Effects of Iron and Oxygen on Chlorophyll Biosynthesis : I. IN VIVO OBSERVATIONS ON IRON AND OXYGEN-DEFICIENT PLANTS (original) (raw)

Corn (Zea mnays, L.), bean (Phaseolus vulgaris L.), barley (Hordeum vudgare L.), spinach (Spuiacia oeracea L.), and sugarbeet (Beta vulgaris L.) grown under iron deficiency, and Potamogeton pectinatus L, and Potamogeton nodosus Poir. grown under oxygen deficiency, contained less chlorophyll than the controls, but accumulated Mg-protoporphyrin IX and/ or Mg-protoporphyrin IX monomethyl ester. No significant accumulation of these intermediates was detected in the controls or in the tissue of plants stressed by S, Mg, N deficiency, or by prolonged dark treatment. Treatment of normal plant tissue with 8-aminolevulinic acid in the dark resulted in the accumulation of protochlorophyliide. If this treatment was carried out under conditions of iron or oxygen deficiency, less protochlorophyllide was formed, but a significant amount of Mg-protoporphyrin IX and Mg-protoporphyrin IX monomethyl ester accumulated. These results are consistent with the presence of an 02, Fe-requiring step between Mg-protoporphyrin IX monomethyl ester and protochlorophyllide. Iron and 02 are essential to a vast array of biological functions. In this investigation, we have attempted to study those effects that are directly related to the Chl biosynthetic pathway. In higher plants, Fe deficiency results in chlorosis. This relationship was carefully documented by DeKock et al. (6) and by Evans (8). Marsh et al. (15) noted an inhibition of '4C incorporation from citrate, succinate, and a-ketoglutarate into Chl in Fedeficient cowpeas. In photosynthetic bacteria, Fe deficiency results in the accumulation and excretion of intermediates in the tetrapyrrole biosynthetic pathway, particularly coproporphyrin (14). This finding led to the hypothesis that coproporphyrinogen oxidase (EC 1.3.3.3) is an Fe-requiring enzyme; and in fact the activity of the enzyme isolated from tobacco leaves was inhibited by chelating agents and stimulated by added Fe2+ (11). Recently, aquatic plants, notably rice and Echinochloa crusgalli (L.) Beauv., were shown to possess metabolic adaptations that allow them to germinate and grow under essentially complete anaerobiosis (20). The shoots produced under anaerobic conditions were chlorotic. Wang (22) reported that E. crusgalli germinated under anaerobic conditions produced shoots devoid of both Chl and Pchl(ide). The ultrastructure of the plastids was very abnormal (19). 02 is required in higher plant tissues for the accumulation of 'Supported by National Science Foundation Grant PCM 7813250.