A. Freezing Tolerance and Low Temperature- induced Genes in 

 Higher Plants 



A specific example of how temperature can affect species 

 distribution is provided by plants of temperate regions. A unique 

 feature of most temperate plants is their ability to survive by 

 developing freezing tolerance in the fall and winter in response to 

 the shortened photoperiod and colder temperatures. 



Most hardy plants develop freezing tolerance when exposed to 

 temperatures between 0-10°C in controlled environments. Since 

 1970, it has been proposed that cold acclimation involves the 

 alteration of gene expression. Because a series of cellular 

 changes occur during the development of cold hardiness, it is 

 thought that specific enzymes might be induced. Molecular 

 approaches amply support this notion; specifically, several "cold 

 inducible" genes have been isolated. Northern blot analysis and 

 nuclear run-on experiments demonstrated that those genes are 

 regulated at the transcriptional level. 



Many temperate plants can detect changes in temperature, and 

 translate the signal into the expression of specific genes, which, 

 in turn, confer freezing tolerance to the cells. Currently, the 

 function of those genes is not known. Future research will 

 characterize these genes, analyze their promoters, and elucidate 

 the function of the gene products. 



B. Bleaching of Corals 



Approximately 30% of the shallow sea floor to 30m in the 

 tropics (i.e., between 30°N latitude and 30°S latitude) is 

 dominated by reef -building corals, and coral reef communities. The 

 stability of these communities worldwide is linked to the sustained 

 residence in the coral's cells of symbiotic dinoflagellates 

 (zooxanthellae) . When the temperature is increased to a few 

 degrees above ambient (to 32°C) , or to 10°C below ambient (to 15°C) , 

 the corals release their zooxanthellae. The result is diminished 

 calcification, loss of the products of zooxanthellae 

 photosynthesis, and death of the corals. 



How does the change in temperature destabilize the coral- 

 dinoflagellate symbiosis, evoke release of zooxanthellae, and 



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