Faculty

JOHN LABAVITCH 2055 Wickson Hall (530) 752-0920 jmlabavitch@ucdavis.edu

Ph.D. (1973)  Biological Sciences, Stanford University, California  Membership in Graduate Groups:  Horticulture & Agronomy Plant Biology Plant Pathology  Courses Taught: BIS 1C - Introductory Plant Biology, with K. Shackel  FRS 001 - Freshman Seminar: Research in Plant Biology: Relevance for Society, Students and Scientists  PBI 201 - Plant Senescence, with M. Reid  PBI 208 - Plant Hormones and Growth Regulators, with S. Abel  PBI 214 - The Higher Plant Cell Wall, with D. Nevins

The primary research focus of my laboratory lies in the study of cell wall polysaccharide structure and the control of development-related cell wall metabolism.  Current projects deal with the analysis of cell wall metabolism in ripening peaches and nectarines which take on a "woolly" texture because of exposure to chilling  temperatures and examination of cell wall changes in tomato fruits which have had their cell wall degrading enzymes modified using molecular genetics techniques.  The work with these genetically engineered tomatoes focuses both on fresh fruit ripening and the biochemistry of fruits as they are harvested and processed (Camara Hurtado et al., 2002.  Changes in cell wall pectins accompanying tomato (Lycopersicon esculentum Mill.) paste manufacture. J. Agric. Food Chem. 50:273-278, in press).

In many studies of ripening physiology we use a tomato pericarp disk model system. Disks cut from the pericarp of green tomatoes can be held in culture dishes and they will ripen over a period of several days.  This system is already proving to be useful in studying ripening-related cell wall polymer synthesis and the influence of cell wall digestion products on several aspects of ripening.  We have shown that pectin-derived oligosaccharides (PDOs) accumulate in developing fruit and can be applied to unripe tomato disks and cause them to ripen faster (Melotto et al., 1994. Cell wall metabolism in ripening fruit. VII. Biologically active pectin oligomers in ripening tomato (Lycopersicon esculentum Mill.)  Fruits.  Plant Physiolgoy 106:575-581).  We are now studying the mechanisms that generate these PDOs and their specific structures and biological activities.  We are also starting an examination of the fruit ripening signal transduction pathway.  This work will use the disk system and the development of additional genetically modified tomato lines.

We are also studying pear and tomato fruit proteins (called PGIPs - polygalacturonase inhibitor proteins) which inhibit fungal enzymes responsible for pectin degradation during pathogenesis.  We have transferred the gene encoding the pear PGIP to tomatoes and have shown that the transgenic tomatoes are more resistant to Botrytis cinerea.  (Powell et al., 2000. Transgenic expression of pear PGIP in tomato limits fungal colonization.  Molecular Plant-Microbe Interactions 13:942-950).  We continue to examine the biochemistry of PGIP action.  Recent work is following up on our observation that PGIPs also inhibit the PGs of the Lygus bug, a serious insect pest of many crop plants. Perhaps PGIPs protect plants against insects, too.