ItsPossible RoleintheEarly Evolution ofPhotosynthetic Organisms

Theeffect ofborononheterocystous andnonheterocystous dinitrogen fixing Cyanobacteria wasexamined. Theabsence of boron inculture mediainhibited growth andnitrogenase activity inNodularia sp.,Chlorogloeopsis sp., andNostoc sp.cultures. Examinations ofboron-deficient cultures showedchanges inheterocyst morphology. However, cultures ofnonheterocystous Cyanobacteria, Gloeothece sp.andPlectonema sp.,growninthe absence ofborondidnotshowanyalteration ingrowth ornitrogenaseactivity. Theseresults suggest arequirement ofboron onlybyheterocystous Cyanobacteria. A possible roleforthis element intheearly evolution ofphotosynthetic organisms is proposed. bycells grownoncombined nitrogen (e.g. nitrate orammonium-N) (4). These results suggested aninvolvement ofboron innitrogenase activity (15). Ourstudy wasdesigned todetermine theboronrequirementindinitrogen-fixin g