Browsing by Author "VARELA, D"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    ABIOTIC CONTROL OF REATTACHMENT IN GELIDIUM-CHILENSE (MONTAGNE) SANTELICES-AND-MONTALVA (GELIDIALES, RHODOPHYTA)
    (1994) SANTELICES, B; VARELA, D
    Many of the agar-producing species of Gelidium and Pterocladia live on calcareous substrata in habitats with strong water movement. The thalli may suffer fragmentation by hydrodynamic drag but the vegetative fragments may reattach through differentiation of bundles of colorless, elongated rhizoids produced by inner and outer cortical cells. These rhizoids pass through intercellular spaces in the cortex, protrude outside the frond and cement the thallus fragments to the substratum. In Gelidium chilense (Montagne) Santelices & Montalva, differentiation and abundance of bundles of attachment cells are stimulated by the presence of calcareous substratum, minor additions (0.5 mM) of Ca2+ to the culture medium and by the highest photon flux density used (50-90 muE.m-2.s-1). Photoperiod does not affect production of bundles of attachment cells. Reattachment time can be as short as 10 days under optimal culture conditions. The significant effects of calcium substratum and dissolved Ca2+ on the differentiation process of these attachment cells is consistent with the high number of reports describing species of Gelidium living associated with calcareous substratum.
  • No Thumbnail Available
    Item
    INTRA-CLONAL VARIATION IN THE RED SEAWEED GRACILARIA-CHILENSIS
    (1993) SANTELICES, B; VARELA, D
    The phenotypic plasticity often found in seaweed populations has been explained only from the perspective of inter-population or inter-individual differences. However, many seaweeds grow and propagate by fragmentation of genetically identical units, each with the capacity to function on its own. If significant differences in performance exist among these supposedly identical units, such differences should be expressed upon the release and growth of these units. In this study we document two such types of variation in the red seaweed Gracilaria chilensis. Populations of sporelings, each grown under similar culture conditions and derived from carpospores shed by the same cystocarp exhibit significant differences in growth. In this species, each cystocarp develops from a simple gametic fusion, and cystocarp fusions occur too infrequently to account for the growth differences observed among recruits. In adult thalli, branches (ramets) derived from the same thallus (genet) and grown under similar conditions exhibit significant variation in growth rates and morphology. These findings have several implications. They suggest that carpospore production is not only an example of zygote amplification but that it also could increase variability among mitotically replicated units. Intra-clonal variability followed by fragmentation and re-attachment may increase intra-population variation which, in species of Gracilaria, is often larger than inter-population variation. In addition, the existence of intra-clonal variability suggests that strain selection in commercially important species may require a more continuous screening of high-quality strains because of frequent genotypic or phenotypic changes in the various cultivars.
  • No Thumbnail Available
    Item
    REGENERATIVE CAPACITY OF GRACILARIA FRAGMENTS - EFFECTS OF SIZE, REPRODUCTIVE STATE AND POSITION ALONG THE AXIS
    (1995) SANTELICES, B; VARELA, D
    Field farming of Gracilaria chilensis in Chile is mainly based on the regenerative capacity of thallus fragments. This study evaluates experimentally the effects on growth of the few organismic determinants that the farmer is capable of effectively handling in the field. No differences were found in the length increments of ramets with and without apices, a surprising result in view of the generally accepted idea that the most important growth meristem in this group of algae is located in the apex of the thallus. Total elongation and increase in weight of fragments with an initial length of up to 20 cm are a function of the initial length of the ramet, suggesting that intercalary growth makes a significant contribution to growth. Vegetative female axes grow faster, (in terms of length and weight) and produce more laterals than fertile female axes, and these faster than fertile tetrasporic branches. No differences in the growth of ramets originating from proximal or distal parts of axes were found.