摘要:

Plastid ultrastructure was correlated with plastid replication and growth during the greening of etiolated tobacco tissue. The plastids grow rapidly, and this growth is correlated with a period of rapid chlorophyll synthesis. Chlorophyll synthesis is correlated with the formation of grana. The plastids divide by constriction and continue to do so after most of the grana have been formed. They contain single membrane‐bound bodies, which are observed less frequently in the last stages of chloroplast maturation. No internal morphological features of the plastids appear to be related to causal aspects of replication.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10084.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

With length of sporangia as a developmental index, the growth relationships of sporangia during differentiation were studied in strobili ofSelaginella bigelovii. The strobili usually contain two rows of megasporangia and two rows of microsporangia with a mega‐ opposite a microsporangium at each node. Prior to the sporocyte stage a sporangium in a megasporangiate row is larger and elongates more rapidly than a sporangium opposite it at the same node in a microsporangiate row. The number of sporogenous cells is similar in sporangia of the same length from both rows until cell multiplication ceases in sporangia of the megasporangiate row, while it continues in sporangia of the same size in the microsporangiate row. The observed growth differences between sporangia of the micro‐ and megasporangiate rows are interpreted as events in the differentiation of two sporangial types.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10085.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Arabidopsis thalianavegetative meristems, growing under short photoperiods, respond to the application of IUdR by precocious floral morphogenesis.3H‐thymidine was used to label cells active in DNA synthesis and study the effect of analogue application on the amount and distribution of DNA synthesis throughout the meristem during 78 hr subsequent to IUdR treatment. Photomicrographs, autoradiographs, and composite plots of label distribution in transparent superimposed sequential sections revealed a non‐uniform distribution of labelling in control vegetative meristems, which typically contained a central and axial core incorporating little3H‐thymidine and a peripheral flanking tunica region which contained densely labelled cells. The ratio of labelled cells in the peripheral region to labelled cells in the central region was about 10:1 in the controls. In meristems pretreated with IUdR there was a brief suppression of3H‐thymidine incorporation during 6–12 hr after treatment, followed by two waves of enhanced incorporation in the peripheral region, and a progressive increase in the frequency of labelled cells in the central core of the meristem. After 78 hr the frequency of labelled cells in the central core of IUdR‐treated meristems was 8‐fold higher than in untreated meristems, and the frequency in the peripheral regions was about the same in both IUdR and control series. The enhancement in amount and uniformity of DNA synthesis after temporary inhibition by IUdR parallels the normal enhancement which is observed when vegetative meristems are transferred to long photoperiods causing floral induction.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10086.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Bud formation and gametophore development were studied in the mossPylaisiella selwynii(Kindb.) Steere and Anderson grown from spores in a liquid medium consisting of inorganic salts. Indoleacetic acid and ethrel increased bud formation within a narrow concentration range. Copious bud formation was obtained with the five cytokinins tested at concentrations varying from 5 X 10−6to 5 X 10−14M. Except for about 10 % of the buds obtained with 6‐γ, γ‐dimethylallylaminopurine at 5 times 10−14m, the cytokinin‐induced buds failed to develop into normal gametophores. Octopine, lysopine, and octopinic acid, substances obtained from crown‐gall tumors, increased bud formation at 10−3m. On lysopine‐treated plants these buds developed into typical gametophores. Gemma‐like structures were obtained with octopine but no gametophores.l‐arginine andl‐lysine, the amino acids which respectively occur in octopine and lysopine, failed to induce gametophore formation although buds were obtained with 10−3mlysine. γ‐Guanidinobutyric acid induced bud formation at 10−3m, but these buds developed into highly abnormal gametophores. The failure of buds obtained with many of these treatments to develop into gametophores appeared to result from the formation of new cell walls in other than the normal geometrical relationship during initial divisions of the pro‐bud. The relevance of the findings to the crown‐gall problem is discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10087.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Original chromosome observations including number for 68 taxa representing 47 genera are reported. Of these, 12 are first reports for species representing ten genera. In nine species multivalent associations (rings or chains) were noted; these were not always accompanied by low pollen stainability. Accessory chromosomes (centric fragments or univalents) were noted in two species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10088.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Dormancy inAmbrosia artemisiifoliaseeds was broken by 8 weeks of stratification. Germination of nondormant seeds was greater in light than in continuous darkness. Embryos of freshly harvested seeds were nondormant. Leaching and scarification did not stimulate germination of the dormant seeds. Exogenous gibberellin (GA3) slightly increased germination of intact dormant seeds, and the effect was greatly increased by scarification. Germination was greater in the light in both tests. Exogenous indoleacetic acid did not stimulate germination of dormant seeds. Endogenous gibberellin and auxin content increased during stratification, and there was also a significant increase in GA during post‐stratification at a favorable germination temperature. Inhibitors in the dormant seeds decreased during stratification and post‐stratification. The high concentration of chlorogenic acid present in dormant seeds increased slightly during stratification. An unknown phenol very similar to chlorogenic acid in fluorescence and U.V. absorption significantly increased after 2 weeks of stratification. A significant decrease in the concentration of a second unidentified phenol occurred after 2 weeks of stratification. It is proposed that dormancy inAmbrosia artemisiifoliamay be controlled by an inhibitor‐promoter complex. The dormant seed is characterized by high inhibitor and low promoter levels. In the nondormant seed the balance was shifted to favor the promoter. Evidence suggests that the inhibitor involved may be abscisic acid and the promoters may be gibberellin and auxin. The content of auxin may be partially controlled by the concentration of phenols.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10089.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

A study of seed coat sculpturing inCordylanthus(Scrophulariaceae—Rhinantheae) using the scanning electron microscope (SEM) shows that seed surface patterns are characteristic and constant for a given species or a group of species. Seeds of 23 species were examined and classified into four types (irregularly crested, deeply reticulate, shallowly reticulate, and irregularly striate) based on differences in the reticulated seed coat. Anatomical studies of sections with the light microscope show that the reticular patterns result from enlargement of the epidermal cells of the integument, followed by formation of characteristic wall patterns through lignification. Seed characters furnish useful data for formulating the taxonomy ofCordylanthusboth on the sectional and subsectional level and for the delimitation of certain species. Seed coat morphology offers evidence for including the genusDicranostegiainCordylanthusand for maintainingC. hispidusandC. palmatusas separate species. The distinctness of two seed coat types within sectionCordylanthussuggests two major phylogenetic lines within this section.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10090.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

The number of cells per vertical column in barley coleoptiles differs in various growth classes; it is highest in tall coleoptiles, intermediate in medium ones, and lowest in short ones. In those that elongate early and grow rapidly, cells per column increased from 88–218 between 12 and 44 hr after the seeds were placed on water; in short coleoptiles they increased to only 85 per column after 115 hr because elongation and division are restricted in these. Cell number does not increase in coleoptiles from seeds irradiated with 250 krad. Variation in the growth pattern of irradiated coleoptiles was similar to that of normal ones, although the range in lengths was reduced. Although the number of cells is much higher in tall controls than in irradiated coleoptiles, the latter can become tall; therefore an increase in cell number during germination does not seem to be a prerequisite for tallness. Coleoptiles 32 mm long, from irradiated seeds, have the same number of cells per column as the shortest ones (6 mm) after 119 hr.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10091.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

The robust emergent leaves ofSparganium eurycarpumandS. americanumare supported by corner fiber masses and large bundle sheaths, but the thin floating leaves ofS. fluctuansandS. minimumhave only moderate bundle sheaths. In emergent types heavily photosynthetic diaphragms bearing vascular bundles are separated from each other in the leaf compartments by three lightly photosynthetic diaphragms without bundles, but in floating types only every other heavily photosynthetic diaphragm has a bundle. Palisade chlorenchyma occurs only at aerial surfaces—abaxial and adaxial in emergent leaves, but only adaxial in floating leaves. Extra photosynthetic areas are provided in emergent leaves by concentrations of chlorenchyma in limited areas on interior partitioning walls, while the remainder of the walls is translucent. Since only 25 % of the diaphragms are heavily photosynthetic, and the others essentially transparent because of their diffusely distributed chloroplasts and large intercellular spaces, a sieve effect exists which allows even the interior parts of thick emergent leaves to photosynthesize.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10092.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Micropylar wall extensions in the egg ofPlumbago capensisarise as small pegs of periodic acid‐Schiff's‐positive material soon after the egg is organized. These inward projections of egg wall increase in size, becoming extensive near anthesis. Some branching of the filiform apparatus occurs. In mature embryo sacs the micropylar portion, with the lowermost portion of the egg included, becomes entrenched in the nucellus. The possible significance of this “gametic transfer cell” is discussed in relation to the apparent absence of synergids from the reduced embryo sac ofPlumbago.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10093.x

出版商:Wiley    

年代:1972

数据来源: WILEY