The long- and short-term movement of carbon in a field crop of winter wheat was investigated with the radioactive tracer carbon-14. The flag leaves of individual plants assimilated a pulse of 14CO2 and the plant parts were assayed subsequently. Groups of plants were pulse-labelled four times during the main period of growth—twice before and twice after anthesis. Plants were harvested and assayed twice weekly after labelling and the time-course of the changes in the amount of 14C recovered from the leaves, stems and ears was observed for each group of plants. Concurrently with these long-term studies, other wheat plants were pulse-labelled, then harvested and assayed 24 h later. The partitioning of 14C between leaves, stem, ear and in some cases roots, was measured over the period from the start of stem elongation to the end of grain filling. Two distinct types of relocation of carbon were observed. Carbon assimilated early in the growth of the plant and used in the growth of new leaves was seen to be partly relocated to the ear. Carbon assimilated 8 d after anthesis was partly stored in the stem, and 15 d later relocated to the ear. This relocation corresponded to a decrease in stem dry mass seen in growth analysis. Little other change in the 14C content of the plants occurred, suggesting that most respiration used current rather than stored assimilate.
In winter wheat (Triticum aestivum L.), the development of a methodology to estimate genetic divergence between parental lines, when combined with knowledge of parental performance, could be beneficial in the prediction of bulk progeny performance. The objective of this study was to relate F2 heterosis for grain yield and its components in 116 crosses to two independent estimates of genetic divergence among 28 parental genotypes of diverse origins. Genetic divergence between parents was estimated from (a) pedigree relationships (coefficients of kinship) determined without experimentation, and (b) quantitative traits measured in two years of field experimentation in Kansas and North Carolina, USA. These distances, designated (1 -r) and G, respectively, provided ample differentiation among the parents. The 116 F2 bulks were evaluated at four locations in Kansas and North Carolina in one year. Significant rank correlations of 0.46 (P = 0.01) and 0.44 (P = 0.01) were observed between G and grain yield and kernel number heterosis, respectively. Although (1 -r) was poorly associated with grain yield heterosis, G and midparent performance combined to account for 50% of the variation in F2 yields among crosses when (1 -r) was above the median value, whereas they accounted for only 9% of the variation among crosses when (1-r) was below the median. Midparent and (1 -r) had equal effects on F2 grain yield (R (2)= 0.40) when G was greater than the median value. A breeding strategy is proposed whereby parents are first selected on the basis of performance per se and, subsequently, crosses are made between genetically divergent parents that have both large quantitative (G) and pedigree divergence (1 -r).
Peroxidase isozymes from winter wheat (Triticum aestivum L. cv Orso) seedlings extracts showed phenoloxidase-like activity, becoming visible on polyacrylamide gels also in the absence of hydrogen peroxide. The results obtained after a characterization of the two activities, based on their substrate specificity, on their selective inhibition, and on the possible occurrence of artifacts, suggested the existence of polyfunctional peroxidase isozymes. Different isozymes possessing only phenol oxidase activity were not found in the same plant material. This appears to be the first evidence of phenoloxidase-acting isoperoxidases in winter wheat.