Developmental Programmed Cell Death Involved in Ontogenesis of Dictamnus dasycarpus Capitate Glandular Hairs

Abstract

Plant glandular trichomes have received much attention due to their commercial and biological value. Recent studies have focused on the development of various glands in plants, suggesting that programmed cell death (PCD) may play an important role during the development of plant secretory structures. However, the development processes and cytological characteristics in different types of plant secretory structures differed significantly. This study aims to provide new data on the developmental PCD of the capitate glandular hairs in Dictamnus dasycarpus. Light, scanning, immunofluorescence labeling, and transmission electron microscopy were used to determine the different developmental processes of the capitate glandular hairs from a cytological perspective. Morphologically, the capitate glandular hair originates from one initial epidermal cell and differentiates into a multicellular trichome characterized by two basal cells, two lines of stalk cells, and a multicellular head. It is also histochemically detected by essential oils. TUNEL-positive reactions identified nuclei with diffused fluorescence or an irregular figure by DAPI, and Evans blue staining showed that the head and stalk cells lost their viability. Ultrastructural evidence revealed the developmental process by two possible modes of PCD. Non-autolytic PCD was characterized by buckling cell walls and degenerated nuclei, mitochondria, plastids, multivesicular body (MVB), and end-expanded endoplasmic reticulum in the condensed cytoplasm, which were mainly observed in the head cells. The MVB was detected in the degraded vacuole, a degraded nucleus with condensed chromatin and diffused membrane, and eventual loss of the vacuole membrane integrity exhibited typical evidence of vacuole-mediated autolytic PCD in the stalk cells. Furthermore, protoplasm degeneration coupled with dark oil droplets and numerous micro-dark osmiophilic substances was observed during late stages. The secretion mode of essential oils is also described in this paper.

Integrated Transcriptomic and Metabolomic Analysis Reveal the Dynamic Process of Bama Hemp Seed Development and the Accumulation Mechanism of α-Linolenic Acid and Linoleic Acid

“…Plant glandular hair is a secretory structure produced by plants that can secrete various secondary substances and other lipophilic and nonlipophilic compounds. 35 We collected seeds at five different developmental stages: 0 days (day0), 7 days (day7), 14 days (day14), 21 days (day21), and 40 days (day40). In the day0 stage, the seeds were transparent and tender green, with the pistil style (15.521 ± 0.037 mm) turning purple-red (Figure 1A,H).…”

Novel Mechanisms Underlying Rubber Accumulation and Programmed Cell Death in Laticiferous Canals of Decaisnea insignis Fruits: Cytological and Transcriptomic Analyses

“…The samples were first pre-fixed with 2.5% glutaraldehyde in 0.1 M phosphate buffer at a pH of 7.0 for 48 h at 4 • C, and then fixed with 1% osmic acid in the same phosphate buffer overnight. After rinsing with the phosphate buffer three times (30 min each time), the samples were dehydrated in an ethanolic series (30%, 50%, 70%, 85%, and 95% one time, and 100% twice, for 30 min each time), prepared with propylene oxide, and finally embedded in Epon 812 resin [21]. Semi-thin sections (1-2 µm) were obtained using a Reichert-Jung ultramicrotome, and then stained with toluidine blue O or methylene blue.…”

“…The cross sections of the Decaisnea insignis fruit samples at stage 2 and stage 4 were first sliced using the hand sectioning technique and then stained with 0.1% Evans blue dissolved in ddH 2 O for 30 min at room temperature [21]. Finally, the samples were washed with distilled water and photographed using a JSZ5BS light microscope (Jiangnan, China) equipped with a Nikon D850 (Nikon, Japan).…”

“…The samples were first pre-fixed with 2.5% glutaraldehyde in 0.1 M phosphate buffer at pH 7.0 for 48 h at 4 • C, and then fixed with 1% osmic acid using the same phosphate buffer overnight. After rinsing with the phosphate buffer three times (30 min each time), the samples were dehydrated using a gradient ethanolic series (30%, 50%, 70%, 85%, and 95% one time, and 100% twice, for 30 min each time), prepared using xylene, and finally embedded in wax [21]. For rubber particle and nucleus locating, 8-10 µm sections of different stages of Decaisnea insignis at different stages were obtained and stained with 2 mg of DAPI in 10 mL of dilution buffer (Bioworld Technology, Nanjing, China), and observed using an epifluorescence microscope.…”

“…Other studies have confirmed that the accumulation of secretions is accompanied by the degeneration of cellular components in plant glands [13][14][15][16][17]. The processes of ontogenesis in pigment glands of Gossypium hirsutum leaves [18]; secretory cavities of Citrus sinensis [19]; trichome cavities, secretory cavities, and capitate glandular hairs of Dictamnus dasycarpus [17,20,21]; and laticiferous canals of Decaisnea insignis [12] were studied, and the results showed that they were typical PCD events during which secretions accumulated. Zhao et al [22] studied the proteomics of laticifer tubules in E. kansui and found that the degradation of cytoplasm was positively correlated with the synthesis of secondary metabolites during the development of lactiferous tubules.…”