No abstract

In 1977 and 1978, all possible single‐cross hybrids between 12 maize (Zea mays L.) inbreds were evaluated for root‐pulling resistance and yield at plant densities of 38,500 and 55,300 plants per ha. Griffing's diallel analysis was used to determine the nature of genetic effects responsible for production of a large root system as estimated by root‐pulling resistance. Both additive and nonadditive genetic effects contributed significantly (P < 0.01) to the expression of root‐pulling resistance. General combining ability effects interacted significantly (P < 0.01) with environmental changes caused by plant densities and by years, in particular. These interactions may reduce effectiveness of selection for root size based on root‐pulling resistance. The correlation of root‐pulling resistance to grain yield was not significant in either year at either plant density, suggesting that selection for increased root size to gain increased corn rootworm tolerance would not result in decreased grain yield.

No abstract

No differences in oxidative phosphorylation or in the per cent of [4-14C]progesterone were found in ovarian mitochondria of immature rats after treatment with 20 IU of pregnant mare serum gonadotropin (PMSG) iv 30 min before killing. However, treatment of immature rats with 20 IU of PMSG sc 54 h prior to killing decreased the ADP:O ratio and increased the per cent of [4-14C]cholesterol conversion. Electron microscopic studies showed that mitochondria with lamellar cristae were prominent in ovaries of untreated rats, while large pleomorphic mitochondria and mitochondria with tubulovesicular cristae dominated in ovaries of PMSG-treated rats. Ovarian homogenates separated by zonal centrifugation showed three peaks od cytochrome oxidase activity which shifted to the heavier end of the gradient after PMSG treatment. These studies suggest that PMSG treatment influences ovarian mitochondria, possibly by stimulating the synthesis of additional functional components and/or the biogenesis of new mitochondria. Aminoglutethimide addition to bovine luteal mitochondria decreased steroidogenesis by 60% when succinate was used as substrate. However, there was a 16% increase in the ADP:O ratio, apparently due to a decrease in oxygen utilization. When oligomycin was added to luteal mitochondria, there was a 30% decrease in the ACP:O ratio but a 300% increase in [4-14C]cholesterol conversion. Dinitrophenol also decreased mitochondrial steroidogenesis. These results suggest that energy obtained from succinate oxidation can be diverted from phosphorylation to support steroidogenesis.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.