OPERATION OF THE XANTHOPHYLL CYCLE IN NONSTRESSED AND STRESSED CELLS OF DUNALIELLA-SALINA TEOD IN RESPONSE TO DIURNAL CHANGES IN INCIDENT IRRADIATION - A CORRELATION WITH INTRACELLULAR BETA-CAROTENE CONTENT
Lg. Phillips et al., OPERATION OF THE XANTHOPHYLL CYCLE IN NONSTRESSED AND STRESSED CELLS OF DUNALIELLA-SALINA TEOD IN RESPONSE TO DIURNAL CHANGES IN INCIDENT IRRADIATION - A CORRELATION WITH INTRACELLULAR BETA-CAROTENE CONTENT, Journal of plant physiology, 146(4), 1995, pp. 547-553
Changes in carotenoid composition were monitored on a diurnal basis in
cells of Dunaliella salina Teed, grown outdoors, under natural irradi
ance in mass culture. Stressed cells contained approximately four time
s more beta-carotene than non-stressed cells. The net change in beta-c
arotene content however, was similar for both treatments and correlate
d closely with changes in photon flux density during the diurnal cycle
. Xanthophyll levels were higher in stressed cells suggesting that exc
ess light was not the only factor involved in stimulating carotenoid a
ccumulation, although xanthophyll content increased in nonstressed cel
ls to a level similar to that of stressed cells, with increasing photo
n flux density. Light-response curves of zeaxanthin and beta-carotene
formation displayed a biphasic nature in stressed cells. In nonstresse
d cells however, zeaxanthin formation was rapid and the descending lig
ht-response curve showed little change in net zeaxanthin levels. High
beta-carotene-containing cells had substantial amounts of zeaxanthin a
nd levels of this carotenoid remained higher in stressed cells through
out the diurnal cycle. Changes in intracellular beta-carotene occurred
coincident with operation of the xanthophyll cycle during the diurnal
period. Non-stressed and stressed cells showed similar de-epoxidation
of the xanthophyll cycle at peak photon flux denisty. Although non-st
ressed cells formed more beta-carotene and zeaxanthin in response to i
ncreasing irradiance, stressed cells formed beta-carotene and zeaxanth
in more rapidly i.e. at lower photon flux density. Zeaxanthin formatio
n in stressed cells occurred as a consequence of violaxanthin de-epoxi
dation. By comparasion, zeaxanthin production in non-stressed cells oc
curred by two probable mechanisms: 1, by rapid de-epoxidation of viola
xanthin and 2, a slow but continuous de novo synthesis which increased
the total zeaxanthin pool.