Red Alga Griffithsia Pacifica Research Articles

Cytological damage to the red alga Griffithsia pacifica from ultraviolet radiation

Cytological damage to the red alga Griffithsia pacifica from ultraviolet radiation

The solution to the cytological paradox of isomorphy.

Cells with polyploid nuclei are generally larger than cells of the same organism or species with nonpolyploid nuclei. However, no such change of cell size with ploidy level is observed in those red algae which alternate isomorphic haploid with diploid generations. The results of this investigation reveal the explanation. Nuclear DNA content and other parameters were measured in cells of the filamentous red alga Griffithsia pacifica. Nuclei of the diploid generation contain twice the DNA content of those of the haploid generation. However, all cells except newly formed reproductive cells are multinucleate. The nuclei are arranged in a nearly perfect hexagonal array just beneath the cell surface. When homologous cells of the two generations are compared, although the cell size is nearly identical, each nucleus of the diploid cell is surrounded by a region of cytoplasm (a "domain") nearly twice that surrounding a haploid nucleus. Cytoplasmic domains associated with a diploid nucleus contain twice the number of plastids, and consequently twice the amount of plastid DNA, than is associated with the domain of a haploid nucleus. Thus, doubling of ploidy is reflected in doubling of the size and organelle content of the domain associated with each nucleus. However, cell size does not differ between homologous cells of the two generations, because total nuclear DNA (sum of the DNA in all nuclei in a cell) per cell does not differ. This is the solution to the cytological paradox of isomorphy.

An investigation of the role of transcellular ion currents in morphogenesis ofGriffithsia pacifica Kylin

Transcellular ion currents are thought to play a role in the induction and maintenance of localized growth in plant cells. In the marine red algaGriffithsia pacifica, two types of cells elongate by localized tip growth, rhizoidal and repair shoot cells. The pattern of growth and morphogenesis in these cells can be altered by environmental and hormonal parameters. We examined the role of localized currents in four developmental processes inG. pacifica: 1. normal elongation of rhizoids, 2. the phototropic response of rhizoids, 3. the re-initiation of growth in dark-starved rhizoids, and 4. morphogenesis of repair shoot cells in the presence and absence of rhodomorphin, an endogenous hormone which regulates growth of these cells.

CHLOROPLAST STRUCTURE AND PIGMENT COMPOSITION IN THE RED ALGA GRIFFITHSIA PACIFICA: REGULATION BY LIGHT INTENSITY1

SUMMARYThe ratio of accessory phycobiliproteins to chlorophyll a is controlled by light intensity in the marine red alga Griffithsia pacifica. The greatest changes in pigment ratios are observed below 300 ft‐c; above 300 ft‐c the response approaches saturation. Ultrastructural examination of chloroplasts of plants grown at different intensities reveals that the number of phycobilisomes per unit of photosynthetic thylakoid changes in direct proportion to the pigment ratios and in inverse proportion to the light intensity.

Cell repair through cell fusion in the red alga Griffithsia pacifica.

When an intercalary shoot cell of the red algaGriffithsia pacifica is killed, the cell may be replaced through the wound-healing process of cell repair. During cell repair the cells on either side of the dead cell cut off new cells towards the dead cell. The superjacent cell produces a rhizoid; the subjacent cell produces an atypical shoot cell. The two new cells grow towards each other through the lumen of the dead cell. When they meet, they fuse; the resulting cell expands laterally to fill the cavity of the dead cell and is transformed into a typical intercalary shoot cell, morphologically and physiologically indistinguishable from the killed cell it replaces. The entire cell repair process takes 24–30 hours. Three aspects of cell repair suggest that intercellular communication occurs across the dead cell; these are a precocious division of the cell below the dead cell, a reversible change in the morphology and growth of the shoot cell which participates in repair, and a definite attraction between the two cells which fuse. Thus during cell repair we find evidence not only for cellular redifferentiation through cell fusion, but also for extracellular substances which change pathways of morphogenesis.

Development in the red alga, Griffithsia pacifica: Control by internal and external factors

Development in the red alga Griffithsia pacifica is affected by both external and internal factors. Under 16:8 photoperiods, both cell division and cell elongation show a diurnal rhythm. The rhythm of division persists for at least 7 cycles in continuous light, and can be reset; this indicates that the timing of cell division is controlled by an endogenous rhythm. Both cell division and elongation require light, but the rate of division of apical cells and the rate of cell elongation are both relatively insensitive to either light intensity or photoperiod. In contrast. division in nodal cells, which leads to branch formation, is strongly promoted by high light intensity or long photoperiods. By manipulating the conditions of illumination, one can obtain Griffithsia plants varying from unbranched to highly branched.

Morphogenesis in the red alga, Griffithsia pacifica: Regeneration from single cells

The regeneration of plants of the red alga Griffithsia pacifica from single, isolated cells is described. Regeneration can start from any cell and is triggered by the removal of an abutting cell. An isolated, single shoot cell forms a shoot and a rhizoidal cell within one day. The shoot then adds new cells by apical division at the rate of 1-2 cells/day; branches are formed at predictable but not fixed locations by budding of subapical cells. Each shoot cell enlarges for 6-8 days. The resulting plant consists of uniseriate, pseudodichotomously-branched shoot filaments with multicellular rhizoidal filaments at their base. The predictability and rapidity of this development combined with the large size of these cells (1.0×0.2 mm) facilitate developmental studies on this organism.

Properties of septal plugs from the red alga Griffithsia pacifica

Septal plugs from the marine red alga Griffithsia pacifica were freed intact from a clean cell wall fraction with cellulase, then isolated. Cytochemical data indicate that the plugs are composed of...