Morphogenesis in a Highly Reduced Plant: The Endophyte of Tristerix aphyllus (Loranthaceae)

Abstract

After the haustorium of the mistletoe Tristerix aphyllus penetrates the epidermis and hypodermis of its host, invasive tissues spread in all directions throughout the host and are not guided to host vascular tissues by tropisms This endophyte exists for an unknown length of time in a juvenile phase, unable to flower, even after contacting host vascular tissues. The adult condition is correlated with the endophyte achieving a volume of at least 49 cm3 and developing large complex strands with their own vascular tissues. After contacting host vascular tissues, further growth mostly involves spreading throughout the host phloem; only a few short, exploratory filaments extend and spread the endophyte to other host vascular bundles. Vertical spread is more rapid than horizontal spread and is fastest within host xylem and phloem, but also occurs in host cortex and pith. The endophyte is both structurally and metabolically much simpler than the vegetative bodies of nonparasitic dicots, but it does not grow as ...