Physiological and Biochemical Changes in Miscanthus after Defoliation.

Giant Miscanthus (Miscanthus x giganteus), a hybrid triploid grass from Asia that has potential as a source of biofuel for the United States was periodically defoliated and the physiological mechanisms that control defoliation tolerance and shoot re-growth were examined.  Our objective was to determine how starch, sugar, amino acid, and protein concentrations are altered in rhizomes, roots, and stem bases of Miscanthus after defoliation.  Miscanthus was established in the greenhouse for two months, and twenty-eight plants, seven samplings of four replicates, were defoliated leaving a four-inch stubble.  Rhizomes, roots and stem bases were washed free of soil, lyophilized, weighed, and ground to pass a 1-mm screen.  Sugars were extracted from tissues using 80% ethanol and assayed using anthrone.  Starch in the ethanol-extracted residue was hydrolyzed, and the resulting glucose was quantified using glucose oxidase.  Buffer-soluble protein and amino-N were extracted and then analyzed using protein dye-binding and ninhydrin, respectively.  SDS gel analysis was used to analyze changes in specific protein concentrations after defoliation.  Shoot mass increased in a linear fashion between Days 6 and 34.  Rhizome mass increased linearly from Days 22 to 34.  Sugar concentrations in all three tissues decreased for 12 days after defoliation and re-accumulated in rhizomes and stem bases between Days 12 and 34.  Starch concentrations in rhizomes, roots, and stem bases also declined after defoliation, reaching their lowest concentration on Day 18.  Thereafter, starch re-accumulated, especially in rhizomes.  Amino-N concentrations in all three tissues increased between Days 0 and 6 then gradually declined to pre-defoliation concentrations by Day 34.  Protein concentration in rhizomes declined by Day 12 and increased between Days 12 and 22.  Large changes in rhizome starch concentrations suggest that this source of organic reserve is important for defoliation tolerance and re-growth of this potential biofuel.