Hydathodes are specialized leaf tissues that mediate guttation, the release of liquid water droplets from vascular plants. They consist of xylem endings, water pores, and the epithem, a tissue of small cells located between the xylem endings and water pores. Although previous studies have provided anatomical descriptions and emerging molecular insights into Arabidopsis thaliana hydathodes, how epithem cells differ from surrounding cells and how the epithem interfaces with surrounding tissues remain incompletely understood. In this study, we examined the anatomy of A. thaliana hydathodes using complementary imaging approaches. Microfocus–X-ray computed tomography visualized the three-dimensional morphology of hydathodes protruding from the abaxial leaf surface. Light microscopy showed that the epithem consisted of densely packed cells with limited intercellular spaces. Quantitative analyses showed that the cross-sectional area of epithem cells was approximately 25–40
Chloroplasts maintain specific intracellular distribution patterns in response to environmental conditions to maximize photosynthetic performance and prevent photodamage. We previously proposed that a chloroplast anchoring mechanism functions to fix chloroplasts at appropriate positions and reported that this machinery is actin-dependent and regulated by Ca2+ (Takamatsu and Takagi 2011). In the present study, we examined the possible involvement of villin, a Ca2+-sensitive actin-binding protein (ABP), in chloroplast anchoring in spinach mesophyll cells. Two antibodies against lily villin proteins, anti-P135ABP and anti-P115ABP, recognized polypeptides of 135 and 120 kDa, respectively, in spinach leaves. These proteins were purified as Ca2+-sensitive ABPs by DNase I affinity chromatography. Immunolocalization analysis revealed distinct labeling patterns for the two proteins. Whereas immunostaining with the anti-P115ABP antibody produced randomly distributed punctate signals in the cytoplasm, the 135-kDa villin-like protein was preferentially localized around chloroplasts and was also detected on isolated chloroplasts. Biochemical analyses further revealed that both villin-like proteins bound phosphatidic acid (PA) and phosphoinositides. Functional analysis further showed that addition of the anti-P135ABP antibody induced detachment of a substantial number of chloroplasts and reduced actin filaments on plasma membrane (PM) ghosts. These results indicate that at least two distinct Ca2+-sensitive villin-like proteins exist in spinach leaves and suggest that the 135-kDa isoform contributes to chloroplast anchoring by maintaining actin organization around chloroplasts.
Acorus calamus L. is a monocotyledonous medicinal plant possessing bioactive compounds, including β-asarone, which exhibits anti-microbial, neuroprotective, and antioxidant effects. However, the biosynthetic pathway of β-asarone in A. calamus remains poorly understood. This study investigated seasonal changes in the accumulation of β-asarone and related phenylpropenes and their associated transcriptome. Leaf, root, and rhizome samples were analyzed by gas chromatography, and leaf samples representing periods with the lowest and highest levels of β-asarone and its related phenylpropene (Z)-methylisoeugenol were selected for comparative transcriptome analysis. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed distinct gene expression patterns during β-asarone accumulation, including the downregulation of most phenylpropanoid biosynthetic genes and upregulation of the genes encoding 4-coumarate-CoA ligase and caffeoyl-CoA O-methyltransferase. Conversely, these genes exhibited different expression patterns during the periods of high (Z)-methylisoeugenol accumulation. This study suggests that β-asarone biosynthesis involves different pathways from predicted phenylpropene routes and provides insights into the seasonal regulation of specialized phenylpropanoid metabolism in A. calamus.
The geographical variation in the strength and direction of selection in highly specialized plant-pollinator mutualisms can lead to different interaction outcomes among populations. In this study, we investigated the mutualistic interaction between an alpine ginger Roscoea purpurea and a long-tongued tabanid fly Philoliche longirostris across eight populations in central Nepal. We measured the flower and fly traits, assessed the visitation behaviour and frequencies of P. longirostris, and quantified the reproductive success of R. purpurea. Our results revealed that in three of the eight populations both nectar distance and corolla-tube length were longer than the fly proboscis length, indicating a clear mechanical mismatch between the interacting traits of plants and the fly. The visitation frequencies of the fly to R. purpurea flowers were substantially lower in the three populations compared to the other five populations, yet the fly did not visit any co-flowering species. In the three populations, the pollen limitation indices for both fruit set and seed set were over 0.95 indicating that plant reproduction was severely pollen limited. We suggest that if the mechanical mismatch is a persistent feature of the populations, it may eventually lead to a mutualism breakdown between R. purpurea and P. longirostris, which would have severe consequences for the existence of both organisms, particularly in the populations encountering mechanical mismatch between the interacting traits.
Escalating climate-induced drought events are increasingly pushing terrestrial plants toward their physiological limits, challenging their growth and ecological acclimation. Metabolic reprogramming represents a critical adaptive strategy under water deficit, in which aspartate aminotransferase (AspAT) serves as a key node by modulating carbon-nitrogen flux, energy metabolism, and amino acid biosynthesis. Although AspAT genes have been implicated in abiotic stress responses in herbaceous species, their roles in woody plants remain poorly characterized. Here, we identified multiple drought-responsive AspAT family members in poplar and further characterized the function of AspAT10. Transgenic poplars overexpressing AspAT10 (OE) exhibited higher drought tolerance than wild-type (WT) controls, maintaining higher growth rates, greater biomass accumulation, and improved leaf water status under drought conditions. Consistent with these phenotypes, OE lines displayed elevated relative water content, photosynthetic performance, and lignin accumulation relative to WT plants. Transcriptome analysis revealed that AspAT10 overexpression was associated with the upregulation of genes involved in amino acid metabolism, as well as pathways related to cuticular wax formation. These findings suggest that AspAT10 may contribute to drought responses through coordinated regulation of metabolic and transcriptional processes, thereby supporting plant growth under drought stress.
