1920 KINETICS OF PHOTOSYNTHESIS CHAP. 37D 



Ionic Deficiency Effects. The inhibition of photosynthesis by the de- 

 ficiency of various mineral salts was described in chapter 13 (p. 336). 

 It was pointed out there that, in certain cases, photosynthesis picks up 

 very fast after the deficiency had been removed, while in others (particu- 

 larly those of ions whose absence affects the formation of chlorophyll) 

 the reco^'ery is much slower. One micronutrient of the first type — 

 manganese — has been studied by several investigators. Gerretsen (1949) 

 found that manganese deficiency causes a reduction in the rate of photo- 

 synthesis in oats (cf. the observations of Emerson and Lewis, p. 338). 

 He surmised that manganese is specifically involved in the oxygen-liberat- 

 ing stage of photosynthesis, and went on to study the effect on manganese 

 salts on the oxidation-reduction potential of chloroplast suspension (c/. 

 chapter 35, p. 1569). 



Pirson and Wilhelmi (1950) found that manganese-deficient Ankistro- 

 desmus falcatus, ^^■hose photosynthesis in saturating light had been re- 

 duced to one-third the normal value, recovered its full efficiency two hours 

 after the addition of manganese salt. This recovery was much more 

 striking than that observed after the relief of potassium or nitrogen defici- 

 ency. The photosynthetic ratio, Qp, was the same in normal and in Mn- 

 deficient cells. The chlorophyll content (per g. dry matter) was, in Mn- 

 deficient cells, only slightly lower than in normal ones. 



Skvorzov (1952) found that addition of 3 mg. Mn salt to one liter tap 

 water increased the rate of photosynthesis of Chladophora, Elodea and Spiro- 

 gyra, in strong light, to 132-143% of controls; no significant effect could be 

 noted in weak light or in darkness. Higher amounts (up to 45 mg. Mn per 

 liter) had no toxic effect {cf. fig. 34C, p. 341). 



Stegman (1940) noted that zinc deficiency has a strong chlorotic effect 

 on Chlorella; addition of zinc leads to rapid formation of chlorophyll. 



Potassium (cf. p. 336). Pirson and Wilhelmi (1950) gave new data 

 illustrating the rapid and parallel recovery of oxygen liberation and carbon 

 dioxide production in potassium-deficient Ankistrodesmus cells, upon pro- 

 vision of sufficient potassium, and prior to any marked increase in chloro- 

 phyll content. Baslavskaya and Zhuravleva (1948) also found a strong 

 effect of the removal of potassium deficiency on photosynthesis in Elodea. 



Nitrate {cf. p. 339). Pirson and Wilhelmi (1950) noted that the (pre- 

 viously described) rapid increase, upon addition of nitrate, of the rate of 

 gas exchange in moderately nitrogen-deficient cultures, affects ^Oi/M more 

 strongly than AC02/A^, so that the ratio Qp increases, 1.5 hours after the 

 addition, to values such as 1.41, and only slowly returns to normal. This 

 indicates strong initial reduction of nitrate (as substitute oxidant either in 

 photosynthesis, cf. p. 540, or in respiration, cf. p. 539). With a culture 

 whose chlorophyll content had been reduced 20% below normal by a more 



