摘要:

In the internodal secondary xylem of tomato (Solanum lycopersicumL. cv. Moneymaker) there are five main groups of secondary xylem elements which can be distinguished in wood macerates of basal internodes of the plant. Their top‐frequency lengths are distinct: ray parenchyma cells (80μm); fusiform parenchyma cells and strands (250μm); vessel members (290μm); tracheids (350μm); and fibrous elements (590μm), although there is overlap in length and morphology. The imperforate axial elements are strikingly diverse and morphologically intergrading, precluding ready classification according to traditional wood anatomical standards. In a novel, more appropriate, flexible categorization the variability in imperforate axial elements is depicted in a morphogram in which pit shape is plotted against cell length and cell morphology. This morphogram organizes the various elements without imposing an absolute classification. It is concluded that the appreciable variation in tomato wood samples results from developmental plasticity. The morphogram elucidates the extent and nature of element variation at the morphological level. Thus, it can be used to record developmental plasticity of wood tissues to assess interplant variation in wood tissue development, as well as intraplant plasticity.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11340.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The anatomical organization of the internodal tomato xylem was studied with the goal to relate xylem architecture, longitudinal flow, and lateral solute displacement in the stem. On account of a vessel member inventory, obtained by maceration, two vessel types were reconstructed distinct in diameter, morphology, and location. Type I: wide vessels (diam 50–160μm), with a relatively constant diameter and low horizontal perforation rims, the widest (in the main areas) often extending over more than one internode in length. Type II: narrow vessels (diam 10–50μm), with occasional vessel dichotomy, average length 5 mm, an irregular diameter, and a meandering vessel lumen due to many oblique and side positions of the perforations. The axial symplast units consisting of various intergrading elements, communicate with the vessel system via sheaths of axial contact cells with a high reducing capacity. The radial symplast units communicate with the vessels via radial contact cells at windows in the axial sheaths. The vessel/symplast interface of the axial and radial symplasts is in the proportion 65:35. The excessive metabolic activity and the high tangential pit frequency of the ray cells mark the rays as the conduits for symplastic xylem‐to‐phloem transfer. Radially fused intercellular spaces in the rays suggest that radial apoplastic solute transfer may also occur.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11341.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Rice embryo development was examined, histochemically and ultrastructurally, from the time of fertilization to embryo maturity. At the time of fertilization, the megagametophyte consists of an antipodal mass of 10–15 cells, parietally positioned along the placental side of the central cell, and, at the micropylar end, two partly fused polar nuclei and the egg apparatus. Hydrolysis of adjacent nucellar tissue suggests the secretion of hydrolytic enzymes by the antipodal mass. The antipodal cells stain intensely for RNA and protein, indicating that they are metabolically active. The egg, supported by two overarching synergids, occupies a small, wall ingrowth‐lined pocket of the central cell that quickly fills with cellular endosperm after fertilization. The endosperm cells, initially supplied with nutrients from wall ingrowth‐derived vesicles, are digested and utilized by the embryo as a nutritive source. The developing embryo is also supplied with assimilates via the nucellus at the base of the embryo until about 8 days after fertilization. After 8 days, the embryo is no longer connected to the nucellus, and the nucellar cells at the base of the embryo are crushed. The zygote is not structurally polarized and contains a central nucleus, amyloplasts, lipid bodies, dictyosomes and extensive dilated ER. The first division of the zygote is transverse and unequal and occurs about 4 hours after fertilization. Embryo development is rapid, and within 24 hr, the embryo consists of 5–8 cells. Organ development begins with scutellum emergence in the 3‐day‐old embryo. The shoot apex organizes and the coleoptile develops from scutellum tissue at 4 days postfertilization, the epiblast emerges at 5 days, and the vascular bundle and root apex differentiate by 6 days after fertilization. Starch begins to accumulate in the basal cells of the 3‐day‐old embryo and deposition proceeds acropetally over the next 9–10 days. Lipid accumulation begins in the basal scutellum in the 6‐day‐old embryo and also proceeds acropetally. Storage protein synthesis is first detected in 6‐day‐old embryos and accumulation again proceeds acropetally, reaching the apex of the scutellum of the 25‐day‐old embryo. The ultrastructure of the 24‐hr‐old embryo is distinctive. The cells are characterized by numerous vesicles, heterochromatin and extensive nuclear evaginations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11342.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The biomechanical role of septate nodes (points of leaf attachment with transverse diaphragms of tissue) in the otherwise hollow aerial stems ofEquisetum hyemaleL. is examined by means of multiple resonance frequency spectra. Resonance frequencies were determined for intact shoots, as well as the same shoots through which metal needles were inserted to destroy septa at nodes. The elastic modulus (E) of shoots, before and after surgical manipulation, was calculated. Shoots with perforated septa had E values from 17 to 32% less than intact shoots. During winter months with subfreezing temperatures, shoots with intact nodal septa accumulated water (in the form of ice) in their internodal pith canals. Values of E calculated for a shoot with intact septa and internodal water, and for the same shoot without septa do not differ significantly. Calculations indicate that the mass of internodal water is a significant fraction of the mass sufficient to deflect and buckle shoots. The added mass of internodal water is sufficient to mask the actual elastic modulus of shoots. The data indicate that nodes with septa significantly influence the flexural rigidity of shoots, but that this influence changes as a function of the quantity of water found in pith cavities.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11343.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

We examined factors affecting the duration of the staminate and pistillate phases in the protandrous flowers ofCampanula rapunculoidesL. (Campanulaceae). Under conditions of natural pollinator visitation, flowers experiencing low rates of pollen removal lasted significantly longer than flowers that had faster rates of pollen removal. Experimental manipulations showed that low levels of pollen removal resulted in extension of the staminate phase. Hand‐pollinations in which we varied the amount and source of pollen showed that when the number of fertilized ovules within an ovary is low, senescence of the flower is delayed, resulting in extension of the pistillate phase. We also report on pollinator foraging patterns within the vertical inflorescences ofC. rapunculoidesand the limiting factor for seed set in this population. The results are relevent to recent suggestions that floral characters often serve to reduce interference between the sexual functions in cosexual plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11344.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

We examined changes in the pattern of leaf variegation in a periclinal chloroplast chimera ofHedera helixL. cv. Goldheart to determine whether stable apical initials exist in the shoot apex. Additional data were obtained by histological analyses. All of the data indicate that four apical initials are present in the third layer of the apex, supporting the model of a structured apical meristem.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11345.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

The size and age distributions ofAcer saccharumMarsh, seedlings were studied in a mature hardwood forest in southeastern Ontario between 26 June and 26 September 1986. Ninety‐one percent of the seedlings surveyed were produced in 1984 which was a mast year for this population of sugar maple. Mean height within quadrats was negatively correlated with the density of two‐year‐old seedlings in the first half of the sampling period, suggesting that competition may be an important factor affecting seedling size. A significant positive correlation in the second half of the sampling period, however, suggested a temporal shift in the pattern of seedling growth in which the shorter, more suppressed seedlings under the higher densities had increased their relative height in response to earlier competition. The sum of the heights of pairs of nearest neighboring seedlings sampled over the survey period was negatively correlated with the distance between them. The sum of the biomasses of pairs of nearest neighboring seedlings collected in October 1986, however, was positively correlated with the distance between them. Variation in the height of two‐year‐old seedlings was unaffected by light intensity but was to some extent accounted for by soil variables, and total percent cover of other species. The density of the two‐year‐old seedlings, however, accounted for the largest percentage of the variation in their mean height. The data suggest that competition between the seedlings derived from mast seeding in 1984 may represent an important component of the process of natural selection affecting this population.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11346.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Seeds ofErodium moschatum(Geraniaceae) were moved on average 56 cm by primary, explosive dispersal and then traveled another 7 cm across the soil surface through activity of the hygroscopic awn, although not necessarily away from the source. In a 10‐day field experiment, 68% of the diaspores buried themselves through activity of the awn. The percentage of seeds becoming buried per day was not correlated with rainfall. More seeds became buried on plant‐littered ground, with litter cover from 8 to 61%, than on bare soil. As soil compaction increased, burial on littered surfaces declined. In laboratory experiments using straw to simulate sparse densities of plant litter, the percent of burial was enhanced, but sticks simulating plant stems did not facilitate burial. In a greenhouse experiment, more buried seeds germinated than unburied seeds. Buried seeds produced seedlings that developed more quickly, had higher survivorship and had greater shoot biomass than those from unburied seeds. Self‐burial also ensured that the radicle was positioned downward, which probably contributed to the observed higher survivorship. Overall, in semiarid grasslands, plant‐littered microhabitats are probably more favorable sites for the placement of seeds than bare areas (e.g., compacted gopher mounds). Littered sites promote self‐burial and burial promotes seedling establishment, survival and growth.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11347.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

Seed set after selfing inE. grandiflorumis often reduced relative to seed set after crossing; however, the compatibility patterns seen are not due to genes of major effect (i.e., S alleles). There is quantitative variation in the proportion of pollen tubes reaching the base of the style after both self‐ and cross‐pollinations. Pollen tubes require between 24 and 72 hr to reach the ovary, but pollen tube growth ceases after 72 hr. When styles were removed from the ovaries 5 days after pollination, between 10 and 80% of the pollen tubes in the stigma had not reached the base of the style. The number of pollen tubes at the base of the style is a much better predictor of seed set than is the number of pollen tubes in the stigma. Pollen tube attrition is not affected by the age of the recipient flower or by the number of pollen donors contributing to the stigmatic pollen pool. The number of pollen tubes reaching the base of the style is dependent upon the source of the pollen and appears to be a decelerating function of the number of pollen tubes present in the stigma.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11348.x

出版商:Wiley    

年代:1989

数据来源: WILEY

摘要:

We have critically evaluated Baum, Estes, and Gupta's (1987) assessment of the genomic system of classification in the tribe Triticeae. They have raised some valid concerns about basing a taxonomic classification on genome relationships. However, some of their objections are ill‐founded. Baum et al.'s contention that genome analysis can only supplement other criteria in assessing phylogeny is inaccurate. Genome analysis by itself has yielded extremely useful information on phylogenetic relationships in the Triticeae, and their assertion that an individual morphological trait be given the same weight as genomic relatedness is not tenable. Moreover, these authors have adopted cladistic algorithms in the Triticeae, an analysis appropriate only in groups where reticulation has not occurred. Evolution in the Triticeae is highly reticulate, the main sources of reticulation being allopolyploidy and homoploid recombinational speciation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1989.tb11349.x

出版商:Wiley    

年代:1989

数据来源: WILEY