Ben-Ami Bravdo

Endo-β-glucosidase from Aspergillus niger grown on a monoterpene glycoside-containing medium

Abstract An endo-β-glucosidase was isolated from Aspergillus niger grown on a medium containing rutin as the sole carbon source, and was partially purified by affinity chromatography. The enzyme was found to be extracellular. Its optimum pH was 3.4, and its optimum temperature 65°. K M values were 1 mM (PNPG) and 1.25 mM (geranyl-β-rutinoside), V max values were 0.22 μmol/min/mg protein (PNPG) and 0.08 μmol/min/mg protein (geranyl-β-rutinoside), and K I was 40 mM (glucose). The enzymes activity was not inhibited by fructose, sucrose or SO 2 , and was enhanced by ethanol. No loss of activity was found after seven days at 50°. M r determined by gel filtration was 120 000. Using polyacrylamide isoelectric focusing gel, a pI of 3.9 was obtained.

Photoacoustic and fluorescence measurements of the chilling response and their relationship to carbon dioxide uptake in tomato plants

The response of tomato plants to various chilling treatments was studied using two approaches for the measurement of photosynthetic activity. One involved the use of a portable fluorometer for the measurement of in-vivo chlorophyll fluorescence, while the other employed a newly introduced photoacoustic system which allowed changes in oxygen evolution to be followed in a leaf disc. A strong correlation was found between results obtained by each system and those obtained by a conventional open gas-exchange system for the determination of CO2 uptake. Both systems of measurements could readily distinguish between the effects of chilling in the dark (at 3° C for 18 h) and chilling at high photon flux density (2000 μmol m-2 s-1 for 5h at 5° C). Chilling in the dark had practically no effect on the quantum yield of oxygen evolution, chlorophyll fluorescence or CO2 uptake, while chilling at excessively high photon flux density resulted in a sharp reduction (50–70%) in the quantum yields obtained. The results support the view that photosystem II cannot be the primary site of damage by chilling in the dark, although it is significantly affected by chilling at high light intensity.

Effect of Post-Veraison Irrigation Level on Sauvignon blanc Yield, Juice Quality and Water Relations

Low (L), medium (M) and high (H) post-veraison daily irrigation levels (1 mm, 2 mm and 3,5 mm, respectively) were applied in a Sauvignon blanc vineyard in the Golan Heights of Israel. Juice Brix levels were higher in the H treatment than in the L treatment. Yields were higher in H treatment than in L treatment in years with high crop level. Shoot elongation ceased at veraison in all three treatments. Average midday leaf water potential (LWP) was -1,4 MPa and -1,9 MPa in the Hand L treatments, respectively. Lower stomata! resistance (R,J was found in the H treatment compared to those in the L and M treatments. A negative correlation between Rs and LWP was observed. Leaf temperatures were higher in the L treatment than in the H treatment. This was mainly attributed to the difference in Rs between treatments. The apparent relationship between R8 and LWP suggests the use of canopy heat balance for irrigation management in warm regions, provided that satisfactory methodologies for boundary-layer resistance and the evaluation of net radiation in vineyards are developed.

Effects of moisture stress on stomatal resistance and photosynthetic rate in cotton (Gossypium hirsutum). 1. Controlled levels of stress.

Abstract The effects of moisture stress on stomatal resistance and on photosynthetic rate were studied in cotton ( Gossypium hirsutum L., cv. Acala SJ-2) under field conditions with drip irrigation in 1984 and in 1985. Moisture stress was evaluated by measuring the minimum midday leaf water-potential, which was kept at two levels (−1.6 and −2.4 MPa) during each of two phenological periods. Stomatal resistance increased and photosynthetic rate decreased as a result of moisture stress. The correlation between stomatal resistance and radiation was lower when the plants were subjected to moisture stress. An exponential asymptotic relationship was found between photosynthetic rate and stomatal resistance. Stomata were found to limit the photosynthetic process in well-watered plants or in midly stressed plants, while mesophyll resistance was the main factor reducing it under more severe moisture stress. In the moisture-stressed plants, mesophyll resistance increased more than did stomatal resistance, and this was associated with a higher internal CO 2 concentration in the leaf ( C i ) and a lower ratio of photosynthetic rate to C i . Under moderate moisture stress the maximum photosynthetic rate was attained at an earlier leaf age, while a more severe stress resulted in a lower photosynthetic rate at all leaf ages.

Detoxification of cassava by Aspergillus niger B-1

Abstract The effects of fermentation of cassava by Aspergillus niger B-1 β-glucosidase on its cyanide and protein content, and the optimal conditions for this enzyme’s activity, were examined. This fermentation process reduced the cyanide content of cassava by 95% to 2 mg/kg, and increased its total protein content by 50%, thereby improving its nutritional value. A significant decrease in cyanogenic glycosides was detected after 3 days of fermentation. The optimal pH for A. nigerβ-glucosidase activity on the cyanogenic glycoside linamarin was determined to be 3, the optimal temperature 55 °C, and its Km 0.3 mM. The findings presented here will facilitate the development of an improved method for detoxification of cassava and for enhancement of its nutritional value.

Xylem-sap zeatin-riboside and dihydrozeatin-riboside levels in relation to plant and soil water status and flowering in ‘Mauritius’ lychee

Abstract The effects of autumnal water stress on the levels of zeatine-riboside and dihydrozeatin-riboside in the shoot xylem-sap and on the intensity of flowering in the following year were studied in commercial lychee ( Litchi chinensis Sonn.) during the 1995/1996 season. Four irrigation treatments were initiated at the beginning of October coinciding with the end of the second vegetative flush after harvest as follows: 0.5, 0.25, 0.125 and 0 Class A pan evaporation coefficient, designated as 100, 50, 25 and 0%, respectively, were applied. Soil and midday stem water potentials were determined several times during October, after the beginning of treatment. Xylem-sap concentrations of trans -zeatin-riboside ( t -ZR) and dihydrozeatin-riboside (DHZR) were determined 20 days after the start of the irrigation treatments. Both soil and midday stem water potentials decreased with the decrease in the irrigation levels. Flowering intensities in the following spring were higher after the reduced irrigation treatments than in the control (100%). DHZR and t -ZR concentrations in the xylem-sap increased with decreasing irrigation level, down to the 25% irrigation level. Cessation of irrigation (0%) resulted in a steep decrease in the t -ZR concentration and a further increase of DHZR. The relationships between plant and soil water status, cytokinin xylem-sap content and flower bud differentiation reported herein suggest that moderate water stress is sufficient to induce fruit bud differentiation without any visible damage to the trees.

Synthesis of lsopropyl-1-thio-Β-D-glucopyranoside (IPTGlc), an inducer ofaspergillus niger b1 Β-glucosidase production

Production of Β-glucosidase inAspergillus niger Bl is subjected to catabolic repression by glucose.Aspergillus niger Bl grown on bran as a carbon source secreted Β-glucosidase. The maximum level of the enzyme was reached after 7 d of fermentation. Addition of 1% glucose to the medium suppressed Β-glucosidase production to undetectable levels. In this study, the organic synthesis of a potential inducer of Β-glucosidase production by A.niger Bl’s reported. Isopropyl-1-thio-Β-D-glucopyranoside (IPTGlc) was synthesized using a two-step organic synthesis protocol. The H-NMR data agreed with those reported previously for the galactoside analog. When IPTGlc was added 24 h after inoculation at a final concentration of 0.4 mM, similar levels of Β-glucosidase were reached 3 to 4 d earlier as compared to fermentation without IPTGlc induction. In practice, this may translate to a more efficient method of producing Β-glucosidase from this fungus.

Fluorescent Screening of Transgenic Arabidopsis Seeds without Germination

In this paper, we describe a reliable method for the screening and selection of Arabidopsis transgenic seeds within minutes without germination. Expression of the Aspergillus niger β-glucosidase gene BGL1 in the plants endoplasmic reticulum was used as a visual marker, together with 4-methylumbelliferyl-β-d-glucopyranoside (MUGluc) as a substrate. Subsequent to incubation in a solution of MUGluc at room temperature for 2 to 15 min, transgenic seeds expressing BGL1 demonstrated a distinct fluorescent signal under UV light. Optimal screening conditions at room temperature were achieved between 75 and 450 μm MUGluc, at a pH of 2.5 to 5.0 and 2 to 5 min of incubation. No significant loss of viability was detected in transgenic seeds that were redried and stored for 45 d after incubation in MUGluc solution for 2 to 150 min. Transgenic plants expressing BGL1 displayed normal phenotypes relative to the wild type. Selection frequency was 3.1% ± 0.34% for the fluorescence selection method, while kanamycin resistant selection resulted in only 0.56% ± 0.13% using the same seed batch. This novel selection method is nondestructive, practical, and efficient, and eliminates the use of antibiotic genes. In addition, the procedure shortens the selection time from weeks to minutes.

Irrigation of Temperate Fruit Trees in Dry and Warm Conditions

Water consumption is an essential process for plants, arising from their need to lose water to the atmosphere through the stomata. The rate of flow which is dictated by the evaporative demands of the atmosphere may expose plants to dehydration in hot climates on the one hand while granting them some benefits such as mineral transport and evaporative cooling of the leaves, on the other. Water is lost from the leaves to the atmosphere through the stomata, the major function of which is to regulate gas exchange between the leaves and the atmosphere. The exchange of CO2 and H2O enables the maintenance of the three fundamental processes of plant metabolism: photosynthesis, transpiration and respiration. The productivity of agricultural crops greatly depends on these processes which govern vegetative and reproductive growth, whereas crop quality is mainly dependent on the interaction between these processes and the formation of primary (various forms of sugars) and secondary metabolites (terpenes, phenols, alcohols, etc.) products of the photosynthetic process. These products serve for energy utilization and quality — compound formation, respectively. The movement of water through the soil — plant- atmosphere continuum (SPAC) is mainly passive, driven by water potential gradients and regulated by resistances along this continuum (Passioura, 1982, Kramer and Boyer, 1995). The gradient between the water potentials at both ends of the continuum, i.e. the soil and the atmosphere, determine the water status of the plant. Extremely low water potentials at either of these two end segments induce water stress in the plant tissue. Since the atmospheric water potential variations are up to three magnitude higher than those of the soil and in most cases are uncontrollable, the major agricultural means of affecting plant water status is irrigation.