USE OF DIVERSE GERMPLASM FOR GENETIC IMPROVEMENT OF RICE
Location: Dale Bumpers National Rice Research Center
Title: ACTIVITIES OF ENZYMES RELATED TO STARCH SYNTHESIS AND FUNCTIONALITY IN SELECTED RICE LINES
Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: January 1, 2006
Publication Date: February 15, 2006
Citation: Bryant, R.J., Counce, P.A. 2006. Activities of enzymes related to starch synthesis and functionality in selected rice lines. Rice Technical Working Group Meeting Proceedings, February 29-March 2, 2006, Houston, Texas. CDROM.
Rice cultivars vary in their functionality from one year to another and from one location to another. Reasons for this variability have more often been speculated about than tested. Very little is known about the role the starch synthesizing enzymes play in influencing the processing quality of rice. Therefore, we sought to study five enzymes that are integral to the production of starch by conducting a two year study in Stuttgart, Arkansas. In that experiment, five U.S. long grain rice cultivars (Cocodrie, Cypress, Francis, Lemont, Wells), three Chinese indicas (Zhe 733, Guichao, Qiguizao), and two F12 lines derived from a cross of Guichao and Lemont (LG 13A and LG 13B) were grown in 2004 and 2005 in field experiments with randomized complete block designs at the University of Arkansas Rice Research and Extension Center in Stuttgart, AR.
Twelve or more panicles between the R6 and R7 growth stages were collected, immediately placed on ice, and stored at -80oC. Crude protein extracts were obtained from R6 rice seeds from each plot with hulls (lemma and palea) and aleurone layer removed. These seeds were then ground frozen and homogenized in buffer. Protein extracts were assayed for sucrose synthase (SS), uridine diphosphoglucose pyrophosphorylase (UGP), starch branching enzyme (SBE), and soluble starch synthase (SSS). Apparent amylose content (AAC), RVA and DSC were determined on the mature seeds after dehulling, milling, and grinding each sample. Head rice yield was also determined.
Cypress had highest head rice yield (70%) and LG 13B had the lowest (46%). The variation in AAC of the U.S. long grains ranged from 0.7% for Lemont to 4.1% for Cocodrie. For the indicas, the AAC variation ranged from 2.0% for Qiguizao and Guichao to 3.0% for ZHE 733. The crosses, LG 13A and 13B, had a variation range of 1.8% and 2.0%, respectively. For DSC, the ranges of To, Tp and Tc for the U.S. long grains were 67.3oC to 68.5oC, 77.4oC to 77.7oC, and 90.3oC to 92.5oC, respectively. Except for ZHE 733, the To, Tp and Tc ranges for the indicas and the crosses were 59.3oC to 61.8oC, 68.7oC to 71.4oC, and 84.8oC to 88.5oC, respectively. ZHE 733 had To, Tp and Tc values of 69.3oC, 79.1oC and 92.8oC, respectively. Cocodrie had the lowest peak viscosity (181 RVU), Francis had the highest (242 RVU), and all the indicas had higher final viscosity, >340 RVU.
In 2004, Zhe 733 and Guichao had the highest SS activity at 39mU/grain each. The crosses, LG 13A and 13B, had the lowest at 21 and17mU/grain, respectively. The U.S. long grains, except Francis, had the highest UGPase activity, whereas the indicas and the crosses, except Guichao, had the lowest. Except for Lemont, the U.S. long grains had significantly higher SBE activity than both the indicas and the crosses. Lemont and Guichao had the highest SSS activity at 4.7 and 4.2mU/grain, respectively, and Cypress had the highest SBE, 22mU/grain.
It has been shown that the synthesis of amylose lags behind that of amylopectin and that SSS has a 10X greater affinity for ADP-glucose. This means that if ADP-glucose is limited, either by the production (low SS activity) of or increase use (high SSS activity) of ADP-glucose, then the amount of AAC will be affected and AAC has been shown to greatly affect processing quality.