Differential invertase activity and root growth between Cu-tolerant and non-tolerant populations in Kummerowia stipulacea under Cu stress and nutrient deficiency

There has been no study on key enzymes in sucrose cleavage in metallophyte plants so far, which may be crucial for the plants’ root growth and heavy-metal tolerance maintenance. Here, we tested the hypothesis that the roots of copper tolerant plants should manifest a higher activity of acid invertases that are rate-limiting in sucrose catabolism than non-tolerant plants both for supporting growth and for their maintaining tolerance under Cu stress. Two populations of Kummerowia stipulacea, one from an ancient waste heap at a Cu mine, and the other from a non-contaminated site, were used in the experiments. The plants were grown in 1/2-fold (control) or 1/20-fold (nutrient deficiency) Hoagland’ solution, with (Cu stress) or without (control) 10 μmol/L Cu²⁺. Plants from the mine proved to be of Cu tolerance. Cu exposure had a stronger inhibition on root growth and thus resulting in a lower root/shoot ratio in the plants of non-mine population compared to the mine population. Cu exposure showed a stronger inhibition of acid invertase activity of Cu non-tolerant plants than Cu-tolerant plants, while neutral/alkaline invertase was insensitive to Cu. A positive correlation between the activity of acid invertases and the root growth and root/shoot ratio was observed. The results indicated an important role of acid invertases in governing root growth and root/shoot biomass allocation in the plants of mine population. The results also suggested that the higher activities in acid invertases of mine population plants might at least partly associate with the plants’ Cu tolerance, and their higher activities in acid invertases in turn played an role in maintenance of the Cu tolerance by supplying carbon and energy for tolerance mechanisms. In addition, the results showed evidence that neutral/alkaline invertase might play a role in compensating for the depression in sucrose catabolism due to Cu-induced inhibition in acid invertases.     

Eco-service enhancement in peri-urban area of coal mining city of Huaibei in East China

After 50 years of coal mining, Huaibei Mine, located at 50 km southeast of Xuzhou City in East China, has grown to a middle-size city of 600,000 people from a small village of 2000 farmers. The Zhahe Valley, with 400 km² of a built-up area and more than 100 km² of subsided peri-urban wetland at the city center, is surrounded by eight exhausted old mines and communities. In cooperation with the local city government, an ecological landuse change assessment and eco-city planning project has been carried out with a focus on the assessment, restoration and enhancement of the wetland as an eco-service to the community. The assessment includes relationships to Green House Gas emissions and heat island effects, as well as measures for a livable, workable, affordable and sustainable human settlement development through industrial transition, landscape design and capacity building. This paper will briefly introduce the main ecological approaches and results of the assessment, including measures such as changing the car-dominated transportation network to a rail-dominated network, transforming the coal-oriented high-carbon industry to a service-oriented low-carbon industry, the C-shape urban form to an O-shape with a green–blue core at the center, and the fragmentized collapsed land to integrative eco-service land.     

Heavy metal accumulation in iron plaque and growth of rice plants upon exposure to single and combined contamination by copper, cadmium and lead

A pot experiment was conducted to evaluate the bioaccumulation of heavy metals and growth response of rice plants after exposure to single and combined contamination by Cu, Cd and Pb. The results showed that the biomass production was not significantly affected by either single or combined treatment of Cu, Cd and Pb. Adding Cu (Cd, or Pb) separately all increased concentrations of the respective element in root and shoot (p < 0.001). In the combined contamination, Pb promoted both root and shoot absorption of Cu and Cd (p < 0.001), and Cu affected Cd and Pb absorption in the root, but Pb concentrations in both root and shoot were not affected by Cd application. The formation of iron plaques varied obviously with soil types. Heavy metal accumulation in iron plaques was induced by the three elements (p < 0.001). Furthermore, the three heavy metals exhibited an interactive relationship as measured by the Cu, Cd, Pb and Fe concentrations in root surface iron plaques. The iron plaques partially inhibited transfer of Pb to root and shoot, but no such effect was observed for Cu and Cd. This research indicates that the interaction among different heavy metal elements is very complex. It is very important to have a clear understanding on the associated mechanism and the consequential impact on plant growth.     

Heavy metal accumulation in iron plaque and growth of rice plants upon exposure to single and combined contamination by copper, cadmium and lead

A pot experiment was conducted to evaluate the bioaccumulation of heavy metals and growth response of rice plants after exposure to single and combined contamination by Cu, Cd and Pb. The results showed that the biomass production was not significantly affected by either single or combined treatment of Cu, Cd and Pb. Adding Cu (Cd, or Pb) separately all increased concentrations of the respective element in root and shoot (p < 0.001). In the combined contamination, Pb promoted both root and shoot absorption of Cu and Cd (p < 0.001), and Cu affected Cd and Pb absorption in the root, but Pb concentrations in both root and shoot were not affected by Cd application. The formation of iron plaques varied obviously with soil types. Heavy metal accumulation in iron plaques was induced by the three elements (p < 0.001). Furthermore, the three heavy metals exhibited an interactive relationship as measured by the Cu, Cd, Pb and Fe concentrations in root surface iron plaques. The iron plaques partially inhibited transfer of Pb to root and shoot, but no such effect was observed for Cu and Cd. This research indicates that the interaction among different heavy metal elements is very complex. It is very important to have a clear understanding on the associated mechanism and the consequential impact on plant growth.     

Cadmium and copper interactions on the accumulation and distribution of Cd and Cu in birch (Betula pendula Roth) seedlings

The effect of different external cadmium (Cd) and copper (Cu) regimes on the concentration of Cd and Cu in roots and shoots of birch (Betula pendula Roth.) seedlings was investigated. The seedlings were grown for 12 days in a weak nutrient solution (containing all essential nutrient elements including 0.025 µM Cu) at pH 4.2 with combinations of additional 0–2 µM CdCl₂ and 0–2 µM CuCl₂. Root and shoot concentrations of Cu were decreased by Cd in all treatments which included 0.1–2 µM of additional Cu in the treatment solution. When no extra Cu was added, only the shoot concentration of Cu was decreased by Cd whereas the root concentration was not affected. The shoot concentration of Cd was decreased by 0.5 and 2 µM of additional Cu in the treatment solution. The root concentration of Cd was decreased by Cu only when the concentration of additional Cu in the treatment solution was equal to or exceeded the concentration of Cd.     

How do plants respond to nutrient shortage by biomass allocation?

Plants constantly sense the changes in their environment; when mineral elements are scarce, they often allocate a greater proportion of their biomass to the root system. This acclimatory response is a consequence of metabolic changes in the shoot and an adjustment of carbohydrate transport to the root. It has long been known that deficiencies of essential macronutrients (nitrogen, phosphorus, potassium and magnesium) result in an accumulation of carbohydrates in leaves and roots, and modify the shoot-to-root biomass ratio. Here, we present an update on the effects of mineral deficiencies on the expression of genes involved in primary metabolism in the shoot, the evidence for increased carbohydrate concentrations and altered biomass allocation between shoot and root, and the consequences of these changes on the growth and morphology of the plant root system.     

Copper tolerance in Silene cucubalus

The uptake, translocation and subcellular distribution of copper as well as its effect on chloroplasts and plastocyanin synthesis were studied in a copper-sensitive and a copper-tolerant population of Silene cucubalus (L.) Wib. As a function of time, the copper concentration in roots of tolerant plants increased more slowly than that in roots of sensitive ones. Translocation to the shoot occurred more rapidly in tolerant plants than in sensitive ones. Although it was accumulated in leaf cells, copper was not accumulated in the chloroplasts of either sensitive or tolerant plants. Chlorophyll content was not affected by copper in tolerant plants, whereas sensitive plants became chlorotic. Plastocyanin synthesis was not enhanced as a result of high copper concentrations and no difference in plastocyanin content between tolerant and sensitive plants was detected. Measurements of copper in purified cell walls revealed that storage of the metal in cell-wall material does not play an important role in tolerance mechanism. Uptake characteristics, distribution and cytoplasmic detoxification of copper are discussed.     

Cadmium accumulation in sunflower plants influenced by arbuscular mycorrhiza

In order to investigate the cadmium (Cd) accumulation patterns and possible alleviation of Cd stress by mycorrhization, sunflower plants (Helianthus annuus L.) were grown in the presence or absence of Cd (20 micromol L(-1)) and inoculated or not inoculated with the arbuscular mycorrhizal fungus (AMF) Glomus intraradices. No visual symptoms of Cd phytotoxicity were observed; nevertheless, in non-mycorrhizal plants the presence of Cd decreased plant growth. The addition of Cd had no significant effect on either mycorrhizal colonization or the amount of extra-radical mycelia that was produced by the AMF. Cd accumulated mainly in roots; only 22% of the total Cd absorbed was translocated to the shoots, where it accumulated to an average of 228 mg Cd kg(-1). Although the shoot-to-root ratio of Cd was similar in both the AMF inoculated and non-inoculated plants, the total absorbed Cd was 23% higher in mycorrhizal plants. Cd concentration in AMF extra-radical mycelium was 728 microg g(-1) dry weight. Despite the greater absorption of Cd, mycorrhizal plants showed higher photosynthetic pigment concentrations and shoot P contents. Cd also influenced mineral nutrition, leading to decreased Ca and Cu shoot concentrations; N, Fe and Cu shoot contents; and increased S and K shoot concentrations. Cd induced guaiacol peroxidase activity in roots in both mycorrhizal and non-mycorrhizal plants, but this increase was much more accentuated in non-mycorrhizal roots. In conclusion, sunflower plants associated with G. intraradices were less sensitive to Cd stress than non-mycorrhizal plants. Mycorrhizal sunflowers showed enhanced Cd accumulation and some tolerance to excessive Cd concentrations in plant tissues.     

Cadmium Tolerance in a Metal-contaminated Population of the Grassland Moss Rhytidiadelphus squarrosus

Two populations of Rhytidiadelphus squarrosus, from metal-contaminated and uncontaminated habitats, differed in their intra- and extracellular Cd contents but had similar cellular levels of Cu. Moss shoots were supplied with a pulse of toxic metal by incubating in Cu or Cd nitrate solutions and effects on respiration, photosynthesis and intracellular K loss were monitored with time after initial exposure. Increasing intracellular Cu levels correlated most closely with a concurrent decline in intracellular K. Photosynthesis also declined in proportion to intracellular Cu; significant Cu-induced stimulation of respiration was observed. The most significant effect of Cd treatment was a decline in photosynthesis in proportion to the intracellular concentration of Cd. Apical segments from both populations showed similar sensitivity to Cu, whereas the metal-contaminated population showed increased resistance to Cd. Sensitivity to Cd increased in the more basal portions of moss gametophores, indicating that apparent resistance of Cd might reflect shoot vitality and age effects. After laboratory growth to eliminate differences in the physiological status of apical segments, it was confirmed that the metal-contaminated population of the moss was photosynthetically more tolerant to Cd at intracellular Cd concentrations found to cause considerable photosynthetic inhibition in the uncontaminated population. The metal-contaminated population of the moss that was tolerant to Cd was not co-tolerant to Cu.     

Superoxide dismutase activity in salt stressed wheat seedlings

We investigated the effect of salt stress on enzymatic activity of superoxide dismutase (SOD) isozymes in shoot and root tissues of salt tolerant and sensitive wheat (Triticum aestivum L. and Triticum durum Defs.) cultivars. Ten day old seedlings were subjected to 0.7 M NaCl stress for 3 and 5 days. Seedlings treated in the same manner without salt stress served as controls. Activity of SOD isozymes in root and shoot extracts was determined by activity staining of native polyacrylamide gels. In both shoot and root extracts of examined cultivars two isozymes of SOD, namely MnSOD and Cu/ZnSOD were identified. Cu/ZnSOD activity comprised 90 % of total SOD activity in both root and shoot tissues. Salt stress caused 1–1.5 fold increase in MnSOD activity of shoots in tolerant cultivars when compared with non-stressed controls. Under stress conditions, compared to controls all cultivars exhibited reduced MnSOD activity in root tissues. Cu/ZnSOD activity, on the other hand, was remarkably enhanced (3–4 fold) in root extracts of the tolerant cultivars, whereas it was reduced in the sensitive ones.     

Characterization of populations of rapid-cycling Brassica rapa L. selected for differential waterlogging tolerance

By challenging a heterogenous population of plants (rapid-cyclingBrassica rapa L.) with waterlogging stress, we selected plantswhich differed in their response to root zone hypoxia. Theseindividuals were placed into ‘tolerant’ and ‘sensitive’populations based on foliage colour after waterlogging and werethen mass-pollinated and re-selected over seven generationsto produce the stable populations described. To assess responsesto root zone hypoxia in the selected populations, plants weregrown for 1 week after germination under normal watering conditionsand then subjected to waterlogging stress for up to 8 d. Undercontrol conditions, no differences were found between the tolerantand sensitive populations in any of the parameters studied.Chlorophyll concentrations in the tolerant population were significantlygreater than the concentrations in the sensitive populationwhen plants had been waterlogged. A similar stress-specificdifference was found in root and shoot dry matter accrual. Assoil redox values (and hence, available oxygen) decreased, anincrease in soluble carbohydrates and starch occurred in theleaves of waterlogged plants. Changes in soluble carbohydrateswere noted as early as 12 h after waterlogging in the sensitiveplants, and starch concentrations were significantly higherfor this population 24 h after waterlogging. Under waterloggedconditions, activities of alcohol dehydrogenase (ADH) and pyruvatedecarboxylase (PDC) increased, phosphoglucomutase and malatedehydrogenase decreased, and malic enzyme and glucose 6-phosphatedehydrogenase did not change. The sensitive population exceededthe tolerant population in activities of ADH and PDC after 18and 48 h of waterlogging, respectively. The results demonstratethat stress-specific differences in population responses towaterlogging can be achieved through recurrent selection. Key words: Waterlogging, carbohydrates, selection, hypoxia, Brassica rapa     

Zonal responses of sensitive vs. tolerant wheat roots during Al exposure and recovery

Aluminium (Al) irreversibly inhibits root growth in sensitive, but not in some tolerant genotypes. To better understand tolerance mechanisms, seedlings from tolerant ('Barbela 7/72' line) and sensitive ('Anahuac') Triticum aestivum L. genotypes were exposed to AlCl(3) 185 μM for: (a) 24 h followed by 48 h without Al (recovery); (b) 72 h of continuous exposure. Three root zones were analyzed (meristematic (MZ), elongation (EZ) and hairy (HZ)) for callose deposition, reserves (starch and lipids) accumulation, endodermis differentiation and tissue architecture. Putative Al-induced genotoxic or cytostatic/mytogenic effects were assessed by flow cytometry in root apices. Tolerant plants accumulated less Al, presented less root damage and a less generalized callose distribution than sensitive ones. Starch and lipid reserves remained constant in tolerant roots but drastically decreased in sensitive ones. Al induced different profiles of endodermis differentiation: differentiation was promoted in EZ and HZ, respectively, in sensitive and tolerant genotypes. No ploidy changes or clastogenicity were observed. However, differences in cell cycle blockage profiles were detected, being less severe in tolerant roots. After Al removal, only the 'Barbela 7/72' line reversed Al-induced effects to values closer to the control, mostly with respect to callose deposition and cell cycle progression. We demonstrate for the first time that: (a) cell cycle progression is differently regulated by Al-tolerant and Al-sensitive genotypes; (b) Al induces callose deposition >3 cm above root apex (in HZ); (c) callose deposition is a transient Al-induced effect in tolerant plants; and (d) in HZ, endodermis differentiation is also stimulated only in tolerant plants, probably functioning in tolerant genotypes as a protective mechanism in addition to callose.     

Physiological responses of Bituminaria bituminosa to heavy metals

Two hydroponic experiments were performed to study the physiological responses to heavy metals (HMs) of two populations of Bituminaria bituminosa (L.) C.H. Stirton (Fabaceae): one (“C2”) from a site contaminated by HMs and one from a non-contaminated site (“LA”). In the first, we studied the effects of elevated concentrations of Zn (12 and 61 μM). Population C2 was more tolerant in terms of root and shoot growth at 61 μM Zn, relative to control plants (1 μM Zn). The similar tissue Zn levels of the two populations suggest that C2 is more tolerant of high tissue Zn. Of the parameters measured that could be related to Zn phytotoxicity (micro and macronutrients, root hydraulic activity, water-extractable Zn and organic acids), none could explain totally the superior tolerance of C2. In the second assay, the effects of Cd (4.4 μM), Cu (7.8 μM) and Zn (76 μM) on plant accumulation of the furanocoumarins (FCs) psoralen and angelicin, which function as feeding deterrents and photo-activated toxins, were assessed. For population C2, all three HMs increased the root FC concentrations, while Cd also raised shoot levels. For LA, Cu raised the root concentrations of both FCs. There was a relationship between plant stress, manifested as proline accumulation and disruption of plant water relations, and increased FC accumulation. Higher tissue levels of FCs likely provide greater protection against bacterial or fungal infection and herbivores.     

Effects of suboptimal root zone temperatures and shoot demand on net translocation of micronutrients from the roots to the shoot of maize

The effects of suboptimal root zone temperatures (RZTs) on net translocation rates from the roots to the shoots and the concentrations of Fe, Mn, Zn, and Cu were examined in maize grown in nutrient solution or soil. Plants were grown at 12 °C, 18 °C and 24 °C RZT. At each RZT, the growth-related shoot demand for nutrients was varied by independently modifying the temperature of the shoot base (SBT) including the apical shoot meristem. The net translocation rates of Mn and Zn from the roots to the shoots were reduced at low RZTs, irrespective of the SBT and of the substrate (soil or nutrient solution). Obviously, the net translocation rates of Mn and Zn at low RZT were mainly regulated by temperature effects on the roots and not by the chemical nutrient availability in the rhizosphere or by shoot growth rate as controlled by SBTs. When both RZT and SBT were reduced, the decrease in net translocation rates of Mn and Zn was similar to the decline in the shoot growth rate and concentrations of Mn and Zn in the shoot fresh matter were not greatly affected or were even increased by low RZT. However, at high SBT and low RZT in nutrient solution, the depressed net translocation rates of Mn and Zn combined with the increased shoot growth resulted in significantly decreased concentrations of Mn and Zn in the shoot, indicating that Mn and Zn may become deficient even at high chemical availability. By contrast to Mn and Zn, the net translocation rates of Fe and Cu at all RZTs were markedly enhanced by increased SBTs. Accordingly, the concentrations of Fe and Cu in the shoot fresh matter were not greatly affected by RZTs, irrespective of the SBTs. These results indicate that the ability of roots to supply Fe and Cu to the shoot was internally regulated by the growth related shoot demand per unit of roots. Deceased 21 September 1996 Deceased 21 September 1996     

Tolerance and bioaccumulation of copper in Phragmites australis and Zea mays

The effects of copper on the growth, tolerance indices, mineral composition (N, P, K, Fe, Zn and Mn) and metal uptake of reed (Phragmites australis [Cav. Trin. ex Steudel]) and maize (Zea mays L.) were investigated in hydroponic experiments at copper concentrations ranging from 0.5 to 157 M Cu. A reduction in root length was shown to be a good indicator of copper toxicity, concentrations of 15.7 and 78.7 M Cu inhibiting root growth in maize and reed, respectively. The reed was significantly more tolerant of copper than maize and at 7.85 M Cu (external concentration), reed can be described as a Cu tolerant plant, and maize as a Cu non-tolerant species. As a result of Cu toxicity, the concentrations of macronutrients N, P and K decreased in both shoot and root of maize, while the concentrations were hardly affected in reed tissues. Fe concentration increased in shoots and roots of maize and in roots of reed with increasing Cu treatments, leading to highly significant (p<0.01) linear relationships between tissue Fe and Cu concentrations. The bioconcentration factor (BCF) of Cu was higher in roots than in shoots of both plant species, ranging from 612 to 1592 in reed for the Cu treatments tested. In the roots of maize, BCF of Cu increased from 349 to 1931 when increasing Cu in nutrient solution from 7.85 M to 78.5 M. Therefore, reed could be useful in wastewater treatments for the removal of Cu. However, the use of reed in phytoextraction of Cu from contaminated soils is limited by the low accumulation rate in shoots and although reed can be more efficient than maize for Cu phytoextraction, harvesting the full biomass, including roots, may be required.     

Growth of Zea mays L. plants with their seminal roots only. Effects on plant development, xylem transport, mineral nutrition and the flow and distribution of abscisic acid (ABA) as a possible shoot to root signal

Maize (Zea mays L.) was grown in quartz sand culture eitherwith a normal root system (controls) or with seminal roots only(‘single-rooted’). Development of adventitious rootswas prevented by using plants with an etiolated mesocotyl andthe stem base was positioned 5–8 cm above the sand. Eventhough the roots of the single-rooted plants were sufficientlysupplied with water and nutrients, the leaves experienced waterdeficits and showed decreased transpiration as trans plrationalwater flow was restricted by the constant number of xylem vesselspresent in the mesocotyl. As a consequence of this restriction,transpirational water flow velocities in the metaxylem vesselsreached mean values of 270 m h^–1 and phloem transportvelocities of 5.2 m h^–1. Despite limited xylem transportmineral nutrient concentrations in leaf tissues were not decreasedin single-rooted plants, but shoot and particularly stem developmentwas somewhat inhibited. Due to the lack of adventitious rootsthe shoot:root ratio was strongly increased in the single-rootedplants, but the seminal roots showed compensatory growth comparedto those in control plants. Consistent with decreased leaf conductance,ABA concentrations in leaves of single-rooted plants were elevatedup to 10-fold, but xylem sap ABA concentrations in these plantswere lower than in controls, in good agreement with the well-wateredconditions experienced by the seminal roots. Surprisingly, however,ABA concentrations in tissues of the seminal roots of the single-rooted plants were clearly increased compared to the controls,presumably due to increased ABA import via phloem from the water-stressedleaves. The results are discussed in relation to the role ofABA as a shoot to root signal. Key words: Zea mays, seminal roots, plant development, xylem transport, mineral nutrition, ABA, shoot-to-root signal     

Effects of copper and mineral nutrition on growth,copper accumulation and mineral element uptake in two Rumex japonicus populations from a copper mine and an uncontaminated field sites

Two Rumex japonicus populations, one from a copper mine and the other from an uncontaminated site, were studied in hydroponic experiments for the plant growth, copper accumulation and mineral nutrient content under excess copper and nutrient deficiency conditions. The tolerance indices of the contaminated population were significantly higher than that of the uncontaminated population, indicating the evolution of Cu resistance in the former. At control and low Cu treatment, there was no difference in Cu accumulation in roots between the two populations. At high Cu (100 μM) treatment, however, the contaminated population accumulated less Cu in roots than the uncontaminated one, suggesting the root exclusion mechanism existing in the former. The contaminated population was also more tolerant to general nutrient deficiency than the uncontaminated one. The results indicated that the contaminated population had evolved not only Cu-tolerance but also tolerance to low nutrient supply. Under Cu stress, the contaminated population had less change in nutrient composition than the uncontaminated one. The similar result was observed in general nutrient deficiency experiment. The results indicated that the mineral composition homeostasis under the stresses was important in metal tolerance and colonizing the Cu-enriched soils for the Cu-tolerant population. At high Cu (100 μM) treatment and general nutrient deficiency treatment, the contaminated population accumulated significantly lower copper and higher phosphorus in both roots and shoots than the uncontaminated one. This was not the case for other mineral nutrients Ca, Mg and Fe except for root Mg and root Fe at Cu treatment. The result suggested that the high Ca-metabolism in R. japonicus was uncorrelated with high Cu-tolerance and that P might play an important role in governing Cu bioaccumulation.     

Comparison of techniques for determining the effect of aluminium on the growth of,and the inheritance of aluminium tolerance in wheat

The effect of Al on the growth of plants derived from the F3 generation of a cross between Al tolerant (Waalt) and Al sensitive (Warigal) wheat cultivars, grown in low ionic strength nutrient solutions, were assessed by a number of methods viz; root length and haematoxylin stain after 3 days exposure to Al and plant top and root yields, and root length and visual assessment for Al damage after 4 weeks growth.Of these methods haematoxylin stain (3 days) and visual assessment at 4 weeks identified the same plants as being sensitive or tolerant to Al and clearly segregated the 2 populations. Consequently these 2 methods were used as standard techniques to determine the ability of the other methods to distinguish between tolerant and sensitive plants.The ratio of plant top: root yields clearly segregated the 2 populations. The 2 populations could not be clearly distinguished based on plant top or root yields, or on root length either after 3 days or 4 weeks exposure to Al.Within the population of tolerant plants, root length was significantly correlated with root weight (r²=0.86) and top weight (r²=0.71). None of these relationships were significant for the population of sensitive plants.These techniques were applied in a number of separate experiments on the F2 and F3 populations from a Waalt × Warigal cross. The results indicate that Al tolerance in wheat is inherited by a single gene and that this gene has incomplete dominance.     

Effect of Cu Toxicity on Growth of Cowpea (Vigna unguiculata)

Accurate determination of the rhizotoxicity of Cu in dilute nutrient solutions is hindered by the difficulty of maintaining constant, pre-determined concentrations of Cu (micromolar) in solution. The critical Cu²⁺ activity associated with a reduction in the growth of solution-grown cowpea (Vigna unguiculata (L.) Walp. cv. Caloona) was determined in a system in which Cu was maintained constant through the use of a cation exchange resin. The growth of roots and shoots was found to be reduced at solution Cu²⁺ activities ≥1.7 μM (corresponding to 90% maximum growth). Although root growth was most likely reduced due to a direct Cu²⁺ toxicity, it is considered that the shoot growth reduction is attributable to a decrease in tissue concentrations of K, Ca, Mg, and Fe and the formation of interveinal chlorosis. At high Cu²⁺ activities, roots were brown in color, short and thick, had bent root tips with cracking of the epidermis and outer cortex, and had local swellings behind the roots tips due to a reduction in cell elongation. Root hair growth was reduced at concentrations lower than that which caused a significant reduction in overall root fresh weight.     

A study on the population dynamics of the perennial plant species Chamaenerion angustifolium (L.) scop.

Summary From a study of differently aged populations of the perennial plant species Chamaenerion angustifolium a concept was deduced concerning the population dynamics of the species. The age structure was determined by counting the rings of periderm in the roots. After the establishment of seedlings vegetative propagation is the main factor in population development. The longevity of populations depends on exogenic factors, since older root samples—if isolated from the population—appeared to be as viable as were younger specimens. The oldest population studied had been able to persist for about thirty years due to the mineral cycle brought about by the population itself. In still developing populations a greater number of shoots tend to sprout from younger roots than from older roots, when compared per unit root weight. The shoot density in full-grown populations (in which further root expansion does not occur) is related to the root biomass per unit area. It was suggested that the allocation of reserve assimilates within the roots is an endogenic factor determining the shoot density. After the early sprouting phase the shoot development depends mainly on environmental factors.