摘要:

Cucurbita maximacv. Warted Hubbard has large fruits up to 10 kg in weight and its seeds have an average weight of about 0.25 g.Cucurbita andreanahas fruits < 1 kg in weight and its seeds have an average weight of about 0.02 g. Within each species fruit weight was highly variable, while seed weight was quite stable. The overall range of variation in seed weight within both species was about 2.5-fold. Embryos of the species with the small seeds (C.andreana) contained less Ca on a per embryo basis than did those ofC.maxima, but on a per gram basis these small embryos contained three times more Ca than the largerC.maximaembryos. WithinC.maximaembryos, Ca varied as much as fivefold, with heavy and long embryos tending to have less Ca per gram tissue than smallerC.maximaembryos. Calcium concentrations withinC.andreanawere not correlated with embryo size.

ISSN:0008-4026    

DOI:10.1139/b88-204

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Hybrid seeds from crosses betweenCurcurbita maximaandCurcurbita andreanawere similar in weight to the seeds of the maternal parents. The calcium concentrations of the hybrid embryos were significantly different from the Ca concentrations of both parent species and tended toward a level intermediate between that of the two parents. However, the hybrids also differed in Ca concentration from each other and each was more similar to its female parent, indicting some maternal influences on Ca accumulation. There was a significant negative correlation between both embryo weight and embryo length and Ca concentration in hybrid embryos of the large seeds ofCucurbita maxima×Cucurbita andreana. The small seeds ofCucurbita andreana×Cucurbita maximahad embryos in which embryo weight was positively correlated with Ca concentration. In both parent and hybrid embryos the Ca concentration of the axis was higher than the concentration in the cotyledons. The axes of all four kinds of embryos had similar Ca concentrations so that the differences found for whole embryos were due to changes in Ca concentrations in the cotyledons.

ISSN:0008-4026    

DOI:10.1139/b88-205

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Neutron activation analysis was used to measure the concentrations of Mg, K, Ca, and P stored in embryos ofCucurbita maxima,Cucurbita andreana, and their reciprocal hybrids. The embryos contained much higher concentrations of Mg, K, and P than Ca. However, Ca was the only one of the four minerals that was significantly different in the four kinds of embryos. Although all four minerals were stored in higher concentrations in the small root–shoot axes than in the large cotyledons, the proportion of total Ca stored in the axis was higher than the proportion of the other three minerals. P was the predominant mineral in the embryos, K was highest in the seed coats. Differences in mineral concentrations of embryo parts and seed coats indicated a marked selectivity in embryo mineral uptake.

ISSN:0008-4026    

DOI:10.1139/b88-206

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The culture of three colonizing dune species in hydroponics indicated that nitrogen (N), phosphorus (P), and potassium (K) were essential for high plant productivity. The K requirement ofOenothera bienniswas lower than that ofCakile edentulaorCorispermum hyssopifolium. The dry weight per plant ofO.bienniswas greater at higher concentrations of N, P, or K; however, the dry weight per plant ofCor.hyssopifoliumwas similar at all concentrations except in the complete absence of N, P, or K.Cakile edentuladid not grow well under any of the nutrient concentrations, probably because of a poor response to hydroponic solutions. The number of live leaves and leaf area ofO.biennisandCor.hyssopifoliumwere affected more by a lack of N and P than K. The nutrient requirements ofCakile edentulawere substantially higher than those of eitherO.biennisorCor.hyssopifolium. It is suggested that the hierarchy in plant size and seed production in field populations may result from variability of available nutrients.Oenothera biennis, a generalist weedy species of farmland, old fields, waste places, and sandy beaches, was less exacting in its requirements of N, P, and K than the two beach specialists,Cakile edentulaandCor.hyssopifolium.

ISSN:0008-4026    

DOI:10.1139/b88-207

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The ultrastructure of mitosis in the algal flagellatesPavlova lutheriandP.salinahas been examined, the observations have been compared with those reported previously from other species included in the class Prymnesiophyceae, and a number of important differences have been noted. For example, mitosis is preceded by the replication of the chloroplasts and flagellar apparatus, but in contrast to other prymnesiophytes, separation of the replicated systems does not occur until a late stage in cell division. Furthermore, there is a close relationship between the spindle microtubules and the fibrous root of the longer of the two markedly unequal flagella, and instead of the usual straight prymnesiophycean spindle, the longitudinal axis of thePavlovamitotic spindle has a marked U- or V-shape which persists throughout metaphase, anaphase, and telophase. It is concluded that such features emphasize the validity of the order Pavlovales as a natural group within the class.

ISSN:0008-4026    

DOI:10.1139/b88-208

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Mycorrhizal infection of white pine (Pinus strobusL.) seedlings was measured after 4 months of exposure to simulated acid rain and ozone, applied either alone or in combination. Increasing rain acidity consistently reduced the number of mycorrhizal short roots. In general, infection decreased linearly versus rain pH. Plants exposed to simulated rain at pH 3.0 had approximately 20% fewer mycorrhizal roots than plants exposed to pH 5.6 rain. The decrease in the number of mycorrhizal roots was a result of decreases both in the number of short roots available for infection and in the percentage of roots infected. Ozone had no effect on mycorrhizal infection if applied 3 alternate days/week at concentrations ranging from 0.02 to 0.14 ppm. However, there were significant changes in infection in plants exposed to ozone for 5 days/week. There was no evidence for an interaction between the two pollutants. Percent mycorrhizal infection was highly correlated with seedling nitrogen concentration across all soil types and rain treatments. These observations suggest that increases in available nitrogen may have been largely responsible for the observed effects of acid rain on mycorrhizae.

ISSN:0008-4026    

DOI:10.1139/b88-209

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The effects of acid rain and ozone on nutrient relations of white pine (Pinus strobusL.) were assessed for potted seedlings grown in each of five forest soils. Ozone treatments consisted of frequent exposure to 0.02, 0.06, 0.10, or 0.14 ppm ozone, while acid rain treatments consisted of exposure to simulated rain of pH 5.6, 4.0, 3.5, or 3.0. Plants were treated with all combinations of acid rain and ozone levels, and treatments were administered for 4 months. Acid rain caused significant leaching of Ca, Mg, K, Mn, Zn, and Cd from leaf litter on the soil surface, and soil Mg and K content declined as well. Concentrations in needles of N, P, K, Ca, Mn, Cd, and Cr were significantly increased as a result of acid rain treatments. In roots, concentrations of N, Mn, Cd, and Cr were significantly elevated as a result of acid rain. Similar increasing but nonsignificant trends were observed for Mg, Zn, and Cu in needles and for P, K, Mg, Ca, and Cu in roots. However, despite the increases in all the major nutrients, the nutrient weight proportions of K:N, P:N, Ca:N, and Mg:N generally declined in pine tissue as a result of acid rain. Although the above relationships were relatively consistent for pine in all soils, significant differences between soils in response to acid rain were observed for some elements. Ozone had significant effects on K, Ca, and Mn concentrations, and interactions between acid rain and ozone were observed for these three elements. In general, the results of these experiments suggest that the effects of acid rain on tree nutrition may be roughly similar in different soils but that the effects on physiology and growth will be heavily influenced by specific soil properties.

ISSN:0008-4026    

DOI:10.1139/b88-210

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Plant species of wind-exposed tundra sites are usually low lying and slow growing. Such a combination probably reduces competitive ability, perhaps to the point of limiting wind-tolerant species to sites with little or no competition, i.e., the most exposed sites, as if there were a trade-off between adaptation to physical conditions and competitive ability. That hypothesis was tested withSalix uva-ursiPursh, an arctic–alpine species common on windy sites in northern Quebec.Salix uva-ursiincreases in abundance with exposure to wind, contrary to other species, but tolerates, even "prefers", the physical conditions found in sheltered sites. These two observations support the idea that interspecific competition limits the distribution ofS.uva-ursi. However, the vigour ofS.uva-ursi(number and size of shoots) is greatest in the sheltered sites, where the other species are more numerous and vigourous. This apparent contradiction between distribution and vigour could find an explanation in the temporal variations in climate. Under favourable conditions, prostrate and slow growth would be a handicap toS.uva-ursi, compared with other species, whereas under harsh conditions, species sensitive to wind and cold would suffer more thanS.uva-ursi. [Translated by the journal]

ISSN:0008-4026    

DOI:10.1139/b88-211

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Labelled (15N) Scots pine (Pinus sylvestrisL.) needle litter was incubated in one laboratory and two field experiments and the nitrogen dynamics was followed during the decomposition process. Release of the litter's original nitrogen began immediately after the start of the decomposition process. Simultaneously an immobilization of nitrogen to the litter took place. Very little of the actual turnover of nitrogen in the litter, which was considerable, was reflected by the dynamics of total nitrogen. The dynamics of nitrogen in the lignin fraction (acid-insoluble substance) was partly different from that of whole litter. The dynamics of total nitrogen coincided so that a net loss of total nitrogen started simultaneously both in whole litter and in the acid-insoluble fraction. As the amount of acid-insoluble substance increased in the early stage, the amount of15N associated to this fraction increased and when a net disappearance of acid-insoluble substance started, a net release of15N from this fraction started simultaneously. This was interpreted to mean that some of the litter's own nitrogen was transformed into compounds that could be incorporated into humic and fulvic acids (e.g., NH3or amino acids), which were analytically recorded as acid-insoluble substance.

ISSN:0008-4026    

DOI:10.1139/b88-212

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Colonization of root tissues in tomato seedlings genetically resistant toFusarium oxysporumf.sp.radicis-lycopersiciJarvis & Shoemaker occurred following exposure to a sublethal concentration of the herbicide glyphosate (1.0 mM for 24 h prior to inoculation). The glyphosate-induced colonization was associated with an inefficiency in incorporation of phenolic materials into the papillae and into the modified cortical cell walls normally formed in response to this pathogen. Glyphosate-induced susceptibility decreased when the glyphosate was applied at 24 or 48 h after inoculation. Plants supplied with exogenousL-phenylalanine failed to exhibit reduced susceptibility after glyphosate exposure. In radial growth bioassays, growth of the fungus was unaffected by 4.0 mM glyphosate. α-Aminooxyacetic acid, an inhibitor of phenylalanine ammonia lyase, also increased the severity of the disease in resistant plants. Glyphosate also induced susceptibility to an isolate ofF.solanif.sp.pisi, which was normally not pathogenic to tomato.

ISSN:0008-4026    

DOI:10.1139/b88-213

出版商:NRC Research Press    

年代:1988

数据来源: NRC