Exposure of freshly harvested avocado fruits to ethylene or CO2increased concentrations of epicatechin and an antifungal diene in the peel. However, the kinetics for the accumulation of these products were greatly different for the two treatments. Following an initial increase caused by ethylene, levels of the diene and epicatechin decreased at the same rate in treated and non-treated fruits and were not different from the untreated controls when disease symptoms ofColletotrichum gloeosporioidesfirst appeared. In CO2-treated fruits, on the other hand, levels of the antifungal diene and epicatechin increased in two stages. An initial increase was observed soon after treatment, similar to the case with ethylene, but a second increase also occurred several days after the end of the first increase. Only CO2-treated fruits exhibited a reduction in fungal decay, indicating that the second increase in epicatechin and the antifungal diene may be causally involved in the delay ofC. gloeosporioidesattack. Exposure of freshly-harvested avocado fruit to ethylene or CO2also increased phenylalanine ammonia lyase (PAL), chalcone synthase (CHS) and flavanone 3 hydroxylase (F3H) activities. F3H activity increased only once in ethylene-treated fruits, but also increased as a second peak in response to CO2treatment. F3H activity closely followed the pattern of epicatechin accumulation. cDNAs clones of avocadopal, chsandf3hwere used to demonstrate that changes in enzyme activities occurred with transcriptional activation of the respective genes in ethylene and CO2treated fruits. Finally, fruits of avocado cultivars naturally resistant to fungal decay contained higher levels of epicatechin that declined slower during ripening. Activities of F3H were also higher in resistant than susceptible cultivars. The data are consistent with the hypothesis that high levels of epicatechin are required for maintenance of concentrations of the antifungal diene sufficient to provide decay resistance during avocado fruit ripening.

Innitial responses to salt shock, that may be involved in the induction of adaptation were investigated. Red beet (Beta vulgaris L.) tissue-slices were exposed to a 1.0-10 min hypertonic diluted artificial sea water (1:5, DASW) shock. Within 1.0 min inositol 1,4,5-trisphosphate content of the tissue increased 2-fold and plasma membrane ATPase activity increased by 45%. Both responses preceded DASW-provoked phosphorylation enhancement of some plasma membrane proteins, which was observed 2.0 min after exposure to the shock. Manoalide and neomycin, inhibitors of phosphoinositide metabolism, prevented all these responses to DASW shock.

Biologia plantarum, an international journal for experimental botany founded in 1959 by Professor Bohumil Němec. Covers all branches of experimental botany ranging from molecular biology and biotechnology to whole-plant and stand functioning.

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.

Inositol 1,4,5-trisphosphate (IP{sub 3}) was determined by competition with ({sup 3}H)-IP{sub 3} for binding to an IP{sub 3} specific protein. A hypertonic mannitol, sorbitol or lactose shock induced an increase in the rate of K{sup +} uptake and raised the IP{sub 3} content of Beta vulgaris slices, excised Vigna mungo and Sorghum bicolor roots, as well as attached V. mungo roots. Increased K{sup +} uptake could also be induced by compounds that artificially induce the PIP cascade, or mimic it's products. A hypertonic shock, administered to intact B. vulgaris slices, further enhanced the phosphorylation of a 20 kD protein in the plasmalemma. Maximal IP{sub 3} content was found 10 min after hypertonic induction and maximal K{sup +} uptake was obtained 10 min later. The effect of a continuous hypertonic treatment on IP{sub 3} content, but not on K{sup +} uptake, was transient. Li{sup +} decreased the rate of IP{sub 3} metabolism.

Lipoxygenase (E.C.1.13.1.13) from the avocado cultivar 'Fuerte' was purified to near homogeniety by affinity chromatography. The enzyme was extracted in potassium phosphate buffer at pH 7.2 in the presence of 2% Triton X-100. Triton was removed from the homogenate by adsorption on 250–350 mesh activated charcoal. Lipoxygenase was partially purified (seven-fold) by 66% acetone precipitation from a 20% acetone supernatant. The precipitate was dissolved in a potassium phosphate buffer at pH 7.2 and loaded on an affinity chromatography column. This single-step chromatographic purification yielded a single lipoxygenase activity peak. The total activity yield of the purification procedure was ca 65% and the degree of enrichment ca 35-fold. The Mr determined by gel filtration and by electrophoresis, was 74 000. Optimum enzyme activity was found at 36° and pH 7.1. The energy of activation, amino acid composition, isoelectric point, kinetic parameters and inhibitory effect of epicatechin were studied. The enzyme was found to obey Michaelis-Menten kinetics. The Km of the avocado lipoxygenase for linoleate was 7.2 × 10−2 mM and the Vmax, was 432 μmol/hr/mg. Epicatechin acted as a competitive inhibitor with a Ki of 9.0 × 10−5 mM.

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 22Na+-labelled sodium chloride to the CaSO4 medium. When 36Cl label was added as well, a pH-jump induced an increase in Cl− uptake in the same slices. The uptake of 86Rb+ 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 H2SO4, its effect on Na+, as well as Cl− uptake was much decreased or abolished.

AbstractAvocado cultivars were defined as susceptible and resistant to Colletotrichum gloeosporioides depending upon the length of the incubation period of the disease after fruit softening. In the susceptible cultivars Fuerte, Horshim, Vurtz, Rincon, and Benik, epicatechin concentration of the peel decreased to 60‐130 μg.g−1, fr. wt. at fruit softening and symptoms appeared on the same or one day later. In the resistant cultivars Hass, Nabal, Netaim and Pinkerton, epicatechin concentration was still 632–1740 μg.g−1 fr. wt. when fruit softening and symptoms appeared only 4‐10 days later. When susceptible Fuerte fruits became soft the concentration of the antifungal compound 1‐acetoxy‐2‐hydroxy‐4‐oxo‐heneicosa‐12,15 diene, had decreased to 120 μg.g−1 fr. wt. and symptoms appeared. In resistant Hass fruits, the antifungal diene was still 238 μg.g−1 fr. wt. at fruit softening; and it had further decreased to 159 μg.g−1 fr. wt. when symptoms appeared, four days later. A modified atmosphere and 0.2 M CaCl2 infiltration both delayed softening of Fuerte fruits; but symptom appearance on these fruits was related to diene decrease and not to fruit softening.The results are discussed in relation to the hypothesis that the susceptibility of avocado cultivars to post‐harvest decay by C. gloeosporioides is related to the degradation of the antifungal diene, catalyzed by avocado lipoxygenase, the activity of which is regulated by the decline of its inhibitor epicatechin.

AbstractThe possible relation between changes in mango fruit composition during ripening and the latency of Alternaria alternata infections was investigated. The main increase in total soluble solids and the decrease in acid content in ripening mangofruits occurred during the initial 13 days after harvest, while symptoms of A. alternata appeared only 5 days later. Susceptibility of resistant peeled mango fruits flesh could not be increased by infiltration with sucrose, at a concentration that sustains maximal growth in vitro.

The growth of C. incanus plants in the soils of northern Israel depends on ecto‐mycorrhiza formation, which is repressed in soils of basaltic origin. It was shown that this dependence is abolished when available phosphate is added to the soils. Key words: Phosphate availabilitymycorrhiza Cistus incanus L.Israelterra‐rosabasaltic protogrumosol

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.

A rather specific inhibitor of calmodulin‐regulated functions, compound 48/80. inhibited 36Cl−, 86Rb+ and 22Na+ absorption by Hordeum vulgare, Phaseolus mungo and Zea mays roots. The compound did not inhibit plasmalemma or tonoplast Mg:2‐ATPase activity; neither did it inhibit or uncouple respiration, or affect ATP content and seemed also not to cause depolarization of the membrane potential of roots cells. Compound 48/80 inhibited the ΔpH‐mediated Cl−‐H+ symport in ATP‐depleted roots.

S OF PAPERS PRESENTED AT THE 10TH CONGRESS OF THE PHYTOPATHOLOGICAL SOCIETY OF ISRAEL Apri l 2 0 2 1 , 1986 The Vo lcan i Cente r , A R O , Bet Dagan, Israel A: EPIDEMIOLOGY OFPLANTDISEASES IMPROVED "SINGLE TILLERS" METHOD FOR LOSS ASSESSMENT IN WHEAT D. SHTEINBERG*, A. MARANI** and A. DINOOR* *Dept. of Plant Pathology and Microbiology and **Dept. of Field and Vegetable Crops, The Hebrew University of Jerusalem, Faculty of Agrieulture, Rehovot, Israel Common methods for loss assessment include establishment of experimentally derived damage functions expressing the relationships between disease level and yield; and estimates, based on the damage functions, of losses in other fields. There are drawbacks to these methods, such as (i) cost, preplanning and prospects for success of the field trials, and (ii) validity of the functions for other fields. In the "single tillers" method the functions are based on hundreds of tillers. The main drawback to it is the validity of estimates derived from single tillers, for a whole crop. The advantages of the method are that (i) it can be applied simply in any desired situation without preplanning and without allocation of field experiments; (it) the damage function is calculated for each field evaluated; and (iii) it is very inexpensive to operate. Attempts to standardize procedures in order to improve the validity of the method were tested in field trials. Tagging only 300 single tillers was found to be the optimal sample size which provided small enough SE values. Disease severity on fiat leaves at the early milk growth stage was the most important disease factor affecting yields. Different loss models were tested (the critical stage model, the multiple regression model, the stepwise regression model, and the area under disease progress curve model) and were found satisfactory for predicting yield losses. The critical stage model, which is simpler than the rest, was then chosen for use under Israeli conditions. By taking into account plant factors unaffected by the disease, percentage of yield variability explained by disease level was improved from previous analyses explaining only 3-8% of the variation, to new analyses explaining 53-78% of the variation. The losses determined by the improved method did not differ significantly from the values calculated from ordinary field trials. "CRWD-1 AND -2" (DECISION MAKERS 1 AND 2): COMPUTERIZED RECOMMENDATION SYSTEMS FOR THE CONTROL OF FOLIAR WHEAT DISEASES D. SHTEINBERG*, A. DINOOR* and A. MARANI** *Dept. of Plant Pathology and Microbiology and **Dept. o.f Field and Vegetable Crops, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, Israel Foliar wheat diseases may develop into epidemics and cause appreciable losses to yields. Epidemic development depends on climatological and agronomical conditions and it is impossible to forecast the specific disease development in each particular field. Decision making, based on the specific agrotechnical, epidemiological and meteorological conditions, is needed for each field. The computerized method "CRWD-I" (Control Recommendations for Wheat Diseases) Phytoparasitica 14:3, t 986 23 7 was designed for use by the farmers. It combines general information from research (built-in information), with specific information for the particular field (information added by the farmer). It offers a strategy of control, based on disease thresholds, the conditions affecting disease development and specific economic conditions. The method was tested in 1985 in two regions (northern Negev and Bet She'an Valley). All recommendations to withhold control and 75% of the recommendations to apply control, proved to be beneficial. Based on these findings, the method was then improved, to include weather forecasts in addition to the consideration of climatic conditions that had prevailed before decision making, which was used in the first version. The "new version, "CRWD-2", will be tested in 1986 in the