THE ROLE OF NADP(H) IN PLANT RESPIRATION

Most major textbooks in plant physiology or general biochemistry state that NAD(H) is used in resPiration and catabolic reactions whereas NA DP(H) is used in photosynthesis and anabolic reactions. In the present paper we review the evidence for a role for NADP(H) in plant respirat ion. NADPH is oxidized in a Ca2+-dependent manner on the outer surface of the inner membrane probably by an unspecific NAD(P)H dehydrogenase . The physiological role of the NADPH oxidation is not known. In the m atrix of plant mitochondria are found NADPH-dependent glutathione redu ctase and NADP+-specific isocitrate dehydrogenase, the latter in addit ion to the classical Krebs cycle enzyme, NAD+-specific isocitrate dehy drogenase. The matrix also contains NADP(H) in low amounts. NADPH is o xidized by a rotenone-insensitive NAD(P)H dehydrogenase on the inner s urface of the inner membrane, which has a high affinity for NADPH. The oxidation is Ca2+-dependent and linked to proton pumping. The dehydro genase has been isolated and consists of a single polypeptide of 26 kD a.