DIFFERENTIAL MORTALITY AMONG COHORTS IN A POPULATION OF ACER SACCHARUM (ACERACEAE) SEEDLINGS

Theoreticians have suggested that genetic changes in long-lived perennial species may show a lag in response to selective pressures. If this suggestion is correct, then these populations should contain subpopulations adapted to dissimilar environments. The present study, employing data on age distributions and gel electrophoresis, provides some evidence for the existence of these genetically differentiated subpopulations among seedlings of Acer saccharum.     

EFFECTS OF FLOODING AND NUTRIENT ENRICHMENT ON BIOMASS ALLOCATION IN ACER RUBRUM SEEDLINGS

A greenhouse experiment was conducted on Acer rubrum seedlings to evaluate the effects of flood frequency on production and allocation of biomass and to test the effects of N and P fertilization on production and allocation. Seedlings from the Dismal Swamp were subjected to three flood treatments (no flooding, intermittent flooding, and continuous flooding) and four enrichment treatments (no enrichment, N additions, P additions, and N + P additions). More continuous flooding resulted in less biomass production. Biomass increased during the study in all treatments except for root mass in the continuously flooded treatment. However, production of abundant adventitious roots compensated for the lack of normal root growth. Root/shoot ratios exhibited the greatest decreases in the continuously flooded plants. Plants with N + P added had significantly more leaf, stem, and total mass than the nonenriched plants four months into the study. The N + P additions had apparently compensated for the effects of flood stress in the continuously flooded plants by the end of the study. The fertilized seedlings accumulated higher concentrations of N and P, but their nutrient use efficiency (biomass production per unit nutrient absorbed) was lower than in the nonenriched plants. Acer rubrum seedlings survive flooded conditions through several adaptations; however, theirgrowth is slowed by continuous flooding.     

PHENOTYPIC PLASTICITY OF BRANCHING PATTERN IN SUGAR MAPLE (ACER SACCHARUM)

Branching patterns of leader shoots and lower branches were compared in 15 sugar maple trees. The number of first-order branches per second-order branch (R_1:2) differed very significantly between leader shoots and lower branches. Values of R_1:2 averaged 6.47 for leaders and 4.06 for lower branches. Stepwise bifurcation ratios between successive higher orders did not differ significantly. The difference in R_1:2 between leader shoots and lower branches within individual trees is the result of developmental-phenotypic interactions, such that the number of leaf-bearing shoots per support shoot decreases over time. These results indicate that branching patterns within individual trees are not stationary, as has commonly been claimed.     

SEASONAL OCCURRENCE OF XYLEM EMBOLISM IN SUGAR MAPLE (ACER SACCHARUM)

Xylem embolism, the reduction of water flow by air-filled vessels, was measured in a stand of 5- to 8-year-old sugar maple (Acer saccharum Marsh.) saplings growing in a nursery bed in northwestern Vermont. Embolism was quantified as percentage loss in hydraulic conductivity of trunk and branch segments relative to maximum values obtained by removing air from vessels by repeated high pressure (173 kPa) perfusions. Ten segments per tree were cut from 6 trees for each of 11 measurement periods spaced at roughly monthly intervals from May 1986 to June 1987. During the 1986 growing season, embolism increased significantly from 11 to 31% in the larger branches and trunk (segment diameter #8805;0.5 cm), but remained at about 10% in twigs (segment diameter <0.5 cm). This was unexpected because the greatest water stess and thus potential for embolism occurs in twigs. During the winter, embolism increased throughout the trees and the trend with diameter was reversed; by February, small twigs were 84% embolized vs. 69% for larger branches and trunk. Dye perfusions showed that winter embolism in trunks was localized on the south side; this may have resulted from water loss by sublimation or evaporation in the absence of water uptake. Beginning in late March, embolism decreased throughout the trees to approximately 20% in June. This decrease was associated with positive xylem pressure of at least 16 kPa which may have originated in the roots, because weather conditions at the time were unfavorable for the generation of stem pressures characteristic of Acer species in early spring.     

SEED DYNAMICS OF ABIES BALSAMEA AND ACER SACCHARUM IN A DECIDUOUS FOREST OF NORTHEASTERN NORTH AMERICA

We studied the seed dynamics of Abies balsamea and Acer saccharum in a sugar maple-yellow birch forest of Québec, Canada. Seed rain was censused every week from spring to autumn in 1988 and 1989. The soil seed bank was sampled four times during the 1988 growing season. Abies seed rain varied significantly between 1988 and 1989. A total of 92.5 ± 7.0 seeds nr^-2 (mean ± 1 SE) were produced in 1988; 1989 seed production was null. Seed viability in 1988 averaged 31.5%. Dispersal during the winter period accounted for ca. 22% of the annual seed crop. The spatial dispersion pattern of the seed rain was contagious for the autumn period, but was not significantly different from random for the winter period. There was only a weak relationship in the spatial distribution of the seed rain between the autumn and winter periods. Abies did not maintain a persistent seed bank on the site; viable seeds were present on the soil only after seed dispersal had started. Postdispersal seed mortality was relatively high, ca. 70%. Acer seed rain started soon after the flowering period, but consisted at that time only of aborted, underdeveloped samaras. Viable seeds were disseminated from September through early winter. Dispersal during the autumn accounted for ca. 98% of the annual seed crop. There were significant differences between seed rain abundance of 1988 and that of 1989 (118.1 ± 9.5 samaras m^-2 and 158.9 ± 16.3 samaras m^-2 in 1988 and in 1989, respectively). Seed viability also varied significantly between the 2 years, i.e., 19% in 1988 and 5% in 1989. For both 1988 and 1989, samaras were contagiously dispersed over the site. There was a significant positive relationship between the spatial distribution of the seed rain in 1988 and that in 1989. Seed rain abundance was high mainly in the proximity of mature Acer trees. As for Abies, Acer did not maintain a persistent seed bank in the soil; viable seeds were present only in the autumn seed bank sampling, after seed fall had started. Postdispersal seed mortality was relatively low, i.e., 20%. Abies and Acer are quite similar in their regenerative traits, and these contrast sharply with those of Betula alleghaniensis, a regular member of this forest community. Differences in regenerative traits may contribute to the coexistence of these tree species considering the gap regime of the system studied.     

VARIATION OF SHOOT MORPHOLOGY AND BIFURCATION RATIO IN SUGAR MAPLE (ACER SACCHARUM) SAPLINGS

Open-grown sugar maple saplings differ qualitatively in their gross morphology when compared with saplings growing in shaded forest understories. Forest-grown saplings have their leaves distributed in a few planar layers, while open-grown saplings exhibit fuller crowns and more profuse branching. In order to quantify these observed differences in branching patterns, ordering methods were applied to twenty saplings each from forest and open sites. Bifurcation ratio, an index of branching previously assumed to be species constant, differed significantly between forest-grown and open-grown saplings. Bifurcation ratios for forest-grown saplings were low, with a mean of 3.19. Values for open-grown saplings were generally higher, with a mean of 7.05. This variation of bifurcation ratio between forest-grown and open-grown sugar maple saplings is the first such variation within any species to be reported. In addition, open-grown saplings were characterized by more extension growth of terminal shoots than forest-grown saplings. These results suggest that sugar maple has a range of branching and light interception characteristics that suit it well in different microenvironments.     

天花粉对小鼠子宫肥大细胞超微结构的影响

本研究用雌性中国１号小鼠１２只,分实验组和对照组,实验组分别腹腔注射天花粉后处死,取子宫组织作超薄切片,电镜观察。在天花粉作用下,常见子宫肥大细胞脱颗粒,呈功能活化状态,并与子宫平滑肌细胞紧密相邻。提示肥大细胞可能通过脱颗粒释放组胺促进子宫平滑肌的收缩。同时,也见肥大细胞与子宫结缔组织中的成纤维细胞,淋巴细胞等密切接触,提示成纤维细胞和淋巴细胞与天花粉作用下子宫肥大细胞的数量增多有关。     

硫对水稻幼苗乙烯产生的影响

水稻幼苗缺硫培养12—15天,叶和根中的乙烯产生量明显降低,缺硫培养时间延长,根的乙烯产生量继续降低,叶的乙烯产生量升高。在缺硫幼苗中供给 SO_4~(2-)和0.1mmol/l 的半胱氨酸,乙烯产生量分别在36和12小时后升高到加硫幼苗的水平。供给0.1mmol/l 蛋氨酸,6小时后的乙烯产生量已高于加硫的幼苗。测定培养13天的幼苗叶片中游离氨基酸表明,缺硫幼苗其蛋氨酸和胱氨酸的含量降低。     

光对水稻(Oryza sativa)幼苗乙醇酸氧化酶活性的影响

水稻黄化幼苗用白光照射3～5小时后可诱导出乙醇酸氧化酶活性。绿色水稻幼苗在黑暗中乙醇酸氧化酶活性逐渐下降以至消失,再给以照光又恢复酶活性。亚胺环己酮对光的诱导及再诱导均有抑制作用。在黑暗中真空渗入乙醇酸于黄化幼苗可诱导出乙醇酸氧化酶活性,渗入乙醇酸加FMN能使酶活性迅速增强。弱的白光以及红、绿,蓝光均有诱导作用。因此认为光的诱导作用是使黄化幼苗形成乙醇酸——作为诱导物,以诱导乙醇酸氧化酶的新合成。光也可以加速叶组织内FMN的合成,从而提高乙醇酸氧化酶的活性。     

Seed Dormancy in Acer: CHANGES IN ENDOGENOUS CYTOKININS, GIBBERELLINS AND GERMINATION INHIBITORS DURING THE BREAKING OF DORMANCY IN ACER SACCHARUM MARSH

The present studies on changes in the levels of cytokinins,gibberellins, and germination inhibitors during stratificationof Acer saccharum sceds suggest that the breaking of dormancyis a phasic process. Stratification at 5°C led to a markedincrease in the butanol-soluble cytokinins after 20 d. Furtherchilling resulted in a loss of cytokinin. The majority of thedetectable cytokinin activity co-chromatographed with zoatin.Similarly, at day 40, acidic gibberellin-like substances increasedand declined with further chilling. A loss of acidic germinationinhibitors was also detected during stratification. The acidicfraction was shown to contain abscisic acid (ABA) by its behaviouron GLC and isomerization with ultra-violet light. Determinationsof endogenous levels of ABA by combined GLC and isotope dilutionmethods indicated a loss of 97.9 per cent ABA during stratification.The data suggest that the breaking of seed dormancy at low temperatureinvolves the initiation of an ordered sequence of events thatinclude the changes in growth hormones necessary to determinethe course of development for the removal of dormancy.     

COMPETITION PROLONGS EXPRESSION OF MATERNAL EFFECTS IN SEEDLINGS OF ERIGERON ANNUUS (ASTERACEAE)

The timing of expression of environmental maternal effects on seedling growth was investigated in greenhouse-grown populations of Erigeron annuus (Asteraceae). Maternal differences were generated in genetically identical lines grown under high and low nutrient conditions. There were significant differences among maternal families within genotypes for seed size, cotyledon size, number of leaves, and rosette diameter. When seedlings were grown individually, effects of the maternal fertilizer treatment on leaf number and rosette diameter were present early but could not be detected after eight weeks. When seedlings from HIGH and LOW lines were grown in competition, the maternal effects and the relative size advantage of seedlings from HIGH parents increased throughout the experiment. Most of the variation among nutrient treatments for seedling size characters could be explained by variation in initial seed size. In the competition experiment, the increasing magnitude of maternal environmental differences over time masked genetic variation for seedling characters; without competition, the relative contribution of genetic variation increased through time. Under competitive conditions that generate persistent maternal effects on fitness, maternal environmental effects may retard natural selection.     

P物质在应激活化小鼠皮肤肥大细胞中的作用

目的探讨P物质(substance P,SP)在应激活化小鼠皮肤肥大细胞中的作用。方法应用Communication box系统使小鼠分别负荷足电击和心理性应激,采用甲苯胺蓝(toluidine blue)染色法、免疫组化ABC技术分别检测皮肤肥大细胞数及SP阳性神经纤维数,以ELISA法检测皮肤中SP含量,以I125放免法测定血浆类固醇浓度。结果躯体性应激和心理性应激均可使血浆类固醇升高,躯体性应激负荷鼠的血浆类固醇激素在第3d达高峰,而后逐渐下降;而心理性应激负荷鼠的血浆类固醇激素在第5d达高峰后逐渐下降。腹腔注射WIN51078可明显降低两种应激负荷所致的血浆类固醇浓度,且对足电击的抑制效果优于心理性应激。足电击和心理性应激均可有意义增强皮肤肥大细胞的活化,增加SP阳性神经纤维数。足电击可使皮肤SP含量呈现有意义的减少,而心理性应激则皮肤SP含量增加,这些变化可因非肽性NK1速激肽受体拮抗剂WIN51078的腹腔注射而抑制。结论SP参与了应激导致的肥大细胞活化机制,同时显示了速激肽受体拮抗剂可能会抑制应激导致的皮肤症状的恶化。     

水体酚类化合物污染对水稻幼苗生长的影响

用０、５０、１００和１５０×１０－６浓度的苯酚溶液处理水稻幼苗,本实验的目的是探讨苯酚对水稻幼苗生长的影响。实验结果如下：苯酚抑制水稻幼苗生长,且随着浓度的增加,其抑制作用越明显。１５０ｐｐｍ是抑制作用最强的浓度。经苯酚处理后的水稻幼苗,其根和茎的生长都抑制了,而鲜重、干重、水分含量和叶绿素含量则明显减少,硝酸还原酶和过氧化物酶活性也下降了。     

铝对水稻幼苗的生理影响

以水稻幼苗为材料研究了铝的植物毒性。将不同浓度的 AlCl 加入培养液,对幼苗处理30天。10ppm 以上的铝明显抑制水稻幼苗根和地上部分的生长。5.0ppm 以上铝可引起毒害症状。铝对根的毒害作用大于对地上部分的作用。铝主要积累在根部,少部分转移到地上部分。5.0ppm 以上的铝对叶绿体 Hill 反应和光合磷酸化作用以及根线粒体呼吸和氧化磷酸化作用均有较明显抑制作用。钙对铝的此种抑制作用有一定拮抗作用。     

GYNOECIAL ONTOGENY AND MORPHOLOGY,AND POLLEN TUBE PATHWAY IN BLACK MAPLE,ACER SACCHARUM SSP. NIGRUM (ACERACEAE)

The black maple (Acer saccharum Marsh, ssp. nigrum [Michx. f.] Desm.) gynoecium displays classical involute carpel development; carpels form, in mid- to late-summer, as two separate, opposite, hood-shaped primordia bearing naked megasporangia on inrolled carpel margins. Megasporogenesis, integument initiation, and carpel closure occur in spring; carpels fuse, forming a biloculate ovary with a short, hollow style and two divergent, dry, unicellular papillose stigmas. Transmitting tissues consist of developmentally and morphologically similar trichomes that form along the apparent carpel margins. The path from stigma to micropyle is open, but pollen tubes do not grow entirely ectotrophically. Germinating at the tip of a stigma papilla, a tube grows, apparently under the cuticle, to the papilla base. It then grows between stigma cells to the style, emerging to grow ectotrophically through the style to the compitum, where it passes into one of the locules. Within a locule, the tube grows over placenta and obturator to the micropyle, then between megasporangium cells to the female gametophyte, spreading over the surface near the egg. This study adds to our sparse understanding of gynoecium development and transmitting tissue in relation to pollen tube growth in naturally pollinated woody plants.