Note: Colonization and invasion of leaves of the aquatic macrophyte Ceratophyllum demersum L. by epiphytic bacteria
1991
Underwood, G.J.C.
The colonization of leaves of the aquatic macrophyte Ceratophyllum demersum L. by epiphytic bacteria, and the hypothesis that bacterial invasion causes leaf senescence, was studied using transmission and scanning electron microscopy and light microscopy. Population densities of epiphytic bacterial communities on Ceratophyllum leaves were positively correlated with leaf age. Initial settlement of bacteria on young leaves appeared to favour the boundaries between epidermal cells. On older leaves, large populations of bacteria were present over the whole surface. One third of senescent Ceratophyllum leaves examined by transmission electron microscopy showed signs of bacterial invasion. Of these, up to 54% of the leaf's epidermal cells contained bacteria. Areas of cell wall degradation were associated with invasive bacteria in senescent leaves. In healthy, nonsenescent leaves, no bacterial invasion was observed. These results suggest that epiphytic bacteria did not cause leaf senescence but probably colonized the internal tissues of leaves once senescence had occurred.
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