摘要:

Microelectrode techniques were used to investigate the electrical properties of leaf cells ofLycopersicon esculentumboth in excised leaflets and in small tissue sections. Most of the recordings were from epidermal cells of the abaxial midrib.Cells were electrically coupled. Apparent resistivity was lowest shortly after impalement (mean value about 1.8 kΩ cm−2) and increased gradually during most experiments. A fluctuation of resistance and potential occurred during the first 5–10 min of many recordings.Potentials between the vacuole and external medium averaged about −125 mV in all preparations, regardless of the external K+content. Vacuolar K+activity averaged about 66 mM. The average Nernst potential for K+would thus be only about −48 mV for an external concentration of 10 mM. Changes of external pH between 5.6 and 8.6 had little or no effect on the potential, but at 4.6 the cells depolarized to about −50 mV and required about 2 h to recover after the pH was raised to 6.6. The potentials were partially dependent on metabolic activity, since CN−or CN−and SHAM together caused marked depolarization.Darkening and illuminating leaf mesophyll cells elicited reproducible transients; associated with the transient light-induced depolarization was a 10–15 mV spike. Changes in illumination had extremely variable effects on the potential of midrib epidermal cells.

ISSN:0008-4026    

DOI:10.1139/b77-060

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Extract containing Ricca's factor depolarizes the membrane potential of at least three types of cells inLycopersiconleaves : mesophyll, midrib parenchyma, and midrib epidermis. The depolarization has been studied in some detail for the epidermal cells, in which depolarization appears to begin without a lag and is completed within 60–90 s. The maximum rate of depolarization is typically about 3 mV s−1. No changes in resistivity, capacivity, or intercellular electrical coupling have been detected during the depolarization.Extract from 0.5 mg fresh leaf tissue in 1 ml of water at pH 6.6 causes threshold depolarization in many experiments, and a concentration only 40 times greater is usually saturating. Raising the pH increases the concentration of factor required for saturation.With subsaturating concentrations of factor, the potential recovers somewhat after depolarization, and when factor-free medium is washed over the tissue the potential depolarizes briefly before returning to its baseline value. With saturating concentrations of factor, the potential depolarizes to an essentially stable level and no transient depolarization occurs when the factor is washed out.The potential remaining after application of a saturating concentration of factor is independent of the initial baseline potential but depends on the concentration of K+in the equilibration medium and in the extract. The saturation level of depolarization is in the range of the Nernstian potential for K+, but whether it is precisely equal to the Nernstian potential for K+has not been established.Evidently, the occurrence and influence of Ricca's factor should be taken into account in all electrophysiological studies of shoot tissue since the factor appears to be released whenever cells are wounded and may be released during other kinds of stress as well.

ISSN:0008-4026    

DOI:10.1139/b77-061

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Antithamnion cruciatum(C.Ag.) Näg. is reported from insular Newfoundland, its most northerly known location in North America. It exhibits a variable morphology occurring as the typical erect form, as a prostrate form, and as a fragmented form by which it perennates. Zonately divided sporangia containing four spores have been observed, but their function is unknown. Culture experiments show that the species grows at 10 °C and above, but fertility was not induced. Cytological studies indicate there is no genetic alternation of generations, and chromosome numbers suggest the population may be polyploid.

ISSN:0008-4026    

DOI:10.1139/b77-062

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The gynoecium of theBegonia tuberhybridaVoss is characterized by the inferior position of its three ovaries, which are united between themselves and with the four or five parts of the perianth. The modifications of this gynoecium are highly diversified, but the most frequent are the variation of number of carpels giving rise to meiomerous or pleiomerous gynoecia and the variation in the position of ovaries which results in the formation of gynoecia of the pattern of another genus of the same family,Hillebrandia(semiinferior ovaries), or of the pattern of the hypothetic flower of Begoniaceae (superior ovaries).The study of the morphology and of the vascularization of these normal or abnormal gynoecia leads to an understanding of the constitution of the carpel and of the ovarian wall in this genus.

ISSN:0008-4026    

DOI:10.1139/b77-063

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A population of the fernOsmunda regalisgrowing in a polluted river was investigated genetically. Previous studies documented a high frequency of postzygotically induced genetic and chromosome damage. This paper describes two categories of gametophytic mutants which occurred in the progeny of this population. A gametophyte phenotype which exhibited a maternal effect on the sporophyte generation when it was the female parent occurred in 7.8% of the spore sample. A gametophyte phenotype which could best be characterized as a neuter calluslike mass occurred in 6.6% of the spore sample. Studies of nearbyO. regalispopulations in non-polluted sites failed to document the presence of such phenotypes in the spore samples.

ISSN:0008-4026    

DOI:10.1139/b77-064

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The cyanide-insensitive respiration of the mitochondrial fraction isolated from etiolated coleoptiles of four cultivars of wheat has been studied under a variety of conditions. Cultivar differences were observed in the apparent capacity of the CN-insensitive pathway ranging from 8 to 35% of the observed state 3 respiration rate. Although Arrhenius plots of the state 3 and state 4 rates were relatively linear from 2.5 to 30 °C, the CN-insensitive oxygen uptake exhibited a distinct maximum rate at about 17.5 °C. Germination of the wheat in the presence of high concentrations of CO2(15–25%) resulted in a dramatic increase in the capacity of the CN-insensitive pathway. Germination in 100% O2appeared to have little effect on either the cytochrome or CN-insensitive electron-transport pathways. However, oxygen did exert a synergistic effect with CO2since germination in 25% CO2in oxygen yielded mitochondria with about twice the CN-insensitive capacity of wheat germinated in 25% CO2in air.

ISSN:0008-4026    

DOI:10.1139/b77-065

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Ultrastructural observations on microbodies in hyphae and sporangia of the oomycete fungusSapromyces elongatusreveal that they consistently develop adjacent to cisternae of endoplasmic reticulum. At maturity they contain a crystalline structure, having a tetragonal lattice with asymmetric spacings of 12 and 13 nm and also several small irregular tubular structures. Mature microbodies also develop numerous villous invaginations, each filled with a cistema of endoplasmic reticulum, the membrane of which is constantly spaced from, and possibly cross bridged to, the microbody membrane. Although microbodies may be appressed to mitochondria, they do not show any associations with lipid droplets. In apparent senescence the crystals remain, but the microbody membrane enlarges greatly with accompanying loss of associated endoplasmic reticulum and dilution of matrix, so that the last recognizable stage is a crystal-containing vacuole. Zoospores contain numerous mature, invaginated microbodies associated with cisternae of endoplasmic reticulum; they are clustered predominantly around the nucleus. The morphology of the microbodies and their possession of crystalline inclusions differ from previously reported oomycete microbodies and may have taxonomic value, whereas the postulated ontogenic sequence and fate of the microbodies are previously unreported and may represent a general mechanism for microbody breakdown.

ISSN:0008-4026    

DOI:10.1139/b77-066

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Gametophytes ofLycopodium obscurumwere grown from spores in axenic culture on a medium containing inorganic nutrients and sucrose. The prothalli developed into thick, disk-shaped gametophytes which bore antheridia. No archegonia were observed on these 1-year-old gametophytes. The morphology of the prothalli in culture was essentially that described for prothalli ofL. obscurumfrom nature. However, theseLycopodiumgametophytes in culture developed without the endophytic fungus which is necessary for the growth of prothalli ofL. obscurumin nature.

ISSN:0008-4026    

DOI:10.1139/b77-067

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Seedlings of resistant (Sr6) and susceptible (sr6) near-isogenic lines of wheat (Triticum aestivumL.) were inoculated with an avirulent (P6) race of stem rust (Puccinia graminis(Pers.) f.sp.triticiEriks. & Henn.) and kept for 2 days at 26 °C where theSr6gene is ineffective, treated with blasticidin S, ethionine, polyoxin D, or buffer, and transferred to 19 °C where theSr6gene is normally effective. One and 2 days later, leaves were stained with Calcofluor and examined by fluorescence microscopy to detect autofluorescing necrotic host cells and Calcofluor-stained stem rust colonies.Blasticidin S was phytotoxic to wheat leaves at concentrations that had no effect on fungal growth during the first 2 days after treatment. At later stages, extensive host necrosis, resulting from the phytotoxicity of this antibiotic, inhibited rust development.Ethionine and polyoxin D strongly inhibited rust development at concentrations that were not phytotoxic. In genotypically resistant leaves treated with ethionine and polyoxin D there were fewer necrotic cells associated with stem rust colonies than in leaves treated with buffer. The spacial distribution of necrotic cells was consistent with the view that necrosis occurs only in cells newly invaded after the temperature was lowered to 19 °C.The observations do not support the concept that host-cell necrosis in the hypersensitive reaction conditioned by this gene results from the death of the fungus.

ISSN:0008-4026    

DOI:10.1139/b77-068

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The carbamate insecticide carbofuran (2,2-dimethyl-2,3-dihydrobenzofuranyl-7-N-methyl carbamate) and three of its metabolites (7-hydroxy-2,2-dimethyl-2,3-dihydrobenzofuran (III), 3,7-dihydroxy-2,2-dimethyl-2,3-dihydrobenzofuran (IV), and 3-keto-7-hydroxy-2,2-dimethyl-2,3-dihydrobenzofuran (V)) stimulated growth in the pea stem segment assay in the presence, but not absence, of a low concentration of indole-3-acetic acid (IAA). The metabolites were more active than carbofuran itself. The synergistic effect on growth was specific with IAA since it was not observed in the presence of other auxins.Metabolites III, IV, and V and, to a lesser degree, carbofuran were found to be inhibitory to IAA degradation catalyzed by pea stem tissue or purified horseradish peroxidase (EC 1.11.1.7). Comparison of the relative activities of the compounds in the inhibition of IAA degradation and in the promotion of plant growth suggests a causal relationship. The implication is that carbofuran may promote plant growth through the inhibitory action of its metabolites on enzymic breakdown of IAA, thus preserving a critical level of IAA required for growth promotion.

ISSN:0008-4026    

DOI:10.1139/b77-069

出版商:NRC Research Press    

年代:1977

数据来源: NRC