Ph.D. / In plants, salicylic acid (SA) is a signaling molecule that regulates disease resistance responses such as systemic acquired resistance (SAR) and the hypersensitive response (HR), and has been implicated in both basal and acquired thermotolerance. It has also been shown that SA enhances heat-induced Hsp/Hsc70 accumulation in plants. In this study, temperature studies revealed that heat shock (HS) at 40 °C for 30 min significantly induced Hsp/Hsc70 accumulation in 3-week old tomato (UC82B) seedlings. Time- and dose-responsive studies showed that 0.1 mM SA for 17 hrs was unable to induce Hsp/Hsc70 but in combination with HS significantly (P > 0.001) potentiated this response. To investigate the mechanism of SA-mediated, heat-induced Hsp/Hsc70 potentiation, tomato seedlings were treated with either SA alone, HS or both, before analyses of hsp70 mRNA, Hsf DNA-binding and gene expression of hsp70, hsfAl, hsfA2 and hsfEll. SA alone established Hsf DNA-binding, but was not accompanied by increased Hsp70 accumulation or expression of hsp70 mRNA. SA had no significant effect on hsfA2 and hsf81 gene expression, but increased the basal levels of hsfAl. In heat-shocked plants, Hsf DNA-binding was enhanced, and increased hsfAl, hsfA2 and hsfB1 expression preceded accumulation of Hsp70. The combined treatment of SA and HS resulted in potentiated Hsf DNA-binding, enhanced expression of hsp70, hsfAl, hsfA2 and hsfB1, leading to potentiated levels of Hsp/Hsc70. Since increased hsp70 and hsf gene expression coincided with increased levels of Hsp70 accumulation, it is likely that the SA-mediated potentiation of Hsp70 is due to the ability of SA to regulate Hsfs during HS. This study therefore proposes a mechanism for the potentiation of Hsp70 by SA in the presence of heat, which might contribute to our understanding of the role SA plays in the heat shock response and thermotolerance.

Plants have evolved mechanisms to defend themselves against pathogen attack. These defense mechanisms consist of a series of inducible responses (including specific recognition of pathogen invasion, signal transduction and defense gene activation) that result in resistance. Plants responses to pathogen invasion also result in the suppression of various housekeeping activities of the cells, thus diverting the cellular resources to defense responses. Systemic acquired resistance (SAR), an inducible defense response enhanced as a result of initial infection with a necrotising pathogen, lead to long-term resistance in a plant. Differential gene expression of genes related to defense in cultured cotton cells and leaf disks that have been challenged with a purified elicitor from Verticillium dahliae, as well as a chemical inducer of defense responses, DL-b-amino-n-butyric acid, were investigated. The mRNA differential display reverse transcriptase polymerase chain reaction (DDRT-PCR) was used to identify differentially expressed genes 5 h after application of either 50 mg mL-1 Verticillium dahliae elicitor or 1 mM DL-b-amino-n-butyric acid to cotton cell suspension cultures and leaf disks. Identified cDNAs up- or down-regulated for this study were classified into seven groups: ‘Transcription factor’, ‘Ubiquitin and Proteasome’, ‘Mitochondria’, ‘Protein kinase/Receptor-like kinase’, ‘Defense/Resistance’, ‘Carbohydrate metabolism/Cell wall’ and ‘Other’. The identified cDNAs up-regulated after Verticillium dahliae elicitor treatment, classified in the ‘Transcription factor’ group, coded for a MYB family transcription factor, zinc finger protein and a RMA1 RING zinc finger protein. The identified cDNA classified in the ‘Mitochondria’ group coded for a cytochrome C oxidase subunit I and II and the cDNA classified in the ‘Protein kinase/Receptor-like kinase’ group coded for a serine/threonine protein kinase. The identified cDNA classified in the ‘Defense/Resistance’ group coded for a disease resistance protein family and the cDNAs classified in the ‘Carbohydrate metabolism/Cell wall’ group coded for a beta-1,4-Nacetylglucosaminyltransferase, a cellulose synthase-like protein, a 3-deoxy-D-manno-octulosonic acid transferase-like protein and a hydroxyproline-rich glycoprotein homolog. In addition, a cDNA classified in the ‘Other’ group, coded for a urea active transporter-like protein. The cDNA identified that was down-regulated after Verticillium dahliae elicitor treatment, classified in the ‘Carbohydrate metabolism/Cell wall’ group, coded for a proline-rich protein family and cDNAs classified in the ‘Other’ group coded for a thioredoxin reductase1 and ‘hookless1’ homologue. Among the identified cDNAs up-regulated after DL-b-amino-n-butyric acid treatment, classified in the ‘Ubiquitin and Proteasome’ group, were a 20S proteasome subunit alpha type 5 and an ubiquitin. The identified cDNA classified in the ‘Mitochondria’ group coded for a NADH dehydrogenase subunit 6, a mitochondrial DNA product. The identified cDNAs classified in the ‘Other’ group coded for an armadillo repeat containing protein and a phosphoinositide-specific phospholipase C. The cDNA identified that was down-regulated after DL-b-amino-n-butyric acid treatment, classified in the ‘Protein kinase/Receptor-like kinase’ group, coded for a casein kinase I like protein. The identified cDNA classified in the ‘Carbohydrate metabolism/Cell wall’ group, coded for a putative glycine rich protein. Also, the identified cDNA classified in the ‘Other’ group, coded for a NADH dehydrogenase subunit F that is coded for by chloroplast DNA. The differential expression of the cDNAs up-regulated after the Verticillium dahliae elicitor treatment was confirmed for seven of the nine cDNA clones with a Reverse Northern dot blot. Also, the differential expression of two cDNAs up-regulated after DL-b-amino-n-butyric acid treatment was confirmed and the induction kinetics was followed with a Reverse Northern dot blot. The mRNAs corresponding to C8B5, the gene encoding an ubiquitin, were detectable after 2.5 h and showed a significant increase in expression up to 7.5 h, after which the expression levels decreased to levels similar to those detected at 2.5 h. The mRNAs corresponding to L4B4, a homologue of an a-type subunit of 20S proteasome, were detectable after 2.5 h with an gradual increase in expression levels up to 7.5 h after which the expression levels decreased to levels similar to those detected at 2.5 h. This study facilitated a better understanding of differential gene regulation during triggering of defense responses in cotton following elicitation with the Verticillium dahliae elicitor and DL-b-aminon- butyric acid. / Prof. I.A. Dubery

M.Sc. / Plant disease can be naturally suppressed by plant growth promoting rhizobacteria and endophytic / endorhizosphere bacteria. Apart from direct antagonism against pathogenic organisms, these plant growth promoting bacteria and endophytes can induce a form of systemic resistance (ISR) in plants. The main bacterial inducing component has been suggested to be the outer membrane lipopolysaccharides (LPS), found in the cell walls of Gramnegative bacteria. Burkholderia cepacia (Pseudomonas cepacia) is a bacterial endophyte that has potential as a biocontrol agent. Although a few studies have indicated that LPS from, certain Pseudorrionads has a protective effect in plants against disease, a controlled investigation has not been attempted previously with a purified preparation of LPS. LPS was isolated from the bacterial cell wall, prepared and characterized by denaturing electrophoresis. Characterization of the LPS also included the determination of 2-keto-3-deoxyoctonate, carbohydrate —, as well as the protein content. The purified LPS was found to possess activity as an elicitor of plant defence responses in tobacco where the induction of pathogenesisrelated (PR) proteins were investigated and electrophoretically analysed. An optimum LPS concentration range of 50-150 14/m1 was determined by studying cell death using the Evans blue procedure. Time and concentration ranges for LPS induced responses were established in cell suspensions, leaf discs, whole leaves and whole plants. It was determined that the PR-protein response could be optimally induced after four days following elicitation with 100 fag/ml LPS. Systemic induction of resistance was tested by treatment of the lower leaves and following the response in the upper leaves; as well as bacterial inoculation of the plant roots followed by PR-protein extraction of the leaves. Treatment of tobacco plants with LPS protected the plants against subsequent infection by the pathogen Phytophthora nicotianae, thereby suggesting a role for LPS as activators of systemic acquired resistance (SAR). It can be concluded from this study that the lipopolysaccharides from Burkholderia cepacia, that were used in this study, are effective local as well as systemic inducers of the defense PR-proteins in Nicotianae tabacum cv Samsun NN. The fact that protection is associated with PR-protein induction distinguishes it from the protection induced by rhizobacteria.

The Russian wheat aphid (RWA) (Diuraphis noxia Kurdjumov) is a major pest of cultivated small grains. It is particularly devastating because of is high reproductive rate which results in the growth of large populations which become damaging to its host plants. Development of resistant barley (Hordeum vulgare L.) cultivars is complicated as resistance is polygenic. As a result, the industry remains at risk now that the RWA has spread throughout South Africa. It has, as recently as, 2013, been identified in the SW Cape, which was previously geographically isolated. This is South Africa‟s principle barley growing region. Now a potentially huge problem exists. Therefore, it is imperative that an alternative to pesticide use is found. Testing potential innate resistance in barley cultivars is thus, critical. In this thesis, I present data on four barely cultivars where I have examined their resistance/ lack of resistance to three known RWA biotypes, RWASA1, RWASA2 and RWASA3. The barley varieties used were two economically important South African malt barley cultivars (S5 and SSG 564) along with two potentially RWA resistant Afghan accessions (CIho 4125 and CIho 4159). The RWA biotype population growth rates on each of the plants were determined over a 14 day period. The aim was to establish baseline data of the effects of RWA population growth on the host plants under ambient CO2 (380 – 400 ppm) conditions. The extent of RWA feeding damage was investigated at the cell level by examining saliva deposition and cell disruption using Transmission Electron Microscopy; at the tissue/vascular level using fluorescence microscopy, to determine the extent of callose formation; at a whole leaf level by recording percent chlorosis and leaf roll; and finally, at a whole plant level by measuring biomass loss.The experiments were repeated under elevated CO2 (450 ppm) to model any changes in RWA/plant interaction with respect to future climate change. The effects of an elevated CO2 environment and RWA feeding on host plant foliar N and C:N ratio were compared to ambient CO2 conditions, to provide a clearer picture of the potential nutrient drain that a feeding RWA colony exacts on its host. Of the varieties tested, the CIho accessions performed better than the two SA barley cultivars as the CIho accessions appeared to express a mild antibiosis resistance response as RWA populations, particularly those of RWASA1, were smaller than those observed on either S5 or SSG 564. In addition, less damage was evident in the two CIho accessions due to RWA feeding. II RWASA2 was the most virulent of the three RWA biotypes tested, followed by RWASA3 while RWASA1 was the least virulent. Under elevated CO2 conditions, RWA feeding damage was exacerbated but the trend of biotype virulence remained the same. Higher aphid population sizes were recorded under elevated CO2, meant that even the more resistant CIho accessions were overcome by the increased demand made by the larger aphid colonies on the host plants. The % foliar N data showed that under elevated CO2 aphid-free control plants had increased N levels in their leaves. Increased “food” supply (as shown by the increased N levels) therefore allowed significantly larger aphid populations to develop on the plants exposed to elevated CO2, due to improved nutrient status of the phloem sap taken up by RWA. The knock-on effect of a higher aphid population was increased cell disruption as a result of extensive probing, extensive formations of wound callose, with the result that phloem damage impeded nutrient flow through the vascular tissues which contributed to chlorosis and (eventually plant) death. The major conclusion from this study is that even a mild CO2 elevation resulted in an increase aphid population which may pose a severe and very real threat to a barley crop. Therefore, without effort to identify and deploy resistant barley cultivars, it could well be possible that future barley cultivation in South Africa may no longer be viable.

Initially, protoplasts were isolated to detect various parameters using flow cytometric analysis. The most efficient ratio of cells to enzyme solution, for digestion of cell walls, needed to be established. To detect whether the time of incubation with the enzyme solution influenced the state or viability of the protoplasts, they were observed periodically under the light microscope during digestion at different concentrations of enzyme solution. After 2 h digestion with light swirling every 20 min, the protoplasts were still intact (Figure 1), and viable as detected with Trypan blue staining (results not shown). Increasing the digestion period led to a decrease in cell membrane integrity. The size of the protoplasts varied between 60 mm and 90 mm. Figure 1 shows the difference between cells before digestion with an enzyme solution and protoplasts after digestion. Size determination of protoplasts was important since the flow tip of the flow cytometer is limited to 100 mm and if the protoplasts exceeded this size, could lead to blockages in the flow tip of the flow cytometer, with ineffective readings and a time consuming clean-up process. / Dr. Marianne J. Cronje

Prof. I.A. Dubery

M.Sc. / Wheat is one of the most extensively grown small grain crops in Southern Africa. It is a staple food source used by humans, animals and other living organisms around the globe (Feldman, 2001). One of the major threats of wheat production in South Africa is the Russian wheat aphid (RWA), (Kurdjumov), (Diuraphis noxia, Homoptera: Aphididae) (Brooks et al., 1994; Du Toit & Walters, 1984). The RWA was first described as a pest in South Africa in 1978 and in the US in 1986. Thereafter it was rapidly reported as becoming a major pest of cereals in these countries (Brooks et al., 1994; Du Toit & Walters 1984). A short life span, asexual reproduction, the development of resistance towards insecticides and rapid colonisation of the host plant are all factors that have made the management of the RWA a difficult task (Dogimont et al., 2010; Hein et al., 1998). As a result of complications such as these, host plant resistance is the most viable option to counter the RWA (Dogimont et al., 2010). The method of feeding of the RWA is detrimental to the plant as they insert their stylets into, and feed primarily from, the phloem sieve elements. This damages the plants through nutrient drainage (Dixon, 1985; Klingler et al., 2009) and results in a variety of symptoms, the most common being chlorosis, necrosis, wilting, stunting, curling of the leaves (which provides the pest with a sheltered environment protected from predators and pesticides), misshapen or nonappearance of new growth, and localised cell death at the site of aphid feeding. The RWA elicits an increase in essential amino acids in the phloem sap, by triggering the breakdown of proteins in infested wheat leaves (Burd & Burton, 1992; Du Toit, 1986; Haley et al., 2004; Ma et al., 1998; Miller et al., 2001; Walters et al., 1980). It also reduces transport of labelled tracers (amino acids) from the feeding site to the roots and other sinks in the plant. This increases the nutrient concentration at the site of aphid feeding by increasing the import of resources from other sites in the plant, mobilising local resources and blocking their export to other organs. The damage of the foliar tissue that occurs as a result of the RWA feeding is thought to play a role in the pest’s ability to increase the nutritional quality of the host plant (Botha et al., 2006; Goggin, 2007; Shea et al., 2000).

M.Sc. / LPS, as a pathogen associated molecular pattern (PAMP) molecule can interact with eukaryotic host cells. Interaction occurs by either direct contact or due to the release of micelles containing LPS from bacterial cell surfaces. LPS activates innate host defence systems in both invertebrate and vertebrate animal/insect cells via analogous pathways, where the lipid A component,is responsible for the activities. LPS from several plant pathogens have been shown to activate a number of defence-related responses in plants. Initial concentration studies and cell viability assays were conducted to assess isonitrosoacetophenone (INAP) and LPS as elicitors of defensive responses in tobacco (Nicotiana tabacum cv. Samsun) cell suspensions. The effective concentrations were found to be 100vM INAP and 100μg/ml LPS. RNA was isolated, quantified and analysed to confirm the quality of the starting material for differential display analysis. The DDRT-PCR technique was successfully applied in order to obtain comparative "displays" of PCR amplicons derived from three sub-divided mRNA pools (i.e. each of the three different anchor primers, per treatment). Significant differences in the profiles of control, INAP and LPS treated cells were observed, indicating that the eliciting agents had prominent effects on cellular homeostasis, resulting in an altered gene expression profile. DDRT-PCR can be technically challenging at a number of steps. Modifications were incorporated to initially obtain differentially expressed transcripts (DETs), as well as reamplify the DETs. 223 Putative DETs were isolated from denaturing polyacrylamide sequencing gels. 172 Putative DETs were re-amplified, of which 126 appeared as good candidates for further analysis. Finally, 96 putative DETs were chosen for reverse Northern analysis. DDRT-PCR has been reported to be plagued by false positives. Reverse Northern analysis confirms the presence of the putative DET from the subdivided RNA pool, as well as affirming the differential expression, compared between the control and inducer blots. 26 DETs were selected for cloning, of which 16 were sequenced. Homologies between the DETs and known sequences were determined using BLASTN and BLASTX alignments, DNAssist software, as well as MIPS alignments to the Arabidopsis genome. Five of the DETs were assigned putative functions in plant signal perception, transduction and the defence response, based on their respective sequence homologies to sequences involved in innate immunity. It is proposed that the DET, HAP3-15, represents the plant equivalent of a component of the innate immunity pathway in mammals and Drosophila. It is further proposed that HAP3-15 represents a S-Receptor kinase protein (SRK), with a defensive role in distinguishing self from potential pathogens. Therefore, as a SRK, HAP3-15 would function as a transmembrane receptor able to conduct an external signal through the membrane to the cytoplasm as a form of signal perception. Subsequently HAP3-15 could ii play a role in phosphorylation cascades through the kinase domain and, consequently, be responsible for signal transduction. In addition, LPS would then represent the ligand creating the signal perceived by the SRK, HAP3-15, with oligosaccharide binding ability. HAP3-15 was also identified as a true positive by the INAP probe in reverse Northerns, implying that both the biological and chemical inducers used, activated the same receptor kinase. Whether the same signalling pathway was followed during the phosphorylation cascades has not been determined. Further analysis will require Northern blots in a time study to investigate the kinetics of induction. In addition, longer sequence information for each of the five DETs needs to be obtained to identify the corresponding genes in order to investigate their roles in innate immunity in plants.

Heat shock proteins (HSP), although not considered classical defence proteins, have general cytoprotective properties, which promote survival of cells and organisms. Hsp70, in particular, provides resistance to the harmful consequences of various forms of otherwise damaging or even lethal stress including pathogen infection. Increased levels of Hsp70, due to stable transfection of cells with hsp70 genes, or elevated expression in response to stress, generally correlate with the hindrance of cell death processes triggered by a variety of noxious stimuli or toxic agents. The effect of lipopolysaccharides (LPS), the major constituent of the outer membrane of the cell wall (envelope) of almost all Gram-negative bacteria, on Hsp70/Hsc70 expression in plants is unknown. In various mammalian systems, LPS has been shown to induce Hsp70 accumulation, along with programmed (apoptotic) cell death. Contrary to the effects of LPS on animal hosts however, LPS does not elicit cell death in plants, but rather pre-treatment with LPS fraction can prevent or delay the so-called hypersensitive response (HR), thus sensitizing plant tissue to respond more rapidly, or to a greater extent, to subsequently inoculated phytopathogenic bacteria. Elevated levels of reactive oxygen species (ROS) reportedly contribute to stress sensing and hsp gene activation, and subsequent Hsp70 induction, during the stress response. Increased ROS production can also trigger cell death via either programmed cell death (PCD), an active (i.e., energy-dependent) physiological suicide mechanism that is genetically regulated, or uncontrolled necrosis, an accidental, lytic form of cell destruction passively triggered by severe trauma or injury. In plants specifically, ROS may be involved in PCD activation during the HR. As a pathogen-associated molecular pattern (PAMP) or general elicitor of defence or resistance-related responses, LPS may trigger some defence-related responses, including an oxidative burst (manifest as increased levels of reactive oxygen species or ROS) in certain plant cells as it does in animal systems. However, there is conflicting evidence that shows that LPS treatment does not elicit an oxidative burst in plants. The aim of this study was to determine the effect of LPS isolated from Ralstonia solanacearum, an extremely harmful soil-borne bacterium that causes Southern wilt in over 200 plant species by infecting the host’s roots and invading the xylem vessels, on Hsp70/Hsc70 accumulation, cell death and ROS production in suspension-cultured tobacco (Nicotiana tabacum) cells, in order to gain a better understanding of the inter-relationship between these three phenomena in plant cells responding to LPS(Ralstonia). Western (immuno)blot analysis was used to study the unknown effect of LPS(Ralstonia) on Hsp70/Hsc70 accumulation in tobacco cell suspensions. LPS(Ralstonia) (all concentrations and time periods studied) generally suppressed Hsp70/Hsc70 accumulation. However, only exposure to 100 μg LPS/ml for 3 h caused a significant reduction (P < 0.05). Therefore, there was an early suppression of Hsp70/Hsc70 accumulation in response to 100 μg LPS(Ralstonia)/ml. To determine whether the observed LPS-mediated attenuation in Hsp70/Hsc70 accumulation was due to an increase in cell death in these cells, we investigated the effect of LPS(Ralstonia) on i) the general viability of the cells, and ii) the integrity of nuclear or genomic DNA extracted from LPS-treated suspension-cultured tobacco cells. The AlamarBlue™ (AB) assay was used to investigate the general cell viability in response to LPS(Ralstonia) treatment. LPS(Ralstonia) (all concentrations and time intervals studied) did not significantly affect the overall viability of the cells. Because treatment of tobacco cell suspensions with LPS(Ralstonia) did not result in a significant decrease (P < 0.05) in AB reduction, it was presumed that LPS(Ralstonia) did not appreciably compromise metabolic activity and was therefore not particularly toxic to these cells. Genomic DNA from cells undergoing PCD-associated internucleosomal DNA fragmentation (IDF) typically runs as a ladder of internucleosomal-sized DNA fragments corresponding to multimers of ca. 180 bp in agarose gels. In contrast, random DNA cleavage, usually manifest as smearing of nuclear DNA following agarose gel electrophoresis, is a token of uncontrolled necrosis. Therefore, if so-called “DNA laddering” is observed following agarose gel electrophoresis of genomic DNA extracted from suspension-cultured tobacco cells exposed to LPS(Ralstonia) then it can be assumed that LPS(Ralstonia) induced PCD. Alternatively, if a long, continuous “necrotic smear” is evident after electrophoretic separation of nuclear DNA from LPS-treated cells then LPS(Ralstonia) clearly induced uncontrolled necrosis. Whether or not LPS(Ralstonia) induced PCD-associated IDF or necrotic smearing was determined by investigating genomic DNA fragmentation (or DNA integrity) in response to LPS(Ralstonia) iii treatment. Although no typical DNA ladders were detected following electrophoresis of DNA isolated from LPS-treated cells, PCD may still have transpired. However, this is highly unlikely. No necrotic smearing was evident in LPS-treated samples either, which verifies the hypothesis that LPS(Ralstonia) (25–100 μg/ml) did not induce uncontrolled necrosis in suspension-cultured tobacco cells. In fact, these concentrations of LPS(Ralstonia) did not seem to significantly compromise DNA integrity given that LPS(Ralstonia) (25–100 μg/ml) generally had no appreciable effect on genomic DNA fragmentation (compared to untreated control samples). Incidentally, 24-h exposure of tobacco cell suspensions to higher concentrations of LPS(Ralstonia) (500 and 1000 μg/ml) may have resulted in partial DNA cleavage and/or degradation. Exposure of tobacco cell suspensions to 400 μg LPS(Burkholderia)/ml for 7 days may also have evoked partial DNA cleavage and/or degradation. Whether this cleavage and/or degradation occurred deliberately by means of a fixed or predetermined mechanism or randomly by an uncontrolled mechanism remains uncertain. Finally, the H2DCF-DA (2′, 7′-dihydrodichlorofluorescein-diacetate) fluorescence assay was used to investigate the effect of LPS(Ralstonia) on ROS production, a common factor in the regulation of HSP expression and cell death activation. LPS(Ralstonia) treatment (25–100 μg/ml) generally increased ROS levels in suspension-cultured tobacco cells (compared to untreated control cells). Exposure to 75 μg LPS(Ralstonia)/ml resulted in a particularly prominent elevation in ROS levels almost instantaneously. Incidentally, higher concentrations of LPS(Ralstonia) (500 and 1000 μg/ml) resulted in decreased ROS levels at some point during the assay. Although LPS(Ralstonia) (100 μg/ml for 3 h) significantly decreased Hsp70/Hsc70 accumulation in tobacco cell suspensions, cell death did not appear to be induced. In fact, LPS(Ralstonia) had no effect on general cell viability and appeared to be ineffective at causing PCD-associated IDF (DNA laddering) or necrotic smearing regardless of concentration or time of exposure. Despite these findings, treatment of suspension-cultured tobacco cells with LPS(Ralstonia) (≤ 100 μg/ml) resulted in a mild increase in ROS production. Although the exact mechanism(s) by which LPS(Ralstonia) suppressed Hsp70/Hsc70 accumulation is elusive, our results suggest that the suppression is not related to excessive LPS-mediated injury caused by excessively high ROS levels or increased cell death. We speculate that the prevention of HR-related PCD often observed in plants that are pre-treated with LPS and subsequently inoculated with phytopathogenic bacteria may be dependent on the LPS-mediated suppression of cytosolic Hsp70 expression. / Dr. M.J. Cronje

D.Phil. (Biochemistry) / Plants are able to recognise and respond to signals from the environment through a complex array of biochemical pathways, which enables them to deter pathogenic micro-organisms and herbivores. Thousands of different structures of low-molecular weight organic compounds / natural products can be produced through an inducible chemical defence system; that can be manipulated for biotechnological purposes. The importance of natural products in medicine, agriculture and industry has led to numerous studies such as this, to understand the biosynthesis and biological activity of these substances...