Cereal Husks: Versatile Roles in Grain Quality and Seedling Performance

The seed is the fundamental unit of the dispersal of dry, dehiscent fruits, in which the fruit splits open at maturity to allow for seed dispersal. However, dry fruits may be indehiscent and therefore represent the dispersal unit (DU). Cereals possess a one-seeded fruit, whereby the seed coat and the fruit coat are fused together to generate the caryopsis. This caryopsis may be covered by floral bracts to generate two types of DUs, namely florets, whereby the caryopsis is enclosed by the lemma and the palea (e.g., Avenasterilis) or spikelet, whereby the floret(s) is further covered by the glumes (Triticum turgidum var. dicoccoides). Here, we highlight the dead coverings enclosing the caryopsis in cereals, namely the husks as an integral component of the dispersal unit that play multifaceted roles in grain biology. Thus, besides protection and dispersal means, the husks function as a rich maternal supply of proteins and metabolites for enhancing growth and development, combat potential pathogens as well as confer tolerance to abiotic stresses. These attributes might have broad implications for crop performance, plant population dynamics and diversity in ecological systems, and for conservation of genetic resources in seed banks.

Differential Response to Single and Combined Salt and Heat Stresses: Impact on Accumulation of Proteins and Metabolites in Dead Pericarps of Brassica juncea

Dead organs enclosing embryos, such as seed coats and pericarps, are emerging as important maternally-derived components of the dispersal unit that affect seed performance and fate. In the face of climate change and increased incidents of heatwaves, we sought to investigate the effect of salinity (S), short episodes of high temperature (HS), and combination of S + HS (SHS), at the reproductive phase, on the properties of dead pericarps of Brassica juncea. Proteome and metabolome analyses revealed multiple proteins and metabolites stored in dead pericarps whose levels and composition were altered under single and combined stress conditions. The protein profile of SHS showed a higher correlation with salt than with HS indicating the dominant effect of salt over heat stress. On the other hand, the analysis of metabolites showed that the profile of SHS has better correlation with HS than with salt. The integration of metabolic and proteomic data showed that changes in TCA cycle intermediates and certain amino acids (e.g., proline) under salt treatments (S and SHS) are highly correlated with changes in proteins involved in their biosynthetic pathways. Thus, accumulation of proteins and metabolites in dead pericarps is differently affected by single and combination of salt and heat stresses. Salinity appears to dominate plant response to combined stresses at the protein level, while heat appears to be the major factor affecting metabolite accumulation in dead pericarps.

Dead but Not Dead End: Multifunctional Role of Dead Organs Enclosing Embryos in Seed Biology

Dry fruits consist of two types, dehiscent and indehiscent, whereby the fruit is splitting open or remains closed at maturity, respectively. The seed, the dispersal unit (DU) of dehiscent fruits, is composed of three major parts, the embryo and the food reserve, encapsulated by the maternally-derived organ, the seed coat. Indehiscent fruit constitutes the DU in which the embryo is covered by two protective layers (PLs), the seed coat and the fruit coat. In grasses, the caryopsis, a one-seeded fruit, can be further enclosed by the floral bracts to generate two types of DUs, florets and spikelets. All protective layers enclosing the embryo undergo programmed cell death (PCD) at maturation and are thought to provide mainly a physical shield for embryo protection and a means for dispersal. In this review article, I wish to highlight the elaborate function of these dead organs enclosing the embryo as unique storage structures for beneficial substances and discuss their potential role in seed biology and ecology.

Pollen biodiversity – why are pollen grains different despite having the same function? A review

The main morphological, cytological and physiological characters of ripe pollen are described, compared, analysed and discussed individually, in multiple combinations and in respect to the female counterpart and the biotic and abiotic components of the environment. This is to try to understand the reasons why pollen grains have the same reproductive function, but at dispersal are morphologically and physiologically different in many respects. The considered characters are: one or more types of grain per species; shape and size; number of cells; types of pollen dispersal unit; sporoderm stratification, furrows, colpori and other kinds of apertures; pollen presentation and array; water content percentage; and mature pollen reserves and osmotics. Some of the pollen features are correlated between themselves, some with the female counterpart or male and female competition, and others with the different components of the environment where the species lives, when it flowers and when pollen presentation occurs.

Accelerated diversification correlated with functional traits shapes extant diversity of the early divergent angiosperm family Annonaceae

BackgroundA major goal of phylogenetic systematics is to understand both the patterns of diversification and the processes by which these patterns are formed. Few studies have focused on the ancient, species-rich Magnoliales clade and its diversification pattern. Within Magnoliales, the pantropically distributed Annonaceae are by far the most genus-rich and species-rich family-level clade, with c. 110 genera and c. 2,400 species. We investigated the diversification patterns across Annonaceae and identified traits that show varied associations with diversification rates using a time-calibrated phylogeny of 835 species (34.6% sampling) and 11,211 aligned bases from eight regions of the plastid genome (rbcL, matK, ndhF, psbA-trnH, trnL-F, atpB-rbcL, trnS-G, and ycf1). Two hypotheses that might explain patterns of diversification—the ‘museum model’ and heterogeneous diversification rates—are also evaluated.ResultsTwelve rate shifts were identified using BAMM: in Annona, Artabotrys, Asimina, Drepananthus, Duguetia, Goniothalamus, Guatteria, Uvaria, Xylopia, the tribes Miliuseae and Malmeeae, and the Desmos-Dasymaschalon-Friesodielsia-Monanthotaxis clade (which collectively account for over 80% of the total species richness in the family). TurboMEDUSA and method-of-moments estimator analyses showed largely congruent results. A positive relationship between species richness and diversification rate is revealed using PGLS. We further explore the possible role of selected traits (habit, pollinator trapping, floral sex expression, pollen dispersal unit, anther septation, and seed dispersal unit) in shaping diversification patterns, based on inferences of BiSSE, MuSSE, HiSSE, and FiSSE analyses. Our results suggest that the liana habit, the presence of circadian pollinator trapping, androdioecy, and the dispersal of seeds as single-seeded monocarp fragments are closely correlated with higher diversification rates; pollen aggregation and anther septation, in contrast, are associated with lower diversification rates.ConclusionOur results show that the high species richness in Annonaceae is likely the result of recent increased diversification rather than the steady accumulation of species via the ‘museum model’. BAMM, turboMEDUSA, and the method-of-moments estimator all indicate heterogeneity in diversification rates across the phylogeny, with different traits associated with shifts in diversification rates in different Annonaceae clades.

Seed dormancy in six cold desert Brassicaceae species with indehiscent fruits

The dispersal unit of many species of Brassicaceae is an indehiscent fruit, but relatively few studies have tested the effect of the pericarp on seed germination in this family. Our aim was to determine the effect of the pericarp on seed dormancy in six species of Brassicaceae native to the cold desert of north-west China. Intact dispersal units and isolated seeds of Chorispora sibirica, Euclidium syriacum, Goldbachia laevigata, Spirorrhynchus sabulosus, Sterigmostemum fuhaiense and Tauscheria lasiocarpa were stored dry at ambient laboratory conditions for 0–12 months and tested for germination in light and in dark at 5/2, 15/2 and 30/15°C. The amount of water absorbed by fruits and by seeds within the fruits was determined. For four species, intact fruits, isolated seeds and isolated seeds plus the removed pericarps were used to test for the mechanical versus possible chemical role of the pericarp in seed dormancy. Fresh isolated seeds, which have a fully developed embryo, germinated to lower percentages and rates than afterripened seeds. Thus, seeds have non-deep physiological dormancy. The pericarp significantly reduced germination, but inhibition was not due to lack of water uptake by seeds or to chemical inhibitors. Afterripened seeds of the six species germinated to 0–50% inside the fruits. We conclude that the pericarp plays a dominant role in seed dormancy of the six study species, and it does so by mechanically restricting embryo growth. Thus, the pericarp has the potential to spread germination over an extended period of time.

Germination of selected Australian native grass species, with potential for minesite rehabilitation

Native grasses have become increasingly important in the post-mining landscape where land rehabilitators try to reconstruct vegetation communities similar to those present before land clearing. So as to include native grasses in these communities, there is a requirement to understand their germination biology, because in the past, many grasses have typically been hard to establish in the final community. The present study found that poor germination of 13 native grass species was due to (1) low percentage of seed fill, (2) low seed viability of filled seeds and/or (3) seed dormancy. Eight species had dormancy treatments investigated. Most were found to exhibit at least one form of dormancy that was either located in the hull structures immediately external to the caryopsis (i.e. the lemma, palea and glumes), within the seed coat (i.e. testa and pericarp, tissues that are found inside the hull, but external to the embryo and endosperm) and/or within the embryo. Seven of the grass species tested were found to have a dormancy mechanism present in two or more locations of their dispersal unit. Germination of the selected native grass species could be improved by (1) processing seeds to enrich the percentage of seeds that are filled, (2) testing viability to ensure a high proportion of the seeds are likely to germinate or (3) using methods to help overcome dormancy and promote germination.