American Association of Cereal Chem- ists/AOAC collaborative study was conducted to evaluate the accuracy and reliability of an enzyme assay kit procedure for measurement of total starch in a range of cereal grains and products. The flour sample is incubated at 95°C with thermostable α-amylase to catalyze the hydrolysis of starch to maltodextrins, the pH of the slurry is adjusted, and the slurry is treated with a highly purified amyloglucosidase to quantitatively hydrolyze the dextrins to glucose. Glucose is measured with glucose oxidase-peroxidase reagent. Thirty-two collaborators were sent 16 homogeneous test samples as 8 blind duplicates. These samples included chicken feed pellets, white bread, green peas, high- amylose maize starch, white wheat flour, wheat starch, oat bran, and spaghetti. All samples were analyzed by the standard procedure as detailed above; 4 samples (high-amylose maize starch and wheat starch) were also analyzed by a method that requires the samples to be cooked first in dimethyl sulfoxide (DMSO). Relative standard deviations for repeatability (RSDr) ranged from 2.1 to 3.9%, and relative standard deviations for reproducibility (RSDr) ranged from 2.9 to 5.7%. The RSDr value for high amylose maize starch analyzed by the standard (non-DMSO) procedure was 5.7%; the value

Plants of malting barley variety Schooner were exposed to 5 days of high temperatures (up to 35°C) during mid grain filling under controlled environment conditions. Grains from heat treated plants accumulated c. 30% less starch than grains from control plants (21/16°C; 14 h day). Reduced starch deposition was not limited by assimilate levels in heat treated grains, but high temperature reduced the conversion of sucrose to starch. The reduction in starch synthesis appeared to result from the effects of diminished catalytic activity of a number of enzymes in the committed pathway of starch synthesis, and/or delayed recovery of enzyme activity in the cooler recovery conditions. Reductions of 11–75% in the activity of the enzymes under investigation followed high temperature exposure. In addition, ADPglucose pyrophosphorylase, branching enzyme and granule bound starch synthase showed increased activity during exposure to moderate temperatures (28–32°C), but reduced activity at high temperatures, while soluble starch synthase showed an immediate loss of activity, even at moderate temperatures. Sucrose synthase and UDPglucose pyrophosphorylase showed the greatest reduction in catalytic activity after plants were returned to cooler conditions. Individual enzymes showed variation in the level of recovery under the cooler temperature conditions which followed the heating period.

Factors contributing to variation in heading date in spring barley were examined in several studies commencing with a survey of developmental variation in a large collection of genotypes and concluding with the molecular genetic analysis of 7 doubled haploid populations. Genotypes varied considerably in their specific responses to photoperiod and vernalisation, and in the duration of a pre-inductive (or juvenile) phase defined in this paper as a 'basic vegetative period'. The latter includes differential genotype responses to ambient temperature and their interaction with photoperiod. Combinations of these largely independent environmental variables account for variation in heading date associated with differences in growing season conditions, particularly geographic region, sowing dates, and cultivar adaptation. Under extended and natural (short) photoperiods, in both summer and winter field plantings, conventional genetic analysis was characterised by simple Mendelian segregation combined with considerable transgressive segregation within distinct early and late flowering subpopulations. Equivalent transgressive segregation characterised molecular genetic analysis that identified 16 quantitative trait loci (QTLs) with contributions ranging from >50% of the variation recorded to <10%. These were dominated by 2 QTLs located on chromosome 2, one of which on 2HS was associated with response to extended photoperiod and the other, located near the centromere, with variation in the duration of the basic vegetative period. As only one population segregated for response to vernalisation, all analyses were restricted to parents and progeny homozygous for no response. Three other QTLs on 1HL, 3HL, and 5HL were primarily associated with vernalised parents and progeny characterised by prostrate seedling growth habits, which questions any assumption of a pleiotrophic association between genes for vernalisation and growth habit.The potential for exploiting markers for selection is considered to be limited by the considerable transgressive segregation observed in lines homozygous for parental alleles, and the limited understanding of the causes of variation in the phenotypic expression of the QTLs identified. Such markers would be useful in the selection of backcrossed progeny and in developing materials for investigating fundamental mechanisms contributing to developmental variation.

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