A 10 bp sequence motif (TCATCTTCTT) which is repeated several times in the 5' non-transcribed region of a barley beta-1,3-glucanase gene is also present in the non-translated regions of over 30 different plant genes which are known to be induced by one or more forms of stress. Gel retardation assays and South-western blotting experiments provide evidence that the motif is the binding site for a tobacco nuclear protein with an apparent molecular weight of 40 kDa. Binding activity is increased when nuclear extracts from salicylic acid-treated plants are analysed compared with extracts from control plants, indicating that the protein itself is either induced or modified under conditions of stress. These observations suggest roles for the 10 bp motif and its binding protein as cis- and trans-acting regulators of gene expression during response to stress.

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The induction and substrate speci®city of cinnamyl alcohol dehydrogenase (CAD, EC 1.1.1.195) was investigated in relation to the deposition of a defensive, syringyl-rich lignin at wound margins in wheat (Triticum aestivum L. cv. Brigadier). Column chromatography of untreated, wounded and elicitor-treated tissues revealed three major CAD forms (CAD-A, -B and -C) of which only CAD-C was responsive to elicitors. Examination of the substrate preference of these fractions indicated p-coumaryl alcohol to be the preferred substrate of CAD-A and CAD-B, whereas sinapyl alcohol was favoured by CAD-C. Activity-stained isoelectric focussing gels revealed in untreated and wounded leaves four CAD isoenzymes with isoelectric points of 4.59 (i), 4.67 (ii), 4.81 (iii), 4.93 (iv). Elicitor treatment generally enhanced the staining of all isoenzymes and resulted in the appearance of two new isoenzymes of 5.22 (v) and pI 5.31 (vi). In activity stained non-denaturing PAGE gels, CAD-C further resolved into two distinct zones of CAD activity. Cinnamyl alcohol dehydrogenase-C was puri®ed to apparent homogeneity and characterisation revealed a 45-kDa subunit peptide which in its native form demonstrated a marked substrate preference for sinapyl alcohol. Overall, the dierential induction and substrate preference of CAD-C are consistent with a defensive role during defensive ligni®cation at wound margins in wheat.Abbreviations: CAD = cinnamyl alcohol dehydrogenase; IEF = isoelectric focussing; pI = isoelectric point Correspondence to: M.S. Barber;

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SUMMARYWe studied aspects of the structure and expression of the genome of Bari 1, a mild strain of cauliflower mosaic virus. Differences were observed between gene products of Bari 1 detected in inclusion body preparations and those of the more typically severe strain, Cabb B-JI. The most striking difference was the gel mobility of the Bari 1 gene VI polypeptide (apparent Mr 70K) which contrasted with that of Cabb B-JI (Mr 62K). This difference was also observed between products of in vitro translation of viral mRNA suggesting that it was not due to post-translational modification. The open reading frame in the nucleotide sequence of the Bari 1 gene VI region was very similar in size to that of other CaMV strains but corresponded to an amino acid sequence with a much lower overall homology and diverged greatly in a 40 base pair sequence in the 3' region compared to gene VI sequences of other strains. The level of the Bari 1 aphid transmission polypeptide P18, the product of gene II, was much lower than that of Cabb B-JI. Some of the possible subcellular consequences resulting from the molecular properties of Bari 1 were examined by electron microscopy. Differences were observed in the composition and intactness of Bari 1 cytoplasmic inclusion bodies compared with those of a severe strain, and the presence of nuclear inclusions.