Nitrate-reductase activity and in vivo nitrate-reduction rate in Ulva rigida illuminated by blue light |
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Authors: | A Corzo F X Niell |
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Institution: | (1) Departamento de Biología y Ecología, Facultad de Ciencias del Mar, Universidad de Cádiz, E-11510 Puerto Real, Spain;(2) Departamento de Ecología, Universidad de Málaga, Campus Universitario de Teatinos s/n, E-29071 Málaga, Spain |
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Abstract: | In the marine green alga Ulva rigida C. Agardh, nitrate reductase (NR) is synergetically induced by blue light and nitrate. The present study examines the effect of blue light and a large NO
3
–
pulse (0.3 mM) on relevant variables of NO
3
–
-assimilation such as NO
3
–
-uptake, intracellular NO
3
–
-storage, NR activity, in vivo NO
3
–
-reduction rate and NO
2
–
and NH
4
+
-accumulation. Nitrate uptake started immediately upon addition of NO
3
–
, suggesting the presence of a constitutive carrier, however in the first 1.5 to 2 h, periods of net NO
3
–
efflux were frequent. After this time, NO
3
–
-uptake and intracellular NO
3
–
-accumulation proceeded linearly with time, suggesting the existence of a different NO
3
–
-uptake mechanism, which seems to be inducible. Our results indicate that in vivo NO
3
–
-reduction is not exclusively dependent on the potential NR activity. In U. rigida, during the first 2 h after a NO
3
–
pulse (300 M) there were clear indications that the induction state of the NO
3
–
-carrier limits the reduction rate of NO
3
–
. Once the induction of the NO
3
–
-transporter had been completed (1.5 to 2 h), the NO
3
–
-assimilation pathway reached a steady state, NO
3
–
-uptake rate, NO
3
–
-reduction rate and NO
2
–
and NH
4
+
-accumulation being linear with time. Since the reduction of NO
3
–
leads mainly to the accumulation of NH
4
+
, we conclude that, after the NO
3
–
-reduction itself, NH
4
+
-fixation into carbon skeletons is the limiting step in the assimilation of NO
3
–
by U. rigida under blue light. |
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Keywords: | |
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