E. Bar et E. Telor, EFFECT OF LIGHT AND OXYGEN ON NITROGENASE ACTIVITY AND DINITROGENASE REDUCTASE (FE-PROTEIN) CONTENT IN AZOLLA-ANABAENA ASSOCIATION, Journal of plant physiology, 144(4-5), 1994, pp. 438-443
Nitrogen fixation in Azolla is regulated by light, in vivo and in vitr
o, and occurs only upon illumination. After long incubation in the dar
k, illumination of Azolla caused a slow recovery of nitrogenase to max
imal activity after 3 h without correlation with either photosynthesis
or the content of soluble sugars. Cyanobiont heterocyst extracts immu
nobloted with anti-Klebsiella or anti-Rhodospirillum Fe-protein antibo
dies showed two reacting polypeptides, one of 30 and the other of 36 k
Da. The content of the 30 kDa polypeptide was not affected by transiti
on of Azolla to 18 h in the dark while the 36 kDa polypeptide complete
ly disappeared in the dark and reappeared within 10 to 30 min of reill
umination. The cyanobiont nitrogenase was active only in the presence
of a detectable amount of the 36 kDa polypeptide, suggesting that it i
s the active form of the Fe-protein. Illumination of Azolla with high
light intensity after a short dark period caused inhibition of nitroge
nase activity and reduced the content of the 36 kDa polypeptide. Nitro
genase was inactivated by high O-2 only in the dark while in the light
nitrogenase was not inhibited and the content of the 36 kDa Fe-protei
n polypeptide was retained.