title: Effect of light on soluble guanylyl cyclase activity in Pharbitis nil seedlings.
abstract: Cyclic GMP acts as a chemical switch in plant cells to modulate cellular reactions. However, its metabolism has not been extensively explored and is still poorly understood. Previous experiments suggest that an endogenous cGMP system could participate in the mechanism of phytochrome controlled photoperiodic flower induction in Pharbitis nil. In order to gain further information on the role of cGMP, we have begun to study the enzyme of cGMP synthesis. In this article, the presence of the enzyme with guanylyl cyclase (GC) activity in soluble protein fractions of P. nil is reported. A large portion of the enzymatic activity is present in the cotyledons, where enzyme activity amounted to 0.45 pmol cGMP/min/mg protein. The enzyme exhibited a K(m) 0.5mM for GTP. A plot of 1/v versus 1/[GTP] was linear and V(max) was 0.74 pmol cGMP/min/mg protein. It was shown that the anti-sGC antibody recognise a 40 kDa protein. Moreover, the NO-donor, sodium nitroprusside (SNP) and YC-1, as a NO-independent stimulator, enhanced enzyme activity. The NS 2028 (a potent GC inhibitor) treatments provoked a 3-fold reduction of the enzyme activity in comparison to the untreated fractions. Furthermore, the influence of light on GC activity was analysed. It was noted that cGMP level increased in cool white light, and darkness inhibited enzyme activity. Exposure to blue light acts to stimulate cGMP formation, whereas in red light a rapid decrease in GC activity was observed that returned to the high level when far-red light was applied after the red light treatment. The results presented in this work strongly argue that an enzyme with guanylyl cyclase activity is present in P. nil organs and its activity is controlled by light via the photoreceptors-dependent pathways.
authors.affiliation: Nicolaus Copernicus University, Institute of General and Molecular Biology, Department of Plant Physiology and Morphogenesis, Gagarina Street 9, PL 87-100 Torun, Poland. asjawors@eagle.biol.uni.torun.pl
authors.forename: Adriana
authors.initials: A
authors.lastname: Szmidt-Jaworska
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Jaworski
authors.forename: Jan
authors.initials: J
authors.lastname: Kopcewicz
mesh_terms: D018548:Cotyledon / Q000187:drug effects / Q000201:enzymology; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006162:Guanylate Cyclase / Q000302:isolation & purification / Q000378:metabolism* / Q000528:radiation effects; D018546:Hypocotyl / Q000201:enzymology; D049915:Ipomoea nil / Q000201:enzymology* / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D018517:Plant Roots / Q000201:enzymology; D036226:Seedlings / Q000201:enzymology* / Q000528:radiation effects; D012639:Seeds / Q000201:enzymology; D013816:Thermodynamics
chemical_list: D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D006162:Guanylate Cyclase; D006152:Cyclic GMP