Choy Sin Hew

The uptake of cadmium by Brassica chinensis and its effect on plant zinc and iron distribution

Abstract A study was made of the uptake of cadmium in solution by an East Asian vegetable— Brassica chinensis (choy sam). Different levels of cadmium (0.1, 1.0 and 10.0 μg/ml) were applied to nutrient solutions and the metal concentration in the various parts of the plants measured. Iron and zinc levels of the plants were also analysed to determine the interelemental relationship among the metals. Cadmium was found to have been translocated to the foliar regions. Also, the uptake of zinc by plants grown in 0.1 μg/ml Cd increased over that of the control but decreased with higher levels of Cd concentration. Iron concentration in the plants rose with increasing levels of Cd, but chlorosis was observed. Reduced yield and chlorosis occurred at Cd concentrations of 1.0 μg/ml and above.

Orchid pseudobulbs - 'false' bulbs with a genuine importance in orchid growth and survival!

Most orchids have conspicuous storage organs. For epiphytic orchids, storage organs are enlarged stems called pseudobulbs. Considerable efforts have been devoted to the study of orchids in recent years. In contrast, few studies have examined the role of pseudobulbs in orchid growth and survival. This paper reviews the photosynthetic role of pseudobulbs, its role in partitioning of assimilates and storage of water, carbohydrate and minerals. Results from the handful of studies of orchid pseudobulbs have shown these specialised structures to be of central importance in the growth and survival of orchids.

The Production of Cytokinin, Abscisic Acid and Auxin by CAM Orchid Aerial Roots

Summary Aerial roots of two monopodial thick-leaved epiphytic orchids (Aranda and Vanda) are a posible source of endogenous plant hormones (abscisic acid, cytokinins, indole-3-acetic acid). Using a monoclonal antibody-based immunoasay, this study also revealed that the levels of plant hormones in root tips of Aranda could vary with root position along the stem, time and growth stages. The levels of plant hormones are usually higher in root tips than elsewhere in the roots. Higher levels of cytokinin (mainly isopentenyladenosine) were detected in root tips of flowering plants than in non-flowering plants of Aranda . Lateral aerial roots(s) could be induced by the removal of root tip. A posible role for these rootderived plant hormones is discused in relation to orchid growth and development.

Photosynthetic utilization of radiant energy by CAM Dendrobium flowers

Abstract14CO2 fixation was observed in orchid Dendrobium flowers; its rate decreased with the flower development. Chlorophyll (Chl) fluorescence in different developmental stages of flowers was compared to other green plant parts (leaf, inflorescence stalk, and fruit capsule). The photochemical efficiency of photosystem 2 (PS2) (Fv/Fm) of a leaf was 14-21 % higher than that of a mature flower perianth (sepal, petal, and labellum) which had a much lower total Chl content and Chl a/b ratio. A higher quantum yield of PS2 (ΦPS2) than in the mature flowers was observed in all green parts. Flower sepals had higher Chl content, Chl a/b ratio, and Fv/Fm values than the petal and labellum. During flower development the Chl content, Chl a/b ratio, Fv/Fm, and qN decreased while ΦPS2 and qP remained constant. An exposure of developing flowers to irradiances above 50 µmol m-2 s-1 resulted in a very drastic drop of ΦPS2 and qP, and a coherent increase of qN as compared to other green plant organs. A low saturation irradiance (PFD of 100 µmol m-2 s-1) and the increase in qN in the flower indicate that irradiation stress may occur since there is no further protection when the flower is exposed to irradiances above 100 µmol m-2 s-1. A low Chl/carotenoid ratio in mature flower perianth as a consequence of Chl content reduction in the course of flower development suggests a relief of irradiation stress via this mean.

Responses of Rubisco and sucrose-metabolizing enzymes to different CO2 in a C3 tropical epiphytic orchid Oncidium Goldiana

Abstract Experiments were conducted in controlled growth chambers to examine the responses of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), sucrose phosphate synthase (SPS) and sucrose synthase (SS), to long term CO 2 enrichment in the tropical epiphytic orchid hybrid Oncidium Goldiana. Furthermore, subsequent changes in activities of these enzymes were monitored following transfer to ambient air. After 2 months of growth, relative growth rate (RGR) in plants grown at elevated CO 2 doubled compared to those grown at ambient CO 2 . Concomitantly, there was a decline in Rubisco activity, Rubisco activation state and Rubisco protein content in CO 2 -enriched plants. In contrast, there was a significant up-regulation of SPS and SS activities. Both leaf sucrose and starch contents were significantly higher in plants grown at elevated CO 2 than that at ambient CO 2 , while leaf total nitrogen content was markedly lower in CO 2 -enriched plants. Following transfer to ambient CO 2 , leaf SPS and SS activities, sucrose and starch content in CO 2 -enriched plants declined sharply within 10 days to the same level of control plants without CO 2 enrichment. Contrary to our expectation, after 20 days of growth at ambient air, Rubisco activity in CO 2 -enriched plants remained much lower than that of control plants, although there was some increase of leaf Rubisco activity. This is primarily due to the consistently low levels of Rubisco protein content in the leaves. Leaf SPS activity was closely associated with leaf sucrose accumulation and SS activity was closely associated with starch accumulation. The activities of SPS and SS in leaf extracts were also closely associated with leaf assimilation rates. It is suggested that (1) the up-regulation of leaf SPS and SS activities might be an acclimation response to optimize the utilization and export of organic-carbon with the increased rate of inorganic-carbon fixation; (2) SPS and SS might play an important role in carbon partitioning between sucrose and starch in O. Goldiana under elevated CO 2 conditions.

Ancient Chinese orchid cultivation: A fresh look at an age-old practice

The ancient practices of ‘Lan’ (orchids) cultivation in China are reviewed, particularly those cultural methods widely practised during the Song (960‐1279 AD) and Ming (1368‐1644 AD) dynasties. These practices are examined in the light of our recent understanding of the physiology and horticultural practices of orchids. # 2001 Elsevier Science B.V. All rights reserved.

Changes in photosynthetic capability and carbohydrate production in an epiphytic CAM orchid plantlet exposed to super-elevated CO2

Abstract The effects on growth in super-elevated (1%) CO2 in terms of photosynthetic capability and carbohydrate production were studied in an epiphytic CAM (Crassulacean acid metabolism) orchid plantlet, Mokara Yellow (Arachnis hookeriana×Ascocenda Madame Kenny). The growth of the plantlets was greatly enhanced after growing for 3 months at 1% CO2 compared with the control plantlets (0.035% CO2). CO2 enrichment produced more than a 2-fold increase in dry matter production. The enhanced root growth at 1% CO2 led to a higher root:shoot ratio. Plantlets grown at super-elevated CO2 had higher Fv/Fm values, a higher photochemical quenching (qP) and a relatively lower non-photochemical quenching (qN). CO2 at 1% appeared to enhance the utilization of captured light energy in the orchid plantlets. CO2 enrichment also increased contents of soluble sugars (glucose and sucrose) and starch in the orchid plantlets. The extra starch formed under 1% CO2 did not cause a disruption of the chloroplasts. Chlorophyll content was higher and a clear granal stacking was evident in young leaves and roots of plantlets grown at 1% CO2. An extensive thylakoid system was observed in the young leaf chloroplasts of the CO2-enriched plantlets indicating an improved development of the photosynthetic apparatus when compared to that of the control plantlets. The increased photosynthetic capacity and enhanced growth of the epiphytic roots under CO2 enrichment would facilitate the generation of more photoassimilates and acquisition of essential resources, thereby increasing the survival rate of orchid plantlets under stressful field conditions.

Nitrogen uptake by tropical orchids

Abstract The uptake of nitrate and ammonium by two terrestrial orchids ( Bromheadia finlaysonia and Cymbidium sinense ) and an epiphytic orchid ( Dendrobium “White Fairy”) in solution culture was studied. The rates of uptake of nitrate and ammonium were linear, with a higher uptake rate for ammonium. The rates of nitrate uptake for Cymbidium and Bromheadia were in the range of 0.3–0.4 μmole g fw −1 hr −1 and for Dendrobium the rate was 0.9 μmole g fw −1 hr −1 . These rates were considerably lower than those of most major crops. SEM studies showed that the velamen of Bromheadia was two cells thick, whereas that of Dendrobium and Cymbidium was eight to 10 cells thick. It is unlikely that the velamen is the major factor in restricting the influx of nitrate or ammonium. Nitrate reductase (NR) and glutamine synthetase (GS) activity was present in the roots and leaves of the three orchids. NR activity was high in the roots but low in the leaves. The reverse was true for GS. The activity of NR and GS was low, but high enough to account for the rate of nitrate or ammonium uptake. It appears that the movement of ions across the transfer junction at the exodermis plays a major regulatory role in ion uptake by orchid roots.

Pattern of photoassimilate partitioning in pseudobulbous and rhizomatous terrestrial orchids

Abstract Photoassimilate partitioning patterns in two terrestrial orchids, Spathoglottis unguiculata and Bromheadia finlaysoniana , were mapped using a 14 CO 2 dosing technique. A highly integrated source-sink photoassimilate partitioning pattern was observed in both orchids. In S. unguiculata , a pseudobulbous terrestrial orchid, all test leaves supplied similar percentages of 14 C-assimilates to all plant parts on a single shoot. In both orchids, the inflorescence during the reproductive stage and the axillary bud during the vegetative stage had the highest sink activity and percentage distribution of 14 C-assimilates. A high percentage of 14 C-assimilates was imported by the pseudobulb of S. unguiculata . The pseudobulb accumulated a higher percentage of 14 C-assimilates (44%) during the vegetative stage than during the flowering stage (21–30%). In B. finlaysoniana , a rhizomatous terrestrial orchid, a high percentage of 14 C-photoassimilates was observed in the stem internodes at all three developmental growth stages (the vegetative stage (stage 1), the flowering stage (stage 2) and the fruiting stage (stage 4)). Sink activities of the rhizome were higher at stages 1 and 4 than at stage 2. A similar pattern of photoassimilate partitioning was observed for B. finlaysoniana grown naturally in its habitat. A polar movement of 14 C-assimilates towards the major sink (inflorescence) was observed in the current shoot of field plants with a competing sink (axillary bud).

Physiology of Cymbidium sinense: A review

Cymbidium sinense is a popular terrestrial orchid in South China. Research involving photosynthesis, photoassimilate partitioning, respiration, water relation, mineral nutrition, growth and development of this orchid are reviewed. It is suggested that understanding C. sinense physiology may be helpful to the improvement of cultivation techniques.