Roots Of Susceptible Plants Research Articles

Activity of components of the antioxidant system in the roots of potato plants at short-term temperature drop and invasion with parasitic nematodes.

The activity of catalase and superoxide dismutase in the roots of susceptible plants and plants exposed to alternating temperatures, which were infected with the phytoparasitic nematode G. rostochiensis, was studied. It was found that, throughout the invasion period, the plants susceptible to invasion exhibited a high activity of these enzymes, which allowed them to maintain an active defense against the oxidative stress caused by the invasion and subsequent life activity of larvae. For the plants exposed to alternating temperatures, a decrease in the activity of catalase and superoxide dismutase at the early stages of invasion and an increase in the activity of these enzymes at the later stages was detected.

Investigations of how phenoxy‐resistant Carduus nutans biotypes survive herbicide spraying

Biotypes of nodding thistle (Carduus nutans) have developed within New Zealand that require over six times the normal rate of MCPA, MCPB or 2,4‐D to kill them. Radiolabelled 2,4‐D was applied to both resistant and susceptible nodding thistle plants to investigate the mechanism of resistance. There was no difference in penetration of the 2,4‐D into the foliage of the resistant and susceptible plants. However some minor differences in translocation were detected, with the 2,4‐D apparently less mobile within the resistant plants. These differences were variable and did not fully explain the resistance. Significantly more radioactivity was released from the roots of susceptible plants. There were also small but significant differences in the quantities of radioactivity that could be removed from within the treated plants by ethanol, suggesting more binding within susceptible plants. Significant differences were detected in rates of metabolism of 2,4‐D within the root systems. More radioactivity was present as water‐soluble compounds in the resistant plants than the susceptible ones. Of the ether‐soluble components extracted, about 14 times more 2,4‐D was estimated to be present in susceptible plants than in resistant plants, with chromatography suggesting that compounds in the resistant plants were metabolites of 2,4‐D.

Investigations into the mechanism of glyphosate resistance in Lolium rigidum

Glyphosate is a widely used non-selective herbicide to which so far only three weed species have evolved resistance. Here, we report on the mechanism of glyphosate resistance in one resistant population of Lolium rigidum (Gaud.). Experiments demonstrate that glyphosate resistance in this population is directly correlated with increased transport of the herbicide to leaf tips. No significant differences in the level of expression of the herbicide target site, EPSP synthase, between resistant and susceptible plants were found and the enzyme is equally sensitive to inhibition by glyphosate in both populations. Similarly, plant metabolism of glyphosate does not contribute to resistance. Resistant and susceptible plants are equally capable of absorbing the applied herbicide. The most notable difference between resistant and susceptible populations is found in the translocation of glyphosate. Following treatment, an accumulation of glyphosate in the roots of susceptible plants is observed, whereas glyphosate accumulates in the leaf tips of resistant plants. Taken together, it seems likely that an alteration to the cellular transport of glyphosate confers resistance.

The Relationship Between Peroxidase Activity and the Resistance of Tomatoes (Lycopersicum esculentum) to Verticillium dahliae

AbstractThe levels of peroxidase activity in roots of non‐infected tomato plants resistant to Verticillium dahliae Kleb., were found to be considerably higher than those in the roots of susceptible plants. Similar differences were found in the leaves but were not significant as in the roots. Peroxidase activity increased in leaves, stems and roots of both susceptible and resistant plants after infection with V. dahliae. The ratio of the increase in leaves and roots of susceptible plants was greater than those of resistant plants. A positive correlation was found between the peroxidase activity in the roots of eleven cultivars/breeding lines and presence of Ve gene.

The effect of calcium nutrition on the sterol content of tobacco roots and their susceptibility toPhytophthora parasiticavar.nicotianae

Abstract The influence of nutrient solutions containing low (25 mg/1) and high (250 mg/1) calcium (Ca) concentrations on the total lipid, free sterol, sterol glycoside and steryl ester content and on the subsequent susceptibility of three flue‐cured tobacco cultivars to black shank, incited by Phytophthora parasitica var. nicotianae was investigated. The total lipid, total sterol and free sterol content differed appreciably among root systems of the three cultivars grown at high Ca. Roots of plants grown at low Ca contained relatively higher proportions of steryl glycosides and lower proportions of free sterols than roots of plants grown at high Ca, although the absolute sterol concentrations also differed significantly among the roots of cultivars grown at low Ca. Black shank disease development was significantly lower in roots of susceptible plants grown at low Ca than in roots of the same cultivar grown at high Ca. The innate susceptibility of the cultivars were not related to the lipid or sterol conte...

The Dynamics of Amino Acid Variations During Pathogenesis and Host Resistance

On the analysis of conclusions, arrived at by different workers regarding amino acid status during pathogenesis and resistance, certain basic trends have emerged. They are as follows: 1. Virus-infected tissues do not show any definite pattern of variation in their amino acid constituents. 2. The roots of susceptible plants, by exuding some nutritionally needed amino compounds in the rhizosphere, evoke fungal pathogenicity, especially of the vascular wilt diseases. Contrary to that, roots of resistant varieties, by secreting inhibitory amino acids, restrain inoculum build-up and retain resistance. 3. Inhibitory potentiality of a particular amino acid maintains resistance in the shoots, too. 4. In the leaves, during fungal pathogenesis presence, increase and depletion of amino acids are more rhythmic than uniform. Even toxins and varied nycto temperature s have their own autonomous effects. There is no definite pattern of the cause and effect of relationship between resistance and susceptibility of the host on one hand and amino acid status of the leaves on the other. 5. Pathogenesis of the leaves due to bacteria have almost the same fluctuating design of their amino acid constituents, as evinced during fungal pathogenesis. 6. Amino acid component of histone and non-histone protein of normal tissue and crown gall tumour tissue do not differ much. In other tumours of bacterial origin, however, tumour tissue has specific amino compounds, absent from normal tissue. 7. In fruits the activity during pathogenesis causes either depletion or loss of amino acids, due to their nutritional utilization by the pathogen. This could also be due to their incorporation during protein synthesis. The increase in the amount of individual amino acids, however, may be due to proteolytic breakdown of the host protein activated by pathogenic enzymes. The myriad conclusions regarding the amino acid status during disease development only accentuate the necessity of investigating this problem in its totality, taking into account the concurrent and concomitant activities leading to synthesis of proteins and phenolics as well as their enzymatic breakdown. Die Auswertung von Versuchsergebnissen, den Status der Aminosäuren in erkrankten und resistenten Wirtspflanzen betreffend, ergibt folgende Trends: 1. Virus-infizierte Gewebe zeigen keine definitive Abweichung in der Zusammensetzung der Aminosäuren. 2. Die Wurzeln empfindlicher Pflanzen fördern Pilzerkrankungen, vor allem Welkekrankheiten im Gefäßsystem, indem sie verschiedene für die Ernährung wichtige Aminoverbindungen ausscheiden. Die Wurzeln resistenter Pflanzen scheiden inhibierende Aminosäuren aus, die einen Befall verhindern. 3. Die Fähigkeit einiger Aminosäuren zur Inhibition erhält auch die Resistenz der Sprosse. 4. In den Blättern verlaufen Zunahme und Entleerung von Aminosäuren bei pilzlichen Erkrankungen nicht gleichmäßig, sondern vielmehr rhythmisch. Eine Beziehung zwischen Empfindlichkeit und Resistenz einerseits und Aminosäurestatus der Blätter andererseits läßt sich nicht ableiten. 5. Für bakterielle Erkrankungen gilt Ähnliches. 6. Die Zusammensetzung der Aminosäuren in Histonen und Nicht-Histonen von normalen und erkrankten (Wurzelkropf) Geweben unterscheidet sich nur wenig. Doch gibt es davon auch Abweichungen. 7. In Früchten verursacht Krankheitsbefall Erschöpfung oder Verlust von Aminosäuren, abhängig von der Nutzung als Nahrungsquelle des Pilzes. Die Erhöhung des Gehaltes an speziellen Aminosäuren kann auf Proteolyse des Eiweißes des Wirtes zurückgeführt werden, welche durch Enzyme des Krankheitserregers verursacht wird. Die Vielzahl der Meinungen hinsichtlich des Aminosäurestatus bei Krankheitsbefall verweist auf die Notwendigkeit, dieses Problem in seiner Gänze zu untersuchen unter Beachtung konkurrierender und begleitender Aktivitäten.

A Comparison of the Endogenous Cytokinins in the Roots and Xylem Exudate of Nematode-resistant and Susceptible Tomato Cultivars

Non-infested roots of a tomato cultivar (Roodeplaat Premier) susceptible to root-knot nema todes contained higher levels of endogenous cytokinins than non-infested roots of a nematode resistant cultivar (Master Fl). In both cultivars nematode infestation increased the cytokinin level in the roots. Sephadex LH-20 fractionation indicated that the xylem exudate of infested susceptible plants contained zeatin and zeatin riboside. In the roots of both cultivars a third compound, which co-eluted with zeatin glucoside, was present. The activity of all three cell division-inducing compounds was higher in the roots of susceptible plants than in roots of nematode-resistant plants. The present results support the hypothesis that cytokinins may be a controlling factor in the development of giant cells.

Incorporation of Atrazine Side-Chain into Amino Acids of Corn

Seedlings of corn (Zea mays L., var. GT-112 RfRf and GT-112, resistant and susceptible, respectively) to 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) were grown 48 hr in sterile Hoagland's solution containing 14C-ethyl-labeled atrazine. More incorporation of the 14C-ethyl side-chain into free amino acids was found in the roots and shoots of GT-112 RfRf than GT-112, based on radioactivity. More radioactivity was found in roots of susceptible plants than in resistant plants; however, the trend was reversed in the shoots.

RECENT STUDIES ON PHYMATOTRICHUM ROOT–ROT

In I923 (20) the disease was recorded in 67 counties of Texas. A recent compilation shows root-rot in I96 counties (text fig. i). It is quite probable that as the studies continue, it will be found that the disease has even a wider distribution. Root-rot has not yet been found in the Plains country around Lubbock, nor in the extreme north of the Texas Panhandle. The absence of the disease from the extreme northern part of the state may be due to the severe winter weather, which may kill out roots of susceptible plants as well as the root-rot fungus itself.