Wounding in higher plants leads to an increased synthesis of specific messenger RNAs. A cDNA clone complementary to a wound-induced message from potato tubers was used to isolate a lambda clone from a genomic library of Solanum tuberosum var. Maris Piper. DNA sequence analysis has shown that this single genomic clone contains two novel wound-induced genes, called win1 and win2, organised in close tandem array. The coding sequences of these two genes are highly homologous and are interrupted by a single intron. However, the sequences of the introns and flanking regions have diverged widely. Win1 and win2 encode cysteine-rich proteins of 200 and 211 amino-acids, respectively, which show striking homologies to several chitin-binding proteins. Southern analysis of genomic DNA has shown that win1 and win2 are members of a small multi-gene family which is estimated to have a minimum of five members per haploid genome of Maris Piper and appears to be conserved within the Solanaceae. We have shown by Northern analysis and S1 mapping that the two genes exhibit differential organ-specific expression after the wounding of a potato plant.

The glutamine synthetase (CS) gene family of Medicago truncatula Caertn. contains three genes related to cytosolic GS (MtCSa, MtCSb, and MtCSc), although one of these (MtGSc) appears not to be expressed. Sequence analysis suggests that the genes are more highly conserved interspecifically rather than intraspecifically: MtCSa and MtCSb are more similar to their homologs in Medicago sativa and Pisum sativum than to each other. Studies in which gene-specific probes are used show that both MtCSa and MtCSb are induced during symbiotic root nodule development, although not coordinately. MtCSa is the most highly expressed CS gene in nodules but is also expressed to lower extents in a variety of other organs. MtCSb shows higher levels of expression in roots and the photosynthetic cotyledons of seedlings than in nodules or other organs. In roots, both genes are expressed in the absence of an exogenous nitrogen source. However the addition of nitrate leads to a short-term, 2-to 3-fold increase in the abundance of both mRNAs, and the addition of ammonium leads to a 2-fold increase in MtCSb mRNA. The nitrogen supply, therefore, influentes the expression of the two genes in roots, but it is clearly not the major effector of their expression. In the discussion section, the expression of the CS gene family of the model legume M. truncatula is compared to those of other leguminous plants.GS (EC 6.3.1.2) is a key enzyme in the nitrogen metabolism of higher plants, catalyzing the assimilation of ammonium to form Gln. This ammonium is derived from the primary nitrogen sources of the plant (through the reduction of soil nitrate and, in the case of legumes, by the symbiotic fixation of atmospheric nitrogen), as well as from other metabolic pathways such as photorespiration, phenylpropanoid metabolism, and the catabolism of amino acids (Lea et al., 1990). These pathways occur to varying extents in different tissues and subcellular locations, which is reflected by the fact that in higher plants GS exists as a number of distinct isoenzymes located in both the cytosol and the chloroplast, which have different activities in different organs (McNally and Hirel, 1983). These multiple isoenzymes are encoded by a small family of genes that, in tum, have been shown to be differentially expressed in both a developmental-and organ-'This work was supported by a fellowship to A.C.S. from the

Transcriptional fusions between the gene encoding win2 from potato and the reporter gene encoding beta‐glucuronidase (GUS) have been used to study the spatial and temporal patterns of wound induced gene activity in transgenic potato and tobacco plants. Gene fusions containing a full length win2 promoter were found to be correctly regulated in response to mechanical wounding in transgenic potato, but not in the heterologous host, tobacco. Sequences greater than 560 bp upstream of the transcription start site of win2 were shown to be important for wound inducibility. The dramatic induction of GUS activity detected using fluorometric assays of extracts of wounded and aged leaves of several independent win2‐‐GUS transformants was consistent with the kinetics of win2 mRNA accumulation. Histochemical analysis of wounded leaves showed that transcription first occurred in cells immediately adjacent to the wound, and was then progressively induced in cells associated with the vascular system at a distance from the wound site. In tubers, a localized response to wounding was observed, and this only spread to other parts of the tuber if it had started to sprout. It was concluded that active vascular transport was necessary for the spread of wound response. Win2‐‐GUS fusions were also expressed as part of normal plant development, as GUS activity was detected in the developing buds and in a layer of cells associated with the lenticels of unwounded tubers.

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