摘要:

An apparent shoot rest period was induced in the 2nd month of growth of alfalfa (Medicago sativaL.) seedlings by a drop in growth temperature from 25:20 °C to 10:7 °C. After prolonged chilling the shoots were replaced by new shoots. Temperature profiles of nodulated root respiration and nitrogenase activity (acetylene reduction and H2evolution) were measured simultaneously in experiments with a flow-through gassing system during 3 months of cold treatment. Net photosynthesis of whole plants was measured in a closed system. More than half the total initial nitrogenase activity and relative efficiency (RE) were lost during the rest period and recovered during regrowth. Acetylene reduction by chilled plants was insensitive to temperature in the 5 – 15 °C range, unlike the temperature dependence of respiration and H2evolution in air. In all temperature profiles of RE the RE was highest at 5 – 10 °C. The RE was minimum 10 – 15 °C during the rest period. The optimum temperature for whole plant net photosynthesis also declined to 10 – 15 °C during chilling and it later flattened out in the cold-acclimated regrowth. Possible mechanisms are discussed.

ISSN:0008-4026    

DOI:10.1139/b89-051

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Seedlings of three cultivars of alfalfa (Medicago sativaL.) were nodulated with two strains of rhizobia (Rhizobium meliloti) and grown with zero N nutrients at 25:20 °C for 6 weeks followed by growth at 10:7 °C for 2 weeks. Acetylene-reducing activity (ARA) was retarded by 10% acetylene to an extent dependent on time, cultivar, strain, and growth temperature. In the usual short term assay for nitrogenase by ARA, the inhibition was not sufficient to explain decreased apparent efficiency of nitrogenase in plants moved to the lower temperature. Inhibition of ARA was associated with correspondingly decreased respiration in cv. Drylander, but in cv. Apollo respiration was not affected. The differential loss of ARA relative to respiratory activity in a day of continuous treatment with 10% acetylene was very distinct and requires an explanation other than altered nodule resistance to diffusion of oxygen.

ISSN:0008-4026    

DOI:10.1139/b89-052

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Seeds of four alfalfa cultivars were grown and the plants cloned by rooting cuttings. Individual plants were root-dip inoculated withVerticillium albo-atrumReinke and Berthold, and scored for relative pathogen resistance by symptom evaluation and reisolation of the fungus during a 7-month period. Nine individual plants were selected: two were resistant to colonization and symptom expression, two remained colonized but were resistant to symptom expression, and five were susceptible. Disease-free cuttings of each selected plant were infused with a mixture of conidia and red vinyl particles which mark primary spore trapping sites. At 168-h postinoculation the colonization ratio was determined for each sample. The colonization ratio is a reliable quantitative measure of invasiveness which is calculated by scoring a section of tissue for the number of secondary colonization sites established per primary trapping site in a given unit of time. The colonization ratio values of the nine selected plants were correlated with the level of disease resistance as determined by two methods: (i) symptom evaluation and pathogen resiolation, and (ii) genetic S1analysis. The colonization ratio, a new measure of fungal invasiveness and host resistance, might be useful in the breeding and assessment of alfalfa cultivars with resistance to Verticillium wilt.

ISSN:0008-4026    

DOI:10.1139/b89-053

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

As part of comparative studies of stromata in the Sclerotiniaceae, mature sclerotial and substratal stromata produced in vitro by 19 species, and 1 form-species, representing 13 genera and 1 form-genus, were examined using light microscopy and histochemical staining. Sclerotial-stromatal taxa wereSclerotinia sclerotiorum,S.trifoliorum,S.minor.Sclerotium cepivorum,Botrytis cinerea,B.porri,Dumontinia tuberose,Ciborinia erythronii,Myriosclerotinia dennisii,M.borealis,Monilinia fructicola, andStromatinia gladioli. Substratal-stromatal taxa wereLambertella subrenispora,Lanzia luteovirescens,Rutstroemia sydowiana,Stromatinia gladioli,Ovulinia azaleae,Sclerotinia homoeocarpa,Scleromitrula shiraiana, andCiboria acerina. Histochemical staining, particularly 0.05% toluidine blue O in benzoate buffer at pH 4.4, was found to be useful in demarcating the zones within stromata: rind, cortex, and medulla. All sclerotia contained extensive reserves of carbohydrates in thick cell walls and copious extracellular matrix, while protein bodies were usually the major cytoplasmic storage reserve. A group of saprophytic, substratal isolates had thin medullary cell walls and less extracellular matrix, and did not store protein but stored large deposits of lipid in cytoplasm. A group of phytopathogenic, substratal-stromatal isolates appeared to be transitional, with anatomical features and extensive cytoplasmic protein body reserves suggesting that they produce indeterminate sclerotial stromata rather than true substratal stromata.

ISSN:0008-4026    

DOI:10.1139/b89-054

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

As part of comparative anatomical, histochemical, and ultrastructural studies of stromata in the Sclerotiniaceae, mature stromata produced in vitro by 11 species representing six genera and one form-genus were examined using transmission electron microscopy. Sclerotial-stromatal taxa wereSclerotinia sclerotiorum,S.trifoliorum,S.minor,Sclerotium cepivorum,Botrytis cinerea,B.porri,Monilinia fructicola, andMyriosclerotinia borealis. Substratal-stromatal taxa wereSclerotinia homoeo-carpa,Rutstroemia sydowiana, andLambertella subrenispora. Three types of rind were observed: a living cellular rind, a dead cellular rind, and a stromatal rind. Sclerotial species were distinguished from stromatal species not only by the rind type, but also by the confluent extracellular matrix around cortical and medullary cell walls. Presence of lacunae in this matrix distinguishedSclerotiniaspp. andM.borealisfromBotrytisspp. andMonilinia fructicola. Rind, cortical, and medullary cells contained abundant storage vacuoles in most taxa. The distribution and proportion of organelles to storage vacuoles differed among taxa. Plugged septal pores with associated Woronin bodies were similar among the taxa where they were observed. Sclerotia ofSclerotium cepivorum, which has no known teleomorph, are ultrastructurally most like sclerotia ofSclerotiniaorBotrytisanamorphs ofBotryotiniaspecies. Substratal stromata ofS.homoeocarpashowed unusually complex cellular organization. Sclerotial stromata ofM.fructicolacontained unusual storage vacuoles with heterogeneous contents.

ISSN:0008-4026    

DOI:10.1139/b89-055

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The erect, upright shoots ofStromatopteris moniliformisMet., a gleicheniaceous fern endemic to New-Caledonia, are studied morphologically and histologically. The shoots are produced by an underground branching system (not studied) and traverse the soil litter. They form dormant buds in their lowermost part and several leaves in the upper part, before the terminal meristem degenerates. Afterwards, the dormant lateral buds start to develop, successively and basipetally, toward the soil litter surface. These also produce dormant buds in their lowermost part and some leaves distally. This fern, therefore, has a bushlike form of dense branching axes, with leaves confined to the tip, unique in this group.

ISSN:0008-4026    

DOI:10.1139/b89-056

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Isoenzymic composition of superoxide dismutases (SODs; EC 1.15.1.1) of legume nodules has been examined by using polyacrylamide gel electrophoresis. The study reveals that Cu plus Zn–SODs and Mn–SODs are widespread in the plant and bacteroidal fractions of nodules, respectively. The number of CuZn–isoenzymes, however, depends on the legume species: three or four inLupinus, three inPhaseolus, two inVigna, and one inGlycine,Trifolium,Pisum, andMedicago. The nodule plant fraction also exhibits Mn–SOD activity, which is, at least inMedicago, of plant origin. Two Mn–isoenzymes are present in most bacteroids as well as in all slow-growing rhizobia, but just one was observed in fast-growing rhizobia. Fe–SOD has not been found in free-living or symbiotic rhizobia. A faint CuZn–SOD activity was detected in the bacteroid fraction ofPhaseolus,Trifolium,Lupinus, andVigna. The high content and complex pattern of SOD isoenzymes in the host cells and bacteroids (despite their relatively anaerobic environment) indicate a substantial production ofin nodulesin vivo, and the necessity for nitrogenase and leghemoglobin protection.

ISSN:0008-4026    

DOI:10.1139/b89-057

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Embryos ofPicea abieswere pulse-treated with benzyladenine for 24 h and then cultured on medium lacking growth regulators. Meristemoids developed on all embryos during the 2nd week after the cytokinin treatment. Cells within the meristemoids divided randomly. As the meristemoids developed, further cell divisions became more organized so that separate regions of meristematic activity could be distinguished within each meristemoid. These meristematic regions developed into individual nodules and each nodule developed further into either a bud meristem or a cataphyll. Cataphylls were composed of unorganized, vacuolated, thick-walled cells whereas bud meristems were composed of organized meristematic cells. Later, xylem elements developed at the base, and needle primordia at the top of bud meristems. The bud apex had cytohistological zonation typical of conifers. The appearance of the developing adventitious buds depended on the number of cataphylls formed per bud as well as on the marginal expansion of the cataphylls.

ISSN:0008-4026    

DOI:10.1139/b89-058

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Substomatal vesicle development ofUromyces transversalison its host, gladiolus, was studied with a scanning electron microscope. Development after penetration occurred in distinct stages; the single infection peg developed into a globose immature substomatal vesicle, which initiated, singly or in pairs, primary hyphae that frequently developed asynchronously. One of the observed elongated primary hyphae delimited a haustorial mother cell. Observations on the orientation of the long axis of the substomatal vesicle in relation to the stomatal slit showed development of the primary hyphae at right angles rather than acute angles or parallel. A similar trend was observed in the substomatal vesicle formed in a nonhost, corn.

ISSN:0008-4026    

DOI:10.1139/b89-059

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Populations of twigs (1-year-old, current branch segments) had similar frequency distributions of twig lengths on branches of five tree species (Quercus coccinea,Acer rubrum,Picea rubens,P.abies,Pinus strobus). The modal number of twigs for each of the species was in the 1, 2, 3, or 4 cm length class, with an exponential decrease in twig number through the 6- to 10-cm class plus a few longer twigs. These characteristic twig frequency distributions developed within the first decade of the life of a branch and were retained as the twig population size changed. Old branches had twigs only less than 5 cm long. The number of new twigs increased as their parent's (2-year-old segments, last year's growth) lengths increased. On parents with more than one twig the terminal twig was longest. Length of the shortest twig, furthest from the terminal, generally increased as parent length increased, but, inAcer rubrum, stayed less than 1 cm. Frequency distributions were determined for the lengths of terminal twigs from parents less than 5 cm long. Mortality of parents in conifers was first indicated when they produced no twigs. A simple computer model simulated growth of twig populations using equations and probabilities to calculate the number and lengths of new twigs formed by parents.

ISSN:0008-4026    

DOI:10.1139/b89-060

出版商:NRC Research Press    

年代:1989

数据来源: NRC