摘要:

The effects of various nitrogenous compounds in concentrations ranging from 10‐4to 10‐3mon the growth and morphology of gemmae ofMarchantia polymorphaL. were investigated under axenic conditions. Only nine of the 24 compounds tested were effective in altering the normal developmental pattern of this plant.l‐Isoleucine,l‐leucine,l‐methionine orl‐threonine resulted in a disruption of the apical regions at concentrations of 10‐3m. The addition of lower concentrations ofl‐arginine,l‐histidine,l‐hydroxyproline,l‐lysine orl‐tryptophan to the nutrient medium resulted in morphological irregularities. These latter abnormal growth patterns were highly specific for the individual amino acids and ranged from lack of air chamber development to complete thallus disorganization. Both the formation and duration of abnormal developmental patterns were dependent upon the concentration of the amino acids employed. Although the experimental results are inconsistent with certain physiological mechanisms such as a general nitrogen toxicity, alternative possibilities are discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb07430.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Abscission was studied inPsoralea argophyllaPursh, a prairie tumbleweed. This process is responsible for the detachment of the stem from its perennial base. In a single plant abscission may proceed through one or more intercalary meristems located at or near ground level. During senescence a separation layer differentiates within each of these meristems. Chemical changes occur within the compound middle lamellae which result in the conversion of insoluble pectic compounds into soluble forms. Cell separation takes place only after removal of the pectic compounds, meristematic activity, and attenuation of cell walls. Unlike reports of other angiosperms the protective layer is not formed adjacent to the separation layer, but forms some distance underground at the stem‐root junction.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb07431.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Dimethyl sulfoxide (DMSO) in concentrations of up to 10% by volume stimulates the uptake of zinc by excised barley roots. In the same concentration it severely depresses uptake of sodium and of rubidium. It does not seem to affect the permeability of the membrane since roots treated with desorption solutions which were 10% in DMSO did not lose more of the preferred ion than did roots desorbed in solutions not containing DMSO. Oxygen utilization (measured in the Warburg respirometer) was reduced when DMSO was present. It is suggested that DMSO is a poisoning agent which interferes with cation transport by attacking some aspect of metabolism and not by influencing the permeability of the membrane.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb07432.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Experiments using controlled environment facilities showed that flowering ofDichondra repenswas promoted by chilling plants at 10 C or below. Optimum length of the chilling period was 5–6 weeks. Unchilled plants did not flower. The flowering stimulus resulting from chilling was destroyed by temperatures above 21 C. Rate of flowering was increased by short days during chilling, but short days could not substitute for the chilling requirement. Optimum daylength for flower initiation following chilling was approximately 14 hr and the optimum temperature was approximately 15 C. Flower buds developed in leaf axils of primary stems and laterals, but stem apices remained vegetative. When the chilling requirement was met flowering continued indefinitely as the plants grew.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb07433.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Actinomycin D affected the morphological type of growth in the gametophytes ofPteridium aquilinumand the distribution of RNA and protein in their particulate fractions. Increasing concentrations of the drug progressively inhibited two‐dimensional growth at the end of a period during which controls had formed typical two‐dimensional plants. RNA was lost maximally from the nuclei‐rich and ribosome‐rich fractions of plants growing in a concentration of actinomycin D which inhibited two‐dimensional growth. The magnitude of changes in protein content of the plants was less striking. Presence of actinomycin D in the medium also suppressed incorporation of uridine‐H3into cytoplasmic fractions of gametophytes. The possibility that two‐dimensional growth in the gametophytes is under control of a newly synthesized messenger RNA, which is sensitive to actinomycin D, is discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb07434.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

A new genus from a Middle Devonian locality near Cairo, N. Y., is described.Actinoxylongen. nov. is based upon pyritic petrifactions. Three orders of branching are present: penultimate branch, ultimate branch, and leaf. The penultimate branch bears spirally arranged ultimate branches and leaves, the leaves apparently replacing the branches in the spiral. The ultimate branches bear opposite to subopposite and decussate leaves. The leaves are non‐planated, unwebbed structures which show at least three dichotomies. Each segment of the leaf is terete as are all other axes. Internally the penultimate branch has a six‐lobed actinostele with mesarch protoxylem areas, one or two per lobe. Secondary xylem is visible in the oldest parts of several specimens. The xylem has helical‐reticulate, reticulate, scalariform and circular‐pitted elements. The presumptive areas of phloem are occupied by cells with dark contents. The cortex is composed of a parenchymatous inner region and a sclerenchymatous outer region. The ultimate branch traces are at first three‐lobed protosteles, later becoming four‐lobed. Several ultimate branch traces also possess secondary xylem while within the cortex of the penultimate branch. The leaf traces are terete strands. Below each forking of a leaf segment there is a corresponding forking of the vascular strand.Actinoxylonis compared with the progymnospermsActinopodium, Svalbardia, Archaeopteris, Siderella, andTetraxylopteris. The anatomy of the penultimate branch ofActinoxylonis similar to that ofActinopodium, Archaeopteris macilenta, andSiderella. The ultimate branch traces ofArchaeopterisandActinoxylonare similar. The ultimate branch stele and pattern of trace formation inActinoxylonis similar to the stelar configuration and trace formation in the r + 2 axes ofTetraxylopteris schmidtii. The unwebbed leaves are similar to those ofArchaeopteris fissilis, Svalbardia, and the terminal units of the Aneurophytales.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb07435.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Vegetative myxamoebae ofAcytostelium leptosomum, a cellular slime mold, have the appearance of typical eucaryotic cells. The presence of dictyosomes has been established. Elongation of the cells during aggregation and culmination appears to be mediated by dense bundles of microfibrils traversing the cells longitudinally. Microtubules are present; however, they are randomly oriented and no correlation can be made with cell elongation or with the direction of the cellulose microfibrils within the stalk. A variety of vesicles, multivesicular bodies, and lysosome‐like vacuoles seems to be involved in producing and transporting stalk material to the vicinity of the stalk. However, only rarely do the vesicles empty their contents directly to the outside of the cells. It seems rather that the fibrillar material of the stalk is assembled near or directly at the plasmalemma, and can then be seen to stream away and become an integral part of the stalk. An unusual structure, the H‐body, is formed in great abundance during culmination indicating its possible involvement in stalk synthesis. The H‐bodies are removed from the cells prior to spore formation together with other portions of the cytoplasm at least partly by a process involving autophagic vacuoles. These vacuoles, which are also present in the spores, appear to be part of a rather complex and extensive vacuolar apparatus including the food vacuoles, contractile vacuoles, lysosome‐like structures, and possibly the H‐bodies. The spore coat consists of a heavy outer wall with a fibrillar substructure and two thin, dense bands lining the inside of the plasmalemma. The fibrillar nature of both the outer spore wall and the stalk was accentuated by using barium permanganate to stain sectioned material.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb07436.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

The changes in cytoplasmic fine structure during the interval between pollination and zygotic division in the megagametophyte ofZea maysare reported. The rate of membrane synthesis appears to be low in the mature unfertilized megagametophyte. This megagametophyte is suggested to be in a state of relative metabolic inhibition. The rate of membrane synthesis is high in the zygote and free nuclear endosperm. After fertilization the swelling of the mitochondria in all cytoplasms is interpreted to reflect a presumed increase in metabolic rate relative to growth. In the zygote and endosperm, endoplasmic reticulum (ER) production is associated with the nuclear envelope. In all of the material the ribosomes not associated with the ER are helical polysomes which increase in length after fertilization. On the basis of permanganate staining, the ribonucleoprotein of the endosperm is suggested to be different from that of the other cytoplasms. The specific plastid form of each cell type does not change during the first few hours after fertilization. Dictyosomes are most numerous and active in the antipodals. They are least numerous in the egg and zygote. The smallest dictyosome vesicles are in the synergids. Dictyosome number and vesicle size increase in the egg and central cell after fertilization. Similarities among the megagametophytes of several angiosperms are enumerated.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb07437.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

The ultrastructure and composition of the egg, zygote, and young embryo ofCapsella bursa‐pastoriswere examined. The egg is a highly polarized cell; one‐half to one‐third of the micropylar end is filled with a large vacuole while the chalazal end contains the nucleus and much of the cytoplasm of the cell. The wall which surrounds the cell is incomplete at the chalazal end. Ribosomes fill the cytoplasm and show little or no aggregation into polysomes. The structure of the nucleolus suggests that ribosomes are not being produced. Following fertilization and the formation of the zygote, the cell decreases slightly in volume as the large central vacuole becomes smaller. The zygote soon increases in size as the small chalazal vacuoles present before fertilization begin to enlarge. The dictyosomes become active and a continuous wall forms around the zygote. Aggregation of the ribosomes begins and numerous polysomes are formed. Before division of the zygote all plasmodesmata between the zygote and the surrounding cells are lost. The first division of the zygote is unequal as a result of its marked polarity. A large basal cell and a small terminal cell are produced. The basal cell appears to contain more protein, RNA, carbohydrate, and cell organelles than the terminal cell. Ribosomal aggregation is even more pronounced at this stage. Starch accumulates in the plastids. Numerous plasmodesmata are present between the terminal and basal cells but there are no connections between the endosperm or other cells. The basal cell divides next to give rise to a three‐celled linear embryo consisting of the basal cell, the suspensor cell, and the terminal cell. The terminal cell stains more intensely for protein and RNA as a result of increased numbers of ribosomes. Starch in all the cells is about equal and reaches a maximum in the embryo at this stage.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb07438.x

出版商:Wiley    

年代:1968

数据来源: WILEY

摘要:

Chromosome numbers are presented for 28 species of the genusPerityle, one putative inter‐sectional hybrid, two species ofAmauria, one species ofEutetras, and one species ofPericome. ForPerityle, initial counts are recorded for 12 species of sect.Laphamia(n= 16, 17, 18, 36, ca. 102) and 11 species of sect.Perityle(n= 11, 12, 13, 16, 17, 18, 19, 34, 51). Chromosome numbers for the two species ofAmauria(n= 18) are first reports for the genus. Including the current information, chromosome numbers have been recorded for 37 of the approximately 50 species recognized forPerityle. At least 24 taxa have numbers ofn= 17, suggesting a base chromosome number ofx= 17 forPerityle.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1968.tb07439.x

出版商:Wiley    

年代:1968

数据来源: WILEY