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Thomas C. Pesacreta

1975 B.S. (Agronomy) Virginia Polytechical Institute and State University, Blacksburg, VA

1982. Ph.D. (Plant Biology) Cornell University, Ithaca, NY

ROOT GROWTH - Roots are essential organs that allow the plant to extract water and minerals from the soil, anchor the plant against physical disturbances, and interact with bacteria and fungi. Roots must be able to do all of these things and also be able to compete with roots from other plants. To do this they must grow. Growth involves two processes that occur in the tips of roots, cell division in the root apex to produce more cells, and cell elongation in the region distal to the root apex so that the newly formed cells can lengthen and thereby push the root deeper into the soil. Implicit in the growth process is that the root apex cells must be supplied with photosynthates from the leaves. Supply occurs through the phloem. It is widely known that angiosperms and ferns have specialized cells called sieve elements that serve as the conduits that supply the root apex cells with photosynthates. Surprisingly, gymnosperms lack such cells in the same region of the root, but only develop them later, much further away from the root apex. The lack of sieve elements near the apex has profound implications for the transport of nutrients. Without sieve elements such transport would presumably have to occur by diffusion, a much slower process than transport through sieve elements. Consequently, gymnosperm roots would be relatively limited with regard to the amount of photosynthate delivered to the root. This limitation seems to reduce their growth rate. The concentration of photosynthates that are being delivered to the root apex, and the delivery pattern are interesting questions for the future.

STARCH CONTENT OF WOOD - Starch is the major photosynthate storage carbohydrate in plants. In land plants, it is stored in every organ, including the wood. The amount of starch in wood seems to vary a great deal with the season. For example, northern hemisphere pines have little in the winter but some tropical species store large amounts then. Such patterns of starch storage in wood have not been closely studied for any species. Surprisingly, the amount of wood starch in some species seems to be a significant percentage of the dry weight of the wood. Consequently, the biofuel potential of such species is not only related to the cellulosic content of the wood, but should also include the starch content. Such a consideration would imply that the design of biofuel production techniques should encompass the utilization of both cellulose and starch, and might result in increased output.

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Thomas C. Pesacreta, Microscopy Center, PO Box 42451, Lafayette, LA 70504 or
Telephone: (337) 482-5233