Gymnosperms Cycads

Cycads are evergreen palm-like plants, from 10 cm to 20 m in height, which once dominated the Earth's forests but are now restricted to subtropical and tropical regions of mostly the southern hemisphere (Brenner et al. 2003; Vessey et al. 2005). Cycads produce coralloid (coral-like) roots (Fig. 4a) that become infected with heterocystous cyanobacteria (Costa and Lindblad 2002; Lindblad and Costa 2002; Vessey et al. 2005; Lindblad 2009) usually from the genus Nostoc, although

Amfigastri Polytrichum

Fig. 2 The liverwort and hornwort symbioses. (a) Fluorescence micrograph of the hornwort Phaeoceros sp. stained with calcofluor, showing the slit-like entrances (one of which is arrowed) through which hormogonia gain entry to the slime cavities beneath. (b) View of the underside of an Erlenmeyer flask containing the liverwort Blasia pusilla grown free of cyanobacteria in shaken liquid medium. (c) Blasia pusilla growing in liquid culture showing three auricles infected in the laboratory with two different Nostoc strains, one brown pigmented (the two auricles to the left) and the other blue-green. (d) Fluorescence micrograph of uninfected Blasia stained with calcofluor. A single auricle can be seen with one inner (lower arrow) and one outer (upper arrow) slime papilla. Bars 50 mm. Photographs (a) and (d) courtesy of S. Babic. (a) and (d) reproduced with permission from Adams (2000) (b) reproduced with permission from Adams (2002a) (c) reproduced with permission from Adams and Duggan (1999)

Fig. 2 The liverwort and hornwort symbioses. (a) Fluorescence micrograph of the hornwort Phaeoceros sp. stained with calcofluor, showing the slit-like entrances (one of which is arrowed) through which hormogonia gain entry to the slime cavities beneath. (b) View of the underside of an Erlenmeyer flask containing the liverwort Blasia pusilla grown free of cyanobacteria in shaken liquid medium. (c) Blasia pusilla growing in liquid culture showing three auricles infected in the laboratory with two different Nostoc strains, one brown pigmented (the two auricles to the left) and the other blue-green. (d) Fluorescence micrograph of uninfected Blasia stained with calcofluor. A single auricle can be seen with one inner (lower arrow) and one outer (upper arrow) slime papilla. Bars 50 mm. Photographs (a) and (d) courtesy of S. Babic. (a) and (d) reproduced with permission from Adams (2000) (b) reproduced with permission from Adams (2002a) (c) reproduced with permission from Adams and Duggan (1999)

Calothrix spp. have been reported on a number of occasions (Costa and Lindblad 2002; Rasmussen and Nilsson 2002; Bergman et al. 2007a, 2008; Gehringer et al. 2010; Thajuddin et al. 2010). Single or multiple strains can infect a coralloid root (Zheng et al. 2002; Costa et al. 2004; Thajuddin et al. 2010) although some Nostoc spp. can be dominant and, at least in the cycad genus Macrozamia, there seems to be little host specialisation by cyanobionts in the field (Gehringer et al. 2010).

Coralloid roots grow out from the tap root, and then upwards, sometimes breaking the soil surface. The mechanism by which the cyanobacteria enter the roots is unknown, although suggestions include lenticels and breaks in the dermal layer (Costa and Lindblad 2002; Vessey et al. 2005; Bergman et al. 2007a) possibly resulting from degradation of the cell wall caused by bacteria and fungi in the cycad

Amfigastri Polytrichum

Fig. 3 The hornwort Leiosporoceros dussii with symbiotic Nostoc. (a) To the left is a young rosette and to the right an older thallus with numerous upright sporophytes. (b) Dark green Nostoc "strands" (arrows) can be seen within the thallus, parallel to the main axis. S sporophyte. (c) Light micrograph of a nearly transverse section of two mucilage clefts (arrows), which provide the entry point for cyanobacterial infection; the Nostoc filaments subsequently spread through channels created by the separation of cells along their middle lamellae. (d) Scanning electron micrograph of a mucilage cleft. Bars 10 mm in (a), 2 mm in (b), 15 mm in (c) and 20 mm in (d). Reproduced with permission from Villarreal and Renzaglia (2006)

Fig. 3 The hornwort Leiosporoceros dussii with symbiotic Nostoc. (a) To the left is a young rosette and to the right an older thallus with numerous upright sporophytes. (b) Dark green Nostoc "strands" (arrows) can be seen within the thallus, parallel to the main axis. S sporophyte. (c) Light micrograph of a nearly transverse section of two mucilage clefts (arrows), which provide the entry point for cyanobacterial infection; the Nostoc filaments subsequently spread through channels created by the separation of cells along their middle lamellae. (d) Scanning electron micrograph of a mucilage cleft. Bars 10 mm in (a), 2 mm in (b), 15 mm in (c) and 20 mm in (d). Reproduced with permission from Villarreal and Renzaglia (2006)

rhizosphere (Lobakova et al. 2003). The cyanobionts occupy a mucilage-filled zone between the inner and outer cortical layers (Fig. 4b). Although coralloid roots develop in the absence of cyanobacteria, infection induces morphological alterations (Sect. 5.4) which increase the area of contact between plant cells and the cyanobiont, to enhance nutrient exchange (Adams 2000; Rai et al. 2000; Costa and Lindblad 2002; Lindblad 2009).

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Responses

  • tiblets welde
    Where does Leiosporoceros dussii (plant) grow?
    3 years ago

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