INDUCTION AFTER CHANGE TO LOWER LIGHT INTENSITY 1355 



The "light adaptation" stage of the induction process (which follows 

 the initial gushes or gulps), has in Chlorella, according to van der Veen, a 

 relatively short duration, and is largely independent from the length of the 

 preceding dark period; (3, 24 or 60 minutes darkness gave similar adapta- 

 tion curves; even after 16 hours in the dark, the light adaptation was 

 about as fast as after 3 minutes darkness) . This behavior differs from that 

 observed by other observers with many other species (cf. figs. 33.6, 9, lib). 



On the whole, the results of van der Veen indicate that transient carbon 

 dioxide exchange at the beginning of light periods may have either a posi- 

 tive or a negative sign, depending on species and treatment of the algae. 

 Combining his results with those of Aufdemgarten, Emerson and co-work- 

 ers, and Bhnks and Skow, one gets the impression that the gulp may be a 

 more general feature than the burst, but that its volume is small and it is 

 usually over in much less than a minute; the burst, on the other hand, 

 may be much more prominent, but slower, reaching a peak only in the 

 second or third minute of illumination, and taking several more minutes to 

 subside. It thus blankets the whole period of normal (negative) long induc- 

 tion. Carbon dioxide induction curves of Chlorcila, obtained by Gaffron 

 (1954) and Rosenberg (1954) by pK measurements, were published too 

 late for detailed discussion here (cf. chapter 37D, section 1) . They showed 

 many complex and interesting features — in particular, 1-3 minute long 

 "stops" (periods of zero gas exchange), interrupting the transition from 

 CO2 liberation in darkness to CO2 consumption in light, and vice versa. 



4. Induction after Change to Lower Light Intensity 



Offhand, one would not expect new induction losses to occur after the 

 cells have been working for a while at full rate at high light intensity, and 

 the illumination then is reduced to a lower level (assuming the illumination 

 was not so strong as to cause damage by photoxidation , induction effects 

 caused by photoxidation will be described in section 7. Gessner (1938) 

 noted that, in the first 15 minutes after an exposure to 80,000 lux, the (un- 

 corrected) rate of photosynthesis of Elodea at 4600 lux was about 30% 

 lower than before; but, in this case, both photoxidation and enhanced 

 respiration might have contributed to the change. More significant are 

 the results of Steemann-Nielsen (1942), obtained with Fucus serratus at low 

 temperature. When the light intensity was reduced from 23,000 to 2300 

 lux at 19.8° C, no marked induction appeared; but, when the same ex- 

 periment was carried out at 4.9°, the rate of oxygen liberation (corrected 

 for respiration) was, in the first 5 minutes after the change, only 34% of 

 the steady rate; the latter was reached after about 25 minutes. A rough 

 check of the carbon dioxide liberation showed a similar induction loss. Ex- 

 periments also were conducted with transitions from 4000 to 2300, from 



