Content uploaded by Choy Sin Hew
Author content
All content in this area was uploaded by Choy Sin Hew
Content may be subject to copyright.
A preview of the PDF is not available
The Presence of Photosynthetic Machinery in Aerial Roots of Leafy Orchids
Abstract
Three photosynthetic enzymes were characterised in extracts from leaves and aerial roots of Aranda ‘Christine 130’. The enzymes from both tissues were similar in activity and kinetic properties. Grana-containing chloroplasts were found in root cells of Vanda suauis . Thus components crucial to photosynthesis are present in aerial roots of these leafy orchids.
... Orchids grow high in the tree canopy to reach available sunlight and shading conditions. The aerial roots of orchids have multiple functions, including the physical support, water and nutrient uptake, and photosynthesis (Ho et al. 1983). The roots of the orchid expressed a high level of PaPHOT1 and a low level of PaPHOT2 (Fig. 3B). ...
... The root biomass of orchid is high (Fig. 3A); therefore, they have ample exposure to sunlight and turn on photosynthetic machinery to support their greater energy needs for plant growth and development. RuBP carboxylase and PEP carboxylase enzyme activities detected in the aerial root of orchids suggest that orchid roots have a photosynthesis function (Ho et al. 1983). Phalaenopsis aphrodite roots are exposed to sunlight. ...
Chloroplast movement is important for plants to avoid photodamage and to perform efficient photosynthesis. Phototropins are blue light receptors in plants that function in chloroplast movement, phototropism, stomatal opening, and they also affect plant growth and development. In this study, full-length cDNAs of two PHOTOTROPIN genes, PaPHOT1 and PaPHOT2, were cloned from a moth orchid Phalaenopsis aphrodite, and their functions in chloroplast movement were investigated. Phylogenetic analysis showed that PaPHOT1 and PaPHOT2 orthologues were highly similar to PHOT1 and PHOT2 of the close relative Phalaenopsis equestris, respectively, and clustered with monocots PHOT1 and PHOT2 orthologues, respectively. Phalaenopsis aphrodite expressed a moderate level of PaPHOT1 under low blue light of 5 μmol.m-2.s-1 (BL5) and a high levels of PaPHOT1 at >BL100. However, PaPHOT2 was expressed at low levels at BL100. Analysis of light-induced chloroplast movements using the SPAD method indicated that orchid accumulated chloroplasts at BL25 and significant chloroplast avoidance movement was observed at >BL100. Virus-induced gene silencing of PaPHOTs in orchids showed decreased gene expression of PaPHOTs and reduced both chloroplast accumulation and avoidance responses. Heterologous expression of PaPHOT1 in Arabidopsis phot1phot2 double mutant recovered chloroplast accumulation response at BL5, but neither PaPHOT1 nor PaPHOT2 was able to restore mutant chloroplast avoidance at BL100. Overall, this study showed that phototropins mediate chloroplast movement in Phalaenopsis orchid is blue light-dependent but their function is slightly different from Arabidopsis which might be due to gene evolution.
... This implies that, in some cases, pseudobulbs might also be capable of expressing some degree of CAM. Moreover, green aerial roots of epiphytic orchids also have the photosynthetic apparatus for CO 2 fixation (Ho et al., 1983;Moreira et al., 2009;Martin et al., 2010) as well as several morphological specializations, such as velamen and exodermis, both designed to trap and absorb water and nutrients (Pridgeon, 1986). However, aerial roots seem to play a minor photosynthetic role for epiphytes (Aschan and Pfanz, 2003), except for some leafless orchids with autotrophic roots. ...
... The view that aerial roots of leafy orchids possess the photosynthetic apparatus for CO 2 fixation but, in general, are not considered sufficiently autotrophic to maintain themselves (Ho et al., 1983;Hew et al., 1984) suggests a more localized role for the presence of CAM in aerial roots of Oncidium under water deficit. However, the larger chlorophyll-containing cells in the Oncidium cortex could provide the photosynthetic machinery and the vacuolar space required for nocturnally accumulating organic acids derived from CO 2 fixation through PEPC activity. ...
... chloroplasts are present in photosynthetic tissues but not in most roots), but studies in non-model plants have shown that these associations are not general. For example, chloroplasts are found in the stems and roots of some trees and orchids (Kwok-ki et al., 1983;Burrows and Connor, 2020). Even in plant model systems such as Arabidopsis, ectopic plastid differentiation has been observed under certain conditions, and these events have been exploited to uncover factors that participate in the differentiation and redifferentiation processes. ...
Plastids are a group of essential, heterogenous semiautonomous organelles characteristic of plants that perform photosynthesis and a diversity of metabolic pathways that impact growth and development. Plastids are remarkably dynamic and can interconvert in response to specific developmental and environmental cues functioning as central metabolic hub in plant cells. By far the best studied plastid is the chloroplast, but in recent years the combination of modern techniques and genetic analyses has expanded our current understanding of plastid morphological and functional diversity in both model and non-model plants. These studies have provided evidence of an unexpected diversity of plastid subtypes with specific characteristics. In this review we describe recent findings that provide insights into the characteristics of these specialized plastids and their functions. We concentrate on the emerging evidence that supports the model that signals derived from particular plastid types play pivotal roles in plant development, environmental, and defense responses. Furthermore, we provide examples of how new technologies are illuminating the functions of these specialized plastids and the overall complexity of their differentiation processes. Finally, we discuss future research directions such as the use of ectopic plastid differentiation as a valuable tool to characterize factors involved in plastid differentiation. Collectively, we highlight important advances in the field that can also impact future agricultural and biotechnological improvement in plants.
... A high presence of chloroplasts was recorded in the cortex. This aspect is well known for Laeliinae [67] and in general for epiphytic orchids; many species have evolved photosynthetic roots to increase photosynthetic areas and consequently carbon gain [72,79,80]. ...
In the context of a symbiotic plant-fungus interaction study concerning Cattleya purpurata, we focused on some aspects of seed morphology and biology, and the early stages of seedling development. Seed morphology was characterized using light and scanning electron microscopy. In vitro seed germination capability was evaluated, comparing symbiotic and asymbiotic methods. The morphology of the seeds was overall comparable to that of other congeneric species, showing classical adaptations related to the aerodynamic properties and to the wettability of seeds, but calcium oxalate druses were identified inside the suspensor cells. Asymbiotic seed germination was successful in all tested media (17.1–46.5%) but was higher on 1/2 Murashige & Skoog. During symbiotic interaction with the fungal strain MUT4178 (Tulasnella calospora), germination rate was significantly lower than that obtained with the best three asymbiotic media, suggesting a low fungal compatibility. Seedling morphology was in line with other taxa from the same genus, showing typical characteristics of epiphytic species. Our observations, in particular, highlighted the presence of stomata with C-shaped guard cells in the leaves, rarely found in Cattleyas (where usually they are reniform), and confirm the presence of tilosomes in the roots. Idioblasts containing raphides were observed in both roots and leaves.
... CAM photosynthesis is found in these plants as evidenced by diurnal cycling of acid levels [50]. The Photosynthetic pathways in roots may differ from those in leaves [51]. ...
Plants have leaves as specialised organs that capture light energy by photosynthesis. However, photosynthesis is also found in other plant organs. Photosynthesis may be found in the petiole, stems, flowers, fruits, and seeds. All photosynthesis can contribute to the capture of carbon and growth of the plant. The benefit to the plant of photosynthesis in these other tissues or organs may often be associated with the need to re-capture carbon especially in storage organs that have high respiration rates. Some plants that conduct C3 photosynthesis in the leaves have been reported to use C4 photosynthesis in petioles, stems, flowers, fruits, or seeds. These pathways of non-leaf photosynthesis may be especially important in supporting plant growth under stress and may be a key contributor to plant growth and survival. Pathways of photosynthesis have directionally evolved many times in different plant lineages in response to environmental selection and may also have differentiated in specific parts of the plant. This consideration may be useful in the breeding of crop plants with enhanced performance in response to climate change.
... In orchids, CAM photosynthesis is strongly associated with the epiphytic habit (Silvera et al., 2009), and many epiphytic orchids also have succulent leaves. While some epiphytic lineages, such as bromeliads, have reduced their root system to an anchoring function (Benzing, 2000), most orchid species evolved photosynthetic roots, a way to increase photosynthetic surface and hence carbon gain (Kwok-ki et al., 1983). Some 300 epiphytic orchid species rely exclusively upon root photosynthesis for carbon gain (Cockburn et al., 1985;Chomicki et al., 2014). ...
UV ‐ B radiation damage in leaves is prevented by epidermal UV ‐screening compounds that can be modulated throughout ontogeny. In epiphytic orchids, roots need to be protected against UV ‐ B because they photosynthesize, sometimes even replacing the leaves. How orchid roots, which are covered by a dead tissue called velamen, avoid UV ‐ B radiation is currently unknown.
We tested for a UV ‐ B protective function of the velamen using gene expression analyses, mass spectrometry, histochemistry, and chlorophyll fluorescence in P halaenopsis × hybrida roots. We also investigated its evolution using comparative phylogenetic methods.
Our data show that two paralogues of the chalcone synthase ( CHS ) gene family are UV ‐ B ‐induced in orchid root tips, triggering the accumulation of two UV ‐ B ‐absorbing flavonoids and resulting in effective protection of the photosynthetic root cortex. Phylogenetic and dating analyses imply that the two CHS lineages duplicated c . 100 million yr before the rise of epiphytic orchids.
These findings indicate an additional role for the epiphytic orchid velamen previously thought to function solely in absorbing water and nutrients. This new function, which fundamentally differs from the mechanism of UV ‐ B avoidance in leaves, arose following an ancient duplication of CHS , and has probably contributed to the family's expansion into the canopy during the Cenozoic.
The leafless orchids are rare epiphytic plants with extremely reduced leaves, and their aerial roots adopted for photosynthesis. The beneficial plant–microbial interactions contribute significantly to host nutrition, fitness, and growth. However, there are no data available on the bacterial associations, inhabiting leafless orchids. Here, we describe the diversity of cyanobacteria, which colonize the roots of greenhouse Microcoelia moreauae and Chiloschista parishii. The biodiversity and structure of the cyanobacterial community were analyzed using a complex approach, comprising traditional cultivable techniques, denaturing gradient gel electrophoresis (DGGE), and phylogenetic analysis, as well as the light and scanning electron microscopy (SEM). A wide diversity of associated bacteria colonize the root surface, forming massive biofilms on the aerial roots. The dominant populations of filamentous nitrogen-fixing cyanobacteria belonged to the orders Oscillatoriales, Synechococcales, and Nostocales. The composition of the cyanobacterial community varied, depending on the nitrogen supply. Two major groups prevailed under nitrogen-limiting conditions, belonging to Leptolyngbya sp. and Komarekiella sp. The latter was characterized by DGGE profiling and sequencing, as well as by its distinctive features of morphological plasticity. The leading role of these phototrophophic and diazotrophic cyanobacteria is discussed in terms of the epiphytic lifestyle of the leafless orchids.
For many years orchids have been among the most popular of ornamental plants, with thousands of species and hybrids cultivated worldwide for the diversity, beauty, and intricacy of their flowers. This book presents over thirty years of research. It describes the structure and relationships among the cells and tissues of leaves, stems, and roots, and is organized systematically in line with the taxonomy expressed in the Genera Orchidacearum Series. The book is illustrated with over 100 photomicrographs and numerous original line drawings.
Many plants have two root systems that differ in origin. One is the primary root system whose origin can be traced back to the radicle developed during embryogenesis. The other is an adventitious root system which arises on parts of the plant not originating from the embryonic root — that is, the roots arise on parts of the shoot. Adventitious roots usually initiate endogenously from tissue within the parent plant (see Chapter 4) though a few cases of exogenous origin are known [1]. Roots which arise on the primary root out of the usual acropetal sequence that characterises lateral roots, either as a normal part of development or after experimental treatment, are sometimes also called adventitious. The term adventive can perhaps be applied to such roots to distinguish them from roots of shoot origin.
The orchids represent one of the largest and most variable families in the plant kingdom. Probably no other family of flowering plants has attracted so much interest by professional botanists and hobbyists than the orchids. This interest has been aroused not only by the exotic beauty of these plants; the fascination derives also from the manifold mechanisms of ecological adaptation developed in the orchid family. Despite the extensive literature on orchids (for review, see Arditti 1979; Dressier 1981), many problems remain to be investigated. This concerns in particular the ecophysiology of orchids. It is our aim to discuss in this chapter a special problem in this field, namely the gas exchange and water relations of epiphytic orchids. Other fascinating aspects of adaptation linked with the epiphytic life of orchids, for instance the ecology of flowering, pollination, and seedling establishment are beyond the scope of our present review. For these aspects the aforementioned monograph by L. Dressier (1981) should be consulted.
