Dianna J. Bowles

The wound response of tomato plants can be inhibited by aspirin and related hydroxy-benzoic acids

Abstract The response of tomato plants to injury or to treatment with cell wall fragments has been studied. Wounding, pectic fragments or chitosan causes the systemic accumulation of proteinase inhibitor proteins. This response can be inhibited by pretreatment of the plants by aspirin. The effect of aspirin is rapid and reversible. Related hydroxybenzoic acids are also inhibitory: the structural specificity required for inhibition is very similar to that demonstrated by others to be required for induction of pathogenesis-related proteins in tobacco.

Identification of calcium-dependent phospholipid-binding proteins in higher plant cells

Calcium‐dependent phospholipid‐binding proteins of apparent M r 33 000 and 35 000 were isolated from suspension cultures of tomato cells. Two‐dimensional gel electrophoresis showed the proteins to have isoelectric points of approx. 5.7 and 5.6, respectively. In the presence of calcium, both proteins bound to liposomes formed from a mixture of phosphatidylserine and phosphatidylcholine, but not to liposomes of phosphatidylcholine alone. Both proteins showed immunological similarities to previously characterized calcium‐dependent phospholipid‐binding proteins (annexins) from Torpedo marmorata and mammalian species. The protein of M r 33 000 cross‐reacted with three separate antisera raised to the annexin Torpedo calelectrin, whereas that of M r 35 000 cross‐reacted with antisera to the bovine annexins p68 and p32/34. We suggest that the two proteins may represent the first identification in higher plants of the annexin family of calcium‐dependent phospholipid‐binding proteins.

Gene expression in nematode-infected plant roots.

SummaryA major pathogen of potato plants (Solanum tuberosum) is the potato cyst nematode (Globodera spp.), which induces localized redifferentiation of a limited number of host cells to form a specialized feeding-site termed the syncytium. A novel strategy utilizing the polymerase chain reaction (PCR) was employed to construct a cDNA library from dissected potato roots highly enriched in syncytial material. The library was differentially screened with cDNA probes derived from the infected root tissue from a compatible interaction and from healthy root tissue. Characterization of one gene identified by the library screen indicated an expression pattern that correlated with events in the immediate vicinity of the pathogen after syncytial establishment. The strategy for library construction and screening could be applicable to the study of gene expression in any plant-pathogen interaction in which the limited supply of cells at the interface of the two organisms precludes a more traditional approach.

Determination of endogenous abscisic acid levels in immature cereal embryos during in vitro culture.

Levels of endogenous abscisic acid (ABA) in immature wheat (Triticum aestivum cv. Timmo) and barley (Hordeum vulgare cv. Golden Promise) embryos have been determined by enzyme-linked immunosorbent assay. Embryos of both cereal species showed an increase in ABA content during development on the parent plant. Immature embryos were excised and cultured in vitro on nutrient media that led to precocious germination or on media containing 9% (w/v) mannitol that maintained their developmental arrest. Barley and wheat embryos responded to these culture conditions in an identical manner with respect to changes in morphology, fresh weight, protein and lectin content. However, in complete contrast, the ABA content of barley embryos increased by an order of magnitude during culture on mannitol, whereas that of wheat embryos showed no significant change. The results are discussed within the context of the role of ABA in the regulation of embryo development.

Traffic and assembly of concanavalin A

Abstract Concanavalin A (ConA) is synthesized and packaged into protein bodies during jackbean development. Recent results have shown that traffic of proteins within the plant cells can be disrupted by monensin, when lectin precursors are mis-routed to the cell surface instead of targeted to their correct intracellular destination. In vivo , ConA is first synthesized as a glycoprotein precursor that is incapable of interacting with carbohydrate. We now know that this precursor is deglycosylated and cleaved into fragments that become reannealed with a post-translational peptide bond to construct the mature protein.

Systemic accumulation of novel proteins in the apoplast of the leaves of potato plants following root invasion by the cyst-nematode Globodera rostochiensis

Abstract Systemic changes in gene expression have been analysed in potato plants following root infection with the cyst nematode Globodera rostochiensis . Root invasion by the pathogen induced major changes to occur in the composition of proteins extracted in intercellular fluid from the leaf apoplastic space. The changes involved the disappearance of innate leaf proteins and the accumulation of novel gene products. Analysis by SDS-PAGE indicated that the leaf polypeptides induced on nematode invasion are not cultivar or nematode pathotype-specific. Aspirin treatment of leaves induced a similar pattern to that induced systemically by nematodes, but several gene products were specific for the latter method of induction. In particular, two abundant [ 125 I]-Con A binding polypeptides of high M r accumulated in intercellular fluid only on aspirin treatment. The results are discussed in the context of the role of the extracellular leaf proteins and their modulation by systemic signals.

Endopeptidase activity in dry harvest-ripe wheat and barley grains

Abstract Endopeptidase activity has been measured in harvest-ripe mature grains of wheat and barley using [ 125 I]-iodoinsulin B chain as an exogenous substrate. High levels of endopeptidase activity were found in the embryo and endosperm of both cereals. The principle activity is that of an acidic carboxyendopeptidase that can be inhibited by pepstatin. This finding has important consequences for isolation protocols of cereal proteins that involve acid extraction.

Lectins as membrane components: implications of lectin--receptor interaction.

There is increasing evidence that carbohydratecontaining components of cellular membranes play a role in recognition phenomena. Attention has centred on glycoproteins and glycolipids as cell membrane receptors for extrace~lular signals [ 1,2]. ~thou~ it is implied that these glycosylated species function in the transmission of signals across the surface membrane, the exact nature of this transmission and the means by which it influences cellular events is little understood 131. Many investigations have shown that carbohydrate-binding proteins (lectins) are located within a wide variety of cells and membranes (reviews [4-61). These results have raised the possibility that endogenous lectins could be involved in cellular communication. It would like to develop this suggestion further and put forward a model in which an underlying principle governing recognition events both between cells and within cells is the specific interaction of a melnbrane-bound lectin with its receptor.

Characterisation of receptors for the endogenous lectins of soybean and jackbean seeds

Soybean (Glycine max) and jackbean (CanavaZia en&for&) are species of legumes that are characterised by large quantities of water-soluble seed lectins [ 11. The major lectin of soybean, soybean agglutinin (SBA) is a glycoprotein with a sugar specificity related to D-galactose. In jackbean, the major lectin, concanavalin A (con A) is a protein with a sugar specificity related to D-mannose. Immunological techniques and peptide sequencing data has demonstrated that seed lectins represent a highly conserved family of proteins in the plant kingdom [2-41. As a way into studying the function of these lectins, we have investigated the nature of the glycoconjugates in the storage tissue of the seeds that the endogenous lectins can recognise.

Changes in abundance of translatable mRNA species in potato roots and leaves following root invasion by cyst-nematode G. rostochiensis pathotypes☆

Changes in gene expression have been studied for the interaction between potato plants carrying the H1 genotype and the potato cyst nematode Globodera rostochiensis. H1 confers resistance to the pathotype Ro1 of the nematode but is susceptible to the pathotype Ro2. Following synchronized infection of the roots with the two pathotypes, polysomal mRNA species have been extracted from root and leaf tissue over a time-course of 6 h to 6 days. Comparison of the pattern of [35S]-labelled translation products from the mRNA, have enabled stage-specific changes to be identified in plants exhibiting a resistance or a susceptible response. n nThe results indicate nematode invasion does not lead to gross changes in the pattern of root gene expression, but does induce rapid and massive changes in leaf gene expression. n nThe changes in both organs involve the appearance of several novel gene products. In addition, in the leaves, genes normally expressed in healthy plants have an altered pattern of expression. Whereas some effects are common to resistant and susceptible plants and most probably reflect general pathogenesis, others are highly specific for the plants interaction with each nematode pathotype.