Abstract
Heme oxygenase-1 (HO-1) and hydrogen peroxide (H2O2) are key signaling molecules that are produced in response to various environmental stimuli. Here, we demonstrate that cobalt is able to delay gibberellic acid (GA)-induced programmed cell death (PCD) in wheat aleurone layers. A similar response was observed when samples were pretreated with carbon monoxide (CO) or bilirubin (BR), two end-products of HO catalysis. We further observed that increased HO-1 expression played a role in the cobalt-induced alleviation of PCD. The application of HO-1-specific inhibitor, zinc protoporphyrin-IX (ZnPPIX), substantially prevented the increases of HO-1 activity and the alleviation of PCD triggered by cobalt. The stimulation of HO-1 expression, and alleviation of PCD might be caused by the initial H2O2 production induced by cobalt. qRT-PCR and enzymatic assays revealed that cobalt-induced gene expression and the corresponding activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), three enzymes that metabolize reactive oxygen species, were consistent with the H2O2 accumulation during GA treatment. These cobalt responses were differentially blocked by co-treatment with ZnPPIX. We therefore suggest that HO-1 functions in the cobalt-triggered alleviation of PCD in wheat aleurone layers, which is also dependent on the enhancement of the activities of antioxidant enzymes.
Highlights
In cereals, the aleurone layer is a secretory tissue that plays an important role in seed germination.Gibberellic acid (GA) produced by the growing embryo during seed germination brings about many of the changes, for example the synthesis of hydrolytic enzymes, such as α-amylase, which occurs in cereal aleurone cells during endosperm mobilization [1,2,3]
In accordance with previously reported results on barley and wheat aleurone layers [5,37,38], we evaluated the changes of cell viability using fluorescein diacetate (FDA) and N-(3-triethyl ammoniumpropyl)-4-(6-[4-(diethylamino) phenyl]-hexatrienyl) pyridinium dibromide (FM 4-64)
Consistent with results from previous studies [4,5,38], GA-induced programmed cell death (PCD) observed in wheat aleurone layers in our experiments became more distinct with time (48 h period; Figure 1A)
Summary
The aleurone layer is a secretory tissue that plays an important role in seed germination. Gibberellic acid (GA) produced by the growing embryo during seed germination brings about many of the changes, for example the synthesis of hydrolytic enzymes, such as α-amylase, which occurs in cereal aleurone cells during endosperm mobilization [1,2,3]. Such hydrolytic enzymes degrade the storage reserves in the starchy endosperm and provide nutrients for the growing embryo. H2O2 acts as a key regulator of multiple physiological processes in plants, including growth, differentiation, senescence and stress responses [20]. Our study reveals a deeper layer of understanding of the molecular mechanism(s) through which cobalt functions in the regulation of plant developmental processes
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