HO-1Mediated By NO Delays GA-induced PCD Of Aleurone Layer In Germinating Rice Seed Under Drought Stress

Drought stress is one of the important environmental factors restricting plant normal growth and development. Seed germination is the beginning of plant growth, the programmed cell death of aleurone layer is the key event in the cereal seed germination. Therefore, all the factors related to the programmed cell death of aleurone layer affect cereal seed germination.Heme oxygenase (HO) has been regarded as a rate-limiting enzyme in heme degradation, conversion from heme to biliverdin (BV), carbon monoxide (CO) and ferrous iron (Fe2+). In recent studies, plant HOs were confirmed to be involved in adventitious and lateral root formation, alleviation of oxidative damage caused by abiotic stress, and other functions. Nitric oxide (NO), a plant growth regulator and a kind of reactive nitrogen species, is involved in various physiological processes of plants, such as growth, development, seed germination, stress responses and programmed cell death.In this study, we chose the rice(Oryza sativa L.)’You Ⅱ128’seeds as research materials for investigating the mechanism of HO-1regulating the programmed cell death of aleurone layer in germinating rice seed under drought stress. The investigating were done by means of pharmacology, anatomy, biochemistry and molecular biology, and combining with staining and microscopy. The results showed that dought stress and exogenous gibberellin (GA) reduced the HO-1gene expression and enzyme activity of aleurone layer in the germinating rice seed, shortening the process of programmed cell death. But, HO-1inducer Hematin (Ht) and NO donor (SNP) retarded the decrease of HO-1activity induced by GA under drought stress, at the same time, HO-1inducer also enhanced HO-1gene expression GA-inducing and delays the aleurone layer PCD of germinating rice seeds under drought stress. In addition, the study of laser scanning confocal microscope (LSCM) combing with NO-specific fluorescent label affirmed that Ht and SNP could increase endogenous NO content in aleurone layer cells of germinating rice seeds. However, HO-1inhibitor zinc protoporphyrin Ⅸ (ZnPPⅨ) effectively reversed HO-1effect. Furthermore, NO specific scavenger c-PTIO effectively blocked the actions of HO-1and NO. Therefore, we conclude that HO-1and NO delay GA-induced programmed cell death of aleurone layer in germinating rice seeds under drought stress, in which HO-1mediated by NO and NO might act downstream of HO-1signaling.