Although P-proteins are an integral component of sieve elements in most plants, their role in phloem development and function has not been experimentally determined. We are using a variety of biochemical and molecular approaches to examine the physiological function of these proteins. I have recently expanded my research program to address questions about plant responses to insect feeding in phloem tissue. There is considerable evidence that insect feeding induces physiological stress in plants resulting in decreased productivity. However, major gaps exist in our knowledge of how plants respond to phloem-feeding insects, especially responses that occur in the phloem tissue.
Aphids feed on phloem sap by inserting their stylets directly into sieve elements of the phloem.
Studies of aphid probing behavior indicate that resistance factors are localized in phloem tissue, suggesting that plant defense responses occur within the sieve element-companion cell complex. Stresses within this tissue could profoundly effect overall plant growth and development. We are investigating the physiological and genetic basis of aphid resistance in melon and identifying aphid responsive genes in Arabidopsis thaliana . Results from this research will provide an opportunity to enhance or introduce resistance to phloem-feeding insects in crop plants. Bostwick, D.E., Dannenhoffer, J.M., Skaggs, M.I., Lister, R.M., Larkins, B.A., and Thompson, G.A., 1992.