50 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1954 



darkness for 20 hours, the hook will open about 20° ; if the red ex- 

 posure is followed by far-red energy in the range of 710 to 1,000 mju. of 

 approximately 100 millijoules, the red effect is almost completely 

 neutralized. The photoreversal can be repeated several times on the 

 same section and the ultimate response is determined by the wave- 

 lengths of the last given exposure. This work is being greatly ex- 

 panded to determine quantitatively the relative energies required and 

 the action spectrum of the photoreversal process. 



Studies have been completed on the effectiveness of various wave- 

 lengths of the spectrum on the opening of the bean hook, using a series 

 of interference filter monochromator units, the design of which was 

 reported previously. With 10 of these units set up in a constant- 

 temperature room, it has been possible to cover the spectrum from 365 

 to 800 mfx at intervals of 10 to 20 m/A. The action spectrum has a strong 

 maximum at 660 plus or minus 5 m;* and evidence of two weak maxima 

 at 620 and 700 ni/x. There are no strong maxima in the blue or green. 

 Work is now in progress on the isolation of a pigment with absorption 

 maxima in the general regions indicated by the action spectrum. Thus 

 far no success has been obtained in isolating such a pigment. 



Excised bean hooks have been exposed to X-ray dosages ranging 

 from 500 to 8,000 roentgens. Dosages up to 2,000 r produce an 

 opening of the dark-grown hooks which is proportional to dosage and 

 which is, in effect, very similar to that produced by red light. Beyond 

 4,000 r, increases in dosage produce a slight decrease in response. 

 If the hooks are treated with weak red light after X-radiation there 

 is a marked inhibition of the effect of the red energy if the X-ray 

 dosage is more than 4,000 r, but a stimulation of the red reaction occurs 

 with a dosage up to 2,000 r. Apparently, X-ray dosages below 1,000 r 

 produce the same type of growth reaction as weak red light. It is 

 not known as yet whether the two are participating in the same basic 

 biochemical system. 



Studies on the effect of auxins on respiratory processes in relation- 

 ship to mitochondrial activity have not to date shown any effect of 

 indoleacetic acid, or 2,4-dichlorophenoxyacetic acid or its ammonium 

 salt, on the uncoupling of oxidative phosphorylation in bean plants 

 or rat livers. Active plant mitochondrial preparations have been se- 

 cured from dark-grown Black Valentine bean plants germinated in 

 gravel culture for 3 to 4 days at 25° C, using the apical stem hook 

 sections to prepare the homogenate. 



EespectfuUy submitted. 



L. B. Aldrich, Director. 



Dr. Leonard Carmichael, 



Secretary/, Smithsonian Institution. 



