Starch Metabolism in the Leaf Sheaths and Culm of Rice

Abstract

The levels of starch and dextrin, free sugars, soluble protein, and enzymes involved in starch metabolism-a-amylase, ,8-amylase, phosphorylase, Q-enzyme, R-enzyme, and ADPglucose starch synthetases-were assayed in the leaf sheaths and culm of the rice plant (Oryza sativa L., variety IR8) during growth.Starch accumulation in the leaf sheaths reached a maximum 10 to 11 weeks after transplanting, the time of development of the rice panicle. Starch granules have been detected in various tissues of the rice plant during its growth (30,33). The starch of the rice endosperm has been the best characterized of these storage granules (8,14,15). Biochemical studies have been done mainly on the starch of the rice grain (5) and on the starch of the rice leaf chloroplasts (27,29).In contrast to the chloroplast starch, which is transitory, the granules in the parenchyma cells of the leaf sheath and culm accumulate during the vegetative growth of the rice plant and decrease sharply during grain development (30,33,36). Starch in these tissues is reported to be translocated to the panicle, where it contributes to the carbohydrate content of the grain (20,33,36 fully characterized, but this starch tends to have the same amylose-amylopectin ratio in both waxy and nonwaxy rices (12,17).Because of these direct and indirect contributions of the starch of these tissues to grain development and yield, we studied the changes in the properties of starch granules of the leaf sheath and culm and in the levels of enzymes involved in starch metabolism during the growth of the IR8 rice plant. The study was made during the 1970 dry season (JanuaryMay). Yoshida and Ahn (36) The plants were then washed, and only tillers of similar size and age were collected. The late tillers were discarded. The leaf sheaths and culms were removed, immediately cooled to 0 C, and the pooled samples (from nine hills) ground to a powder in the presence of Dry Ice in a Waring Blendor and stored at -20 C. Since the culms were short and small in the early samples before booting, they were not separated from the leaf sheaths. The elongated culms were prepared separately from the leaf sheaths in the samples taken 11, 12, and 14 weeks after transplanting. The panicles were excluded from the culms for all samplings. Leaf blades were discarded since they store very little starch (30,36).Portions of the powdered preparations were homogenized at 0 C (1:3 w/v) with 0.1 M tris-HCl buffer (pH 7.0) for 3 min in a VirTis homogenizer. The homogenate was filtered through four layers of cheesecloth and centrifuged at 27,000g for 10 min at 0 C. The supernatant fluid was decanted and the residue was saved for starch preparation. Protein was precipitated from the supernatant fluid by the addition of solid (NH)-,SO4 to 80% saturation for 30 min at 0 C. Fractions of this suspension were apportioned into several centrifuge tubes and the protein was collected by centrifuging for 10 min at 0 C at 27,000g. Essentially all the enzyme activities assayed were recovered in the precipitat...

Grain setting defect1, Encoding a Remorin Protein, Affects the Grain Setting in Rice through Regulating Plasmodesmatal Conductance

“…The distribution of starch granules in the parenchyma cells of the leaf sheath and culm reflect the state of photoassimilate translocation (Lian and Tanaka, 1967;Yoshida and Ahn, 1968;Perez et al, 1971). Starch accumulation in the stems of wild-type and gsd1-D plants was examined at the booting, flowering, and grain-filling stages.…”

The Effect of the Amount of Nitrogen Fertilizer on Starch Metabolism in Leaf Sheath of Japonica and Indica Rice Varieties during the Heading Period

“…Starch accumulation in leaf sheaths reaches a maximum at the panicle development stage immediately before anthesis and starch content of the leaf sheath decreases rapidly during grain fi lling stage (Perez et al, 1971). Cock and Yoshida (1972) estimated that approximately 21% of the carbohydrate in the rice grain is derived from the starch accumulated temporarily in the culm including the leaf sheath before heading.…”

Temporal and Spatial Variations of Carbohydrate Content in Rice Leaf Sheath and Their Varietal Differences

“…To fi nd the regulator of the starch content in each segment of the leaf sheath, we measured the activities of SuSy, AGPase, STS, GBSS and BE. SuSy cleaves sucrose to provide carbon source for starch and the other four enzymes are closely related to starch metabolism in leaf sheath (Perez et al, 1971;Watanabe et al, 1997;Hirose et al, 1999). The activities of SuSy, AGPase, STS, and BE increased from the apical segment to the basal segment in the leaf sheath of both Nipponbare and IR65598-112-2 (Fig.…”

“…In rice leaf sheaths, Perez et al (1971) fi rst investigated the activities of enzymes involved in carbohydrate metabolism in total leaf sheaths at different growth stages, and showed that the activity of GBSS closely paralleled the starch content of leaf sheaths. Watanabe et al (1997) examined the starch content of the leaf sheaths at different nodal positions, and found that the second leaf sheath from the fl ag leaf sheath accumulated 4-fold more starch than the sixth leaf sheath, and that the starch content closely correlated with the activities of BE, STS, GBSS and AGPase.…”