Differential regulation of fluorescent alkaloid metabolism between idioblast and lacticifer cells during leaf development in Catharanthus roseus seedlings

Ontogenesis of the anastomosed laticifers of Allamanda cathartica (Apocynaceae) and the chemical nature of the stem latex

Laticifers are secretive structures with important roles in controlling abiotic and biotic stress through the external release of viscous and bioactive latex emulsions composed of alkaloids, terpenes, flavonoids, proteins, and mucilage. Allamanda cathartica is an attractive ornamental neotropical shrub that produces abundant latex with medicinal potential. The laticifers of this species, their origins, structural types, and distribution in the primary and secondary structures of the stem were investigated, and the chemical nature of latex was determined. Anatomical, histochemical, and ultrastructural evaluations of the stem apex were performed through light and electronic microscopy. Laticifers are abundant in the primary structure, being distributed in the cortex, outer primary phloem, and pith. Their branching, anastomosing structural type develops by the dissolution of the transverse and lateral walls of precursor meristematic cells, followed by protoplast fusion. The laticifers in the secondary structure are distributed amid the axial parenchyma cells of the phloem. The latex of A. cathartica is an emulsion composed mainly of mucilage and terpenes, and it is the first time that this laticifer system has been described.

Integration of cell differentiation and initiation of monoterpenoid indole alkaloid metabolism in seed germination of Catharanthus roseus

In Catharanthus roseus, monoterpenoid indole alkaloids (MIAs) are produced through the cooperation of four cell types, with final products accumulating in specialized cells known as idioblasts and laticifers. To explore the relationship between cellular differentiation and cell type-specific MIA metabolism, we analyzed the expression of MIA biosynthesis in germinating seeds. Embryos from immature and mature seeds were observed via stereomicroscopy, fluorescence microscopy, and electron microscopy. Time-series MIA and iridoid quantification, along with transcriptome analysis, were conducted to determine the initiation of MIA biosynthesis. In addition, the localization of MIAs was examined using alkaloid staining and imaging mass spectrometry (IMS). Laticifers were present in embryos before seed maturation. MIA biosynthesis commenced 12 h after germination. MIAs accumulated in laticifers of embryos following seed germination, and MIA metabolism is induced after germination in a tissue-specific manner. These findings suggest that cellular morphological differentiation precedes metabolic differentiation. Considering the well-known toxicity and defense role of MIAs in matured plants, MIAs may be an important defense strategy already in the delicate developmental phase of seed germination, and biosynthesis and accumulation of MIAs may require the tissue and cellular differentiation.

The leaf idioblastome of the medicinal plant Catharanthus roseus is associated with stress resistance and alkaloid metabolism

Catharanthus roseus leaves produce a range of monoterpenoid indole alkaloids (MIAs) that include low levels of the anticancer drugs vinblastine and vincristine. The MIA pathway displays a complex architecture spanning different subcellular and cell type localizations, and is under complex regulation. As a result, the development of strategies to increase the levels of the anticancer MIAs has remained elusive. The pathway involves mesophyll specialized idioblasts where the late unsolved biosynthetic steps are thought to occur. Here, protoplasts of C. roseus leaf idioblasts were isolated by fluorescence-activated cell sorting, and their differential alkaloid and transcriptomic profiles were characterized. This involved the assembly of an improved C. roseus transcriptome from short- and long-read data, IDIO+. It was observed that C. roseus mesophyll idioblasts possess a distinctive transcriptomic profile associated with protection against biotic and abiotic stresses, and indicative that this cell type is a carbon sink, in contrast to surrounding mesophyll cells. Moreover, it is shown that idioblasts are a hotspot of alkaloid accumulation, suggesting that their transcriptome may hold the key to the in-depth understanding of the MIA pathway and the success of strategies leading to higher levels of the anticancer drugs.

Morphology, anatomy, and histochemistry of three species of Jatropha: a contribution to plant recognition and selection

Jatropha, a traditional medicinal plant known for its anti-inflammatory, antimicrobial, anticancer, antiviral, antidiabetic, and anticoagulant properties, was the subject of our study. We examined the morphology and chemical composition of three Jatropha species using cross- and longitudinal sections of fresh samples, observed with light microscopy. Histochemical analysis was conducted using various reagents to reveal the metabolites present. Anatomically, the distinguishing feature among the three Jatropha species was the presence of secretory cavities. These structures were identified in the petiole and stem bark of J. multifida, while in J. gossypiifolia and J. curcas they were present in roots. The stem bark cells of J. gossypiifolia were roundish in shape, whereas the others were rectangular. Laticifers were detected in the leaves, petioles, and stem bark of all three Jatropha species, while idioblasts were present in almost all organs. Histochemical tests revealed that excretory idioblasts and laticifers in Jatropha species contained alkaloids, phenolics, lipophilic compounds, and terpenoids. The cuticle of non-glandular trichomes contained terpenoids, while phenolic compounds were found within the secretory cavities. These findings contribute to the identification of Jatropha species and provide valuable insights for the selection and collection of specific plant organs containing bioactive compounds.

Laticifer ontogenesis and the chemical constituents of Marsdenia zehntneri (Apocynaceae) latex in a semiarid environment

Anastomosed laticifers with intrusive growth produce latex containing methyl comate and betulin with economic and ecological value in arid environments. Climatic factors influence laticifer development in the apical meristem and vascular cambium. Latex is a complex emulsion with high medicinal as well as ecological value related to plant survival. Marsdenia zehntneri is a shrubby plant that grows on limestone outcrops in the semiarid regions of Brazil. We sought to characterize the ontogenesis of the laticifers of this species and to relate that process to climatic seasonality and phenology through anatomical, ultrastructural, and micro-morphometric evaluations of the apical meristem and vascular cambium. The histochemistry of the secretory structure was investigated and the chemical composition of the latex was analyzed. Phenological assessments were performed by monitoring phenological events for 1 year. The laticifers network of M. zehntneri permeates the entire primary and secondary body of the plant, providing a wide distribution system of defensive compounds. Its laticifers, of a distinct mixed type (anastomosed, with intrusive growth), are numerous and voluminous in the apical meristem but scarce and minute in the secondary phloem. Latex secretion involves the participation of oleoplasts, polysomes, and dictyosomes. Methyl 2,3-dihydroxy-ursan-23-oate, methyl 3-hydroxy-ursan-23-oate, and betulin are encountered in high proportions in the latex and have ecological and medicinal functions. The development of primary laticifers is related to the resumption of apical meristem activity with increasing day length at the end of the austral winter. The development of secondary laticifers is related to high summer temperatures and rainfall that favor vascular cambium activity. The wide distribution of laticifers, their seasonal pattern of secretion, and their latex composition contribute to the adaptation of M. zehntneri to its natural environment.

Imaging MS Analysis in Catharanthus roseus

To understand how the plant regulates metabolism, it is important to determine where metabolites localize in the tissues and cells. Single-cell level omics approaches in plants have shown remarkable development over the last several years, and this data has been instrumental in gene discovery efforts for enzymes and transporters involved in metabolism. For metabolomics, Imaging Mass Spectrometry (IMS) is a powerful tool to map the spatial distribution of molecules in the tissue. Here, we describe the methods which we used to reveal where secondary metabolites, primarily alkaloids, localize in Catharanthus roseus stem and leaf tissues.