摘要:

Corolla elongation and the roles of plant hormones in this process inGaillardia grandifloraVan Houtte ray flowers were examined. The sterile ray flowers elongated during a 2‐day period, and corolla growth was accompanied by fresh and dry weight increases and epidermal cell elongation (greatest near the base of the corolla) but not by cell division. Corollas excised from young ray flowers were measured during treatment in vitro with solutions of plant growth regulators. They elongated in response to gibberellins and fusicoccin but did not respond to auxins, cytokinins, abscisic acid, ethylene, or inhibitors of ethylene biosynthesis. Sequential and simultaneous hormone applications indicated no additive or synergistic effects between hormones, but auxin did reduce gibberellin‐promoted growth. Analyses of endogenous auxins showed no significant variation, and ethylene production decreased prior to elongation, while a 20‐fold increase in endogenous gibberellin activity was observed just prior to rapid corolla elongation. It appears that corolla growth inGaillardiais accomplished by an increase in gibberellin activity alone, that multiple hormone interactions are not important in the control of corolla growth, and that part of the mode of action of gibberellin is acid‐induced growth.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12478.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Community responses to fire of five major vegetation associations of the Lake Wales Ridge were investigated during a 5‐yr post‐fire period. Vegetation of southern ridge sandhills, sand pine scrub, scrubby flatwoods, flatwoods, and swales was sampled using permanent line transects and quadrats in both burned and unburned (control) areas. Fire passed through the mosaic of vegetation leaving a pattern of unburned and lightly to severely burned areas. There was little change in soil chemistry (pH, K, P, Mg) with the exception of a short‐lived increase in Ca. Vegetation recovery rates, measured by percentage cover and Horn's Index, were rapid. Typically, less than 2 yr was needed for recovery of poorly drained flatwoods and swale associations and 1 to 4 years for better drained scrubby flatwoods and southern ridge sandhills. Species diversity (H′) increased significantly following fire at poorly drained sites due to increased evenness, but was largely unchanged at better drained sites. There was virtually no change in vascular plant species composition for the sprouting associations. Fire is not a succession‐initiating disturbance in the Clementsian sense. The species present prior to burning either resprout soon after fire or resist fire, thus rapidly restoring the preburn conditions. Limited data suggest fire in the associations dominated by seeding species likewise does not initiate a relay type succession. The ridge vegetation exhibits marked resiliency to fire as a result of an evolutionary history of a stressful environment including winter droughts, acidic, nutrient‐poor sand substrates, and frequent lightning‐caused low intensity burns.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12479.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Shoot apical meristems are interpreted as either structured, that is having a permanent set of apical initials, or stochastic, having apical initials which represent “... momentary representatives of the continuous meristematic residue at the apex of the relevant layer or zone” (Newman, 1965). The two main parameters of stochastic growth are the average number of apical initials (α) and the number of mitotic cycles (r) of the initials and their daughter cells prior to the random selection of subsequent initials. Mathematical analysis and computer simulation studies of stochastic growth have shown that if one starts with 1 mutant initial and α‐1 nonmutant initials, eventually a mosaic plant results. The frequency of shoot apices composed of mutant cells is 1/α and the frequency of shoot apices composed of only nonmutant cells is (1 – α)/α. These asymptotics are only attained after considerable growth, thus mericlinal chimeras can persist for many nodes and give the appearance that a permanent set of initials is present.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12480.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

The previously described mathematical model of stochastic apical meristem growth (Klekowski and K.‐Fukshansky, 1984) was used to study the fate of initials with disadvantageous genotypes. Such initials are heterozygous for somatic mutations with some dominant effects and consequently have lessened viabilities (V<1) in contrast to initials with only wild type alleles (V= 1). Computer simulation studies show a dramatic increase in the loss of such mutations with increasing number of apical initials and/or the number of cell divisions of the initials and their daughter cells before the subsequent set of initials are chosen. Among plants with stochastic apices (most seed plants and some lower vascular plants), the major phylogenetic and ontogenetic trends are correlated with the development of apices with greater buffering against mutations. Whether these correlations reflect a causal relationship is of course unknown.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12481.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

The responses of native plant species to prescribed and lightning‐caused burns were recorded using permanent line transects and quadrats, sampled over a 5‐yr period, 1977–1982. The dominant species of more frequently burned associations (southern ridge sandhills, scrubby flatwoods, flatwoods, swales, and seasonal ponds) either recover from fire by sprouting or survive by resisting fire, rather than by seeding. The dominants of less frequently burned associations (sand pine and rosemary scrub) are killed by fire and recover by seeding.Quercus myrtifolia, Q. inopina, Q. chapmanii, Q. geminata, Serenoa repens,andSabal etoniaexhibited resiliency, rapidly returning to their preburn levels of dominance. Of the palmettos,Serenoaresponded more vigorously thanSabal.Vegetation measures forGaylussacia dumosaandVaccinium myrsinitesincreased and then decreased dramatically after fire with 2‐, and 3‐ to 4‐yr cycles, respectively.Myrica ceriferavarpusilla, Quercus minima,andHypericum reductumwere more gradual in their responses. A strong inverse relationship, mediated by both abiotic and biotic factors, was found between density and accumulated aboveground biomass inHypericum edisonianum. Pinus elliottiivardensashowed a high degree of resistance to fire with several abiotic and biotic variables affecting mortality. A number of species exhibited an increased incidence of flowering after fire. Late spring/summer fires stimulated a vigorous flowering response inAristida stricta, Panicum abscissum,andAndropogonspp., whereas winter fires encouraged only a vegetative response. The ridge species do not require fire in the sense of maintaining a fire subclimax. Rather, fire revitalizes species’ populations, but does not initiate succession in the Clementsian sense.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12482.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

In the apparently “empty” axils of the needles ofTaxus baccata, Sequoia sempervirens, Sequoiadendron giganteum, Cryptomeria japonica, Thuja occidentalis,andThujopsis dolabratapersisting detached meristems were found, which are derived from superficial layers of the apical eumeristem. InT. baccatadelayed development of minute axillary buds occurs from these meristems after 1–4 yr on the intact plant. In the other conifers, development of additional axillary buds from these meristems was induced by natural frost damage or by artificial pruning and disbudding. The discovery of these detached meristems is discussed with regard to the regenerative capacity of the conifers in comparison to other plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12483.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Two morphogenetic patterns have contributed to phylogenetic diversification within the Gesneriaceae: accrescence of one of the paired cotyledons (anisocotyly), which serves to differentiate the subfamily Cyrtandroideae; sustained growth of the accrescent cotyledon accompanied by prolonged suppression and displacement of the embryonic apical meristem, which gives rise to an acaulescent, dorsiventral vegetative plant body (phyllomorph) and further serves to differentiate species of Cyrtandroideae found in two tribes and several genera includingStreptocarpus.It was possible to prevent cotyledonary accrescence and induce caulescence at will, either by supplying exogenous GA3or inhibiting auxin transport in species ofStreptocarpusthat normally manifest an extreme, phyllomorphic morphology. It was also possible to induce sustained, phyllomorphic development of cotyledons that are normally non‐accrescent with exogenous cytokinin. Therefore morphogenetic capacities previously thought to be “lost” or “lacking” in subgenusStreptocarpusand, with respect to isocotyly, the tribe Cyrtandroideae, are, in fact, present but suppressed. An hypothesis regarding the role of hormones with respect to morphogenesis and phylogeny ofStreptocarpusis suggested.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12484.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Light exposure caused massive areas of callus to develop from primary roots of aseptically culturedDiöon eduleseedlings. Callus initiation and continued growth was due to cortical cell hypertrophy and subsequent periclinal cell division. Callus initiation occurred in the subdermal cortex and developed radially and centripetally from the locus of initiation. Callus formation encompassed virtually all of the cortex, but did not incorporate any of the vascular tissues. With very large calluses, sectors of internal periderm arose between the developing callus and the remaining quiescent cells of the inner cortex. Most of the callus cells were typical, vacuolate parenchyma with cellulose walls, and large, multilobed amyloplasts. Callus also contained idioblasts with globular deposits of polyphenols. Adjacent cortical cells were typical parenchyma with peripheral cytoplasm, but contained small plastids with little starch accumulation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12485.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

Radicles and adventitious roots of the soap plant are contractile and through their activity, mature bulbs of this species are buried to depths of 20–30 cm. Experiments were performed to determine rates of contraction and displacement of the shoot apex resulting from activity of the contractile radicle and the first several adventitious roots. The average displacement was 23.2 mm over a 10‐wk period and 63.8 mm over 29 weeks. Small glass beads and abortive seeds served as controls and showed no displacement through the soil column. Measurements from longitudinal and transverse sections of contracted and uncontracted portions of radicles revealed average increases of 26–64% in radial dimensions and 40–56% decreases in longitudinal dimensions of inner and middle cortical cells (excluding the endodermis) following contraction. Cells of the outermost cortex (excluding the exodermis) decreased in average longitudinal dimensions by 18–26% before becoming distorted and collapsed as contraction was completed. Average volumes of innermost cortical cells decreased by 15–54%, while two or three cell layers of the middle cortex, adjacent to collapsed outer cortical cells, increased in volume up to 75%. These middle cortical cells are identified as the “active” cells which, by their growth, are responsible for the shortening of the root. Throughout the process of contraction, the stele remains straight and undistorted, although the closer spacing of tracheary element secondary wall thickenings following contraction suggests longitudinal compression of the stele. The average number of cortical cells per transverse section does not differ in contracted and uncontracted roots and no evidence is found to support the “interdigitation” hypothesis of root contraction. However, reorientation of middle cortical cell expansion may be the mechanism of root contraction inChlorogalum pomeridianum.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12486.x

出版商:Wiley    

年代:1984

数据来源: WILEY

摘要:

The leaflets ofErythrina herbacea,a leguminous plant native to subtropical North America, undergo daily movements. During the night, leaflets are oriented with their tips pointing downwards and show no rotation around the midrib of each leaflet. In the morning, leaflets rise, passing through a horizontal orientation and, somewhat before noon, reach a maximum average midrib elevation of approximately sixty degrees above the horizontal plane. Simultaneously, each leaflet rotates about the midrib by an average angle of forty to fifty degrees. These leaflet movements result in an initial increase in the relative leaflet surface area presented to the sun during the morning, a decrease in interception of direct solar radiation around noon, followed by a second maximum in light interception in early afternoon.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1984.tb12487.x

出版商:Wiley    

年代:1984

数据来源: WILEY