Thallus cortex

Garty, J., Karary, Y., Harel, J., Lurie, S., 1993b. Temporal and spatial fluctuations of ethylene production and concentrations of sulfur, sodium, chlorine and iron on/in the thallus cortex in the lichen Ramalina duriaei (De Not.) Bagl. Environ. Exp. Bot. 33, 553-563. 

Two vanadium bromoperoxidases that differ in carbohydrate content [26,33] have been isolated from A. nodosum. The most abundant bromoperoxidase, V-BrPO-I, was found in the thallus, and the other bromoperoxidase, V-BrPO-II, was reported to be present on the thallus surface [26], A previous report also concluded that V-BrPO is present in two different locations of A. nodosum, one in the cell walls of the transitional region between the cortex and medulla of the thallus and the other in the cell wall of the thallus surface [34], More recent experiments demonstrate that vanadium-dependent bromoperoxidase activity is present in both the cortical and surface protoplasts of M. pyrifera [35], L. saccharina, and L. digitata [36], The biosynthesis of V-BrPO in the protoplasts of L. saccharina has been shown using [35S]-methionine [36], The vanadium bromoperoxidases are all acidic proteins [26] with very similar amino acid compositions [37], V-BrPO (A. nodosum) has been crystallized, although refined structural data have not been reported yet [38], A different isolation procedure, based primarily on a two-phase extraction system, has been described [39,40], This procedure works well for certain types of algae (e.g., Laminaria) but not for the isolation of V-BrPO from A. nodosum, the principal source of V-BrPO for the mechanistic studies. 

Spot test This test has been used universally as rapid, nrm-specific means for detecting the presence of certain unspecified lichen substances. This test is most convenient and simple to perform, even under field conditimis. However, this is only a preliminary step in the process of identification of lichens or its substances. In order to identify accurately the secondary metabolite present in the lichen thaUus, one has to perform more sensitive test such as TLC or HPLC. Spot test is carried out by placing a small drop of reagent on the lichen thallus, either directly on the upper surface (cortex) or on the medulla. In the later case, the cortex is scraped or superficially cut with the help of a blade. The reagents used are 10 % aqueous KOH solution (K), saturated aqueous solution of bleaching powder (NaOCla) or calcium hypochlorite (Ca(OCl)2) (called as Q and 5 % alcoholic... 

The habit of a lichen is due not only to the overall growth form, but is often the result of special anatomical characteristics. For example, the shape of the thallus surface depends on the anatomy of the cortex. External appearance and internal structure are interdependent. 

Most lichens are more complex in structure. The algae are restricted to a particular layer in the thallus and besides the algal zone there is at least one other defined layer, the medulla, which contains no algae. Other layers, a cortex for example, may also be developed. These thalli with a stratified organization are called heteromerous (Fig. 93). 

Vegetative Structures of the Cortex. The anatomy of the lower cortex of the thallus can differ from that of the upper cortex even in the same species. The shape of the outermost cells of the cortex has an important influence on the habit of the lichen. The surface is often covered with a thin homogenous cuticle, but in a number of lichens the outermost cells... 

The layers of the thallus—upper cortex, algal layer, medulla, and lower cortex—are more or less present in all heteromerous lichens. Those lichens with a radially organized thallus are no exception. Here the only difference is... 

In Umbilicaria pustulata the cortex of the isidia (Fig. 96) is not formed secondarily but the cortex of the thallus grows upwards and surrounds the medullary tissue from their initiation. 

In Peltigera the Nostoc symbionts of the cephalodia come from outside the thallus and are trapped by hairs on the surface of the thallus (Darbishire, 1927). The algae fall on the thallus and stimulate the growth of the hairs which envelope them (Fig. 131). More hyphae then participate resulting in the formation of the cephalodium (Fig. 132). This older cephalodium seems to stand on stilts (Fig. 133). In its lateral layer a cortex is differentiated. The cortex of the thallus disintegrates beneath the cephalodium and a direct contact between medullary hyphae and cephalodium thus is achieved. 

Internal cephalodia are formed in a similar manner. Here, too, the algae are trapped by the hyphae of the cortex (Jordan, 1970 Jordan and Rickson, 1971 Moreau, 1928). They are enmeshed by a thick layer of fungal cells and pressed into the thallus, where the cephalodium is eventually formed (Fig. 126). The enmeshing hyphae form a bundle which pushes the algae inside. Usually, the algae penetrate via the lower surface of the thallus but sometimes they seem to enter via the upper surface of the lichen. If this happens the cephalodium lies above the algal layer, which is pushed deeper into the medulla (Fig. 127). 

Many of the types of tissues and cells found in the cortex and medulla of lichens are present also in the fruiting body, especially in the exciple. These structures are treated in Chapter 2 but there are some examples of the way these tissue types may become altered in the anatomy of the thallus adjoining the ascocarp. 

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