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The hypothesis that a wild-type strain of Xylella fastidiosa would restore the ability of rpfF mutants blocked in diffusible signal factor production to be transmitted to new grape plants by the sharpshooter vector Graphocephala atropunctata was tested. While the rpfF mutant was very poorly transmitted by vectors irrespective of whether they had also fed on plants infected with the wild-type strain, wild-type strains were not efficiently transmitted if vectors had fed on plants infected with the rpfF mutant. About 100-fewer cells of a wild-type strain attached to wings of a vector when suspended in xylem sap from plants infected with an rpfF mutant than in sap from uninfected grapes. The frequency of transmission of cells suspended in sap from plants that were infected by the rpfF mutant was also reduced over threefold. Wild-type cells suspended in a culture supernatant of an rpfF mutant also exhibited 10-fold less adherence to wings than when suspended in uninoculated culture media. A factor released into the xylem by rpfF mutants, and to a lesser extent by the wild-type strain, thus inhibits their attachment to, and thus transmission by, sharpshooter vectors and may also enable them to move more readily through host plants. © 2014 The American Phytopathological Society.

The bacterial ice nucleation gene inaZ confers production of ice nuclei when transferred into transgenic plants. Conditioning of the transformed plant tissue at temperatures near 0 degrees C greatly increased the ice nucleation activity in plants, and maximum ice nucleation activity was achieved only after low-temperature conditioning for about 48 h. Although the transgenic plants contain similar amounts of inaZ mRNA at both normal and low temperatures, low temperatures are required for accumulation of INAZ protein. We propose that the stability of the INAZ protein and thus ice nucleation activity in the transgenic plants is enhanced by low-temperature conditioning.

The complexation of cupric ions added to solutions of different organic compounds and to culture media was determined using an ion-specific electrode to ascertain the toxic forms of copper. Toxicity of Cu 2+ to copper-sensitive and copper-tolerant strains of Pseudomonas syringae was reduced in the presence of all organic compounds tested, including 100 mM solutions of glucose, fructose, sucrose, succinate, and particularly citrate. The apparent toxicity of copper solutions was reduced 30× or more in the presence of organic solute (...)