摘要:

Root hairs ofElodea canadensisdevelop only from cells which undergo a particular series of developmental steps. These cells, the trichoblasts, are formed as the smaller, proximal product of an asymmetric division, and immediately enter a prolonged phase of synthesis. Histochemical tests show that large amounts of RNA and protein accumulate in the vastly enlarged nucleolus and cytoplasm, while histone increases in the enlarging nucleus. Cytophotometry shows that DNA in the nucleus reaches polyploid levels. Throughout the synthetic phase, almost to the point of root hair initiation at 9.5 mm proximal to the meristem initials, vacuolation is delayed and the trichoblasts elongate less extensively. All results suggest that this synthesis is the type which normally follows cell division, but is greatly enhanced in the trichoblast. In contrast, the initially larger atrichoblasts only accumulate RNA, DNA, and protein in the region from 1 mm to 2 mm proximal to the meristem tip, and they then enter a phase of extensive vacuolation and elongation.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06142.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Chloroplast development during sporogenesis inMnium cuspidatum, M. medium, M. rostratum, Aulacomnium heterostichum, Bartramia pomiformis, andTimmia megapolitanais as follows: During the early mitotic divisions in the sporogenous area of the capsule the number of plastids is reduced from many to one cup‐shaped plastid per sporogenous cell. This single plastid divides during the early spore‐mother‐cell stage. A second division of plastids produces four plastids within each spore‐mother‐cell. A massive accumulation of starch occurs within each of the four plastids. Following meiosis, the single plastid allocated to each spore produces distinct lobes that are “blebbed” off as proplastids. A photosynthetic membrane system is established within the many proplastids as each spore matures.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06143.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Petrified specimens of pteridosperm foliage assignable toReticulopteris muensteri(Eichwald) Gothan andNeuropteris rarinervisBunbury were found in a Middle Pennsylvanian age coal ball from central Iowa. The presumed close affinity of these two foliage taxa is supported by various anatomical similarities including hydathode‐like vein terminations and non‐papillate lower epidermises with high stomatal density. Comparison of the foliar anatomy of these neuropterids to that of the xeromorphic taxaAlethopteris sullivanti(Lesquereux) Schimper andA. lesquereuxiWagner show striking differences which suggest that these neuropterid and alethopterid taxa were adapted to markedly different habitats.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06144.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Initiation of adventitious bud formation in vitro from Douglas fir cotyledons required both cytokinin and auxin at concentrations of 5 μM BAP and 5 nM NAA. Histological observations showed that these adventitious buds arose de novo from cells residing in hypodermal layers. Development of adventitious buds in culture was characterized by the sequential appearance of four anatomically distinguishable structures: 1) meristemoid, 2) bud primordium, 3) shoot apex with needle primordia, and 4) adventitious bud. The anatomical structure of tissue culture‐produced buds was similar to that of vegetative buds produced on intact plants. Cultured cotyledons capable of producing adventitious buds (bud culture) were compared with bud‐callus and callus cultures initiated by 5 μM BAP plus 5 μM NAA and 5μM NAA alone without BAP, respectively. Results showed that, during early stages of the culture period (i.e., prior to the appearance of meristemoid structure), cell division of bud culture was mainly located in hypodermal layers, whereas for the other culture types, bud‐callus and callus cultures, cell division occurred randomly in all tissues.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06145.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Potential sources of fixed nitrogen in a Colorado desert environment were examined by the acetylene reduction method at the Deep Canyon Desert Research Center, near Palm Desert, California. In field and greenhouse studies all members of the generaAstragalus, Dalea, Lotus, Lupinus, Melilotus, andProsopisexamined formed active nodules (acetylene reduction) with indigenous soil bacteria. No evidence of nodulation was foundfor Acacia greggii, Cercidium floridum, orHoffmannseggia microphylla. Lotus tomentelluswas estimated to fix 0.1 kg N ha−1by the time of flowering under field conditions. Several members of the genusDaleashowed substantial rates of acetylene reduction in the greenhouse:D. emoryi, 16.1 + 3.5,D. mollissima, 11.4 + 3.7,D. schottii2.9 + 1.7, D. spinosa2.5 + 0.4 μmoles ethylene plant−1hr−1. In greenhouse assays where water was supplied continuously, blue‐green algal‐lichen crusts reduced acetylene at an average rate of 11.0 + 5.7 nmoles ethylene cm−2hr−1with a maximum of 57.1. But when in situ assays were done following irrigation of a field plot with 2.3 cm of water, much lower activities were observed with a maximum activity of only 6.4 nmoles cm−2hr−1.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06146.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

Two factors which affect leaf ontogeny and ultimate leaf size: (1) the rate and duration of cell expansion, and (2) the rate and duration of cell division, were examined for their role in the slower early leaf growth rate and the smaller size of fully expanded leaves of plants exposed to ultraviolet‐it (UV‐B 280‐320 nm) radiation.Rumex patientiaL. was grown in controlled environment chambers under enhanced UV‐B radiation (equivalent to daily solar UV‐B irradiation at 40°N latitude in mid‐May with an atmospheric ozone concentration of 0.20 atm‐cm) and control treatments. The pattern of growth as expressed in changes of mean cell size in two distinct cell types, tissue cell density, and length of the entire leaf blades are consistent with the hypothesis that the radiation primarily affects cell division rather than cell expansion. Furthermore, it appears that the radiation probably alters the rate rather than the duration of the cell division phase. An understanding of the mechanism of radiation damage should facilitate prediction of how this stress may interact with other stresses to which plants are normally subjected. Species with normally prolonged periods of cell division during leaf expansion may be particularly impacted if solar UV radiation were intensified as a result of atmospheric ozone reduction.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06147.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

The widely used fungicide, benlate, was tested for its effect(s) on gametophyte development in the fernCeratopteris thalictroides(L.) Brongn. The active ingredient of benlate, benomyl, represents 50% of the fungicide by weight. Seven concentrations of benomyl were tested onC. thalictroidesgametophytes: 0, 0.001, 0.01, 0.1, 1.0, 10.0 and 100 mg/l. Five developmental stages were observed for possible effects of benomyl. These were 1) germination, and the initiation of 2) antheridia, 3) notch meristems, 4) archegonia, and 5) sporophytes. Overall inhibition was greatest at 100 mg/l benomyl. At 10 mg/l and 100 mg/l, sporophyte initiation was completely blocked. This was probably the consequence of two characteristics found only on gametophytes growing on medium containing 10 mg/l and 100 mg/l benomyl. These characteristics were lack of sperm motility and production of callus growths in the areas proximal to the notch meristems, just proximal to the younger archegonia. Besides blocking the completion of sexual reproduction, the highest concentrations tested also produced smaller (cell number) and chlorotic gametophytes (especially at 100 mg/l). The bigametophyte population (made up of hermaphroditic and male gametophytes) was changed from 51% hermaphrodites (at 0 mg/l benomyl) to 26% hermaphrodites at 100 mg/l. This would, since only hermaphrodites possess archegonia, also decrease the potential for the production of sporophytes.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06148.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

The genetic control of isozymes fromCitrusand its near relatives was determined for three gene/enzyme systems: glutamate oxaloacetate transaminase, phosphoglucose isomerase and phosphoglucose mutase. These enzymes are controlled by four genes having 19 codominant alleles, 12 of which occur inCitrussubgCitrus. Formal genetic studies were carried out with F, biotypes and F1populations of known origin. When biotypes were grouped into traditionally recognized species to examine genetic affinities within and between species, a remarkable pattern of uniformity of genotype combinations was found within a species, and every species had an unique combination. Because many economically important cultivars produce asexual(nucellar) as well as sexual(zygotic) embryos, a central problem of the breeder is to distinguish these when plants are young, long before fruiting. Isozyme markers can be used with varying degrees of efficiency, depending on the genotypes of the particular parents, to distinguish nucellar seedlings from those of zygotic origin.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06149.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

A new species ofTrigonocarpusBrongniart is described from the level of the Herrin (No. 6) Coal (Carbondale Formation, Kewanee Group) at Carterville, Illinois. The seed is three dimensionally preserved by authigenic cementation and exhibits a well preserved nucellar cast, integument and micropylar region. The specimen represents the largest pteridosperm compression‐impression seed collected in North America and measures 10 cm from the apex of the micropyle to the chalazal end, and at least 5 cm in breadth.Trigonocarpus leeanussp. n. is compared to the remaining forty‐three taxa within the genus, and specifically withTrigonocarpus grandisLesquereux, the one species with dimensions approaching it. An emended diagnosis, with designation of a lectotype, is presented forTrigonocarpus grandis. Correlation of the features displayed byTrigonocarpus leeanussp. n. and the petrified taxa withinPachytestaBrongniart is attempted.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06150.x

出版商:Wiley    

年代:1978

数据来源: WILEY

摘要:

During years with good winter rainfall, ephemeral plants can contribute considerably to primary production in the upper Sonoran Desert. This study was designed to compare ephemeral community productivity and production efficiency within the different microhabitats created by trees, shrubs and open spaces in a Sonoran Desert ecosystem. Ephemerals were periodically harvested in the different habitats and dried for biomass and caloric determinations. The caloric data were compared to total solar input into the different microhabitats in order to determine production efficiencies of each stand. Productivity rates were also determined for the total community for the sample period, winters of 1972‐74. Both productivity and production efficiency were highest under the shade ofCercidium. The highest production efficiency occurring in the shaded sites was 5.03% which approaches the theoretical maximum photosynthetic efficiency level. The production efficiency of the entire ephemeral community for the whole growing season was only 0.17% during an optimal year, demonstrating the influence of the environment in the interspaces on productivity and solar conversion in the desert.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1978.tb06151.x

出版商:Wiley    

年代:1978

数据来源: WILEY