Megasporogenesis, megagametogenesis, and embryogenesis in Dendrobium nobile (Orchidaceae)

Megasporogenesis, megagametogenesis and embryogenesis of Liparis elliptica (Orchidaceae), with special note to the development of unique unitegmal ovule

Megasporogenesis, megagametogenesis and embryogenesis of Liparis elliptica (family Orchidaceae, tribe Malaxideae, subtribe Malaxidinae) have been studied. It was shown that the L. elliptica embryo sac is monosporic and develops from the chalazal cell of the megaspore triad according to the modified Polygonum type. The embryo sacs are reduced to four-six nuclei. The suspensor is unicellular, spherical in shape, originating from the basal cell (cb). A unique feature of L. elliptica is the unitegmal ovule, which distinguishes this species from other members of the tribe Malaxideae. The seed coat is formed by an outer layer of the single internal integument. Reduction of the outer integument is a rare feature for epiphytic orchid species with photosynthetic leaves.

The orchid seed coat: a developmental and functional perspective

Orchid seeds are 'dust-like.' The seed coat is usually thin, with only one to a few cell layers. It originates from the integuments formed during ovule development. In orchids, the outer integument is primarily responsible for forming a mature seed coat. The inner integument usually fails to develop after fertilization, becomes compressed, and collapses over the expanding embryo. Hence, the seed coat is formed from the funiculus, chalaza, and outer integumentary cells. The outermost layer of the seed coat, the testa, is lignified, usually at the radial and inner tangential walls. The subepidermal thin-walled layer(s), the tegmen, subsequently cold, resulting in seeds having only a single layer of seed coat cells. In some species, cells of the inner integument remain alive with the ability to synthesize and accumulate lipidic and or phenolic compounds in their walls covering the embryo. This cover is called the 'carapace,' a protective shield contributing to the embryo's added protection. A developmental and functional perspective of the integuments and seed coat during seed development and germination is presented in this review.

Suspensor differentiation in the embryogenesis of Liparis from sections Cestichis and Blepharoglossum (Malaxidinae, Orchidaceae)

Embryological features were used for the first time as a taxonomic attribute to confirm the difference between closely related taxa in the subtribe Malaxidinae. It was shown that the branched shape of the suspensor in Liparis elegans and L. parviflora from the section Blepharoglossum distinguishes these species from the inflated suspensor without a neck, which is characteristic of the embryos of L. viridiflora and L. dendrochiloides from the section Cestichis. Differentiation of the development and shape of the suspensor is an additional embryological criterion in favor of separating the genus Blepharoglossum from the genus Liparis.

Megasporogenesis and Megagametogenesis in Coelogyne speciosa subsp. fimbriata (J.J.Sm.) Gravendeel (Orchidaceae Juss.)

Understanding the critical stages in ovule development is essential for optimizing in vitro seed propagation, cryopreservation, and indirect somatic plant embryogenesis. We studied the main stages of the megasporogenesis and megagametogenesis of Coelogyne speciosa subsp. fimbriata (J.J.Sm.) Gravendeel by confocal laser scanning microscopy. The ovule is anatropic, tenuinucellate, bitegmal, and funicular. The embryo sac is monosporic, Polygonum-type, bipolar, and usually 8-nuclear, but in cases of a reduction in the last mitotic division, it is 6-nuclear. Endosperm formation was not detected. The formation of a functional megaspore occurred 65–70 days after pollination (DAP), while the formation of a mature embryo sac and fertilization occurred after 85–100 DAP.

Megasporogenesis, megagametogenesis, and embryogenesis in Maxillaria crassifolia (Lindl.) Rchb.f. (Cymbidieae, Orchidaceae)

Maxillaria crassifolia (Lindl.) Rchb.f. belongs to the polyphyletic genus Maxillaria Ruiz & Pav., which currently is the subject of several taxonomic research. There are conflicting descriptions of megasporogenesis, megagametogenesis, and embryogenesis in orchids from the tribe Cymbidieae, in general, and in the genus Maxillaria, in particular. In the present report, all stages of embryonic development of M. crassifolia were examined using confocal fluorescence microscopy. Some features of the development of the ovule and embryo, which distinguish M. crassifolia from other species of the tribe Cymbidieae were identified. The T-shaped arrangement of megaspores is formed by dividing the micropylar megaspore of the dyad. The megagametophyte develops according to the modified Polygonum-type with an unstable number of nuclei in the embryo sacs. The nucleus of the central cell varies in composition and may include unfused micropylar and chalazal nuclei and daughter nuclei formed during their division. The sequence of embryonal divisions is strictly structured. A special variant of embryogenesis, the Cymbidium-type Maxillaria-variant, has been described. Its characteristic features are the strictly apical nature of embryonic divisions, the absence of basal cell (cb) division, the formation of one to three pairs of tubular suspensor cells, and the localization of all suspensor cells within the inner integument.

[Rapid screening of 84 pesticide residues in dendrobium by Sin-QuEChERS Nano purification column with gas chromatography-tandem mass spectrometry]

A rapid screening method for 84 pesticide residues in dendrobium perfringens parent material with different polarities was developed using a Sin-QuEChERS Nano clean-up column combined with gas chromatography-tandem mass spectrometry (GC-MS/MS). The differences in extraction efficiency of the targets were compared with different extraction solvents (acetonitrile containing 1% acetic acid, acetone) and methods (immersion with or without water). The purification effect and extraction recoveries of Sin-QuEChERS Nano method and classical dispersive solid-phase extraction (dSPE), solid-phase extraction (SPE) and QuEChERS were systematically compared using Dendrobium nobile samples. The differences in matrix effects between the Sin-QuEChERS Nano method, which was more effective in purification, and the dSPE method were also analyzed. The purification effects of three commercially available Sin-QuEChERS Nano purification columns (simple matrix purification column, complex matrix purification column and herbal purification column) were compared. The applicability of the purification methods were also verified by using different parts of Dendrobium nobile samples (stems, leaves and flowers). From the results, it could be concluded that weighing 2.00 g and the samples in 5 mL of water for 20 min, followed by extraction with acetonitrile containing 1% acetic acid was more effective. The average extraction recovery of the target components by Sin-QuEChERS Nano purification method was 90.5%, which further identified Sin-QuEChERS Nano-Chinese medicine purification column as the preferred purification column for dendrobium purification. The target components were separated by a DB-1701MS quartz capillary column (30 m×0.25 mm×0.25 μm) with programmed temperature rise, detected by multiple reaction monitoring (MRM) mode, and quantified by matrix-matched solution external standard method. The GC-MS/MS assay was used for the methodological validation of the 84 representative pesticides within Dendrobium officinale and Dendrobium nobile was carried out by GC-MS/MS detection method. The results indicated that the targets showed excellent linear correlation in different scopes with correlation coefficients (r2) >0. 990. The limits of detection (LODs, S/N=3) of the method were 1.5 to 5.8 μg/kg, and the limits of quantification (LOQs, S/N=10) ranged from 5.0 to 15.0 μg/kg. The spiked recoveries of the target pesticides under different spiked levels were 68.7%-116.2%, and the relative standard deviations (RSDs, n=6) were less than 15%. Compared to other typical pretreatment methods, the Sin-QuEChERS Nano method provided better performance in terms of purification. The method not only effectively removed pigments, organic acids, and alkaline interferents, but also saved preparation time. Losses due to solvent transfer were also avoided and no further vortexing or centrifugation was required, making it a simplified and effective extraction and purification procedure. The method was sensitive, rapid, simple and reliable. It effectively improved the detection efficiency during the rapid screening of pesticides in dendrobium and presented a strong practical application value. In addition, the developed method could further expand the types of target pesticides and could be used to detect more pesticide residues in foods and Chinese herbal medicine. The established Sin-QuEChERS Nano method was used for the analysis of authentic samples. The applicability of the method was evaluated by analyzing a total of 80 samples collected from Anlong, Libo, Dushan, and Yanhe County in Guizhou Province. The types of samples included dendrobium maple, Dendrobium nobile (flowers, stems, leaves) and Dendrobium officinale (flowers, stems, leaves, powder, tablets). At least one pesticide residue was detected in 12 samples, with a detection rate of 15%. The five pesticides with higher detection rates and residues were chlorpyrifos (0.08-0.5 mg/kg), chlorothalonil (0.06-3.2 mg/kg), propanil zinc (0.03-0.15 mg/kg), methyl parathion (0.04-0.23 mg/kg) and cyhalothrin (0.10-2.68 mg/kg). Except for the pesticides in maximum residue limits (MRLs), the pesticide residues detected from dendrobium samples were below the limits set by Chinese national standard (GB 2763-2021) and local standard DBS 52/048-2020.

Insights into the molecular evolution of fertilization mechanism in land plants

Comparative genetics and genomics among green plants, including algae, provide deep insights into the evolution of land plant sexual reproduction. Land plants have evolved successive changes during their conquest of the land and innovations in sexual reproduction have played a major role in their terrestrialization. Recent years have seen many revealing dissections of the molecular mechanisms of sexual reproduction and much new genomics data from the land plant lineage, including early diverging land plants, as well as algae. This new knowledge is being integrated to further understand how sexual reproduction in land plants evolved, identifying highly conserved factors and pathways, but also molecular changes that underpinned the emergence of new modes of sexual reproduction. Here, we review recent advances in the knowledge of land plant sexual reproduction from an evolutionary perspective and also revisit the evolution of angiosperm double fertilization.