Lower and Upper Critical Zinc Levels in Relation to Cotton Growth and Development

Solution culture experiments in the greenhouse were conducted to determine the lower and upper critical Zn levels relative to early cotton (Gossypium hirsutum L.) growth and development. Upland cotton ‘Coker 310’ was grown in nutrient solution with fourteen Zn levels ranging from 0 to 10,000 μg/liter. The plants were grown for 31 days, harvested and analyzed for Zn. At Zn levels of less than 20 μg/I, top dry weight, root dry weight, plant height, node number and squares produced were reduced as compared to plants supplied with adequate Zn. Toxicities were induced at 2000 μg/I and higher. Root dry weight was not influenced by Zn levels to 10,000 μg/I. The lower critical Zn levels where Zn is required at a minimum concentration for maximum growth were from 8 to 11 μg/I in blades 1 through 5, respectively. The upper critical Zn levels where maximum Zn concentration in blade tissue can be tolerated for maximum growth were from 130 to 300 μg/g for blades 1 to 5, respectively. Blade 3, the recently matured leaf, was selected as the representative tissue for analysis. The lower and upper critical Zn levels in blade 3 were 11 and 200 μg/g, respectively.     

Trace Metal Contents of Selected Seeds and Vegetables from Oil Producing Areas of Nigeria

The concentrations of accumulated trace metals in selected seeds and vegetables collected in the oil producing Rivers State of Nigeria were investigated. The values were compared with those of seeds and vegetables cultivated in Owerri, a less industrialized area in Nigeria. The lead (Pb) and cadmium (Cd) contents of the seeds obtained from Rivers State ranged between 0.10 and 0.23 μg/g dry weight, while those of the seeds cultivated in Owerri fell below the detection limit of 0.01 μg/g dry weight. The highest manganese (Mn) level (902 μg/g dry weight) was found in Irvingia garbonesis seeds cultivated in Rivers State. Similarly, the highest nickel (Ni) value (199 μg/g dry weight) was also obtained in I. garbonesis, however, in the seeds sampled in Owerri. The highest copper (Cu), zinc (Zn), and iron (Fe) levels (16.8, 5.27, and 26.2 μg/g dry weight, resp.) were detected in seeds collected in Rivers State. With the exception of Talinum triangulae, Ocinum gratissimum, and Piper guineese, with Pb levels of 0.09, 0.10, and 0.11 μg/g dry weight, respectively, the Pb and Cd levels in the vegetables grown in Owerri fell below the detection limit of 0.01 μg/g dry weight. The trace metal with the highest levels in all the vegetables studied was Mn, followed by Fe. The highest concentrations of Ni and Cu occurred in vegetables collected from Rivers State, while the highest level of Zn was observed in Piper guineese collected in Owerri, with a value of 21.4 μg/g dry weight. Although the trace metal concentrations of the seeds and vegetables collected in Rivers State tended to be higher than those of the seeds and vegetables grown in Owerri, the average levels of trace metals obtained in this study fell far below the WHO specifications for metals in foods.     

Effect of zinc supply on growth of three species of Eucalyptus seedlings and wheat

Summary Effects of zinc supply on shoot and root dry weight, root length, zinc concentrations and carbonic anhydrase activity were measured in 52 day old seedlings ofEucalyptus maculata, E. marginata, E. patens and wheat grown in a zinc deficient soil in the glasshouse.Symptoms of zinc deficiency in the eucalyptus and wheat appeared within 20 to 35 days. Eucalypt seedlings had short internodes and small necrotic leaves, reduced dry weight of shoots and roots, root length and zinc concentrations in young leaves; the measurable level of leaf carbonic anhydrase activity decreased to zero. Similar responses also occurred in wheat.The level of zinc fertilizer required for normal growth of Eucalyptus seedlings is therefore likely to be similar to that used for wheat and other agricultural crops.     

Quantified elemental changes inAspidisca cicada andVorticella convallaria after exposure to aluminium, copper, and zinc

Summary Data on metal-induced elemental changes in eukaryotic unicellular organisms, such as protozoa, are rare. This study focused on two species of ciliate protozoa,Aspidisca cicada andVorticella convallaria, both common and abundant in activated sludge. Elemental changes in cells exposed to aluminium, copper, and zinc were determined by scanning electron microscopy-electron probe X-ray microanalysis. X-ray emission spectra obtained from cells 2 h after resuspension in Chalkley's medium (control) showed clear, characteristic peaks for magnesium, silicon, phosphorus, sulphur, potassium, and copper. These elements were also routinely detected in all cells resuspended in metal solution. Spectra obtained from cells treated with aluminium or zinc showed additional distinct peaks for aluminium and zinc. In copper-treated cells enhanced copper peaks were seen. Mean aluminium levels were low inA. cicada control cells (0.14mg/g of dry weight) but higher in cells treated with 0.50 ppm (0.69 mg/g of dry weight) and 2.00 ppm aluminium (2.07 mg/g of dry weight).A. cicada was ten times more sensitive to copper than to the other metals, and thanV. convallaria. There was a significantly higher concentration of copper inA. cicada cells treated with 0.20 ppm copper (2.94 mg/g of dry weight) than in control cells (2.16 mg/g of dry weight). InA. cicada cells treated with 0.50 and 2.00 ppm zinc significantly higher levels of zinc (2.41 and 2.07 mg/g of dry weight, respectively) were observed than in the control (0.41 mg/g of dry weight). After treatment with 0.50 ppm and 2.00 ppm aluminium, aluminium was significantly higher in the treatedV. convallaria cells (1.58 and 0.67 mg/g of dry weight, respectively) than in control cells (0.14 mg/g of dry weight). After treatment with 2.00 ppm copper there was significantly more copper in treatedV. convallaria cells (3.63 mg/g of dry weight) than in controls (2.08 mg/g of dry weight). InV. convallaria cells treated with 0.50 ppm and 2.00 ppm zinc there was an increase in the amount of zinc in cells (1.30 and 2.68 mg/g of dry weight, respectively) compared with control cells (0.34 mg/g of dry weight). Data on other changes in intracellular elements in both species, after 2 h exposure to aluminium, copper, and zinc medium are given. In both species, there was uptake and/or accumulation of aluminium, copper, and zinc when the external concentration of the metal was increased. Intracellular elemental levels were altered by sublethal and toxic external concentrations of the metals studied.A. cicada was ten times more sensitive to copper than to aluminium or zinc, and thanV. convallaria to the metals studied.     

ACCUMULATION OF NICKEL AND ZINC BY WESTERN NORTH AMERICAN GENERA CONTAINING SERPENTINE-TOLERANT SPECIES

Nickel and zinc were determined in 57 taxa of western North American genera containing serpentine-tolerant species. The studies resulted in the identification of three varieties of Thlaspi montanum (var. montanum, var. siskiyouense, and var. californicum) which are hyperaccumulators (> 1,000 μg/g dry mass) of nickel. These three taxa together with the previously reported Streptanthus polygaloides are the only hyperaccumulators of nickel so far reported for continental America. Significantly higher than normal nickel values (up to 664 μg/g) were recorded for the serpentinophyte Viola cuneata. Elevated zinc levels (> 1,000 μg/g dry mass) were also recorded in four of the Thlaspi taxa and confirm the tendency of many species of this genus to accumulate zinc. It is suggested that hyperaccumulation of nickel by the three varieties of T. montanum is a neo-endemic rather than palaeo-endemic process and that the precursor of these varieties is T. montanum var. montanum from non-mineralized soils.     

<Emphasis Type="Italic">Marchantia polymorpha</Emphasis> L.: A Bioaccumulator

Mussoorie in the western Himalayas of India, a popular tourist destination, was selected for air pollution monitoring. The study was carried out applying thalloid liverwort species Marchantia polymorpha L. as a tool. Moss bags containing M. polymorpha was transplanted at residential, highly and less polluted areas to obtain comprehensive and comparative data. Lead content, along with some essential micronutrients viz. zinc, manganese, and copper, as well as some physiological parameters total chlorophyll, sugar, protein, catalase and peroxidase activity were analyzed. The highest accumulation of lead (Pb) in M. polymorpha plants was highest in summer season , i.e., 2276 μg/g dry weight. The correlation of metals and physiological parameters has been made to get clear view of the effects of lead on physiology and essential micronutrients.     

Mineral nutrient disorders of root crops of the Pacific: Preliminary observations on sweet potato (Ipomoea batatas)

Solution culture was used to characterise deficiencies or toxicities of several essential elements in Ipomoea batatas cv. Wanmun, and to define the critical concentrations of these elements in young mature leaves during vegetative growth. Tentative critical concentrations for deficiency, expressed on the basis of dry weight of leaf blade, were: nitrogen 3.8%, phosphorus 0.17%, potassium 2.4%, magnesium 0.12%, manganese 20g/g and zinc 10g/g. For manganese and zinc toxicities it was possible only to designate the range within which the critical concentration occurred. Visible symptoms are briefly described.     

CARBON ALLOCATION IN MACROCYSTIS PYRIFERA (PHAEOPHYTA): INTRINSIC VARIABILITY IN PHOTOSYNTHESIS AND RESPIRATION1

Measurements of net photosynthesis (PS, O₂ evolution), dark respiration (R, O₂ consumption), and light and dark carbon fixation (¹⁴C) were conducted on whole blades, isolated blade discs, sporophylls, apical scimitars and representative portions of stipe and holdfast of the giant kelp Macrocystis pyrifera L.C. Ag. On a dry weight basis, highest net PS rates were observed in apical scimitar segments and whole blades (3.81 and 3.07 mgC · g dry wt^?1· h^?1, respectively), followed by sporophylls (1.42 mgC·g dry wt^?1· h^?1) and stipe segments (0.15 mgC·g dry wt^?1· h^?1). No PS capacity was observed in holdfast material. Respiration rates showed similar ranking ranging from 1.22 mgC·g dry wt^?1·h^?1 for apical scimitar to 0.18–0.22 mgC·g dry wt^?1· h^?1 for holdfast material. Considerable within blade variability in both PS and R was also found. Steepest PS and R gradients on both an areal and weight basis were found within immature blades followed by senescent and mature blade material. Highest net PS rates were associated with the blade tips ranging from 3.08 (mature blades) to 10.3 mgC·dry wt^?1·h^?1 (immature blades). Highest rates of R generally occurred towards the basal portions of blades and ranged from 1.03–1.80 mgC·g dry wt^?1·h^?1 for immature blades. The variability within and between blades was high, with coefficients of variation approaching 50%. The observed patterns can be related to the decreasing proportionment of photosynthetic tissue and increasing proportionment of structural tissue as occurs from the blade tip to the blade base. Rates of light carbon fixation (LCF) revealed longitudinal profiles similar to oxygen measurements for the different blade types, with the absolute rates being slightly lower. Patterns of dark carbon fixation (DCF) were less easily interpreted. Highest rates of DCF (0.04–0.06 mgC·g dry wt^?1·h^?1) occurred at the basal portions of immature and senescent blades. Longitudinal profiles of total chlorophyll (a + c) on both an areal and weight basis were very similar to the profiles of PS. Normalized to chlorophyll a, PS displayed an unusual longitudinal profile in immature tissue; however, such profiles for mature and senescent tissues were similar to those for PS on an areal basis. It was demonstrated that it is difficult, if not impossible, to select single tissue discs that are representative of whole blades. The metabolic longitudinal profiles reveal a characteristic developmental pattern; the previous working definitions of immature, mature, and senescent blades, based on morphology and frond position thus have a physiological basis.     

Causes of reduced leaf‐level photosynthesis during strong El Niño drought in a Central Amazon forest

Sustained drought and concomitant high temperature may reduce photosynthesis and cause tree mortality. Possible causes of reduced photosynthesis include stomatal closure and biochemical inhibition, but their relative roles are unknown in Amazon trees during strong drought events. We assessed the effects of the recent (2015) strong El Niño drought on leaf‐level photosynthesis of Central Amazon trees via these two mechanisms. Through four seasons of 2015, we measured leaf gas exchange, chlorophyll a fluorescence parameters, chlorophyll concentration, and nutrient content in leaves of 57 upper canopy and understory trees of a lowland terra firme forest on well‐drained infertile oxisol. Photosynthesis decreased 28% in the upper canopy and 17% in understory trees during the extreme dry season of 2015, relative to other 2015 seasons and was also lower than the climatically normal dry season of the following non‐El Niño year. Photosynthesis reduction under extreme drought and high temperature in the 2015 dry season was related only to stomatal closure in both upper canopy and understory trees, and not to chlorophyll a fluorescence parameters, chlorophyll, or leaf nutrient concentration. The distinction is important because stomatal closure is a transient regulatory response that can reverse when water becomes available, whereas the other responses reflect more permanent changes or damage to the photosynthetic apparatus. Photosynthesis decrease due to stomatal closure during the 2015 extreme dry season was followed 2 months later by an increase in photosynthesis as rains returned, indicating a margin of resilience to one‐off extreme climatic events in Amazonian forests.     

Photosynthetic response of three climber plant species to osmotic stress induced by polyethylene glycol (PEG) 6000

We examined the photosynthesis response to osmotic stress in three climber plant species, Pharbitis nil (Linn.) Choisy, Lonicera japonica Thunb, and Parthenocissus tricuspidata (Sieb.et Zucc.) Planch. All climber plants were exposed to osmotic stress induced by polyethylene glycol (PEG) 6000 at 4 levels (slight, moderate, severe osmotic and the control) for 30?days. Photosynthesis response was determined by measuring leaf photosynthesis, chlorophyll fluorescence, carbonic anhydrase activity and stable carbon isotope ratios. P. nil maintained high photosynthetic activity under long-term moderate osmotic stress due to both stable photosystem II photochemical efficiency and high carbonic anhydrase activity. L. japonica maintained high photosynthetic activity under long-term moderate stress due to high carbonic anhydrase activity rather than photosystem II photochemical efficiency. P. tricuspidata tolerated only short-term moderate osmotic stress and long-term slight osmotic stress because its response was mainly stomatal limitation, with the lowest photosynthetic activity and hardly any carbonic anhydrase activity. Carbonic anhydrase activity was inversely correlated with stable carbon isotope ratios. The regulation by carbonic anhydrase was probably the reason for P. nil and L. japonica to tolerate long-term moderate osmotic stress. The selection on the species should consider the differential adaptation mechanism to osmotic stress during the development of drought-resistant plants.     

Growth,chlorophyll and mineral nutrient studies on phalaris arundinaceae L. in three scottish lochs

Growth, chlorophyll and mineral nutrients studies were made in Phalaris arundinaceae L. in three Scottish lochs of varying nutrient status from March to November in 1975. The maximum shoot height and shoot dry weight attained by the plants were approximately 160 cm and 4 g respectively. Seasonal changes in the chlorophyll levels in the Phalaris leaf were studied and two peaks were found, one in April and the other in June–July. Maximum chlorophyll level attained was 9 mg g^–1 leaf dry weight. The changes in the mineral levels in the root, stem, leaf and inflorescence parts of the plants from the three lochs were also assayed throughout the growing season. A total of eight mineral elements were studied, including carbon, nitrogen, phosphorus, potassium, sodium, calcium, magnesium and iron. Variations in both the mineral concentrations and their pattern of changes during the study period among the plants from the lochs were observed and discussed.     

Effects of grazing on the quantity and quality of freshwater Aufwuchs

Qualitative and quantitative measures of the Aufwuchs (scum flora) on artificial substrates in situ were used to evaluate the effects of grazing by freshwater pulmonate snails in a shallow pond in southeastern Michigan. Grazer densities of 216 snails/m² marked reduced standing crop so that after 45 days grazed substrata had 6.46 mg dry weight, 604 µg C and 4.18 µg chlorophyll a as compared to controls with 30.62 mg dry weight, 3699 µg C and 6.29 µg chlorophyll a, all on a per dm² basis.Grazing did not change carbon per mg dry matter but caused significant increases in both µg chlorophyll a (control, 0.206; and grazed, 0.649 µg chlorophyll a/mg dry weight, P < 0.01) and nitrogen (control, 8.3; and grazed, 24.2 µg N/mg dry weight, P < 0.001) after 45 days. Both abundance and diversity of the attached community was reduced by grazing from 24 taxa and 80,889 individuals/cm² on control to 8 taxa and 501 individuals/cm² on grazed substrates. Mean productivity of the Aufwuchs was significantly (P < 0.001) reduced by grazing from 76.3 µg C/(dm²·day) on control to 17.7 µg C/(dm²·day) on grazed substrata.Snails were very efficient at clearing smooth surfaces of living cells, detritus, and particulate inorganic matter. There was little evidence of selectivity except for an apparent inability to remove some of the smallest cells (e.g. Cocconeis sp.) probably for mechanical reasons.     

Galanthamine production by Leucojum aestivum L. shoot culture in a modified bubble column bioreactor with internal sections

Shoot culture of summer snowflake (Leucojum aestivum L.) was successfully cultivated in an advanced modified glass‐column bioreactor with internal sections for production of Amaryllidaceae alkaloids. The highest amounts of dry biomass (20.8 g/L) and galanthamine (1.7 mg/L) were achieved when shoots were cultured at 22°C and 18 L/(L·h) flow rate of inlet air. At these conditions, the L. aestivum shoot culture possessed mixotrophic‐type nutrition, synthesizing the highest amounts of chlorophyll (0.24 mg/g DW (dry weight) chlorophyll A and 0.13 mg/g DW chlorophyll B). The alkaloids extract of shoot biomass showed high acetylcholinesterase inhibitory activity (IC₅₀ = 4.6 mg). The gas chromatography–mass spectrometry (GC/MS) profiling of biosynthesized alkaloids revealed that galanthamine and related compounds were presented in higher extracellular proportions while lycorine and hemanthamine‐type compounds had higher intracellular proportions. The developed modified bubble‐column bioreactor with internal sections provided conditions ensuring the growth and galanthamine production by L. aestivum shoot culture.     

Photoautotrophic Growth and Photosynthesis in Cell Suspension Cultures of Chenopodium rubrum

A method is described for growing cell suspension cultures of Chenopodium rubrum photoautotrophically for prolonged periods of time. By using a two-tier culture vessel the growth medium with the cells was separated from the CO₂ reservoir. Definite CO₂ concentrations were established by a K₂CO₃/KHCO₃ buffer. Photoautotrophic growth in C. rubrum cell suspension cultures was correlated with the CO₂ level. At 0.5% CO₂ the cell cultures contained 68 μg chlorophyll/g fresh weight and showed an increase in fresh weight of about 80% in 18 days. At 1% CO₂ an increase in fresh weight of 165% in 18 days was observed. The chlorophyll content rose up to 84 μg/g fresh weight. The photoautotrophic growth was also greatly influenced by the 2,4-D content of the medium. Cell growth was enhanced by lowering the auxin concentration. Best growth was attained (210% increase in fresh weight) at 10^?8M 2,4-D. The photosynthetic activity of the cells was measured by the light dependent ¹⁴CO₂ incorporation. At 0.5% CO₂ the cell suspensions assimilated about 100 μmol CO₂/mg chlorophyll × h. In the presence of 1% CO₂ the light driven assimilation was raised up to 185 μmol CO₂/mg chlorophyll × h. In both cases, the dark incorporation of CO₂ was merely 1.8% of the values obtained in light.     

Chlorophyll Destruction in Lemon Fruit by Light and 2',4'Dichloro 1-Cyanoethane-sulphonanilide

Chlorophyll content decreased when excised lemon fruits were exposed to light. A quantitative model for the photodestruction of chlorophyll exhibited reasonable agreement with data on in vivo destruction of chlorophyll. Photodestruction of chlorophyll was enhanced by treating fruit with 2′,4′-dichloro-l-cyanoethane-sulphonanilide (R33417). Measurable enhancement of chlorophyll destruction was observed with concentrations of R33417 as low as 10 μg/l. Maximum activity was achieved at approximately 600 μg/1. R33417 treatment enhanced photodestruction of chlorophyll to a greater extent at higher photon flux densities.     

Plant metal content, growth responses and some photosynthetic measurements on field-cultivated wheat growing on ore bodies enriched in Cu

Some elemental levels, morphological and photosynthetic characteristics and cellular metabolites of wheat plants (Triticum aestivum L. cv. Vergina) growing in the field on an ore body (Cu concentration in the soil 3050 ug g^?1) were compared to control plants growing in the same environment where the Cu concentration in the soil was 140 μg g¹. The concentrations of Cu, K, Pb, Zn, Mg and Fe were higher in the ore plants but Ca was lower. Growth of the ore plants was inhibited, with decreased height (25%), weight (5%), leaf area (7%) and leaf dry weight (5%) compared to the control plants. Leaf protein concentration of the ore plants was 16. 2 mg cm² leaf area, 63% of that of the control plants. The ore plants were chlorotic and chlorophyll concentration was 3. 8 μg cm^?2 leaf area, 6. 4 times lower than that in the control plants. Ribulose 1. 5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4. 1. 1. 39) activity was 13. 4 μmol CO₂ fixed (mg dry weight)^?1 min^?1, 164% of the activity in control plants. Therefore, growth inhibition did not appear to result from inhibition of the dark reactions of photosynthesis. High Rubisco activity appears to be maintained to permit maximal CO₂ fixation rates whenever energy is available. Parameters of chlorophyll fluorescence F_m, F_v, I_1/2 and F_v/F_m were lower in the ore-grown plants than in control plants; F_m was higher. These values indicate that there is a decrease in the pool size of the electron acceptors on the reducing side of photosystem II (PSII), a destruction of PSII centres and interference in the photochemistry of PSII. The nitrogen content, soluble sugars, starch and lipid content were lower in ore-grown plants. Lower carbohydrate levels appear to result from low photosynthetic activity. The fatty acid composition of lipids was similar in both groups. A lower proportion of polyunsaturated fatty acids was found in the ore-grown plants. Stress caused by high Cu concentration in the soil appears to affect the light reactions of photosynthesis leading to growth inhibition.     

The effect of triacontanol on micropropagation of balm, Melissa officinalis L.

 Triacontanol, a long-chain primary alcohol was found to be an effective growth regulator in the micropropagation of balm, Melissa officinalis. In both the multiplication and the rooting phase, concentrations of 2, 5, 10 and 20 μg triacontanol per liter were applied. After 4 weeks of culture, the fresh weight of shoots was measured in the multiplication phase and root formation, photosynthetic activity, chlorophyll content and the fresh and dry weights of shoots were analyzed in the root induction phase. In the multiplication phase, 5 μg/l triacontanol was found to be the optimal concentration, while in the rooting phase 2 μg/l was the most effective. Triacontanol increased the number and length of roots, and it enhanced shoot growth, fresh weight, and the chlorophyll content, but it had no effect on the dry weight and the photosynthetic activity of the plants. Results of our work demonstrate that triacontanol can be applied as an effective growth regulator in the tissue culture of balm. Received: 3 December 1997 / Revised: 24 February 1998 / Accepted: 26 February 1999     

Limnological Studies in a Tropical Man-Made Lake (Lagartijo Reservoir) Venezuela

The purpose of this study was to evaluate the present limnological conditions of Lagartijo reservoir (North central Venezuela) and to compare them with conditions reported in early studies. Lagartijo reservoir supplies an important part of the water demand for Caracas city and wide fluctuations on water volume occur annually. Relevant physical, chemical and biological data were obtained from three sampling stations between July 1990 and April 1992. The reservoir was permanently stratified with a well defined thermocline. The main tributary (Lagartijo river), with a temperature about 6° C colder than the surface temperature of the reservoir, flows through the hypolimnion producing distinct chemical and biological properties. The average of the daily integral phytoplankton photosynthesis was 1550 mg C m⁻² d⁻¹. The present annual average of the net photosynthetic activity is about 40% lower than the reported for 1970 and corresponds to an apparent decrease in phytoplankton biomass and to the reduction of the euphotic zone. Photosynthetic activity was higher for the wet season than for the dry season. Actual chlorophyll a concentration in the euphotic zone averages 4.9 μg l⁻¹. Abundance of zooplankton was significantly decreased in comparison to 1976. Mean zooplankton biomass (dry weight) for the upper 10 m layer was 596 μg l⁻¹. Copepods accounted for most of this biomass, followed by cladocerans and rotifers. For the first time, a freshwater medusa (probably Craspedacusta sowerbyi) was collected from Venezuelan waters.     

Antihypertensive Effect of an Extract of Passiflora edulis Rind in Spontaneously Hypertensive Rats

Orally administered methanol extract of Passiflora edulis rind (10 mg/kg or 50 mg/kg) or luteolin (50 mg/kg), which is one of consistent polyphenols of the extract, significantly lowered systolic blood pressure in spontaneously hypertensive rats (SHRs). Quantitative analysis by liquid chromatography tandem mass spectrometry (LC-MS/MS) showed that the extract contained 20 μg/g dry weight of luteolin and 41 μg/g dry weight of luteolin-6-C-glucoside. It also contained γ-aminobutyric acid (GABA, 2.4 mg/g dry weight by LC-MS/MS or 4.4 mg/g dry weight by amino acid analysis) which has been reported to be an antihypertensive material. Since the extract contained a relatively high concentration of GABA, the antihypertensive effect of the extract in SHRs might be due mostly to the GABA-induced antihypertensive effect and partially to the vasodilatory effect of polyphenols including luteolin.     

The response of maize seedlings to cadmium stress under hydroponic conditions

The effects of cadmium (Cd) supply level in nutrient solution (0, 12.5, 25, 50, 100, 200, 400, and 800 μM) on growth, Cd accumulation ability, and the related physiological indices of maize (Zea mays L.) seedlings were studied under hydroponic conditions. The results showed that the increments in the shoot height and biomass were stimulated at relatively low external Cd supply levels (<100 μM), while they were inhibited at Cd supply levels over 200 μM. Cd accumulation ability of the maize seedlings also showed the similar stimulation/inhibition pattern as shoot growth, and the Cd contents in the shoots and roots reached the peaks (389.5 and 505.5 mg/kg dry wt, respectively) at 50 μM Cd. The contents of chlorophyll a, chlorophyll b, and carotenoids in the maize leaf blades decreased with increasing external Cd supply level. At the highest Cd supply level (800 μM), the contents of chlorophyll a, chlorophyll b, and carotenoids in the leaf blade were only 38.9, 46.0, and 29.7% of the control plants, respectively. Moreover, chlorophyll b was more sensitive to the Cd stress than chlorophyll a. The increased proline content in the leaf blade of maize seedlings resulted from external Cd stress indicates that maize can adapt to the adversity menace via changing the content of proline.