Effect of heat stress on wheat proteins during kernel development in wheat near-isogenic lines differing at Glu-D1 * Sibel Irmak a,b , Hamid A. Naeem a,c, * , George L. Lookhart a , Finlay MacRitchie a a Department of Grain Science and Industry, Kansas State University, Manhattan, Kansas 66506, USA b Department of Chemistry, Arts and Sciences Faculty, University of Cukurova, Balcali 01330, Adana, Turkey c Department of Food Science, University of Manitoba, 250 Ellis Building, Winnipeg, MB R3T2N2, Canada Received 8 November 2007; received in revised form 7 December 2007; accepted 13 December 2007 Abstract Two near-isogenic lines of the wheat variety Lance having Glu-D1a (HMW-GS 2 þ 12) and Glu-D1d (HMW-GS 5 þ 10) were subjected to several regimes of heat stress. In 2001, the temperature regimes were (i) 20/16 (day/night,  C) from planting to maturity, (ii) 20/16 except for a 3-day heat treatment of 35/20, 25 days after anthesis and (iii) 20/16 until 25 DAA, after which plants were subjected to 40/25 until maturity. In 2002, treatments (i) and (iii) were the same while treatment (ii) used a temperature of 40/25  C for 3 days at 25 DAA. Seed was collected at 3-day intervals starting from 16 days after anthesis and analyzed for protein composition by SE-HPLC. The line with the Glu-D1d allele showed an earlier polymerization of glutenin than its allelic counterpart and a higher molecular weight of glutenin at maturity, this being deduced from measurements of the percentage of unextractable polymeric protein. It is postulated that the timing and rate of glutenin polymerization, and the timing of high temperature application may be the key factors contributing to an explanation of the effect of heat stress on functionality. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Grain filling; Heat stress; Molecular weight; Near-isogenic lines 1. Introduction Inconsistency of quality is one of the biggest problems for processors in the wheat industry and may lead to high costs as- sociated with adjusting variables to compensate for variations. These variations may arise from changes in seasonal condi- tions or from different growing locations. Of the different en- vironmental effects, one of the greatest in certain regions (e.g. in the Great Plains area of the U.S.) is thought to be that of heat stress; i.e. high temperature during the period just before harvest. Heat stress is known to produce loss of yield as well as loss of quality (Blumenthal et al., 1993; Finney and Fryer, 1958; Stone and Nicholas, 1994). These effects may be expected to increase as a result of the present trend of rising temperatures globally (Hennessy, 1994). It has been reported that daily mean temperatures up to 30  C during grain filling increased dough strength, and that as temperature increased above 30  C dough strength decreased (Randall and Moss, 1990). One approach to counteracting the effects is to develop genotypes having resistance to heat stress. To this end, some studies have been encouraging in demonstrating that naturally occurring variability in heat stress tolerance exists among wheat varieties (Blumenthal et al., 1995a; Stone and Nicholas, 1994). In particular, there is evidence (Blumenthal et al., 1995b) that lines possessing the Glu-D1d allele (HMW-GS 5 þ 10) tend to be more tolerant than lines possessing the Glu-D1a allele (HMW-GS 2 þ 12). The present work is a continuation of studies on the protein composition of near-isogenic lines during grain development Abbreviations: DAA, days after anthesis; HMW-GS, high molecular weight glutenin subunits; SE-HPLC, size exclusion-high performance liquid chromatography; UPP, unextractable polymeric protein. * Contribution No. 07-253-J from the Kansas Agricultural Experiment Station, Manhattan, KS 66506, USA. * Corresponding author. Department of Food Science, University of Mani- toba, 250 Ellis Building, Winnipeg, MB R3T2N2, Canada. Tel.: þ1 204 4746564; fax: þ1 204 4747630. E-mail address: hnaeem@ms.umanitoba.ca (H.A. Naeem). 0733-5210/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcs.2007.12.002 Journal of Cereal Science 48 (2008) 513e516 www.elsevier.com/locate/jcs