The complete chloroplast genome of Bothriochloa ischaemum.

Bothriochloa ischaemum (Linn.) 1936 is a high-quality perennial forage in Loess Plateau of China. In this study, we sequenced and characterized the complete chloroplast genome of B. ischaemum, which was a circular DNA of 138,316 bp in length, including a large single copy (LSC) region of 80,226 bp, a small single copy (SSC) region of 12,526 bp, and the circular DNA was separated by a pair of identical inverted repeat regions (IRs) of 22,782 bp each. A total of 134 genes were identified, including 87 protein-coding genes, 39 tRNA genes, and eight rRNA genes. Phylogenetic tree showed that B. ischaemum was closer to B. decipiens and B. alta, genus Bothriochloa was closely related to genus Pseudanthistiria. Our findings will be helpful for better understanding of genetic diversity of Bothriochloa plants.

The complete chloroplast genome of Medicago ruthenica cv. 'Taihang' (Fabaceae) from Shanxi, China.

Medicago ruthenica is an important perennial forage with multiple characteristics of resistance. In this study, we sequenced and characterized the complete chloroplast genome of M. ruthenica 'Taihang', which is 124, 254 bp in length. A total of 108 genes were identified, including 74 protein-coding, 30 tRNA, and four rRNA genes. Phylogenetic analysis based on 27 chloroplast genomes showed that M. ruthenica 'Taihang' has a close relationship with M. ruthenica from Qinghai Province, China. The data are useful in better understanding the genetic diversity and stress resistance of Medicago and contribute to the phylogenetic study of Trifolieae.

Physiological and proteomic analysis reveals the impact of boron deficiency and surplus on alfalfa (Medicago sativa L.) reproductive organs.

Boron (B), an essential element for increasing seed yield and germinability in alfalfa (Medicago sativa L.), plays a vital role in its reproductive processes. However, effects of B stress on physiological and proteomic changes in reproductive organs related to alfalfa seed yield and germinability are poorly understood. In order to gain a better insight into B response or tolerance mechanisms, field trials were designed for B deficiency (0 mg B L-1), B sufficiency (800 mg B L-1), and B surplus (1600 mg B L-1) application during alfalfa flowering to analyze the proteomics and physiological responses of alfalfa 'Aohan' reproductive organs. Results showed that B deficiency weakened the stress-responsive ability in these organs, while B surplus reduced the sugar utilization of 'Aohan' flowers and caused lipid membrane peroxidation in 'Aohan' seeds. In addition, four upregulated stress responsive proteins (ADF-like protein, IMFP, NAD(P)-binding Rossmann-fold protein and NAD-dependent ALDHs) might play pivotal roles in the response of 'Aohan' reproductive organs to conditions of B deficiency and B surplus. All of the above results would be helpful to understand the tolerance mechanisms of alfalfa reproductive organs to both B deficiency and B surplus conditions, and also to give insight into the regulatory role of B in improving seed yield and germinability in alfalfa seed production. In summary, B likely plays a structural and regulatory role in relation to lipid metabolism, carbohydrate metabolism, amino acid metabolism, and signal transduction, thus regulates alfalfa reproductive processes eventually affecting the seed yield and germinability of alfalfa seeds.

Metabolomic analyses of alfalfa (Medicago sativa L. cv. 'Aohan') reproductive organs under boron deficiency and surplus conditions.

Boron (B) deficiency and surplus are the main factors that affect plant growth and yield. A better understanding of the response mechanisms of plant reproductive organs to stress induced by B deficiency and surplus could provide new insights to potential strategies for improving seed yield and quality. In this study, we aimed to elucidate the mechanisms of tolerance to B-induced stress in the reproductive organs of alfalfa (Medicago sativa L. cv. 'Aohan'). We initially used five B concentrations (0 mg B L-1, 400 mg B L-1, 800 mg B L-1, 1200 mg B L-1, and 1600 mg B L-1) to determine the B deficient, sufficient, and surplus levels in the field. Secondly, we examined changes in metabolite profiles of alfalfa 'Aohan' reproductive organs in response to B deficiency (0 mg B L-1), B sufficiency (800 mg B L-1), and B surplus (1600 mg B L-1) conditions using gas chromatography-mass spectrometry (GC-MS). Flowers and seeds from alfalfa 'Aohan' showed different metabolite profiles and resistance capacity under B deficiency and surplus conditions. B deficiency led to the excessive accumulation of sugars and phenolic compounds in alfalfa 'Aohan' and seeds, respectively, thus causing abscission or the abortion of reproductive organs. In contrast, B surplus severely reduced the levels of metabolites associated with amino acid and carbohydrate metabolism, resulting in the flowers falling and, therefore, low seed yield. Overall, B deficiency predominantly reduced seed yield and quality of alfalfa 'Aohan', while B surplus mainly affected seed yield of alfalfa 'Aohan'.

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.

Assessing of the contributions of pod photosynthesis to carbon acquisition of seed in alfalfa (Medicago sativa L.).

The distribution of carbon from a branch setting pod in alfalfa was investigated during the seed development of seeds to determine the relative contribution of pod and leaf photoassimilates to the total C balance and to investigate the partitioning of these photoassimilates to other plant organs. A 13Clabeling procedure was used to label C photoassimilates of pods and leaves in alfalfa, and the Δ13C values of a pod, leaves, a section of stem and roots were measured during seed development on day 10, 15, 20 and 25 after labeling of the pod. The results showed that the alfalfa pod had photosynthetic capacity early in the development of seeds, and that pod photosynthesis could provide carbon to alfalfa organs including seeds, pods, leaves, stems and roots, in addition to leaf photosynthesis. Photosynthesis in the pod affected the total C balance of the alfalfa branch with the redistribution of a portion of pod assimilates to other plant organs. The assimilated 13C of the pod was used for the growth requirements of plant seeds and pods. The requirements for assimilated C came primarily from the young pod in early seed development, with later requirements provided primarily from the leaf.

Proteomic and Physiological Analysis of the Response of Oat (Avena sativa) Seeds to Heat Stress under Different Moisture Conditions.

Seeds lose their viability when they are exposed to high temperature and moisture content (MC) during storage. The expression and metabolism of proteins plays a critical role in seed resistance to heat stress. However, the proteome response to heat stress in oat (Avena sativa) seeds during storage has not been revealed. To understand mechanisms of heat stress acclimation and tolerance in oat seeds, an integrated physiological and comparative proteomic analysis was performed on oat seeds with different MC during heat stress. Oat seeds with 10% and 16% MC were subjected to high temperatures (35, 45, and 50°C) for 24 and 2 days, respectively, and changes in physiological and biochemical characteristics were analyzed. The results showed that seed vigor decreased significantly with temperature increase from 35 to 50°C. Also, the proline content in 10% MC seeds decreased significantly (p < 0.05) whereas that in 16% MC seeds increased significantly (p < 0.05) during heat treatment from 35 to 50°C. There were no significant differences in malondialdehyde content in 10% MC seeds with temperature from 35 to 50°C, but a significant (p < 0.05) decline occurred in 16% MC seeds at 45°C. Proteome analysis revealed 21 significantly different proteins, including 19 down-regulated and two up-regulated proteins. The down-regulated proteins, notably six heat shock proteins and two ATP synthases, have important roles in the mobilization of carbohydrates and energy, and in the balance between synthesis and degradation of other proteins during seed deterioration. The up-regulation of argininosuccinate synthase participated in proline biosynthesis at 16% MC, which is important for maintaining reactive oxygen species homeostasis for the resistance of heat stress. In summary, heat-responsive protein species and mitochondrial respiratory metabolism were sensitive to high temperature and MC treatment. These studies provide a new insight into acclimation and tolerance to heat stress in oat seeds.

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.