摘要:

The fine structure of the zoospore ofPhysoderma gerhardtiSchroeter is described. It possesses a single very large lipid body (sometimes accompanied by several smaller ones) situated laterally to the nuclear cap – nucleus complex and is associated with electron-dense material (the microbody) and the single large posteriorly located mitochondrion. The single posterior flagellum proximally terminates in a kinetosome just short of the posterior cone-shaped end of the nucleus. The kinetosome lies in a deep groove in the mitochondrion and is associated with this organelle by striated rootlets. The kinetosome terminates in electron-dense material from which an array of microtubules arises. These microtubules run along the sides of the cone-shaped nucleus and nuclear cap. There is an accessory centriole lying close to and more or less parallel with the kinetosome. The cytoplasm contains a small amount of smooth endoplasmic reticulum and several inclusion bodies in the anterior region and several small vacuoles in the posterior region of the cell. The general internal organization of the zoospore ofPhysoderma gerhardtimore nearly resembles that of a blastocladiaceous fungus than of any chytrid thus far investigated.

ISSN:0008-4026    

DOI:10.1139/b78-160

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

As in other mosses, the opening of an antheridium for sperm release inPolytrichumoccurs with the swelling of thickened walls in the cells at the tip of the antheridium. Although the tip cells are distinguishable by their shape and slightly thicker walls at early stages of development, the addition of the wall layer that swells seems to occur only during the last few 10ths of a millimetre of antheridial elongation. Changes in the vacuome and the accumulation of cytoplasmic vesicles differentiate the cytoplasm of tip cells from that in other jacket cells, but dictyosomes are few or absent in tip cells. Autophagic activity occurs in the protoplasts of tip cells as they near maturity.

ISSN:0008-4026    

DOI:10.1139/b78-161

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Nemophila menziesiitypically bears perfect, protandrous. self-compatible but predominantly outcrossed flowers. In one population ofNemophila menziesiivar.intermediaat Point Reyes, California, approximately 25% of the plants are completely male sterile. The flowers of these pistillate plants possess only small rudiments of stamens and lack anthers entirely. This phenotype is constant in nature as well as under cultivation. Male sterility appears to be inherited cytoplasmically, but there is at least one nuclear fertility-restoring allele in the population. The fertility-restoring allele may be at a single multiallelic locus, recessive to one nonfertility-restoring allele and dominant to another nonfertility-restoring allele, or there may be fertility-restoring alleles present at two or more loci. The population carries a significant load of deleterious recessive alleles at other loci, as evidenced by floral abnormalities and partial pollen abortion in some of the progeny from selfed hermaphrodites. Male sterility appears to be maintained in this population because the obligately outcrossed male steriles produce progeny which are more fit than the progeny produced from selfed hermaphrodites. Self-fertilization of hermaphrodites is probably higher in this population than in most populations of the species because the oligolectic-pollen-collecting bees, which are the normal pollinators ofN. menziesii, are not present at this locality. Gynodioecy probably became selectively advantageous when the outcrossing ancestors of this population were subjected to drastic increases in the rate of self-fertilization owing to changes in pollinator fauna.

ISSN:0008-4026    

DOI:10.1139/b78-162

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Cytological and histological studies were conducted on cotyledonary shoots of leafy spurge (Euphorbia esulaL.) after the removal of the epicotyl. Growth owing to cell elongation was observed as early as 4 h in the proximal part of the shoot. Nuclear divisions were present in the distal part of the shoot and were not affected significantly by decapitation. They did not contribute to the early increase in length of the shoot. An increase of mitotic activity after 40 h and of shoot length after 72 h was observed; the latter was interpreted to be due to shoot xylem connections with the hypocotylary stele.

ISSN:0008-4026    

DOI:10.1139/b78-163

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Three distinct Douglas-fir (Pseudotsuga menziesii) ectomycorrhizae formed by newly recognized varieties ofByssoporia(Poria)terrestrisare described. They are named according to tree species and fungus as follows:P. menziesii+B. terrestrisvar.lilacinorosea. P. menziesii+B. terrestrisvar.parksii, andP. menziesii+B. terrestrisvar.sublutea. Each mycorrhiza is macroscopically and microscopically defined, including surrounding mycelium and attached rhizomorphs. Cultural characteristics of the three fungal symbionts grown on potato dextrose agar medium are briefly noted.

ISSN:0008-4026    

DOI:10.1139/b78-164

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The evergreen characteristic ofLobelia dortmannaL. involves biomass and nutrient conservation. Although 60% of the maximum, midsummer biomass overwinters, little or no new tissue is produced between October and early May. Annual net production, estimated from the rate of leaf turnover, is less than the maximum biomass (P/B = 0.69 per year). Nitrogen and P concentrations are lowest in mid-August, when the amount of each analyzed element per square metre is near its maximum (N, P, Ca, Mg, Na, K). Autumnal uptake of N may contribute 25% of the next season's growth requirements, but P uptake is largely offset by losses during the winter. Fruiting and sterile plants have similar contents of N, P, and K in late July, but the fruiting plants are richer in Ca, Mg, Na, Fe, Mn, and Zn. At the maximum depth limit of the population in Mirror Lake, New Hampshire (2.3 m), flowering is absent and seedlings are sparse, suggesting reproductive failure as a controlling factor at the margin of the population.

ISSN:0008-4026    

DOI:10.1139/b78-165

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

A mathematical analysis of the relative sizes of the apical and basal cells of 100 published figures of two-celled embryos is used to show that contrary to the contemporary opinion, the size relationships of the two cells are widely varied. Certain factors having a bearing on the size of these cells are discussed.

ISSN:0008-4026    

DOI:10.1139/b78-166

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Spectrophotometric titrations and conductivity measurements show thatNitellacell walls contain nonexchangeable Ca2+cations which are probably chelated by COO−anions and donor groups such as OH (from polysaccharides) or NH (from proteins).A large part of these calcium ions are removed by acidification of the external medium. Subsequent augmentation of COO−groups increases the number of exchange sites available for H+and K+ions. The variation of the carboxylic groups concentration (α) is thus not fully accounted for by the pK of polygalacturonic acids but is also related to changes within the constitutive calcium of the cell wall.

ISSN:0008-4026    

DOI:10.1139/b78-167

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

[U-14C]glucose was fed in tracer amount to corn coleoptiles and the distribution of14C was observed after 8.5 h in air, 5% oxygen (extinction point), or nitrogen, in the presence or absence of 2,4-dinitrophenol 9 × 10−6 M. Restriction of oxygen caused increased loss of labelled sugars, mainly between the extinction point and zero oxygen. This accounted for about half of the increase in14CO2and [14C]ethanol, the rest resulting from diversion of14C from synthesis of insoluble tissue compounds. Addition of 2,4-dinitrophenol produced similar results. The data are consistent with current theories of the relation of oxygen and oxidative phosphorylation to the regulation of glycolytic reactions but indicate additional effects in the tissue.The metabolism of exogenous [14C]glucose did not represent that of endogenous substrate. At the extinction point, CO2from respiration of unlabelled endogenous substrate was less than in air while,14CO2from exogenous substrate was greater. The existence and the possible nature of an overriding control of glycolysis in the aerobic state of the tissue are considered.

ISSN:0008-4026    

DOI:10.1139/b78-168

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

A procedure is presented for the purification of DNA from tobacco callus cells. The procedure can be scaled up for the preparation in large quantity of DNA free of RNA, protein, and polysaccharide. The DNA prepared by this procedure has the same melting temperature and buoyant density as tobacco DNA prepared by previously published procedures and is of sufficient purity to be used for analysis of the reassociation kinetics of tobacco callus DNA. The DNA has been used as a source for the isolation of tobacco single-copy DNA.

ISSN:0008-4026    

DOI:10.1139/b78-169

出版商:NRC Research Press    

年代:1978

数据来源: NRC