Root anatomy and rhizosphere ultrastructure in tropical seagrasses

Root morphology and histology and rhizosphere ultrastructure differ slightly among four species of tropical seagrasses: Thalassia hemprichii (Ehrenb.) Aschers. (Hydrocharitaceae) and Cymodocea serrulata (R. Br.) Aschers. & Magnus, Halodule uninervis (Forsk.) Aschers. and Syringodium isoetifolium (Aschers.) Dandy (Cymodoceaceae). Bacterial colonies have been observed in the rhizospheres of these four seagrass species. Bacteria penetrate the epidermal cell and lyse the thick polysaccharide materials in the walls of both epidermal and exodermal cells. Suberized lamellae in the walls of the epidermal and exodermal cells are more resistant, but bacterial colonies eventually occur in both types of cells. It is suggested that these rhizosphere bacterial colonies are probably not pathogenic but are mutualistic and may be involved in nitrogen fixation and nutrient uptake by seagrass roots.