light and the pigment 109 



Phytochrome and Other Photomorphogenic Responses 



As mentioned above, the action of phytochrome is very general in 

 the plant kingdom. Table 7-1 contains the examples which have 



Table 7-1. Plant Growth Responses under the Control 

 OF THE Phytochrome System 



Most of the following responses are listed in 8, 10, 18, 19 or 36. Some 

 of the less well-known examples, or some not listed in these reviews, 

 have references cited in the table. 



I . Time-independent responses, the degree of response usually related 

 to the amount of F-phytochrome produced by irradiation. 



A. Elongation or enlargement responses. 



1. Stem elongation of vascular plants. 



2. Petiole elongation. 



3. Root growth (54,71). 



4. Leaf enlargement. 



5. Plumular hook unfolding (for interesting response in lettuce, 

 see 65). 



B. Pigment formation. 



1. Anthocyanin formation in various systems such as apple or 

 turnip skin, cabbage leaves, etc. 



2. Carotene formation in tomato skins. 



3. Activation of the chlorophyll synthesizing mechanism. 



C. Process initiation. 



1. Germination of many seeds and some spores (e.g. in moss, 

 fern, see 39 and 65). 



2. Growth in the dark on a sucrose medium (heterotrophic 

 growth) of Lemna minor or of fern gametophyte (64). 



3. Turning of chloroplasts towards the light in the green alga 

 Mougeotia (50). 



4. Change to the gametophyte in a sporophyte culture of a moss 

 {Psycomitriiim pinforme) in response to 10 minutes far-red 

 light before darkness (unpublished data of L. Bauer, Botan- 

 isches Institut, Tiibingen). 



5. Initiation of timing in certain circadian rhythms (61), 



II. Time-dependent responses: photoperiodism. The degree of response 

 may be highly quantitative but also time dependent. 



1. Flower initiation in long-day and short-day plants. 



2. Normal and abnormal floral development in many species (e.g. 

 sex determination in hemp, 44; cleistogamy, in which flowers fail 

 to open and complete development, 43 ; and phylloidy of bracts 

 in which bracts increase in size and resemble foliage leaves if floral 

 induction is minimal, 49). 



3. Various morphological responses of the vegetative plant to day- 

 length (e.g. succulency of Crassulacea, tuber or bulb formation, 

 and inhibition of axillary buds in cocklebur, 41). 



4. Development of various reproductive structures in bryophytes (40). 



5. Germination of certain seeds. 



6. Onset of dormancy in many plants, sometimes breaking of 

 dormancy. 



7. Carbon dioxide fixation in succulents. 



