Changes in Phenolic Acids in Groundnut Leaves Infected with Rust

Quantitative changes of individual phenolic acids in rust-infected groundnut leaves were studied at various stages of disease development. There was no qualitative change in the phenolic acids. However, the concentration of the phenolic compounds increased due to infection more particularly of chlorogenic and trans and cis caffeic acids.     

Leaf phenolics of three willow clones differing in resistance to Melampsora rust infection

Leaf phenolic composition in three Salix myrsinifolia Salisb. clones (V8, V45, and V43), inoculated with Melampsora rust, was analyzed to detect local rust-induced alterations during different stages of infection (2, 7, and 21 days after inoculation [DAI]). Phenolic levels and percentage of uredial area varied significantly between clones. In the most resistant clone,V8, the levels of some phenolic compounds were lower in rust-infected plants than in control plants at the initial stages of rust infection, suggesting a rapid response of phenolic metabolism to rust attack. Moreover, the clone V8 contained the highest constitutive (+)-catechin level. In clone V45, rust infection caused the most pronounced increase in the levels of individual phenolics at 7 DAI. This increase may have been effective in retarding the subsequent spread and development of rust. In the most susceptible clone V43, rust-induced phenolic responses were less pronounced and delayed. The results suggest that in specific willow-rust interactions, constitutive levels of phenolics, as well as induced phenolic responses, may contribute to the expression of rust resistance. In general, rust-induced alterations in willow phenolic levels are highly specific to genotype and compound and vary depending on the stage of rust development.     

An EST library from Puccinia graminis f. sp. tritici reveals genes potentially involved in fungal differentiation

The rust fungus Puccinia graminis f. sp. tritici is an obligately biotrophic pathogen on wheat plants and thus difficult to investigate. Hence, little is known about this fungus at the molecular level. We constructed a differential suppression subtractive hybridization cDNA-library from rust-infected vs. healthy wheat plants. The majority of expressed sequence tags (ESTs) showed similarities to fungal sequences. Semiquantitative RT-PCR using mRNA from rust-infected leaves, and from axenically grown, differentiating and nondifferentiating young rust colonies as well as sporulating and nonsporulating mature mycelia revealed rather diverse expression patterns for different ESTs, shedding new light on their potential involvement in differentiation and host-pathogen interaction.     

Effect of Ophiobolus graminis infection on the growth of wheat and barley

Glasshouse experiments are reported, in which the development of young wheat and barley plants was examined following inoculation with Ophiobolus graminis (Sacc.) Sacc. The dry weight, leaf area, tiller number and water content of the shoot were reduced by infection. Reductions were equally severe in wheat and barley. The seminal root system of both was severely attacked and its growth retarded. Inoculated plants, however, translocated a greater proportion of their total assimilates to the root system and produced more adventitious roots than healthy plants. As a result there was an increase in both the number and proportion of healthy roots on these plants following the initial infection of their root systems. This effect was more pronounced in barley than in wheat. It is suggested that this may in part account for the reported relative tolerance of barley to take-all attack under field conditions.     

小麦体内生化物质在抗蚜中的作用

综述了小麦体内生化物质的抗蚜作用 ,主要包括不同抗性品种对麦蚜的影响、小麦体内氨基酸、糖类、酚类物质、生物碱和非蛋白氨基酸等与抗蚜性的关系 ,以及蚜虫对小麦体内抗虫生化物质的诱导作用 ,并提出了深入研究小麦生化物质与抗蚜性关系的前景和意义。     

The effect of barley yellow dwarf virus on the amino acid composition of spring wheat

Leaf extracts of barley yellow dwarf virus-infected and healthy spring wheat (cv. Highbury) plants at three growth stages were analysed by gas liquid chromatog-raphy to determine their free amino acid content. Eleven free amino acids were identified. Virus infection increased the total amino acid content of sampled leaves at each growth stage but more so at the later stages. Alanine and glutamine were consistently present in greater amounts in infected than in healthy leaves at all three growth stages.     

Root exudates of plants

Summary Comparisons have been made of the amount and composition of seed and seedling exudates in barley, wheat, cucumber, and bean. Except in the case of wheat a greater proportion of the total nitrogen content in the seed exudates was formed by protein and peptide nitrogen than by nitrogen of free amino acids. In contrast, the greater part of the total nitrogen in the exudates of seedlings was formed by free amino acid nitrogen, except in the case of barley. Peptides represented 8 to 26 per cent of the protein and peptide fraction in seed exudates, the highest amount being found in bean. On an equal weight basis, the spectrum of amino acids released from seeds and seedlings differed little between barley, wheat and cucumber; greater differences were observed in bean exudates. Seedlings exuded reducing substances to a considerably greater extent than seeds. The spectrum of reducing sugars in seed and root exudates differed greatly, especially in the case of keto sugars. Differences in the organic acid spectra were small, except for bean plants, the seedling exudate of which contained more organic acids with a richer spectrum than seed exudate. Both seeds and seedlings of cucumber exuded a small quantity and a poor spectrum of organic acids.     

Die Veränderungen der Peroxydaseaktivität von Weizen- und Gerstenblättern nach der Infektion mit obligaten Parasiten

A study was performed on the influence of obligate parasitesErysiphe graminis Dc. andPuccinia hordei Ott4 on peroxidase activity in barley leaves, namely in both susceptible and resistant varieties. Attention was also paid to peroxidase activity in a susceptible wheat variety infected withPuccinia striiformis West. The following results were obtained: In leaves of wheat and harley plants an enzyme was revealed which oxidized pyrocatechol and guajacol only in the presence of hydrogen peroxide. This enzyme can be inactivated by heating and strongly inhibited by cyanide. Evidently peroxidase is concerned. Peroxidase in susceptible varieties of wheat and barley is markedly activated after infection with parasites mentioned above, this activation reaching maximum at the periode of parasite sporulation. On the other hand the barley varieties resistant toE. graminis andP. hordei, exhibit only a slight or no increase in peroxidase activity at this period. Thus we come to the conclusion that peroxidase does not probably appear to be the cause of the resistance of these varieties. It seems that in tissues attacked by obligate-parasites the intensity of its activation can be a result of the infection intensity.     

Nutritional enhancement of host plants by aphids - a comparison of three aphid species on grasses

Three aphid species were compared with respect to ability of enhancing the nutritional quality of their host plants. Rhopalosiphum padi, which does not induce macroscopic changes in its host plants, was compared with Schizaphis graminum and Diuraphis noxia, both of which induce distinctive types of chlorotic lesions. Phloem sap samples were collected from severed stylets of feeding aphids and from exudates of cut leaves of plants uninfested or infested with each aphid species. Samples were analyzed for concentrations of individual amino acids.Compared to R. padi, S. graminum ingested phloem sap with a two-fold higher concentration of amino acids and a much higher proportion of essential amino acids. Similar differences between these two aphid species were observed on both wheat and barley. For each aphid species, the absolute concentrations of amino acids and the relative proportions of essential amino acids were similar between the two host plants. Effects of D. noxia were similar to those of S. graminum, though less dramatic. Exudates from leaves infested with each aphid species showed relative concentrations of individual amino acids that were similar to those in the corresponding stylet exudates. Based on comparison of stylet exudates and cut leaf exudates from infested and uninfested plants, R. padi seems to have little effect on amino acid composition of phloem. Changes in the phloem induced by both S. graminum and D. noxia appear to be systemic, affecting at least the whole leaf they are feeding on. The changes observed for D. noxia and for S. graminum are likely to be nutritionally advantageous for the aphids and are expected to affect the aphids' dependence on nutritional supplementation by intracellular symbionts (Buchnera).     

Effect of methyl jasmonate (MeJA) on biochemical responses of wheat seedlings infected by Fusarium culmorum

Fusarium culmorum is a ubiquitous soil-borne fungus which is able to cause foot and root rot on different small-grain cereals, in particular wheat and barley. Wheat (Triticum aestivum L.) is among the oldest and most extensively grown of all crops. Systemic acquired resistance (SAR) is a pathogen-induced disease resistance response in plants that is characterized by broad spectrum disease control. SAR is an important component of the disease resistance repertoire of plants. The effect of the resistance inducer, methyl jasmonate (MeJA), was tested by seed-soaking to determine whether this resistance inducer controlled root rot of wheat caused by F. culmorum. MeJA is an inducing disease resistance in a number of dicotyledonous and monocotyledonous plant species. This research has been conducted to determine the effect of MeJA seed treatment on chlorophyll a, chlorophyll b, total protein, peroxidase (POD) enzyme, phenolic compounds and phenylalanine ammonia lyase (PAL) factors. MeJA, which is an important chemical inducer of SAR, can activate resistance to pathogen infection in commercial crops. Seeds treated with MeJA showed an elevation in the total chlorophyll, carotenoid and activity of defence-related enzymes, POD and PAL.     

Allelopathic Interactions Involving Phenolic Acids

A major concern regarding allelopathic interactions involving phenolic acids in no-till systems pertains to the fact that concentrations of individual phenolic acids recoverable from field soils are well below levels required for inhibition of germination and seedling growth in laboratory bioassays. Field soils contain a variety of phenolic acids as well as other toxic and nontoxic organic compounds that are available to interact with seeds and roots; whereas in laboratory bioassays, with few exceptions, single phenolic acids have been tested. Studies of mixtures of phenolic acids and other toxic (e.g., methionine) and nontoxic (e.g., glucose) organic compounds in laboratory bioassays indicate that the action of a single phenolic acid is not representative of the actions of such mixtures. Specifically, as the number of phenolic acids added to soil increased, concentrations of the individual phenolic acids required to bring about a growth inhibition declined. The addition of other organic compounds (e.g., glucose, methionine) to the soil also reduced the concentration of a phenolic acid (e.g., p-coumaric acid) required for growth inhibition. These results support the hypothesis that in the field mixtures of phenolic acids and other organic compounds can cause inhibitory effects even though the concentrations of individual compounds are well below their inhibitory levels.     

Control of wild oat (Avena fatua) using some phenolic compounds I – Germination and some growth parameters

The percentage of germination of wild oat was significantly inhibited by increasing the concentrations of phenolic compounds. Ferulic acid was the most effective compound which completely inhibited germination at a concentration of 3.0 mM. At the same time, wheat and barley were slightly affected with different concentrations of the four phenolic compounds. The percentage of germination of wheat significantly decreased with increasing of ferulic acid reaching a maximum inhibition at 3.0 mM concentration. On the other hand, the germination of wheat was not affected with the other three phenolic compounds. The percentage of germination of barley was not affected with all phenolic compounds except for hydroxy phenolic acetic acid which has significant effect at a concentration of 3.0 mM. Salicylic acid significantly inhibited the growth parameters gradually in wild oat, wheat and barley. The shoot/root ratio was decreased in wild oat and barley, while the ratio increased in wheat. The growth parameters were completely inhibited at 3.0 mM of ferulic acid for both wild oat and wheat but slightly inhibited for barley. The shoot/root ratio was increased in all concentrations of ferulic acid except at 3.0 mM which was completely inhibited for both wild oat and wheat, while the ratio was increased in all treatments of ferulic acid in the case of barley. The growth parameters were highly significant and decreased in wild oat, wheat and barley with increasing the concentrations of hydroxybenzoic acid and hydroxyphenyl acetic acid. The shoot/root ratio was not changed in all concentrations except at 3.0 mM in the case of wild oat, the ratio was decreased at 2.0 and 3.0 mM in the case of wheat, while the ratio increased in most of hydroxybenzoic acid concentrations in the case of barley. The shoot/root ratio was increased with increasing of the hydroxyphenyl acetic acid concentrations.     

Earlier onset of DNA fragmentation in leaves of wheat compared to barley and rye

We have found extensive nucleosomal fragmentation of native DNA extracted from leaves of healthy cereal plants, as indicated by ladder patterns on agarose gels and TUNEL staining. The time of first appearance of fragmentation differed among cereals. Native DNA from the first leaf of 10-day-old plants formed a clear ladder pattern of multiples of 180 bp fragments in wheat and triticale but not in barley and oats. In one cultivar of rye a weak ladder pattern occurred but not in another. Freezing and thawing of samples before DNA extraction resulted in much more extensive DNA fragmentation in wheat but not in rye and barley, indicating that DNA-degrading enzymes are present in the cytoplasm of wheat, but not in barley and rye, at this stage. In barley, nucleosomal fragmentation was first detected in 25-day-old plants. These results indicate that programmed cell death takes place in developing leaves of young cereal plants, but that the time of onset differs among cereal species.     

Interaction between barley yellow dwarf virus and rust in wheat, barley and oats, and the effects on grain yield and quality

In three separate experiments, the upper leaf surface of the fifth formed leaf of wheat cv. Highbury, the fourth and fifth leaves of barley cv. Julia and the third and fourth leaves of oat cv. Mostyn were inoculated in a spore settling tower with wheat brown rust (Puccinia recondita f. sp. tritici), barley brown rust (P. hordei) or oat crown rust (P. coronata f. sp. avenae), respectively. Fewer pustules developed on distal portions of leaves of plants infected with barley yellow dwarf virus (BYDV) than on similar portions of leaves from virus-free plants. There were no significant differences in the number of pustules on proximal leaf portions. In barley and oats, the number of pustules on distal leaf portions was negatively correlated with the amount of yellowing of the leaf areas scored. In wheat, symptoms of BYDV were mild and leaves were little affected by yellowing. The latent period of rust on wheat and oats was not affected by BYDV. In barley, BYDV reduced the latent period of rust on leaf 5, but not on leaf 4, and reduced it on proximal, but not distal, leaf portions. In other experiments, BYDV reduced the yield of wheat and oats by 44% and 66%, respectively, while BYDV-infected barley was almost sterile. The appropriate rust reduced the yield of wheat, barley and oats by 33%, 13% and 86%, respectively. When infected with both BYDV and rust, yield of wheat and oats was reduced by 63% and 91%, respectively. Neither BYDV nor rust affected the percentage crude protein content of wheat grain, nor did rust affect that of barley. In oats, BYDV and rust each significantly increased crude protein of grain, but rust infection of BYDV-infected plants tended to reduce it.     

Amino Acid and Peptide uptake in the scutella of germinating grains of barley, wheat, rice, and maize

Scutella separated from germinating grains of barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), rice (Oryza sativa L.), and maize (Zea mays L.) took up the four amino acids and the three peptides tested from incubation media. The uptake of amino acids by wheat scutella was similar to that of barley scutella and was via at least four uptake systems: two nonspecific amino acid uptake systems, one system specific for proline, and another system specific for basic amino acids. The scutellum of rice apparently has two nonspecific systems and a system specific for the basic amino acids, but the proline-specific system is lacking. The scutellum of maize seems to have the same systems as the scutellum of rice, but one (or both) of the nonspecific systems differs from that of the other species studied in taking up arginine only slowly. No great differences were observed in the uptake of peptides in the four species studied. The rates of uptake of different amino acids and peptides were of the same order of magnitude in the four cereals. The fact that carboxypeptidase activities in the endosperms of wheat and barley are 20-to 100-fold higher than those in rice and maize, does thus not seem to be reflected in the uptake properties of the scutella.     

Some effects of barley yellow dwarf virus on spring and winter cereals in glasshouse trials

The tolerance of spring and winter varieties of wheat, oats and barley to infection by barley yellow dwarf virus (BYDV) was examined in glasshouse tests. Severely affected plants were stunted and grain yields were considerably decreased because of decreases in both ear number and numbers and sizes of grains. Winter barley varieties were very susceptible and many were killed by BYDV infection. The winter wheat varieties were more widely tolerant than those of oats and barley. Individual seedling symptoms, although correlated with reductions in yield, could not be relied upon for accurate classification of all varieties in order of their susceptibility to infection. Symptoms of seedling infection incorporated into an index of infection permit estimates to be made o eventual decreases in yield by applying the formula DY = 1.4 × (SH+LA+LL)+18. Thus decrease in grain yield (DY) can be related to decreases in height (SH) and leaf length (LL) and increases in leaf area discoloured (LA) in seedling plants infected with BYDV.     

Taphrina maculans reduces the therapeutic value of turmeric (Curcuma longa)

Rhizomes of turmeric are used in several culinary preparations. They have been used as household remedies since time immemorial. Phenolics are found in plants only and they play a great role in human health. The high performance liquid chromatography of different parts of healthy and infected plants reveals that the phenolic acid content is reduced in diseased tissues including rhizomes which are commonly consumed by human beings in several countries of the world. Results also showed that the infected leaves had maximum phenolic acids as compared to healthy leaves which indicate that due to infection the amount of phenolic acids increased. We report for the first time that leaf spot (Taphrina maculans) of turmeric (Curcuma longa), which is an important disease, reduces the quantity and number of phenolics thereby damaging the therapeutic properties of turmeric.     

Root exudates of plants

Summary The composition of the root exudates of barley and wheat in the initial growth phases was investigated; amino acids, organic acids, sugars and certain aromatic compounds could be identified. A knowledge of the composition of root exudates is important from the standpoint of the interaction between the plants and the micro-organisms in the rhizosphere. Some aspects of the rhizosphere effect connected with the present work are discussed.     

Some effects of barley yellow dwarf virus on spring and winter cereals in field trials

The tolerance of spring and winter cultivars of wheat, barley and oats to infection by barley yellow dwarf virus (BYDV) was examined in field tests. Sererely affected plants were stunted and grain yields were considerably reduced. These changes in infected spring barley cultivars were associated with decreases in both ear length and number and sizes of grain. Most barley and oat cultivars were more susceptible than wheat cultivars. Yield losses decreased with successively later dates of inocultaiton, the yield response being characteristic of the tolerance of individual cultivars. Differences between tolerant and susceptible cultivars were insignificant in most cases where infection occurred after growth stage 7. Individual seedling symptoms assessed in April and May were more closely related to each other and to yield losses than those recorded in March and June. The incorporation of seedling symptoms into indices of infection permits estimates of decrease in yield to be made by applying the formulae, DY = (LC+LA+SH)/3 to barley cultivars and DY = 1.7 × (LC+LA+SH)/3 - 7 to oat cultivars. Thus decreases in grain yield (DY) can be related to decreases in seedling height (SH) and increases in percentage of leaf area discoloured (LA) and intensity of discoloration (LC). Plot symptoms of infection, scored on a 0–7 scale, offered a more convenient method of assessment than individual seedling symptoms. Plot scores (PA) were closely correlated with other seedling symptoms and with decreases in grain yield (DY), and can thus be used to estimate yield losses by substituting into the formula, DY = 14PA (April)-8. This formula was found to be applicable to all cereal cultivars examined in N.I.A.B. trials, there being no distinction between wheat, barley and oats.     

Are Pathogenesis-Related Proteins Induced by Meloidogne javanica or Heterodera avenae lnvasion?

Changes in root- and leaf-soluble proteins were investigated in tomato after invasion by the root-knot nematode Meloidogyne javanica, or in barley and wheat after invasion by the cereal cyst nematode Heterodera avenae. Infection of susceptible tomato plants by M. javanica did not cause any change in the soluble-protein composition of leaves or roots compared with uninoculated plants at an early infection stage. No pathogenesis-related proteins (chitinase, glucanase, or P-14) were induced in the leaf apoplast. Changes in leaf proteins were not observed after invasion of wheat cultivars by H. avenae, whereas, in barley, a few changes in intercellular leaf proteins were recorded in resistant cultivars. These changes, however, were not the same among different H. avenae-resistant cultivars. Protein changes were found at an early stage of infection in barley and wheat roots infected with H. avenae, but no difference was found between resistant and susceptible cultivars.