阔叶树的叶形曲线方程：—适于叶面积计算的数学模型

树木的叶形可以看作一个平面几何图形。这种几何图形可用解析方程给予表达,我们把这种解析方程称为叶形曲线方程。由于叶形是一个左右对称,而上下不对称的图形,也就是说叶的最宽处绝大多数不在叶的中部,少数在     

八种针阔叶幼树清晨叶水势与土壤含水量的关系及其抗旱性研究

一、前言土壤是植物根系的生活环境,是供给植物赖以生存的水分和养分的源泉。干旱区的植物尤其是树木常常由于土壤供水不足而限制其自然分布和生长。根据土壤-植物-大气连续体系     

Resistance in the wild crop relatives Avena macrostachya and Hordeum bogdani to the aphid Rhopalosiphum padi

In previous screening tests the two wild crop relatives Avena macrostachya (Bal., ex Coss. et Dur.) and Hordeum bogdani (Wil.) demonstrated a high degree of resistance to the aphid Rhopalosiphum padi (L.). In a choice situation using wild and cultivated oats and barley, alate aphids settled in lower numbers on the wild species. The results were, however, variable in the Avena combination. Nymph production was significantly higher, development time shorter and adult weight higher on the cultivated varieties. From the third instar and onwards the excretion of honeydew was significantly lower on the resistant plants. In general the honeydew contained less than 1% free amino acids although excreta from H. vulgare contained 3.5%. The percentage of free amino acids found in the honeydew was similar for all plant species (5.2–7.6%) except for H. vulgare, on which the aphids excreted 22% of the amounts ingested. Amino acids excreted in high proportions on all plants included asparagine, -aminobutyric acid, glutamic acid, and glycine. Tissue sectioning did not reveal any obvious mechanical barriers to stylet penetration. The potential use of these wild species as sources for aphid resistance breeding in oats and barley is considered.

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Résumè Lors d'examens systématiques antérieurs, Avena macrostachya (Bal. ex Coss. & Dur.) et Hordeum bogdani (Wil.) ont présenté une résistance élevée au puceron Rhopalosiphum padi (L.). Lorsqu'ils avaient un choix comprenant de l'avoine et de l'orge cultivés, les pucerons ailés ont atterri en nombres moins importants sur les espèces sauvages. Les résultats étaient cependant variables dans le complexe avoine. La production de nymphes et le poids des adultes étaient plus élevés sur espèces cultivées, ainsi que la durée du développement était plus longue sur les espèces sauvages. A partir du troisième stade, l'excrétion de miellat a été significativement plus faible sur les espèces résistantes. En général, le miellat y contenait moins de 1% d'acides aminés bien que sur H. vulgare il en contînt 3,5%. Les pourcentages d'acides aminés libres du miellat étaient semblables sur toutes les plantes (5,2–7,6%), à l'exception de H. vulgare sur lequel les pucerons excrétaient 22% des taux ingérés. Les acides aminés excrétés en fortes quantités sur les différentes plantes, comprenaient l'asparagine, l'acide -aminobutyrique, l'acide glutamique et la glycine. Des coupes de tissus n'ont révélé aucun obstacle mécanique clair à la pénétration des stylets. Les possibilités d'utiliser ces espèces sauvages comme source de résistance aux pucerons dans la sélection de l'avoine et de l'orge ont été examinées.

     

Pyrrolizidine alkaloids of probable host-plant origin in the pronotal and elytral secretion of the leaf beetle Oreina cacaliae

Oreina cacaliae (Coleoptera, Chrysomelidae) produces in its elytral and pronotal defensive secretion seneciphylline N-oxide together with small amounts of another pyrrolizidine alkaloid tentatively identified as senecionine N-oxide. This is a strong departure from the chemical composition of the defensive secretions in related species, characterized by complex mixtures of cardenolides, synthesized by the beetles from cholesterol. It is suggested that O. cacaliae sequesters the alkaloids from its host-plant, Adenostyles leucophylla. Other specimens of O. cacaliae from far distant populations feeding on Senecio nemorensis, Petasites paradoxus or P. album also produced pyrrolizidine alkaloids, but not O. speciosissima feeding on the same food plants and producing cardenolides. In addition to pyrrolizidine alkaloids, O. cacaliae secretes ethanolamine, which is also found in all the cardenolide-producing species.     

Interacting effects of increased tannin levels on leaf-mining insects

Tannin-rich extracts were painted on leaves of Q. emoryi (Fagaceae) that contained first instar larvae of a leaf miner, Cameraria sp. (Lepidoptera: Gracillariidae, Agrifoliella group), to test the role of tannins in increasing parasitism, while controlling for changes in protein content and physical damage. Miners from leaves that were treated with tannins had higher rates of parasitism by hymenopterans, but decreased mortality from other causes. The negative and positive effects of tannins balanced since overall larval survivorship was equivalent for leaf miners on tannin-enriched and control leaves. The tannin-rich extract also affected larval development because pupal weight was decreased for leaf miners in treated leaves. Tannins can have both adverse and beneficial effects on these phytophagous insects.

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Résumé Des extraits riches en tanins ont été étalés sur des feuilles de Quercus emoryi contenant des chenilles de ler stade de Cameraria sp., pour contrôler l'influence du tanin dans l'accroissement du parasitisme sans modifier la teneur en protéines ni provoquer de dommages physiques. Les mineuses de feuilles traitées avaient des taux plus élevés de parasitisme par les hyménoptères, mais une diminution des autres causes de mortalité. Les effets négatifs et positifs des tanins se sont équilibrés, puisque la survie des mineuses était la même pour les feuilles traitées que pour les témoins. Les extraits riches en tanin ont agi sur le développement larvaire puisque le poids des chrysalides des mineuses de feuilles traitées était plus faible. Les tanins peuvent ainsi avoir des effets nuisibles et bénéfiques sur ces insectes phytophages.

     

Mannitol metabolism in cultured plant cells

Non-structural storage carbohydrates were measured in 9-day-old barley ( Hordeum vulgare L. cv. Brant) primary leaves. Accumulation rates of starch, sucrose and total non-structural carbohydrates (TNC) were approximately linear when measured between 2- and 12-h of light. Progressively higher TNC accumulation rates were observed at higher irradiance levels (i.e., comparing 250, 550 and 1050 ·mol m⁻² s⁻¹). Synthesis of a low-molecular-weight fructan also was enhanced by high irradiances. Low irradiance treatments decreased leaf sucrose levels and there was a corresponding increase in the lag period preceding starch synthesis in the light. Increased starch accumulation rates were usually observed when sucrose concentrations were high. These and other results suggested that cytosolic sucrose concentrations affected starch metabolism in the chloroplast. However, sucrose accumulation rates increased and starch storage decreased when barley seedlings were transferred from 20 to 10°C during the light period. Lowering the night temperature from 20 to 10°C for a single dark period 8-days after planting increased the TNC content of barley primary leaves at the beginning of day nine. In this experiment, TNC accumulation rates of treated and untreated leaves were similar. Changes in the accumulation rate of TNC were usually observed within 2- to 4-h after barley seedlings were exposed to altered environmental conditions. Monitoring rapid changes in leaf carbohydrate levels is a sensitive method for assessing the effects of environmental treatments on photosynthetic metabolism.     

Developmental profiles of three embryo-lethal maize mutants lacking leaf primordia: ptd*-1130, cp*-1418, and bno*-747B

The defective kernel (dek) mutants of maize are altered in both their embryo and endosperm development. Earlier studies have indicated that some of the dek mutants are unable to form shoot apical meristems or leaf primoirda. We have examined three embryo lethal dek mutants of this type, ptd*-1130, cp*-1418, and bno*-747B, to obtain a developmental profile for each. Allelism tests show that these three mutants are not allelic. Embryos were examined in early, mid-, and late kernel development as well as at kernel maturity by dissection and sectioning procedures and also at kernel maturity by scanning electron microscopy. All three mutants lag behind normal embryos in their rate of development. Embryos of ptd*-1130 reached the transition stage by early kernel development and progressed no further but underwent cell enlargement and necrosis during late kernel development. Embryos of cp*-1418 reached an early coleoptilar stage by midkernel development. They subsequently increased in size but did not form any leaf primordia. At kernel maturity, they no longer had a shoot apical meristem but often had a well formed root meristem. They appeared to remain healthy and did not become necrotic. Embryos of bno*747B reached the early coleoptilar stage by early kernel development but progressed no further. By kernel maturity, they had grown into masses of irregularly shaped embryonic tissue that no longer resembled any normal embryo stage but were not necrotic. None of these three mutants responded to attempts to support continued embryo development when cultured, but all three mutants formed callus on N6 and MS media supplemented with 2,4-D. These results indicate that these mutants are all uniformly blocked at specific stages early in embryonic development, have different subsequent developmental fates, and represent three different genes performing unique functions that are essential for embryogenesis.     

Mechanics of circadian pulvini movements in Phaseolus coccineus L.

The circadian movement of the lamina of primary leaves of Phaseolus coccineus L. is mediated by antagonistic changes in the length of the extensor and flexor cells of the laminar pulvinus. The cortex of the pulvinus is a concentric structure composed of hexagonal disc-like cells, arranged in longitudinal rows around the central stele. Observations with polarization optics indicate that the cellulose microfibrils are oriented in a hoop-like fashion in the longitudinal walls of the motor cells. This micellation is the structural basis of the anisotropic properties of the cells: tangential sections of the extensor and flexor placed in hypotonic mannitol solutions showed changes only in length. As a consequence a linear correlation between length and volume was found in these sections. Based on the relationship between the water potential (which is changed by different concentrations of mannitol) and the relative volume of the sections and on the osmotic pressure at 50% incipient plasmolysis, osmotic diagrams were constructed for extensor and flexor tissues (cut during night position of the pulvinus). The bulk moduli of extensibility, , were estimated from these diagrams. Under physiological conditions the values were rather low (in extensor tissue below 10 bar, in flexor tissue between 10 to 15 bar), indicating a high extensibility of the longitudinal walls of the motor cells. They are strongly dependent on the turgor pressure at the limits of the physiological pressure range.In well-watered plants, the water potentials of the extensor and flexor tissues were surprisingly low,-12 bar and-8 bar, respectively. This means that the cells in situ are by no means fully turgid. On the contrary, the cell volume in situ is similar to the volume at the point of incipient plasmolysis: the cell volumes of extensor and flexor cells in situ were only 1.01 times and 1.1 times larger, respectively, than at the point of incipient plasmolysis, whereas at full turgidity (cells in water) the corresponding factors were 1.8 and 1.5. It is suggested that the high elasticity of the longitudinal walls, the anisotropy of the cell walls, and the low water potential of the sections which is correlated with slightly stretched cell walls in situ, are favourable and effective for converting osmotic work in changes in length of the pulvinus cells, and thus for the up and down movement of the leaf.Symbols volumetric elastic modulus - _i instantaneous volumetric elastic modulus - _i stationary volumetric elastic modulus - weight-averaged stationary bulk modulus of extensibility - ₀ osmotic pressure of the vacuole of a cell at the point of incipient plasmolysis - weight-averaged osmotic pressure of the vacuoles of the tissue at 50% incipient plasmolysis - water potential