Abstract
Roots of <em>Gladiolus </em>x <em>hybridus </em>Van Houtte plants infected with aster yellows phytoplasma were examined. The infected plants had a reduced root system in comparison to control plants. Their roots were thinner and the stele organisation was changed. Phytoplasmas were present in sieve tubes, companion cells and phloem parenchyma cells of the infected plant roots. Free calcium ions were localized in the cells of infected plants. Cells of the stele of infected roots, especially these infected with phytoplasmas, showed an increase of calcium antimonite deposits in theirs protoplasts. Also the number of calcium antimonite deposits increased in sieve tubes of infected roots. The deposits were present on plasma membrane, around the sieve tube plate and also in the lumen of the sieve tube. The increase of free calcium ions in sieve tubes did not cause the occlusion of sieve tube pores. Companion cells and some parenchyma cells with phytoplasmas did not react to phytoplasma infection with an increase of Ca<sup>2+</sup> ions in protoplast. The parenchyma cells showing signs of degeneration reacted with high increase of calcium ions. The Ca<sup>2+</sup> ions were present mainly in cytoplasm of infected parenchyma cells. There were calcium antimonite deposits in infected plant roots xylem elements and in intracellular spaces of cortex parenchyma. Such deposits were not present in control plants.
Highlights
IntroductionPhytoplasmas (previously called mycoplasmalike organisms or MLOs) are divided into 20 groups, among which the aster yellows (AY) group is one of the biggest (Seemuller et al 1998)
Phytoplasmas are divided into 20 groups, among which the aster yellows (AY) group is one of the biggest (Seemuller et al 1998)
The structure of thicker roots from infected plants resembled that of the lateral roots from control plants, both because of the presence of parenchyma cells in the middle of stele and because of the similar vessels diameter (Fig. B, C)
Summary
Phytoplasmas (previously called mycoplasmalike organisms or MLOs) are divided into 20 groups, among which the aster yellows (AY) group is one of the biggest (Seemuller et al 1998). AY phytoplasmas have been found in many herbaceous as well as in some woody plants producing typical symptoms like witches-broom, flower distortion and virescence. AY disease of gladiolus has been widely distributed throughout the USA, were it was first described in 1952 (Magie et al 1952). The disease caused by phytoplasma was found in commercially produced Gladiolus plants by Kamiñska et al (1999). Several processes important for plant functioning, such like phloem and xylem transport, have been proposed to be regulated by changes in free Ca2+ (Brauer et al 1998; Dematry et al 1984). Knoblauch et al (2001) showed that crystalloid p-protein disperses and occludes sieve plate pores after injury. This process was controlled by calcium fluxes. Ca2+ has been proposed to participate in regulation of enzymes (Avdiushko et al 1997)
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