112 THE METABOLISM OF ALGAE 



nitrogen content. ^^^ On return to a medium suitable for 

 growth nitrogen-starved cells show an unusually high rate 

 of nitrogen assimilation^^^' -^-' ^^-' ^'^^ a phenomenon that 

 has already been discussed in Chapter IV. 



Cells of various species of Chlorella and Scefiedesmiis have 

 been found to show abnormally high respiratory quotients, 

 i.e. AC02/-A02 = i*2 to 2-0, when transferred from a 

 medium containing glucose and an ample nitrogen supply, 

 in which they were growing, to one deficient in available 

 nitrogen. ^^® There is no evidence that these high values 

 result from the oxidation of organic acids but they may be 

 the result of the formation of more reduced products, such 

 as fats, from stored carbohydrate. This behaviour is evi- 

 dently similar to that of diatoms such as Pimmlaria spp., 

 which accumulate conspicuous amounts of fat in the course 

 of 48 hours following transference from a natural environ- 

 ment to glucose or sucrose solutions. ^^^ 



Determinations of photosynthetic quotient have generally 

 been made with material transferred from growing cultures 

 to conditions of higher light intensity and the values avail- 

 able in the literature give some indication of the direction 

 of metabolism in nitrogen-starved cells as well as provid- 

 ing evidence that algae of different classes show similar 

 metabolic behaviour under these conditions. The values 

 given in Table 10 are all close to unity, indicating that a 



TABLE 10 



PHOTOSYNTHETIC QUOTIENTS (Qi'=A02/-AC02), WITH THEIR 



STANDARD DEVIATIONS, OF VARIOUS ALGAE EXPOSED TO 



HIGH LIGHT INTENSITIES 



Class Species Qp 



Chlorophyceae . . . Chlorella sp.^^' i-o9±o-oo8 



C. pyrefioidosa^^^ i-09±o-05 



HorfTiidium flacddum-^^ i -oi ±0-034 



Bacillariophyceae . . Nitzschia closteriutn^'^ i-04±o-03 



N.palea-^ i-03±o-o3 

 Euglenineae .... Englena gracilis var. 



bacillaris^^-' I'oSs 



Dinophyceae. . . . Per idi fiitmi sp.-^ i-03±o-oi 



Rhodophyceae . . . Gelidium cartilagineum-^* 0-95 ±0-049 



Myxophyceae . . . Synechococcus sp.^"^" i-o8±o-03 



