Jacob Friedman

Plants used for the treatment of diabetes in Israel

In an extensive ethnobotanical survey (130 informants) of the medicinal plants of Israel, 16 species were found to be used for hypoglycaemic treatments. The list includes Achillea fragrantissima (Forssk.) Sch.-Bip, Ammi visnaga (L.) Lam, Atriplex halimus L., Capparis spinosa L., Ceratonia siliqua L., Cleome droserifolia (Forssk.) Del., Eryngium creticum Lam., Inula viscosa (L.) Ait., Matricaria aurea (Loefl.) Sch.-Bip, Origanum syriaca L., Paronychia argentea Lam, Prosopis farcta (Banks et Sol.) Macbride, Salvia fruticosa Mill., Sarcopoterium spinosum (L.) Sp., and Teucrium polium L.; eight of them (marked with an asterisk) are first recorded here as used for this purpose.

IS IAA THE MAJOR ROOT GROWTH FACTOR SECRETED FROM PLANT-GROWTH-MEDIATING BACTERIA

The phytotoxic or promoting effect of bacterial secretions on root growth of young lettuce seedlings (Lactuca sativa) was measured under axenic conditions. It was assumed that the inhibitory or promoting effects of either deleterious rhizobacteria (DRB) or of plant growth promoting rhizobacteria (PGPR) were auxin mediated. To avoid measurements of either parasitism or competition, seedlings were placed adjacent to bacterial colonies, with no contact between the organisms. Auxin excretion rate, evaluated by thin-layer chromatography (TLC) combined with Salkowskis reagent, indicated that all bacteria examined produced and released indole-3-acetic acid (IAA). High levels of IAA (76.6 μM) were excreted by four DRB (Micrococcus luteus, Streptoverticillium sp., Pseudomonas putida, and Gluconobacter sp.) during 84 hr of incubation. High concentrations of IAA released by DRB accounted for the suppression of root growth. Other unidentified fractions in the eluates of DRB also inhibited root elongation, but to a lesser extent. Like DRB, four isolates of PGPR (Agrobacterium sp., Alcaligenes piechaudii, and two different strains of Comamonas acidovorans) secreted IAA, but at lower levels (16.4 μM during a similar period of incubation). PGPR secreted growth promoting substances other than IAA, and these are now being investigated.

Seeds as allelopathic agents

Inhibitors of germination or of growth, highly diversified chemicals are commonly found in higher plants. They occur in vegetative organs as well as in seeds or other dispersal units. Nonprotein amino acids, when present, are mainly found in seeds where they can occur in extremely high concentrations. Density of seeds, rate of emanation of inhibitors, their amount and effectiveness, all determine allelopathic potential of seeds. To induce allelopathy, rate of emanation of inhibitors must be fast and of sufficient duration. Our observations in coffee seedsCoffea arabica L. indicate that rate of emanation of the inhibitor caffeine is highly enhanced during senescence of seeds, suggesting that when allelopathic potential of seeds is evaluated the presence of both young and old seeds should be considered. In many plants seeds are liberated close to the parent plant, the zone where seed-induced allelopathy may occur. Large numbers of seeds are usually produced in order to ensure establishment; greater number and mass of seeds may also increase allelopathic inhibition of competing vegetation.

Allelopathic bacteria and their impact on higher plants.

Referee: Dr. Kermit Cromack, Jr., Dept. of Forest Science, Oregon State University, Corvallis, OR 97331 The impact of allelopathic, nonpathogenic bacteria on plant growth in natural and agricultural ecosystems is discussed. In some natural ecosystems, evidence supports the view that in the vicinity of some allelopathically active perennials (e.g., Adenostoma fasciculatum, California), in addition to allelochemicals leached from the shrubs canopy, accumulation of phytotoxic bacteria or other allelopathic microorganisms amplify retardation of annuals. In agricultural ecosystems allelopathic bacteria may evolve in areas where a single crop is grown successively, and the resulting yield decline cannot be restored by application of minerals. Transfer of soils from areas where crop suppression had been recorded into an unaffected area induced crop retardation without readily apparent symptoms of plant disease. Susceptibility of higher plants to deleterious rhizobacteria is often manifested in sandy or so-called skeletal soils. Evaluation of phytotoxic activity under controlled conditions, as well as ways to apply allelopathic bacteria in the field, is approached. The allelopathic effect may occur directly through the release of allelochemicals by a bacterium that affects susceptible plant(s) or indirectly through the suppression of an essential symbiont. The process is affected by nutritional and other environmental conditions, some may control bacterial density and the rate of production of allelochemicals. Allelopathic nonpathogenic bacteria include a wide range of genera and secrete a diverse group of plant growth-mediating allelochemicals. Although a limited number of plant growth-promoting bacterial allelochemicals have been identified, a considerable number of highly diversified growth-inhibiting allelochemicals have been isolated and characterized. Some species may produce more than one allelochemical; for example, three different phyotoxins, geldanamycin, nigericin, and hydanthocidin, were isolated from Streptomyces hygroscopicus. Efforts to introduce naturally produced allelochemicals as plant growth-regulating agents in agriculture have yielded two commercial herbicides, phosphinothricin, a product of Streptomyces viridochromogenes, and bialaphos from S. hygroscopicus. Many species of allelopathic bacteria that affect growth of higher plants are not plant specific, but some do exhibit specificity; for example, dicotyledonous plants were more susceptible to Pseudomonas putida than were monocotyledons. Differential susceptibility of higher plants to allelopathic bacteria was noted also in much lower taxonomical categories, at the subspecies level, in different cultivars of wheat, or of lettuce. Therefore, when test plants are employed to evaluate bacterial allelopathy, final evaluation must include those species that are assumed to be suppressed in nature. The release of allelochemicals from plant residues in plots of ‘continuous crop cultivation’ or from allelopathic living plants may induce the development of specific allelopathic bacteria. Both the rate by which a bacterium gains from its allelopathic activity through utilizing plant excretions, and the reasons for the developing of allelopathic bacteria in such habitats, are important goals for further research.

Chemotypic differentiation in indigenous populations of Foeniculum vulgare var. vulgare in Israel

Abstract Chemical analysis of the volatile fraction of oleoresins from fruits of seven natural populations of Foeniculum vulgare var. vulgare (bitter fennel), from the wild and after cultivation indicated the presence of two groups of populations. The first included three indigenous populations with a profile of constituents similar to that observed in their cultivated representatives, suggesting a high chemical heritability. In the second group, with four populations, the major chemical constituents exhibited higher differences between the natural populations and their cultivated representatives, suggesting a lower heritability. Cluster analysis within the first group revealed a remarkable similarity between the chemical composition of the oleoresins from plants in nature, and that of their cultivated representatives, suggesting two different chemotypes: a trans-anethole chemotype, represented by the populations of the Negev desert and of the northern coastal plane, and an estragole dominated chemotype of a northeastern population of Mt. Dov. It is conjectured that northwestern winds, during the flowering season (July–October) restrict free westwards movement of pollinators. As a result, panmictic pollination is adversely affected, enhancing isolation and genetic differentiation. In populations of lower heritability, chemical response to cultivation was variable. In two mountainous populations (Mt. Tayyasim and Mt. Meron) cultivation had reduced trans-anethole, whereas in two other populations of lower elevations (Ramat-ha’Sharon and Ma’alot-Tarshicha), cultivation had decreased the relative content of estragole and elevated that of trans-anethole. Either chemotypic differentiation or phenotypic plasticity increases within species chemical variability, but the specific ecological roles of these essential oils remain to be uncovered.

Biosynthesis of estragole and t-anethole in bitter fennel (Foeniculum vulgare Mill. var. vulgare) chemotypes. Changes in SAM:phenylpropene O-methyltransferase activities during development

Abstract Estragole and t-anethole are the major constituents of the essential oils of bitter fennel chemotypes (Foeniculum vulgare Mill. var. vulgare. Apiaceae). Cell-free extracts from bitter fennel tissues display O-methyltransferase activities able to in vitro methylate chavicol and t-anol to produce estragole and t-anethole, respectively, by utilizing S-adenosyl- l -methionine as a methyl group donor. Analysis of different plant parts of an estragole-rich chemotype, indicated an association between estragole accumulation and chavicol O-methyltransferase activity during development. Young leaves displayed higher levels of O-methyltransferase activity than old leaves. In developing fruits O-methyltransferase activity levels increased until the wasty stage was reached and then dramatically decreased. This chemotype also displayed t-anol O-methyltransferase activity at higher levels than chavicol O-methyltransferase activity although these tissues accumulate mainly estragole. O-methyltransferases activities extracted from a high-t-anethole fennel chemotype also methylated t-anol and chavicol at comparable rates. Thus, although the chemotypes greatly differ in their phenylpropenoids composition, both are efficient in in vitro forming t-anethole and estragole.

Water Response of the Hygrochastic Skeletons of the True Rose of Jericho (Anastatica hierochuntica L.)

SummaryThe hygrochastic apparatus in Anastatica hierochuntica was investigated from the standpoint of morphology of the skeleton and fruit and its contribution to the regulation of seed dispersal in accordance with the water conditions.Water absorption by the dry skeletons upon shoot immersion under laboratory conditions is a rapid process requiring only a few minutes. It is followed by a slow opening of the curled branches of the skeleton. Maximal opening is attained by the saturated skeletons in approximately 2h. Absorption of water and subsequent opening occur also when only the main root of the skeleton is immersed in water. The process was duplicated also by intact skeletons irrigated in situ. Skeletons closure in response to evaporation is initially slow, noticable curling of the branches obtained only after 60% of the water is lost from the saturated skeletons. Opening of the skeleton exposes most of the fruits to the force of falling raindrops. The fact that no spontaneous opening of fruits occurred under most laboratory procedures of skeleton immersion suggests that in nature two successive processes occur: the skeletons must first uncurl-hygrochasticly so that raindrops can impinge forcefully on the appendages of the fruit valves and thus cause seed release by ombrohydrochory. Under adequate rainfall, the first fruits to open are those at the outer infructescences; heavier rainfall will release seeds from the upper fruits of the inner infructescences, and later, from fruits at their bases. The force that binds the valves of the fruits to the septa is variable, its strength correlated with different structure of the fruist at different positions on the skeleton. This ensures a rate of seed release commensurate with the rainfall, and secures at least a minimum of water for the first seeds. The heterogeneity of skeleton populations insofar as age of the plants is concerned, further ensures that seed dispersal in a given area will be proportional to the amount of rainfall.

Highly potent germination inhibitors in aqueous eluate of fruits of Bishop's weed (Ammi majus L.) and avoidance of autoinhibition

The aqueous eluate from fruits ofAmmi majus (Bishops weed, Umbelliferae) remarkably inhibited germination of adjacent seeds ofAnastatica hierochuntica, lettuce, or tomato but had no effect on intact fruits ofAmmi. Similar inhibition was found in dark or in light, except that seeds ofA. hierochuntica were significantly more inhibited in the dark than in the light. Xanthotoxin was isolated, identified, and found to account for about a sixth of the inhibitory activity of the eluate. After fruits ofAmmi were submerged in a large volume of water for 4 days, the fruits still exuded enough inhibitors to prevent germination ofA. hierochuntica, lettuce, or tomato. Data support also the proposal that the phytotoxins are compartmentalized between the inner and the outer fruit envelopes. The inner layer excludes inhibitors from the embryo and autotoxicity is thus avoided, whereas the outer one ensures a gradual liberation of the phytotoxic compounds. This, as well as the high reactivity of the eluate, the high densities ofAmmi fruits in nature, and their relatively limited annual germination, suggest chemical inhibition of neighboring plant species other thanAmmi. Hence, in addition to their chemical protection against predators of either lower or higher organisms, furanocoumarins in fruits ofAmmi majus may contribute to its success as a weed.

ABORTIFACIENT POTENTIAL FOR THE EPIGEAL PARTS OF PEGANUM HARMALA

The effect of methanol and acetone extracts of the epigeal parts of Peganum harmala, a common medicinal plant among Bedouins in Israel, was studied on several parameters of reproduction in female rats. The methanol extract at a dose of 2.5 g/kg/day, offered in food or in drinking suspension for 30 days, significantly prolonged diestrus by 1.0 day. The methanol extracts at doses of 2.0, 2.5 and 3.5 g/kg/day appeared to produce a dose-dependent significant decrease in litter size. No change in the physical and nutritional status of the animals and no adverse toxicological effects were observed.

Allelopathy and autotoxicity

Abstract Theophrases (285 bc ) and later Pliny recognized the existence of ‘interference’ among plants and noted it significance in agriculture. However, involvement of plant-produced chemicals in plant-plant interactions was first suggested by the Swiss botanist M.A.-P. de Candole in 1832. This was later emphasized by Hoy and Stickney in 1881, who observed the effect of black walnut ( Juglans nigra ) on surrounding vegetation. Years later (1973), Molisch coined the term allelopathy to include both harmful and beneficial biochemical interactions between all types of plants and interactions involving microorganisms. This definition was later adopted Rice (1983) and is accepted at the present time.