The rate of oxygen consumption by cabbage seeds increased on imbibition and there was a further sharp increase on germination. This was delayed in artificially aged seeds of low vigour. The increases in oxygen consumption reflect the increased oxidation of carbohydrates via respiratory pathways. The activities of key regulatory enzymes of glycolysis and the oxidative pentose phosphate pathway were measured in aged and unaged seed lots of cabbage. Differences in the activities of glucose 6-phosphate dehydrogenase and pyrophosphate:fructose 6-phosphate 1-phosphotransferase were correlated with the rate of germination (T50) in seed lots with large differences in seed vigour induced experimentally by artificial aging. However, the activities of these enzymes could not be used to distinguish between untreated seed lots which had smaller vigour differences apparent only under stress. The enzymes are presumably not controlling and determining seed vigour, but merely reflecting actual seed performance under the current conditions.

Development of muscle is critically dependent on several hormones which in turn are regulated by nutritional status. We therefore determined the impact of mild postnatal undernutrition on key markers of myofibre function: type I slow myosin heavy chain (MyHC) isoform, myosin ATPase, succinate dehydrogenase and α-glycerophosphate dehydrogenase. In situ hybridization, immunocytochemistry and enzyme histochemistry were used to assess functionally distinct muscles from 6-week-old pigs which had been fed an optimal (6 % (60 g food/kg body weight per d)) or low (2 % (20 g food/kg per d)) intake for 3 weeks, and kept at 26°C. Nutritional status had striking muscle-specific influences on contractile and metabolic properties of myofibres, and especially on myosin isoform expression. A low food intake upregulated slow MyHC mRNA and protein levels in rhomboideus by 53 % (P < 0·01) and 18 % (P < 0·05) respectively; effects in longissimus dorsi, soleus and diaphragm were not significant. The oxidative capacity of all muscles increased on the low intake, albeit to varying extents: longissimus dorsi (55 %), rhomboideus (30 %), soleus (21 %), diaphragm (7 %). Proportions of slow oxidative fibres increased at the expense of fast glycolytic fibres. These novel findings suggest a critical role for postnatal nutrition in regulating myosin gene expression and muscle phenotype. They have important implications for optimal development of human infants: on a low intake, energetic efficiency will increase and the integrated response to many metabolic and growth hormones will alter, since both are dependent on myofibre type. Mechanisms underlying these changes probably involve complex interactions between hormones acting as nutritional signals and differential effects on their cell membrane receptors or nuclear receptors.