摘要:

Enzymes active in the developing root epidermis ofElodea canadensisMichx. were demonstrated by histochemical techniques. The future root‐hair‐forming cells (trichoblasts) showed a period of elevated activity more extensive than the one previously reported in trichoblasts of another species for dehydrogenases (glucose‐6‐phosphate, pyruvate, lactate, succinic, isocitrate, glutamate), phosphatases (acid, ATPase, 5‐nucleotidase), cytochrome oxidase, and peroxidase. This elevated activity extended from the time of trichoblast formation up to the point of root hair outgrowth, even for enzymes not previously demonstrated in trichoblasts: alkaline phosphatase, NADH diaphorase, NADPH diaphorase, esterase, and leucine aminopeptidase. Glucose‐6‐phosphatase and aryl sulfatase were not detected. The single exception to this pattern was phosphorylase activity, which intensified only just prior to and during root hair outgrowth. The more generalized activity pattern is considered to indicate the so‐called meristematic character of these cells in terms of both macromolecular synthesis and lack of specialization. It is suggested that specific root hair development begins just prior to initiation, at the point marked by elevated phosphorylase activity.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10794.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

During vegetative growth aerial shoots ofFlagellaria indicabifurcate regularly at intervals even though axillary meristems are absent. Dichotomy involves no change in the cytohistological organization of the apical meristem; the shoot apex simply enlarges in the plane of distichy, a median furrow appears, and two new equal centers of meristematic activity are constituted in a process of continuous growth. Dichotomy can occur at any stage in the plastochron, and the morphology of the leaf immediately below the fork may be modified under the influence of the two new meristematic centers. The first leaf on each of the new apices is always on the same side, so there is no mirror image symmetry. The suggestion that dichotomy is the result of precocious axillary branching is discussed but rejected.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10795.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

The ontogeny of vascular bundles in the nodal region ofPopulus deltoidesBartr. was examined to understand more thoroughly the structure‐function relation between leaf and stem. Three vascular traces from the stem independently enter each leaf in the nodal region. At the base of each developing leaf a region was observed in which both bundle size and vascular development was reduced; this region was referred to as the constricted zone. The constricted zone was described quantitatively at 13 locations within the nodal region of a leaf at LPI 5 by determining the number of metaxylem vessels and the total metaxylem vessel area in each of the three leaf traces. A plot of these data showed a distinct minimum value for total metaxylem vessel area within the constricted zone of each trace; the location of this minimum value was referred to as the constriction plane. Each vascular bundle within the nodal region is composed of independent subsidiary bundles that originate within the constricted zone. These bundles provide a direct connection between the leaf lamina and the stem. The node was defined anatomically on the basis of the ontogenetic development of the subsidiary bundles. The node began at the initial exit point of the central trace from the vascular cylinder and extended distally to the constriction plane. This definition allowed us to quantify the limits of each node. The origin of the initiating layer and metacambium was also examined within the nodal region. These precursors of the cambium develop continuously and acropetally from the stem into the leaf. The developmental implications of the constricted zone and the metacambium within the nodal region are discussed with respect to wood formation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10796.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Three widespread ploidy levels have evolved inClaytonia virginica, a diploid represented byn= 8, 7, and 6 races, a triploid primarily byn= 12 and 11, and a tetraploid byn= 16, 15, 14, and other aneutetraploids. In addition, sporadic higher polyploids (5x–24x) occur throughout eastern North America. These data are considered briefly in relation to meiotic behavior, to coexistence of major cytotypes, and to speciation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10797.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Studies ofProsopis tamarugoPhil. leaflet surfaces by scanning and transmission electron microscopy disclosed an aggregate coating of basic wax structures of various shapes along with large semi‐vertical plates. The basic structures, with some degree of variation, were also present onP. velutinaWoot. and on several otherProsopisspecies which had been previously investigated. However, the plates, about 3 μm in size, were observed only onP. tamarugo.The basic wax structures were first observed on very young leaflets, about 6 h after emergence from the apical bud. The plates appeared after 24 to 72 h. Both plates and basic structures were larger on seedlings grown in a low (20–25%) relative humidity as compared to high (70%) humidity. When grown side‐by‐side in the greenhouse, leaflets ofP. tamarugoseedlings were more isolateral in structure than those ofP. velutina, suggesting a greater xeromorphic adaptation. The unusual epicuticular configuration described could be a mechanism that enhances the foliar absorption of atmospheric moisture, or at least minimizes cuticular transpiration, thereby aiding survival of this unique tree in its native habitat of northern Chile.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10798.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

The relationship of seasonal variation in isozymes to systematic studies at the infraspecific level is evaluated. Isozyme variation in peroxidases, esterases, and α‐terpineol dehydrogenases was evaluated monthly for one year inJ. scopulorumSarg. Zymograms of α‐terpineol dehydrogenases showed one nonvariable band. Isoperoxidases varied quantitatively but not qualitatively, this variation being correlated with seasonal growth and dormancy. Isoesterases showed qualitative variation, with two types of esterases being produced. One type showed seasonal variation and a second was nonvariable. The presence of two types of isoesterases may reflect differing physiological roles for each. The esterase results showed that care should be taken during investigations of isozymes at the population level to assure phenological similarity.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10799.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Electron microscopic examination of thin sections showed that the blepharoplast of a young spermatid ofPhaeocerosconsists of two side‐by‐side centrioles and an accumulation of osmiophilic, granular matrix at their proximal ends. Lying between these nearly parallel organelles is a dark‐staining body that will later disappear at the onset of flagellogenesis. For a brief period the centrioles are oriented perpendicular to the nuclear surface so that the granular matrix at their proximal ends is confluent with the nuclear envelope; furthermore, the nucleoplasm immediately in front of the centrioles becomes densely staining. The multilayered structure (MLS) develops directly under the centrioles. It comprises a band of 12 microtubules (the S1stratum) and three lower strata (S2–4) whose constitutent lamellae are oriented at an oblique angle to the S1axis. While the S1tubules grow rearward over the nucleus which forms a beak adjacent to the posterior end of the lamellar strata, the centrioles are transformed into basal bodies with the distal growth of the axonemes and the proximal growth of the central cartwheels and lowermost triplets. The proximal ends of the basal bodies and the S1tubules overlying the lamellar strata are invested with osmiophilic matrix that extends down to the S2layer and may temporarily occlude the lamellar plates. At the onset of nuclear elongation an anterior mitochondrion becomes situated close beneath the lamellar strata which extend laterally beyond the S1tubules.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10800.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Chromatin condensation begins as the multilayered structure (MLS) inPhaeocerosreaches its maximally structured differentiation. As nuclear elongation and chromatin condensation proceed, the S2–4strata disappear, and the nuclear beak extends between the S1and the nearly spherical anterior mitochondrion. In a mature sperm the mitochondrion is elongate and lies completely anterior to the blunt front end of the nucleus. The 12 S1tubules extend over the anterior mitochondrion and nucleus, but their number becomes reduced to five at the level where the nucleus' midportion is constricted. The anterior ends of the S1tubules lie embedded in a rather conical osmiophilic crest. Flagellar insertion is restricted to the extreme anterior tip of the S1tubules. The locomotory apparatus inPhaeocerosis compared with that of other bryophytes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10801.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Net primary production (NPP) is an important function of plant communities which has not often been examined seasonally in a forested ecosystem. The major objective of the study was to measure above‐ground NPP seasonally and relate it to phenological activity on a hardwood forest watershed at Coweeta Hydrologic Laboratory, North Carolina. NPP was estimated as the increase in biomass, estimated from regression equations on diameter. Diameter increases were measured by vernier tree bands. Phenological observations were made on bud break, leaf emergence, flowering, mature fruit, leaf senescence, and leaf fall. The species studied intensively wereAcer rubrum, Quercus prinus, Carya glabra, Cornus florida, andLiriodendron tulipifera. Liriodendronwas found to be the most productive species per individual, butQuercus prinuswas the most productive per unit ground area. The total watershed estimate of aboveground NPP was 8,754 kg ha‐1yr‐1and included 47.9% leaves, 33.2% wood, 7.8% bark, 4.8% reproductive tissues, 4.2% loss to consumers, and 2.1% twigs. Increases in leaf biomass were most rapid in the spring, but woody tissue production peaked in June and continued through August. Since leaf production peaked in the spring, the plants' photosynthetic machinery was activated early in the growing season to support woody tissue production, which followed the period of rapid leaf growth, and reproductive activity. Flowering occurred during the leaf expansion period except forAcer rubrum, which flowered before leaf emergence. Fruit maturation occurred during late summer to early fall, when there were no additional biomass increases.Acer rubrumwas an exception as its fruit matured during the period of leaf expansion.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10802.x

出版商:Wiley    

年代:1977

数据来源: WILEY

摘要:

Nutrient dynamics in vegetation play an important role in determining the circulation and storage of nutrients in an ecosystem. The major objectives of this study were to estimate the plant nutrient pools (K, Ca, Mg, and Na) on a hardwood forest watershed at Coweeta Hydrologic Laboratory, North Carolina, on a seasonal basis and to relate any observed trends to seasonal productivity and phenology. Late‐summer nutrient standing crops in the vegetation were calculated to be 551 kg/ha Ca, 233 kg/ha K, 48 kg/ha Mg, and 48 kg/ha Na. Nitrogen, P, and K concentrations in the leaves decreased seasonally, whereas Ca concentrations increased and Mg and Na concentrations remained relatively constant. Nutrient concentrations in the woody portion of the plants remained relatively constant. Standing crops of all nutrients increased seasonally with slight decreases of N and K in the leaves in the fall. Major conclusions of the study were 1) individual species and different plant components have nutrient storage‐pool turnover times ranging from one year to several hundred years. Canopy species are important in long and short term nutrient cycles; nutrient‐rich understory species such asCornus floridaare important in the annual cycle; and evergreen species are important in cycles of intermediate length because of nutrient storage in their perennial leaves. 2) Even though most of the annual nutrient uptake is recycled the same season (92%, 79%, 93% and 68% of K, Ca, Mg, and Na uptake, respectively), the total accumulation of nutrients is considerable in a mature forest stand.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1977.tb10803.x

出版商:Wiley    

年代:1977

数据来源: WILEY