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Rhythms in magnesium ion inhibition and hysteretic properties of nitrate reductase in the CAM plant Bryophyllum fedtschenkoi
Author(s) -
Lillo Cathrine,
Smith Lucy H.,
Nimmo Hugh G.,
Wilkins Malcolm B.
Publication year - 1996
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1996.tb00685.x
Subject(s) - darkness , photoperiodism , nitrate reductase , rhythm , magnesium , biology , biochemistry , chemistry , botany , enzyme , medicine , organic chemistry
Nitrate reductase (NR, EC 1.6.6.1) was tested in crude extracts of leaves from Bryophyllum fedtschenkoi plants growing under alternating light/darkness as well as in excised leaves kept in continuous light or darkness. In most extracts NR activity was inhibited 20–80% by 5 m M Mg 2+ A light or darkness shift (30 min darkness) during the first part of the photoperiod gave an increase in the Mg 2+ inhibition and a decrease in NR activity. Magnesium ion inhibition of NR also showed diurnal variations. Strongest inhibition was found in extracts made during the latter part of the photoperiod and start of the dark period. Pre‐incubation of crude extracts with ATP increased Mg 2+ inhibition, indicating that phosphorylation of NR is involved in regulation of NR in Crassulacean acid metabolism (CAM) plants. In continuous light an increase in Mg 2+ inhibition occurred after 20 h and 40 h, indicating a rhythm in the phosphorylation of NR. A delay in the production of nitrite in the assay (hysteresis) was generally seen in extracts susceptible to Mg 2+ inhibition. The rhythms related to NR activity showed the same period length (20 h) as the rhythm in CO 2 exchange. However, in contrast to the rhythm in CO 2 exchange, NR rhythms were strongly damped in continuous light. In constant darkness the rhythms were even more damped. The results show that post‐translational modification of CAM NR is influenced by light/darkness and by an endogenous rhythm.