Extraction of Total Available Carbohydrates from Grass and Legume Tissue

Abstract

Carbohydrates are the primiiary source of reserve energy stored in the vegetative organs of biennial and perennial forage plants. Reserves of available carbohydrates are essential to survival and to the production of plant tissues during periods when carbohydrate utilization exceeds photosynthetic activity. Total available carbohydrate3 levels and trends in storage organs are useful in indicating the periods of storage and usage and are useful in evaluating the potential of plants for regrowth and production following defoliation. A number of nmethods have been used to extract total available carbohydrates from forage plant tissue. However, the method of extraction use(l will influence greatly the values obtained because The common perennial and biennial forage legumes, such as alfalfa, red clover, wlhite clover, and sweetclover, are characterized by the accumulation of sucrose and starch (3, 9, 11 ). Extraction of total available carbohydrates from these species has been accomiiplished largely by the takadiastase enzyme method developed by Weinmann (16,17) or with acid solutions (8, 10). The common perennial forage g,rasses belong to 2 groups according to the type of reserve carbohydrate stored. Grasses native to tropical and subtropical latitudes, such as bermudagrass, bahiagrass, and dallisgrass, are characterized by the accumulationi of sucrose and starch. Extraction of total available carbohyclrates has been done as cdescribed above for legumes (17, 18). Grasses native to temperate latitudes, such as timothy and orchardgrass, accunmulate sucrose and fructosan ( 1, 4, 7, 12, 13). Extraction of total available carbohydrates has been accomplished by acid hydrolysis (8) or with water (1, 14, 15) since fructosan is soluble in water. Starch, however, is largely water-insoluble. This stucly was initiated to compare enzynme, dilute acid, and wxater extraction methods for the estimation of total available carbohydrates in forage plant tissue. Timothy stem bases and alfalfa roots were used as the test tissues. Timothy stores the largest proportion of its reserve carbohydrates as fructosan in the stem bases (4, 7). Alfalfa stores most of its reserve carbohydrates as starch in the roots (3).