Physiological Plant Pathology最新文献

Photosynthesis and chloroplast functioning is examined within pustules of Uromyces muscari on bluebell leaves at different stages of development from presporulation to green island formation. Green island tissue is shown to be photosynthetically active by ¹⁴CO₂ fixation, OZ evolution and in vivo chlorophyll fluorescence kinetics. Chloroplast measurements indicate that, whilst there is little reduction in chloroplast number per unit area in pustules of U. muscari, the chloroplast volume, the chlorophyll concentration and the ratio of chlorophyll a : b decline, suggesting that chlorophyll is lost from individual chloroplasts. Oxygen evolution, both per unit area and per unit chlorophyll, is reduced in pustules in comparison to green areas of an infected leaf and to uninfected leaves. Two major parameters of in vivo chlorophyll fluorescence kinetics (Fvar and F.) are progressively reduced in pustules. This suggests that non-cyclic electron transport, and general chloroplast integrity, are impaired as the disease develops. These results are discussed in the context of current theories concerning the mechanisms by which parasites induce a block in the electron transport chain, and a new model is proposed, based on a change in the chlorophyll content of the photosystem reaction centres.

Race 32 of Puccinia graminis f.sp. tritici sporulated in vitro on a chemically defined medium whose amino acid and carbohydrate composition corresponded to that of the susceptible wheat cultivar Little Club. Sporulation was affected by pH, heat-treatment of the medium and the spore-density of the inoculum. Good mycelia( growth was promoted at high inoculum density, low volume of culture medium, and when no heat treatment, or only limited heat treatment, was given during sterilization of the medium. When these conditions were reversed and at pH 5·2, sporulating colonies occurred. Under optimal conditions the first urediospore bearing colonies could be detected 10 days after inoculation of the medium. Several hundred fertile colonies could be detected up to day 20. Typical teliospores were usually found for the first time at day 30. Differentiation of infection structures had a negative effect on sporulation.

Groundsel (Senecio vulgaris L.) was grown at three soil temperatures (ambient, and −2 and 6 °C) in an unheated glasshouse during winter in order to examine how a combination of unavailability of soil water due to freezing and of infection by rust (Puccinia lagenophorae Cooke) would affect water relations and growth. Measurements were continued after plants were transferred to a controlled environment room (10 ° C, 12 h light per day) for recovery.

Low soil temperatures for 2 or 6 weeks reduced leaf water potential (ψ₁) and, over the shorter period, rust exacerbated this reduction. Turgor potential (ψ_p) also fell during soil freezing, more so in rusted than control plants, but both regained turgor rapidly when freezing ended. However, rust prevented a return to pre-freezing ψ₁ during the recovery period. Rust reduced the gain in total dry weight (about 70% of which was leaf dry weight) in plants held at ambient soil temperatures and increased the loss of dry weight of plants held at low soil temperatures; loss of root tissue may have contributed to the inability of rusted plants to regain normal ψ₁ during recovery. In both healthy and rusted plants, specific leaf area (area per unit weight) tended to decrease during low temperature treatment and to increase during recovery. Rust inhibited the increase in leaf area during the recovery period, probably because it lowered ψ₁ and, consequently, increases in dry weight were inhibited by rust, particularly in plants previously held at −2 °C.

Distributions of the hydrolytic enzymes acid phosphatase and non-specific esterase in compatible barley coleoptiles inoculated with Erysiphe graminis fsp. hordei were investigated histochemically by light and electron microscopy. The four different enzymes investigated-acid β-glycerophos-phatase, acid naphthol AS-TR phosphatase, indoxyl acetate esterase and naphthol AS-D acetate esterase—had similar localization patterns. Reaction products were distributed generally in the fungal and host cells, but distinct accumulations were found in certain regions and structures at the encounter sites, including appressoria, penetration pegs, haustoria, papillae, and host cytoplasm. Most papillae showed conspicuous amounts of reaction products, suggesting that papilla formation includes depositions from secretory vesicles derived from the lysosomal system in host cells. There was a marked difference in the apparent concentration of hydrolytic enzyme activity between normal-size papillae accompanied by haustoria (sites of successful penetration) and oversize papillae (sites of unsuccessful penetration). Hydrolytic enzymes, localized most intensively in a lAyer of the oversize papillae, may confer resistance to fungal ingress by degrading components of the penetration pegs.

6-Methoxymellein production by cultured carrot cells was elicited by the addition of partial hydrolysates of the pectic substances of carrot cells obtained with pectinase or trypsin. The crude elicitor preparations were fractionated by anion exchange and gel filtration chromatography and resolved into several fractions. The elicitors, which had been purified from the pectinase hydrolysate, were almost completely destroyed by a subsequent treatment with pectinase. However, treatment with Pronase E did not have a significant effect on the activity of the same elicitor preparations indicating that the essential constituent of these elicitors is oligouronide. On the other hand, pectic fragments of carrot cells obtained by tryptic digestion contained at least two distinct types of elicitor active component. One of them lost activity after treatment with Pronase E after it was resistant to pectinase. In contrast, the activity of the other elicitor was reduced by pectinase treatment. It is likely that elicitor for phytoalexin production in carrot is not a single molecular species but rather heterogenous pectic fragments containing an essential moiety such as oligouronide or peptide.

Fusaric acid treatments induced a greater proportion of the total ion content to leak out from mature tomato leaf tissues than from young leaf tissues. Delaying senescence by treating the plants with kinetin reduced the effects of the toxin on leaf tissue as measured by chlorophyll degradation.

T-toxin treatments of maize leaves also induced greater percentage leakage from older leaves than from young leaves.

The higher chlorophyll contents of tomato plants grown with high nitrate nitrogen levels compared to plants grown with low nitrate levels indicated greater juvenility in the former tissues than in the latter. The ratio of phospholipids to free sterols increased with increasing levels of nitrogen fertilization, indicating possible changes in membrane composition. These results indicate that young tissues or tissues in which the juvenile state is prolonged by growing the plants with high levels of nitrate nitrogen or by kinetin treatments have greater non-specific resistance to toxins than mature of senescing tissues.

Immunodiffusion, immunoelectrophoretic and crossed immunoelectrophoretic analyses of rice antigens in relation to sheath rot disease revealed a serological relationship between susceptible rice cultivars and isolates of the causal organism of sheath rot, Acrocylindrium oryzae. One precipitin band was observed when the antigen preparation of A. oryzae was cross-reacted with its own antiserum or against the antisera of four susceptible rice cultivars. No precipitin band was detected between the antiserum of the resistant cv. Mahsuri and antigen preparations from three isolates of A. oryzae or between the antigens of the resistant cultivars Mahsuri and Rupsail and the antiserum of A. oryzae. Crossed-immunoelectrophoretic tests confirmed that there was a common antigen between Mahsuri and Jaya, and between Mahsuri and CR-126-42-1. The precipitin band between the antigen preparation of Jaya and A. oryzae was found to be similar.

Respiratory inhibition, electrolyte leakage, cytological alterations and expression of plant symptoms were induced in Zea mays by treatment with fusaric acid concentrations greater than 10⁻⁴M. Early cytological changes included an increased release of secretory product, inhibition of secretory vesicle formation, curling of dictyosomes, elongation and stacking of endoplasmic reticulum cisternae, and swelling of mitochondrial cristae. Longer toxin treatments resulted in decreased numbers of polyribosomes, increased vacuolation and a reduction in the electron density of mitochondrial matrices. When early cytological changes had occurred, respiratory activity was partially inhibited although electrolyte loss was not yet evident. The preceding results are discussed in relation to the proposed mechanism of action and role of this toxin in plant disease.