Induction and floral determination in the terminal bud of Nicotiana tabacum L. cv. Maryland Mammoth,a short-day plant

Floral determination in the terminal bud of the short-day plant Nicotiana tabacum cv. Maryland Mammoth has been investigated. Plants grown continuously in short days flowered after producing 31.4±1.6 (SD) nodes while plants grown continuously in long days did not flower and produced 172.5±9.5 nodes after one year. At various ages, expressed as number of leaves that were at least 1.0 cm in length above the most basal 10-cm leaf, one of three treatments was performed on plants grown from seed in short days: 1) whole plants were shifted from short days to long days, 2) the terminal bud was removed and then rooted and grown in long days, and 3) the terminal bud was removed and then rooted and grown in short days. Whole plants flowered only when shifted from short days to long days at age 15 or later. Only rooted terminal buds from plants at age 15 or older produced plants that flowered when grown in long days. Only terminal buds from plants at age 15 or older that were rooted and grown in short days produced the same number of nodes as they would have produced in their original locations while buds from younger plants produced more nodes than they would have in their original locations. Thus, determination for floral development in the terminal bud, as assayed by rooting, is simultaneous with the commitment to flowering as assayed by shifting whole plants to non-inductive conditions.Abbreviations LD long day(s) - SD short day(s) - DN dayneutral     

Reversible effects of moderately elevated temperature on the distribution of excitation energy between the two photosystems of photosynthesis in intact avocado leaves

Initial (F_o), maximum (F_m) and steady-state (F_s) levels of modulated chlorophyll fluorescence were measured in intact avocado leaves (Persea americana Mill.) during state 1-state 2 transitions using a combination of modulated and non-modulated lights with synchronized detection. Under normal temperature conditions (20°C), transition from state 2 to state 1 was associated with a substantial increase (about 20%) in F_m and F_o whereas the F_m/F_o ratio remained constant, reflecting increased absorption cross-section of PS II. On the contrary, at moderately elevated temperature (35°C), these fluorescence changes were very limited, indicating marked inhibition of the state regulation. The fraction of light distributed to PS II () was calculated from the F_o, F_m and F_s levels for both types of leaves. In control leaves, varied from 48% (in state 2) to values as high as 58% (in state 1). In contrast, mild heat treatment resulted in values close to 50% in both states, indicating the inability of heated leaves to reach extreme state 1. The results suggested that avocado leaves under moderately elevated temperature conditions are blocked in a state close to state 2. This effect was shown to occur in a non-injurious temperature range (as shown by the preservation of the (photoacoustically monitored) oxygen evolution activity) and to be rapidly reversed upon lowering of the temperature. Thermally induced development of state 2 (independent on the light spectral quality) could possibly be a protective mechanism to avoid photodamage of the heat-labile PS II by high light intensities which usually accompany heat stress in the field.     

Effect of incubation temperature on the hatching of rotifer resting eggs collected from sediments

Sediment samples from Loch Leven, Scotland, were incubated at 5°C, 10°C and 15°C to induce hatching of rotifer resting eggs. The emergent animals were identified and counted. The temperature which induced hatching varied among the nine species studied. These results are discussed in relation to seasonality and temperature preferences previously recorded for the most abundant species. Resting egg densities of 2.2–13.9 eggs cm^–3 were recorded in the upper 5 cm of sediment.     

Single potassium channels in membranes of isolated mesophyll barley vacuoles

Summary Voltage-dependent K channels could be identified in on-cell and excised patch-clamp records on membranes of isolated plant cell vacuoles. The current through a membrane patch is dominated by a channel population with a conductance of about 121 pS in symmetrical 250mm KCl solution. The single channel adopts at least two conducting levels the 121-pS state being most frequently observed. The channel shows outward rectification, representing a cation flux into the vacuoles. The rectification appears to be caused by a vanishing open probability and a short channel lifetime at hyperpolarizing voltages. A selectivity ratio of potassium over sodium of about 6 was derived as an estimate. Occasionally, an additional population of K channels with a single-channel conductance of approximately 18 pS is observed. This channel type exhibits outward rectification as well.     

Effect of Hirschmanniella caudacrena on the Submersed Aquatic Plants Ceratophyllum demersum and Hydrilla verticillata

In vitro pathogenicity tests demonstrated that Hirschmanniella caudacrena is pathogenic to Ceratophyllum demersum (coontail). Symptoms were chlorotic tissue, deformed stems, and, finally, death of the plant. Inoculum densities of 500 nematodes per 5-cm-long cutting in a test tube containing 50 ml of water resulted in death and decay of some of the cuttings within 8 weeks; 100 nematodes killed the plants in 12 weeks, and 50 and 25 nematodes killed them in 16 weeks. The lowest inoculum level of 10 nematodes did not seriously affect the plants at 16 weeks when the experiment was terminated. A second test conducted outdoors in glass jars containing 3 liters of water and two cuttings weighing a total of 15 g fresh weight showed damage, but results were not statistically significant. Hydrilla verticillata inoculated with H. caudacrena was not affected seriously.     

实夜蛾属二近缘种对寄主植物次生物质的反应:次生物质对幼虫生长和食物利用的影响

实夜蛾属(Heliothis)的棉铃虫(H. armigcra)和烟青虫(H. assulta)是近缘种,幼虫期取食多种相同的植物,其中含有不同的次生物质.本项工作是在人工饲料中分别加入0.5%的烟碱、番茄苷、棉子酚、丹宁酸等饲养早期六龄的幼虫,测定它们对生长和食物利用的影响.结果表明这些次生物质对两种幼虫有不同的作用:烟碱对棉铃虫没有明显影响,但对烟青虫的取食却有一定的刺激作用.丹宁酸、棉子酚、番茄苷可抑制两种幼虫的生长,而以番茄苷抑制烟青虫的生长最为显著.番茄苷主要通过抑制取食来影响幼虫的生长,而丹宁酸和棉子酚则具有降低消化率的作用.通过次生物质对这两种幼虫效应的比较可知,棉铃虫有较大的忍耐力.     

Revision of the plant geographical territories of Israel and Sinai

The phytogeographical territories of Israel and Sinai are revised using a large mass of species distribution data. With the help of chorotype frequencies for 25 km² individual squares in Israel, territories were defined on the basis of the first two most frequent chorotypes. The similarity of boundaries in the resulting phytogeographical map with a physiognomic map suggests that the latter may be used in preliminary stages of the preparation of plant geographical maps.     

Feeding responses to solanaceous allelochemicals by larvae of the tobacco hornworm, Manduca sexta

Feeding responses of the oligophagous tobacco hornworm to allelochemicals prevalent in their host plants were determined in food choice-tests using filter paper discs laced with a test solution or water (control). Six solanaceous alkaloids, tomatine, tomatidine, solanine, solanocapsine, atropine and nicotine, were tested and only tomatine and solanocapsine were found to influence preference behavior. Solanocapsine (5 mM) deters feeding whereas tomatine (1 mM) stimulates feeding slightly. No synergistic effect of either tomatine or tomatidine with sucrose was found.The responses to tomatine are affected by previous feeding experience. Tomatine slightly stimulates feeding in larvae reared on tomato (Lycopersicon esculentum), but slightly deters feeding in larvae reared on Jerusalem cherry (Solanum pseudocapsicum). Such induced preference is absent for the other alkaloids tested, which indicates that these alkaloids do not by themselves induce preferences for the plants containing them.The non-alkaloid allelochemicals, chlorogenic acid, rutin, and 2-tridecanone also influenced food choice behavior. Chlorogenic acid is slightly stimulatory at its natural concentration (1mM), but strongly deterrent at higher concentrations. Rutin stimulates feeding in a concentration-dependent manner. Its activity must be due to the glycosylated structure, because both the aglycone (quercetin) and the sugar moiety (rutinose) are neutral. Removal of the glucose part of rutin, as in quercitrin, results in feeding deterrent activity. 2-Tridecanone is neutral at its concentration in cultivated tomato (1 mM), but strongly deterrent and toxic at higher concentrations. Preference behavior is not affected by solanesol, GABA, and a mixture of host plant compounds stimulatory for anothe solanaceous-specific feeder, the Colorado potato beetle (Leptinotarsa decemlineata).We conclude that the prevalent solanaceous alkaloids and other allelochemicals tested do not play important roles in food selection of the tobacco hornworm, although some may make small contributions.

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Résumé Des experiences de choix de chenilles oligophages de M. sexta ont été réalisees avec des disques de papier filtre imbiles d'eau ou de solutions des substances allélochimiques dominantes dans les plantes consommées. Sur les six alcaloïdes de solanées examinés: tomatine, tomatidine, solanine, solanocapsine, atropine et nicotine, seuls la tomatine et la solanocapsine ont influé sur le choix; la solanocapsine (5 mM) empêche la prise de nourriture, tandis que la tomatine (1 mM) la stimule légèrement. Aucun effet synergique de la tomatine ou de la tomatidine n'a été observé en présence de sucrose.La réponse à la tomatine est modifiée par la prise de nourriture antérieure. Elle stimule légèrement l'alimentation de chenilles élevées sur tomates (Lycopersicon esculentum), mais dissuade légèrement les chenilles élevées sur Solanum pseudocapsicum. II n'y a pas d'action induite semblable avec les autres alcalïdes examinés, ce qui indique que ces alcaloïdes ne peuvent pas induire par eux-mêmes de préférences pour les plantes qui les contiennent.Des substances allélochimiques non-alcaloïdes: acide chlorogénique, rutine, et 2-tridécanone, influent aussi sur le comportement de choix alimentaire. L'acide chlorogénique est légèrement stimulant à sa concentration naturelle (1 mM), mais fortement dissuasif aux concentrations supérieures. La rutine stimule la prise de nourriture en fonction de sa concentration. Son activité doit être due à sa structure glucosylate, puisqu'aussi bien l'aglycone (quercitine) que la moiteé sucrée (rutinose) sont neutres. La suppression de la partie glucose de la rutine, comme dans le cas de la quercitine, a un effet dissuasif. A sa concentration dans la tomate cultivée (1 mM), le 2-tridécanone est neutre, mais il est fortement dissuasif et toxique à des concentrations supérieures.Le comportement de choix n'est pas modifié par le solanésol, le GABA, et par un mélange de composés végétaux stimulant un consommateur spécifique de solanées, comme le doryphore (Leptinotarsa decemlineata).Nous pouvons conclure que les principaux alcaloïdes et autres substances allélochimiques des solanées que nous avons examinés n'interviennent pas d'une façon importante, mais peuvent avoir une influence secondaire, dans les choix alimentaires de Manduca sexta.