316 A. R. KRALL 



time (100 minutes) as other leaves show when exposed to the same 

 conditions for 36 hours, indicating essentially complete equilibration 

 of the phosphate ester pools M^ith the supplied inorganic phosphate. 

 In Expt. 2, however, a much larger P*^ content was found in both 

 PGA* and HDP both percentage-wise and on a total count basis 

 when the dark exposures lasted as long as 24 to 36 hours. The low 

 absolute amount of isotopic phosphate incorporated was probably a 

 result of lower transpiration in the darkened plant. 



The next three lines are data representative of a set of ten experi- 

 ments done under oxygen tensions of from about 0.25% O2 to 1% 

 O2 using either red or yellow ilhmiination. No significant variation 

 was found in P" distribution under the same illumination over this 

 range of oxygen partial pressure. The differences under the two 

 lights were significant. The mean value for the per cent P" in ATP 

 was 0.75 in red illuminated leaves and 1.86 in those under yellow 

 light. The difference, 1.11%, had a standard deviation of 0.28% 

 and was shown by the t test to be significant at the 1% probability 

 level. In these same ten experiments the sugar monophosphates 

 contained on the average 1.5 times as much P'^ ^^ the red as in the 

 yellow illuminated leaves. No significant differences were observed 

 in the P^^ content of the PGA or hexose diphosphate fractions, nor 

 did the total P^- esterified by the tissue under the two conditions 

 show a significant difference. 



An experiment was done in which a batch of leaves was exposed 

 to P^^ for 4 hours in air in w^hite light and to air for 12 hours in dark- 

 ness. A control lot of leaves was extracted without exposure to in- 

 hibitor or light. Another lot was exposed to yellow light under CO 

 containing 0.4% CO2 and 1% O2. A third lot was exposed to white 

 light under this gas mixture. Both were inactivated after 70 minutes 

 exposure to the inhibitor. In the presence of the inhibitor neither the 

 white nor yellow light seemed effective in increasing the organic phos- 

 phate level above that formed in darkness in air. Rather, a sharp drop 

 in ATP level was seen on exposure to CO under either quality of il- 

 lumination. 



The last four lines in Table I show the results of exposing the leaves 

 to a CO mixture containing 5% oxygen under four different con- 



* Abbreviations used are PGA for 2- or 3-phosphoglyceric acid, HDP for hexose 

 diphosphate, ATP for adenosine triphosphate, HMP for hexose monophosphate, 

 and triose PO4 for 3-phosphogIyoeraldehyde. 



