176 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



tion are being recorded and correlated with plant growth responses of 

 living material produced in natural daylight and in controlled en- 

 vironment conditions. The greenliouse and controlled environment 

 rooms, with such special features as automatically controlled changing 

 light intensities and daylengths to reproduce natural conditions, have 

 been developed and installed. The system for measuring smi and sky 

 radiation has been developed and includes specially constructed 

 thermopiles with filters which automatically measure solar radiation. 

 A digital recording system has been adapted, with automatic data 

 processing equipment for handling a larger amount of information, to 

 register all data on punched tape. Measurements are being made at 

 3-minute intervals for six different wavebands simultaneously. Direct 

 measurements with photomultipliers using interference filters at two 

 specific wavelengths, 660 and 730 m/x, indicate that there is an ap- 

 preciable shift of as much as two-fold in the ratio of red to far-red 

 near sunrise and sunset. These shifts may be of significant import in 

 determining the effective daylength for biological responses which 

 utilize the phytochrome system. 



The biological phase has been initiated, and at periodic intervals the 

 plant material cultivated under precisely controlled conditions is 

 observed and measured, and the data are recorded for purposes of com- 

 parison and correlation. It is expected that the degree and/or fre- 

 quency of physiological responses initiated by photochemical stimuli 

 will demonstrate a direct correlation with measured daily and seasonal 

 fluctuations in the energy and quality of solar radiation as observed 

 over relatively long periods of time. 



It has been shown previously by Dr. W. M. Dugger, Jr., and Dr. 

 O. C. Taylor at the Air Pollution Research Center, University of 

 California at Riverside, that PAN (peroxyacetyl nitrate) is an oxi- 

 dant, naturally present in smog, which produces necrotic lesions on 

 young leaves in the presence of light. These previous observations 

 also suggested that PAN might be affecting the photosynthetic system 

 of the plant. Thus, an attempt was made to determine if the intra- 

 cellular site of PAN action could be determined. The spectral sensi- 

 tivity of the light requirement in producing damage in bean seedlings 

 in the presence of the smog oxidant was determined cooperatively 

 with Drs. Dugger and Taylor, and this action spectrum indicates an 

 interaction with a carotenoid pigment having a strong absorption be- 

 tween 400 and 500 m/i. There is a residual small amount of damage 

 for all wavelengths out to 700 mix. 



A concentration of 4 ppm PAN for 100 seconds with an intensity of 

 200 /Aw/cm^ produces appreciable leaf damage. No leaf damage is 

 observed if plants are kept in the dark immediately prior to or im- 

 mediately following the fumigation with PAN with simultaneous 



