Benjamin Jacoby

Is sodium proton antiport ubiquitous in plant cells

Summary Excised roots or storage tissue slices from 16 crop plant species were screened for the presence of a Na + /H + antiporter at the plasma membrane and tonoplast of their cells. The pH-gradient dependent decrease of Na + uptake by ATP-depleted tissues served as an indication for such antiport at the plasma membrane. Metabolic-energy dependent uptake by the tissues, in the presence of excess K + , indicated the functioning of Na + /H + antiport at the tonoplast. Evidence for Na + /H + antiport was found in four species and for its absence in five species. In seven species the evidence was not unequivocal. It was concluded that the presence of a Na + /H + antiporter is not an ubiquitous characteristic of plant cells.

Induction of antifungal resorcinols in flesh of unripe mango fruits and its relation to latent infection by Alternaria alternata

Abstract A mixture of antifungal compounds, consisting primarily of 5-(12-cis-heptadecenyl)-resorcinol and 5-pentadecylresorcinol was found at fungitoxic concentrations in the peel, but not in the flesh of unripe mango fruit. The unpeeled fruits were resistant to Alternaria alternata, but freshly peeled fruits were susceptible. The flesh of peeled mango fruits became resistant to A. alternata infections within 24 h after peeling. During this period the concentration of the 5-substituted resorcinols increased from 30 to 80 μ g−1 fresh weight and continued to increase to reach a concentration of 160 μ g−1 fresh weight 96 h after peeling. A browning reaction, accompanied by increased activity of the enzyme phenylalanine ammonia lyase (PAL), also occurred in the flesh as a result of peeling. Cycloheximide inhibited browning and PAL activity in the fruit flesh, but not the synthesis of 5-substituted resorcinols and the development of resistance to A. alternata. Anaerobiosis prevented flesh browning, the development of resistance in peeled fruits, and the increase in concentration of the antifungal 5-substituted resorcinols. This work provides further evidence for the involvement of antifungal resorcinols in the latency of A. alternata in unripe mango fruits.

Some characteristics of the Mg-ATPase of isolated red beet vacuoles

Abstract Mg-ATPase activity was demonstrated in isolated beetroot vacuoles. Phosphatase and Mg-ATPase activities were distinguished by inhibition of the phosphatase with molybdate. Phosphatase activity was found to be confined to the vacuolar sap, while ATPase activity was found in both the sap and the tonoplast membrane pellet. The Mg-ATPase was inhibited by N,N′-dicyclohexylcarbodiimide (DCCD) but not by ouabain and oligomycin. Mg-ATPase activity was enhanced by chlorides of various monovalent organic and inorganic cations. The pH optimum of Mg-ATPase activity was 7.0–7.5.

Inhibitors of avocado lipoxygenase: their possible relationship with the latency of Colletotrichum gloeosporioides☆

Linoleate oxidation by avocado lipoxygenase was inhibited in vitro in the presence of the specific inhibitor 5,8,11,14-eicosatetraynoic acid (ETYA). Infiltration with ETYA of avocado discs inoculated with Colletotrichum gloeosporioides delayed symptom development at concentrations where the fungus itself was not affected. Subsequently, a natural inhibitor of avocado lipoxygenase was isolated from peels of unripe avocado fruits and identified as epicatechin. It inhibited avocado lipoxygenase with a Ki of 0·64 μm. The concentration of epicatechin in unripe fruits was 514 μg g− fresh weight of peel; this decreased during ripening to 8 μg g−1 fresh weight, before symptoms of C. gloeosporioides infections were expressed. A comparison of two cultivars with differing susceptibility to C. gloeosporioides showed that the concentration of epicatechin decreased faster in the cultivar in which symptoms appeared first. An atmosphere containing 50 μg l− ethylene enhanced the decrease of the lipoyxygenase inhibitor in avocado fruits and shortened the period before symptoms of disease were expressed. In over-mature, firm and naturally infected fruits hanging in the orchard the concentration of epicatechin was 260 μg g− in the area of the peel without symptoms and only 27 μg g− in that showing symptoms of infection. The results are discussed in relation to the hypothesis that the latency of the infection of avocado fruit by C. gloeosporioides may be accounted for by the degradation of the preformed antifungal compound, cis,cis-1-acetoxy-2-hydroxy-4-oxo-heneicosa-12, 15-diene, which is catalysed by avocado lipoxygenase, and that the in vivo lipoxygenase activity may increase during ripening owing to the decline in the levels of its endogenous inhibitor epicatechin.

Assessment of Na+/H+ antiport in ATP-depleted red beet slices and barley roots

Abstract Sodium uptake by ATP-depleted beet slices was strongly decreased when an external pH-jump, from 7.0 to 3.9, accompanied the addition of 22 Na + -labelled sodium chloride to the CaSO 4 medium. When 36 Cl label was added as well, a pH-jump induced an increase in Cl − uptake in the same slices. The uptake of 86 Rb + was not affected by a similar pH-jump. The pH-jump enhanced Cl − uptake in both ATP-depleted barley and corn roots; but Na + uptake was affected only in barley and not in corn roots. When the pH-jump to 3.9 was produced with permeable acids instead of H 2 SO 4 , its effect on Na + , as well as Cl − uptake was much decreased or abolished.

Adsorption of systemic pesticides on ground stems and in the apoplastic pathway of stems, as related to lignification and lipophilicity of the pesticides☆☆☆

Abstract The adsorption of five systemic fungicides (carbendazim, triadimefon, nuarimol, triarimol, and fenarimol) and one herbicide (fluometuron) on ground stems and in the apoplastic pathway of excised pepper, cotton, and bean stems was studied. Adsorption on ground and water extracted stems, as well as retention in the apoplast of excised stems, increased with the 1-octanol/water partition coefficients of the pesticides. Methylation of ground stems increased their adsorption capacity (carbendazim excluded), while extraction with organic solvents did not affect it. Woody stems adsorbed more of the pesticides than herbaceous ones. Binding of pesticides in the apoplastic pathway of stems seems to be related to their degree of lignification and to the lipophilicity of the pesticides.

The sequence of death of haustoria and host cells during the hypersensitive reaction of oat to crown rust

Abstract The sequence of events leading to host cell death (hypersensitive reaction) was investigated in an incompatible combination and a fungicide or heat treated compatible combination of Avena sativa L and Puccinia coronata var. avenae . A quantitative comparison of the time course of the death of haustoria and of host cells was made. The first microscopically observable event in the natural as well as in the induced hypersensitive reaction, was the death of haustoria in still intact host cells; death of host cells occurred later. Light and electron micrographs of dead haustoria in apparently intact host cells are presented. It is concluded that in rust infected oat plants haustorial damage precedes host cell death in the natural and in the induced hypersensitive reaction.

Oligomycin effect on ion absorption by excised barley roots and on their ATP content.

SummaryChloride absorption by excised barley roots from dilute solutions is more oligomycin-sensitive than its absorption from more concentrated solutions and than K+ and Na+ absorption from dilute as well as concentrated solutions. Oligomycin decreased the ATP content of excised barley roots. The mode of oligomycin interference with ion absorption by plant cells is discussed.

Absorption, retention and translocation of the systemic fungicide triarimol in plants☆☆☆

Abstract Only very small quantities of triarimol are exported from bean leaves to other plant organs. Triarimol is acropetally transported in the xylem sap of bean explants, however, considerable amounts of it are loosely bound in transit. The bound material is released by additional amounts of water passing through the explant. When barley roots or bean leaf slices are incubated in a medium containing triarimol the fungicide is accumulated so that much higher concentrations are present than in the medium. The retention and accumulation of triarimol by plant tissue is a nonmetabolic process resulting from weak binding to proteins. It is suggested that the translocation of triarimol in the apoplast as well as in the symplast of plants depends on the rate of water flux through the system and on the intensity of its binding.

The fungicide or heat induced hypersensitive reaction of oats to crown rust: relations between various treatments and infection type

Compatible combinations of Avena sativa L. and Puccinia coronata Cda. var. avenae F & L were treated with oxycarboxin or exposed to supra-optimal temperatures. The results varied according to the time interval between inoculation and treatment and the intensity of the treatment. Early treatments and high intensities stopped the rust infection with no subsequent macroscopic manifestation of hypersensitivity or disease. Milder treatments induced a hypersensitive reaction and still later treatments did not prevent infection. The appearance of a hypersensitive reaction was related to the presence of dead haustoria, while an immune reaction occurred when the infection was stopped before the production of haustoria.