Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/31/2005
Publication Date: 6/21/2005
Citation: Li, L., Atichokudomchai, N., Blanco, M.H., Jane, J. 2005. Development of starch granules in maize kernels [abstract]. International Starch Convention, June 21-23, 2005. Institute of Biochemical Physics RAS, Moscow, Russia. 2005 CDROM.
Technical Abstract: Maize kernels of self-pollinated inbred line B73, grown in Ames IA, were harvested on 0, 5, 6, 8, 10 12, 14, 20 and 30 days after pollination (DAP). The kernels were used for starch granule development studies. Starch in the endosperm was first observed on 6 DAP. Starch granules in the kernels that were harvested on 6 – 12 DAP were very small, stained brown color with iodine, and did not show Maltese cross when viewed under a polarized microscope. A small amount of starch granules (<2% of dry weight) was found in the endosperm on 12 DAP. The starch content of the endosperm increased rapidly from 14 DAP (10.7%) to 30 DAP (88.9%). Shapes of starch granules in immature endosperm (up to 10 DAP) appeared fractured, shrunken, and in irregular shapes. Whereas, starch granules in the endosperm of 12 and 14 DAP showed perfect spherical shape, but some became polygonal when it reached 30 DAP. The different shapes of starch granules during kernel development could be attributed to that the rate of starch biosynthesis in the endosperm before 10 DAP was slow. Thus the starch granules were not filled and packed tightly and tended to fracture and shrink. Diameters of starch granules isolated from kernels of 14 DAP were around 4-6 'm and that of 30 DAP were 5-20 'm. The gelatinization temperature of starch increased with maturation, the onset gelatinization temperature increased from 61.3'C on 8 DAP, 63'C on 12 DAP, to 67.5'C on 20 and 30 DAP. Percentage retrogradation of gelatinized endosperm starch after being stored at 4'C for seven days also increased from 26.4% (8 DAP) to 48.7% (14 DAP), and then decreased to 42.7% (30 DAP). The differences in the retrogradation rate and iodine stain color were mainly related to the amylose content and amylopectin branch-chain length. Amylose contents of starch granules, determined using gel permeation chromatography, increased from 12.8% on 12 DAP to 30.8% on 30 DAP. Average branch chain length of amylopectin increased from 23.6 anhydroglucose units (AGU) (10 DAP) to 26.7 AGU (14 DAP), and then decreased to 25.4 AGU (30 DAP). The change in the branch chain-length of amylopectin was in agreement with that obtained by using surface gelatinization of mature starch granules.