De-Etiolation of Wheat Seedling Leaves: Cross Talk between Heme Oxygenase/Carbon Monoxide and Nitric Oxide

Yahui Liu,Wenbiao Shen,Langlai Xu,Xinna Li,Prasun K Datta

doi:10.1371/journal.pone.0081470

Abstract

Greening of etiolated plants is predominantly stimulated by light but the complete molecular mechanism is still unknown. Multiple studies currently focus on the important physiological effects of heme oxygenase (HO)/carbon monoxide (CO) in plants. In this report, firstly, the role of HO/CO in light-induced de-etiolation process was investigated. We discovered that light could significantly increase HO activities, HO-1 gene expression, CO release, and chlorophyll accumulation, all of which were sensitive to zinc protoporphyrin (ZnPPIX), the potent inhibitor of HO-1, respectively. Both HO-1 inducer hematin (H) and CO aqueous solution were able to relieve etiolation in wheat seedling leaves under completely darkness by up-regulating endogenous HO/CO system, so as nitric oxide (NO) donor sodium nitroprusside (SNP) did. Similarly, endogenous NO production was also boost in response to light, SNP, hematin and CO aqueous solution in wheat seedling leaves. Additionally, the restoration of chlorophyll contents was blocked, when the inhibitor of mammalian nitric oxide synthase NG-nitro-L-arginine methylester hydrochloride (L-NAME) or the specific scavenger of NO 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO) was added, respectively. Furthermore, the inducible effects of light were different from those of SNP, hematin, and CO on Pfr accumulation and PHYA transcripts. However, all of sodium nitroprusside (SNP), hematin, and CO could accelerate NO emission, which suggested that HO/CO in wheat seedlings de-etiolation under dark-light transition may have a cross talk with NO.

Highlights

De-etiolation of etioplasts lack of chlorophyll is a complex developmental process that is triggered predominantly by light
Light-induced wheat seedlings de-etiolation is sensitive to ZnPPIX, the potent inhibitor of heme oxygenase (HO)-1 In Arabidopsis, genetic analysis of the HY1 locus showed that hy1 mutant plants display long hypocotyls and decrease chlorophyll accumulation consistent with a substantial deficiency in photohematin and 1.0% carbon monoxide (CO) aqueous solution was observed
Similar increase in fluorescence was not apparently observed when AF 4DA, the negative control probe for DAF-2 DA, was applied, respectively. These results reveal that an induction of endogenous nitric oxide (NO) production in the seedling leaves might be a critical event in above effects elicited by light, sodium nitroprusside (SNP), hematin, and CO aqueous solution during de-etiolation process

Summary

Introduction

De-etiolation of etioplasts lack of chlorophyll is a complex developmental process that is triggered predominantly by light. One of the important light-dependent steps is the phototransformation of protochlorophyll (ide) to chlorophyll (ide) [1]. During the subsequent greening period, the rapid accumulation of chlorophylls occurs. Plants have developed elaborate photo sensory systems to optimize its growth and development to daily and seasonal changes. The complete molecular mechanisms by which light regulates development are largely unknown. Heme oxygenases (HOs, EC 1.14.99.3) were originally identified in animals [2], which catalyzes the first and rate-limiting step in the degradation of heme. Ample evidence currently supports the notion that HO serves to provide potent cytoprotective effects in many models of oxidant-induced cellular and tissue injury both in animals and plants. Recent works have indicated the enhancement of HO activities and transcripts in the antioxidant defense system in soybean leaves subjected to lower levels of cadmium (Cd) stress or UV-B irradiation [3,4]

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