DIFFERENTIAL RESPONSE OF NITRATE REDUCTASE AND SUCROSE-PHOSPHATE SYNTHASE-ACTIVATION TO INORGANIC AND ORGANIC SALTS, IN-VITRO AND IN-SITU

Citation
Sc. Huber et al., DIFFERENTIAL RESPONSE OF NITRATE REDUCTASE AND SUCROSE-PHOSPHATE SYNTHASE-ACTIVATION TO INORGANIC AND ORGANIC SALTS, IN-VITRO AND IN-SITU, Physiologia Plantarum, 92(2), 1994, pp. 302-310
Citations number
29
Categorie Soggetti
Plant Sciences
Journal title
ISSN journal
00319317
Volume
92
Issue
2
Year of publication
1994
Pages
302 - 310
Database
ISI
SICI code
0031-9317(1994)92:2<302:DRONRA>2.0.ZU;2-N
Abstract
Studies were conducted to compare the modulation of beta-nicotinamide adenine dinucleotide (NADH):nitrate reductase (NR; EC 1.6.6.1) and suc rose-phosphate synthase (SPS; EC 2.4.1.14) with respect to regulation by the inorganic anions, phosphate (P-i), sulfate and tungstate. Follo wing inactivation of both enzymes in vivo by transferring spinach plan ts (Spinacia oleracea L. cv. Bloomsdale) to a darkened growth chamber, spontaneous reactivation occurred in vitro when desalted leaf extract s were preincubated at 25 degrees C prior to assay. All three inorgani c anions inhibited SPS activation in vitro and also reduced the light activation of SPS in situ when they were fed to excised leaves via the transpiration stream. As expected, feeding tungstate to excised leave s prevented the light-dependent increase in extractable NR activity. H owever, in contrast to SPS, the light activation of NR in situ was rel atively unaffected by P-i and sulfate, and in vitro, both anions stimu lated (rather than inhibited) the reactivation of NR. Part of the stim ulation by P-i and sulfate was the result of increased ionic strength, and stimulation could also be demonstrated with other inorganic and o rganic salts. In the presence of high ionic strength (0.1 to 0.2 M KCl ), the rate of NR activation in vitro was relatively constant when the pH of the preincubation medium was varied from pH 6.5 to 8.0, whereas in the absence of added salt the rate of activation was nearly zero a t pH 6.5 but increased progressively as pH was raised. The stimulation by salts could be reversed, in part, by glycerol and ethylene glycol suggesting that hydrophobic interactions might play some role in the a ctivation of NR.