Citrus replant problem in Iraq II. Possible role of allelopathy

The role of allelopathy in citrus replant problems was investigated in Iraq. The failure of citrus seedlings to grow normally in old citrus orchards was not caused by differences between old and non-citrus soils in electrical conductivity, pH, organic matter, soil texture and those minerals tested. Extracts of soil collected from old citrus orchards significantly reduced the growth of sour orange seedlings. Extracts and decaying sour orange roots reduced the growth of sour orange seedlings as did extracts of non-senescent sour orange leaves and decaying senescent leaves. Thus it appears that allelopathy is at least partly involved in the citrus replant problem.     

Endophage-ectophage ratios and plant defense

Summary Endophagous folivores, which are concealed inside leaf tissue for much of their life cycle, or which live externally but feed internally, should be more successful on heavily defended plants than ectophagous species. This is because endophages are more facile at feeding selectively and can manipulate tissue development to avoid physical and chemical defenses and to enhance nutrition. As a result, endophage-ectophage ratios should increase on more heavily defended hosts. This pattern will likely be strengthened by negative asymmetrical interactions with ectophages and pathogens, which may displace endophages from lightly defended hosts. The hypothesis predicts that endophages should be particularly abundant in resource-poor habitats which seem to support a preponderance of heavily defended hosts. Although data do not yet exist for a rigorous test, several observed cases where endophage distributions seem biased toward heavily defended hosts are at least consistent with the hypothesis. Plant defense levels may have little influence on the total number of herbivores associated with a host, but I suggest that guild structure can be profoundly altered.     

Regeneration of plants from hypocotyl protoplasts of rapessed (Brassica napus L. var. oleifera) cultivars

Protoplast cultures were prepared from hypocotyls of ten spring rapeseed cultivars. Protoplasts from all genotypes tested formed calli, and shoots were regenerated from calli of nine of the genotypes at frequencies varying from 15 to 76%. The regenerating cultivars fell into a high regenerating group (>60% and a low regenerating group <25%).     

Host plant recognition in monophagous weevils: specificity in feeding responses of Ceutorhynchus constrictus and the variable effect of sinigrin

Host plant relations of the monophagous weevil Ceutorhynchus constrictus Marsh. (Coleoptera: Curculionidae: Ceutorhynchinae) feeding on garlic mustard, Alliaria petiolata (Bieb.) Cavara & Grande (Cruciferae) were studied in the laboratory. Most other crucifers were rejected in choice tests using garlic mustard as a reference plant, but Brassica nigra, Sinapis alba and Thlaspi arvense were as acceptable as the host plant. Flowering plants of Descurainia sophia were acceptable while young plants of this species were not. The most important feeding stimulants in extracts of garlic mustard were uncharged, water soluble compounds. The most abundant glucosinolate in garlic mustard, sinigrin, was a feeding stimulant, too. However, the feeding stimulatory activity of sinigrin was only expressed in the presence of still unidentified uncharged compounds from garlic mustard leaves. Host plant relations in monophagous crucifer-feeding insects is discussed in relation to the distinctness of glucosinolate patterns found in their host plants.

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Zusammenfassung Ceutorhynchus constrictus Marsh. (Coleoptera: Chrysomelidae: Ceutorhynchinae) ist ein monophager Rüsselkäfer, der an Knoblauchhederich frisst. Das Wirtswahl-Verhalten dieses Käfers ist im Labor untersucht worden. Die meisten Crucifiren waren im Wahlversuche nicht akzeptiert, wenn Knoblauchhederich als Vergleichspflanze vorhanden war. Von Brassica nigra, Sinapis alba, und Thlaspi arvense wurden im Vergleich gleiche Mengen verzehrt wie von der Wirtspflanze. Blühende Descurainia sophia Pflanzen wurden, im Gegensatz zu Jungpflanzen der gleichen Art, angenommen. Die wichtichsten Phagostimulanten in Extrakten von Knoblauchhederich-Blättern waren ungeladene, wasserlösliche Substanzen. Das häufigste Glukosinolat im Knoblauchhederich, Sinigrin, war auch ein Phagostimulant. Doch war die phagostimulierende Wirkung von Sinigrin nur in Kombinationen mit noch nicht identifizierten, ungeladenen Substanzen aus Knoblauchhederich-Blätter nachweisbar. Wirtspfanzen-Beziehungen von monophagen Insekten werden diskutiert im Zusammenhang mit der Eigenart des Glukosinolat-Inhaltes ihrer Wirtspflanzen.

     

The effect of glucosinolates on responses of young Phyllotreta nemorum larvae to non-host plants

All recorded host plants of Phyllotreta nemorum L. (Coleoptera: Chrysomelidae) contain glucosinolates and belong to the plant families Brassicaceae (Cruciferae), Resedaceae and Capparaceae. The acceptability of 56 plant species from 28 other plant families (non-hosts) for young larvae has been studied in the laboratory. None of these species were fully acceptable for initiations of leaf mines when intact untreated leaves were presented, and only one species, Malva silvestris L. (Malvaceae), was partially acceptable. The acceptability of some species increased when leaf discs were presented instead of intact leaves; but the highest percentages of mine initiations occurred in leaf discs treated with the glucosinolate, sinigrin. A stimulatory effect of sinigrin could be demonstrated in experiments with 7 plant species: Papaver dubium L., Papaver rhoeas L., Fumaria officinalis L., Malva silvestris L., Pisum sativum L., Campanula latifolia L. and Lactuca sativa L. The majority of species remained unacceptable even after treatment with glucosinolates.The main causes for these differences between plant species are supposed to be differences in contents of deterrents and/or other stimulants for mine initiation. These possibilities are discussed in relation to the content of allelochemicals in acceptable plants and the position of these plants in botanical classifications.

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Zusammenfassung Phyllotreta nemorum L. ist ein oligophager Erdfloh, der an Cruciferen und anderen Glukosinolat-haltigen Pflanzenarten gebunden ist. Die Imagines fressen Löcher in die Blätter und die Weibchen legen ihre Eier in den Boden. Die Larven sind Blattminierer. Nach dem Schlüpfen im Boden klettern sie an die Pflanzen hoch, und die Einbohrung und der Anfang der Minierung erfolgt in eines der unteren Blätter der Wirtspflanze.Die Wirkung von Glukosinolaten auf die Einbohrung von Junglarven in Pflanzenarten, die keine natürliche Inhalt von Glukosinolaten haben, ist in Laborexperimenten untersucht worden. 56 Pflanzenarten aus 28 Familien wurden präsentiert teils als unbehandelte Blätter und teils als Glukosinolatbehandelte Blattscheiben. Unbehandelte Blätter von nicht-Glukosinolathaltigen Arten waren immer unbefriedigend für die Larven. Nur in eine Art, Malva silvestris L. war die Frequenz der Einbohrung ein bisschen höher als 10%. Eine signifikante Erhöherung der Anzahl eingebohrten Larven nach der Sinigrin-behandlung erfolgte in 7 Pflanzenarten: Papaver dubium L., P. rhoeas L., Fumaria officinalis L., Malva silvestris L., Pisum sativum L., Campanula latifolia L. und Lactuca sativa L. Doch blieben die meisten Pflanzenarten (84%) auch nach der Sinigrin-Behandlung unbesiedelt.Pflanzenarten, die nach der Sinigrin-Behandlung nicht besiedelt werden enthalten vielleicht frasshemmende Stoffe, oder ihnen fehlen noch weitere Frass-stimulierende Stoffe. Diese Möglichkeiten werden diskutiert in Zusammenhang mit den Inhalt von Allelochemikalien in besiedelten Pflanzenarten und mit ihrer taxonomischer Position.

     

Effects of water level fluctuation on the growth ofNelumbo nucifera Gaertn. in Lake Kasumigaura,Japan

Investigations were made of the growth ofNelumbo nucifera, an aquatic higher plant, in a natural stand in Lake Kasumigaura. A rise of 1.0 m in the water level after a typhoon in August 1986 caused a subsequent decrease in biomass ofN. nucifera from the maximum of 291 g d.w. m⁻² in July to a minimum of 75 g d.w. m⁻². The biomass recovered thereafter in shallower regions. The underground biomass in October tended to increase toward the shore. The total leaf area index (LAI) is the sum of LAI of floating leaves and emergent leaves. The maximum total LAI was 1.3 and 2.8 m² m⁻² in 1986 and 1987, respectively. LAI of floating leaves did not exceed 1 m² m⁻². The elongation rates of the petiole of floating and emergent leaves just after unrolling were 2.6 and 3.4 cm day⁻¹, respectively. The sudden rise in water level (25 cm day⁻¹) after the typhoon in August 1986 caused drowning and subsequent decomposition of the mature leaves. Only the young leaves were able to elongate, allowing their laminae to reach the water surface. The fluctuation in water level, characterized by the amplitude and duration of flooding and the time of flooding in the life cycle, is an important factor determining the growth and survival ofN. nucifera in Lake Kasumigaura.     

Common antigenic determinants in the glycoproteins of plants,molluscs and insects

An antiserum raised against -fructosidase isolated from the cell walls of suspension-cultured carrot cells cross-reacts with many plant proteins and hemocyanin ofHelix pomatia. The shared epitope appears to be a small complex glycan with a (1–2)-linked xylose residue attached to the -linked mannose residue of the core of an asparagine-linked oligosaccharide. There is strong cross-reactivity with the proteins of many seed plants, molluscs and insects, and no cross-reactivity with the proteins of fungi, algae, mosses, ferns, or any of the vertebrates tested. Xylose-containing glycans appear to increase the immunogenicity of the proteins to which they are attached, and we suggest that they may be responsible for some allergic responses of people that are repeatedly exposed to plant or insect proteins.     

A role for haemoglobin in all plant roots?

Abstract. We have found haemoglobin in plant roots whereas previously it has been recorded only in nitrogen fixing nodules of plants. Haemoglobin occurs not only in the roots of those plants that are capable of nodulation but also in the roots of species that are not known to nodulate. We suggest that a haemoglobin gene may be a component of the genome of all plants. The gene structure and sequence in two unrelated families of plants suggests that the plant haemoglobins have had a single origin and that this origin relates to the haemoglobin gene of the animal kingdom. At present we cannot completely rule out the possibility of a horizontal transfer of the gene from the animal kingdom to a progenitor of the dicotyledonous angiosperms but we favour a single origin of the gene from a progenitor organism to both the plant and animal kingdoms. We speculate about the possible functions of haemoglobin in plant roots and put the case that it is unlikely to have a function in facilitating oxygen diffusion. We suggest that haemoglobin may act as a signal molecule indicating oxygen deficit and the consequent need to shift plant metabolism from an oxidative to a fermentative pathway of energy generation.     

Growth and development of maxipak wheat as affected by soil salinity and moisture levels

The effect of soil salinity and soil moisture on the growth and yield of maxipak wheat (Triticum aestivum L.) was studied in a lath-house experiment in whih, chloride-sulphate salt mixtures were used to artificially salinize a sandy loam soil from Al-Jadyriah Baghdad. Five soil salinity levels of ECe's equal to 1.7 (Control) 4.2, 5.8, 8.1, 9.4 and 11.0dSm^–1 were prepared and used at 3 levels of available soil moisture depletion, namely, 25, 50, and 75% as determined by weight. Both growth (vegetative) and yield components were studied throughout the growing season.Results showed that increasing the soil salinity from 1.7 to 11.0 dSm^–1, and decreasing the available soil water from 75 to 25% resulted in independent and significant decreases in Mazipak wheat growth and yield components at different stages of plant development. Root growth showed more sensitivity to both available soil water and soil salinity level than other components. It has been concluded that at soil salinity levels of more than 8.0 dSm^–1, available soil water became a limiting factor on wheat growth and the maintenance of 75% of available soil water during the growth period is recommended to obtain satisfactory grain yield.     

Voltage-dependent channels permeable to K+ and Na+ in the membrane ofAcer pseudoplatanus vacuoles

Summary The patch-clamp technique in whole-cell configuration was used to study the electrical properties of the tonoplast in isolated vacuoles fromAcer pseudoplatanus cultured cells. In symmetrical KCl or K₂ malate solutions, voltage- and time-dependent inward currents were elicited by hyperpolarizing the tonoplast (inside negative), while in the positive range of potential the conductance was very small. The specific conductance of the tonoplast at –100 mV, in 100mm symmetrical KCl was about 160 S/cm². The reversal potentials (E _rev) of the current, measured in symmetrical or asymmetrical ion concentrations (cation, anion or both) were very close to the values of the K⁺ equilibrium potential. Experiments performed in symmetrical or asymmetrical NaCl indicate that Na⁺ too can flow through the channels. NeitherE _rev nor amplitude and kinetics of the current changed by replacing NaCl with KCl in the external solution. These results indicate the presence of hyperpolarization-activated channels in tonoplasts, which are permeable to K⁺ as well as to Na⁺. Anions such as Cl^– or malate seem to contribute little to the channel current.