Heme Oxygenase-1 Delays Gibberellin-Induced Programmed Cell Death of Rice Aleurone Layers Subjected to Drought Stress by Interacting with Nitric Oxide.

Huangming Wu,Huiping Chen,Yan Zheng,Jing Liu,Heting Zhang

doi:10.3389/fpls.2015.01267

Abstract

Cereal aleurone layers undergo a gibberellin (GA)-regulated process of programmed cell death (PCD) following germination. Heme oxygenase-1 (HO-1) is known as a rate-liming enzyme in the degradation of heme to biliverdin IXα, carbon monoxide (CO), and free iron ions (Fe2+). It is a critical component in plant development and adaptation to environment stresses. Our previous studies confirmed that HO-1 inducer hematin (Ht) promotes the germination of rice seeds in drought (20% polyethylene glycol-6000, PEG) conditions, but the corresponding effects of HO-1 on the alleviation of germination-triggered PCD in GA-treated rice aleurone layers remain unknown. The present study has determined that GA co-treated with PEG results in lower HO-1 transcript levels and HO activity, which in turn results in the development of vacuoles in aleurone cells, followed by PCD. The pharmacology approach illustrated that up- or down-regulated HO-1 gene expression and HO activity delayed or accelerated GA-induced PCD. Furthermore, the application of the HO-1 inducer Ht and nitric oxide (NO) donor sodium nitroprusside (SNP) not only activated HO-1 gene expression, HO activity, and endogenous NO content, but also blocked GA-induced rapid vacuolation and accelerated aleurone layers PCD under drought stress. However, both HO-1 inhibitor zinc protoporphyrin IX (ZnPPIX) and NO scavenger 2-(4-carboxyphenyl0-4, 4,5,5-tetramethylimidazoline-l-oxyl-3-oxide potassium salt (cPTIO) reserved the effects of Ht and SNP on rice aleurone layer PCD under drought stress by down-regulating endogenous HO-1 and NO, respectively. The inducible effects of Ht and SNP on HO-1 gene expression, HO activity, and NO content were blocked by cPTIO. Together, these results clearly suggest that HO-1 is involved in the alleviation of GA-induced PCD of drought-triggered rice aleurone layers by associating with NO.

Highlights

Programmed cell death (PCD) plays a critical role in regulating plant development and in protecting from stress
polyethylene glycol-6000 (PEG) treatment alone significantly inhibited the transcription level of the heme oxygenase-1 (HO-1) gene in rice aleurone layers, whereas PEG co-treated with Ht and Sodium nitroprusside (SNP) led to the attenuation of PEGinduced HO-1 gene expression
Haematin blocked the decrease of Gibberellic acid (GA)-induced ascorbate peroxidase (APX) and CAT activities, and resulted in the decrease of H2O2 level, and these effects were reversed by HO-1 inhibitor Zinc protoporphyrin IX (ZnPPIX) (Wu et al, 2011)

Summary

Introduction

Programmed cell death (PCD) plays a critical role in regulating plant development and in protecting from stress. Previous investigations have declared that the typical morphological features of PCD occurring in the dying cereal aleurone cells include the fusion of small protein storage vacuoles (PSVs) into bigger ones, which eventually result in a single, large, spherical vacuole occupying almost the entire cytoplasmic area (Bethke et al, 1999). This process of developing vacuoles is referred to an vacuolation (Domínguez et al, 2004). To date, studies on the features of aleurone layer cells in the germinating cereal seeds during PCD have mainly focused on barley, whereas those of other cereals including rice have not been investigated

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