Differential effects of nitric oxide on peroxidase and H₂O₂ production by the xylem of Zinnia elegans

Abstract

Sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) are two nitric oxide (NO)-releasing compounds that, when used at 5·0 mol m -3 concentrations, are capable of releasing NO in the aqueous phase at a rate of 35 ± 4 and 47 ± 5 µmol m -3 s -1 , respectively. For this reason, the effect of SNP and SNAP on coniferyl alcohol peroxidase and on H 2 O 2 production by the lignifying xylem of Zinnia elegans (L.) has been studied in order to ascertain whether NO, which is a synchronizing chemical messenger in animals and an air pollutant, has any effect on these plant-specific metabolic aspects. The results showed that both SNP and SNAP provoke an inhibition in the mol m -3 concentration range of the coniferyl alcohol peroxidase activity of a basic peroxidase isoenzyme present in the intercellular washing fluid of Z. elegans. The effect of these NO-releasing compounds on peroxidase was confirmed through histochemical studies, which showed that xylem peroxidase was totally inhibited by treatment with these NO donors at 5·0 mol m -3 , and by NO at a concentration change rate of 55 ± 5 and 110 ± 9 µmol m -3 s -1 . However, SNP, at 5·0 mol m -3 , does not have any effect on H 2 O 2 production by the xylem of Z. elegans. The fact that SNP and SNAP are two structurally dissimilar compounds which only share the common ability to release NO in aqueous buffer, and that similar results were obtained when using NO itself, suggest that NO could be considered as an inhibitor of coniferyl alcohol peroxidase which does not affect H 2 O 2 production in the xylem of Z. elegans.Key-words: Zinnia elegans; coniferyl alcohol oxidation; H 2 O 2 production; inhibition; nitric oxide; peroxidase; xylem.Abbreviations: IWF, intercellular washing fluid; pCMB, pchloromercuribenzoic acid; SNAP, S-nitroso-N-acetyl-penicillamine; SNP, sodium nitroprusside; TMB, 3,3',5,5'-tetramethylbenzidine. INTRODUCTIONNitric oxide (NO) is a paramagnetic relatively stable freeradical molecule involved in many physiological processes in animals, where it serves as a synchronizing chemical messenger involved in vasorelaxation, platelet inhibition, neurotransmission, cytotoxicity and immunoregulation (Anbar 1995). In animal cells, NO is synthesized by the enzyme NO synthase (Knowles 1997), and most of its biological regulatory properties have been explained on the basis of its capacity to act as an iron ligand in haemoproteins (Stamler, Singel & Loscalzo 1992). Dual (activating or inhibitory) effects of NO on haemoproteins have been described (Tsai 1994), and the nature of the effect has been suggested to depend to a great extent on the resting state (oxidation state) of the haemoprotein, which conditions the ligand properties and the electronic configuration of the haem iron (Tsai 1994). In the case of catalase, it has been shown that NO reversibly binds to the haem of catalase and inhibits H 2 O 2 breakdown with a K i of about 0·2 mmol m -3 (Brown et al. 1997).Evidence is emerging to support the possibility that NO may also act as chemical mess...

Nitric oxide production by the differentiating xylem of Zinnia elegans

“…Regardless of this uncertainty, NO does not affect O 2 ·-/H 2 O 2 production by the lignifying xylem (Ferrer & Ros Barceló, 1999) or H 2 O 2 production by isolated plant mitochondria (one of the organelles involved in H 2 O 2 production during programmed cell death) (Yamasaki et al, 2001). This is not surprising since the synthesis of both O 2 ·-/H 2 O 2 and NO in plant cells is simultaneously coordinated in response to environmental/ hormonal stimuli with no negative crosstalk between them (Delledonne et al, 1998).…”

“…This is especially important since NO appears to be a key upstream signal of the last step in lignin biosynthesis, i.e. the monolignol assembly (Ferrer & Ros Barceló, 1999;Ros Barceló et al ., 2002a).…”

Nitric oxide counters ethylene effects on ripening fruits

“…97 Likewise, NO affects the functioning of plant POD involved in cell wall lignification since it easily forms an iron-nitrosyl complex with haem iron. 98 Free radical scavenging ability of NO has been demonstrated to preferentially quench o-quinone radicals, causing interruption of normal browning reactions occurring at the cut surfaces of fruit. 99 On the other hand, the protection offered by NO to organic acids, particularly of ascorbic acid and vice versa may complement each other, converging in the prevention of browning.…”

Assessment of Cambial Activity and Xylogenesis by Microsampling Tree Species: An Example at the Alpine Timberline

“…However, knowledge of cell physiology is still inadequate for interpreting the information collected at the molecular level, and studies on genetic modifications are underway, while basic studies on xylogenetic processes and wood production are being neglected (Chaffey 2002). In the past decade, xylogenesis has been studied in non-woody plants like Arabidopsis (Berleth et al 2000;Chaffey et al 2002) and Zinnia elegans (Ferrer & Ros Barceló 1999;Groover & Jones 1999;Ros Barceló et al 2002), applying molecular techniques. However, precise information on radial growth processes in a forest environment can only be obtained from woodproducing plants like trees, but this type of information is still largely incomplete or even lacking (Savidge 2003).…”