Identification of phytoplasmas in eggs, nymphs and adults of Scaphoideus titanus Ball reared on healthy plants.

A survey for the presence of aster yellows-related phytoplasmas in the different life stages of Scaphoideus titanus was carried out by means of PCR and nested-PCR assays. Using a phytoplasma 16Srl group-specific primer pair followed by RFLP analysis of amplified products, we were able to detect and identify phytoplasmas from eggs, newly hatched nymphs, fourth and fifth instar nymphs and adults reared on ten phytoplasma-free Vicia faba seedlings. Two of these broad beans became infected, whereas PCR failed to detect phytoplasmas in the same ten plants before leafhopper rearing. These results suggest the possibility of transovarial transmission of aster yellows-related phytoplasmas in S. titanus.

Biochemical and electron microscopic evidence that cell nucleus negatively controls mitochondrial genomic activity in early sea urchin development.

Enucleated halves of sea urchin eggs obtained by centrifugation contain almost all the mitochondrial population of the egg. Removal of the nucleus followed by parthenogenetic activation stimulates the incorporation of [3H]thymidine into the mitochondrial DNA, whereas no such incorportion is observed in activated whole eggs. The block is not the result of a modification in the permeability of the mitochondrial membrane. Electron microscopic observations demonstrated duplication of mitochondrial DNA molecules in activated enucleated halves. No duplication was found in the mitochondrial DNA from activated whole eggs or from nonactivated enucleated halves. We conclude that the cell nucleus exerts a negative control on the activity of the mitochondrial genome through some short-lived nuclear substance(s).