Abstract
BackgroundStarch consists of two types of molecules: amylose and amylopectin. The objective of this study was increase understanding about mechanisms related to starch accumulation in hulless barley (Hordeum vulgare L.) grain by measuring temporal changes in (i) grain amylose and amylopectin content, (ii) starch synthase activity, and (iii) the relative expressions of key starch-related genes.ResultsThe amylopectin/amylose ratio gradually declined in both Beiqing 6 and Kunlun 12. In both cultivars, the activities of adenosine diphosphate glucose pyrophosphorylase, soluble starch synthase (SSS), granule bound starch synthase (GBSS), and starch branching enzyme (SBE) increased steadily during grain filling, reaching their maximums 20–25 days after anthesis. The activities of SSS and SBE were greater in Ganken 5 than in either Beiqing 6 or Kunlun 12. The expression of GBSS I was greater in Beiqing 6 and Kunlun 12 than in Ganken 5. In contrast, the expression of SSSI, SSSII and SBEI was greater in Ganken 5 than in Beiqing 6 and Kunlun 12. The peak in GBSSI expression was later than that of SSSI, SSSII, SBEIIa and SBEIIb. The GBSSI transcript in Kunlun 12 was expressed on average 90 times more than the GBSSII transcript.ConclusionsThe results suggest that SBE and SSS may control starch synthesis at the transcriptional level, whereas GBSSI may control starch synthesis at the post transcriptional level. GBSSI is mainly responsible for amylose synthesis whereas SSSI and SBEII are mainly responsible for amylopectin synthesis in amyloplasts.
Highlights
Starch is the main end product of carbon fixation during photosynthesis
Starch accumulation Starch, amylose, and amylopectin contents increased across time in all three cultivars (Fig. 2a, c, e)
The starch content was less in Beiqing 6 than in Kunlun 12 at 10, 15, 20, and 25 days after anthesis (DAA); the difference between the two cultivars became less with time
Summary
Starch consists of two major components, amylose and amylopectin. Amylopectin is composed of short α-1,4-linked chains of glucose. About 5% of these chains are linked together by α-1,6 linkages (Manners 1989; Buléona et al 1998; Preiss and Sivak 1998). Amylose is composed of glucose chains; less than 1% of these chains are linked by α-1,6 branches (Imberty et al 1991). The structure and relative proportion of amylose and amylopectin are the primary determinants of the physical and chemical properties of starch. Starch consists of two types of molecules: amylose and amylopectin. The objective of this study was increase understanding about mechanisms related to starch accumulation in hulless barley (Hordeum vulgare L.) grain by measuring temporal changes in (i) grain amylose and amylopectin content, (ii) starch synthase activity, and (iii) the relative expressions of key starch-related genes
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