摘要:

The effects of red or far-red light flashes on partially hydrated lettuce seeds were found to be undiminished by subsequent dry, dark storage for more than 1 year before germination. Upon rehydration of the seeds photoreversal of the latent response could be induced by a red or far-red light flash at any time during the entire period.

ISSN:0008-4026    

DOI:10.1139/b72-084

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Ribosomes isolated from the chloroplasts of spinach leaves show the presence of RNA-degrading activity. The activity is optimal at pH 6.0 and at temperatures between 37 and 40 °C. The activity is cation-independent, exhibits exonuclease properties, and is considerably more pronounced under conditions in which the ribosome particles are in the dissociated state. The results are interpreted as showing that the RNA-degrading activity is a component part of the free ribosome population in the chloroplast.

ISSN:0008-4026    

DOI:10.1139/b72-085

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

When the cotyledons of 6-day-old seedlings ofChenopodium rubrumwere removed at various intervals after exposure to a single 13.5-h dark period, defoliation during the first 6 h after darkness prevented flowering. If the cotyledons remained on the plant for a further 5 or more hours flowering gradually increased. Within 20 h after the end of the dark period, the cotyledons had completed their essential role and subsequent defoliation had no influence on flowering. A cotyledon area of about 30 mm2was required for maximal floral induction.It can be concluded that a transmissible factor—often termed floral stimulus—was produced in the cotyledons following a short-day exposure. It is also apparent that flowering inChenopodium rubrumdepends on the generation of a floral stimulus in short days, rather than on control by a transmissible inhibitor of flowering produced under long days.After arrival of the floral stimulus at the apex there was a doubling from 2% to 4% in the percentage of cells undergoing mitosis. This increased value of the mitotic index was maintained during floral development and probably reflected an increased rate of cell division. There were rapid and sometimes rhythmic fluctuations in the percentage of dividing cells.

ISSN:0008-4026    

DOI:10.1139/b72-086

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The cytoplasmic streaming ofChara brauniiis investigated and evidence is presented to show:(i) that it is not affected by magnetic fields;(ii) that its cross-sectional variation is that which would be expected if the cytoplasm, tonoplast, and vacuolar sap behaved like a simple, viscous fluid;(iii) that its cessation following an electrical excitation does not depend upon an influx of calcium ions from the medium surrounding the cell.

ISSN:0008-4026    

DOI:10.1139/b72-087

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Seeds ofAsclepias syriacaL. (milkweed) have an inherent dormancy and these seeds could be forced to germinate by various treatments including stratification, cutting or removal of the seed coat, gases, alternating temperature, and a number of chemicals. Of the various treatments, the growth regulators kinetin and gibberellic acid were most effective in overcoming dormancy and a combination of these two had a synergistic effect. The increased germination percentage after 5 weeks of stratification was not accompanied by an increase in endogenous gibberellin levels. Treatment of the seeds with abscisic acid after stratification resulted in a complete inhibition of germination whereas treatment with kinetin resulted in an increase in germination. It is concluded that dormancy in milkweed seeds could be broken by many factors and regulated by an intricate interplay between growth promoters and inhibitors.

ISSN:0008-4026    

DOI:10.1139/b72-088

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

A low molecular weight material isolated from ascites fluid has been found to stimulate the incorporation of tritiated thymidine in tobacco pith cells kept on a radioactive White's basic medium. The stimulatory effect is not species, order, or kingdom specific.

ISSN:0008-4026    

DOI:10.1139/b72-089

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The root tissues ofEuphorbia esulaandE. cyparissiasform callus on chemically defined medium. Both species require an exogenous supply of auxin for growth, but the appearance and color of the tissue and their responses to kinetin, 2,4-dichlorophenoxyacetic acid (2,4-D) and indoleacetic acid (IAA) are different. The tissue growth is more satisfactory with α-naphthaleneacetic acid (NAA) than with 2,4-D, IAA, or 4-amino-3,5,6-trichloropicolinic acid (picloram). Gibberellic acid has no effect. The callus tissues ofE. esulabecome intensely green under light but are not autotrophic.Triglycerides, palmitic acid, and β-sitosterol are the major lipid constituents of the callus tissue ofE. esula. Chromatographic analysis reveals no significant differences in the composition of extracts from the non-green and green tissues. Long-chain aldehydes, alcohols, and triterpenes found in the plant are not detected in the cultures.

ISSN:0008-4026    

DOI:10.1139/b72-090

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The formation of both peroxidase and phenol oxidase was induced by culturing slices of Jerusalem artichoke tubers under aerobic conditions at 30 °C. The rate of enzyme degradation in the tuber slices was measured after applying cycloheximide, a strong inhibitor of protein synthesis, or by culturing the tissues under anaerobic conditions. Peroxidase decayed according to a first order process with a half-life of 8.3 h while phenol oxidase was found to be more stable (half-life about 70 h). The increase in the level of enzymes after the slicing treatment was achieved through a stimulation of the rate of enzyme synthesis rather than a decrease in the rate of destruction.

ISSN:0008-4026    

DOI:10.1139/b72-091

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Although none of the morphologic characters separatingPicea pungensfromP. engelmanniiis absolute, a hybrid index analysis of 21 populations strongly supports a conclusion that the two species do not hybridize when they occur together in the same habitats. The characters most useful in separating the species are listed, and the geologic history ofP. pungensis speculated upon.

ISSN:0008-4026    

DOI:10.1139/b72-092

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The apical meristem ofP. pratensisis hemi-ellipsoidal, the plane of bilateral symmetry being readily recognizable. On each side of the apex a prominent pair of tiers of surface cells straddles the line of the plane of symmetry from the upper limit of the active promeristem and extends basipetally into the first and frequently second foliar primordia. Initiation of a new foliar primordium (phytomer) is centered in one or the other of the paired tiers. Occasionally, a single cell in a tier appears to undergo initial mitotic activity. The specific tier of initial activity determines the deviation from symmetry of the whole phytomer including that of the leaf at the top of the phytomer and of the lateral bud at its bottom. The subtending leaf does not determine the deviation from the plane of symmetry of the axillary bud. The first leaf of the axillary bud (not the prophyll) is positioned with its point of origin, hence its midrib, displaced away from the plane of symmetry of the main stem and with its larger semicircumference towards the main stem. Thus the deviation from bilateral symmetry of all the organs of the phytomer and the initial deviation from symmetry of the organs produced by the axillary bud are determined originally by the specific tier of cells in the promeristem of the main shoot that is stimulated into initial activity. This initial orientation of the axillary bud is the first of the many orientations that determines the pathway through the soil that the rhizome will ultimately follow.

ISSN:0008-4026    

DOI:10.1139/b72-093

出版商:NRC Research Press    

年代:1972

数据来源: NRC