Distribution of phytoplasmas in infected plants as revealed by real-time PCR and bioimaging.
Phytoplasmas are cell wall-less bacteria inhabiting the phloem and utilizing it for their spread. Infected plants often show changes in growth pattern and a reduced crop yield. A quantitative real-time polymerase chain reaction (Q-PCR) assay and a bioimaging method were developed to quantify and localize phytoplasmas in situ. According to the Q-PCR assay, phytoplasmas accumulated disproportionately in source leaves of Euphorbia pulcherrima and, to a lesser extent, in petioles of source leaves and in stems. However, phytoplasma accumulation was small or nondetectable in sink organs (roots and sink leaves). For bioimaging, infected plant tissue was stained with vital fluorescence dyes and examined using confocal laser scanning microscopy. With a DNA-sensitive dye, the pathogens were detected exclusively in the phloem, where they formed dense masses in sieve tubes of Catharanthus roseus. Sieve tubes were identified by counterstaining with aniline blue for callose and multiphoton excitation. With a potentiometric dye, not all DNA-positive material was stained, suggesting that the dye stained metabolically active phytoplasmas only. Some highly infected sieve tubes contained phytoplasmas that were either inactive or dead upon staining.
Christensen
Nynne Meyn
NM
Department of Plant Biology, The Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Copenhagen, Denmark.
Nicolaisen
Mogens
M
Hansen
Michael
M
Schulz
Alexander
A
D030008:Catharanthus / Q000382:microbiology*; D028481:Euphorbia / Q000382:microbiology*; D005456:Fluorescent Dyes; D018613:Microscopy, Confocal / Q000379:methods; D045582:Phytoplasma / Q000502:physiology*; D010935:Plant Diseases / Q000382:microbiology*; D018517:Plant Roots / Q000382:microbiology; D018547:Plant Stems / Q000382:microbiology; D016133:Polymerase Chain Reaction / Q000379:methods*; D013194:Staining and Labeling / Q000379:methods
D005456:Fluorescent Dyes