Keratinolysis by Absidia cylindrospora and Rhizomucor pusillus: biochemical proof

Absidia cylindrospora and Rhizomucor pusillus, causal agents of phycomycoses, were cultured on sterile natural keratins in a mineral solution and the keratin degradation products analyzed. The excess of sulphur was removed by oxidation to inorganic sulphate and thiosulphate, which were the main products of sulphitolysis of keratin. The proteolytic activity of the two fungi depended on the nature of the keratin substrate. Human scalp hair was the most favoured keratin substrate by both the fungi.     

Synergistic effect of 1-aminocyclopropane-1-carboxylic acid and ethylene during senescence of isolated carnation petals

The effects of ethylene (C₂H₄), (2-chloroethyl)phosphonic acid (ethefon) and 1-aminocyclopropane-1-carboxylic acid (ACC) on senescence of isolated intact petals and of upper petal parts of carnation flowers ( Dianthus caryophyllus L. cv. White Sim) were investigated.
Isolated upper petal parts did not respond to treatment with ethefon or ACC. These tissues did, however, show severe wilting in intact petals that were treated with ethefon or ACC. When isolated upper petal parts were simultaneously treated with ACC and ethefon or ACC and ethylene, a marked synergistic effect on senescence was found. Treatment of isolated petals with radiolabeled ACC led to the accumulation of radiolabeled ACC and N-malonyl-ACC (MACC) in the upper parts. The formation of ethylene and the malonylation of ACC were inhibited by pretreatment of the flower with the inhibitor of ethylene action, silver thiosulphate (STS), which indicates that both were induced by endogenously produced ethylene. Treatment of isolated upper parts with ACC slightly increased their ethylene production. However, when these petal parts were simultaneously treated with ethylene and ACC, the conversion of ACC to ethylene was markedly stimulated.
The results indicate that, in intact petals, ethylene may be translocated from the basal to the upper part where it stimulates the activity of the ethylene-forming enzyme (EFE), thereby making the tissue receptive to ACC.
In addition, it was found that upon incubation of petal portions in radiolabeled ACC, both the petal tissue and the incubation solutions produced radiolabeled carbon dioxide. This was shown to be due to microorganisms that were able to metabolize the carbon atoms in the 2 and 3 position of ACC into carbon dioxide.     

Prevention of floret abscission for Agapanthus praecox requires an adequate supply of carbohydrate to the developing florets

Vase solutions of 2.5 or 5% (w/v) sucrose markedly reduced the abscission of all open florets and buds on cut Agapanthus praecox stems. Pulsing cut stems with these solutions was not as effective as continuous treatments. Pulse treatments with 10% sucrose for 4–24 h were relatively ineffective at reducing floret and bud abscission but longer pulses of 48 h reduced abscission. The relative ineffectiveness of sucrose pulse treatments appeared to be due to the low water uptake of the stems (1–3 ml/day). Reducing the number of florets and buds on an inflorescence reduced abscission of florets and buds, and increasing stem length from 25 cm to 50 cm decreased bud abscission. This reduction in abscission is possibly due to the increased availability of assimilates for the remaining buds and florets or reduced competition for assimilates. Exogenous ethylene treatments (9 µl/L for up to 24 h) had no effect on abscission, although STS treatment (4 mM, 4 h) significantly reduced floret abscission when stems were held in vase solutions of sucrose. We conclude that postharvest floret abscission in A. praecox is influenced primarily by the availability of assimilates to the developing florets.     

Physiological response of cut rose flowers to cold storage

The effects of low temperature storage on the physiology of cut rose flowers ( Rosa hybridaL. cv. Mercedes) were studied. Extension of cold storage or increase in temperature (from 3 to 8°C) was accompanied by shortening of vase life and advancement of petal senescence, as reflected in an advance in the timing of the rise in ethylene production and an increase in membrane permeability (ion leakage). Although storage at a relative humidity (RH) of 65% reduced petal water content by 20% in comparison with flowers stored at 95% RH, it did not shorten vase life. The progression of petal senescence was measured during storage at 3°C and during aging at 22°C. Both ethylene production rates and membrane microviscosity measured by fluorescence depolarization increased with time at 3°C and at 22°C, but more slowly at 3°C. At 3°C membrane permeability measured by ion leakage did not increase. Following cold storage the rate of ethylene production in the petals was increased by up to eight times the rate in unstored flowers. Silver thiosulphate extended the vase life of both stored and fresh flowers equally by 2 days, but did not increase the life of stored flowers to that of treated fresh flowers. It is concluded that the primary effect of cold storage on roses is to slow down senescence and that the continued slow senescence leads to shorter vase life. The possible occurrence of sequential processes during senescence and the effects of temperature on these processes is discussed.     

Effects of waterborne complexing agents on silver uptake and depuration in rainbow trout

Rainbow trout Oncorhynchus mykiss ( c . 60 g) were exposed for 1 week to 0·1 μM silver as AgNO₃ in ion poor water (Ca c . 150 μM, pH c . 8, water temperature 13° C) with or without waterborne organic matter (27 mg C l⁻¹ as Aldrich humic acid), thiosulphate (5 μM Na₂S₂O₃) or chloride (4 mM KCl). Organic matter decreased Ag accumulation by the gills initially, but did not decrease Ag accumulation by plasma or liver. Thiosulphate decreased the amount of Ag accumulated by the gills for the entire 1 week exposure but had no effect on Ag concentrations in the plasma, liver or bile. Chloride had no effect on Ag uptake in any of the tissues examined. All three complexing agents reduced the decreases in plasma Na and Cl concentrations caused by Ag. To study the effects of waterborne complexing agents on Ag depuration, rainbow trout were exposed to 0·1 μM AgNO₃ for 1 week then placed for 8 days in Ag‐free, ion poor water with or without waterborne organic matter (55 mg C l⁻¹) or thiosulphate (5 μM). These complexing agents did not alter depuration of Ag from the gills, plasma, liver or bile. Thus, once Ag has entered a fish, subsequent elimination of internal Ag is not affected by external complexing agents.     

A comparison of the effects of mechanically-induced stress,ethephon and silver thiosulphate on the growth of cauliflower seedlings

Mechanically-induced stress (MIS) was applied to cauliflower seedlings by brushing with paper for 1.5 minutes each day. With the possible exception of the effect on leaf 1 thickness, none of the growth responses induced by MIS were significantly nullified by spraying the seedlings with the ethylene inhibitor, silver thiosulphate (STS). The ethylene-releasing compound, ethephon, induced some changes in cauliflower growth similar to those caused by MIS, such as reduced shoot and leaf 1 weight, a reduction in cotyledon and leaf 1 area, and an increase in the thickness of leaves 1 and 2. However, other effects of ethephon were different from those of brushing. Petiole length and diameter and the weight and area of leaf 2 were reduced by brushing but generally increased by ethephon. STS reversed, at least partially, most of the ethephon effects on growth, thus demonstrating that it acts as an inhibitor of ethylene action in cauliflower.The results are discussed in relation to the possible endogenous control of MIS growth responses by endogenous ethylene and auxin.     

Oxidation of micronized elemental sulphur in soil

The rate of oxidation of micronized elemental sulphur in three soils was measured over a range of temperatures between 2 and 20°C. Temperature had a marked effect with a Q₁₀ (temperature coefficient) between 1.9–3.1. The period for 50% oxidation varied between 6–10 days at 20°C to between 36–42 days at 2°C. All the oxidation curves showed an initial lag. At 20°C the oxidation rate was four times that of flowers of sulphur and was related to the smaller particle size. Additives (wetting and dispersing agents) in the commercial micronized sulphur preparation used (‘Thiovit’) were inhibitory at high concentrations but stimulatory at low concentrations. The significance to field conditions is discussed.     

High-frequency transformation ofArabidopsis thaliana byAgrobacterium tumefaciens

Incorporation of 5 mg/L silver thiosulphate into media for seed germination and callus induction, as used in the transformation protocol originally described by Valvekens et al. (1988), was found to increase the frequency of regeneration of transformants ofArabidopsis thaliana ecotypes C24 and Landsbergerecta by at least 10- to 100-fold. Other factors, such as density of the bacterial inoculation culture, density of the root explants and duration of bacteria-plant cocultivation period, were also found to influence the efficiency of recovery of transformants.     

Ultrastructural localization of silver deposits in the receptacle cells of carnation flowers

Carnations were treated with a silver thiosulphate complex to prevent wilting of the flowers. The ultrastructural localization of silver and sulphur in the receptacle tissue was investigated by electron microscopy. Electron-dense deposits were present in the receptacle tissue. Coarse-grained deposts (diam. 60–100 nm) were predominantly observed at the inner side of the cell wall, whereas fine-grained deposits (diam. 20–60 nm) were predominantly present inside the cell-wall region and in the intercellular spaces. These particles were analyzed for chemical elements by X-ray analytical electron microscopy (Philips EM 400 plus Edax energy dispersive analyzer, type 711). In both types of deposits, the presence of silver and sulphur was verified. Point analysis revealed that in both precipitates the S/Ag ratio was of the same order.Abbreviations CTEM conventional transmission electron microscope - STEM scanning transmission electron microscope The AEM unit is a joint unit of the Erasmus University of Rotterdam, the University of Leyden, and the Health Organization TNO. The analytical microscope was purchased with a grant from the Dutch Organization for Pure Scientific Research (ZWO) through BION