Developmental and cytological studies in the Rhodophyceae

Knaggs, Fred W (1963) Developmental and cytological studies in the Rhodophyceae. PhD thesis, University of Glasgow.

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The present studies have been concerned with the ecology, morphology, cytology, and life-history of two members of the genus Rhodochorton; R. floridulum (Dillwyn) Mg., and R. purpureum (Lightf.) Rosenvinge, both of which are of common occurrence on the shores of Britain. Rhodochorton floridulum. The general ecology of the species was inVesti sites: Ardneil Bay (Ayrshire) and Portmahomack Bay (Easter Ross) and compared with that observed at other sites in Scotland and England. These surveys were found to correspond with published information concerning the ecology of the species in other parts of its geographical distribution. It has been observed that the morphology of the species is subject to environment three distinct ecological forms can be recognised: the mound form, typically found on rocks in the mid-littoral region; of gently Sloping sheltered sand beaches; the low-lying mat form, commonly found at low water mark and below, as well as on more exposed shores, and the pendant form, confined to vertical rock surfaces in sheltered 4 localities. The species has been found to be more morphologically complex than had previously been thought, and branches of specialised function, responsible for the form And compactness of the plant as well as its ability to bind sand, can be recognised. The species has been cultured under controlled conditions in order to provide a continuous supply of material suitable for Cytological examination and to enable the investigation in vitro of the life-history. It has been observed that under certain conditions of culture which promote vigorous vegetative growth sporangial degeneration occurs, and preliminary experiments have shown that if the cultures are screened with solutions of various dyes this degeneration may be prevented. This suggests that certain inhibitory wavelengths of light are present in the incident radiation, possibly wavelengths in the region of 515mu since eosin yellow which absorbs strongly in this region has been shown to be effective in preventing degeneration. The germination of the totraspores has been followed in culture. The microscopic plants which they produce are dioecious and bear sexual organs similar to those of other Florideae. Although these plants remain healthy for many months fertilisation does not appear to occur readily under the conditions of culture and the form of the carposporophyte is consequently unknown. It is of interest that in external form the plants are similar to certain species of Acrochaetium, though the chromatophore is of the type characteristic of floridalum. Using acetocarmine as a nuclear stain the number of chromosomes in the cells of the tetrasporophyte has been shown to be in the region of 20, and meiosis has been observed in the ,formation of. the spores. The nuclear cycle is therefore diplohaplontic. The life history may be of an unusual and unrecorded type involving a aplohaplontic nuclear cycle and.a trimorphic somatic cycle. If the discovery of the carposporophyte confirms the existence of such a cycle R. floridululcan be, placed close to that group of algae, having a similar nuclear cycle together with a diphasic somatic cycle (in which the tetresporophyte and the gametophyte are morphologically similar). It is possible that either of these life histories represents the evolutionary precursor of the other. Rhodochorton purpureum. R. purpureum has been described by earlier authors as occurring in a number of ecological forms over a wide range of ecological conditions. The present study has confirmed the ecological and morphological adaptability of the species. The forms studied in the field have been cultured in the laboratory under conditions similar to those developed for R. Floridulum, and it has been observed that under constant and identical, conditions the forms undergo morphological modification such that the original differences between them are progressively reduced. The result of these changes is such that Smaller forms, e.g. forma purpureum and globosa develop Characters similar to the larger forma intermedium. The smaller forms may therefore be Considered to be ecologically stunted rather than genetically determined. Since it has been observed that features such as cell length and breadth, branching at the presence or absence of tetrasporangia may be influenced by culture, these features appear to be of little value as taxonomic characters within the group. The chromosome complement of the somatic cells of the tetrasporophyte has been shown to be in the-region of A), while that of the spores is half this number. It seems likely, therefore, that reduction division takes the sporangium end that the nuclear cycle is diplehaplontio. Only the early stages of spore germination have been soon and consequently the nature of the plants to which they give rise is unknown. It seems likely however that they will be morphologically dissimilar to the tetrasporophytc so that the life-cycle may be similar to that of R. floridulum.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: E Conway
Keywords: Botany
Date of Award: 1963
Depositing User: Enlighten Team
Unique ID: glathesis:1963-73182
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56

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