Behavioral quiescence and sensitivity to exogenous compounds in J2 Heterodera glycines.

摘要

The ability to survive exposure to toxins is a requirement for all organisms. Plant-parasitic nematodes are frequently exposed to a wide range of chemicals in the soil environment, many of which are toxic. Despite exposure to toxins, plant-parasitic nematodes have succeeded in becoming a significant source of damage to agriculture. The soybean cyst nematode, Heterodera glycines , is a plant-parasitic nematode which causes extensive damage to soybeans with subsequent economic loss to producers. The hatched second-stage juvenile (J2) of H. glycines is a non-feeding stage which must survive exposure to toxins in the soil environment to successfully infect its host. This dissertation explores how J2 H. glycines survive exposure to exogenous toxins.There is an extensive literature on survival of nematodes to various environmental extremes. One commonality seen among nematodes surviving difficult environmental conditions is the induction of behavioral quiescence. In addition to survival of environmental extremes, plant-parasitic nematodes are often found in a quiescent state without an obvious environmental cause. We found that quiescent J2 H. glycines are less sensitive to exogenous toxins than active nematodes across a range of toxins and methods to induce quiescence. This quiescence-mediated sensitivity to exogenous compounds is likely due to a reduction in the penetration of compounds when the nematode is in a quiescent state. The pathway of chemical entry was determined by utilizing a fluorescent compound, fluorescein isothiocyanate (FITC) and physically occluding nematode orifices. A detailed examination of the use of FITC was undertaken to demonstrate its usefulness for chemical/nematode interaction studies. Further work was done to examine the effect of various pharmacological compounds on the incorporation of FITC. Octopamine was found to reduce quiescence and allowed for greater penetration of FITC.Finally, a more in-depth analysis of quiescence-mediated sensitivity to exogenous toxins was performed using plant-derived isothiocyanate compounds which have potential as nematicidal compounds. Behavioral and lethality measurements were compared for the ability to detect differences in toxin exposure between quiescent and active nematodes.This dissertation will provide insights into the development of more efficient chemical control methods for plant-parasitic nematodes.