No abstract

Following previous findings that cadmium (Cd) induces heme oxygenase-1 (HO1) gene expression in alfalfa seedling roots, we now show that the decreased glutathione (GSH) and ascorbic acid (AsA) contents, induction of HO-1 gene expression and its protein level by Cd was mimicked by a GSH depletor diethylmaleate (DEM). Meanwhile, above Cd- or DEM-induced decreased GSH content followed by HO-1 up-regulation could be strengthened or reversed differentially by the application of a selective inhibitor of GSH biosynthesis L: -buthionine-sulfoximine (BSO), or exogenous GSH and AsA, respectively. The antioxidative behavior of HO-1 induction was further confirmed by histochemical staining for the detection of loss of membrane integrity in a short period of treatment time. Additionally, the induction of HO-1 transcript was inhibited by the transcriptional inhibitor actinomycin D (ActD) or protein synthesis inhibitor cycloheximide (CX, especially). In contrast, the level of HO-2 transcript did not change upon various treatments. Together, above results suggested that Cd-induced up-regulation of HO-1 gene expression is associated with GSH depletion, which is at least existing transcriptional regulation level, thus leading to enhanced antioxidative capability transiently.

Rice is most sensitive to heat stress at the flowering stage, with different degrees of heat damage in spikelets and leaves. To investigate the heat damage in spikelets and flag leaves, two rice genotypes, N22 (heat‐tolerant) and GT937 (heat‐sensitive), were subjected to a heat‐stress treatment (40 °C for 15 days). The results showed that more damaging was found in spikelets than in flag leaves and the heat stress significantly decreased the seed‐setting rate by 12.41 % in N22 and by 65.02 % in GT937. However, the difference in the net photosynthetic rate of the flag leaf between heat‐stressed and control was not significant. Moreover, the difference of temperatures in spikelets and flag leaves was attributed to the differences in heat dissipating. Under heat stress, the transpiration rate was significantly higher in flag leaves than in spikelets, and the temperature in flag leaves were at least 4 °C cooler than in spikelets. Although the spikelet temperatures did not differ significantly between the two genotypes under heat stress, spikelets of GT937 were more severely damaged than those of N22, which might result from the differences in the antioxidant capacities between genotypes. Results showed that little difference of superoxide dismutase, peroxidase and catalase activities of spikelets was found in N22, while significant reduction was found in GT937 under heat stress, compared with control. These results suggest that organ temperature is controlled mainly by transpirational cooling, and that heat stress is an indirect result of oxidative stress, rather than a direct result of heat damage.

No abstract

Using pharmacological and biochemical approaches, the functional roles of heme oxygenase-1 (HO-1) induction in cadmium (Cd)-stressed alfalfa (Medicago sativa) seedling roots caused by a metalorganic complex (β-cyclodextrin-hemin, β-CDhemin, CDH) and the well-known HO-1 inducer hemin, were investigated and compared. Cd-stressed seedling roots exhibited severe oxidative damage, whereas up-regulation of HO-1 by CDH and hemin pretreatment prevented this toxic response, as evidenced by the decrease of lipid peroxidation as well as the alleviation of growth inhibition and Cd accumulation. Reestablishment of glutathione (GSH) and reactive oxygen species (ROS) homeostasis were observed. Upon Cd stress, 0.01 μM CDH and 10 μM hemin pretreatment alleviated lipid peroxidation to almost the same extent and the CDH was highly potent. The modulation of the transcripts and total activities of ascorbate peroxidase (APX) and superoxide dismutase (SOD) were regulated by CDH and hemin, respectively. We also noticed that the potent HO-1 inhibitor zinc protoporphyrin IX (ZnPP) significantly reversed the CDH-driven cytoprotective roles. Additionally, β-CD was found to be ineffective in the alleviation of lipid peroxidation. Taken together, the data suggested that HO-1 induction mediated by CDH provides critical protection against Cd-induced oxidative damage and toxicity partly by lowering the Cd accumulation.