Composition and Structure of Starch from Taproots of Contrasting Genotypes of Medicago sativa L.

Abstract

The objective of this study was to examine the composition and branch chain lengths of alfalfa (Medicago sativa L.) The 12-KI absorbance properties of the low molecular weight starches from roots of the low starch genotype indicated that some branching may be present. The distribution of chain lengths from amylopectin did not change during starch degradation and reaccumulation for the high starch genotype. In the low starch genotype, the proportion of low molecular weight branches having a degree of polymerization between 1 and 30 was decreased at the very low starch concentrations observed on the 14th day of regrowth. Higher concentrations and/or quantities of starch in roots of the high starch genotype were not associated with greater rate of herbage regrowth, when compared to the low starch genotype.

Starch Grain Distribution in Taproots of Defoliated Medicago sativa L.

“…6) produced significantly more herbage than the HSt line. This difference in herbage regrowth between the two lines is similar to that previously reported (8 This spatial separation in starch grain degradation and synthesis reflects a separation in starch metabolism at the cellular level. As molecular approaches are used to study regulation of amylase activity in alfalfa taproots after defoliation, cellular differences in starch metabolism should be considered.…”

“…Nevertheless, our findings can help explain previous data describing patterns of starch metabolism in alfalfa taproots. Fankhauser et al (8) examined changes in polysaccharide composition of taproot starch of the HSt and LSt lines after defoliation. They found no change in starch composition until concentrations in taproots of the LSt line declined below 20 g kg-'.…”

“…The HSt and LSt lines were obtained from plant introduction accession numbers 211607 and 237213, respectively (8). Vegetative cuttings were established in peat pots and grown in the greenhouse (27 ± 5°C) until they were transplanted into the field on May 11.…”

“…Defoliation of alfalfa can also cause starch concentrations in taproots to decrease as much as 70% from levels present before defoliation (8). This loss of starch has been associated with regrowth of shoots and root respiration (13).…”

Defoliation Influences Starch Granule Distribution and Structure in Medicago sativa L. Taproots as Revealed by SEM and TEM

“…Starch decline is associated with regrowth of alfalfa shoots and, upon establishment of adequate shoot mass, taproot starch levels rise again [15][16][17][18][19][20]. In alfalfa reserve starch is stored in parenchyma cells of bark and wood tissues in mature taproots [14,21]. Intact amyloplast structures containing multiple starch granules during periods of active starch synthesis was shown in alfalfa taproots [14].…”