Enhances their ability to absorb nutrients from their surroundings
Hyphae. The mushroom and its subterranean mycelium are a continuous network of hyphae. Reproductive structure. The mushroom produces tiny cells called spores. Spore-producing structures 20 m Mycelium Figure 31.2
Figure 31.12 Rhizopus growing on bread ASEXUAL REPRODUCTION Mycelium Dispersal and germination MEIOSIS KARYOGAMY PLASMOGAMY Key Haploid ( n ) Heterokaryotic ( n + n ) Diploid Sporangium Diploid nuclei Zygosporangium (heterokaryotic) 100 m Young zygosporangium (heterokaryotic) SEXUAL REPRODUCTION Dispersal and germination Mating type (+) Mating type ( ) Gametangia with haploid nuclei 50 m Sporangia Mycelia have various mating types (here designated +, with red nuclei, and , with blue nuclei). 1 Neighboring mycelia of different mating types form hyphal extensions called gametangia, each walled off around several haploid nuclei by a septum. 2 A heterokaryotic zygosporangium forms, containing multiple haploid nuclei from the two parents. 3 The sporangium disperses genetically diverse, haploid spores. 7 4 This cell develops a rough, thick-walled coating that can resist dry environments and other harsh conditions for months. 5 When conditions are favourable, karyogamy occurs, followed by meiosis. 6 The zygosporangium then breaks dormancy, germinating into a short sporangium. The spores germinate and grow into new mycelia. 8 9 Mycelia can also reproduce asexually by forming sporangia that produce genetically identical haploid spores.
Vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels
(a) The cup-shaped ascocarps (fruiting bodies) of Aleuria aurantia give this species its common name: orange peel fungus. (b) The edible ascocarp of Morchella esculenta, the succulent morel, is often found under trees in orchards. (c) Tuber melanosporum is a truffle, an ascocarp that grows underground and emits strong odors. These ascocarps have been dug up and the middle one sliced open. (d) Neurospora crassa feeds as a mold on bread and other food (SEM). 10 m Figure 31.16a–d
The life cycle of Neurospora crassa, an ascomycete
Figure 31.17 Dispersal ASEXUAL REPRODUCTION Germination Mycelium Conidiophore Germination Dispersal Mycelia Asci Eight ascospores Ascocarp Four haploid nuclei MEIOSIS KARYOGAMY PLASMOGAMY SEXUAL REPRODUCTION Diploid nucleus (zygote) Ascogonium Ascus (dikaryotic) Dikaryotic hyphae Mating type ( ) Conidia; mating type ( ) Key Haploid ( n ) Dikaryotic ( n n ) Diploid (2 n ) Ascomycete mycelia can also reproduce asexually by producing haploid conidia. 7 Neurospora can reproduce sexually by producing specialized hyphae. Conidia of the opposite mating type fuse to these hyphae. 1 A dikaryotic ascus develops. 2 Karyogamy occurs within the ascus, producing a diploid nucleus. 3 The diploid nucleus divides by meiosis, yielding four haploid nuclei. 4 The developing asci are contained in an ascocarp. The ascospores are discharged forcibly from the asci through an opening in the ascocarp. Germinating ascospores give rise to new mycelia. 6 5 Each haploid nucleus divides once by mitosis, yielding eight nuclei. Cell walls develop around the nuclei, forming ascospores (LM).
(a) Fly agaric ( Amanita muscaria ), a common species in conifer forests in the northern hemisphere (b) Maiden veil fungus ( Dictyphora ), a fungus with an odor like rotting meat (c) Shelf fungi, important decomposers of wood (d) Puffballs emitting spores Figure 31.18a–d
The life cycle of a mushroom-forming basidiomycete
Figure 31.20 PLASMOGAMY Dikaryotic mycelium Basidiocarp (dikaryotic) KARYOGAMY Key MEIOSIS Gills lined with basidia SEXUAL REPRODUCTION Mating type ( ) Mating type ( ) Haploid mycelia Dispersal and germination Basidiospores Basidium with four appendages Basidium containing four haploid nuclei Basidia (dikaryotic) Diploid nuclei Basidiospore 1 m Basidium Haploid ( n ) Dikaryotic ( n n ) Diploid (2 n ) Each diploid nucleus yields four haploid nuclei. Each basidium grows four appendages, and one haploid nucleus enters each appendage and develops into a basidiospore (SEM). 6 Two haploid mycelia of different mating types undergo plasmogamy. 1 A dikaryotic mycelium forms, growing faster then, and ultimately crowding out, the haploid parental mycelia. 2 3 Environmental cues such as rain or temperature changes induce the dikaryotic mycelium to form compact masses that develop into basidiocarps (mushrooms, in this case). The basidiocarp gills are lined with terminal dikaryotic cells called basidia. 4 Karyogamy in the basidia produces diploid nuclei, which then undergo meiosis. 5 When mature, the basidiospores are ejected, fall from the cap, and are dispersed by the wind. 7 In a suitable environment, the basidiospores germinate and grow into short-lived haploid mycelia. 8
Are enormously important in natural ecosystems and agriculture
Increase plant productivity
RESULTS RESULTS Researchers grew soybean plants in soil treated with fungicide (poison that kills fungi) to prevent the formation of mycorrhizae in the experimental group. A control group was exposed to fungi that formed mycorrhizae in the soybean plants’ roots. EXPERIMENT The soybean plant on the left is typical of the experimental group. Its stunted growth is probably due to a phosphorus deficiency. The taller, healthier plant on the right is typical of the control group and has mycorrhizae. CONCLUSION These results indicate that the presence of mycorrhizae benefits a soybean plant and support the hypothesis that mycorrhizae enhance the plant’s ability to take up phosphate and other needed minerals. Figure 31.21