Polysaccharide synthesis by Phanerochaete chrysosporium during degradation of kraft lignin

Summary Phanerochaete chrysosporium (Sporotrichum pulverulentum) produced an extracellular glucan type polysaccharide when grown in a chemostat under nitrogen limitation. When cells were transferred to a standing mode of cultivation in the presence of excess glucose (6 gl^–1), the amount of non-glucose total carbohydrates in the culture increased from 0.58 gl^–1 to 1.76 gl^–1 during 15 day experiments. The change in total carbohydrates was due to an increase in extracellular and cell-bound glucan type polysaccharide. This increase occured simultaneously with formation of mycelial mats and appearance of ligninolytic activity. When the cultures were agitated under atmospheric oxygen rather than 100% O₂, their non-glucose total carbohydrate content increased to 2.15 gl^–1 in 4 days. The excess polysaccharide formation had an inhibitory effect on lignin degradation as more lignin was degraded by cells with lower polysaccharide content. The lignin that was associated with cells after the degradation had stopped could be further degraded by new active cells.     

The effect of humus substances on the level of free amino acids in wheat plants

The presence of potassium humate (commercial sample of Humussäure Riedel-de Haën A. G., Seelze-Hannover) in distilled water led to an increase in the content of alanine, aspartic and glutamic acid in the overground parts of wheat plants as compared with the content of these substances in control plants grown in distilled water. In plants cultivated on nutrient solutions a higher level of alanine and glutamic acid and a considerably lower level of amides was found than in plants grown in distilled water and in water with humate. Generally the content of amino acids was higher in the overground parts than in the roots after a cultivation period of one week as well as of 14 day. In the overground parts of 1 days old plants the level of aspartic acid, asparagine and alanine was found to be higher and that of glutamine lower than in seven days old plants. In the roots of the examined plants a decrease of the amino acid content accurred almost in all cases after a cultivation period of 14 days as compared to one of 7 days.     

Effects of dietary β-1,3-glucan, chitosan or raffinose on the growth, innate immunity and resistance of koi (Cyprinus carpio koi)

This study was performed to determine the efficacy of three immunomodulators viz., β-1,3 glucan, chitosan and raffinose on the innate immune response of koi, Cyprinus carpio koi. Kois were divided into 4 groups and each group was fed with diets supplemented with or without immunostimulant for 56 days. Total leukocyte counts (WBC), the non-specific humoral (lysozyme, alternative complement pathway and superoxide dismutase) and cellular (phagocytic capacity and respiratory burst activity) responses were determined and compared with controls (no supplement) after 7, 14, 21 and 56 days of feeding. The results of 8 weeks feeding trial showed that β-1,3 glucan supplementation significantly enhanced koi growth, whereas other immunostimulants did not. Variation in the levels of responses was?evident among different supplements. Compared with chitosan or raffinose, β-1,3 glucan could maintain the immunity of kois at a higher level during the experimental period. However, continuously applying β-1,3 glucan, chitosan or raffinose into the diet caused immunity fatigue in koi. No significant change in alternative complement pathway (ACP) activity was observed for any of the three supplements over the four different periods. After feeding for 14 days, the total leukocyte count (WBC), respiratory burst activity and superoxide dismutase (SOD) activity of the kois fed with chitosan or raffinose continuously remained relatively unchanged, subsequently decreased on the 56th day, but SOD did not. Meanwhile, lysozyme activity was no longer significantly higher on the 7th day, and for phagocytic capacity on the?14th day. After 56 days, these three immunostimulants groups also exhibited a decrease in the cumulative symptom rates compared to the controls when challenged with Aeromonas veronii. These results indicated that dietary intake containing immunostimulants could enhance the immune responses of koi and improve its resistance to infection by A.veronii. Especially supplementation with β-1,3 glucan to the kois for 56 days showed considerable improvement in the growth, survival and immune response of the kois.     

Cryptococcus neoformans responds to mannitol by increasing capsule size in vitro and in vivo

The polysaccharide capsule of the fungus Cryptococcus neoformans is its main virulence factor. In this study, we determined the effects of mannitol and glucose on the capsule and exopolysaccharide production. Growth in mannitol significantly increased capsular volume compared with cultivation in glucose. However, cells grown in glucose concentrations higher than 62.5 mM produced more exopolysaccharide than cells grown in mannitol. The fibre lengths and glycosyl composition of capsular polysaccharide from yeast grown in mannitol was structurally different from that of yeast grown in glucose. Furthermore, mannitol treatment of mice infected intratracheally with C. neoformans resulted in fungal cells with significantly larger capsules and the mice had reduced fungal dissemination to the brain. Our results demonstrate the capacity of carbohydrate source and concentration to modify the expression of a major virulence factor of C. neoformans. These findings may impact the clinical management of cryptococcosis.     

Structure of extracellular polysaccharide produced by lignin-degrading fungus Phlebia radiata in liquid culture

The extracellular material (EM) produced by the white rot fungus Phlebia radiata cultured in an N-limited liquid medium was studied. Carbohydrate analysis showed maximum concentration of glucose as the major monosaccharide component of EM was found on postinoculation day 9. Beyond day 9 of cultivation the proportion of glucose decreased suggesting that the glucan component of EM had been further metabolized. The analysis of EM at day 9 revealed the presence of the following monosaccharides (in relative %): glucose (62); galactose (16); mannose (13); xylose (4); and fucose (5). The carbohydrate analysis together with the presence of protein in EM corresponds to a mixture of glucan and glycoprotein. Purification by trypsin treatment yielded an enriched glucose-containing extracellular polysaccharide (EPS). Methylation analysis identified EPS as (1-3)-beta-D-glucan highly branched at C-6. The structure of the glucan was confirmed by 13C-NMR spectroscopy. The results suggest that P. radiata's EPS is entangled with a glycoprotein in a complex that makes the extracellular sheath surrounding the hyphae.     

Vectoring of Pepino mosaic virus by bumble‐bees in tomato greenhouses

Pepino mosaic virus (PepMV) has become an important viral disease of greenhouse tomatoes worldwide. The ability of bumble‐bees (Bombus impatiens), used for pollination, to acquire and transmit PepMV was investigated, and the prevalence of PepMV in plants and bumble‐bees in commercial tomato greenhouses was determined. PepMV infection in plants was determined using enzyme‐linked immunosorbent assay, while in bumble‐bees direct real‐time PCR was used. In the first experiment, the bumble‐bees were exposed for 14 days to PepMV‐infected plants. After 14 days, almost all bumble‐bees were PepMV positive both in the hive (78.5 ± 17.5%) and in the flowers (96.3 ± 3.6%). In the second experiment, bumble‐bees were released into a greenhouse with both PepMV‐infected source plants and healthy non‐infected target plants for 14 days. At the end of the experiment, 61.0 ± 19.5% of the bees collected from the hive and 83.3 ± 16.7% of the bees sampled from the flowers were PepMV positive. Bumble‐bees transmitted PepMV from the infected to the healthy non‐infected tomato plants. Two weeks after bumble‐bee release, the virus was detected in leaf, fruit and flower samples of formerly healthy plants. After 6 weeks, the percentage of PepMV positive samples from the target plants increased to 52.8 ± 2.8% of the leaves and 80.6 ± 8.4% of the fruits. In the control greenhouse without bumble‐bees, the target plants did not become infected. Based on the infection levels in flowers, fruits and leaves, the PepMV infection occurred possibly first in the pollinated flowers, and then spread from the fruit that developed from the flowers to other parts of the plant. In commercial greenhouses where PepMV was present, 92–100% of the plants and 88–100% of the bumble‐bees were PepMV positive. No infected plant samples were found in the control commercial greenhouse, but a small number of bumble‐bees (10%) tested PepMV positive.     

In vitro system for studying interactions between Citrus exocortis viroid and Gynura aurantiaca (Blume) DC. metabolism and growing conditions

Citrus exocortis viroid (CEVd) is an economically important plant pathogen, which infects a broad range of hosts. In order to investigate complex interactions among viroid, host-growing conditions, and plant secondary metabolism, we setup an in vitro system for the cultivation of CEVd-infected and viroid-free Gynura aurantiaca (Blume) DC. shoots. Both basal Murashige and Skoog (MS) medium and MS medium supplemented with cytokinines supported the growth of shoots, but viroid-free shoots performed better than infected ones. The addition of cytokinines induced an increase in the concentration of purple-reddish pigment, cyanidin tetra-glucoside (GAA), which did not depend on the presence of viroid. The differences in single strand conformation polymorphism patterns between CEVd sequence variants obtained from plants grown on medium supplemented with cytokinines and those obtained from plants grown on basal MS medium or in the greenhouse, indicated that cytokinines may influence not only the plant metabolism, but also the viroid population structure.     

High level accumulation of α-glucan in maize kernels by expressing the <Emphasis Type="Italic">gtfD</Emphasis> gene from <Emphasis Type="Italic">Streptococcus mutans</Emphasis>

Glucosyltransferases (GTFs, EC.2.4.1.5) are bacterial enzymes that catalyze the polymerization of glucose residues from sucrose, leading to the production of high molecular weight glucan with α-1,3 /α-1,6 linkages. Such glucans, with many potential food and industrial applications, do not normally exist in higher plants. We fused a mutant form of the gtfD gene from Sreptococcus mutans with the maize (Zea mays L.) chloroplastic Brittle 1 transit peptide for amyloplast targeting. This construct, driven by the ubiquitin promoter, was introduced into maize by Agrobacterium-mediated transformation. We developed a novel HPLC-based method that enabled us differentially to distinguish transgene glucan from other endogenous polysaccharides in maize kernels. Using this method, we screened over 100 transgenic plants for the presence of GTF-produced glucan whose content varied between 0.8 and 14% of dry weight in the mature transgenic seeds. The mature transgenic plants were indistinguishable from wildtype plants in growth rate and morphology. Furthermore, starch granule size in the transgenic maize kernel was unaffected by the accumulation of the foreign polysaccharide. Mutation in Sh2, which encodes a subunit of ADP-glucose pyrophosphorylase, had no effect on glucan accumulation caused by gtfD expression. Our results indicated that high levels of novel carbohydrate polymer can be accumulated in crop plants through transgene technology.     

The effect of NO3- and NH4 + ions on enzymes involved in nitrogen assimilation inPisum sativum L

Nitrate reductase level in leaves of pea plants is higher than in roots despite of the lower content of endogenous nitrate. Addition of ammonium ions to nutrient solution containing nitrate decreases nitrate reductase level in leaves estimatedin vivo while its level estimatedin vitro is increased. Glutamine synthetase (GS) level in roots decreases during short (24 and 48 h) and long (14 d) term cultivation of seedlings in solutions containing ammonium ions. This decrease occurs in leaves only after the long term influence of ammonium ions. Level of this enzyme is higher in plants grown in the presence of nitrogen (ammonium and nitrate) as compared to those grown without the nitrogen. Level of glutamate dehydrogenase in roots is increased after both short and long term cultivation of plants in the presence of ammonium ions.     

EFFECTS OF SINGLE AND MULTIPLE EXPOSURES OF FERULIC ACID ON THE VEGETATIVE AND REPRODUCTIVE GROWTH OF PHASEOLUS VULGARIS BBL-290

Phaseolus vulgaris BBL-290 plants were grown in growth chambers in the Southeastern Plant Environment Laboratory and exposed to either single (at seedling, flower, or podfill) or multiple (biweekly or weekly) treatments of ferulic acid (FA). In the first experiment, plants were harvested one week after FA treatment (0, 1.0, 2.0 mM) and at final harvest (56 days old). FA delayed leaf expansion during the seedling and flowering stages. The total plant leaf area and the plant dry weight of plants treated with 1.0 and 2.0 mM FA as seedlings were reduced one week after treatment by 38–48%. The total plant leaf area and the plant dry weight of plants treated at flowering with 2.0 mM FA were reduced by 25% one week after treatment. Treatment with 2.0 mM FA at podfill caused the senescence and abscission of older leaves and reduced total plant leaf area, plant dry weight and mean pod dry weight by 54, 40, and 48%, respectively, one week after treatment. The plants treated at the seedling and flowering stages recovered by final harvest. In a subsequent experiment, FA (0, 0.50, 1.0, 1.5 mM) reduced total plant leaf area at the seedling and flowering stages but not at podfill. The youngest expanding leaves were most sensitive to FA at flowering. The leaf area of these leaves was reduced by 35 and 25%, one and two weeks after treatment, respectively. Their absolute growth rates were reduced from 31 to 56% one week after treatment at flowering. Their relative growth rates were reduced by 50% one week after treatment. Growth rates then recovered within two weeks after treatment. In the final experiment, biweekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area but did not affect any other growth parameters. Weekly exposures of FA (0.25, 0.50, 0.75, 1.0) reduced total plant leaf area up to 34%, absolute growth rate up to 58%, leaf number up to 31% and pod number up to 58%. As the frequency of exposure to FA increased, the concentration necessary to affect bean plant growth and development decreased.     

Biochar successfully replaces activated charcoal for in vitro culture of two white poplar clones reducing ethylene concentration

Biochar (BC) is a carbon rich product resulting from the biomass pyrolysis process and there have been no reports until now on BC effects in tissue cultures as a suitable substitute for activated charcoal (AC). The results of an experiment on two clones of white poplar (Populus alba L.) grown in culture media with different amounts of BC (0, 0.5 and 1.5?g/dm³) showed that its addition did not damage the plants and there were no significant differences comparing the data obtained for the same concentrations of AC. Both BC and AC addition was shown to increase root dry biomass and number of roots per shoot and these effects appeared to be independent of genotype and concentrations of the added products. A greater elongation was also recorded for shoots grown on a substrate containing BC than those grown on media without BC. These effects did not seem to be caused by darkening due to the addition of BC as there are no significant differences between the temperatures of the different culture media, but are probably due to the adsorption of molecules such as ethylene. Indeed, during the experiment, the hormone concentration in the atmosphere was lower in vials containing the media with BC than the BC-free ones after 14 and 21?days: the lower amount of ethylene in the medium with BC could explain the difference in shoot elongation and the abundant root biomass since high ethylene concentration could inhibit organogenesis.     

Production of flavonoids and polysaccharide by adding elicitor in different cellular cultivation processes of Glycyrrhiza uralensis Fisch

In this study, callus and cell suspension were induced from seedlings of licorice (G. uralensis). In addition, it was revealed that the appropriate concentration of sucrose could promote the callus growth and increase the content of polysaccharide. The methyl jasmonate (MJ) and phenylalanine (PHE) could enhance the callus growth and content of flavonoids for G. uralensis. For producing more flavonoids and polysaccharide, two-stage cultivation was performed. In the first step, 30 g L^?1 sucrose was fed into a 5-L balloon-type bubble bioreactor on 8th day of culture to enhance cell production and metabolite production. In a two-stage cultivation process, PHE (2 mM) and MJ (5 mg L^?1) were added into a 5-L balloon-type bubble bioreactor after 10 days of culture. Using a fed-batch cultivation strategy (30 g L^?1 sucrose was fed into a 5-L balloon-type bubble bioreactor on 8th day), polysaccharide production was enhanced to 1.19 g L^?1, which was 2.12-fold greater than that in batch cultivation. The flavonoids yield (55.42 mg L^?1) which was about 22 % higher than that in batch cultivation was obtained on 21st day. In a two-stage cultivation process, the polysaccharide content was increased by 1.14- and 2.12-fold compared with fed-batch cultivation and batch cultivation on 15th day. Meanwhile, total flavonoids yield (132.36 mg L^?1) on 15th day, was increased by 2.26- and 2.67-fold compared with fed-batch cultivation and batch cultivation. In conclusion, two-stage cultivation process combined with the sucrose and elicitor treatment could promote both the callus growth and the secondary metabolites accumulation.     

EARLY STARVATION1 specifically affects the phosphorylation action of starch‐related dikinases

Starch phosphorylation by starch‐related dikinases glucan, water dikinase (GWD) and phosphoglucan, water dikinase (PWD) is a key step in starch degradation. Little information is known about the precise structure of the glucan substrate utilized by the dikinases and about the mechanisms by which these structures may be influenced. A 50‐kDa starch‐binding protein named EARLY STARVATION1 (ESV1) was analyzed regarding its impact on starch phosphorylation. In various in vitro assays, the influences of the recombinant protein ESV1 on the actions of GWD and PWD on the surfaces of native starch granules were analyzed. In addition, we included starches from various sources as well as truncated forms of GWD. ESV1 preferentially binds to highly ordered, α‐glucans, such as starch and crystalline maltodextrins. Furthermore, ESV1 specifically influences the action of GWD and PWD at the starch granule surface. Starch phosphorylation by GWD is decreased in the presence of ESV1, whereas the action of PWD increases in the presence of ESV1. The unique alterations observed in starch phosphorylation by the two dikinases are discussed in regard to altered glucan structures at the starch granule surface.     

Trichoderma spp. as elicitors of wheat plant defense responses against Septoria tritici

Leaf blotch of wheat is a widespread and highly active disease that affects wheat production. In addition to the use of chemicals and proper cultivation methods, microbial antagonists are used to control plant pathogens. Trichoderma spp. stimulate a systemic induced response in plants. Therefore, the efficacy of Trichoderma spp. against wheat leaf blotch was evaluated under greenhouse conditions. The susceptible plants were sprayed with Septoria tritici conidiospores. In order to select an efficient method of pretreatment with Trichoderma spp., leaf spraying and seed coating with 14 isolates were tested in 2003 and 2004. The extent of leaf necrosis area and pycnidial coverage was estimated. Antagonism was assessed by the capacity of each Trichoderma spp. isolate to restrict the progress of leaf blotch, 21 days after inoculation. Of the two methods, seed coating was more efficacious against leaf blotch than leaf spraying. Amongst the 14 isolates tested, the isolate prepared from T. harzianum (Th5) produced the highest level of protection. None of the treatments caused changes in plant stem diameter or dry weight. Trichoderma spp. did not get into leaves while S. tritici was present, even in asymptomatic leaf extracts. In addition, the leaf apoplast antifungal proteolytic activity was measured in plants 7, 15, and 22 days after sowing. This antifungal action decreased in plants only inoculated with S. tritici, but increased in those grown from seeds coated with the T. harzianum (Th5) isolate. This increase conferred resistance to the susceptible wheat cultivar. The endogenous germin-like protease inhibitor coordinated the proteolytic action. These results suggest that T. harzianum stimulates a biochemical systemic induced response against leaf blotch.     

Changes in composition of harvested mushrooms (Agaricus bisporus)

Post-harvest changes in the biochemical composition of the mushroom were studied. Non-structural polysaccharide was found at levels greater than 10% dry wt in the fresh mushroom. After 4 days storage, the level had decreased to below 5% dry weight. The polysaccharide appeared to contain only glucose residues joined by α-1,4 and α-1,6 linkages. The chitin content of cell walls increased by ca 50% during 4 days storage, while cell wall glucan decreased. There was a large increase in urea content.     

Interactions between the unicellular red alga Rhodella reticulata (Rhodophyta) and contaminated bacteria

AIMS: To define the role of the bacterial strains LR1 and LR3 in the Rhodella cell destruction caused by Cytophaga sp.LR2. METHODS AND RESULTS: The bacteria were obtained from algal culture with destruction. They were isolated in pure culture and tested for biochemical activities using Polymicrotest. The ability of bacteria to degrade and utilize the algal polysaccharide was investigated. The bacteria were grown in a media containing Rhodella polysaccharide as a sole carbon source. The level of the reducing sugars in the culture media was determined. Scanning electron microscopy (SEM) was used to define the location of bacteria in extensively and intensively cultivated Rhodella reticulata previously infected by Cytophaga sp. LR2. CONCLUSIONS: The lysis of Rhodella reticulata cells is due to the joint action of the three bacterial strains with the former pathogen Cytophaga sp. LR2 playing the main role. The accumulation of the polysaccharide and the excreted metabolites of the strains LR1 and LR3 stimulated the development of Cytophaga sp. LR2. The adaptation of the strain to particular conditions of alga cultivation and the utilization of polysaccharide as a sole carbon source supported its stable growth in alga suspension and destruction of Rhodella cells. SIGNIFICANCE AND IMPACT OF THE STUDY: The predominance of Cytophaga sp. LR2 over the two other contaminants and the lysis of Rhodella reticulata cells resulted from the ability of the bacterium to attach to the algal polysaccharide sheath. The formation of slime and extrusions facilitated the phenomenon of bacterial adhesion to the algal surface as well as the formation of colonial alga - bacterial spherules. The sedimentation of these aggregates decreased the ability of the algal strain to photosynthesize, led to the lysis of the cells and finally caused the death of Rhodella.     

Effects of Temperature on the Growth and Physiological Characteristics of Dendrobium officinale (Orchidaceae)

In this paper, we studied the response of photosynthesis and growth in Dendrobium officinale to temperature under the control experiment to provide a theoretical basis for its cultivation. Temperature had a significant effect on the photosynthetic rate (Pn) of Dofficinale. The light saturated photosynthesis at ambient CO2 concentration (Pmax) of the plants were highest at 30℃. High photosynthetic rate at 30℃ were related to the more balance between the maximum rate of electron transport and maximum rate of RuBP mediated carboxylation. Moreover temperature also showed a significant effect on the growth and polysaccharide content of D.officinale′s stem. The polysaccharide content of Dofficinale at 20℃ was significantly higher than that at other temperatures, while the stem length, stem node number, stem fresh weight and stem dry weight were achieved the highest point at 30℃. The results showed that, the temperature of 30℃ was more appropriate for the photosynthesis of Dofficinale, while the plants at 20℃ have higher polysaccharide content.     

Carbohydrate metabolism of cactus in a desert environment

The concentration of glucan, mucilage, soluble carbohydrates, and malic acid were determined in Opuntia bigelovii Engelm. during a 23-week period. The experiment began during the dry summer by irrigation to stimulate Crassulacean acid metabolism and was followed by 13 weeks of drought. After the 13-week drought period, the plants were irrigated throughout a 10-week period until late December. The maximum level of malic acid determined each day at dawn decreased throughout the drought period and increased after irrigation. High levels of malic acid occurring at dawn are indicative of active Crassulacean acid metabolism. Soluble carbohydrates also decreased during drought and increased after irrigation. Both glucan and mucilage increased slightly for about 9 weeks during the drought period and then began to decrease. Irrigation was accompanied by a further decrease in concentration of glucan and mucilage. Since both glucan and mucilage changed in a similar manner and since their concentrations in the tissue are correlated, it is hypothesized that both function as storage carbohydrates. Whereas glucan is the nocturnal substrate for malic acid synthesis, there are no data to support or refute a similar hypothesis for mucilage.     

Differential inhibition of branching enzyme in a morphological mutant and in wild type Neurospora. Influence of carbon source in the growth medium.

1. A morphological mutant of Neurospora crassa, smco 9, (R2508) that exhibits colonial morphology when grown on sucrose or on maltose, showed a partial reversal of this morphology toward that of the wild type when it was grown on potato starch or on isomaltose. 2. A common feature of both potato starch and isomaltose is the presence of alpha-1, 6 glucosidic linkages. This suggested that these morphological effects might be due to differences in alpha-1,4 glucan: alpha-1,4 glucan 6 glycosyltransferase, (EC 2.4.1.18) commonly known as "the branching enzyme". 3. The branching enzyme was purified from wild type, Neurospora crassa, and from the semicolonial mutant, R2508, both grown on sucrose or on potato starch. It has a molecular weight of 140,000 as estimated by gel filtration on a Bio Gel A 1.5 m column. This enzyme plus phosphorylase a in an unprimed reaction catalyzes the synthesis of a branched polysaccharide in vitro. 4. No branching enzyme activity was apparent in extracts of the mutant R2508, grown on potato starch until a thermolabile inhibitor was removed by fractionation on a DEAE column. 5. This inhibitor has a molecular weight greater than 100,000 as estimated on a P-100 polyacrylamide gel column. The specificity of the inhibitor is not absolute in that it inhibits glycogen synthetase in addition to the branching enzyme in Neurospora.     

Influence of some metal chelators and light regimes on bioaccumulation and toxicity of Cd2+ in duckweed (Lemna gibba)

A factorial culture experiment was designed to investigate the influence of light regimes and of some metal chelators on the accumulation of cadmium by Lemna gibba L. The plants were grown in a complete nutrient solution containing Cd²⁺ concentrations ranging from 0 to 27 μ M with or without EDTA, ethylenediamine-N,N'- bis -( o -hydroxyphenylacetic acid) (EDDHA) or salicylic acid. Each experiment was run for eight days in 18 h:6 h light:dark or continuous light. An increase in the Cd²⁺ concentration in plants and a simultaneous drop in accumulation efficiency (ratio of Cd²⁺ concentration in plants to the initial Cd²⁺ concentration in the nutrient solution) with increasing ambient Cd²⁺ levels was best represented by regression power curves. At the lowest Cd²⁺ concentration which caused a significant decrease in the relative growth rate of duckweed, there was a decrease in manganese and zinc and an increase in the iron level in the plants. EDDHA and EDTA protected in some cases against the toxic action of cadmium without preventing its uptake by plants. It was thus observed that 9 μ M or higher levels of Cd²⁺ were toxic to Lemna gibba depending on the chelator and light regime. Duckweed grown in continuous light produced, in general, more dry matter and hence accumulated more cadmium.