plant surface microbiology.pdf

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James F. White Jr. et al.
Fig. 7. Two stromata
(arrows) of Atkinsonella
hypoxylon on culms of
Danthonia spicata (¥4)
Studies on Atkinsonella hypoxylon and A. texensis in vitro have demonstrated
that certain media additives will induce the fungus to develop in a way
comparable to that seen on the host grass inflorescence primordia (Bacon and
White 1994). When these claviciptaleans are grown on media containing agar
(1 %), basal salts (Murashige and Skoog; Sigma Chemical Company, Inc.), and
glucose (3 %), colonies are white, with no aerial mycelium or conidia of any
type. This is an undifferentiated mycelium, the fungus equivalent of ‘callus tissue’.
Stroma-like colonies with gray pigmentation, sporodochia producing
ephelidial conidia, and a layer of neotyphodial conidiogenous cells and conidia
can be induced by inclusion of 100 ppm of the cytokinin zeatin or kinetin
(Research Organics, Inc. Cleveland, Ohio) in the medium. The stroma-like
states in culture are most striking when the grass cytokinin zeatin is
employed. Partial induction of stroma-like states may be induced through use
of 1 % citrate (sodium or potassium salt) and 0.1–0.5 % acetate (sodium or
potassium salt). With acetate in the medium the gray pigmentation is seen to
develop, but differentiated reproductive cells do not form. With citrate in the
medium, pigmentation, sporodochia and ephelidial conidia form, but the
neotyphodial conidia do not form. Because induction of differentiation is
incomplete with the use of acetate and citrate, we believe that these compounds
are not the primary cues for stroma differentiation, but instead may
be indirectly causing differentiation by turning on secondary metabolism
pathways. On the other hand, cytokinins are plant hormones and are expected
to be present in the developing ovary tissues embedded within the fungal
stroma since ovaries produce cytokinins for regulation of their own development
(Miller 1961; Mauseth 2003). Thus the presence of cytokinins may be a