Oquist G, Huner NPA
Effects of Cold-Acclimation on the Susceptibility of Photosynthesis to Photoinhibition in Scots Pine and in Winter and Spring Cereals - a Fluorescence Analysis
Functional Ecology: 1991 5:91-100
Winter and spring varieties of cereals and seedlings of Scots pine were exposed to a low temperature regime of 4-5-degrees-C for the induction of frost hardiness. The effect of cold acclimation on the susceptibility of photosynthesis to photoinhibition was analysed using variable chlorophyll fluorescence. Winter rye responded with an increased resistance to photoinhibition upon cold hardening, whereas low temperature acclimated spring barley and Scots pine showed no increase in resistance to photoinhibition. In the case of winter rye, the leaves had to develop at low temperature in order to acquire increased resistance to photoinhibition. It is suggested that resistance to photoinhibition of photosynthesis under low temperature acclimation of cereals is important for the induction of frost hardiness. The importance of leaf orientation for the susceptibility of photosynthesis to photoinhibition at low temperatures was demonstrated, horizontal leaves were more photoinhibited than were vertical leaves (light coming from above). Most species and cultivars studied exhibited some photoinhibition during cold acclimation. Even weak light of a PPFD of 50-mu-mol m-2 s-1 under long day conditions and 5-degrees-C can induce photoinhibition of Scots pine. It is concluded that photoinhibition of photosynthesis under low temperature conditions no longer should be considered only as a high light response and that light probably is a much more significant stress factor under low temperature regimes than previously thought. The inability of the evergreen Scots pine to acquire an increased resistance to photoinhibition is discussed in relation to its natural habitat, where low temperatures and high light often occur together during winter. It is suggested that photoinhibition of photosynthesis under conditions when overall photosynthesis is limited by temperature provides a means for controlled dissipation of excessive excitation as heat. In this view photoinhibition is a naturally occurring phenomenon of significant physiological and ecological importance for evergreen species in cold, temperate climates.
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