摘要:

Xylem parenchyma transfer cells are present in the stele of the root tissue adjacent to emergent effective root nodules of garden pea (Pisum sativum), red kidney bean (Phaseolus vulgaris), broad bean (Vicia faba), soybean (Glycine max), and mung bean (Vigna radiata), two types of ineffective pea nodules, and emergent lateral roots of pea. The xylem parenchyma transfer cells contain many polyribosomes and mitochondria near the wall ingrowths which are located adjacent to pits in the xylem elements. Pericycle transfer cells also occur in the three types of pea nodules. In effective pea nodules wall ingrowths begin to form in the pericycle cells 5 days after inoculation withRhizobium leguminosarum; at this stage rhizobia are only present in the root hair but the cortical cells have enlarged and some have undergone mitosis. The wall ingrowths begin to form in the xylem parenchyma cells 7–8 days after inoculation or the approximate time that rhizobia begin to be released from the infection thread. In both instances the wall ingrowths begin to form before the onset of dinitrogen reduction although previous workers have suggested that a flux of nitrogenous compounds (containing fixed N) induces their formation. The development of wall ingrowths in ineffective pea nodules also occurs independently of nitrogen fixation. Similarly, the wall ingrowths located near soybean nodules also begin to develop before the onset of nitrogen fixation.

ISSN:0008-4026    

DOI:10.1139/b79-308

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The development of preemergent and early emergent stages of soybean (Glycine max) and garden pea (Pisum sativum) root nodules has been studied utilizing the superior preservation and resolution obtained by noncoagulative fixatives and subsequent embedding in plastic. In both species, extensive mitotic activity and cytological changes occur in the root cortical cells while the infection thread is restricted to the infected root hair cell. In soybean the central mass of infected tissue is derived mainly from the outer layer of cortical cells whereas the inner cortical cells contribute extensively to the infected tissue of the pea nodules. The temporal and spatial patterns of mitosis differ in the nodules of the two species. Mitotic activity is restricted to a nodule meristem and occurs over a period of many weeks in pea nodules. In soybean nodules, mitotic activity occurs throughout the central zone and before decreasing, persists over a period of a few weeks. The timing and distribution of mitotic activity affects nodule morphogenesis.

ISSN:0008-4026    

DOI:10.1139/b79-309

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Primary leaves of near-isogenic lines of Chinese Spring wheat, either with or without the temperature-sensitive resistance geneSr6, were inoculated with an avirulent race of stem rust, maintained at 19, 26, or 28 °C, and harvested 1–4 days after inoculation. The infected tissues were examined with an electron microscope to determine the effects of these temperatures on the expression of theSr6gene. At 26 °C in theSr6line about one-half of the haustoria in mesophyll cells were disorganized or collapsed. None of the haustoria in epidermal cells showed any structural abnormality. In the susceptible (sr6) line, most haustoria were structurally normal at 26 °C whether they were in mesophyll or epidermal cells. There were no signs of disorganization or necrosis of infected host cells of either (Sr6orsr6) line at 26 °C. At 28 °C in both lines, all haustoria in mesophyll cells were necrotic or collapsed, but those in epidermal cells were not. No host cell necrosis was observed in genotypically resistant leaves. At 19 °C, most haustoria and invaded mesophyll cells in theSr6line were necrotic. In the invaded epidermal cells neither haustoria nor host protoplasts were necrotic. In contrast, in a backcross line of Marquis wheat containing resistance geneSr5and infected with an avirulent race, both invaded mesophyll and epidermal cells were necrotic.

ISSN:0008-4026    

DOI:10.1139/b79-310

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The interaction between avirulent wheat stem rust and wheat mesophyll cells containing the temperature-sensitiveSr6gene for stem rust resistance was studied by electron microscopy. Mesophyll cells that were invaded at 26 °C (conditioning compatibility) did not develop any signs of incompatibility after they were transferred to 19 °C, at which temperature incompatibility is normally expressed. In host tissue that appeared to be invaded after the change from 26 to 19 °C, the early ultrastructural symptoms of incompatibility were a more electron-dense and often perforated invaginated host plasmalemma, disruptions of the noninvaginated host plasmalemma, vacuolation of the cytoplasm, and accumulations of electron-dense material along the membranes of the vacuoles. At later stages in the development of incompatible interactions, the electron-dense accumulations along the vacuole membranes increased in size and occurred along chloroplast and mitochondrial membranes. Eventually, the entire protoplasts were electron dense and collapsed. In haustoria and haustorial mother cells, incompatibility was usually expressed by a uniform increase in electron density of the cytoplasm. In theSr6/P6interaction at 19 °C, host cell necrosis was not always accompanied by fungal necrosis orvice versa. InSr5/P5interactions, which were examined for comparison, the intracellular symptoms of incompatibility were similar to those of theSr6/P6interactions.

ISSN:0008-4026    

DOI:10.1139/b79-311

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Reproductive strategies were analyzed in intertidal populations of two seagrasses of the genusZosterato test the application ofr–Kselection theory to a novel habitat.Zostera americanahas appeared in the study area recently and is spreading rapidly. It grows in the mid to upper intertidal regions and is anr-strategist; i.e., a rapidly growing, essentially annual plant that uses a large proportion (up to 25%) of its resources for flowering.Zostera marina, the native eelgrass, grows in the mid to low intertidal regions and is a K-strategist; i.e., a perennial that uses a large proportion of its resources for maintenance via rhizomes and roots. Considering that the environment becomes less predictable for marine plants on a gradient from the lower to the upper end of the intertidal zone, then the two seagrasses behaved as predicted by the theory.

ISSN:0008-4026    

DOI:10.1139/b79-312

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Nitrosoguanidine was used as a mutagenic agent to obtain 4 constitutive and 20 temperature-sensitive mutations ofPhyllosticta maydisfor increased virulence on a single host line. The temperature-sensitive mutants were of three types: those temperature sensitive on agar and not on the host, those temperature sensitive on the host and not on agar, and those temperature sensitive on both agar and the host. These mutations for increased virulence are interpreted to indicate that host–parasitic specificity is for incompatibility, and that increases in virulence involve selected losses in function, rather than gains. The pattern of temperature sensitivity of certain mutants indicates that avirulence may be one pleiotrophic function of genes which otherwise function in support of basic life processes for the organism.

ISSN:0008-4026    

DOI:10.1139/b79-313

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Five distinct forest communities were recognized along a 3-km transect. These are, listed in order of decreasing elevation: (i) open black spruce/feathermoss -Cladonia, (ii) closed black spruce/feathermoss, (iii) open black spruce/Sphagnum, (iv) black spruce woodland/Eriophorum, and (v) whitespruce/alder/Calamagrostis(restricted to a narrow band adjacent to a stream). Several techniques of ordination were used to recognize these five forest communities plus two intergrades: (open black spruce/feathermoss -Cladonia) - (Sphagnum) and open black spruce/Sphagnum- woodland/Eriophorum.The distribution of two-thirds of the plant species was highly correlated with vegetation–slope zones. Results of the fit of Gaussian curves also suggest that vegetation boundaries were well placed. The distribution of the four soil series in the area was well correlated with vegetation–slope zones: three were limited to one zone each. Permafrost, absent from the soil on the ridgetop and upper slope, was generally within 40 to 50 cm of the surface elsewhere and tended to be at shallower depths as elevation decreased. The most striking differences in forest floor properties were found in the white spruce zone compared with the six black spruce dominated zones. The white spruce forest floor was markedly thinner and had higher levels of nutrients. In the six black spruce dominated zones, forest floor thickness and concentrations of N and Mg tended to increase with distance downslope, and P and K decreased.

ISSN:0008-4026    

DOI:10.1139/b79-314

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

In axenic cultures of flax rust (Melampsora lini) colonies are initiated after a lag period of 12–20 days, depending partly on incubation temperatures. Colony initiation is completely inhibited by removal of a volatile factor which is absorbed by KOH in the air space of the culture flask. The fungus remains sensitive to this inhibition for 8–10 days, i.e., until shortly before visible colonies would normally have developed. While in the presence of KOH, the fungus is not killed; cultures grow normally after removal of the KOH.Although conclusive evidence must await further work, the available data strongly suggest that carbon dioxide is responsible for this effect.

ISSN:0008-4026    

DOI:10.1139/b79-315

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Entomophthora canadensisn. sp. is described and illustrated, and its morphological development traced. The new species differs from all other species of the genus, by its distinctively shaped conidia, long–elliptical to nearly cylindrical, average 25.0 μm × 10.0 μm, and its ornamented azygospores, verruculose to lightly rugulose, average 34.0 μm diameter. It is compared withE. aphidis, within which it has been included, andE. sphaerosperma, the species it most closely resembles.Entomophthora canadensisis currently known only from populations of the aphidSchizolachnus piniradiatae, in red pine plantations in Ontario, Canada.

ISSN:0008-4026    

DOI:10.1139/b79-316

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Pollen-cone and seed-cone buds broke dormancy about 2 weeks before vegetative buds on the same tree. Pollen mother cells, which had over-wintered at pachytene or the diffuse stage of meiosis, resumed meiosis and tetrads of microspores were formed by mid-March. Wingless five-celled mature pollen developed by mid-to late April when pollination occurred.When development resumed after dormancy a ring of meristematic tissue formed the integument around the nucellus. The integument tip developed a short abaxial tip and a large adaxial lobe on which developed numerous long stigmatic hairs. A slit-like micropyle remained between the two lips. Several pollen grains usually adhered to the stigmatic hairs and then the two lips grew into the micropyle, engulfing the pollen. No pollination drop was observed. Within the micropylar canal, pollen greatly elongated then formed a pollen tube when the elongated pollen contacted the nucellus.Megaspore mother cells underwent meiosis at the time of pollination. Female gametophyte development, which was the same as in most other members of the Pinaceae, was completed in early June and two to five archegonia were formed. Fertilization occurred in early June, 6 to 8 weeks after pollination. A 16-celled proembryo developed. Simple polyembryony was common but cleavage polyembryony was not observed. Embryo development was similar to other members of the Pinaceae. Embryos and seeds were mature by mid-August.Normal appearing but inviable seed is common inL. occidentalisbecause the ovule is fully enlarged and the seed coat well developed at fertilization. Inviable seed commonly resulted from the absence of pollination, inviable pollen, lack of fertilization, later ovule abortion, or embryo abortion, primarily during early embryonic stages. Flat empty seed also occurred and resulted from abortion of the megaspore mother cell or early female gametophyte.

ISSN:0008-4026    

DOI:10.1139/b79-317

出版商:NRC Research Press    

年代:1979

数据来源: NRC