KINETIC ANALYSIS OF PHOTOPERIODISM 



455 



Table II. Kinetic Classification of the Red, Far-Red Photoresponses 



Class 



Graded growth 

 responses: pho- 

 tomorphogenic 



II. Time-phase 

 controlled 

 responses : 

 photoperiodic 



Type of Response 



1. Cell elongation 



2. Anthocyanin 

 synthesis 



3. Chloroplast 

 development 



4. Requirements for 

 heterotropic 

 growth 



1. Photoperiodism 



2. Photoperiodic 

 chlorosis 



3. Dormancy 



4. Seed germination 



Characteristics Common to Class 



1. Action spectra of induction with 

 maximum in the red (660 m^t) 



2. Photoreversibility by far red 



3. Low threshold energy requirement 



4. Rate limited; radiant energy elli- 

 ciency increases with time of expo- 

 sure 



5. Lack of reciprocity, It = f(t) 



6. Graded response 



7. Log energy response, no early satu- 

 ration 



8. Independent of time-phase 



1. Action spectra of induction with 

 maximum in the red (660 m/j,) 



2. Photoreversibility by far red 



3. Low threshold energy requirement 



4. Rate limited; radiant energy effi- 

 ciency increases with time of expo- 

 sure 



5. Lack of reciprocity, It = f(t) 



6. Responses tend to be ungraded or 

 threshold type 



7. Energy response complex function of 

 time, saturated at low irradiance 



8. Highly dependent on time-phase of 

 irradiation 



the kinetic behavior for certain properties are the same in both classes, 

 whereas in other respects they are quite different. However, each class 

 is relatively homogeneous in regard to the complexities of the kinetic 

 behavior. The two classes may be divided into: (1) the photomor- 

 phogenic responses in which the rate is some continuous, graded 

 function of the radiant energy and relatively unrelated to any time 

 phasing of the application of the light, and (2) the photoperiodic 

 reactions which result in ungraded or threshold type responses in 

 which, over a relatively narrow range of incident energy, one can 

 proceed from no measurable response to a maximal response and the 

 response level is a critical function of the time-phase of the light appli- 

 cation to the environmental dark-light cycle. Typical responses of the 



