Chlorophyll Content Of Seedlings Research Articles

Photosynthetic and Physiological Responses to Combined Drought and Low–Temperature Stress in Poa annua Seedlings from Different Provenances

Combined drought and low–temperature stress is a crucial factor affecting turfgrass establishment and limiting the sustainability of the turfgrass industry in drought– and cold–prone regions. In this context, we evaluated the effects of regular watering (the soil water content was 80% of the maximum water–holding capacity of the field) at room temperature (25 °C) and combined drought (the soil water content was 30% of the maximum water–holding capacity of the field) and low–temperature (0 °C) stress on the morphology, photosynthesis, and physiology of wild Poa annua seedlings from different provenances (‘PA’, ‘WY’, ‘NX’ and ‘YC’). Results indicated that the combined drought and low–temperature stress changed the morphological and growth indicators of seedlings in four provenances to different extents. Moreover, combined drought and low–temperature stress reduced the net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), water use efficiency (WUE), and chlorophyll content in seedlings from four provenances. However, intertemporal CO2 concentration (Ci), relative electrical conductivity (REC), the contents of malondialdehyde (MDA), proline (Pro), soluble sugars (SS), the superoxide anion (O2•−) production rate, the contents of hydrogen peroxide (H2O2) and hydroxyl radical (·OH), the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were all increased. The increase in ‘PA’ was much greater than that in ‘NX.’ The comprehensive evaluation results showed that the order of combined drought and low–temperature resistance of seedlings from the four provenances was ‘PA’ > ‘YC’ > ‘WY’ > ‘NX’, which corresponded to the order of the morphological damage symptoms. In conclusion, ‘PA’ may maintain stronger combined drought and low–temperature resistance by improving the cellular water absorption and retention capacity, enhancing the function of the antioxidant defense system, and maintaining the integrity of the cell membrane, which is a crucial germplasm resource for breeding combined drought and low–temperature resistance in Poa annua.

GREENING THE GROWTH: UNVEILING THE IMPACT OF COMPOST EXTRACT ON SEED GERMINATION AND SOIL-COMPOST MIXTURES ON BIOMASS YIELD AND LEAF CHLOROPHYLL CONTENT

The study, conducted between March and April 2019 at Bangladesh Agricultural University, evaluated the effects of compost extract on the germination, biomass production, and leaf chlorophyll content of rice, wheat, maize, and cowpea seedlings grown in different soil-compost mixtures. The treatments for the germination study were: T0=Control (only water), T1=1:1 compost extract and water, T2=1:5 compost extract and water, T3=1:10 compost extract and water, and T4=1:20 compost extract and water. The treatments for the biomass production and leaf chlorophyll content of seedlings were: T0=Control (500g soil), T1=250g soil and 250g compost, T2=375g soil and 125 g compost, T3=450g soil and 50g compost, T4=500g soil and compost extract (1:10 extract and water), T5=500g soil and compost extract (1:50 compost extract and water) and T6=500g soil and compost extract (1:100 compost extract and water). Data were collected on seed germination at 24, 48 and 72 hrs. of seed placement and those for biomass production and leaf chlorophyll content. Municipal solid waste compost- extract exerted beneficial effect on the germination of rice, wheat, maize and cowpea seeds. Growing seedlings in soil-compost mixtures increased the biomass production and leaf chlorophyll content of rice, wheat, maize and cowpea seedlings but compost- extract showed negative effect.

Potassium transporter KUP9 participates in K+ distribution in roots and leaves under low K+ stress

Potassium (K) is a major essential element in plant cells, and KUP/HAK/KT-type K+ transporters participate in the absorption of K+ into roots and in the long-distance transport to above-ground parts. In Arabidopsis thaliana, KUP9 is involved in the transport of K+ and Cs+ in roots. In this study, we investigated KUP9 function in relation to the K+ status of the plant. The expression of KUP9 was upregulated in older leaves on K+-depleted medium, compared to the expression of the other 12 KUP genes in the KUP/HAK/KT family in Arabidopsis. When grown on low K+ medium, the kup9 mutant had reduced chlorophyll content in seedlings and chlorosis in older rosette leaves. Tissue-specific expression of KUP9 determined by KUP9 promoter:GUS assay depended on the K+ status of the plants: In K+ sufficient medium, KUP9 was expressed in the leaf blade towards the leaf tip, whereas in K+ depleted medium expression was mainly found in the petioles. In accordance with this, K+ accumulated in the roots of kup9 plants. The short-term 43K+ tracer measurement showed that 43K was transferred at a lower rate in roots and shoots of kup9, compared to the wild type. These data show that KUP9 participates in the distribution of K+ in leaves and K+ absorption in roots under low K+ conditions.

Volatile compounds of Bacillus pseudomycoides induce growth and drought tolerance in wheat (Triticum aestivum L.)

The plant growth-boosting biofilm-forming bacteria Bacillus pseudomycoides is able to promote growth and drought stress tolerance in wheat by suppressing the MYB gene, which synthesizes Myb protein (TaMpc1-D4) through secreted volatile compounds. In the present study, Triticum aestivum seeds were inoculated with five distinct bacterial strains. The growth, germination rate, root-shoot length, RWC, and chlorophyll content of seedlings were investigated. Furthermore, the levels of soluble sugars, proteins, H2O2, NO, cell death, and antioxidant enzymes (CAT, SOD, POD, and APX) were observed throughout the growth stage. All of the results showed that B. pseudomycoides had a substantially higher ability to form biofilm and promote these traits than the other strains. In terms of molecular gene expression, B. pseudomycoides inoculation strongly expressed the Dreb1 gene by silencing the expression of MYB gene through secreted volatile compounds. For identifying the specific volatile compound that silenced the MYB gene, molecular docking with Myb protein was performed. Out of 45 volatile compounds found, 2,6-ditert-butylcyclohexa-2,5-diene-1,4-dione and 3,5-ditert-butylphenol had a binding free energy of − 6.2 and − 6.5, Kcal/mol, respectively, which predicted that these compounds could suppress this protein's expression. In molecular dynamics simulations, the RMSD, SASA, Rg, RMSF, and hydrogen bonding values found assured the docked complexes' binding stability. These findings suggest that these targeted compounds may be suppressing Myb protein expression as well as the expression of Dreb1 and other drought response genes in wheat. More research (field trial) into plant growth and drought stress is needed to support the findings of this study.

Alleviative effects of magnetic Fe3O4 nanoparticles on the physiological toxicity of 3-nitrophenol to rice (Oryza sativa L.) seedlings.

In the present study, we explored whether magnetic iron oxide nanoparticles (MNPs-Fe3O4) can be used to alleviate the toxicity of 3-nitrophenol (3-NP) to rice (Oryza sativa L.) seedlings grown under hydroponic conditions. The results showed that 3-NP from 7 to 560 μM decreased the growth, photochemical activity of the photosystem II (PS II), and chlorophyll content of the seedlings in a concentration-dependent manner. In the presence of 3-NP, 2,000 mg L−1 MNPs-Fe3O4 were added to the growth medium as the absorbents of 3-NP and then were separated with a magnet. The emergence of MNPs-Fe3O4 effectively alleviated the negative effects of 3-NP on rice seedlings. In addition, the long-term presence of MNPs-Fe3O4 (from 100 to 2,000 mg L−1) in the growth medium enhanced the growth, production of reactive oxygen species (ROS), activities of antioxidant enzymes, photochemical activity of PS II, and chlorophyll content of the rice seedlings. These results suggest that MNPs-Fe3O4 could be used as potential additives to relieve the physiological toxicity of 3-NP to rice seedlings.

PHYSIOLOGICAL AND BIOCHEMICAL CHANGES OF TOMATO PLANTS UNDER BACTERIAL INFLUENCE

Tomato (Lycopersicon esculentum L) is one of the most important vegetable crops widely grown around the world. However, the global economic productivity of this crop is limited to a number of phytopathogens. Bacterial spotting and mild rot of tomatoes caused by Pseudomonas syringae pv. tomato and Pectobacterium carotovorum subsp. carotovorum, are one of the most common bacterial diseases that cause significant losses and reduce both the quality and quantity of fruits and impair the nutritional value of tomatoes. Tomato plants are affected by these pathogens throughout the growing season, the lesion is characterized by chlorosis, necrosis and rot. The aim of the study was to analyze the impact on the physiological and biochemical parameters of tomato sprouts affected by pathogens of P. syringae pv. tomato and P. carotovorum subsp. саrotovorum. It was found that strains of P. syringae pv. tomato IZ202014 and P. carotovorum subsp. carotovorum IZ207 cause a 30-40% decrease in germination energy and seed germination of Black Prince, Northern Queen, Riddle and Liana tomatoes compared to the control. According to the analysis of physiological and biochemical parameters, the most resistant to pathogens P. syringae pv. tomato, P. carotovorum subsp. carotovorum variety Northern Queen. Treatment of tomato plants with a suspension of the studied strains causes a decrease in chlorophyll content in seedlings by 58-93%. According to the chlorophyll a/b ratio, the Northern Queen and Black Prince varieties have the highest resistance to bacterial damage. Under the influence of cell suspensions of P. syringae pv. tomato IZ202014 and P. carotovorum subsp. carotovorum IZ207 showed changes in the activity of enzymes of the antioxidant system in tomato seedlings, which indicates a decrease in the oxidative processes of cells.

Effect of continuous light on antioxidant activity, lipid peroxidation, proline and chlorophyll content in Vigna radiata L.

Longer photoperiod in form of continuous light (24-h photoperiod without dark interruption) can alter the various physiological and biochemical processes of the plant. This study aimed to evaluate the effects of continuous light on various biochemical parameters associated with the growth and development of Vigna radiata L. (mung bean). The findings showed that leaf size and chlorophyll content of seedlings grown under continuous light were significantly greater than control plants subjected to 12h light/12h dark (12/12h). The activity of antioxidant enzymes superoxide dismutase (SOD, 30.81%), catalase (CAT, 16.86%), guaiacol peroxidase (GPOD, 12.27%), malondialdehyde, (MDA, 39.31) and proline (14.81%) were notably higher in 24/0h light period than 12/12h light period grown seedling at an early stage (on Day 6) while they were constant at the later stage of development. Increased activity of amylase and invertase reveals higher assimilation and consumption of photosynthetic products. This study revealed that plants were stressed at first. However, they gradually became acclimated to continuous light and efficiently used the excess light in carbon assimilation.

Efficacy of Rhizobacteria to Promote the Growth and Increase the Yield of Several Rice Cultivars

Rice is still play important role as staple food for most of Indonesian population; consequently Indonesia is greatly relying on rice production to maintain food security. This plant is commonly cultivated with intensive use of synthetic agrochemicals such as synthetic chemical fertilizers and pesticides. However, the improper use of agrochemicals may result in adverse effects to the environment including biotic and abiotic components. This study was conducted to evaluate the efficacy of rhizobacteria formulation to promote the growth and increase the yield of four rice cultivars that commonly grown in Indonesia i.e . Ciherang, Cigeulis, Inpari 33, and IR64. Experiment was done in a green house with three concentrations of rhizobacteria formulation i.e. 0%, 1%, and 2% (v/v). Several parameters were observed in this study such as seedling height, leaf chlorophyll content of seedling, plant height at 50 days after transplanting (DAT), leaf chlorophyll content at 50 DAT, number of tillers per plant at 50 DAT, number of productive tillers per plant, and yield per plant. Results showed that significant interactions were observed between rice cultivar and concentration of rhizobacteria formulation in all parameters observed. Rice cultivar IR64 consistently showed superior growth and yield among four rice cultivars tested. Except for cultivar IR64, rhizobacteria concentration at 2% showed superior results compared to 1% and 0% for all parameters observed. This study proved that rhizobacteria formulation containing Stenotrophomonas maltophilia Sg3 and Enterobacter cloacae Al7Kla effectively promoted the growth and increase the yield of four rice cultivars that commonly cultivated in Indonesia, suggested that this rhizobacteria formulation is promising bio-agent to be used for rice production in Indonesia. Keywords: Rhizobacteria, plant growth promotion, rice yield DOI: 10.7176/JBAH/11-16-03 Publication date: August 31 st 2021

Effects of Solanum lycopersicum rootstock on biomass, amnio acid content and reactive oxygen species metabolism of grafted seedlings under salt stress

To explore the mechanism of Solanum lycopersicum rootstock function in enhancing salt tolerance of grafted seedlings, we examined the growth, Na+ accumulation, amino acid contents and active oxygen metabolism (ROS) in three grafted seedlings treated with and without 175 mmol·L-1 NaCl conditions. RS grafted seedlings were formed by split grafting using salt-sensitive variety 'Zhongza 9'(S) as scion and salt-tolerant variety 'OZ-006'(R) as rootstock, while the other two experiment materials were the scion self-grafted (SS) and rootstock self-grafted (RR) seedlings. The results showed that NaCl stress significantly increased the salt damage index and Na+ content, concomitantly with substantial decrease in growth rate and chlorophyll content of seedlings. More-over, there were significant differences among the grafting combinations, with an order of SS>RS>RR. NaCl stress significantly increased total amino acid content in the leaves and roots of the grafted seedlings. The amino acid contents were significantly higher than those in the control. There were 9 kinds of amino acid in RR and RS leaves, and 8 kinds in RR and RS roots, with the most significant change in proline. Only 2 and 4 kinds of amino acids in leaves and roots of SS were significantly higher than those in control, respectively. Amino acid contents among three grafted seedlings showed RR>RS>SS under NaCl stress. The contents of amino acid in RR and RS leaves increased by 32.8% and 16.6% compared with SS, and those in RR and RS roots increased by 53.1% and 32.5%, respectively. The changes of ROS were caused by NaCl stress, which enhanced the activities of antioxidant enzymes, the production rate of O2-· and MDA content in both leaves and roots. Among different grafted seedlings, RR had the most prominent increase of antioxidant enzymes activities in leaves and roots, followed by RS, and SS showed the smallest. The active oxygen levels among the three grafted seedlings were show as SS>RS>RR. In summary, rootstock alleviated salt damage of grafted seedlings by inhibiting Na+ transport upward, enhancing amino acid content and antioxidant enzyme activities. The salt tolerance ability showed remarkable difference among three different combinations of rootstock and scion, with a order of RR>RS>SS. Our results suggested that salt tolerance of S. lycopersicum grafted seedlings was mainly affected by the ability of rootstock salt tolerance, followed by scion, and also closely related to the regulation of both amino acid and active oxygen metabolism in seedlings.

Proteomic analysis of wheat seeds produced under different nitrogen levels before and after germination

The objective of this study was to investigate differentially abundant proteins (DAPs) of wheat seeds produced under two nitrogen levels (0 and 240 kg/ha) before and after germination. We selected samples at 8 and 72 h after imbibition (HAI) to identify DAPs by iTRAQ. The results showed 190 and 124 DAPs at 8 and 72 HAI, respectively. Alpha-gliadin and chlorophyll a-b binding protein showed the biggest difference in abundance before and after germination. In GO enrichment analysis, the most significantly enriched GO term was nutrient reservoir activity at 8 HAI and endopeptidase inhibitor activity at 72 HAI. Moreover, many DAPs involved in mobilization of stored nutrients and photosynthesis were mapped to KEGG pathways. Dough development time, dough stability time and seedling chlorophyll content under N240 were significantly higher than those under N0, which validated the results of proteomic analysis. These results are crucial for food nutrition and food processing.

Water-Soluble Carbon Nanoparticles Improve Seed Germination and Post-Germination Growth of Lettuce under Salinity Stress

Seed germination is a critical developmental phase for seedling establishment and crop production. Increasing salinity stress associated with climatic change can pose a challenge for seed germination and stand establishment of many crops including lettuce. Here, we show that water soluble carbon nanoparticles (CNPs) can significantly promote seed germination without affecting seedling growth. Twenty-seven varieties of lettuce (Lactuca sativa) were screened for sensitivity to germination in 150 and 200 mM NaCl, and six salt-sensitive varieties (Little Gem, Parris Island, Breen, Butter Crunch, Muir, and Jericho) were selected and primed with 0.3% soluble carbon nanoparticles. Pretreatment with CNPs significantly improved seed germination under 150 mM NaCl and high temperature. CNP treatment slightly inhibited the elongation of primary roots but promoted lateral root growth and accumulation of chlorophyll content of seedlings grown under salt stress. Despite different lettuce varieties exhibiting a distinct response to nanoparticle treatments, results from this study indicate that soluble nanoparticles can significantly improve lettuce seed germination under salinity stress, which provide fundamental evidence on the potential of nanoparticles in agricultural application to improve crop yield and quality under stressful conditions.

ROS Produced via BsRBOHD Plays an Important Role in Low Temperature-Induced Anthocyanin Biosynthesis in Begonia semperflorens

Low temperature (LT) is an important elicitor that triggers anthocyanin biosynthesis. To investigate whether the reactive oxygen species (ROS) produced via RBOH are involved in this process, we analysed the function and mechanism of ROS produced via RBOH during LT-induced anthocyanin biosynthesis in Begonia semperflorens Link & Otto. The results showed that BsRBOHD transcription was upregulated in LT-grown seedlings at the 3rd hour, which was followed by the upregulation of anthocyanin-biosynthesis genes at the 5–9th hour, leading to anthocyanin accumulation on the 2nd day. The LT-induced increases in ROS production, BsRBOHD and anthocyanin-biosynthesis gene transcription, and anthocyanin content were abolished by the pre-treatment of seedlings with DPI [an inhibitor of nicotinamide adenine nucleoside phosphorylase (NADPH) oxidase or DMTU (a H2O2 scavenger)], but were promoted by pre-treatment with NADPH (a substrate of NADPH oxidase). Changes in the chlorophyll fluorescence parameters showed that pre-treatment of DPI or DMTU alleviated the LT-induced decrease in the seedling chlorophyll content and a/b ratio, which subsequently alleviated the LT-induced decreases in the ABS/CSm, TRo/CSm, RC/CSm, ETo/CSm and REo/CSm values. In contrast, NAPDH pre-treatment intensified these changes. Therefore, we suggest that ROS produced via BsRBOHD may be involved in the LT-induced anthocyanin biosynthesis by strengthening the overaccumulation of ROS produced by the overexcitation of PSII reaction centres and overflux from $${\text{Q}}_{{\text{A}}}^{ - }$$ to NADP+ in B. semperflorens.

Physio-biochemical analyses in seedlings of sorghum-sudangrass hybrids that are grown under salt stress under in vitro conditions

Abstract Objective This study was conducted to analyze the physio-biochemical responses of two sorghum-sudangrass (Sorghum bicolor × Sorghum Sudanese Stapf.) hybrid (“Aneto” and “Sugar Graze”) seedlings exposed to salt stress. Materials and methods Sorghum-sudangrass hybrid seeds sown in MS medium containing 50 and 100 mM NaCl. The activity of antioxidant enzymes (SOD, CAT, GR, APX), chlorophyll (a, b, and total), malondialdehyde (MDA), and proline levels measured in 14 days old seedlings. Results As a result of the study, the activity of antioxidant enzymes (CAT, SOD, APX, and GR), malondialdehyde (MDA), proline and chlorophyll contents of seedlings of cv. “Aneto” increased. On the other hand, SOD activity, proline, and chlorophyll content increased while CAT, APX, GR activity, and malondialdehyde (MDA) content decreased in seedlings of cv. “Sugar graze”. Conclusion Overall, the results showed that the cv. “Aneto” was less affected by the adverse effects of salt stress than the cv. “Sugar graze”. This study is essential for revealing biochemical responses of 14 days old Sorghum-Sudanese hybrid seedlings against salt stress. These study findings can use in breeding programs for sorghum plants.

The plant growth-promoting potential of the mesophilic wood-rot mushroom Pleurotus pulmonarius.

To demonstrate the plant growth-promoting potential of a wood-decay mushroom. A wild strain of a white rot fungus (Pleurotus pulmonarius) was found to convert 10mmoll-1 L-tryptophan (TRP) to approximately 15μgml-1 indole-3-acetic acid (IAA) under the optimal growth conditions of 30°C and pH 5 for 15days. Results of gas chromatography-mass spectrometry indicated IAA synthesis through the indole-3-pyruvic acid pathway when using cellulose as a sole carbon source. The mycelium as well as the culture filtrate promoted the growth and chlorophyll content of seedlings. In a monocotyledonous plant (rice), the number of lateral roots was increased experimentally, whereas in a dicotyledonous plant (tomato), the fungus led to an increased length of shoots and roots. TRP-dependent IAA production was demonstrated for the first time for P. pulmonarius and may be responsible for enhancing plant growth in vitro. Synthesis of IAA as the most prevalent phytohormone in plants has been demonstrated for soil microfungi. Pleurotus pulmonarius is reported as an IAA-producing wood-decay macrofungus. The higher temperature optimum of P. pulmonarius isolated from subtropical environment compared to other Pleurotus species from temperate regions makes it more suitable for application in subtropical/tropical regions.

Germination of soybean seeds exposed to the static/alternating magnetic field and algal extract.

In the present study, the effect of the static and alternating magnetic field applied individually and in combination with an algal extract on the germination of soybean seeds (Glycine max (L.) Merrill) and chlorophyll content was examined. The exposure time of seeds to the static magnetic field was 3, 6, and 12min, whereas to the alternating magnetic field was 1, 2.5, and 5min. The static magnetic field was obtained by means of a permanent magnets system while the alternating magnetic field by means of magnetic coils. Algal extract was produced from a freshwater macroalga-Cladophora glomerata using ultrasound homogenizer. In the germination tests, 10% extract was applied to the paper substrate before sowing. This is the first study that compares the germination of soybean seeds exposed to the static and alternating magnetic field. The best effect on the germination and chlorophyll content in seedlings had synergistic action of the static magnetic field on seeds for 3min applied together with the extract and alternating magnetic field used for 2.5min. It is not possible to clearly state which magnetic field better stimulated the germination of seeds, but the chlorophyll content in seedlings was much higher for alternating magnetic field.

The Effects for Delaying Banana Seedling Growth through Spraying Growing Retardants on Stem Apex

Replanting is always required for banana farmers. Selecting growth retardants is important for banana seedling companies. Stem apex contained many gibberellins. Seven treatments were performed onto stem apex of banana seedlings in this research. Results showed that heights of seedlings sprayed with paclobutrazol (200 mg/L), dniconazole (200 mg/L), and dniconazole + brassins (200 mg/L + 0.1 mg/L) were significantly lower than those of seedlings sprayed with water. Paclobutrazol was the ideal retardant for delaying the growth of leaf if stem apex was selected as a treated candidate. Fresh weights of seedlings of all seven treatments were significantly less than that of control. For delaying the growth of fresh weight of banana seedlings, chlormequat chloride (200 mg/L) was the best choice. Reducing power of roots of seedlings treated with 100 ml of paclobutrazol (200 mg/L) was significantly higher than that of seedling treated with water. Chlorophyll contents of seedlings treated with growth retardants were significantly higher than that of seedlings treated with water.

Effect of Used Lubricating Oil Contaminated Soil on Seed Germination and Early Growth Performance of Wild -Type Legume, Crotalaria retusa L.

Contamination of soil due to used lubricating oil (ULO) has become a common environmental issue, especially in major cities worldwide. This may affect negatively on overall soil quality and may pose a risk to biota. Phytoremediation is a novel green technological approach, which uses plants to remove organic and inorganic pollutants from contaminated soil, air and water and can be usefully used to clean up ULO contaminated soil. Screening of plant species with tolerance to ULO contamination is the most critical initial step in phytoremediation. The aim of the present study is to evaluate tolerance of Crotalaria retusa L. to ULO-contaminated soil. Germination of C. retusa seeds in soils with 1-5% w/w ULO contamination levels was tested according to the ISO method, with five replicates per treatment and ten seeds per replicate. Percentage inhibition of seed germination, root growth and biomass were measured at 48 and 72 hours of incubation. Results showed 100% seed germination in the control (uncontaminated soil) and all treatments indicating high tolerance of tested seeds to germinate in ULO-contaminated soil. However, there was a significant (p<0.05) reduction in root length of seedlings in all treatments above 3% w/w ULO. Therefore, a further pot experiment was carried out using ULO contamination levels of 0.5%, 1%, 1.5%, 2%, 2.5% and 3% w/w ULO. A fully randomized block design (RBD) was employed with 4 replicates per treatment and control. Percentage biodegradation of ULO and shoot height were measured monthly and at the end of a three month exposure chlorophyll a, b, total chlorophyll content, shoot height, root length, shoot system biomass and root system biomass were all measured. Results indicated time-dependent increases in percentage biodegradation of different treatments. At three months, percentage biodegradation was 52.2%, 43.8%, 35.6%, 32.2%, 25.2% and 22.0% for the 0.5-3.0% w/w ULO treatments, respectively. A decrease in growth parameters was observed with an increase in ULO contamination levels. However, the calculated IC50values inferred that the substantial negative effects resulted only on plants grown in soil with contamination levels greater than 2% w/w. There were no significant differences in chlorophyll contents of seedlings under any treatments. Therefore, from the present study we can conclude that C. retusa is able to grow in soils contaminated with ULO up to a level of 2% w/w without showing any negative effects. This result highlights the potential of C. retusa for the phytoremediation of ULO contaminated soil. Keywords: Crotalaria retusa, Phytoremediation, Used lubricant oil Acknowledgements: National Research Council, Sri Lanka (Grant No. 16-144) for financial assistance

Ecophysiological responses of Camellia japonica (Naidong) to different light and water conditions

Camellia japonica (Naidong), a Tertiary relict species with abundant morphological characteristics and special genetic characteristics, is the northernmost distributed population of C. japonica. The seedlings of Naidong were subjected to two light regimes (65%, 15% of full sunlight, respectively) and three water supply regimes (75%, 50% and 25% of field capacity, respectively). Our objectives were to reveal the ecophysiological responses of Naidong under different drought and shade conditions and to examine the four existing hypotheses explaining the responses of Naidong seedlings to the interactions of shade and drought. The results showed that 15% of full sunlight reduced the growth of seedlings. Compared with those under 65% of full sunlight condition, the net photosynthetic rate, transpiration rate and chlorophyll content of seedlings under 15% of full sunlight condition were decreased by 63.3%, 82.9% and 17.5%, respectively. In contrast, the specific leaf area, leaf water content and maximal quantum yield under 15% of full sunlight condition were enhanced by 60.3%, 8.3% and 6.4%, respectively. Drought limited the growth of seedlings,decreased their height and basal diameter. The net photosynthetic rate, transpiration rate and stomatal conductance of seedlings significantly decreased with the increases of drought stress, with their minimum values being 0.83 μmol·m-2·s-1, 0.30 μmol·m-2·s-1 and 11.56 mmol·m-2·s-1, respectively. With the increases of drought stress, the contents of peroxidase and catalase showed a general declining trend, but the contents of malondialdehyde and proline significantly increased. The treatment 15% of full sunlight alleviated the negative effects of drought on Naidong seedlings, which supported the above-ground facilitation hypothesis. Our results indicated that Naidong seedlings could respond and acclimate to environmental changes through various mechanisms, and the seedlings might normally grow under broad ranges of light and water stresses. In addition, providing ideal light and water conditions for the Naidong seedlings could facilitate its application in gardening.

Inoculation of oil palm seedlings in Malaysia with white-rot hymenomycetes: Assessment of pathogenicity and vegetative growth

The pathogenicity of white-rot hymenomycetes isolated from oil palm (Elaeis guineensis Jacq.) trunks and their effect on the vegetative growth of oil palm seedlings were investigated under nursery condition. The hymenomycetes were selected based on their potential antagonistic ability against the pathogen Ganoderma boninense from a previous study. Rubber wood blocks (RWB's) pre-colonized with either one of the seven hymenomycetes or the pathogen G. boninense PER 71 were placed in direct contact with the roots of three-month-old oil palm seedlings using a sitting technique. After nine months, the seedlings inoculated with G. boninense were severely infected and the infection had spread throughout the seedlings, causing basal stem rot. By contrast, the fronds and boles of the seedlings inoculated with each of the seven hymenomycetes were symptomless until the end of the 18-months study. The frond length of seedlings inoculated with Trametes lactinea FBW or Clitopilus prunulus ST3 was about 2.7-fold greater than those of seedlings inoculated with G. boninense PER 71. Similarly, after nine months, the chlorophyll content of seedlings inoculated with Lentinus tigrinus FBJ G3 or Pycnoporus sanguineus FBR was approximately 60 or 59 SPAD units, respectively, which was significantly higher than that of seedlings inoculated with G. boninense PER 71. The seedlings inoculated with each of the seven hymenomycetes showed a similar growth pattern in terms of frond count, plant girth, plant height and frond length, at nine months. These findings suggested the non-pathogenic nature of the selected seven white-rot hymenomycetes on oil palm seedlings and their possible use as biological control agents against the BSR pathogen, G. boninense. The findings should be further explored for their biocontrol potential under natural field conditions.

Effects of Zn2+ Stress on Seed Germination and growth of seedling

The effects of Zn2+ stress on seed germination, seedling growth and chlorophyll content were studied in order to better understand the effect of heavy metal Zn on the growth and development of green plants. The concentration gradient of Zn2+ was 20, 50,100,150,200,300,500,700mg / L, and deionized water was used as control. The results showed that under the Zn2+ stress condition, the germination index of the rhubarb seeds increased with the increase of Zn2+ concentration. Germination potential, germination rate and germination index were the highest when Zn2+concentration was 100mg / L, the conductivity was the lowest at zinc concentration of 100mg / L, the root length, stem length and chlorophyll content of Zn2+ gradually reduced. The results showed that the amount of Zn2+ could promote seed germination, but the root length, bud length and chlorophyll content of seedlings could be affected by different degrees. The zinc fertilizer should be used in the production.