ROLE OF PLANT HORMONES IN 

 DORMANCY OF SEEDS 



ALEXANDRA POLJAKOFF-MAYBER 



Department of Botany, Hebrew University, 

 Jerusalem (Israel) 



The importance ascribed to plant hormones in controlling 

 various functions and processes of plant growth and behaviour 

 is increasing rapidly. 



The first group of plant hormones isolated and identified was 

 that of the auxins. These were discovered in connection with 

 studies on stem elongation, and extension growth is still the 

 basis of some bioassay methods for this group of hormones. 

 They are sometimes designated as plant growth substances^' -. 

 In this group are classified all the substances causing extension 

 growth and having in their structure an unsaturated arom.atic 

 nucleus and a side chain terminating in a carboxyl group or 

 one that is easily oxidized to a carboxyl. The best known 

 representative of this group is 3-indolyacetJc acid (lAA). 



As research was extended, it was proved that the same sub- 

 stances actually aff'ect numerous and very variable aspects of 

 plant development, such as root initiation, cambial activity, 

 apical dominance, leaf abscission, fruit growth and many 

 others^- 3. For many years the auxins were the only identified 

 group of hormones; other hormones such as the 'calins' and the 

 'florigens' were postulated, but not isolated or identified. 



Recently, two new groups of substances were isolated and 

 their effect on plant development allows us to include them 

 among the plant hormones; these are the gibberellins and the 

 kinins. The gibberellins were first isolated as products of fungal 

 metabolism^' 5. and kinetin, the best known compound among 

 the kinins, was artificially produced from nucleic acids^. In due 

 course it was shown that higher plants apparently contain 

 substances of similar structure and activity. 



Evidence will be brought here to show that the three groups 



References p. 172 



