Physiological Plant Pathology最新文献

Acala S,J,2 cotton plants were tagged and observed individually every week in the field through the entire growing season to identify the physiological time when foliar symptoms of verticillium wilt first appeared. The midday leaf water potentials (ψ₁) of newly diseased plants were consistently lower than those of comparable healthy plants. Midday ψ₁ of newly diseased plants ranged from −15·7 to −24·6 bars with an average of −19·4 bars, whereas those of healthy plants ranged from −11·2 to −19·3 bars with an average of −14·7 bars. Differences in midday ψ₁ between healthy and newly diseased plants were greater prior to than after boll set. Leaf water potentials of cotton plants with disease symptoms that first appeared before boll set returned to normal about 3 weeks after the onset of foliar symptom development. However, when foliar symptoms first appeared after boll set, the midday ψ₁ of diseased plants remained consistently lower than that of comparable healthy plants for the remainder of the growing season. Healthy plants continued to grow during the early stages of boll set (before the peak boll stage), whereas growth of diseased plants with foliar symptoms was greatly reduced or stopped. The results indicate that water stress was one of the main reasons for growth retardation and lint yield reduction of cotton plants which developed foliar symptoms of verticillium wilt during early stages of plant development.

Cultured apple cells were rapidly injured by pectin lyase (PL) from Monilinia fructigena. Changes in the staining of the plasmalemma and cytoplasm were observed concomitant with the loss of vital staining. Paramural bodies, containing vesicles apparently derived from the plasmalemma, were present at an early stage of injury. Further injury was indicated by pseudoplasmolysis, increased vacuolation and cytoplasmic collapse. Methylated pectin was rapidly lost from the walls of treated cells. However, the gross integrity of the cell walls appeared little changed during the early stages of injury. Cell wall degradation appeared to accompany rather than precede severe injury. ATPase activity was localized by a lead capture method at the plasmalemma of cultured cells. A considerable increase in lead stain within the cytoplasm occurred after PL treatment but it still remained localized at the plasmalemma even in apparently severely injured cells. Freeze fracture replication did not reveal any major modification of the plasmalemma after PL treatment even when considerable injury had occurred.

Extracts of three virulent strains of Endothia (Cryphonectria) parasitica and three hypovirulent strains derived from them were assayed for enzyme activities that would produce oxalate. Oxaloacetate acetylhydrolase (E.C. 3.7.1.1), the enzyme that converts oxaloacetate to oxalate and acetate, was at least four times higher in extracts of the virulent strains than in extracts of the hypovirulent strains. The level of activity of this enzyme could account for the formation of all the oxalate produced by the virulent cultures. When extracts of hypovirulent strains were added to extracts of virulent strains, the measured rate was less than the sum of the two rates. The inhibition did not change when the hypovirulent extract was either dialysed or boiled. No enzyme activity for the conversion ofglycolate or glyoxylate to oxalate could be detected in any of the extracts.

There was no apparent difference between the virulent and hypovirulent strains of the fungus on the basis of intracellular organic acid content except that fumarate concentration was lower in extracts of hypovirulent strains. The amounts of oxalate produced by the virulent strains when grown on solid medium with malate (an immediate precursor of oxaloacetate) and fumarate were much higher than when they were grown on solid medium with glycolate. Two of the hypovirulent strains produced no oxalate on any of the substrates. However, the hypovirulent strain which had the highest oxaloacetate acetylhydrolase activity produced oxalate cultured on malate and fumarate but none on glycolate.

The effect of infection with different viruses on the chromatin-associated protein constitution of young, developing tobacco leaves was investigated using SDS and two dimensional polyacrylamide gel electrophoresis. When systemic mosaic symptoms had developed, marked changes in the protein profile were evident. Tobacco mosaic virus (TMV) infection induced two additional protein bands with molecular masses of approximately -116 kD and 20 kD, respectively. Infection with a “green” isolate of cucumber mosaic virus (CMV) induced the formation of a single protein of about 28 kD, whereas the yellow strain P6 induced the formation of a slightly different protein of about 29 kD. The 20 kD protein induced by TMV was identified serologically as the virus coat protein, and the two CMV-induced proteins co-migrated with the coat proteins of the respective inducer strains. Virus infections resulting in necrosis, whether the virus remained localized in the inoculated leaves or became systemic, did not induce any changes in chromatin-associated proteins. Neither treatment with l-aminocyclocpropane-l-carboxylic acid, which induced premature senescence in young, developing leaves, nor natural senescence of old leaves oil flowering plants induced any changes comparable to TMV infection. Since purified TMV coat protein did not associate with chromatin upon incubation in vitro with nuclei from non-infected tobacco plants, the interaction of viral coat protein with host chromatin in infected plants is considered to be specific. The possibility that this association plays a role in symptom expression is discussed.

A low molecular weight (less than 3000) phytotoxic polypeptide fraction was partially purified from the protein-lipopolysaccharide (PLP) complexes produced in culture by a strain of Verticillium dahliae pathogenic on potato. The toxic fraction was host-specific and antigenically identical to the high molecular weight PLP. Immunodiffusion and immunofluorescence assays showed that a substance is present in stems and tubers of infected potato plants which was antigenically related to the low molecular weight toxin. When used as a tool for screening new potato varieties for tolerance to Verticillium wilt disease, the low molecular weight toxin was more reliable than the PLP because non-specific sensitivity to macromolecules was not observed.

Stems of cotton plants (Gossypium hirsutum L., cv. Acala SJ-2) growing in the greenhouse and field were inoculated with conidial suspensions of T9 (defoliating) and SS4 (nondefoliating) pathotypes of Verticillium dahliae Kleb. In the greenhouse, leaves of T9-inoculated plants had higher water potentials (ψ₁) and relative water contents (RWC) than the healthy controls until the occurrence of defoliation about 10–12 days after inoculation. In contrast, ψ₁ and RWC decreased in SS4-inoculated plants about 6–8 days after inoculation. Increases in stomatal resistance (R₁) and proline concentration were associated with the development of water stress in leaves of SS4-inoculated plants. Proline accumulation in T9-inoculated plants was much less than in SS4-inoculated plants, but it occurred about 2–4 days earlier and was accompanied by an increase in free amino-nitrogen and a decrease in the chlorophyll content of leaves. Stomatal resistance in T9-inoculated plants increased about 2–4 days earlier and remained higher than that of SS4-inoculated plants until the occurrence of defoliation. The higher water status of T9-inoculated plants compared with healthy controls suggests that, in contrast to SS4-inoculated plants, accelerated senescence rather than water stress is the major effect of infection.

Previous observations of enhanced ethylene production in cotton plants infected by the defoliating, T9 pathotype of V. dahliae were confirmed in the greenhouse. ACC (1-aminocyclopropane-l-carboxylic acid) appeared to be an intermediate in the pathway for ethylene production in diseased cotton plants.

In the field, midday ψ₁ of SS4-inoculated plants dropped rapidly about 5–8 days after inoculation, and the decrease in ψ₁ was accompanied by an increase of R₁ and proline concentration in leaf tissues. T9-inoculated plants had higher midday ψ₁ values than healthy plants up to the fourth day; however, by the eighth day after inoculation the ψ₁ of T9-inoculated plants had declined to about the same values as those of SS4-inoculated plants. Water stress in SS4-inoculated plants was associated with vascular dysfunction whereas water stress in T9-inoculated plants appeared to be associated more with accelerated senescence and defoliation.