POLLINATION OF THE ARROYO WILLOW,SALIX LASIOLEPIS: ROLE OF INSECTS AND WIND

We studied the relative roles of insects and wind as pollen vectors for the arroyo willow, Salix lasiolepis Benth. through insect exclosure studies at two elevational sites. Insect pollination resulted in production of 99.9% of seeds at a low elevation site (2,130 m) and at a high elevation site (2,450 m) with wind playing an exceedingly small role. Few pollen grains reached individual pistillate catkins despite the presence of abundant airborne willow pollen near male plants. In flowers that showed evidence of receipt of wind transferred pollen, due to their swollen appearance, we found only 1.74 fertilized ovules per flower and that 90.9% of these fertilized ovules were aborted by the maternal plant. In contrast, flowers open to insect visitation possessed 7.00 fertilized ovules per flower, 83.3% of which became filled seeds. We tested for the existence of apomictic seed production through use of closed bags that excluded both insect-and wind-transferred pollen but found no evidence of seed produced in this treatment. Additional control studies documented that wind treatment bags did not impede pollen flow while neither wind or closed bags influenced seed set in our treatments.     

MORPHOLOGY AND ANATOMY OF RESIN GLANDS IN SALIX LUCIDA (SALICACEAE)

Resin glands on the first leaves to emerge occur at the tip of each marginal dentation of the lamina and stipule, and on the adaxial surface of the stipule and lamina bases (the latter often extend onto the petiole). Successive emerging leaves show increases in number of basilaminar glands, because increasingly elaborate multiglandular stalks develop. Glands in all locations are conical or domed, with a palisade-like epidermis subtended by 5–6 layers of parenchyma which contains druse crystals. A single vascular bundle (sometimes two or three) ends in a small knob of tracheary elements. Glands usually secrete liquid resin that covers the gland and surrounding area and under certain conditions, particularly in low humidity, resin is extruded as a filament from a pore in the gland apex, a mode of resin secretion not described previously. Glands secreting liquid resin have an apical dimple, but presence of a pore has not been established.     

PATTERNS OF GENETIC VARIATION IN SALIX SECTION LONGIFOLIAE (SALICACEAE)

Enzyme electrophoresis was used to examine genetic relationships within a taxonomically complex group of diploid willows (Salix section Longifoliae). Forty-eight populations representing seven morphogeographic taxa were analyzed for 15 putative enzyme loci. Levels of genetic variation (A, P, H_e, and H_T) differed greatly among populations, but were generally lower than those reported for other species with similar life history traits. In populations and species from southern latitudes, where populations tend to be smaller and more isolated, genetic variation decreased and population differentiation increased. Genetic identity values suggest that the section is divisible into four major elements: 1) Salix interior, 2) S. taxifolia, 3) the S. exigua group, and 4) S. melanopsis. The first three occupy eastern, southern, and western portions of the continent, respectively. Salix melanopsis is sympatric with the S. exigua group in western North America, but is ecologically distinct. The S. exigua group is differentiated into four major geographic entities: S. hindsiana from west of the Sierras in California and southwest Oregon, S. sessilifolia from west of the Cascades in central Oregon to British Columbia, and a northern and southern race of S. exigua in the Intermountain West. The relationships suggested by allozyme data do not agree with traditional taxonomic concepts. Evidence of hybridization was obtained at five points where taxa come into contact, and Salix fluviatilis may be of hybrid origin. Taxonomic confusion appears to be largely the result of frequent hybridization events and overemphasis of a few highly variable morphological traits. The section appears to be a syngameon undergoing geographic speciation, with one taxon gaining reproductive isolation by a shift in habitat preference.     

EFFECTS OF SOIL WATERLOGGING ON THE ENERGY STATUS AND DISTRIBUTION OF SALIX NIGRA AND S. EXIGUA (SALICACEAE) IN THE ATCHAFALAYA RIVER BASIN OF LOUISIANA

The influence of soil waterlogging on the distribution and energy status of Salix nigra and S. exigua were studied in the field and laboratory. Differential flooding in natural stands of Salix spp. and under controlled conditions in the greenhouse demonstrated that S. nigra was more tolerant of waterlogged soil conditions than was S. exigua. Salix nigra exhibited a significantly higher leaf energy status and greater ability to oxidize waterlogged soil when flooded than did S. exigua. However, S. exigua appeared to be more tolerant of moisture stress than S. nigra as indicated by the significantly higher leaf resistances to water vapor exchange and higher leaf water potentials of S. exigua. These data support the theory that the reason S. nigra inhabits lower elevation sites than S. exigua in the Atchafalaya River Basin may be the differential tolerance of these two species to soil waterlogging on one extreme and moisture deficiencies on the other.     

THE ELASTIC MODULI AND MECHANICS OF POPULUS TREMULOIDES (SALICACEAE) PETIOLES IN BENDING AND TORSION

Changes attending leaf development in the mechanical behavior and elastic moduli of the petioles of Populus tremuloides Michx. were examined in terms of total leaf weight (Wt), lamina and petiole weight (Wl and Wp), petiolar length (L), and lamina surface area (A). A primary concern was the extent to which two elastic moduli (Young's modulus E and the shear modulus G) of petioles changed over time and were correlated with one another. E and G were measured by means of multiple resonance frequency spectra, and together with the dimensions of cross sections through petioles, these two elastic moduli were used to estimate the stiffness of petioles in simple bending and torsion. Petiolar bending was predicted by means of a model incorporating expressions for both the bending stiffness (El) and torsional rigidity (GJ), where I is the second moment of area and J is the torsional constant. The predictions from these models were compared to observed petiolar bendings due to Wl. Additionally, the frequency of the oscillatory motion of leaves (placed in a wind tunnel with a 1 m sec^-1 ambient wind speed, directed normal to the blade of the leaf) was determined. Results indicate that L, A, Wl, Wp, and Wt were positively correlated with the age of leaves (crudely estimated as a function of leaf plastochron index, LPI); these morphometric parameters were also correlated with the magnitudes of E and G. Also, G was positively and linearly correlated with E, and was, on the average, an order of magnitude less than E. EI and GJ were positively correlated with LPI. The relationships among E, G, EI, C and Wl, Wp, Wt are discussed in terms of leaf allometries.     

鱼类免疫因子的母体传递及其对子代的保护作用

母源性免疫即母体传递给子代的免疫力。动物在个体发育早期不具备或仅具备极其有限的免疫应答能力,它们主要依靠母源性免疫来抵抗各种病原微生物的攻击。研究表明, 哺乳动物在出生前可以把抗体直接传递给胚胎。       

柳属植物在秦岭地区的分布和分化

本文对秦岭地区41种柳属植物采用简约性分析讨论形态演化,采用聚类分析讨论地理分布式样和分化。秦岭地区有较完整的多雄蕊类群→两雄蕊类群→单雄蕊类群的演化。其分布式样和区系特征和邻近地区即华北、华中和西南成分联系密切,表现出明显的过渡性质,其中青藏高原成分占重要地位,特别可以从太白山分布上去说明。本区的地理分化也被青藏高原成分和华中成分所作用。     

GROWTH AND DEMOGRAPHY OF POPULATIONS OF BIOMPHALARIA PFEIFFERI (GASTROPODA, PLANORBIDAE) IN THE LABORATORY

The growth and demography of the freshwater snail Biomphalariapfeifferi, an intermediate host of the parasitic worm Schistosomamansoni in Eastern Zaire, were investigated in the laboratoryunder two conditions of crowding. Both individual and populationgrowth were depressed by crowding. Crowding reduced growth rateand all the variables and parameters related to reproduction(fecundity, instantaneous birth rate, net reproduction rate),but did not affect maximum size, survivorship, instantaneousdeath rate and life expectancy. The mechanism involved in theseeffects is likely to be exploitation competition for especiallyprofitable food items such as diatoms. (Received 10 November 1986;     

玉米地土壤呼吸作用对土壤温度和生物因子协同作用的响应

基于2005年玉米(Zea mays)生长季土壤呼吸作用及其影响因子的动态观测资料,分析了玉米地土壤呼吸作用的日和季动态及其对土壤温度和生物因子协同作用的响应。结果表明,玉米地土壤呼吸作用的日变化为不对称的单峰型,其最小值和最大值分别出现在6∶00~7∶00和13∶00左右;玉米生长季中,土壤呼吸速率波动较大,其均值为3.16 μmol CO₂·m^-2·s^-1,最大值为4.87 μmol CO₂·m^-2·s^-1,出现在7月28日,最小值为1.32 μmol CO₂·m^-2·s^-1,出现在5月4日。在土壤呼吸作用日变化中,土壤呼吸速率(SR)与10 cm深度土壤温度(T)呈显著的线性关系:SR=αT+β。在整个生长季节,玉米净初级生产力(NPP)与直线斜率(α)呈显著正相关,生物量(B)也明显影响直线的截距(β)。基于此,建立了玉米地土壤呼吸作用动态模型SR=(aNPP+b)T+cB²+dB+e。土壤呼吸作用季节变化的大部分(97%)可以由土壤温度、NPP和生物量的季节变化来解释。当仅考虑土壤温度对土壤呼吸作用的影响时,指数方程会过大或过小地估计了土壤呼吸强度。该文的结果强调了生物因子在土壤呼吸作用季节变化中的重要作用,同时指出土壤呼吸作用模型不仅要考虑土壤温度的影响,在生物因子影响土壤呼吸作用的温度敏感性时,还应该把生物因子纳入模型。     

THE ROLES OF HETEROCHRONY AND HETEROBLASTY IN THE DIVERSIFICATION OF LEAF SHAPES IN BEGONIA DREGEI (BEGONIACEAE)

The relationship between shape variation in the transitional series of leaves and in adult leaves was examined in seedlings of seven morphs of Begonia dregei using several quantitative methods of shape analysis. There is variation in the shape of adult leaves among individuals as well as in juvenile leaves within individuals in B. dregei. As an individual grows, there is a gradual transition in leaf shape from the symmetrical, oval, smooth-margined leaves through a series of more than ten transitional leaves to a stable adult leaf shape. There appear to be two basic patterns to the acquisition of adult traits. Traits that differ among morphs are acquired gradually throughout the entire transitional series while those that are similar among morphs are acquired by about leaf 5 and remain stable through the later juvenile leaves. There is no identity of leaf shape between the earlier leaves of some morphs and the later leaves of others. Evolutionary diversification in adult leaf morphology in this species is not related to simple changes in ontogeny of the whole plant.     

STUDIES ON THE LEAF OF POPULUS DELTOIDES (SALICACEAE): MORPHOLOGY AND ANATOMY

Mature field- and growth-chamber-grown leaves of Populus deltoides Bartr. ex Marsh. were examined with light and scanning electron microscopes to determine their vasculature and the spatial relationships of the various orders of vascular bundles to the mesophyll. Three leaf traces, one median and two lateral, enter the petiole at the node. Progressing acropetally in the petiole these bundles are rearranged and gradually form as many as 13 tiers of vascular tissue in the petiole at the base of the lamina. (Most leaves contained seven vertically stacked tiers.) During their course through the midrib the tiers “unstack” and portions diverge outward and continue as secondary veins toward the margin on either side of the lamina. As the midvein approaches the leaf tip it is represented by a single vascular bundle which is a continuation of the original median bundle. Tertiary veins arise from the secondary veins or the midvein, and minor veins commonly arise from all orders of veins. All major veins–primaries, secondaries, intersecondaries, and tertiaries–are associated with rib tissue, while minor veins are completely surrounded by a parenchymatous bundle sheath. The bundle sheaths of tertiary, quaternary, and portions of quinternary veins are associated with bundle-sheath extensions. Minor veins are closely associated spatially with both ad- and abaxial palisade parenchyma of the isolateral leaf and also with one or two layers of paraveinal mesophyll that extend horizontally between the veins. The leaves of growth-chamber-grown plants had thinner blades, a higher proportion of air space, and greater interveinal distances than those of field-grown plants.     

THE ROLES OF PLANT HORMONES IN STYLE AND STIGMA GROWTH IN GAILLARDIA GRANDIFLORA (ASTERACEAE)

Style and stigma elongation and stigma unfolding, and the roles of plant hormones in these processes in Gaillardia grandiflora Van Houtte were investigated. Style and stigma elongation in vivo began just after anthesis, and style elongation was accompanied by epidermal cell elongation (greatest near the stigma) and a fresh weight increase, but not by cell division or a dry weight increase. The stigma unfolded after the style and stigma elongated. Style-stigma units excised from young disc flowers of this composite were measured as they responded to plant growth regulators applied singly, as well as in sequential and simultaneous combinations, in vitro. Style elongation was promoted by auxin, was inhibited by gibberellins and ethylene, and was unaffected by other growth regulators. Stigma elongation followed a similar pattern of response. Endogenous auxin levels and ethylene production showed parallel variation and endogenous gibberellin levels showed inverse variation with style and stigma elongation. Stigma unfolding was more sensitive to auxin applications and was promoted by applied ethylene. Ethylene production showed parallel variation and endogenous auxin levels showed inverse variation with stigma unfolding. AVG and Co²⁺ applications decreased auxin-induced style elongation and fusicoccin promoted all of the growth responses of style-stigma units in vitro. A gibberellin-auxin-ethylene-acid growth interaction mode of control is proposed for these three growth processes.     

Secreted Versus Membrane-anchored Collagenases: RELATIVE ROLES IN FIBROBLAST-DEPENDENT COLLAGENOLYSIS AND INVASION*

Fibroblasts degrade type I collagen, the major extracellular protein found in mammals, during events ranging from bulk tissue resorption to invasion through the three-dimensional extracellular matrix. Current evidence suggests that type I collagenolysis is mediated by secreted as well as membrane-anchored members of the matrix metalloproteinase (MMP) gene family. However, the roles played by these multiple and possibly redundant, degradative systems during fibroblast-mediated matrix remodeling is undefined. Herein, we use fibroblasts isolated from Mmp13^−/−, Mmp8^−/−, Mmp2^−/−, Mmp9^−/−, Mmp14^−/− and Mmp16^−/− mice to define the functional roles for secreted and membrane-anchored collagenases during collagen-resorptive versus collagen-invasive events. In the presence of a functional plasminogen activator-plasminogen axis, secreted collagenases arm cells with a redundant collagenolytic potential that allows fibroblasts harboring single deficiencies for either MMP-13, MMP-8, MMP-2, or MMP-9 to continue to degrade collagen comparably to wild-type fibroblasts. Likewise, Mmp14^−/− or Mmp16^−/− fibroblasts retain near-normal collagenolytic activity in the presence of plasminogen via the mobilization of secreted collagenases, but only Mmp14 (MT1-MMP) plays a required role in the collagenolytic processes that support fibroblast invasive activity. Furthermore, by artificially tethering a secreted collagenase to the surface of Mmp14^−/− fibroblasts, we demonstrate that localized pericellular collagenolytic activity differentiates the collagen-invasive phenotype from bulk collagen degradation. Hence, whereas secreted collagenases arm fibroblasts with potent matrix-resorptive activity, only MT1-MMP confers the focal collagenolytic activity necessary for supporting the tissue-invasive phenotype.In the postnatal state, fibroblasts are normally embedded in a self-generated three-dimensional connective tissue matrix composed largely of type I collagen, the major extracellular protein found in mammals (1–3). Type I collagen not only acts as a structural scaffolding for the associated mesenchymal cell populations but also regulates gene expression and cell function through its interactions with collagen binding integrins and discoidin receptors (2, 4). Consistent with the central role that type I collagen plays in defining the structure and function of the extracellular matrix, the triple-helical molecule is resistant to almost all forms of proteolytic attack and can display a decades-long half-life in vivo (4–6). Nonetheless, fibroblasts actively remodel type I collagen during wound healing, inflammation, or neoplastic states (2, 7–13).To date type I collagenolytic activity is largely confined to a small subset of fewer than 10 proteases belonging to either the cysteine proteinase or matrix metalloproteinase (MMP)² gene families (4, 14–18). As all collagenases are synthesized as inactive zymogens, complex proteolytic cascades involving serine, cysteine, metallo, and aspartyl proteinases have also been linked to collagen turnover by virtue of their ability to mediate the processing of the pro-collagenases to their active forms (13, 15, 19). After activation, each collagenase can then cleave native collagen within its triple-helical domain, thus precipitating the unwinding or “melting” of the resulting collagen fragments at physiologic temperatures (4, 15). In turn, the denatured products (termed gelatin) are susceptible to further proteolysis by a broader class of “gelatinases” (4, 15). Collagen fragments are then either internalized after binding to specific receptors on the cell surface or degraded to smaller peptides with potent biological activity (20–24).Previous studies by our group as well as others have identified MMPs as the primary effectors of fibroblast-mediated collagenolysis (20, 25, 26). Interestingly, adult mouse fibroblasts express at least six MMPs that can potentially degrade type I collagen, raising the possibility of multiple compensatory networks that are designed to preserve collagenolytic activity (25). Four of these collagenases belong to the family of secreted MMPs, i.e. MMP-13, MMP-8, MMP-2, and MMP-9, whereas the other two enzymes are members of the membrane-type MMP subgroup, i.e. MMP-14 (MT1-MMP) and MMP-16 (MT3-MMP) (13, 27–29). From a functional perspective, the specific roles that can be assigned to secreted versus membrane-anchored collagenases remain undefined. As such, fibroblasts were isolated from either wild-type mice or mice harboring loss-of-function deletions in each of the major secreted and membrane-anchored collagenolytic genes, and the ability of the cells to degrade type I collagen was assessed. Herein, we demonstrate that fibroblasts mobilize either secreted or membrane-anchored MMPs to effectively degrade type I collagen in qualitatively and quantitatively distinct fashions. However, under conditions where fibroblasts use either secreted and membrane-anchored MMPs to exert quantitatively equivalent collagenolytic activity, only MT1-MMP plays a required role in supporting a collagen-invasive phenotype. These data establish a new paradigm wherein secreted collagenases are functionally limited to bulk collagenolytic processes, whereas MT1-MMP uniquely arms the fibroblast with a focalized degradative activity that mediates subjacent collagenolysis as well as invasion.     

水在菌紫质光循环和质子泵中的作用

用圆二色仪和闪光动力学先谱仪分别测量了空气干燥紫膜薄层的圆二色谱及紫膜LB膜的M_(412)的衰减过程.在于燥紫膜的圆二色谱上出现412nm的正峰,它是光循环中间体M_(412)的特征峰.在无水介质中,紫膜LB膜中的BR仍能进行先化学循环而检测到中间体M_(412),但M_(412)的衰减速度减慢,产生M_(412)的堆积,质子化过程受阻.在有水的介质中,只要有足够的H~+存在,紫膜LB膜中的BR的中间体M_(412)的衰减速度明显加快.说明水介质的H~+是完成正常光化学循和质子化过程必不可少的.