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Blue‐light‐induced pH changes associated with NO 3 − , NO 2 − and Cl − uptake by the green alga Monoraphidium braunii
Author(s) -
APARICIO P. J.,
WITT F. G.,
RAMÍREZ J. M.,
QUIÑONES M. A.,
BALANDÍN T.
Publication year - 1994
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1994.tb00534.x
Subject(s) - blue light , irradiation , titration , chemistry , red light , nuclear chemistry , radiochemistry , inorganic chemistry , botany , biology , physics , optics , nuclear physics
In M. braunii , the uptake of NO 3 − and NO 2 − is blue‐light‐dependent and is associated with alkalinization of the medium. In unbuffered cell suspensions irradiated with red light under a CO 2 ‐free atmosphere, the pH started to rise 10s after the exposure to blue light. When the cellular NO 3 − and NO 2 − reductases were active, the pH increased to values of around 10, since the NH 4 + generated was released to the medium. When the blue light was switched off, the pH stopped increasing within 60 to 90s and remained unchanged under background red illumination. Titration with H 2 SO 4 of NO 3 − or NO 2 − uptake and reduction showed that two protons were consumed for every one NH 4 + released. The uptake of Cl − was also triggered by blue light with a similar 10 s time response. However, the Cl − ‐dependent alkalinization ceased after about 3 min of blue light irradiation. When the blue light was turned off, the pH immediately (15 to 30 s) started to decline to the pre‐adjusted value, indicating that the protons (and presumably the Cl − ) taken up by the cells were released to the medium. When the cells lacked NO 3 − and NO 2 − reductases, the shape of the alkalinization traces in the presence of NO 3 − and NO 2 − was similar to that in the presence of Cl − , suggesting that NO 3 − or NO 2 − was also released to the medium. Both the NO 3 − and Cl − ‐dependent rates of alkalinization were independent of mono‐ and divalent cations.