218 moderator: s. hestrin 



(IV) hiduction of Cryptobiosis 



Moderator: Perhaps if we make a list of elements which 

 induce or break dormancy in different organisms we might find 

 a few common denominators for the different systems. 



Halvorson : Dormancy in micro-organisms was once thought 

 to be induced by unfavourable conditions. This is not so. But I 

 think it is true that the inducement to form spores is occasioned 

 by a change in the nutritional environment, and this perhaps 

 may be true in other systems as well. 



Koller: The basic similarity in the various dormancy- 

 inducing and -breaking mechanisms is the fact that they are all 

 triggered by the environmxcnt. 



Lees: I agree. We have factors like dryness and lack of food 

 as well as guide factors such as photoperiod. The response to 

 the latter allows anticipation of unfavourable conditions. The 

 dormancy-controlling factors are remarkably similar in buds 

 and insects. In both cases induction is by photoperiod and 

 breaking by chilling. But how far does this similarity really go? 

 The guide stimuli are shared, but different response mechanisms 

 have been evolved. 



Moderator: It is a credo of biochemists that there must be 

 some common mechanism. We can only discover it by looking 

 'under the skin'. The zoologist is trained to see many differences 

 and dissimilarities. Specifically one asks whether the several 

 photoreceptive and 'endogenous clock' mechanisms encountered 

 in different species are not in principle similar? We know so 

 little, it is perhaps better not to try to answer this particular 

 question yet. We are now concluding our discussion for today, 

 but I would very much like you to give some thought to the 

 following questions by way of preparation for our second 

 session. Is there perhaps an important experiment which you 

 would like to see performed in this field? If so, would you like 

 to describe it? Secondly, could you point to a biological system 

 particularly suitable to the study of cryptobiosis? Can you 

 suggest quantitative procedures which would facilitate a more 

 exact approach to our problems? 



