Progress 01/15/03 to 01/14/06
Outputs
High temperatures prior to harvest (heat stress) is a major cause of inconsistency of wheat quality. In addition to the negative effects on yield, heat stress is associated with decreased dough strength and impaired bread-making performance. These effects may vary from one location to another as well as from one season to another and this can lead to high costs for processors. The present study has used isogenic wheat lines which have been grown in the greenhouse and subjected to different temperature regimes in growth cabinets. Both short bursts of high temperature and prolonged periods of high temperature have been used to mimic conditions that typically occur in the field. Kernels were collected at 3-day intervals during grain development and analyzed for protein composition by Size-Exclusion High Performance Liquid Chromatography. Quality of the mature grain for each treatment was assessed by the SDS-Sedimentation Test. A critical stage in determining the quality
of the mature grain is the post-translational polymerization of glutenin from its subunits (the gene products). This process begins to occur roughly midway between anthesis (flowering) and maturity. The large glutenin molecules are responsible for the strength and elasticity of dough. It was found that the timing (and thus the rate) of polymerization of glutenin varied for the different genotypes that were compared as well as the environmental conditions. Wheat lines possessing strength-contributing High Molecular Weight Glutenin Subunits (e.g. 5+10 at Glu-D1 and 17+18 at Glu-B1) began polymerizing at an earlier stage (by several days) than their allelic counterparts (2+12 and 20x+20y). Also, under severe heat stress, the reduction in dough strength was less for lines with the former glutenin subunits. The results give insight into how genetic composition might be manipulated to meet the objective of developing varieties with high resistance to heat stress.
Impacts
This study has shown how genetic composition influences the rate of formation of glutenin polymers that are responsible for dough strength and elasticity. The effect of high temperature is to hinder the polymerization step. This knowledge can be applied in wheat breeding programs to develop varieties with increased resistance to heat stress.
Publications
- Irmak, S. and MacRitchie, F. 2006. Effect of duration and intensity of heat stress during grain filling on two near-isogenic wheat lines. World Grains Summit, San Francisco. Abstract in Program Book (p. 151).
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Progress 01/01/05 to 12/31/05
Outputs
High temperatures prior to harvest (heat stress) is a major cause of inconsistency of wheat quality, a costly problem for processors. In addition to negative effects on yield, heat stress is associated with decreased dough strength and breadmaking quality. To increase understanding of heat stress effects on quality, near-isogenic wheat lines differing only at one locus (Glu-B1 or Glu-D1) have been grown in the greenhouse and subjected to different temperature regimes in growth chambers. This included short bursts of high temperature (up to 40oC) and prolonged high temperatures to mimic the conditions that typically occur in the field. Kernels were collected at three-day intervals during grain development and analyzed for protein composition. Quality of the mature grain was evaluated by the SDS-Sedimentation test. A critical stage has been found in the polymerization of subunits to form the large glutenin molecules that contribute to dough strength. This polymerization
occurs midway between anthesis and maturity and the timing is dependent on allelic composition. The effect of heat stress on quality appears to be determined by interaction between the timing of polymerization and the timing of the heat stress. Another part of this project has involved the use of progeny from a cross between a heat resistant wheat variety (Fang) and a heat susceptible variety (Batavia). These lines have shown a range of susceptibility to heat stress and the protein composition is being measured to throw light on the allelic composition required for heat stress resistance.
Impacts
These studies are elucidating how heat stress effects on wheat quality are influenced by genetic (and thus protein) composition. The long term aim is to assist wheat breeders to develop lines with increased resistance to heat stress.
Publications
- Naeem, H.A. and MacRitchie, F. 2005. Polymerization of glutenin during grain development in near-isogenic wheat lines differing at Glu-D1 and Glu-B1 in greenhouse and field. Journal of Cereal Science 41:7-12 (Contribution No. 04-437-1 from the Kansas Agricultural Experiment Station, Manhattan, KS 66506).
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Progress 01/01/04 to 12/31/04
Outputs
High temperatures prior to harvest (heat stress) is a major reason for inconsistency of wheat quality, a big problem for processors. To increase understanding of heat stress effects, isogenic wheat lines have been grown in the greenhouse and subjected to different temperature regimes in growth chambers. Kernels have been collected at intervals during grain development and analyzed for protein composition. A critical stage has been found in the polymerization of subunits to form the large glutenin molecules that contribute to dough strength. Differences in timing of this polymerization between isogenic lines in relation to application of heat stress leads to different effects on quality. This has given insight into the problem which will help to plan strategies for developing varieties with increased resistance to the effects of heat stress.
Impacts
The short term aim in this work is to better understand how heat stress affects protein composition and, in turn, functional properties of flour in baked products. The longer term aim is to assist wheat breeders to develop lines with increased resistance to heat stress. Flour variable end-use performance is the major quality control problem in bakeries.
Publications
- Naeem, H.A. and MacRitchie, F. 2004 Polymerization of glutenin during grain development in near-isogenic wheat lines differing at Glu-D1 and Glu-B1 in greenhouse and field. Journal of Cereal Science (in press).
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Progress 01/01/03 to 12/31/03
Outputs
Seasonal high temperatures prior to wheat harvest is a cause of loss of yield as well as losses of milling and baking quality, particularly in the Great Plains area. This gives rise to additional costs for processors associated with the need to adjust processes to cope with the variations. The objective of the present project is to study the changes in protein content and composition during grain development resulting from applications of controlled heat stresses. The rationale for the work is that the quality of the mature grain depends on events occurring during plant growth and grain filling. If these events can be understood, this will allow strategies to be put in place for development of heat shock-resistant wheat lines and minimize the detrimental effects of heat stress. Near-isogenic wheat lines of the variety Lance (Lance A and Lance B) have been grown in growth chambers under the following conditions: 1, 25/20oC day/night (control); 2. 35/20oC day/night for
three days, 25-28 days after anthesis; 3. 40/25oC day/night for three days, 25-28 days after anthesis; 4. 40/25oC day/night, applied at 25 days after anthesis and continued to maturity. The aim has been to mimic conditions that occur in the field where heat stress may be a short heat stress for a few days or a prolonged period of high temperature. For all four treatments, grain was collected at three-day intervals from 15 days after anthesis until maturity. The kernels were immediately frozen in liquid nitrogen and later freeze-dried. Wet and dry weights were measured and protein determinations made. The grain was then ground to powder ready for analysis. The samples are presently being analyzed for protein composition using Size-Exclusion HPLC. One of the measurements expected to give valuable information is that of molecular size which has been found to be critical to explaining the loss of strength associated with heat stress.
Impacts
The use of near-isogenic wheat lines is proving valuable for relating protein composition to functional properties. This provides information for wheat breeders to use in breeding varieties with enhanced functionality. A specific type of wheat protein called a chain terminator should be useful for manipulating functionality using conventional or novel breeding methods.
Publications
- Naeem, H. and MacRitchie, F. 2003. Heat stress effects on wheat proteins during grain development. 10th International Wheat Genetics Symposium, Paestum, Italy. Proceedings of Symposium, pp 455-458.
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