Commelina erecta is a successful weed species. The aims of this study were to analyse the morpho-anatomy of the fruit and dimorphic seeds of the weed C. erecta, the dynamics and type of dormancy, and water entry. Flowers and fruits at different development stages were processed using standard anatomical techniques. Besides, experiments of imbibition, germinability and water entry were performed on both seed types. In the fruit of C. erecta, free and coated seeds are developed within dehiscent and indehiscent carpels, respectively. Dehiscent carpels open through a region of mechanical weakness in the dorsal vascular bundle. This region does not form in the indehiscent carpel. The main anatomical differences between the two seed types were observed in the testa and in the number of covering layers. Imbibition experiments showed that the covering of both seed types is water permeable, so these seeds lack physical dormancy and may exhibit physiological dormancy. Germinability experiments showed that the dormancy in free seeds is variable throughout the reproductive season, whereas, in coated seeds, it is high throughout the reproductive season. The embryotega is an area where the hardness of the seed coat is interrupted and facilitates water entry. Differences in the morpho-anatomy of carpels result in the formation of dimorphic seeds with different covering layers and different germination properties. These different properties allow some seeds germinate immediately after falling from the mother plant, and others to be incorporated into the seed bank. These results are useful for designing weed management strategies in agroecosystems.

Soil salinization is an increasing agricultural problem around the world, affecting crop productivity and quality. Seed germination and seedling establishment are susceptible to salt stress. Suaeda liaotungensis is a halophyte with strong salt tolerance that produces dimorphic seeds to adapt to the saline environment. Differences in physiological characteristics, seed germination, and seedling establishment in response to salt stress between dimorphic seeds in S. liaotungensis have not been reported. The results showed that brown seeds had significantly higher H2O2 and O2-. levels and betaine content, as well as POD and CAT activities, while they had significantly lower MDA and proline contents and SOD activity than black seeds. Light promoted the germination of brown seeds in a certain temperature range, and brown seeds could reach a higher germination percentage in a wide temperature range. However, light and temperature had no effect on the germination percentage of black seeds. Brown seeds had higher germination than black seeds under the same NaCl concentration. The final germination of brown seeds was significantly decreased as salt concentration increased, whereas this had no effect on the final germination of black seeds. POD and CAT activities, as well as MDA content, in brown seeds were significantly higher than those in black seeds during germination under salt stress. Additionally, the seedlings from brown seeds were more tolerant to salinity than those from black seeds. Therefore, these results will give an in-depth understanding of the adaptation strategies of dimorphic seeds to a salinization environment, and better exploitation and utilization of S. liaotungensis.

Seed dimorphism has been thought to be a bet-hedging strategy that helps plants survive in the disturbed environment and has been widely studied for its ecological adaptation mechanism. Many studies showed that seed-associated microorganisms play an important role in enhancing plant fitness, but information regarding endophytic bacteria associated with dimorphic seeds is limited. This study explores the influence of seed coat structure and seed phytochemical properties on the community composition and diversity of endophytic bacteria of dimorphic seeds of Suaeda glauca. In this study, we used 16S rRNA high-throughput gene sequencing method to compare the community composition and bacterial diversity between brown and black seeds of Suaeda glauca.
A significant difference was observed in seed coat structure and phytochemical properties between brown and black seeds of S. glauca. Total 9 phyla, 13 classes, 31 orders, 53 families, 102 genera were identified in the dimorphic seeds. The dominant phyla were Proteobacteria, Firmicutes, and Actinobacteria. The results showed that seed dimorphism had little impact on the diversity and richness of endophytic bacterial communities but significantly differs in the relative abundance of the bacterial community between brown and black seeds. At the phylum level, Actinobacteria tend to be enriched significantly in brown seeds. At the genus level, Rhodococcus, Ralstonia, Pelomonas and Bradyrhizobium tend to be enriched significantly in brown seeds, while Marinilactibacillus was mainly found in black seeds. Besides, brown seeds harbored a large number of bacteria with plant-growth-promoting traits, whereas black seeds presented bacteria with enzyme activities (i.e., pectinase, cellulolytic and xylanolytic activities).
The endophytic bacterial community compositions were significantly different between dimorphic seeds of Suaeda glauca, and play an important role in the ecological adaptation of dimorphic seeds by performing different biological function roles. The endophytic bacterial communities of the dimorphic seeds may be influenced mainly by the seed coat structureand partly by the seed phytochemical characteristics. These findings provide valuable information for better understanding of the ecological adaptation strategy of dimorphic seeds in the disturbed environment.

BACKGROUND: RNA-sequencing analysis is increasingly utilized to study gene expression in non-model organisms without sequenced genomes. Aethionema arabicum (Brassicaceae) exhibits seed dimorphism as a bet-hedging strategy - producing both a less dormant mucilaginous (M+) seed morph and a more dormant non-mucilaginous (NM) seed morph. Here, we compared de novo and reference-genome based transcriptome assemblies to investigate Ae. arabicum seed dimorphism and to evaluate the reference-free versus -dependent approach for identifying differentially expressed genes (DEGs).
RESULTS: A de novo transcriptome assembly was generated using sequences from M+ and NM Ae. arabicum dry seed morphs. The transcripts of the de novo assembly contained 63.1% complete Benchmarking Universal Single-Copy Orthologs (BUSCO) compared to 90.9% for the transcripts of the reference genome. DEG detection used the strict consensus of three methods (DESeq2, edgeR and NOISeq). Only 37% of 1533 differentially expressed de novo assembled transcripts paired with 1876 genome-derived DEGs. Gene Ontology (GO) terms distinguished the seed morphs: the terms translation and nucleosome assembly were overrepresented in DEGs higher in abundance in M+ dry seeds, whereas terms related to mRNA processing and transcription were overrepresented in DEGs higher in abundance in NM dry seeds. DEGs amongst these GO terms included ribosomal proteins and histones (higher in M+), RNA polymerase II subunits and related transcription and elongation factors (higher in NM). Expression of the inferred DEGs and other genes associated with seed maturation (e.g. those encoding late embryogenesis abundant proteins and transcription factors regulating seed development and maturation such as ABI3, FUS3, LEC1 and WRI1 homologs) were put in context with Arabidopsis thaliana seed maturation and indicated that M+ seeds may desiccate and mature faster than NM. The 1901 transcriptomic DEG set GO-terms had almost 90% overlap with the 2191 genome-derived DEG GO-terms.
CONCLUSIONS: Whilst there was only modest overlap of DEGs identified in reference-free versus -dependent approaches, the resulting GO analysis was concordant in both approaches. The identified differences in dry seed transcriptomes suggest mechanisms underpinning previously identified contrasts between morphology and germination behaviour of M+ and NM seeds.

The halophyte Salicornia europaea L. is a widely distributed salt-tolerant plant species that produces numerous dimorphic seeds. We studied germination and recovery in dimorphic seeds of Central Asian S. europaea under various salinity conditions. We also tested the effects of various salts on Na+ and K+ accumulation during plant development from germination to anthesis under greenhouse conditions. We found good germination (close to control) of large seeds under NaCl between 0.5 and 2%, Na2SO4 and 2NaCl + KCl + CaCl between 0.5 and 3%, and 2Na2SO4 + K2SO4 + MgSO4 between 0.5 and 5%. For the small seeds, we found stimulating effects of chloride salts (both pure and mixed) under 0.5-1% concentrations, and sulfate salts under 0.5-3%. Both types of seeds showed high germination recovery potential. Salt tolerance limits of the two seed types during germination and at the later stages of development were very similar (4-5%). During plant growth the optimal concentrations of mixed chloride and sulfate salts ranged from 0.5 to 2%. The mechanisms of salt tolerance in the two seed types of S. europaea appear to differ, but complement each other, improving overall adaptation of this species to high salinity.

Suaeda salsa is an annual euhalophytic herb that produces dimorphic seeds, such as small black seeds and big brown seeds. In the present study, the fatty acid composition, content of total phenols, flavonoids, carotenoid and inorganic ions in dimorphic seeds of the species collected in the field were measured. There was no significant difference in total oil content between black and brown seeds. Seed total oil content was approximately 19% based on dry weight. The most abundant fatty acid was linoleic acid, and the content was 76.3 and 70.5% of total fatty acids in black and brown seeds, respectively. Furthermore, the contents of total phenols, flavonoids, carotenoids and inorganic ions in brown seeds were higher than those in black seeds, which might be the mechanism of higher salt tolerance of brown seeds than black seeds. The ecological, physiological and genetic mechanisms of the different abilities of nutrition accumulation in black and brown seeds of S. salsa are also discussed and worthy to be investigated in the future.

Seed heteromorphism observed in many halophytes is an adaptive phenomenon toward high salinity. However, the relationship between heteromorphic seed germination and germination-related hormones under salt stress remains elusive. To gain an insight into this relationship, the roles of gibberellins (GAs) and abscisic acid (ABA) in regulating germination of Suaeda salsa dimorphic brown and black seeds under salinity were elucidated by studying the kinetics of the two hormones during germination of the two seed types with or without salinity treatment. Morphological analysis suggested that brown and black are in different development stage. The content of ABA was higher in dry brown than in black seeds, which gradually decreased after imbibition in water and salt solutions. Salt stress induced ABA accumulation in both germinating seed types, with higher induction effect on black than brown seeds. Black seeds showed lower germination percentage than brown seeds under both water and salt stress, which might be attributed to their higher ABA sensitivity rather than the difference in ABA content between black and brown seeds. Bioactive GA4 and its biosynthetic precursors showed higher levels in brown than in black seeds, whereas deactivated GAs showed higher content in black than brown seeds in dry or in germinating water or salt solutions. High salinity inhibited seed germination through decreasing the levels of GA4 in both seeds, and the inhibited effect of salt stress on GA4 level of black seeds was more profound than that of brown seeds. Taken together higher GA4 content, and lower ABA sensitivity contributed to the higher germination percentage of brown seeds than black seeds in water and salinity; increased ABA content and sensitivity, and decreased GA4 content by salinity were more profound in black than brown seeds, which contributed to lower germination of black seeds than brown seeds in salinity. The differential regulation of ABA and GA homeostases by salt stress in dimorphic seeds might provide a strategy for S. salsa plants to survive adverse environmental conditions.

A new species of Vigna Savi, subgenus Ceratotropis (Piper) Verdc., Vignayadavii S.P. Gaikwad, R.D. Gore, S.D. Randive & K.U. Garad, sp. nov. is described and illustrated here. It is morphologically close to Vignadalzelliana (Kuntze) Verdc. but differs in its underground obligate cleistogamous flowers on positively geotropic branches, hairy calyx, small corolla, linear style beak and dimorphic seeds with shiny seed coat.

BACKGROUND: As important components in saline agriculture, halophytes can help to provide food for a growing world population. In addition to being potential crops in their own right, halophytes are also potential sources of salt-resistance genes that might help plant breeders and molecular biologists increase the salt tolerance of conventional crop plants. One especially promising halophyte is Suaeda salsa, a euhalophytic herb that occurs both on inland saline soils and in the intertidal zone. The species produces dimorphic seeds: black seeds are sensitive to salinity and remain dormant in light under high salt concentrations, while brown seeds can germinate under high salinity (e.g. 600 mm NaCl) regardless of light. Consequently, the species is useful for studying the mechanisms by which dimorphic seeds are adapted to saline environments. S. salsa has succulent leaves and is highly salt tolerant (e.g. its optimal NaCl concentration for growth is 200 mm). A series of S. salsa genes related to salt tolerance have been cloned and their functions tested: these include SsNHX1, SsHKT1, SsAPX, SsCAT1, SsP5CS and SsBADH. The species is economically important because its fresh branches have high value as a vegetable, and its seed oil is edible and rich in unsaturated fatty acids. Because it can remove salts and heavy metals from saline soils, S. salsa can also be used in the restoration of salinized or contaminated saline land.
METHODS: Because of its economic and ecological value in saline agriculture, S. salsa is one of the most important halophytes in China. In this review, the value of S. salsa as a source of food, medicine and forage is discussed. Its uses in the restoration of salinized or contaminated land and as a source of salt-resistance genes are also considered.