A Proxy Analysis of Nonstructural Carbohydrate in Rice Plan by Using the Gravimetric Method.

Abstract

To develop a rapid determination of nonstructural carbohydrate (NSC) in rice plant, the availability of gravimetric analysis was examined. A plant sample of 0.5 g in 30 mL of distilled water was heated on a hot plate. After the cooling, 20 mL of phosphate buffer (KH2PO4 ; 12.08 gL-1, Na2HPO4·12H2O ; 3.98 gL-1, NaN3. ; 0.025 gL-1) containing 1.5 mg of α-amylase and 0.5 mg of amyloglucosidase was added to it. The mixture was incubated at 40°C for 24 hours with continuous shaking, then filtrated through filter paper (Advantic Toyo, No. 5A), its dry weight being predetermined. The residue on the paper was washed out with distilled water, then dried and weighed. The nonreducing sugar in the filtrate was hydrolyzed in 15 mL of boiling 0.04M H2SO4. In the gravimetric analysis, the concentration of all water-soluble substrate (NSCWS) was determined from the difference between dry weights of sample and residue. In the calorimetric analysis, the concentration of reducing sugar equivalent to glucose (NSCGL) was determined by using the ρ-hydroxybenzotic acid hydrazine method. Although no significant relationship between NSCWS and NSCGL in leaf blade was noted, significantly high positive correlations (r2g0.912) were found between them in leaf sheath + culm and panicle, irrespective of cultivation conditions and growth stages. An analysis of errors associated with the determination of NSCWS and NSCGL revealed that the gravimetric method gave a higher accuracy than the calorimetric method did, even when NSCWS was converted into NSCGL by linear regression equations. Also, NSCWS was more effectively incorporated with the near infrared spectroscopic method to quickly determine NSC. These results indicate that the gravimetric analysis is useful for a proxy determination of NSC in rice leaf sheath + culm and panicle.