Poster: Plant insect-nematode interactions

Abs # 497: Cytokinin and wound signal interaction reduces weight of gypsy moth larvae feeding on poplar

Presenter:	Lawrence, Susan D., lawrencs@ba.ars.usda.gov
Authors	Lawrence, Susan D. (A)   Dervinis, Chris  (B)   Davis, John  (B)
Affiliations:	(A): USDA-ARS, BARC-West, IBL Bldg 011A, Rm 214 Beltsville, MD 20705 (B): University of Florida, School of Forestry, Newin-Ziegler Hall, Gainesville, FL 32601

Genes induced by mechanical wounding are thought to be involved in defense against insect pests. Efforts to find these genes led to the discovery of a wound-induced cytokinin repressed kinase (CRK1)-like gene. This led to questioning what effect cytokinin plays on wound-induced genes in general. Four wound-induced (win) genes were examined. In all cases the wound-induced expression was enhanced by cytokinin. This result was confirmed at the protein level for WIN3 and 4. Since wound-induced genes seemed to be enhanced by cytokinin treatment, we asked if plants wounded and exposed to cytokinin would be detrimental to insect growth. Larval weight gain was significantly affected by plant wounding and cytokinin, but this was dependent on the position of the feeding leaf within the sink-to-source gradient from LPI 3 (sink) to LPI 6 (source). Larvae on the sink leaf, on the wounded and cytokinin treated plant grew to 55.5% of larvae feeding on unwounded cytokinin treated plants. We reasoned that cytokinin treatments could enhance the sink strength of young leaves and thus increase wound signal movement to sinks. To test the hypothesis that cytokinin stimulated the rate of long-distance sugar transport from source to sink, indirectly accelerating wound signal transport into sink leaves, we fed radiolabeled sucrose to source leaves and measured radiolabel movement in the developing leaf zone. Radiolabel movement from source leaves to sink leaves was unchanged by whole-plant treatment with cytokinin while the level of wound-induced trypsin inhibitor RNA was higher in sink leaves of cytokinin treated plants. This suggests that cytokinin plays a role in increasing the defense response but this is not related to enhanced source-to-sink sugar (by inference wound signal) movement.