Dendrobium Cv Research Articles

1-MCP microbubbles reduce chlorophyll degradation and maintain the quality of Dendrobium cv. Burana Jade orchid flowers

The effect of 1-methylcycloprepene microbubbles (1-MCP-MBs) on reducing chlorophyll degradation, prolonging vase life and maintaining the quality of Dendrobium cv. ‘Burana Jade’ inflorescences was investigated. The inflorescences were immersed in 50 ppm 1-MCP-MBs or tap water (control) for 5 min and then held at 23 ± 1 °C for 12 days. The 1-MCP-MB-treated inflorescences exhibited increased water uptake and significantly higher fresh weight than the controls. The results also showed that 1-MCP-MBs remarkably delayed bud opening and flower abscission, accompanied by suppression of ethylene production and a lower respiration rate than that of controls. Additionally, the treatment maintained the green color (hue angle value was comparable to initial storage day) of the inflorescences by delaying chlorophyll degradation related to inhibition of chlorophyllase and Mg-dechelatase activities. 1-MCP-MBs prolonged the vase life of Dendrobium cv. ‘Burana Jade’ up to 12 days, which was 2-fold longer than that of the control (approximately 5 days only). The results suggest that 1-MCP-MBs have the potential to be another alternative to conventional methods (fumigation) in prolonging vase life and maintaining the quality of Dendrobium orchids with the advantage of a shorter treatment time.

Differential expression of ethylene biosynthetic and receptor genes in pollination-induced senescence of Dendrobium flowers

Following successful pollination, Dendrobium orchid flowers rapidly undergo senescence. In Dendrobium cv. Khao Chaimongkol, compatible pollination resulted in faster ethylene production and more rapid development of senescence symptoms, such as drooping, epinasty, venation and yellowing, compared with non-pollinated controls or pollination with incompatible pollinia. The DenACS1 and DenACO1 genes in the perianth of florets that had been pollinated with compatible pollinia were expressed more highly than those in non-pollinated open florets. Incompatible pollinia reduced the expression of DenACS1 and DenACO1 genes in the perianth. Transcript levels of the ethylene receptor gene DenERS1 and signaling genes DenEIL1 and DenERF1 showed differential spatial regulation with greater expression in the perianth than in the column plus ovary following compatible pollination. Compatible pollinia increased ethylene production concomitant with premature senescence and the increased expression of the DenACS1 and DenACO1 genes, and suppressed the ethylene receptor gene DenERS1, whereas incompatible pollinia did not stimulate ethylene production nor induce premature senescence but induced higher expression of DenERS1 both in the perianth and in the column plus ovary. These results suggest that the increased ethylene production in open florets pollinated with compatible pollen was partially due to an increase in the expression of DenACS1 and DenACO1 genes. The compatible pollinia induced a negative regulation of DenERS1 which may play an important role in ethylene perception and in modulating ethylene signaling transduction during pollinia-induced flower senescence.

Study on the Effect of Auxin in In vitro Root Regeneration and Survival of Dendrobium cv. Sonia Earsakul

The investigation was carried out during 2017-2019 at the Tissue Culture Laboratory, Department of Horticulture, NU: SASRD, Nagaland to study the influence of different auxins in varied doses on in vitro root regeneration of Dendrobium cv. Sonia Earsakul. The different treatments used are IBA, NAA and IAA @ 0, 0.5, 1, 1.5 and 2 mgL-1 respectively. The study revealed that among the different treatments IBA @1 mg/l resulted in the longest root length (5.97 cm), longest shoot length (7.8 cm), highest survivability during primary hardening (34.30%) and secondary hardening (94.29%).

Evaluation of Low Cost Protected Structure for Commercial Cultivation of Dendrobium Cv. Sonia under Assam Condition

Background: Dendrobiums are most popular high value cut flowers which require special attention during cultivation. In Assam, Dendrobium orchids are normally grown under iron frame shade net houses which are quite vulnerable to cold injury during extreme winter period and heavy rain during monsoon period. Further, the existing structures are very costly which is not affordable by small and marginal farmers of Assam. Keeping in view the current study was aimed to evaluate a suitable low cost protected structure for commercial cultivation of Dendrobium cv. Sonia under Assam condition. Methods: An experiment was conducted in the Horticulture Experimental Farm, Assam Agricultural University, Jorhat, during 2018-2019 which was laid out in factorial completely randomized design with 10 treatment combinations replicated five times. The first factors comprised 5 numbers of low cost protected structures viz., G1, G2, G3, G4 and G5. The second factors comprised T1-1 tier and T2-2 tiers. Result: The results revealed that among the protected structures, healthy growth and better quality flowers were obtained under G1 (Bamboo frame structure covered with fixed 200 micron UV film with top ventilated and 50% agro shade net as ceiling) protected structure followed by G4. Between the tiers, T2 was found to be superior in respect of the growth characters as well as most of the flower characters. So, this treatment combination is merits consideration for commercial growers of Assam to bring about timely and quality flower production of Dendrobium cv. Sonia.

Influence of inorganic nutrients on growth, flowering and quality of Dendrobium cv. Singapore white

Dendrobium orchid cv. Singapore White is cultivated commercially for cut flower purpose. The performance of this orchid in response to the different nutrient concentrations was evaluated under the agro-climatic conditions of Kodagu during 2017-2020. Twelve nutrient doses were applied as foliar sprays at weekly intervals to study their effect on vegetative growth, flower production and quality parameters of the cut flowers. Plant height, number of leaves plant-1, leaf area, number of pseudobulbs plant-1, number of spikes plant-1 year-1, number of flowers spike-1 and spike length varied significantly with the nutrient doses. Foliar spray of 30:20:20 NPK 0.1% at weekly intervals recorded the maximum plant height of 53.21cm, number of spikes plant-1year-1 (10.01) with spike length of 44.43 cm and 16.20 flower spike-1.

Influence of inorganic nutrients on growth, flowering and quality of Dendrobium cv. Singapore white


 
 
 Dendrobium orchid cv. Singapore White is cultivated commercially for cut flower purpose. The performance of this orchid in response to the different nutrient concentrations was evaluated under the agro-climatic conditions of Kodagu during 2017-2020. Twelve nutrient doses were applied as foliar sprays at weekly intervals to study their effect on vegetative growth, flower production and quality parameters of the cut flowers. Plant height, number of leaves plant-1, leaf area, number of pseudobulbs plant-1, number of spikes plant-1 year-1, number of flowers spike-1 and spike length varied significantly with the nutrient doses. Foliar spray of 30:20:20 NPK 0.1% at weekly intervals recorded the maximum plant height of 53.21cm, number of spikes plant-1year-1 (10.01) with spike length of 44.43 cm and 16.20 flower spike-1.
 
 

Dendrobium orchid polysaccharide extract: Preparation, characterization and in vivo skin hydrating efficacy

ObjectiveDendrobium spp., the major globally commercializing tropical orchid, has been continuously used in Chinese medicine. However, preparation and standardization of this therapeutic orchid including its clinical evidence for topical application are sparely to be exploited. MethodsMaceration of the white orchid (Dendrobium cv. Khao Sanan) in water was varied on the extraction time. The extraction yields and total polysaccharide content of the extracts were compared. The best extract condition was selected, standardized, and evaluated on safety and skin hydrating efficacy in human volunteers. ResultsThe extraction for 3 h gave the extract with polysaccharide content that significantly (P < 0.001) greater than the other extraction times with the following specification: yield [(35.60 ± 2.51)%], moisture content [(7.65 ± 0.21)%], total polysaccharide, sugar, reducing sugar and ash content [(72.95 ± 2.37)%, (34.38 ± 0.00)%, (16.28 ± 0.00)%, and (0.12 ± 0.00)%], pH (4.42 ± 0.01), viscosity [(15.07 ± 0.12) cps] swelling and water absorption capacities [(10.00 ± 0.00)%, (1.19 ± 0.24) g/g]. This antioxidative polysaccharide caused no skin irritation with a better skin hydrating efficacy than the untreated skin and the benchmark as examined in 22 Thai volunteers. ConclusionWhite Dendrobium is ready to be supplied as a specialty ingredient with a safe and efficient profile for skin dryness therapy. This innovative application of the identified traditional Chinese medicinal herb flows in the main stream of the consumers’ preferences and demand upon natural derived products.

Morphophysiological characters of Dendrobium var. Yellow Splash as influenced by bioinoculants and different levels of benzyladenine

Dendrobium is the most commonly grown tropical orchid species in India and Kerala. They are highly specific about their nutrient requirement. The use of bio-inoculants in crop production of ornamentals has opened up a new possibility of using them for improving the growth and yield of orchids. Hence the objective of study was to evaluate the response of Dendrobium cv. Yellow Splash to different kinds of bio-inoculants viz., AMF, Azospirillum and a microbial consortia PGPR Mix – 1 developed from KAU, along with 50, 100 and 150 ppm of benzyladenine. The experiment consisted of ten different treatments involving bio-inoculants and benzyladenine. Plant height and number of leaves were maximum in the plants inoculated with AMF along with 100 ppm benzyladenine. Treatment comprising of Azospirillum and 100 ppm benzyladenine was superior in terms of other morphological parameters like leaf breadth, leaf area and plant spread. Maximum leaf length and highest number of shoots were observed in plants inoculated with Azospirillumand 150 ppm benzyladenine. Considering the floral parameters, both quantitative and qualitative attributes were found to be superior in the treatment consisting of AMF along with 150 ppm benzyladenine. Highest root length was observed under the treatment AMF along with 100 ppm benzyladenine while number of roots and root volume were maximum in the plants inoculated with Azospirillum and 150 ppm benzyladenine. Plants inoculated with AMF and 100 ppm benzyladenine had highest chlorophyll content while highest stomatal frequency was observed under the treatment Azospirillum and 100 ppm BA. From the study it could be concluded that inoculation of Dendrobium orchids with bio-inoculants like AMF and Azospirillum can significantly improve the morphological characters of the plants which in turn influence the production of quality spikes.

Morphophysiological characters of Dendrobium var. Yellow Splash as influenced by bioinoculants and different levels of benzyladenine

Dendrobium is the most commonly grown tropical orchid species in India and Kerala. They are highly specific about their nutrient requirement. The use of bio-inoculants in crop production of ornamentals has opened up a new possibility of using them for improving the growth and yield of orchids. Hence the objective of study was to evaluate the response of Dendrobium cv. Yellow Splash to different kinds of bio-inoculants viz., AMF, Azospirillum and a microbial consortia PGPR Mix – 1 developed from KAU, along with 50, 100 and 150 ppm of benzyladenine. The experiment consisted of ten different treatments involving bio-inoculants and benzyladenine. Plant height and number of leaves were maximum in the plants inoculated with AMF along with 100 ppm benzyladenine. Treatment comprising of Azospirillum and 100 ppm benzyladenine was superior in terms of other morphological parameters like leaf breadth, leaf area and plant spread. Maximum leaf length and highest number of shoots were observed in plants inoculated with Azospirillumand 150 ppm benzyladenine. Considering the floral parameters, both quantitative and qualitative attributes were found to be superior in the treatment consisting of AMF along with 150 ppm benzyladenine. Highest root length was observed under the treatment AMF along with 100 ppm benzyladenine while number of roots and root volume were maximum in the plants inoculated with Azospirillum and 150 ppm benzyladenine. Plants inoculated with AMF and 100 ppm benzyladenine had highest chlorophyll content while highest stomatal frequency was observed under the treatment Azospirillum and 100 ppm BA. From the study it could be concluded that inoculation of Dendrobium orchids with bio-inoculants like AMF and Azospirillum can significantly improve the morphological characters of the plants which in turn influence the production of quality spikes.

Effects of Culture Media on Phytophthora palmivora Growth, α-elicitin Production and Toxicity to Dendrobium

Four culture media were evaluated for their ability to induce Phytophthora palmivora growth and produce culture filtrate (CF), and to determine a CF concentration and culture period effective for in vitro screening of black rot resistance in Dendrobium cv. ‘Earsakul’. Mycelial fresh weights of P. palmivora cultured in potato dextrose broth (PDB; the most commonly used medium for fungi), pea sucrose broth (PSB; a medium frequently used for Phytophthora spp.), and Murashige and Skoog broth (MSB; the most popular plant tissue culture medium) were found to be significantly higher than that in the newly developed modified oat meal broth (MOMB). When the total proteins of CFs were analysed with SDS-PAGE, a protein band of 10.5 kDa MW was found in CFs from all media with the highest level in PSB. LC-MS/MS analysis identified this protein as α-elicitin that had an identical amino acid sequence to the α-elicitin hibernalin of P. hibernalis and syringicin from P. syringae. The optimum conditions for in vitro selection of Dendrobium for black rot resistance using α-elicitin-containing CFs were also determined by evaluating the CF toxicity on Dendrobium protocorm-like bodies (PLBs) when cultured in all media supplemented with 0, 30, 50 and 100% CFs for seven, 14 and 21 d. The levels of PLB necrosis varied according to medium types, CF concentrations and culture periods. The maximum percentage of PLB necrosis (100%) was obtained in PSB supplemented with 50 and 100% CFs, and the severity of PLB necrosis was highest when treated with 100% CF for 14 and 21 d.

Ethylene-induced water soaking in Dendrobium floral buds, accompanied by increased lipoxygenase and phospholipase D (PLD) activity and expression of a PLD gene

After a short exposure to exogenous ethylene, the tepals of floral buds on Dendrobium cv. Juree Red inflorescences exhibited water-soaking, preceded by an increased in electrolyte leakage. Phospholipase D (PLD; EC 3.1.4.4) and lipoxygenase (LOX; EC 1.13.11.12) activities in the tepals showed a large increase after ethylene exposure, prior to the increase in electrolyte leakage. Ethylene also increased expression of a DenPLD gene in tepals. However, this was too late to account for the early rise in PLD activity. 1-Methylcyclopropene (1-MCP, which is an antagonist of ethylene perception) reduced the increase in DenPLD expression. The expression of a DenLOX gene was down-regulated by ethylene and up-regulated by 1-MCP, thus did not account for the increase in LOX activity. It was previously found that exposure to 5°C resulted in water soaking and PLD activation, for which endogenous ethylene was required. The present data strongly suggest that these chilling effects are caused by endogenous ethylene. Chilling-induced ethylene apparently resulted in plasma membrane damage, possibly due to PLD and LOX activity.

Influence of plant growth promoters and growing systems on physiological parameters of Dendrobium cv. EARSAKUL

The study was carried out to investigate the influence of plant growth promoters and systems of growing on physiological parameters of Dendrobium cv. EARSAKUL. The main objective was to assess the response of combination of nutrients, plant growth regulators and plant growth promoting root endophyte (PGPRE) in two age groups of Dendrobium cv. EARSAKUL plants (six month old and three year old at planting time) under three growing systems viz., two level shade house (S 1 ), top ventilated polyhouse (S 2 ) and fan and pad system (S 3 ). Results revealed that leaf area (29.99 m), relative growth rate (0.013 g g day) and number of stomata (41.14) were highest in six month old plants, whereas, dry matter production (20.92 g plant) and crop growth rate (0.148 g m day) were highest in three year old plants in the treatment POP + OM + VW + PGPRE + bone meal + GR (T 4 ). Dry matter production (14.27 g plant), crop growth rate (0.131 g m day), rate of photosynthesis (6.36 μmol CO 2 m s) and transpiration rate (6.56 μmol m s) during day time were highest in the treatment POP + OM + VW + PGPRE + bone meal (T 3 ) in six month old plants. Among the systems of growing, maximum values for physiological parameters were recorded in top ventilated polyhouse. The interaction of plant growth promoters and systems of growing had significant effect on physiological parameters.

Effect of various plant growth promoters and growing conditions on flowering of Dendrobium cv. EARSAKUL

The investigation on 'Flowering response of Dendrobium cv. EARSAKUL to plant growth promoters in different growing conditions' was conducted at College of Horticulture, Vellanikkara, Kerala. Results revealed that, among plant growth promoters, the treatment POP + OM + VW + PGPRE + Bone meal + GR (T 4 ) resulted in longer spike (31.34 cm), more flower count (6.54) and longer vase life (30.00 days), whereas, the treatment NPK + GR + OM + VW + PGPRE + Bone meal (T 6 ) was the best with respect to time taken for first flower opening (14.52 days) and number of spikes per plant (2.62) in six month old plants. In three year old plants, the treatment POP + OM + VW + PGPRE + Bone meal + GR (T 4 ) was the best with respect to time taken for flowering (283.91 days), days to last flower opening (10.98 days), number of spikes (2.63) and vase life (28.26 days), whereas, length of the spike (30.46 cm) and number of flowers (5.08) were the highest in the treatment NPK + GR + OM + VW + PGPRE + Bone meal (T 6 ). Among three systems of growing, top ventilated polyhouse (S 2 ) had maximum influence on flower characters. In interaction, the combination of POP + OM + VW + PGPRE + Bone meal + GR (T 4 ) and top ventilated polyhouse (S 2 ) was significantly superior in flower characters irrespective of the age of the plants.

Sucrose feeding of Cut Dendrobium inflorescences promotes bud opening, inhibits abscission of open flowers, and delays tepal senescence

Inflorescences of Dendrobium cv. Khao Sanan were held in distilled water (controls) or in solutions containing two antimicrobial compounds (silver nitrate and 8-hydroxyquinoline sulfate) with or without 4gL−1 sucrose or 4gL−1 glucose. Sugar+antimicrobial compounds promoted bud opening and largely prevented abscission of open flowers. It also resulted in a delay of tepal senescence. No clear effect was found of sucrose feeding on the concentrations of sucrose, glucose and fructose in the tepals of open flowers, but an increase in sucrose, glucose, and fructose concentrations was found in the column+labellum. It is concluded that the effect of sugar feeding on abscission and tepal senescence might relate to a reduction of ethylene sensitivity. It was previously concluded that tepal senescence in Dendrobium flowers was not regulated in the tepals but in the column. It is not clear how the increased in sugar levels in the column+labellum relates to the delay of tepal senescence after sugar feeding.

Presence and expression of the Ds-Red gene in the transgenic protocorm-like body of the Dendrobium cv. Burana White

Four transgenic lines of the Dendrobium cv. Burana White containing the target DsRed gene were obtained following the microprojectile bombardment. Protocorm-like bodies (PLBs, etiolated), cut into 3-5 mm in size, were used as target material for bombardment. Gold particles (0.9 µm) coated by the mixed plasmids (pITB-DsRED with DsRed gene along with the plasmid pITB-BAR with bar gene) (Molar ratio 3:1, respectively) were bombarded into PLBs by the BIO-RAD PDS-1000/He. After 2-day co-bombardment, PLBs were cultured on the Knudson C (1946) selection medium (1 mg/l of BA) with 1-3 mg/l of phosphinothricin (PPT) for several selection cycles. The transient expression of the DsRed gene (2 days after bombardment) was confirmed with a positive result. The PCR analysis of the DsRed, bar genes showed the expected DNA bands - 350 bp, 500 bp, respectively. For the detection of the DsRED fluorescence, the transgenic PLBs (etiolated and green) were illuminated with a hand-held LED spotlight (for yellow-green light - 560 nm wavelength) and photographed by the CANON digital camera in combination with a red filter. Furthermore, the expression of the DsRED protein in PLB was also readily identifiable under day light/white fluorescent lamp. These results indicate that DsRed is a suitable reporter for genetic transformation of Dendrobium and this system could be used in fundamental research, especially the change of flower color due to the biochemical product of the transgene. This is the first result on genetic transformation of Dendrobium with the DsRed gene for generating transgenic PLBs which can be excited for emitting strong red fluorescence

Sonication-assisted Agrobacterium-mediated transformation of the ACC gene to interfere the production of ethylene in spring Dendrobium cv. ‘Sanya’

In the present study, a protocol was developed to obtain stable lines of the spring Dendrobium cv. ‘Sanya’ via Sonication-Assisted Agrobacterium-mediated Transformation (SAAT) of protocorm-like bodies (PLBs). Agrobacterium tumefaciens strain LBA4404 was used with the binary vector YF9078 containing the inverted repeat (IR) of ACC gene (IRACC) for the inhibition of ethylene production, the neomycin phosphotransferase II gene (NPTII) gene as a selectable marker for kanamycin resistance, and an intron-containing β-glucuronidase gene (gus-int) as a reporter gene. PLBs were treated for 10 min with ultrasound (40 kHz) and subsequently inoculated with Agrobacterium suspension for 60 min. The addition of 100 μM acetosyringone (AS) during the preculturing, inoculation and co-cultivation resulted in the highest efficiency of gene transformation (1.04%). Following co-cultivation, PLBs were cultured on selective medium containing 200 mg/l kanamycin and 250 mg/l cefotaxime. Proliferating PLBs were repeatedly selected for kanamycin resistance, and stable transformed lines were generated. Incorporation and expression of transgenes were confirmed by GUS histochemical assay, PCR analysis, Southern blot analysis, and real-time reverse transcription-polymerase chain reaction (RT-PCR). A total of five Southern blot positive transgenic lines were obtained. The ability for ethylene suppression by small potted transgenic plants was measured. The results showed that it was significantly higher in transgenic lines than in untransformed control; different strains exhibited marked variation; and this was related to their cDNA expression.

Ethylene-regulated hastening of perianth senescence after pollination in Dendrobium flowers is not due to an increase in perianth ethylene production

Flowers of Dendrobium cv. Kenny were hand-pollinated using pollinia from cv. Sakura. This resulted in a large increase in flower ethylene emission and rapid perianth (tepal) senescence. The increase in flower ethylene emission was correlated in time with an increase in ethylene emitted by the column (the fused stigma, style and stamens) plus the ovary. No ethylene emission was observed from perianth parts that were isolated at various periods after pollination. The increased ethylene emission by the column plus ovary was correlated with an increase in ACC synthase and ACC oxidase activity in these flower parts. The perianth parts, in contrast, only showed an increase in ACC oxidase activity, following pollination. The data show that pollination-induced early perianth senescence in Dendrobium is mediated by increased ethylene biosynthesis by the column + ovary, and not due to increased ethylene biosynthesis in the perianth parts. Apparently, ethylene synthesized in the gynoecium diffuses to the perianth parts where it induces senescence. The data are very similar to those found previously in pollinated Phaleanopsis orchids and in emasculated Cymbidium orchids, with the exception that ethylene was emitted from the tepals of these two orchids and not from Dendrobium.

Do plastids in Dendrobium cv. Lucky Duan petals function similar to autophagosomes and autolysosomes?

In animal cells a double-membrane-bound structure, the autophagosome, encloses a portion of the cytoplasm. The encapsulated material becomes digested after fusion of the autophagosome with a vesicle containing lytic enzymes. The autophagosome is then termed autolysosome. In intact plants, structures similar to animal autophagosomes/autolysosomes have been found only in a few types of cells. Additionally, some early papers indicated that plastids can function similar to autophagosomes/autolysosomes. Here, we report that plastids in Dendrobium cv. Lucky Duan petals produced an endocytosis-like invagination of the two outer membranes. The opening between the invagination space and the cytoplasm was almost isodiametric, less than 0.2 μm in diameter. The volume of the space formed by the invagination had a maximum of about half of the total plastid volume. Staining of the invagination lumen for acid phosphatase, a marker of organelles showing autophagic activity, was positive. Membranes and numerous ribosomes were observed inside the lumen of the invagination. The structure of the material inside the lumen varied from that of the cytoplasm to uniform electron-translucent, indicating that the enclosed cytoplasmic material became completely digested. No support was found for the idea that the material engulfed by the plastid or the whole plastid became transferred to a vacuole. Taken together, the data suggested the hypothesis that plastids in Dendrobium petal mesophyll cells can function in a way similar to both autophagosomes and autolysosomes in animal cells.

Ethylene-sensitive and ethylene-insensitive abscission in Dendrobium: Correlation with polygalacturonase activity

We previously showed that the abscission of floral buds of the orchid Dendrobium cv. Miss Teen was absent in controls but highly promoted by ethylene, whilst open flowers also did not abscise without ethylene but were not responsive to ethylene. Here, we determined the activities of three enzymes in the abscission zone (AZ): polygalacturonase (PG), β-1,4-glucanase (cellulase), and pectin methylesterase (PME). In the AZ of floral buds an increase in PG activity coincided with the ethylene-induced abscission. A small increase was found in the AZ β-1,4-glucanase (cellulase) activity, shortly after the end of ethylene treatment of the flower buds and a few days before the onset of abscission. The activity of pectin methylesterase (PME) in the AZ of floral buds was not affected by ethylene. In the AZ of flowers that had just opened no increase in enzyme activity was observed after ethylene treatment. The data indicate a role of PG, and possibly of β-1,4-glucanase, in abscission. The data also suggest that the reason for the decrease in ethylene sensitivity of the abscission zone, during flower opening, lies upstream from the induction of enzyme activity in the AZ.

Do mitochondria in Dendrobium petal mesophyll cells form vacuole-like vesicles?

Using transmission electron microscopy, we investigated the ultrastructure of mitochondria in petal mesophyll cells of the orchid Dendrobium cv. Lucky Duan, from the time of floral opening to visible petal senescence. Cells close to the vascular bundle contained many mitochondria, some of which showed internal degeneration. This inner mitochondrial breakdown was accompanied by an eightfold increase in mitochondrial volume. Small electron-dense granules (approximately 0.04 mum in diameter) at the periphery of the mitochondrial matrix remained. These granules were used as an indicator of still later stages of mitochondrial development in these cells. The apparent final stage of mitochondrial degeneration was a single-membrane-bound vesicle, resembling a vacuole. No evidence was found for the idea that mitochondria became transferred (intact or degenerated) into a lytic vacuole. Taken together, the data suggest the hypotheses that (a) mitochondria in cells close to the vascular bundle in petals of open Dendrobium cv. Lucky Duan flowers undergo large-scale internal degeneration and that (b) such degenerating mitochondria form vacuole-like vesicles.