Biology Reference
In-Depth Information
of peroxidase have fully operative H
2
O
2
scavenging mechanisms. The increase of acid and alkaline
phosphatases correlated well with the disappearance of polyphosphate granules in the akinetes that
constitute the phosphate reserves of vegetative cells (Keck and Stich, 1957; Talpasayi, 1963; Wolk,
1973). Sarma and Mehta (1985) suggested that akinete formation in
A
.
torulosa
in presence of sodium
β-glycerophosphate was due to the ability of the organism to solubilize such bound phosphate groups
and utilized it for growth and akinete differentiation. GS has been recognized as the key enzyme
for the incorporation of ammonia into the metabolic pool in cyanobacteria (Haselkorn, 1978). The
activity of GS declined coinciding with maturation phase signifying that nitrogen fi xation process
slows down at the time of akinete differentiation. This is supported by the observations of Sutherland
et al
. (1979) who noticed a lowering of nitrogenase activity at the time of akinete differentiation
in
Nostoc
PCC 7524. In addition, ATPase activity decreased from initiation through maturation
phase to the mature akinete phase (Sarma and Swarn Kanta, 1982). A comparison of the activities
of GS, glutamate pyruvate transaminase (GPT) and glutamate oxoglutarate transaminase (GOT)
from different nutrient conditions inducing and inhibiting akinete differentiation revealed akinete
formation occurred in nutrient combinations where GS activity decreased (Sarma and Swarn Kanta,
1982). Subsequent studies on the metabolic activities of
A
.
doliolum
(Rao
et al
., 1984) and
F
.
muscicola
(Singh and Kashyap, 1988) confi rmed the above observations.
II. FACTORS AFFECTING AKINETE DIFFERENTIATION
1) Environmental factors
:
Light and temperature have been shown to regulate akinete development
in cyanobacteria. Wolk (1965) found 80 ft. c. light intensity to be optimum for akinete formation
in
A
.
cylindrica
. Increase of light intensity lowered akinete frequency in
Nostoc
PCC 7524. Akinete
differentiation was reported in presence of light in
A
.
torulosa
and
No
.
spumigena
and dark incubated
cultures of these cyanobacteria did not differentiate akinetes (Sarma and Swarn Kanta, 1979; Pandey
and Talpasayi, 1980). The quality of light required for akinete differentiation in
No
.
spumigena
was
noted to be red, yellow and blue regions of the spectra (Pandey and Talpasayi, 1980). Possible
involvement of red light in the akinete differentiation of
A
.
torulosa
was reported by Fernandes
and Thomas (1982). Akinete formation was highest in red light when compared to white and green
lights but blue light reduced akinete production considerably in
Aph
.
fl os-aquae
(Thompson
et al
.,
2009). On the other hand, light limitation due to increase in culture density and self-shading has
been suggested to be the major factor for akinete formation (Fay, 1969b; Fay
et al
., 1984; Wyman and
Fay, 1986; Nichols and Adams, 1982; Herdman, 1987, 1988). Light limitation was found to induce
the formation of akinetes in
A
.
cylindrica
(Nichols
et al
., 1980),
A
.
circinalis
(Fay
et al
., 1984) and
G
.
echinulata
(Wyman and Fay, 1986). Light limitation does not seem to be the main trigger in
A
.
circinalis
(van Dok and Hart, 1996).
Temperatures above 20ºC (up to 30ºC) enhanced akinete frequency in
A
.
cylindrica
(Wolk,
1965). Increase of temperature to 30-35ºC induced akinete formation in
No
.
spumigena
in a minimal
medium or in distilled water (Pandey and Taplpasayi, 1981). Incipient desiccation appeared to be the
trigger for akinete formation in
A
.
variabilis
and
N
.
linckia
(Reddy, 1983b). In a number of planktonic
cyanobacteria temperature seems the main trigger for akinete formation (Li
et al
., 1997).
2) Nutritional factors
:
Of the nutritional factors phosphate defi ciency, carbon and nitrogen sources
have received greater attention.
(i) Phosphate (P) defi ciency and nitrogen assimilation
:
P-defi ciency has been recognized as the most
signifi cant factor governing akinete development in
A
.
cylindrica
,
A
.
doliolum
,
A
.
torulosa
,
A
.
circinalis
,
