In
the cold light of day
Many
green plants are damaged by exposure to cold, sunny conditions. Not only is
there the likelihood of freezing damage but also of damage to the
photosynthetic machinery, such as photo-bleaching. The linkage between cold and
light damage is discussed by Rapacz et al., Kraków and Czgestochowa,
Poland (pp.
689–699) in relation to cereals. They point out that the cold-response
gene COR14b is also involved with chloroplast redox metabolism: COR14b mRNA
increases following cold treatment but accumulation of the protein is also
regulated post-transcriptionally by the redox state of chloroplast plastocyanin.
The authors thus investigated the effects of cold-acclimation on both
cold-tolerance and tolerance to high light in four barley (Hordeum vulgare) cultivars.
Acclimation at 2 °C for 14 d significantly increased the freezing tolerance of
all four cultivars, such that the temperature causing 50 % lethality dropped in
14-d acclimation to –12 °C in the least cold-tolerant cultivar and to –15 °C in
the most cold-tolerant. Cold-acclimation also led to increased tolerance of
high light and an increased photosynthetic capacity when exposed to high light
conditions after cold acclimation. The authors went on to study the expression
of several proteins involved in cold acclimation and/or in
photosynthetic metabolism; here we focus on Cor14b. In cultivars that had
greater basic freezing tolerance and less basic light tolerance, COR14b mRNA
and Cor14b protein accumulated quickly during acclimation but then declined (although
not back to control levels). In cultivars with less basic freezing tolerance
and greater basic light tolerance, mRNA and protein accumulated more slowly but
higher levels were maintained through 14-d acclimation. We may conclude that
the results obtained by the authors are symptoms of a network of interacting
events enabling the plant to link together different aspects of its activity in
response to environmental stresses – a nice example of what is now fashionably
called systems biology.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
