Biology Reference
In-Depth Information
Figure 13:
(A) A mass coralloid roots of
Cycas revoluta;
(B) A coralloid root magnifi ed. Photographs courtesy and copyright
Jody L. Haynes, The Cycad Society, Inc. (www.cycad.org)
Color image of this figure appears in the color plate section at the end of the topic.
Wittmann
et al
. (1965) have observed that the coralloid roots of
M
.
communis
are bacteria-free. The
presence of other eukaryotic algae, fungi and bacteria has never been observed in the coralloid roots
along with cyanobionts (Grilli-Caiola, 1980). Obukowicz
et al
. (1981) demonstrated the presence of
phenolic deposits in the mucilaginous material of algal zone by ferric chloride ultrahistochemistry
of
Cycas revoluta
-
Anabaena
symbiosis. The presence of excessive phenolic deposits (in adjacent cells
of the plasma membrane, endoplasmic reticulum within the plastids and at the periphery) in the
surrounding host tissues facilitates the exclusion of other microorganisms and permits only
Anabaena
into the coralloid roots. They noted intracellular localization of cyanobionts confi rming the earlier
observations of Grilli (1963) and Nathanielsz and Staff (1975b).
Studies on the ultrastructure and developmental cycle of symbionts living in the coralloid
roots (of
C
.
circinalis
,
C
.
revoluta
,
C
.
rumphii
,
E
.
altensteinii
,
E
.
lebomboensis
,
E
.
lehmannii
,
E
.
longifolius
,
E
.
natalensis
,
E
.
umbeluxiensis
,
E
.
villosus
,
M
.
communis
and
Dioon edule
) revealed that all the symbionts
have characteristics of
Nostoc
with vegetative cells and enlarged heterocysts but without akinetes.
However, symbionts showed a gradual and continuous increase in the frequency of heterocysts
