Submitted to: International Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2007
Publication Date: 10/29/2008
Citation: Sherman, T.D., Bowling, A.J., Barger, T.W., Vaughn, K.C. 2008. The vestigial root of dodder (Cuscuta pentagona) seedlings. International Journal of Plant Science 169(8):998-1012. Interpretive Summary: Dodders are a group of parasitic weeds that cause great financial loss to growers around the world, but many facets of their basic biology remain unknown. Some of these unique facets could be exploited for possible control. Although young dodder seedlings have a structure that resembles a root, this structure never penetrates the soil and seems to wither and die even before the seedling has attached to the host plant. Structural and biochemical studies reveal that this structure is really not even a root, but a highly modified swollen bit of shoot tissue. Our data indicate that the swollen end of tissue provides a stable support for the expanding shoot tissue and a source of nutrients that can be used to sustain further shoot growth. These results are important in identifying a new Achille's heel in this pernicious weed for potential weed control.
Technical Abstract: Seedlings of dodder have no leaves nor cotyledons and the terminal root-like structure lasts only a few days before death. Structural and biochemical studies indicate that the terminal appendage of the dodder, although differentiated from the shoot, has few characteristics of root tissue. The root has no meristem nor cap and the vascular tissue ends bluntly at the terminus of the seedling. The root tissue swells rapidly, due to the loss of cortical microtubules and the weakening/loosening of the cortical cell walls. The vascular strand is not separated from the cortical cells by a pericycle, as is typical root tissue. A waxy cuticle surrounds the root that would actually delay water uptake into the seedling. By 5-7 days after germination, the root is completely senescent, with massive cellular collapse. The dodder root, although not truly a root, appears to add structural stability to the young seedling and allows a net movement of the seedling by treadmilling reserves to the growing shoot tissue.