Kuo, J. Protoplasma (1984) 121: 1. doi:10.1007/BF01279746
Fungal hyphae which grow throughout the leaf apoplast in the subtidal form of the seagrassZostera muelleri Irmisch ex Aschers, from Victoria, Australia, have been studied by light and transmission electron microscopes. The hyphae were not found in the roots and rhizomes of the same plant. They do not occur in any vegetative organs of the intertidal form of Z.muelleri from the same locality, or in the other twenty-four seagrass species examined. Hyphae are branched in mesophyll tissues but they avoid the leaf surface, the septa in the air lacunae system and some xylem elements. The hyphae are completely embedded in the intercellular substance and cell walls of host tissues, except for those which project into air lacunae. The walls of these hyphae have low electron density and an uneven inner surface outline. The plasmalemma has a wavy and electron dense appearance. The hyphae contain nuclei, extended smooth endoplasmic reticulum, mitochondria with weak cristae, ribosomes, vacuoles, microbodies, electron dense lipid droplets, and Golgi apparatus but no plastids or starch grains. It is suggested that the hyphae are symbiotic in function but not pathogenic. They may obtain solute from the plant through the apoplastic transport processes in host tissues and oxygen from the air lacunae system in the seagrass. On the other hand, the network of apoplast hyphae may enhance solute transfer within the leaf of the subtidal form ofZ. muelleri.