Hydrogen-Rich Water Alleviates Freeze-Induced Seedlings Oxidative Damage And Salt-Triggered Seed Germination Inhibition In Rice

Hydrogen is a bioactive molecule in plant, which not only regulates root morphological pattern, but confer plants tolerance to several abiotic stresses, including drought, paraquat, salinity and heavy metals. However, the participation of hydrogen mitigating oxidative damage triggered by freezing stress in rice seedlings and seeds germination inhibition induced by salt is still unknown.In this report, the role of H2 in modulating freezing tolerance was investigated. Freezing stress not only brought about seedling growth inhibition and the decreased photosynthetic activity, but also led to the alteration of reactive oxygen species homeostasis. An early response, the increased H2 emission was also observed. Subsequently, the pretreatment with hydrogen-rich water (HRW), which was used to characterize physiological roles of H2, could dose-dependently mitigate the inhibition of rice seedling growth and the injury of plasma membrane induced by freeze. HRW at 50% saturation, being the maximum responses, could alleviate the decrease of chlorophyll content and photosynthetic activity triggered by freezing stress. Meanwhile, the lipid peroxidation and the overproduction of ROS were decreased. These results matched with the changes of total and isozymatic activities of superoxide dismutase (SOD), guaiacol peroxidase (POD), and catalase (CAT). In comparion with freezing stress alone, time-courese analysis showed that miR398 transcripts were down-regulated and its targets Cu/Zn-SOD1 (CSD1) and Cu/Zn-SOD2 (CSD2) expression level raised by HRW. By contrast, miR319 transcripts were differentially increased, showing a relative inverse correlation with the decreased levels of its target genes PCF5 and PCF8. In summary, the results of this investigation suggested that an increase in H2 production triggered by freezing stress contributes to the enhancement of freezing tolerance by the improvment of photoysthetic acitivty and the reestablishment of ROS homeostasis, at least paritally via miR398 and miR319.Additionally, this study investigated molecular mechanism of hydrogen-rich water (HRW)-mediated enhancement of tolerance against salinity stress during rice seed germination. A combination of physiological and molecular approaches was used to study the effect of HRW on the alleviation of salinity stress. A 100 mM NaCl stress caused the increase of H2 release in germinating rice seeds. With respect to samples treated with 100 mM NaCl alone, exogenous HRW pretreatments differentially attenuated the inhibition of seed germination and seedling growth caused by salinity. Further results showed that both 50%(in particular) and 100% concentration of HRW could activate α/β-amylase activity, thus accelerating the formation of reducing sugar and total soluble sugar. HRW also enhanced total, isozymatic activities or corresponding transcripts of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX). These results were confirmed by the alleviation of oxidative damage, as indicated by a decrease of thiobarbituric acid reactive substances (TBARS). Additionally, the ratio of potassium (K+) to sodium (Na+) in both the shoot and root parts was increased. Together, our results suggested that exogenous HRW treatment on rice seeds may be a good option to alleviate salinity stress.