Don Kaplan - his legacy: Influencing teaching and research
Sanders, William B. .
A feeling for the superorganism: the lichen thallus and its significance in understanding plant structure.
Basic principles of plant morphology may be observed in a diverse, polyphyletic assemblage of organisms, giving coherence to a broad, structural-ecological concept of "plant". These organisms typically share photosynthetic nutrition and the consequent challenges of light capture, gas exchange and water balance. Their form is expressed in a framework of cell walls and wall-associated substances that serve as structural building material. Remarkable examples of plant form are provided by lichens, symbioses in which two microorganisms -- fungus and alga -- together produce a macrophytic thallus. The fungus usually serves as the main structural component of the thallus, in a striking metamorphosis from its typical mycelial form. Some lichens, however, are constructed predominantly of algal sheath material. Ontogeny of the lichen thallus in nature has been studied by placing transparent substrates among tropical leaf-dwelling lichen communities. These tiny crustose lichens readily colonize the smooth surfaces of plastic cover slips, allowing early developmental stages to be monitored with light microscopy. Such studies show a variety of reproductive strategies, including dispersal of organized vegetative propagules containing both symbionts and relichenization of separately dispersed fungal and algal symbionts. Different patterns and mechanisms of symbiont coordination in thallus ontogeny can be observed. Construction of the superorganimal lichen thallus from separate, originally autonomous cellular elements is fundamentally different from the partitioning process that generates multicellular forms in conventional plants. The generation of strikingly convergent morphologies from these different processes provides further support for the view of plant form as an emergent property at a level of organization independent of cellularity.
1 - Centro de Ciencias Medioambientales, CSIC,, Calle Serrano 115 bis,, Madrid, E-28006, Spain
Presentation Type: Symposium
Location: Ballroom 2 (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 1:55 PM