Hoagland Nutrient Solution Research Articles

Light availability drives tree seedling success in a subtropical coastal dune forest in South Africa

In subtropical coastal dune forests of South Africa, the microenvironment of tree seedlings is largely influenced by a pervasive understorey woody herb, Isoglossa woodii. We examined whether the additional shading by I. woodii explains the competitive response of tree seedlings from these forests. Seedlings of four common mid- to late-successional tree species (Diospyros natalensis, Euclea racemosa, Sideroxylon inerme and Apodytes dimidiata) were grown at three densities of I. woodii in a common garden experiment under greenhouse conditions. The seedlings were grown at 1.6% and 13.5% of full sunlight and supplied with 1% and 10% nitrogen in half-strength Hoagland's nutrient solution. Total biomass and biomass allocation parameters were used to measure the competitive response of the seedlings. Seedlings attained maximum biomass at high light and high nutrient levels and showed species- and light-specific responses to biomass of I. woodii neighbours. Seedlings' allocation to roots increased with increasing light levels but decreased at higher nutrient levels. The leaf mass fraction (LMF) response to light and nutrient levels was opposite to that shown by root allocation. Specific leaf area (SLA) and leaf area ratio (LAR) decreased with increasing light conditions but were not responsive to manipulation of nutrients. The presence of I. woodii neighbours reduced LMF whilst the responses of SLA to neighbours depended on the light level and species. Leaf trait responses to manipulation of light conditions, I. woodii neighbour density and soil nutrient concentration are complex but overall demonstrate an overwhelming role of light in influencing seedling establishment in coastal dune forests. The competitive response of these seedlings to low irradiance reiterates the notion of phenotypic clustering at the seedling stage amongst shade tolerant tree species, which promotes seedling persistence and gradual transition into the tree layer. Our results highlight the role of additional understorey shading by the herb stratum in influencing tree recruitment dynamics and ultimately tree community structure in many of Africa's tropical lowland forests.

In vitro evaluation of excess copper affecting seedlings and their biochemical characteristics in Carthamus tinctorius L. (variety PBNS-12).

The present study was focused to recognize the changes in the Safflower (Carthamus tinctorius L. variety PBNS-12), when exposed to different concentration of copper (25, 50 and 100μM) along with control (0.5μM) for 10 and 20 days. This experiment used Hoagland's nutrient solution to meet the external nutrient conditions, which includes micro and macronutrients equivalent to soil solution with copper sulphate (CuSO4. 5H2O) as a metal stress. The plant samples were harvested after 10 and 20 days. The effect of increased concentrations of copper was indicated by the reduction in overall growth with reduced fresh and dry weight. Copper stress caused significant increase in the non- enzymatic antioxidants (polyphenols and flavonoids) in leaves of treated safflower seedlings as compared to the control. Also, enhanced accumulation of proline was observed in the safflower leaves. In response to excess copper concentration, the level of MDA content was found to be increased. The results showed that the copper has time and dose-dependent effects on safflower seedlings.

Antioxidative defense mechanism of the ruderal Verbascum olympicum Boiss. against copper (Cu)-induced stress

AbstractThe endemic Verbascum olympicum has characteristics that allows it to live in degraded areas of Uludağ Mountain, Turkey and therefore known as a ruderal species. In this study, V. olympicum seeds collected from Uludağ Mountain were grown in the Hoagland nutrient solution, under hydroponic conditions. The activity of antioxidative enzymes (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX) were examined to demonstrate the role of antioxidative mechanism in the seedlings exposed to different Cu concentrations (0, 50, 250, 500 μM) for seven days. Also, certain growth parameters (such as the water content, biomass production, soluble protein), the level of lipid peroxidation, cell membrane injury and permeability were investigated. As a result, some toxic effects are observed following the application of 500 μM Cu, after the seedlings growing in 50 and 250 mM Cu concentrations showed high resistance and survived in hydroponic conditions. Our findings provide information about the resistance of V. Olympicum seedlings to oxidative stress caused by excessive Cu concentrations.

Effects on antioxidant enzyme activities and osmolytes in Halocnemum strobilaceum under salt stress

The seedlings of Halocnermum strobilaceum were cultivated in 0.5% hoagland nutrient solution containing 0.0%, 0.9%, 2.7% and 5.4% of NaCl as well as composite salt (Na+, Ca2+, K+, Si4+) for 20 days; all the contents are in weight ratio. Succulent level, inorganic ions (Na+, K+), organics such as betaine, proline, malondialdehyde, and antioxidant enzyme activities including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), betaine aldehyde dehydrogenase (BADH) were measured to reveal its salt tolerance mechanism. When the composite salt concentration reaches 5.4%, SOD activity level, and MDA content is five times the control group; when it reaches 2.7%, the succulent level of seedlings, and the content of K+ in roots is nearly two times the NaCl treatment; the dry weight is more than three times the control group; with the NaCl treatment, MDA is three times the contrast; when the salt concentration is 2.7%, POD reaches the maximum. Results indicate that Si4+, K+, and Ca2+ from composite salt in the roots of H. strobilaceum improved the water-holding capacity. The activities of antioxidant enzyme were raised by the accumulation of proline and betaine, which increased the salt tolerance. The absorption of K+ promoted the high ratio of K+/Na+ and alleviated the damage of cell membranes of H. strobilaceum, which is associated with osmotic contents such as betaine and proline.

Cadmium Removal from Aqueous Solutions Using <I>Macaranga peltata</I>:A Potential Plant for Phytoremediation

The concentration of heavy metals in the environment is increasing at an alarming rate due to the high rate of industrialisation and intensive agricultural practices over the past few decades. Since most of the heavy metals are persistent and toxic in nature, they significantly reduce agricultural productivity and pose severe threat to human beings through food chain contamination. In recent years, phytoremediation has gained considerable attention as a solar driven green technology for the removal of heavy metals. In the present study we examined the Cadmium (Cd) removal potential of Macaranga peltata - one of the woody species emerging in early successions ‐ found very common in Kerala. The experiment was conducted in batch mode for a period of 20 days in three different concentrations of Cd (0.5, 1.5, and 2.5 mg/L) in two different mediums (distilled water and 10% Hoagland nutrient solution). The percentage removals of Cd by M. peltata from three treatments in distilled water were 98, 93 and 89% respectively, where as in the case of Hoagland nutrient medium it was 90, 89 and 82% respectively. The results show higher removal efficiency in distilled water as compared to Hoagland nutrient medium. The analysis of the plants revealed that most of the Cd was accumulated in the roots followed by stem and leaf. Cd accumulation also affected the chlorophyll content of the plant at higher concentrations. The study shows that M. peltata is a promising plant for the phytoremediation of Cd. Since most of the earlier studies on phytoremediation were carried out using smaller plants with less biomass production and growth rate, the use of M. peltata -one of the fastest growing tree species in the present study receives special attention.

Sugar-Induced Tolerance to the Salt Stress in Maize Seedlings by Balancing Redox Homeostasis

Effects of exogenous glucose (Glc) and sucrose (Suc) on salt resistance, (glucose-6-phosphate dehydrogenase) G6PDH activity, ASA-GSH cycle and reactive oxygen species metabolism in maize leaves were studied. Seedings at two leaf stage were pretreated by 1/2 Hoagland nutrient solution with 0.5 mmol•L-1 Glc, Suc and mannitol for 3 days, some seedlings were left in normal nutrient solution and isotonic maninitol as control and permeability control respectively. Then the plants were cultured by 1/2 Hoagland solution at the concentration of 150 mmol•L-1 NaCl for 4 days or 6 days. The results showed that pretreatment with 0.5 mmol•L-1 glucose and sucrose for 3 days significantly decreased the thiobarbituric acid reactive substances (TBARS), H2O2 contents and increased ASA, GSH contents, ASA/DHA, GSH/GSSG ratio and G6PDH activity in leaves of maize seedings under salt stress. We also found that sucrose pretreatment induced the increase of Ca2+-ATPase and maintained the balance of Ca2+ contents under salt stress. In addition, compared with S treatment, isotonic mannitol pretreatment did not induce any changes of the physiological and biochemical indicators that meant it could not cause improvement of biological indicators of maize seedings. These results indicate that exogenous glucose and sucrose improved ASA-GSH cycle efficiency by participating in the pentose phosphate pathway (OPP), therefore enhanced antioxidant capacity and reduced the damage of active oxygen free radical, and the G6PDH activity induced by glucose and sucrose might serve as signal molecules and be involved in salt resistance of maize seedings.

Research Concerning the Influence of Fertilization on Some Physiological Processes and Biochemical Composition of Lavender (Lavandula Angustifolia L.)

Abstract The aim of the research was to study the influence of phosphorus (P) and potassium (K) fertilization on the main physiological processes in lavender and biochemical characterization of essential oil obtained by steam distillation. Physiological processes studied were the photosynthesis and transpiration intensity. The material used for herbal purposes includes commercial genotype of lavender (Lavandula angustifolia L.). Experiment was carried out under controlled conditions and fertilization was performed with a modified Hoagland nutrient solutions. For biochemical analysis were used average samples of lavender leaf, stem and flowers. Separation and analysis of compounds was performed by gas chromatography analysis coupled with mass spectrometry (GC-MS). Transpiration intensity was performed by successive mass determinations from leaves and resulted values were reported per unit leaf area. The rate of photosynthesis was measured by Qubit Systems CO 2 analysis package. Researches were performed in the laboratory of Plant Physiology within the Faculty of Horticulture and Forestry and Plant extracts laboratory, Faculty of Food Processing Technology, from Banat University of Agricultural Sciences and Veterinary Medicine Timisoara. Following the experiment, it was found that potassium fertilization has a positive effect both on the photosynthesis and transpiration. Linalool (30.398%), lynalil acetate (23.609%), camphor (8.844%), borneol (5.49%) and eucalyptol (3.964%), were determined as the main compounds from over 50 identified through biochemical analysis of the essential oil.

Determination of arsenic extraction by Vetiveria zizanioides (L.) Nash plant for phytoremediation application

ABSTRACT There is contradiction about Vetiveria zizanioides (L.) Nash as arsenic hyperaccumulator. The suitability of V. zizanioides plant for Arsenic (As) tolerance and accumulation in the plant biomass has been investigated for phytoremediation application. Plants were treated with 0, 25, 50, 75, 100 and 150 mg L−1 As levels in Hoagland nutrient solution. Arsenic accumulation in shoot and root biomass was determined after 14 days. Metal extraction competency from matrix and accumulation in the above ground plant part revealed that V. zizanioides accumulate As at a low level. Inefficiency of As accumulation by this plant relates to the absence of arsenate reductase activity, transcript of the arsC gene which is crucial for As detoxification. Though, the V. zizanioides system sustains low-level As stress, it is not suitable for As phytoextraction.

Phytoremediation of petroleum hydrocarbons by using a freshwater fern species Azolla filiculoides Lam

ABSTRACTIn this study, the phytoremediation capacity of Azolla filiculoides Lam. for the water resources contaminated with petroleum hydrocarbons was investigated. The plants were grown in nitrogen-free Hoagland nutrient solution containing 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% crude oil under greenhouse conditions for 15 days. Although the growth rate of the plants were not negatively influenced by the presence of crude oil in the media for the concentration of 0.005% and 0.01% v/v, a gradual impeding effect of crude oil in the growth media has been observed at concentrations 0.05–0.1%. More than 0.1% crude oil in the growth medium ostensibly retarded the growth. For example, 0.2% oil in the media reduced growth approximately 50% relative to the control, and the presence of crude oil at concentrations 0.3% or more were lethal. The data about the percentage of plant growth, fresh weight increase and root growth clearly indicated that the tolerance level of A. filiculoides plants to crude oil ranges between 0.1% and 0.2%. In comparison to control samples, the biodegradation rate of total aliphatic and aromatic (phenathrene) hydrocarbons at 0.05–0.2% oil concentrations, was 94–73% and 81–77%, respectively. On the other hand, in case of further increases in oil concentration in media, i.e.; 0.3–0.5%, the biodegradation rate was still higher in the experimental samples, respectively 71–63% and 75–71%. The high biodegradation rates of petroleum hydrocarbons in the experimental samples suggested that A. filiculoides plants could be a promising candidate to be used for the phytoremediation of low crude oil contaminated precious freshwater resources.

The effects of salinity stress on morphological characteristics, mineral nutrient accumulation and essential oil yield and composition in Mentha canadensis L.

Mint (Mentha canadensis L.) is one of the most important plants to produce essential oil. The aim of this study was to investigate the effects of NaCl salinity on the morphological characteristics, mineral content and essential oil yield and composition of M. canadensis L. through cultivating rhizome segments in sand tanks irrigated with full-strength Hoagland nutrient solution containing different concentrations of NaCl (0, 50, 100, 150mM). Meanwhile fresh and dry weights of three plant parts (leaves, stems and roots) were measured, the morphological characteristics including plant heights, root and branch length, stem diameter and number of branches were also examined. The mineral element contents were determined using an ICP atomic emission spectrometer. The essential oils were extracted and analyzed by GC and GC–MS. The result showed that biomass and water content of all plant parts were significantly reduced at even the lowest (50mM) salt concentration treatment, of which, the reduce in aerial parts was more remarkable than that in roots. The salinity treatment also reduced plant height, root and branch length, number of branches and nodes. Na+ accumulation increased significantly in all three plant parts, the Na+/K+ ratio increased with increasing concentration of NaCl, and the highest was found in the leaves, followed by stems, then roots. The essential oil content was strongly reduced in salt-treated plants. Salinity had no effect on the content of oxygenated monoterpenes but it increased the menthone and pulegone contents, while a decreased concentration of menthol under saline condition was observed.

Evaluation of Lettuce Genotypes for Salinity Tolerance

Lettuce is one of the most commonly used salad vegetables and considered to be a relatively salt-sensitive crop. Salinity is a major constraint to crop production in all important lettuce growing regions of the United States, and the water quality problem is exacerbated by climate change. To identify salt-tolerant lettuce genotypes, 178 cultivars and germplasm accessions (56 butterhead, 39 crisphead, 35 romaine, 33 leaf, and 15 wild types) were selected from a preliminary screening of more than 3800 genotypes, and tested for salinity tolerance in sand cultures under greenhouse conditions. Plants were grown in Hoagland nutrient solution, either with or without 30/15 mm NaCl/CaCl2, and leaf fresh and dry mass (FM and DM), chlorophyll index, and maximal photochemical efficiency (Fv/Fm) were measured 4 weeks after plants were transplanted. Generally, salinity decreased lettuce shoot FM and DM, increased DM/FM ratio and chlorophyll index, and had no effect on Fv/Fm. Some lettuce varieties showed salt tolerance (less than 15% reduction in FM), such as PI 342515, PI 358020c, ‘Morgana’, ‘Amerika’ (butterhead), ‘Laura’ (crisphead), PI 289023, PI 273577, PI 278066, PI 177425 (romaine), PI 171676a, PI 177423, PI 342477, and PI 358018b (leaf). The results indicate that lettuce genotypes differ greatly in their salt sensitivity, which could be useful for growers to choose cultivars and for breeders to improve lettuce adaptation to salinity stress.

EARLY INDUCTION OF SPROUTING ON SEED TUBERS OF YAM (Dioscorea spp.) SOON AFTER TUBER INITIATION IN A HYDROPONICS SYSTEM

SUMMARYProlonged inability of yam tubers to sprout/germinate is associated with the expression of tuber dormancy, and the start of dormancy in tubers is linked to the onset of tuber formation. Although the plant hormone, abscisic acid (ABA) is known to regulate the onset and maintenance of dormancy in tubers, there are no known method(s) of inducing shoot growth (sprouting) on seed yam tubers that are harvested at 240 days after vine emergence or earlier. Therefore, this study was conducted to: (1) determine whether the absorption of fluridone, a reputed ABA inhibitor, prior to or during early seed yam tuber formation would induce sprouting, and (2) determine the effect of fluridone on early shoot growth. The study was a 2×4 factorial experiment arranged in a Completely Randomized Design (CRD) with eight treatment combinations replicated three times. Two species of yam with long dormancy durations were used: D. rotundata var TDr 131 and D. alata var TDa 98/01166; and three concentrations of fluridone were tested (30, 50, 100 µM). Young plants (69 days after vine emergence) of TDr 131 and TDa 98/01166 were grown in a coco coir medium hydroponics system using Hoagland's Nutrient Solution, with or without the test fluridone concentrations. In all fluridone treatments, most leaves of both species of yam had 30–90% of their surface bleached while the stems appeared purplish. In both Controls, all the newly formed seed tubers that were harvested at 90 and 104 days after vine emergence were dormant (devoid of any new shoots/sprouts). In contrast, over 70% of the seed tubers that developed in 30 and 100 µM fluridone had at least one new shoot, particularly in TDa 98/01166. The fluridone treatments did not significantly affect tuber weight or vegetative growth parameters like dimensions and number of leaves. This study has shown that the duration from vine emergence of the old tuber to sprouting of the new tuber can be reduced by more than half if young plants absorbed fluridone during early tuber development.

Hydroponic screening of black locust families for heavy metal tolerance and accumulation

abstractPresent work examines phytoextraction potential of four black locust families (half-sibs 54, 56, 115, and 135) grown hydroponically. Plants were treated with 6 ppm of cadmium (Cd), 100 ppm of nickel (Ni), and 40 ppm of lead (Pb) added in Hoagland nutrient solution, accompanying with simultaneously applied all three metals. Responses to metals exposure among families were different, ranging from severe to slight reduction of root and shoot biomass production of treated plants. Calculated tolerance indices are indicating tested families as highly tolerant (Ti > 60). Family 135 had the lowest tolerance index, pointing that it was highly susceptible to applied metals. Comparing photosynthetic activities of tested families it has been noticed that they were highly sensitive to stress induced by heavy metals. Net photosynthetic rate of nickel treated plants was the most affected by applied concentration. Cadmium and nickel concentrations in stems and leaves of black locust families exceeded 100 mg Cd kg−1 and 1000 mg Ni kg−1, in both single and multipollution context. On the contrary, accumulation of lead in above ground biomass was highly affected by multipollution treatment. Tf and BCF significantly varied between investigated treatments and families of black locust. Concerning obtained results of heavy metals accumulation and tolerance of black locust families can be concluded that tested families might be a promising tool for phytoextraction purposes, but it takes to be further confirmed in field trials.

Physiological characterization of maize tolerance to low dose of aluminum, highlighted by promoted leaf growth

Main conclusionEffects of a low aluminum (Al) dose were characterized. The Al supplement inhibited root growth but enhanced leaf growth in maize lines with different Al sensitivities.High levels of Al are phytotoxic especially in acidic soils. The beneficial effects of low Al levels have been reported in some plant species, but not in maize. Maize is relatively more sensitive to Al toxicity than other cereals. Seedlings, at the three leaf stage, of four Chinese maize foundation parent inbred lines with different Al tolerances, were exposed to complete Hoagland’s nutrient solution at pH 4.5 supplemented with 48 μM Al3+ under controlled growth conditions, and then the Al stress (AS) was removed. The leaf and root growth, root cell viability, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ions (K+, Ca++ and Mg++), photosynthetic rate and chlorophyll, protein and malondialdehyde contents in tissues were assayed. In conclusion, a low Al dose inhibits root growth but enhances leaf growth in maize. The Al-promoted leaf growth is likely a result of increased protein synthesis, a lowered Ca++ level, and the discharge of the growth-inhibitory factors. The Al-promoted leaf growth may be a ‘memory’ effect caused by the earlier AS in maize. Al causes cell wall rupture, and a loss of K+, Ca++ and Mg++ from root cells. CAT is an auxiliary antioxidant enzyme that works selectively with either SOD or POD against AS-related peroxidation, depending on the maize tissue. CAT is a major antioxidant enzyme responsible for root growth, but SOD is important for leaf growth during AS and after its removal. Our results contribute to understanding how low levels of Al affect maize and Al-resistant mechanisms in maize.

Physiological Evaluation of Alkali-Salt Tolerance of Thirty Switchgrass (Panicum virgatum) Lines.

Soil salt-alkalization is a major limiting factor for crop production in many regions. Switchgrass (Panicum virgatum L.) is a warm-season C4 perennial rhizomatous bunchgrass and a target lignocellulosic biofuel species. The objective of this study was to evaluate relative alkali-salt tolerance among 30 switchgrass lines. Tillers of each switchgrass line were transplanted into pots filled with fine sand. Two months after transplanting, plants at E5 developmental stage were grown in either half strength Hoagland’s nutrient solution with 0 mM Na+ (control) or half strength Hoagland’s nutrient solution with 150 mM Na+ and pH of 9.5 (alkali-salt stress treatment) for 20 d. Alkali-salt stress damaged cell membranes [higher electrolyte leakage (EL) ], reduced leaf relative water content (RWC), net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (Tr). An alkali-salt stress tolerance trait index (ASTTI) for each parameter was calculated based on the ratio of the value under alkali-salt stress and the value under non-stress conditions for each parameter of each line. Relative alkali-salt tolerance was determined based on principal components analysis and cluster analysis of the physiological parameters and their ASTTI values. Significant differences in alkali-salt stress tolerance were found among the 30 lines. Lowland lines TEM-SEC, Alamo, TEM-SLC and Kanlow were classified as alkali-salt tolerant. In contrast, three lowland lines (AM-314/MS-155, BN-13645-64) and two upland lines (Caddo and Blackwell-1) were classified as alkali-salt sensitive. The results suggest wide variations exist in alkali-salt stress tolerance among the 30 switchgrass lines. The approach of using a combination of principal components and cluster analysis of the physiological parameters and related ASTTI is feasible for evaluating alkali-salt tolerance in switchgrass.

Effect of Low pH and Aluminum Toxicity on the Photosynthetic Characteristics of Different Fast-Growing Eucalyptus Vegetatively Propagated Clones.

Knowing how acid soils and aluminum in soils may limit the growth of Eucalyptus trees in plantations is important because these plantations grow in many tropical and subtropical regions. Seedlings of four vegetatively propagated Eucalyptus clones, E. grandis × E. urophylla ‘GLGU9’(G9), E. grandis × E. urophylla ‘GLGU12’ (G12), E. urophylla × E. camaldulensis ‘GLUC3’ (G3) and E. urophylla ‘GLU4’(G4), were subjected to liquid culture with Hoagland nutrient solution for 40 days, then treated with four different treatments of acid and aluminum for 1 day. The four treatments used either pH 3.0 or 4.0 with or without added aluminum (4.4 mM) in all possible combinations; a control used no added aluminum at pH 4.8. Subsequently, the photosynthetic parameters and morphology of leaves from eucalypt seedlings were determined and observed. The results showed that the tested chlorophyll content, net photosynthetic rate, transpiration rate and water use efficiency were apparently inhibited by aluminum. Under uniform Al concentration (4.4 mM), the Al-induced limitation to photosynthetic parameters increased with pH, indicating acid stimulation to Al toxicity. Among all treatments, the most significant reduction was found in the combination of pH 3.0 and 4.4 mM Al. The photosynthetic and transpiration rates showed similar trends with G9 > G12 > G3 > G4, suggesting that G9 and G12 had higher Al-tolerance than other two clones. Microscopic observation revealed changes in leaf morphology when exposed to Al stress; for example, a reduced thickness of leaf epidermis and palisade tissue, the descendant palisade tissue/spongy tissue ratio and leaf tissue looseness. Overall, the acid and aluminum stress exerted negative effects on the photosynthetic activity of eucalypt seedlings, but the differences in tolerance to Al toxicity between the clones were favorable, offering potential to improve Eucalyptus plantation productivity by selecting Al tolerant clones.

Effects of Phosphate on Arsenate Uptake and Translocation in Nonmetallicolous and Metallicolous Populations of Pteris Vittata L. Under Solution Culture

An arsenic hyperaccumulator, Pteris vittata L., is common in nature and could occur either on As-contaminated soils or on uncontaminated soils. However, it is not clear whether phosphate transporter play similar roles in As uptake and translocation in nonmetallicolous and metallicolous populations of P. vittata. Five populations were used to investigate effects of phosphate on arsenate uptake and translocation in the plants growing in 1.2 L 20% modified Hoagland's nutrient solution containing either 100 μM phosphate or no phosphate and 10 μM arsenate for 1, 2, 6, 12, 24 h, respectively. The results showed that the nonmetallicolous populations accumulated apparently more As in their fronds and roots than the metallicolous populations at both P supply levels. Phosphate significantly (P < 0.01) decreased frond and root concentrations of As during short time solution culture. In addition, the effects of phosphate on As translocation in P. vittata varied among different time-points during time-course hydroponics (1–24 h). The present results indicated that the inhibitory effect of phosphate on arsenate uptake was larger in the three nonmetallicolous populations than those in the two metallicolous populations of P. vittata.

Differences in salt tolerance between diploid and autotetraploid apple seedlings exposed to salt stress

Autotetraploid plants of apple (Malus domestica) cultivar ‘Hanfu’ and ‘Gala’ were induced from leaves by colchicine treatment. There were obvious morphological differences in the leaves of diploid and autotetraploid plants. We treated the diploid and autotetraploid apple seedlings with 200mmolL−1 NaCl for 8days in 0.5× Hoagland's nutrient solution and measured the physiological characters and the expression of aquaporin genes in leaves at different times during treatment. The results showed that the response of the autotetraploid to salt stress was better than that of the diploid; the relative water content (RWC) decreased in both over time, but the RWC was higher in the autotetraploid than in the diploid for the duration of the salt stress treatment. The proline content and the accumulation of malondialdehyde (MDA) were higher in the diploid than the autotetraploid, with both increasing over the course of the treatment. We also showed that the expression of aquaporin genes (MdPIP1;1, and MdTIP1;1) decreased initially before peaking at 24h and then rapidly declining at 48h and 96h. The relative expression levels in the autotetraploid were higher than in the diploid at all sampling times, and were 4 to 10-fold higher at 24h. Our results show that autotetraploid apple possesses better salt tolerance than diploid, which may be associated with the higher levels of expression of aquaporin genes in response to salt stress. The results of our study will make a practical and theoretical contribution to the breeding of polyploid apple cultivars.

The Effect of the Ionic Strength of Nutrient Solution on Gas Exchange, Ionic Concentration and Leaf Biomass of Annona emarginata (Schltdl.) H. Rainer Variety ‘Terra-Fria’ Seedlings

The present study aimed to test the hypothesis that different levels of the availability of mineral nutrients from Hoagland and Arnon's nutrient solution no. 2 affect the photosynthesis, ionic concentration and biomass production in seedlings of Annona emarginata (Schltdl.) H. Rainer variety ‘terra-fria’. Seedlings were grown in a hydroponic setting with 100% ionic strength and with ionic strength reduced to 75%, 50%, and 25%. Ionic strengths intermediate resulted in higher rates of carbon net assimilation and plants grown under these conditions increased biomass as well ionic concentrations of calcium, magnesium and sulfur. The ‘terra-fria’ plants with nutrient solutions of 50% and 75% ionic strength exhibited higher ionic concentrations, instantaneous carboxylation efficiency and biomass production. It can be concluded that the ‘terra-fria’ does not require the maximum mineral nutrients availability from Hoagland and Arnon's nutrient solution to achieve high primary productivity and intermediate ionic strengths can even reduce the time required for rootstock formation.

Consequences of chilling stress on watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] germplasm lines at seedling stage

A total of sixty one germplasm lines of watermelon were selected based on differences in fruit size. First year (2012), the young seedlings were exposed to low temperature stress 20/10 ± 2°C (day/night) for 15/9 hours (day/night, 21:00 to 06:00 HR) inside the growth chamber for 1-week, then second stress treatment 10/5 ± 2°C was given, and seedlings were maintained at this for continuous 10 days. The control seedlings were throughout maintained at 28 ± 2°C till the end of experiment. Thirteen best performing germ plasmlines were selected based on different growth and physiological traits. Second year (2013), these young seedling were subjected to chilling stress (5/5 ± 2°C, day/night) for 15/9 hours (day/night, 21:00 to 06:00 HR). The seedlings were raised in plug trays filled with commercial soil mixture and kept moist with Hoagland nutrient solution on daily basis. Based on the present experimental findings, 10102, 10124, 10398, and 10491 were selected as best performing germplasm lines for more most of traits (shoot dry weight per plant, stem length per plant, leaf number per plant, root length per plant) studied in chilling stress, and also maintained high cellular membrane integrity, chlorophyll fluorescence, protein content, and peroxidase activity. Hence, chilling stress 5°C was considered to be as better critical range for facile means of selecting tolerant and sensitive germplasm lines at young seedling stage in watermelon based on different growth parameters studied.