Responses of Heterodera glycines and Meloidogyne incognita to exogenously applied neuromodulators

Abstract

Biogenic amines regulate important behaviours in nematodes and are associated with pharyngeal activity in plant-parasitic nematodes. A robust behavioural assay based upon nematode body movements was developed to expand the study of these and other neuroregulators in plant-parasitic nematodes. Dopamine, octopamine and serotonin each had significant but differing effects on the behaviour of soybean cyst nematode Heterodera glycines and root-knot nematode Meloidogyne incognita juveniles. Body movement frequency was increased twofold in H. glycines by 5 mM dopamine (P = 0.0001), but decreased by 50 mM dopamine in H. glycines (88%) and M. incognita (53%) (P < 0.0001). Movement frequency in both species was increased by 50-70% (P < 0.0001) by 50 mM octopamine, and 5 mM octopamine increased M. incognita movement frequency more than twofold (P < 0.0001). Movement frequency in each species was reduced by more than 90% by 5 mM serotonin (P < 0.0001). While amplitude of body movement in H. glycines was unaffected by any amine, it was significantly reduced in M. incognita by all amines (P < 0.0006). Stylet pulsing frequencies in either species were unaffected by dopamine or octopamine, but 5 mM serotonin stimulated pulsing in H. glycines by nearly 13-fold (P < 0.0001) and in M. incognita by more than 14-fold (P < 0.0001). The invertebrate neuropeptide FLRFamide (N-Phe-Leu-Arg-Phe) increased M. incognita body movement frequency 45% (P = 0.02) at 1 mM but did not affect stylet activity. Finally, H. glycines egg hatch was completely suppressed by 50 mM serotonin, and partially suppressed by 50 mM dopamine (75%; P < 0.0001) and 50 mM octopamine (55%; P < 0.0001).

Neurobiology of plant parasitic nematodes

“…The effects of dopamine, octopamine and 5-HT (5-hydroxytryptamine or serotonin) have been further examined on the behaviour of J2 stage Heterodera glycines and Meloidogyne incognita (Masler 2007). Interestingly, dopamine, 5 mM, stimulated frequency of body movements in H. glycines while inhibiting movement when applied at 50 mM, suggesting it may be acting at multiple receptor sites.…”

“…However, extracts of the three species examined using HPLC gave a number of immunoreactive fractions, indicating several different FLPs were present and that these differed between the species. The effects of FLRFamide have been examined using M. incognita (Masler 2007). FLRFamide, 1 mM, enhanced the frequency of movement but had no effect on stylet activity.…”

Serotonin in Trichinella pseudospiralis: An immunocytochemical study

“…Some studies have been made on neurotransmitters in plant nematodes (Holden-Dye & Walker, 2011). According to Masler (2007Masler ( , 2008 5-HT infl uences the general motility, the egg laying process and the stylet activity of Heterodera glycines and Meloidogyne incognita. The effect of serotonin on the reproductive behavior of Heterodera schachtii has also been recorded (Jonz et al, 2001).…”

Responses of Heterodera glycines and Meloidogyne incognita to exogenously applied biogenic amines

“…To monitor J2 activity and behaviour, aliquots (15 μl drops) containing ca 7-10 J2 were placed on a glass microscope slide, and observed at either 40× or 100× magnification. Infective juvenile behaviour scores were based upon the lateral motion of the anterior portion of the worm (Masler, 2007). A lateral motion was defined as any change in direction from a previous position, or resumption of movement in the same direction after a momentary pause.…”

“…Globodera rostochiensis stylet pulsing in response to serotonin was correlated with stimulation of pharyngeal musculature (Rolfe & Perry, 2001), and associated with male reproductive behaviour in H. schachtii (Jonz et al, 2001). Dopamine, octopamine and serotonin all reduced hatching in H. glycines and had varied effects on J2 movement in H. glycines and M. incognita (Masler, 2007). The current report examines the responses of H. glycines and M. incognita to dopamine, octopamine and serotonin, and provides the first comprehensive quantitative analysis of the effects of BAs on hatching and infective juvenile behaviour in plant-parasitic nematodes.…”