The development of chloroplast ultrastructure and Hill reaction activity during leaf ontogeny in different maize (Zea mays L.) genotypes

Changes in Hill reaction activity (HRA) and ultrastructure:of mesophyll cel l (MC) chloroplasts were studied during the ontogeny of third leaf of maize plants using polarographic oxygen evolution measurement, transmission elec tron microscopy, and stereology. The chloroplast ultrastructure was compare d in young (actively growing), mature, and senescing leaves of two differen t inbreds and their reciprocal F1 hybrids. Statistically significant differ ences in both HRA and MC chloroplast ultrastructure were observed between d ifferent stages of leaf ontogeny. Growth of plastoglobuli was the most stri king characteristic of chloroplast maturation and senescence. The chloropla sts in mature and senescing leaves had a more developed system of thylakoid s compared to the young leaves. Higher HRA was usually connected with highe r thylakoid volume density of MC chloroplasts.