M. Havaux, RAPID PHOTOSYNTHETIC ADAPTATION TO HEAT-STRESS TRIGGERED IN POTATO LEAVES BY MODERATELY ELEVATED-TEMPERATURES, Plant, cell and environment, 16(4), 1993, pp. 461-467
Photosystem II (PSII) is considered to be one of the most thermolabile
aspects of photosynthesis. In vivo measurements of chlorophyll fluore
scence and photosynthetic oxygen evolution in 25-degrees-C-grown potat
o leaves (cv. Haig) indicated that the threshold temperature T(C) abov
e which PSII denatures was indeed rather low - about 38-degrees-C - wi
th temperatures higher than T(C) causing a rapid and irreversible loss
of PSII activity. The present study demonstrates the existence of ada
ptive processes which rapidly adjust the in vivo thermal stability of
PSII in response to temperature increase. Transfer of potato leaves fr
om 25-degrees-C to temperatures slightly lower than T(C) (between 30 a
nd 35-degrees-C) was observed to cause an upward shift of the T(C) val
ue without any appreciable loss of PSII activity. This increase in PSI
I thermotolerance was substantial (around +5-degrees-C in the Haig cul
tivar), rapid (with a half-time of approximately 20 min) and slowly re
versible at 25-degrees-C (>24h). As a consequence, high temperatures (
e.g. 40-degrees-C) which caused a complete and irreversible inhibition
of the PSII function had very little effect in 35-degrees-C-treated l
eaves, thus suggesting that the above-described PSII changes could be
of prime importance for the plant's behaviour in the field. Accordingl
y, the rise in T(C) at 35-degrees-C was much larger (+8-degrees-C) in
Sahel, a stress-resistant potato variety, than in the heat-sensitive H
aig cultivar.