Genome Size and Labellum Epidermal Cell Size Are Evolutionarily Correlated With Floral Longevity in Paphiopedilum Species

Genome size is known to influence phenotypic traits in leaves and seeds. Although genome size is closely related to cellular and developmental traits across biological kingdoms, floral longevity is a floral trait with important fitness consequence, but less is known about the link between floral longevity and sizes of genomes and cells. In this study, we examined evolutionary coordination between genome size, floral longevity, and epidermal cell size in flowers and leaves in 13 Paphiopedilum species. We found that, across all the study species, the genome size was positively correlated with floral longevity but negatively associated with labellum epidermal cell size, and a negative relationship was found between floral longevity and labellum epidermal cell size. This suggested that genome size is potentially correlated with floral longevity, and genome size has an important impact on life-history trait. In addition, genome size was positively correlated with leaf epidermal cell size, which was different from the relationship in flower due to different selective pressures they experienced or different functions they performed. Therefore, genome size constraints floral longevity, and it is a strong predictor of cell size. The impact of genome size on reproduction might have more implications for the evolution of flowering plants and pollination ecology.

Effects of experimental warming on Betula nana epidermal cell growth tested over its maximum climatological growth range

Numerous long-term, free-air plant growth facilities currently explore vegetation responses to the ongoing climate change in northern latitudes. Open top chamber (OTC) experiments as well as the experimental set-ups with active warming focus on many facets of plant growth and performance, but information on morphological alterations of plant cells is still scarce. Here we compare the effects of in-situ warming on leaf epidermal cell expansion in dwarf birch, Betula nana in Finland, Greenland, and Poland. The localities of the three in-situ warming experiments represent contrasting regions of B. nana distribution, with the sites in Finland and Greenland representing the current main distribution in low and high Arctic, respectively, and the continental site in Poland as a B. nana relict Holocene microrefugium. We quantified the epidermal cell lateral expansion by microscopic analysis of B. nana leaf cuticles. The leaves were produced in paired experimental treatment plots with either artificial warming or ambient temperature. At all localities, the leaves were collected in two years at the end of the growing season to facilitate between-site and within-site comparison. The measured parameters included the epidermal cell area and circumference, and using these, the degree of cell wall undulation was calculated as an Undulation Index (UI). We found enhanced leaf epidermal cell expansion under experimental warming, except for the extremely low temperature Greenland site where no significant difference occurred between the treatments. These results demonstrate a strong response of leaf growth at individual cell level to growing season temperature, but also suggest that in harsh conditions other environmental factors may limit this response. Our results provide evidence of the relevance of climate warming for plant leaf maturation and underpin the importance of studies covering large geographical scales.

Siliplant1 protein precipitates silica in sorghum silica cells

Silicon is absorbed by plant roots as silicic acid. The acid moves with the transpiration stream to the shoot, and mineralizes as silica. In grasses, leaf epidermal cells called silica cells deposit silica in most of their volume using an unknown biological factor. Using bioinformatics tools, we identified a previously uncharacterized protein in Sorghum bicolor, which we named Siliplant1 (Slp1). Slp1 is a basic protein with seven repeat units rich in proline, lysine, and glutamic acid. We found Slp1 RNA in sorghum immature leaf and immature inflorescence. In leaves, transcription was highest just before the active silicification zone (ASZ). There, Slp1 was localized specifically to developing silica cells, packed inside vesicles and scattered throughout the cytoplasm or near the cell boundary. These vesicles fused with the membrane, releasing their content in the apoplastic space. A short peptide that is repeated five times in Slp1 precipitated silica in vitro at a biologically relevant silicic acid concentration. Transient overexpression of Slp1 in sorghum resulted in ectopic silica deposition in all leaf epidermal cell types. Our results show that Slp1 precipitates silica in sorghum silica cells.

Plant SYP12 syntaxins mediate evolutionarily conserved general immunity to filamentous pathogens

Many filamentous fungal and oomycete plant pathogens invade by direct penetration through the leaf epidermal cell wall and cause devastating plant diseases. In response to attack, plants form evolutionarily conserved cell autonomous defense structures, named papillae and encasements, that are thought to block pathogen ingress. Previously, the syntaxin PEN1 in Arabidopsis, like its orthologue ROR2 in barley, was found to mediate pre-invasive immunity towards powdery mildew fungi, where it assures the timely formation of papilla defense structures. However, this powdery mildew-specific function of PEN1 in papilla timing, thought to take place at the trans-Golgi network, does not explain how plants generally ward off other filamentous pathogens. In the present study, we found that PEN1 has a second function, shared with its closest homologue SYP122, in the formation of papillae, as well as encasements. This second function provides pre-invasive immunity towards highly diverse non-adapted filamentous pathogens, underlining the versatility and efficacy of these defense structures. PEN1 and SYP122 belong to the broadly conserved land plant syntaxin clade SYP12, suggested to function in specialized forms of polarized secretion. In support of this, complementation studies using SYP12s from the basal plant, Marchantia polymorpha, showed that the SYP12 clade immunity function has survived 450 My of independent evolution. As saprophytic filamentous land fungi predate plant terrestrialization, we suggest ancestral land plants evolved the SYP12 clade to provide a durable immunity to facilitate their life on land.

Siliplant1 (Slp1) protein precipitates silica in sorghum silica cells

SummarySilicon is absorbed by plant roots as silicic acid. The acid moves with the transpiration stream to the shoot, and mineralizes as silica. In grasses, leaf epidermal cells called silica cells deposit silica in most of their volume by unknown mechanism.Using bioinformatics tools, we identified a previously uncharacterized protein in sorghum (Sorghum bicolor), which we named Siliplant1 (Slp1). Silica precipitation activity in vitro, expression profile, and activity in precipitating biosilica in vivo were characterized.Slp1 is a basic protein with seven repeat units rich in proline, lysine, and glutamic acid. A short peptide, repeating five times in the protein precipitated silica in vitro at a biologically relevant silicic acid concentration. Raman and NMR spectroscopies showed that the peptide attached the silica through lysine amine groups, forming a mineral-peptide open structure. We found Slp1 expression in immature leaf and inflorescence tissues. In the immature leaf active silicification zone, Slp1 was localized to the cytoplasm or near cell boundaries of silica cells. It was packed in vesicles and secreted to the paramural space. Transient overexpression of Slp1 in sorghum resulted in ectopic silica deposition in all leaf epidermal cell types.Our results show that Slp1 precipitates silica in sorghum silica cells.

Of puzzles and pavements: a quantitative exploration of leaf epidermal cell shape

SummaryThe epidermal cells of leaves lend themselves readily to observation and display many shapes and types: tabular pavement cells, complex trichomes, and stomatal complexes1. Pavement cells fromZea mays(maize) andArabidopsis thaliana(arabidopsis) both have highly undulate anticlinal walls and are held as representative of monocots and eudicots, respectively. In these two model species, we have a nuanced understanding of the molecular mechanisms that generate undulating pavement cell shape2–9. This model-system dominance has led to two common assumptions: first, that particular plant lineages are characterized by particular pavement cell shapes; and second, that undulatory pavement cell shapes are common enough to be model shapes. To test these assumptions, we quantified pavement cell shape in the leaves of 278 vascular plant taxa and assessed cell shape metrics across large taxonomic groups. We settled on two metrics that described cell shape diversity well in this dataset: aspect ratio (degree of cell elongation) and solidity (a proxy for margin undulation). We found that pavement cells in the monocots tended to have weakly undulating margins, pavement cells in ferns had strongly undulating margins, and pavement cells in the eudicots showed no particular degree of undulation. Indeed, we found that cells with strongly undulating margins, like those of arabidopsis and maize, were in the minority in seed plants. At the organ level, we found a trend towards cells with more undulating margins on the abaxial leaf surface vs. the adaxial surface. We also detected a correlation between cell and leaf aspect ratio: highly elongated leaves tended to have highly elongated cells (low aspect ratio), but not in the eudicots. This indicates that while plant anatomy and plant morphology can be connected, superficially similar leaves can develop through very different underlying growth dynamics (cell expansion and division patterns). This work reveals the striking diversity of pavement cell shapes across vascular plants, and lays the quantitative groundwork for testing hypotheses about pavement cell form and function.

A study of epidermal leaf anatomy of 18 Euphorbia taxa from Kerman Province, Iran

Euphorbia is the largest genus of Euphorbiaceae widely distributed all over the world. The genus members grow naturally in different parts of Iran and nearly 96 species of Euphorbia have been listed in the country. Investigations show that the traits of foliar epidermis have taxonomic values. That is why the features of epidermal leaf anatomy of 18 Euphorbia taxa were studied in the present study. Plant samples were collected from Kerman Province, Iran, and identified using available references. Semi-permanent slides were prepared of adaxial and abaxial leaf epidermis. Then the slides were studied using light microscopy and some epidermal leaf anatomy characteristics stomata types, trichomes, the shape and type of epidermal cell, and their walls were examined. Photomicrographs were taken from each sample. Results showed that stomata type were stable among the species. Not only leaf epidermal cell shapes differed between the taxa, but also in some species they varied between the abaxial and adaxial surfaces. These conditions hold true for cell wall patterns. Some of the studied taxa had simple and uniseriate trichomes on the epidermal surfaces, in most of them trichomes were present on both leaf surfaces, while in one species trichomes were seen on the abaxial surface. Our findings confirmed that some of the anatomical traits, such as the absence or presence of trichomes, epidermal cell shape, and anticlinal cell wall patterns had taxonomic value and are useful in the identification of taxa.