Adriana B. Andreu

Accumulation of cytosolic glyceraldehyde-3-phosphate dehydrogenase RNA under biological stress conditions and elicitor treatments in potato

Plants respond to pathogen infection and environmental stress by regulating the coordinate expression of many stress-related genes. In plants, the expression of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is induced under environmental stress. This work was aimed at investigating whether the expression pattern of cytosolic GAPDH is also modulated upon infection of potato plants (Solanum tuberosum L.) with the late blight fungal agent Phytophthora infestans. Northern blot analysis showed the accumulation of the GAPDH gene transcripts in leaves and stems of inoculated potato plants. When tuber discs were treated with eicosapentaenoic acid (EPA), an elicitor found in P. infestans, GAPDH gene transcripts level increased. This increase was parallel to that of the hydroxymethyl glutharyl coenzyme A reductase (HMGR), an enzyme involved in pathogen defense reactions. Glucans obtained from P. infestans cell wall acts sinergistically with EPA on GAPDH and HMGR gene induction. Salicylic acid, an endogenous signal for inducing systemic acquired resistance, was also effective in stimulating the GAPDH transcript accumulation in potato leaves. These experiments suggest that related multi-component factors, which are part of both primary and secondary metabolism, are probably regulated by similar signal transduction pathways when they are induced under biotic or abiotic stress conditions.

Effect of glucans from different races of Phytophthora infestans on defense reactions in potato tuber

It has been proposed that susceptibility of potato to Phytophthora infestans would be a consequence of suppression and /or delaying of defense reactions by a soluble glucan which is released by compatible races of the fungus. In this report, the reaction of potato tuber slices (Solanum tuberosum cv. Huinkul) infected with either race I (1,4,7,8,10,11) or C (1,4,10,11) of Phytophthora infestans was studied. Race C grew better on slices than race I. Glucans from both races were isolated and their effect on the accumulation of phytoalexins and glucanases in tuber slices was studied. The glucans from the less virulent race (I) did not affect the accumulation of phytoalexins and glucanases in tuber slices infected or elicited with eicosapentaenoic acid, whereas the glucans from race C produced 70% inhibition of phytoalexin accumulation and reduced by 50% the induction of glucanase activities. Purified glucanases from potato degraded the glucans from race C but not from race I. The results reported here show that, at least on this cultivar, glucans from both races affected defense responses in a different manner, which could reflect structural differences between these glucans.

Production of phytoalexins, glycoalkaloids and phenolics in leaves and tubers of potato cultivars with different degrees of field resistance after infection withPhytophthora infestans

SummaryThe kinetics of accumulation of phytoalexins, glycoalkaloids and phenolics was studied in two potato cultivars differing in their degrees of field resistance when infected withPhytophthora infestans. Tuber slices and leaves of cvs Pampeana INTA (high degree of field resistance, free of R genes) and Bintje (susceptible) were infected with race C (complex race 1, 3, 5, 7, 11) ofPhytophthora infestans. Phytoalexins and phenolics accumulated in tuber and leaf tissues which had been inoculated. The levels of these compounds in the susceptible cv. Bintje were relatively low and similar to those found before inoculation. Leaves of cv. Pampeana INTA had a very high glycoalkaloid content, suggesting that glycoalkaloids may play a role in protection of leaves against the fungus. However, we could find no correlation between resistance and glycoalkaloid content of tubers. Our results suggest a major role of phytoalexins, phenolics and glycoalkaloids in the complex mechanisms of field resistance.

Defence reactions in two potato cultivars following infection with two races ofPhytophthora infestans

SummaryThe kinetics of accumulation of chitinases, glucanases and phytoalexins were studied in two potato cultivars, differing in their degrees of vertical and horizontal resistance, when infected with two races ofPhytophthora infestans. Tuber disks of cvs Kennebec (susceptible, low horizontal resistance) and Huinkul (tolerant, high horizontal resistance) were infected with either race “0” (avirulent) or “C” (complex, race 1.3.5.7.11) ofPhytophthora infestans. Extracts of tuber tissue (0–7 days) from cv. Kennebec infected with race “0” showed a strong increase in phytoalexin production and in chitinase and glucanase activities when compared with those infected with race “C”. These results indicate that race “C” is able to block defensive reactions. No significant differences were observed in cv. Huinkul infected with both races. The contribution of these reactions to horizontal resistance is unknown, and our results would not support a conclusive role for them in the interaction.

Phenotypic Expression of Resistance to Phytophthora infestans in Processing Potatoes in Argentina

Ten potato cultivars were evaluated in Argentina for foliage and tuber susceptibility to Phytophthora infestans, the oomycete pathogen causing late blight. Pathogen isolates collected from two major potato production regions in the country were polymorphic for specific virulence and isozyme banding patterns, although diversity was found among and not within specific locations. Four of the cultivars were found to be highly resistant in foliage, having little disease in the field and greenhouse and race-specific resistance is suspected. One of these is Russet Burbank, which is highly susceptible in the United States. Cultivar Shepody was the most susceptible and was assigned a value of 8, which was used together with area under disease progress curve values to calculate scale values of the other cultivars on a 1 to 9 susceptibility scale (where 9 is highly susceptible). Cultivar Ranger Russet had values of about 2.5 and resistance could be race-non-specific. The other cultivars for which race incompatibility did not appear to be a problem had susceptibility values between 4 and 8. Foliage susceptibility values for greenhouse and field were correlated. Foliage and tuber susceptibility were also correlated, although with exceptions and only one cultivar, Innovator, was highly resistant in tubers. The two isolates chosen for assessment of foliage susceptibility in the greenhouse differed for aggressiveness in separate tests where components were measured; however, no cultivar-by-isolate interaction was measured. Cultivars with high levels of putative race-specific foliage resistance should be used with constant monitoring in Argentina.ResumenSe evaluaron diez cultivares de papa en Argentina para susceptibilidad de follaje y tubérculo a Phytophthora infestans, el oomiceto patógeno causante del tizón tardío. Aislamientos del patógeno colectados de dos regiones importantes productoras de papa en el país fueron polimórficos para virulencia específica y para patrones de bandas de isoenzimas, aunque la diversidad que se encontró fue entre y no dentro de localidades específicas. Se encontró que cuatro de los cultivares fueron altamente resistentes en follaje, con poca enfermedad en el campo e invernadero, sospechándose de resistencia específica a razas. Una de ellas es Russet Burbank, que es altamente susceptible en los Estados Unidos. El cultivar Shepody fue el mas susceptible, con un valor de 8, que se usó junto con los valores del área bajo la curva de progreso de la enfermedad para calcular valores de escala de los otros cultivares en una escala de susceptibilidad de 1 a 9 (donde 9 es altamente susceptible). El cultivar Ranger Russet tuvo valores cercanos a 2.5 y la resistencia pudo ser no específica para razas. Los otros cultivares, para los cuales la incompatibilidad de las razas no parecía ser problema, tuvieron valores de susceptibilidad entre 4 y 8. Se correlacionaron los valores de susceptibilidad del follaje para el invernadero y el campo. Así también se correlacionó la susceptibilidad de follaje y tubérculo, aunque con excepciones y solo un cultivar, Innovator, fue altamente resistente en tubérculos. Los dos aislamientos escogidos para análisis de susceptibilidad del follaje en el invernadero difirieron en agresividad en pruebas separadas en las que se midieron los componentes; no obstante, no se midió la interacción cultivar-aislamiento. Los cultivares con altos niveles de supuesta resistencia del follaje específica a razas deberían de usarse con monitoreo constante en Argentina.

Properties of potato lectin fractions isolated from different parts of the tuber and their effect on the growth of Phytophthora infestans

Phytophthora infestans grew better on slices from the stem end than the rose end of potato tubers ( Solanum tuberosum ) cv. Huinkul. Lectin preparations from the rose end and the stem end were obtained by affinity chromatography on powdered chitin or Sepharose- N,N′,N″ -triacetyl chitotriose and their properties were compared. Two to three times more protein was associated with the lectin from the rose end than the one from the stem end. Differences in electrophoretic properties as well as carbohydrate content were observed between the two preparations. Total haemagglutinating activity of the preparation from the stem end was 10 times higher and specific activity was 30 times higher than that of the lectin from the rose end. However, 1 mg ml −1 of a β -glucan isolated from the walls of P. infestans inhibited agglutination by the lectin from the stem end by 40% while 4 mg ml −1 was required to produce the same degree of inhibition with the rose end preparation. In addition, the lectin preparation from the rose end had 4–10 times the hydrolytic activity on the β -glucan than the lectin from the stem end. Since, under certain conditions, this β -glucan may suppress phytoalexin accumulation in potato, these results could in part explain the differential development of the fungus on different zones of tuber. The fungus can also be inhibited by addition of lectin from the rose end to slices from either end.

Characterization and in vitro expression patterns of extracellular degradative enzymes from non-pathogenic binucleate Rhizoctonia AG-G.

Many filamentous fungi produce an array of extracellular enzymes that acting in cell walls release elicitors of the plant defense response These enzymes may therefore be important in biocontrol applications. The aim of this study was to characterize extracellular degradative enzymes produced by a non-pathogenic binucleate isolate of Rhizoctonia AG-G. The fungus was grown in liquid culture supplemented with pectin, polygalacturonic acid or glucose as a carbon sources and filtrates of the culture media were analyzed for the detection of pectinolytic and glucan hydrolytic enzymes. Using only pectin as a carbon source, secretion of polygalacturonases and methylesterases was found. When the liquid medium was supplemented with polygalacturonic acid, only polygalacturonase activity was detected. However, when glucose was used as carbon source β-1,3 and β-1,6 glucanases activities were detected, using laminarin and pustulan as substrates, but none of the pectinolytic activities were found. These enzymes were partially purified and characterized. The β-(1,3)(1,6) glucanase and polygalacturonase enzymes showed to be active against cell wall polysaccharides from potato sprouts. These enzymes may have an important role in fungus-plant cell wall interaction. This is the first study about the production of extracellular enzymes by non-pathogenic binucleate Rhizoctonia AG-G.