RESUMO
Brassinosteroids (BRs) play pivotal roles in modulating plant growth, development, and stress responses. In this study, a Medicago truncatula plant pretreated with brassinolide (BL, the most active BR), enhanced cold stress tolerance by regulating the expression of several cold-related genes and antioxidant enzymes activities. Previous studies reported that hydrogen peroxide (H2O2) and nitric oxide (NO) are involved during environmental stress conditions. However, how these two signaling molecules interact with each other in BRs-induced abiotic stress tolerance remain largely unclear. BL-pretreatment induced, while brassinazole (BRZ, a specific inhibitor of BRs biosynthesis) reduced H2O2 and NO production. Further, application of dimethylthiourea (DMTU, a H2O2 and OH- scavenger) blocked BRs-induced NO production, but BRs-induced H2O2 generation was not sensitive to 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO, a scavenger of NO). Moreover, pretreatment with DMTU and PTIO decreased BL-induced mitochondrial alternative oxidase (AOX) and the photosystem capacity. However, pretreatment with PTIO was found to be more effective than DMTU in reducing BRs-induced increases in Valt, Vt, and MtAOX1 gene expression. Similarly, BRs-induced photosystem II efficiency was found in NO dependent manner than H2O2. Finally, we conclude that H2O2 was involved in NO generation, whereas NO was found to be crucial in BRs-induced AOX capacity, which further contributed to the protection of the photosystem under cold stress conditions in Medicago truncatula.
Assuntos
Brassinosteroides/farmacologia , Resposta ao Choque Frio , Peróxido de Hidrogênio/metabolismo , Medicago truncatula/metabolismo , Óxido Nítrico/metabolismo , Transdução de Sinais , Aclimatação , Óxidos N-Cíclicos/farmacologia , Sequestradores de Radicais Livres/farmacologia , Imidazóis/farmacologia , Medicago truncatula/efeitos dos fármacos , Proteínas Mitocondriais/genética , Proteínas Mitocondriais/metabolismo , Oxirredutases/genética , Oxirredutases/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Tioureia/análogos & derivados , Tioureia/farmacologiaRESUMO
Boea hygrometrica (B. hygrometrica) can tolerate severe desiccation and resume photosynthetic activity rapidly upon water availability. However, little is known about the mechanisms by which B. hygrometrica adapts to dehydration and resumes competence upon rehydration. Here we determine how B. hygrometrica deals with oxidative stress, excessive excitation/electron pressures as well as photosynthetic apparatus modulation during dehydration/rehydration. By measuring ROS generation and scavenging efficiency, we found that B. hygrometrica possesses efficient strategies to maintain cellular redox homeostasis. Transmission electron microscopy (TEM) analysis revealed a remarkable alteration of chloroplast architecture and plastoglobules (PGs) accumulation during dehydration/rehydration. Pulse-amplitude modulated (PAM) chlorophyll fluorescence measurements, P700 redox assay as well as chlorophyll fluorescence emission spectra analysis on leaves of B. hygrometrica during dehydration/rehydration were also performed. Results showed that the photochemical activity of PSII as well as photoprotective energy dissipation in PSII undergo gradual inactivation/activation during dehydration/rehydration in B. hygrometrica; PSI activity is relatively induced upon water deficit, and dehydration leads to physical interaction between PSI and LHCII. Furthermore, blue-native polyacrylamide gel electrophoresis (BN-PAGE) and immunoblot analysis revealed that the protein abundance of light harvesting complexes decrease markedly along with internal water deficit to restrict light absorption and attenuate electron transfer, resulting in limited light excitation and repressed photosynthesis. In contrast, many thylakoid proteins remain at a basal level even after full dehydration. Taken together, our study demonstrated that efficient modulation of cellular redox homeostasis and photosynthetic activity confers desiccation tolerance in B. hygrometrica.
Assuntos
Magnoliopsida/fisiologia , Fotossíntese/fisiologia , Antioxidantes/metabolismo , Clorofila/metabolismo , Cloroplastos/fisiologia , Desidratação , Metabolismo Energético , Homeostase , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Células Vegetais/metabolismo , Células Vegetais/fisiologia , Tilacoides/metabolismo , Água/metabolismoRESUMO
Recent studies reported that brassinosteroids (BRs) can induce plant tolerance to different environmental stresses via the nitric oxide (NO) signaling pathway. Previous reports have indicated that alternative oxidase (AOX) plays an important role in plants under various stresses. The mechanisms governing how NO is involved as a signal molecule which connects BR with AOX in regulating stress tolerance are still unknown. Recently, we found that Nicotiana benthamiana seedlings which were pretreated with BR have more tolerance to salt stress, accompanied with an increase of CN-resistant respiration. Our results suggested that pretreatment with 0.1 µM brassinolide (BL, the most active brassinosteroid) alleviated salt-induced oxidative damage and increased the NbAOX1 transcript level. Application of 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-1-oxyl-3-oxide (cPTIO, an NO scavenger) or virus-induced gene silencing of nitrate reductase (NR) and nitric oxide synthase (NOS)-like enzyme compromised the BRs-induced alternative respiratory pathway. Furthermore, pretreatment with specific chemical inhibitors of NR and NOS or gene silencing experiments decreased plant resistance to salt stress which also compromised BRs-induced salt stress tolerance. In conclusion, NO is involved in BRs-induced AOX capability which plays essential roles in salt tolerance in N. benthamiana seedlings.
RESUMO
Exogenous application of sodium nitroprusside (SNP) would enhance the tolerance of plants to stress conditions. Some evidences suggested that nitric oxide (NO) could induce the expression of alternative oxidase (AOX). In this study, Medicago truncatula (Medicago) was chosen to study the role of AOX in the SNP-elevated resistance to salt stress. Our results showed that the expression of AOX genes (especially AOX1 and AOX2b1) and cyanide-resistant respiration rate (Valt) could be significantly induced by salt stress. Exogenous application of SNP could further enhance the expression of AOX genes and Valt. Exogenous application of SNP could alleviate the oxidative damage and photosynthetic damage caused by salt stress. However, the stress resistance was significantly decreased in the plants which were pretreated with n-propyl gallate (nPG). More importantly, the damage in nPG-pretreated plants could not be alleviated by application of SNP. Further study showed that effects of nPG on the activities of antioxidant enzymes were minor. These results showed that AOX pathway played an important role in the SNP-elevated resistance of Medicago to salt stress. AOX could contribute to regulating the accumulation of reactive oxygen (ROS) and protect of photosystem, and we proposed that all these were depend on the ability of maintaining the homeostasis of redox state.
Assuntos
Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Medicago truncatula/fisiologia , Proteínas Mitocondriais/genética , Nitroprussiato/farmacologia , Oxirredutases/genética , Proteínas de Plantas/genética , Espécies Reativas de Oxigênio/metabolismo , Antioxidantes/metabolismo , Respiração Celular , Medicago truncatula/efeitos dos fármacos , Medicago truncatula/enzimologia , Medicago truncatula/genética , Proteínas Mitocondriais/metabolismo , Oxirredutases/metabolismo , Fotossíntese/efeitos dos fármacos , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/enzimologia , Folhas de Planta/genética , Folhas de Planta/fisiologia , Proteínas de Plantas/metabolismo , Tolerância ao Sal , Plântula/efeitos dos fármacos , Plântula/enzimologia , Plântula/genética , Plântula/fisiologia , Estresse FisiológicoRESUMO
Drought is one of the most significant abiotic stresses that restrict crop productivity. Medicago truncatula is a model legume species with a wide genetic diversity. We compared the differential physiological and molecular changes of two genotypes of M. truncatula (Jemalong A17 and R108) in response to progressive drought stress and rewatering. The MtNCED and MtZEP activation and higher abscisic acid (ABA) content was observed in Jemalong A17 plants under normal conditions. Additionally, a greater increase in ABA content and expression of MtNCED and MtZEP in Jemalong A17 plants than that of R108 plants were observed under drought conditions. A more ABA-sensitive stomatal closure and a slower water loss was found in excised leaves of Jemalong A17 plants. Meanwhile, Jemalong A17 plants alleviated leaf wilting and maintained higher relative water content under drought conditions. Exposed to drought stress, Jemalong A17 plants exhibited milder oxidative damage which has less H2O2 and MDA accumulation, lower electrolyte leakage and higher chlorophyll content and PSII activity. Furthermore, Jemalong A17 plants enhanced expression of stress-upregulated genes under drought conditions. These results suggest that genotypes Jemalong A17 and R108 differed in their response and adaptation to drought stress. Given the relationship between ABA and these physiological responses, the MtNCED and MtZEP activation under normal conditions may play an important role in regulation of greater tolerance of Jemalong A17 plants to drought stress. The activation of MtNCED and MtZEP may lead to the increase of ABA content which may activate expression of drought-stress-regulated genes and cause a series of physiological resistant responses.