Biology Reference
In-Depth Information
Fig. 1.1
Course of a typical optimal quantum yield curve of the brown alga
Pylaiella littoralis
during an inhibition phase of 120 min with an irradiance of 500
m
mol m
2
s
1
and a subsequent
period of recovery under 10
m
mol m
2
s
1
white light. Points show yield measurements (
F
v
/
F
m
)
dependent on the time course. The
dashed line
shows the kinetics of the slow process, the
dotted
line
those of the fast process, and the
solid line
the kinetics of the predicted process combined by
the slow and the fast kinetics. Mean values
SD,
n ¼
3,
r
2
¼
0.999 (after Hanelt
1998
)
This explains why the course of recovery shows generally two phases (Hanelt
et al.
1997a
,
b
,
c
). Using these equations the data of the optimal quantum yield can
be well fitted with a coefficient of determination of
r
2
0.99 (Fig.
1.1
).
In conclusion, the fast process could represent photoprotection or the activity of
the xanthophyll cycle and the slow process the course of photoinactivation or the
occurrence of D
1
damage and/or inactivation of reaction centers. Algae which are
adapted to dim light conditions show a higher fraction of the slow process, whereas
the reaction of algae adapted to strong light conditions mainly consist of the fast
reaction e.g., Fig.
1.1
(Hanelt
1998
).
First field experiments on photoinhibition in macroalgae were done by Huppertz
et al. (
1990
). They showed that the midday depression of photosynthesis was
clearly caused by photoprotection. Specimens of the brown alga
Fucus serratus
living in intertidal rock pools and, hence, are covered by water during low tide,
showed a considerable decrease of photosynthetic activity under excessive natural
light conditions. The photoinhibitory state is conserved by moderate desiccation in
air in this species because the thalli show the same state of photoinhibition after
reabsorbing water as measured before they became uncovered during falling tide.
Thereafter it was demonstrated that the photosynthetic oxygen production
measured at nonsaturating fluence rates and the optimal quantum yield (
F
v
/
F
m
)
show an approximately inverse course in comparison with the fluence rate of
daylight during the day (Hanelt
1992
; Hanelt et al.
1993
).
According to the recent review of Murchie and Niyogi (
2011
) the mechanisms
included in photoprotection regulate absorption and dissipation of light energy. The
immobility of plants does not allow leaving temporarily high light-exposed areas,
