Sensory qualities of whole wheat pan bread : influence of farming system, milling and baking technique

Wheat quality, a complex term, depends upon intentional use for unambiguous products. The foremost determinants of wheat quality are endosperm texture (grain hardness), protein content and gluten s...

/pdf/grain-hardness-a-major-determinant-of-wheat-quality-jbhy2kdiju.pdf

Grain hardness: a major determinant of wheat quality.

Kernel texture of wheat is a primary determinant of its technological properties. Soft kernel texture phenotype results when the Puroindoline a and Puroindoline b genes are present and encode the wild-type puroindolines PINA and PINB, respectively, and various mutations in either or both gene(s) result in hard phenotypes. A wealth of information is now available that furthers our understanding regarding the spatial and temporal regulation of expression of Puroindoline genes. Through the use of model membranes and synthetic peptides we also have a clearer understanding of the significance of the cysteine backbone, the tryptophan-rich domain (TRD) and the helicoid tertiary structures of PIN proteins in relation to their membrane-active properties. Many studies suggest individual yet co-operative modes of action of the PIN proteins in determining kernel texture, and significant evidence is accumulating that the proteins have in vivo and in vitro antimicrobial activities, shedding light on the biological roles of this unique ensemble of proteins. The puroindolines are now being explored for grain kernel texture modifications as well as antimicrobial activities.

Molecular genetics of puroindolines and related genes: regulation of expression, membrane binding properties and applications

The large genome and polyploidy of wheat (Triticum aestivum L.) makes it diffi cult to identify desirable genetic changes based on phenotypic screening due to gene redundancy. Forward genetics is, therefore, more diffi cult in wheat than in diploid plants. A modifi ed TILLING (Targeting Induced Local Lesions IN Genomes) method including the harvest of fi ve heads per M1 plant, storage of M 2 seeds, using unlabeled primers and agarose gels for mutation detection, and crossing of useful mutants for desired grain quality was explored in this report. A soft wheat cultivar, QAL2000, and a hard wheat cultivar, Ventura, were mutagenized with ethyl methanesulfonate (EMS). Screening of the waxy genes Wx-A1 and Wx-D1 in 2348 EMS-treated M2 plants allowed identifi cation of 121 mutants, including silent, missense, and knockout (truncation) mutations. A complete waxy wheat was successfully bred in 18 mo by crossing two truncation mutants (Wx-A1-truncation and Wx-D1-truncation; Wx-B1 is naturally null in both mutants). Screening of two puroindoline genes (Pina and Pinb) in QAL2000 identifi ed 19 mutants. A hard grain variant of a soft cultivar was identifi ed due to a mutation in Pinb caused by a premature stop codon. Background mutations were observed and further self-fertilization or crossing with a wild type was performed to eliminate deleterious mutations. With the rapid accumulation of wheat genomics information, many potential target genes of interest can be screened for mutations in these TILLING populations.

K.-M. Turnbull

Papers

Endosperm texture in wheat