene, as well as changes in polyamine metabolism and increases in the activities of several phenylpropanoid and flavonoid pathway enzymes. The activities of superoxide dismutase and peroxidases that protect cells from the oxidative damage caused by hydroxyl radicals, H2O2 and superoxides also increase. However, ozone-induced changes in plant cells at the gene level are almost unknown. The limited data available suggest close similarities between ozone-induced and pathogen-induced defence responses in plants. Several general defence genes that have been cloned in other studies will soon be applied to studies of gene expression in ozone-exposed plants. The use of molecular biological tools in ozone research should enable the development of highly specific and sensitive molecular markers for biomonitoring ozone-induced injuries in plants. Methionine (e) AdoMe sperm idine Spermine -^ Ethylene Figure 2. Biosynthesis of ethylene and polyamines in plants.Known inhibitory (-) interactions of the pathways are indicated by the dashed lines. Ozone is known to induce ethylene synthesis, transcription of the ACC synthase gene, changes in the polyamine concentrations and induction of ADC activity. Abbreviations used: AdoMet = S-adenosyl methionine; ACC= 1-aminocyclopropane-1-carbocylic acid. Enzymes catalysing the reactions are indicated by the following numbers: 1, ACC synthase; 2, ACC oxidase; 3, AdoMet decarboxylase; 4, ornithine decarboxylase; 5, arginine decarboxylase; 6, spermidine synthase; 7, spermine synthase; 8, AdoMet syntethase.Received 2 September 1993,

Hemieellulose xylan is a major non-eellulose eomponent of wood. Xvlan hvdrol\-/,iii;.; activin' was detected iii eulture media of G. dbietitid. C. dbietitid grew well on xylan. Pme needle extract H V decreased x\'lanase aetivitv.

The rooting capacity in young and mature clones of S. sempervirens in vitro after wounding and treatment with indole-3-butyric acid (2.5x10 "5 M IBA) was linked with the characterisation of the hormone levels of indole-3-acetic acid (IAA)-related compounds and abscisic acid (ABA) in the bases of cuttings (5 mm long) during the first 4 days of the root inductive period. HPLC-ELISA and MS methods were used.Both clones rooted only in the presence oflBA but theauxin treatment was more efficient with young clone (60%, 10 days after treatment, 3 roots in average) than with mature one (30%, 13 days after treatment, only one root). High levels in IAA and IAA-aspartate (IAAsp) were measured in young clone whereas mature clone accumulated mainly IBA and indole acetonitrile (IAN). IBA treatment had no effect on ABA levels in young clone but induced high accumulation of ABA in mature clone. Hence, the different rooting capacity between clones could be related with quantitative changes in auxin and ABA metabolism.