Dynamics of annatto pigment synthesis and accumulation in seeds of Bixa orellana L. revealed by integrated chemical, anatomical, and RNA-Seq analyses

Bixin is a commercially valuable apocarotenoid pigment found in the seed aril of Bixa orellana. The dynamics and regulation of its biosynthesis and accumulation during seed development remain largely unknown. Here, we combined chemical, anatomical, and transcriptomic data to provide stage-specific resolution of the cellular and molecular events occurring during B. orellana seed development. Seeds at five developmental stages (S1-S5) were used for analysis of bixin content and seed anatomy, and three of them (S1, S3, and S4) were selected for Illumina HiSeq sequencing. Bixin accumulated in large quantities in seeds compared with other tissues analyzed, particularly during the S2 stage, peaking at the S4 stage, and then decreasing slightly in the S5 stage. Anatomical analysis revealed that bixin accumulated in the large central vacuole of specialized cells, which were scattered throughout the developing mesotesta at the S2 stage, but enlarged progressively at later stages, until they occupied most of the parenchyma in the aril. A total of 13 million reads were generated and assembled into 73,381 protein-encoding contigs, from which 312 were identified as containing 1-deoxy-D-xylulose-5-phosphate/2-C-methyl-D-erythritol-4-phosphate (DOXP/MEP), carotenoid, and bixin pathways genes. Differential transcriptome expression analysis of these genes revealed that 50 of them were sequentially and differentially expressed through the seed developmental stages analyzed, including seven carotenoid cleavage dioxygenases, eight aldehyde dehydrogenases, and 22 methyltransferases. Taken together, these results show that bixin synthesis and accumulation in seeds of B. orellana are a developmentally regulated process involving the coordinated expression of DOXP/MEP, carotenoid, and bixin biosynthesis genes.

Utilisation of Toluidine blue O pH 4.0 and histochemical inferences in plant sections obtained by free-hand

For the observation of plant material under a light microscope, free-hand sectioning is usually the fastest and most practical procedure. The staining of the obtained cuts is a crucial step and the action mechanism of the dye is variable. Toluidine blue O is a cationic dye whose metachromatic potential for free-hand sections has long been known. Thus, this work aimed at analysing the performance of Toluidine blue O for this type of sectioning with a systematic and comparative approach. The action of Toluidine blue O pH 4.0 was tested for both fresh and previously clarified free-hand sections from leaves of different species of plant. These sections were compared with sections embedded in glycol-methacrylate resin stained with the same dye or submitted to different histochemical tests. The fresh sections obtained by free-hand and stained with Toluidine blue O permitted the accomplishment of histochemical inferences, with the advantage of maintaining the natural colours from the tissues. The previously clarified sections presented the advantage of having a clearer image, allowing a better cellular delimitation. We concluded that Toluidine blue O is very informative for sections of plant material obtained by free-hand, being, therefore, a procedure that is fast, inexpensive and with excellent results.

Anatomy of the floral, bract, and foliar nectaries of Triumfetta semitriloba (Tiliaceae)

Triumfetta semitriloba Jacq. (Tiliaceae) is a tropical weedy species with floral nectaries and glands located at the margins of the leaves. The objectives of this work were to describe the anatomy of these secretory structures and to analyze their exudates. Sucrose, glucose, and fructose were identified in the product released by these secretory structures, characterizing them as nectaries. The nectaries of T. semitriloba are of a specialized type; a secretory epidermis comprised of pluricellular and multiserial nectariferous trichomes covers a nectariferous parenchyma, vascularized by phloem and xylem. A mass of phenolic compounds occurs in the head cells of the nectariferous trichomes of the foliar and bract nectaries; however, it is absent in trichomes of the floral nectary. The leaf and bract nectaries differed from those from flowers in their length and diameter. Structural features of the nectaries of T. semitriloba are typical of other taxa of the Malvales.Key words: foliar anatomy, histochemistry, Malvales, nectaries, Tiliaceae, Triumfetta semitriloba.