Epidendrum Radicans Research Articles

Genetic inference of orchid colonization of a Costa Rican lava flow

AbstractThe dispersal and colonization of plant populations allow species to occupy novel habitats, migrate, and undergo range shifts in response to changing environmental factors and, as such, are fundamental ecological processes for ensuring the long‐term persistence of species. Natural landscape disturbance often generates habitats available for colonization. Patterns of colonization and population expansion can be inferred from the levels and partitioning of genetic variation of plant populations with known disturbance histories, such as recent volcanic eruptions. We sampled and mapped 496 individuals from two populations of the colonizing terrestrial orchid, Sobralia chrysostoma, on the 1992 lava flow of Volcán Arenal in central Costa Rica. We used neutral co‐dominant markers to genotype individuals and estimate population genetic statistics. Both populations had high mean levels of genetic diversity (P = 100%; AP = 3.31; He = 0.259) suggesting that the lava flow was colonized by numerous individuals that likely originated from multiple source populations. However, significant spatial genetic structure (SGS) was only present in one population at the smallest distance class (≤2 m) and was low (r = 0.032). That these large and genetically diverse populations had such low SGS and an absence of SGS, respectively is contrary to expectations and differs significantly from the pattern in Epidendrum radicans (Orchidaceae), with which S. chrysostoma is growing sympatrically. Our results suggest that these two populations either consist primarily of immigrant individuals or that seeds produced in situ dispersed over longer distances, thereby producing larger seed shadows and greater overlap of seed shadows.

Genetic inference of orchid population dynamics on different‐aged lava flows in Costa Rica

AbstractColonization is a fundamental ecological process that is important for the persistence of species, particularly when a changing environment necessitates range shifts. Vacant habitats available for colonization often arise from landscape disturbance. Colonization and population expansion processes can be inferred by examining the levels and spatial distribution of genetic variation of plant populations with known disturbance histories. Samples (N = 690) of the terrestrial orchid, Epidendrum radicans, were collected from five lava flow sites on the slopes of Volcán Arenal in Costa Rica that last experienced major eruptions in 1968 and 1992. Individuals were also sampled (N = 188) from four regional populations. Samples were characterized using 15 nuclear genetic markers and analyzed using population genetics statistics. Genetic diversity within sites was moderate (He = 0.092–0.192). Contrary to expectation, diversity tended to be lower on the older lava flows (0.131 vs. 0.172) which may reflect their more sheltered topography that restricted pollen/seed immigration, and/or greater intra‐ and interspecific competition. Genetic diversity measures indicate that the lava flows were colonized by numerous individuals that likely originated from multiple sources while spatial genetic structure (SGS) statistics indicate that most recruitment in the study sites subsequent to colonization resulted from in situ reproduction and localized seed deposition. Younger sites had significantly greater SGS over larger distances which reflects fewer reproductive events, and less spatial and temporal overlap of seed shadows relative to the older sites. Clones were also generally smaller on the younger sites (≤3 m vs. ≤8 m).

Epidendrumradicans Fungal Community during Ex Situ Germination and Isolation of Germination-Enhancing Fungi.

Orchids exhibit varying specificities to fungi in different microbial environments. This pilot study investigated the preference of fungal recruitment during symbiotic germination of Epidendrum radicans Pav. ex Lindl. Two different orchid substrates were used for ex situ seed baiting: pine bark and rotten oak leaf, with Basidiomycota and Ascomycota as the respective dominant groups. Both substrates promoted seed germination, with a higher protocorm formation rate on pine bark (65.75%). High-throughput sequencing characterized the fungal communities of germinated protocorms. Basidiomycota was the dominant group in protocorms that symbiotically germinated on both substrates. The family-level community structures of endophytic fungi in protocorms that symbiotically germinated on both substrates were close to those of protocorms that germinated in vitro on MS1 medium. For protocorms, the dominant fungal groups recruited from substrates differed at the genus level; from pine bark, they were genera belonging to unclassified Sebacinales (41.34%), Thanatephorus (14.48%) and Fusarium (7.35%), while, from rotten oak leaf, they were Rhizoctonia (49.46%), Clitopilus (34.61%), and Oliveonia (7.96%). Four fungal isolates were successfully obtained and identified as belonging to the family Tulasnellaceae, genera Ceratobasidium and Peniophora, which could promote seed germination to the seedling stage. The data indicate that endophytic fungi for E. radicans germination on two different substrates are affected at the genus level by the substrate, with a degree of specificity at the family level.

Mycorrhizal Compatibility and Germination-Promoting Activity of Tulasnella Species in Two Species of Orchid (Cymbidium mannii and Epidendrum radicans)

In nature, Orchidaceae seeds establish a relationship with orchid mycorrhizal fungi to obtain essential nutrients for germination. The orchids, Cymbidium mannii and Epidendrum radicans, have significant ornamental and economic value. We isolated and cultured mycorrhizal fungi from C. mannii, E. radicans, and C. goeringii roots. Three strains of fungi, Tulasnella calospora (Tca), T. asymmetrica (Tas), and T. bifrons (Tbi), were identified using ITS-rDNA sequencing. Their mycorrhizal compatibility, germination-promoting effects, and symbiosis with the seeds of C. mannii and E. radicans were studied in vitro using various concentrations of oatmeal agar (OA) medium. Tca exhibited significant seed-germination-promoting effects on C. mannii (92.1%) and E. radicans (84.7%) on 2.0 and 4.0 g/L OA, respectively. For Tbi and Tas, the highest germination percentages were observed on 4.0 g/L OA in E. radicans (73.60% and 76.49%, respectively). Seed germination in C. mannii was enhanced by high oatmeal concentrations (8.0 and 12.0 g/L) during symbiosis with Tas, whereas Tbi had no effect regardless of OA concentration. Tca exhibited high compatibility with C. mannii and E. radicans, and the oatmeal concentration of the medium affected this compatibility. The findings of this study will aid in the propagation of endangered orchid species for conservation and commercial purposes using mycorrhizal technology.

Physiological responses of orchids to prolonged clinorotation

Creation of plant-based bioregenerative life support systems is crucial for future long-duration space exploring missions. Microgravity is one of the major stresses affecting plant growth and development under space flight conditions. Search for higher plant genotypes resilient to microgravity as well as revealing of biological features which could be used as markers of such resilience is rather urgently needed. The objective of this study was to analyze physiological and biochemical responses of three orchid species representing different life forms (terrestrial and epiphytic), growth types (monopodial and sympodial) and pathways of CO2 fixation to long-term (24 months) clinorotation which modeled the combined effect of two stress factors: hermetic conditions and microgravity. Three years old meristematic orchids Cypripedium flavum, Angraecum eburneum, Epidendrum radicans, representing different life forms, types of branching shoot system and pathways of CO2 fixation, were used as test-plants. The microgravity was simulated using three-dimensional (3-D) clinostat equipped with two rotation axes placed at right angles (rotation frequency was 3 rpm) in controlled conditions of air temperature, illumination, air humidity and substrate moisture. The control plants were grown in the similar plastic vessels but not hermetically sealed and without clinorotating in the same environmental conditions. The vital state of the test plants was assessed using characteristics of mineral nutrition, content of photosynthetic pigments, free amino acids, soluble proteins, DNA and RNA, enzymatic and non-enzymatic antioxidants. The results of this study confirmed that orchids grown under simulated microgravity and kept in hermetically-sealed vessels were subjected to oxidative stress, which could be responsible for the observed inhibition of basic physiological processes such as mineral nutrition, metabolism of aminoacids, protein biosynthesis and photosynthesis. Monopodial orchids C. flavum and A. eburneum demonstrated better adaptation to prolonged clinorotation as compared to sympodial E. radicans. In particular, the latter demonstrated some stimulation of mineral nutrition processes (i.e. K, N, Fe, Mn, Zn accumulation), content of photosynthetic pigments, proline and superoxide dismutase activity. Long-lasting clinorotation induced adaptive changes of antioxidant systems in the studied orchids (e.i. increase in carotenoids and proline content and stimulation of superoxide dismutase activity), which helped to maintain the main physiological functions at stable level in the above-mentioned stressful conditions. The following biochemical characteristics in the studied orchids could be considered as markers of resilience to simulated microgravity and hermetic conditions: 1) an increase in the accumulation of non-enzymatic (proline, carotenoids) and enzymatic antioxidants (superoxide dismutase); 2) ability to maintain stable balance of mineral nutrients; 3) increase in the content of photosynthetic pigments; 4) increase in the content of proteinogenic amino acids and soluble proteins; 5) increase in the DNA content or RNA/DNA ratio. Our studies have also demonstrated a correlation between orchid ecomorphological characteristics such as type of branching with their adaptive responses to prolonged clinorotation. We observed no correlation between the studied life form of orchids, ecotype or the pathway of CO2 fixation and their resilience to prolonged clinorotation. This research can be a starting point for studying the relationships between ecomorphological features of various orchids and their resilience to microgravity conditions in the search for biological markers of microgravity tolerance in species of higher plants.

Physiological responses of orchids to prolonged clinorotation

Creation of plant-based bioregenerative life support systems is crucial for future long-duration space exploring missions. Microgravity is one of the major stresses affecting plant growth and development under space flight conditions. Search for higher plant genotypes resilient to microgravity as well as revealing of biological features which could be used as markers of such resilience is rather urgently needed. The objective of this study was to analyze physiological and biochemical responses of three orchid species representing different life forms (terrestrial and epiphytic), growth types (monopodial and sympodial) and pathways of CO2 fixation to long-term (24 months) clinorotation which modeled the combined effect of two stress factors: hermetic conditions and microgravity. Three years old meristematic orchids Cypripedium flavum, Angraecum eburneum, Epidendrum radicans, representing different life forms, types of branching shoot system and pathways of CO2 fixation, were used as test-plants. The microgravity was simulated using three-dimensional (3-D) clinostat equipped with two rotation axes placed at right angles (rotation frequency was 3 rpm) in controlled conditions of air temperature, illumination, air humidity and substrate moisture. The control plants were grown in the similar plastic vessels but not hermetically sealed and without clinorotating in the same environmental conditions. The vital state of the test plants was assessed using characteristics of mineral nutrition, content of photosynthetic pigments, free amino acids, soluble proteins, DNA and RNA, enzymatic and non-enzymatic antioxidants. The results of this study confirmed that orchids grown under simulated microgravity and kept in hermetically-sealed vessels were subjected to oxidative stress, which could be responsible for the observed inhibition of basic physiological processes such as mineral nutrition, metabolism of aminoacids, protein biosynthesis and photosynthesis. Monopodial orchids C. flavum and A. eburneum demonstrated better adaptation to prolonged clinorotation as compared to sympodial E. radicans. In particular, the latter demonstrated some stimulation of mineral nutrition processes (i.e. K, N, Fe, Mn, Zn accumulation), content of photosynthetic pigments, proline and superoxide dismutase activity. Long-lasting clinorotation induced adaptive changes of antioxidant systems in the studied orchids (e.i. increase in carotenoids and proline content and stimulation of superoxide dismutase activity), which helped to maintain the main physiological functions at stable level in the above-mentioned stressful conditions. The following biochemical characteristics in the studied orchids could be considered as markers of resilience to simulated microgravity and hermetic conditions: 1) an increase in the accumulation of non-enzymatic (proline, carotenoids) and enzymatic antioxidants (superoxide dismutase); 2) ability to maintain stable balance of mineral nutrients; 3) increase in the content of photosynthetic pigments; 4) increase in the content of proteinogenic amino acids and soluble proteins; 5) increase in the DNA content or RNA/DNA ratio. Our studies have also demonstrated a correlation between orchid ecomorphological characteristics such as type of branching with their adaptive responses to prolonged clinorotation. We observed no correlation between the studied life form of orchids, ecotype or the pathway of CO2 fixation and their resilience to prolonged clinorotation. This research can be a starting point for studying the relationships between ecomorphological features of various orchids and their resilience to microgravity conditions in the search for biological markers of microgravity tolerance in species of higher plants.

Algal associates and the evidence of cyanobacterial nitrogen fixation in the velamen roots of epiphytic orchids

The hanging velamen roots in epiphytic orchids are unique kind of aerial roots in the plant world. The diverse kinds of microbial associates in it suggest its ecological and functional complexities. In this context, diversity and population characteristics of the entire algal flora in the velamen roots of four tropical epiphytic orchids Acampe praemorsa, Rhynchostylis retusa, Epidendrum radicans and Oncidium sphacelatum from different geographic locations of Kerala state, India were explored and compared. The potential nitrogen-fixing activity (NFA) of cyanobacteria in the velamen roots was analysed by acetylene reduction assay to understand the nitrogen-fixing role of cyanobacterial species in the same as a source of nitrogen to the host. The total nitrogen content of the velamen roots and leaves was compared to generate indirect evidence of accumulation of nitrogen in roots by primary addition through nitrogen fixation. Altogether 24 species of algal associates were isolated from the velamen roots of four epiphytic orchids. A majority of algae were found as cyanobacterial species; many of them are well-known nitrogen-fixing categories. The total tissue nitrogen content of the velamen roots was found significantly higher than that of leaves. The NFA of cyanobacteria in the velamen roots revealed its potential role in nitrogen fixation. This preliminary level empirical evidence is sufficient to consider the velamen roots of epiphytic orchids as an ecologically complex aerial ‘organ ecosystem’ with microbial partnerships for nutritional support, especially nitrogen availability in epiphytic orchids.

Soluções crioprotetoras na conservação de sementes de orquídea estrela e orquídea bambu em nitrogênio líquido

An alternative for the conservation of orchid species threatened with extinction is the seeds preservation for long periods by cryopreservation. This work aimed to evaluate the influence of cryogenic solutions on the orchids Epidendrum radicans and Arundina bambusifolia seeds cryopreservation in liquid nitrogen. Seven treatments were performed: 0.4 M sucrose; 2 M glycerol; PVS1; PVS2; PVS3; PVS2 + 1% phloroglucinol and the control. After liquid nitrogen removal, half of the seeds were subjected to tetrazolium test, and another half was in vitro cultured. After 30 days seed germination was evaluated. There was no significant difference between A. bambusifolia and E. radicans in tetrazolium test and seeds germination. On the other hand, it was observed that in A. bambusifolia tetrazolium and seed germination tests the solutions of PVS1, PVS2, PVS2 + 1% phloroglucinol showed the best results. E. radicans seeds with 4% water content cryopreservation does not require the use of cryoprotectant. On the other hand, cryoprotectant´s use resulted in positive effect in maintenance and viability preservation of A. bambusifolia seeds. PVS1, PVS2 and PVS2 + 1% phloroglucinol showed best seeds survival rates after cryopreservation in liquid nitrogen.

Vegetative anatomical adaptations of Epidendrum radicans (Epidendroideae, Orchidaceae) to epiphytic conditions of growth

The anatomical properties of leaf, stem, and root of Epidendrum radicans Pav. ex Lindl., belonging to the subfamily Epidendroideae (Orchidaceae) were investigated for adaptations to stressed habitats. The anatomical investigation revealed that leaves of E. radicans have a thick cuticle (3–4 µm) and paracytic type of stomata. Foliar epidermal cells are conical on the adaxial surface and rectangular in the abaxial surface, distinct hypodermis absent, and uniseriate fiber bundles are arranged in both sides of the leaves. The foliar mesophyll is homogenous and starch grains and raphides present. The leaf sheath covering the stem have cuticle restricted to the outer surface and air spaces are present. The stem has a cuticulerized uniseriate epidermis and a uniseriate hypodermis. The cortex and a parenchymatous ground tissue of the stem are separated by a layer of sclerenchymatous band. Vascular bundles are collateral and their size generally increases from the periphery towards the center. A sclerenchymatous patch covers the phloem pole, whereas the xylem is covered by thin-walled parenchymatous cells. The roots possess Epidendrum-type velamen. Cover cells present. Uniseriate dimorphic exodermis consists of U-thickened long cells and thin-walled passage cells. The endodermal cells O-thickened, pericycle sclerenchymatous, xylem 10–14 arched. The pith is sclerenchymatous, but parenchymatous at the center. The anatomical examination of E. radicans revealed adaptations to moisture stress conditions like thick cuticle covering the leaves and stem, water storage cells, multilayered velamen and dimorphic exodermis.

Reguladores de crescimento na redução do porte da orquídea Estrela-de-Fogo para comercialização em vaso

Fire-of-star (Epidendrum radicans Pav. ex Lindl.) is a terrestrial orchid, native to Brazil, tussocks with leafy stems, always with many adventitious roots, releasing its long inflorescence with about 1.0 m from the apex of the stem, showing great potential in floriculture, but long flowering stem complicates their marketing vase. The objective of this study was to evaluate the effect of paclobutrazol (PBZ) and mepiquat chloride (CLM) the reduction of the size of the orchid E. radicans. Plants with an average height of 15 cm were cultivated in a greenhouse with 50% shading. The growth regulators used were PBZ at doses of 0; 5; 10; 15 and 20 mg L-1, and the CLM at doses of 0; 1; 2; 3; 4 and 5 mg L-1. The frequency of application was fortnightly, totaling ten applications. The experiment was installed on a randomized complete blocks, one block to the PBZ with 5 treatments and 10 replications and another block to the CLM, with 6 treatments and 10 replications. Data were submitted to analysis of variance at 5% probability and significance when seen performed regression analysis. The variables evaluated were number shoots, plant height (cm), number of flower stems and leaf area. The results indicated that E. radicans treated with 5 mg L-1 PBZ were 50% lower in height than the control plants. When CLM treated with a dose of 1 mg L-1 plants were 25% lower in height than the control plants, maintaining its aesthetic characteristics suitable for marketing in vases. Growth regulators in the applied doses did not affect the number of shoots and flower stems. PBZ treated plants had 50% of their leaf area compared to control while those treated with CLM doses remained with the same average leaf area of control.

Growth regulators in the development of potted Epidendrum radicans orchid

Epidendrum is a terrestrial orchid with great potential for commercialization. However, its considerable height makes it difficult for transport and commercialization. Many species have been controled with growth regulators, including orchids and other ornamental plants. The aim of this study was to evaluate the efficiency of two plant growth regulators, paclobutrazol and chlormequat chloride (CCC), on the vegetative growth of potted Epidendrum radicans orchid aiming height control. Paclobutrazol (Cultar) was applied at doses of 0, 5, 10 and 20 mg L-1, and the CCC (Cycocel) at doses of 0, 2000, 4000 and 6000 mg L-1. The regulators were applied once or twice a month, via substrate irrigation. Plants were assessed every two months for plant height, number of shoots per pot and number of inflorescences per pot. CCC had no effect on the final height of Epidendrum radicans at the doses applied. Paclobutrazol was effective in controlling plant height at doses of 10 and 20 mg L-1. None of the products influenced the number of inflorescences produced. Chlormequat chloride at a dose of 6000 mg L-1 stimulated the production of shoots. Key words: Paclobutrazol, chlormequat chloride, reduction in height.

Performance of Orchid Species in Shevaroy Hills of Eastern Ghats

Performance of 24 orchid species was assessed in the net-house of Horticultural Research Station, Tamil Nadu Agricultural University, Yercaud. Among the species studied, plant height was significantly high (105cm) in Spathoglotts plicata. At the end of the vegetative stage, number of leaves was maximum (30) in Aerides. Leaf was longest (49.8cm) and widest (17.6cm) in Rhyncostylis retusa. Paphiopedilum insigne produced largest flower size (14.4cm across). Pedicel length was highest in Phaius tankervillae (10.3cm) and Renanthera inshootiana (7.1cm). Aerides multiflorum recorded lowest pedicel length (1.24cm). Epidendrum radicans and Spathoglottis plicata produced flowers round the year. Lucia virides recorded maximum life (29 days) on plant, followed by Arachnanthe clarkei (18 days), Dendrobium densiflorum (18 days) and Oncidium flexosum (16 days), while, minimum (6 days) was observed in two orchid species, Aerides crispum and Cattleya sp. Maximum (23 days) vase life was recorded in Lucia virides. Results of the investigation thus reveal that among the 24 orchid species studied, Epidendrum radicans, Lucia virides and Paphiopediluminsigne performed better in terms of vegetative and floral characters under Shevaroy hill condition.

IN VITRO MORPHOGENESIS OF FIVE ORCHIDS

IN VITRO MORPHOGENESIS OF FIVE ORCHIDS

Comparative effects of four plant growth retardants on growth of Epidendrum radicans

SummaryThe effect of paclobutrazol, triapenthenol, daminozide and chlormequat chloride on the growth of Epidendrum radicans was studied over one year. Paclobutrazol and triapenthenol were applied as soil drenches at 5, 10 and 20 mg –1, while 1000, 2000 and 4000 mg l–1 daminozide and 2000, 4000 and 6000 mg l–1 chlormequat chloride were applied as foliar sprays. Main and lateral shoot growth restriction (54-75%) was obtained by all doses of paclobutrazol and 20 and 10 mg l–1 triapenthenol. Daminozide at 4000 and 2000 mg l–1 restricted only main shoot growth. Chlormequat chloride at 6000 mg –1 had a similar effect but caused leaf toxicity symptoms, as white spots. The effect of the four growth retardants on shoot growth restriction followed the order paclobutrazol>triapenthenol> daminozide>chlormequat chloride. The number of lateral shoots developed during the treatment period and the main and lateral shoot diameter were not affected by any chemical used. Leaf length was much reduced (46-62%) by all doses of paclobutrazol and the two higher doses of triapenthenol and to a lesser extent (13-29%) by all doses of daminozide and the lower dose of triapenthenol, while it was not affected by chlormequat chloride. Leaf width was restricted (13-37%) by the two higher doses of paclobutrazol, triapenthenol and daminozide and the highest dose of chlormequat chloride. Leaf thickness was much increased (52-76%) by all doses of paclobutrazol and the two higher doses of triapenthenol. The lower dose of triapenthenol and daminozide, and all doses of chlormequat chloride, caused a smaller increase in leaf thickness (17-37%). Seven and a half months after the end of treatments paclobutrazol was the most persistent of the growth retardants used. For compact E. radicans pot plants, without special needs of support, a 10 mg l–1 paclobutrazol soil drench applied monthly is recommended.

INFLUENCE OF IN VITRO CULTURE MEDIUM ON EPIDENDRUM RADICANS SEED GERMINATION, SEEDLING GROWTH AND EX VITRO ESTABLISHMENT

In vitro propagation of Epidendrum radicans (E. ibaguense) by seed, and the ability for ex vitro acclimatization and establishment of the seedlings was studied in this work. Liquid and agar-solidified (8 g l -1 ) MS and VW media enriched with 1 mg l -1 NAA, 1 mg l -1 BA and 15% coconut milk were compared. Two experiments were carried out, one with sparse (50 seeds/vase) and another with dense (∼250 seeds/vase) sowing. Liquid media compared to solid gave much longer seedlings, as well as higher percentage of protocorm like bodies (PLBs) and branched seedlings. High percentage of the responded seeds formed PLBs in liquid VW. In the case of dense plating, liquid MS gave more vigorous seedlings and the seedlings grown on liquid MS were established ex vitro at a much higher percentage. After germination, activated charcoal addition (2 g l -1 ) to the growing medium increased ex vitro establishment of those seedlings grown on liquid and solid VW and on solid MS medium.

Efficient production of protocorm-like bodies and plant regeneration from flower stalk explants of the sympodial orchid Epidendrum radicans

A simple and efficient micropropagation method was established for direct protocorm-like body (PLB) formation and plant regeneration from flower stalk internodes of a sympodial orchid, Epidendrum radicans. Small transparent tissues formed on surfaces and cut ends of flower stalk internodes on a modified half-strength Murashige and Skoog basal medium with or without thidiazuron (TDZ) after 1–2 wk of culture. In the light, the transparent tissues enlarged and turned into organized calluses on most of the explants. However, PLBs formed only on a medium supplemened with 0.45 μM TDZ within 2 mo. of culture. Sucrose, NH4NO3, and KNO3 were used in media to test their effects on PLB proliferation and shooting. The best response on number of PLBs per tube was 23.6 at 40 gl−1 sucrose, 825 mgl−1 NH4NO3, and 950 mgl−1 KNO3, and the highest number of PLBs with shoots was found at 10 gl−1 sucrose, 825 mgl−1 NH4NO3, and 950 mgl−1 KNO3. Homogenized PLB tissues produced by blending were used to test the effects of four cytokinins [TDZ, N6-benzyladenine (BA), zeatin-riboside, and kinetin] on PLB proliferation and shoot formation. The best responses on number of PLBs per tube, proliferation rate, and number of PLBs with shoots per tube were obtained at 4.44 μM BA, 0.28 μM zeatin-riboside, and 1.39 μM kinetin, respectively. Normal plantlets converted from PLBs on the same TDZ-containing medium after 1 mo. of culture. The optimized procedure required about 12–13 wk from the initiation of PLBs to plantlet formation. The regenerated plants grew well with an almost 100% survival rate when acclimatized in a greenhouse.

Involvement of exodermal passage cells in mycorrhizal infection of some orchids

Roots with velamen of three orchids were examined for mycorrhizal infection: an epiphytic orchid Stanhopea tigrina, a lithophyte Dendrobium kingianum and a terrestrial Epidendrum radicans. Approximately 50% of all exodermal cells were passage cells that remained non-lignified. Long cells of the exodermis were lignified, but not suberized. A similar proportion of passage cells was infected in young and old root sections. Most coils were located in the three cell layers of cortex beneath the exodermis. A larger proportion of coils was collapsed in the older part of the roots of D. kingianum and E. radicans.

Survival and Growth of Transplanted Orchid Seedlings Enhanced by DCPTA

The growth-enhancing property of DCPTA was tested on transplanted seedlings of Brassolaeliocattleya × Hort. (Blc. Bryce Canyon × Lc. Pirate King), Dendrobium × Blume. Hickham Deb, Epidendrum radicans Pav. ex Lindl., Lueliocattleya × Rolfe Prism Palette `The Clown', and Phalaenopsis × Blume. [Pink Zebra × (Jutta Brungor × Music)]. After 3 to 6 months of greenhouse growth, plants treated with 30 μm DCPTA produced a 2- to 3-fold increase in root growth compared to the controls. Shoot growth, root: shoot ratio, and the survival of DCPTA-treated plants were increased significantly when compared with controls. Chemical name used: 2-(3,4-dichlorophenoxy)triethylamine (DCPTA).

Shootlessness, Velamentous Roots, and the Pre-Eminence of Orchidaceae in the Epiphytic Biotope

Roots of representative epiphytic orchids were examined for anatomical detail, desiccation resistance and evidence of CAM activity. Those “shootless” taxa examined (Campylocentrum pachyrrhizum (Reichenb. f.) Rolfe, Harrisella porrecta Reichenb. f.) Fawc. & Rendle, and Polyradicion lindenii (Lindl.) Cogn. ex Urban) and a semi-shootless type (Kingidium taeniale (Lindl.) P. F. Hunt) bear thinner or eroded velamina and greater volumes of cortical intercellular space than do those of the leafy forms tested (Campylocentrum sellowii (Reichenb. f.) Rolfe, Encyclia tampensis (Lindl.) Small, Epidendrum radicans Pavon ex Lindl., Phalaenopsis amabilis (L.) Blume, Rangaeris amaniensis (Krzl.) Summerhayes and Vanda parishii (Reichenb. f.)). Shootless species also bear a more elaborate aeration apparatus at the velamen-cortex interface. Structurally distinct cortical cells located in this region may regulate gas exchange across the exodermis. Velamen thickness varies greatly among the ten species, as does the development of outer tangential walls of U cells in the underlying exodermis. Desiccation resistance under laboratory conditions was more closely related to root surface-to-volume ratio (S/V) than to any other measured anatomical parameter, including velamen development. Modes of carbon gain and the possible pathway for movement of fungus-borne carbon into an orchid's pool of assimilates are described, as is the possible significance of these processes to survival in forest canopy habitats.

SHOOTLESSNESS, VELAMENTOUS ROOTS, AND THE PRE-EMINENCE OF ORCHIDACEAE IN THE EPIPHYTIC BIOTOPE.

Roots of representative epiphytic orchids were examined for anatomical detail, desiccation resistance and evidence of CAM activity. Those "shootless" taxa examined (Campylocentrum pachyrrhizum (Reichenb. f.) Rolfe, Harrisella porrecta Reichenb. f.) Fawc. & Rendle, and Polyradicion lindenii (Lindl.) Cogn. ex Urban) and a semi-shootless type (Kingidium taeniale (Lindl.) P. F. Hunt) bear thinner or eroded velamina and greater volumes of cortical intercellular space than do those of the leafy forms tested (Campylocentrum sellowii (Reichenb. f.) Rolfe, Encyclia tampensis (Lindl.) Small, Epidendrum radicans Pavon ex Lindl., Phalaenopsis amabilis (L.) Blume, Rangaeris amaniensis (Krzl.) Summerhayes and Vanda parishii (Reichenb. f.)). Shootless species also bear a more elaborate aeration apparatus at the velamen-cortex interface. Structurally distinct cortical cells located in this region may regulate gas exchange across the exodermis. Velamen thickness varies greatly among the ten species, as does the development of outer tangential walls of U cells in the underlying exodermis. Desiccation resistance under laboratory conditions was more closely related to root surface-to-volume ratio (S/V) than to any other measured anatomical parameter, including velamen development. Modes of carbon gain and the possible pathway for movement of fungus-borne carbon into an orchid's pool of assimilates are described, as is the possible significance of these processes to survival in forest canopy habitats.