Reactive oxygen species scavenging enzymes and down-adjustment of metabolism level in mitochondria associated with desiccation-tolerance acquisition of maize embryo

Elevated CO2 exposure induces core browning in Yali pears by inhibiting the electron transport chain

Pears may be affected by core browning during storage, reducing their commercial value. The effect of CO₂ stress on the core browning process in Yali pears was investigated. Exposure to a 4% CO₂ atmosphere significantly increased the core browning and reduced titratable acidity and soluble solids content. The activity of succinate dehydrogenase and peroxidase was reduced in CO₂-stressed pears, whereas the levels of H₂O₂ and malondialdehyde were increased. Transmission electron microscopy revealed significant damage to cellular membrane structure in the core tissues of CO₂-stressed pears. In addition, CO₂-stressed pears showed increased polyphenol oxidase activity. These results suggest that high concentrations of carbon dioxide can accelerate core browning in pears by inhibiting the activities of enzymes in the electron transport chain, resulting in increased levels of free radicals that damage cellular membranes.

Integration of small RNA, degradome and proteome sequencing in Oryza sativa reveals a delayed senescence network in tetraploid rice seed

Seed of rice is an important strategic resource for ensuring the security of China's staple food. Seed deterioration as a result of senescence is a major problem during seed storage, which can cause major economic losses. Screening among accessions in rice germplasm resources for traits such as slow senescence and increased seed longevity during storage is, therefore, of great significance. However, studies on delayed senescence in rice have been based mostly on diploid rice seed to date. Despite better tolerance have been verified by the artificial aging treatment for polyploid rice seed, the delayed senescence properties and delayed senescence related regulatory mechanisms of polyploid rice seed are rarely reported, due to the lack of polyploid rice materials with high seed set. High-throughput sequencing was applied to systematically investigate variations in small RNAs, the degradome, and the proteome between tetraploid and diploid rice seeds. Degradome sequencing analysis of microRNAs showed that expression of miR-164d, which regulates genes encoding antioxidant enzymes, was changed significantly, resulting in decreased miRNA-mediated cleavage of target genes in tetraploid rice. Comparisons of the expression levels of small RNAs (sRNAs) in the tetraploid and diploid libraries revealed that 12 sRNAs changed significantly, consistent with the findings from degradome sequencing. Furthermore, proteomics also showed that antioxidant enzymes were up-regulated in tetraploid rice seeds, relative to diploids.

Influence of exogenous ascorbic acid and glutathione priming on mitochondrial structural and functional systems to alleviate aging damage in oat seeds

BACKGROUND

Loss of vigor caused by seed aging adversely affects agricultural production under natural conditions. However, priming is an economical and effective method for improving the vigor of aged seeds. The objective of this study was to test the effectiveness of exogenous ascorbic acid (ASC) and glutathione (GSH) priming in the repairing of aged oat (Avena sativa) seeds, and to test the hypothesis that structural and functional systems in mitochondria were involved in this process.

RESULTS

Oat seeds were artificially aged for 20 days at 45 °C, and were primed with solutions (1 mmol L^- 1) of ASC, GSH, or ASC + GSH at 20 °C for 0.5 h before or after their aging. Seed germination, antioxidant enzymes in the ASC-GSH cycle, cytochrome c oxidase (COX) and mitochondrial malate dehydrogenase (MDH) activities, and the mitochondrial ultrastructures of the embryonic root cells were markedly improved in aged oat seeds through post-priming with ASC, GSH, or ASC + GSH, while their malondialdehyde and H₂O₂ contents decreased significantly (P < 0.05).

CONCLUSION

Our results suggested that priming with ASC, GSH, or ASC + GSH after aging could effectively alleviate aging damage in oat seeds, and that the role of ASC was more effective than GSH, but positive effects of post-priming with ASC and GSH were not superior to post-priming with ASC in repairing aging damage of aged oat seeds. However, pre-priming with ASC, GSH, or ASC + GSH was not effective in oat seeds, suggesting that pre-priming with ASC, GSH, or ASC + GSH could not inhibit the occurrence of aging damage in oat seeds.

Transcriptomic Profiling Reveals Metabolic and Regulatory Pathways in the Desiccation Tolerance of Mungbean (Vigna radiata [L.] R. Wilczek)

Mungbean (Vigna radiate L. Wilczek) is an important legume crop for its valuable nutritional and health benefits. Desiccation tolerance (DT) is a capacity of seeds to survive and maintain physiological activities during storage and under stress conditions. Many studies of DT have been reported in other legume crop, such as soybean and Medicago truncatula with little studies in the mungbean. In this study, the transcript profiles of mungbean seeds under different imbibition times were investigated for DT using RNA-sequencing (RNA-seq). A total of 3210 differentially expressed genes (DEGs) were found at the key period of DT (3-18 h of imbibition). Gene ontology (GO) and KEGG analysis showed that the terms of "response to stimulus," "transcription regulator," "methylation," and "starch and sucrose metabolism" were enriched for DT. Clustering analysis also showed that many transcription factors (MYB, AP2, and NAC), HSPs, embryogenesis abundant (LEA) proteins, and genes encoding methyltransferase and histone were differentially expressed. Nine of these DEGs were further validated by quantitative RT-PCR (qRT-PCR). Our study extends our knowledge of mungbean transcriptomes and further provides insight into the molecular mechanism of DT as well as new strategies for developing drought-tolerant crops.

Mitochondrial structural and antioxidant system responses to aging in oat (Avena sativa L.) seeds with different moisture contents

We observed the relationship between lifespan and mitochondria, including antioxidant systems, ultrastructure, and the hydrogen peroxide and malondialdehyde contents in 4 h imbibed oat (Avena sativa L.) seeds that were aged with different moisture contents (4%, 10% and 16%) for 0 (the control), 8, 16, 24, 32 and 40 d at 45 °C. The results showed that the decline in the oat seed vigor and in the integrity of the mitochondrial ultrastructure occurred during the aging process, and that these changes were enhanced by higher moisture contents. Mitochondrial antioxidants in imbibed oat seeds aged with a 4% moisture content were maintained at higher levels than imbibed oat seeds aged with a 10% and 16% moisture content. These results indicated that the levels of mitochondrial antioxidants and malondialdehyde after imbibition were related to the integrity of the mitochondrial membrane in aged oat seeds. The scavenging role of mitochondrial superoxide dismutase was inhibited in imbibed oat seeds aged at the early stage. Monodehydroascorbate reductase and dehydroascorbate reductase played more important roles than glutathione reductase in ascorbate regeneration in aged oat seeds during imbibition.

Change in desiccation tolerance of maize embryos during development and germination at different water potential PEG-6000 in relation to oxidative process

Desiccation tolerance is one of the most important traits determining seed survival during storage and under stress conditions. However, the mechanism of seed desiccation tolerance is still unclear in detail. In the present study, we used a combined model system, desiccation-tolerant and -sensitive maize embryos with identical genetic background, to investigate the changes in desiccation tolerance, malonyldialdehyde (MDA) level, hydrogen peroxide (H₂O₂) content and antioxidant enzyme activity during seed development and germination in 0, -0.6 and -1.2 MPa polyethylene glycol (PEG)-6000 solutions. Our results indicated that maize embryos gradually acquired and lost desiccation tolerance during development and germination, respectively. The acquirement and loss of desiccation tolerance of embryos during development and germination were related to the ability of antioxidant enzymes including superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), catalase (CAT, EC 1.11.1.6), glutathione reductase (GR, EC 1.6.4.2) and dehydroascorbate reductase (DHAR, EC 1.8.5.1) to scavenge reactive oxygen species (ROS) and to control MDA content. Compared with treatment in water, PEG-6000 treatment could markedly delay the loss of desiccation tolerance of germinating embryos by delaying water uptake and time course of germination, increasing GR activity and decreasing MDA content. Our data showed the combination of antioxidant enzyme activity and MDA content is a good parameter for assessing the desiccation tolerance of maize embryos. In addition, H₂O₂ accumulated in mature embryos and PEG-treated embryos after drying, which was at least partially related to a longer embryo/seedling length in rehydration and the physiological mechanisms of priming.

The role of recovery of mitochondrial structure and function in desiccation tolerance of pea seeds

Mitochondrial repair is of fundamental importance for seed germination. When mature orthodox seeds are imbibed and germinated, they lose their desiccation tolerance in parallel. To gain a better understanding of this process, we studied the recovery of mitochondrial structure and function in pea (Pisum sativum cv. Jizhuang) seeds with different tolerance to desiccation. Mitochondria were isolated and purified from the embryo axes of control and imbibed-dehydrated pea seeds after (re-)imbibition for various times. Recovery of mitochondrial structure and function occurred both in control and imbibed-dehydrated seed embryo axes, but at different rates and to different maximum levels. The integrity of the outer mitochondrial membrane reached 96% in all treatments. However, only the seeds imbibed for 12 h and then dehydrated recovered the integrity of the inner mitochondrial membrane (IMM) and State 3 (respiratory state in which substrate and ADP are present) respiration (with NADH and succinate as substrate) to the control level after re-imbibition. With increasing imbibition time, the degree to which each parameter recovered decreased in parallel with the decrease in desiccation tolerance. The tolerance of imbibed seeds to desiccation increased and decreased when imbibed in CaCl(2) and methylviologen solution, respectively, and the recovery of the IMM integrity similarly improved and weakened in these two treatments, respectively. Survival of seeds after imbibition-dehydration linearly increased with the increase in ability to recover the integrity of IMM and State 3 respiration, which indicates that recovery of mitochondrial structure and function during germination has an important role in seed desiccation tolerance.

Proteomic profiling and redox status alteration of recalcitrant tea (Camellia sinensis) seed in response to desiccation

Tea seed is believed to be recalcitrant based on its sensitivity to chilling or drying stress. Reactive oxygen species (ROS) and alterations in cytosolic redox status have been implicated in intolerance to desiccation by recalcitrant seed, but there is little information available regarding how ROS are regulated in seeds susceptible to drying stress. We investigated changes in protein expression and activity in tea embryo in response to desiccation using physiological and proteomic methods. Results showed that desiccation treatment dramatically induced the accumulation of H(2)O(2) in tea embryos, accompanied by increased activities of antioxidant enzymes like ascorbate peroxidase (APX) and superoxide dismutase (SOD). Proteomic analyses also demonstrated that 23 proteins associated with defense response, metabolism and redox status were up-regulated following desiccation. Increase in antioxidants, ascorbic acid (AsA) and catalase (CAT) (H(2)O(2) scavengers) partially assuaged desiccation damage to tea seed, resulting in improved germination rates. Higher accumulation of H(2)O(2) aggravated desiccation damage to seeds leading to lower germination activity. We propose that desiccation causes an over-accumulation of ROS that are not efficiently scavenged by increased levels of antioxidant enzymes. High levels of ROS alter the redox status and are detrimental to seed viability. Reducing ROS to appropriate concentrations is an efficient way to reduce desiccation damage and improve germination rates of recalcitrant seeds.