Peroxidase, Protein, and Growth Responses of Cultured Tomato Pith Explants
Tomato pith explants that were cultured on a simple semi-solid medium were analyzed for changes in peroxidase activity, protein, and growth during a seven day period. Changes in the soluble peroxidase fraction were similar to those observed previously in wounded intact tissue. Protein synthesis, the presence of a carbon-energy source, aerobic conditions, and calcium are required for induction and increases in soluble peroxidase. Although induction had been demonstrated previously without an exogenous nitrogen source, quantitative changes in protein were related to the amount of peroxidase increases. There is some evidence to suggest that tomato pith explants are capable of using tris, a buffer used in the culture medium, as a nitrogen source to support protein synthesis. Original peroxidase activity in the cell wall bound fraction increased only when there was a large net increase in protein. Cultured and incubated pith explants showed a rapid growth due to cell enlargement during the first day in culture or solution. Young, but mature, explants grew more than older mature explants. Sustained growth after the first several hours requires components in the culture medium. This study is preliminary to further research investigations of the controls of growth and differentiation in an easily manipulated plant cell system. This in vitro system might help identify those factors that control developmental events in intact tissues after wounding.
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