Benefits of clean development mechanism application on the life cycle assessment perspective: a case study in the palm oil industry

This study performed an assessment on the beneficial of the Clean Development Mechanism (CDM) application on waste treatment system in a local palm oil industry in Malaysia. Life cycle assessment (LCA) was conducted to assess the environmental impacts of the greenhouse gas (GHG) reduction from the CDM application. Calculations on the emission reduction used the methodology based on AM002 (Avoided Wastewater and On-site Energy Use Emissions in the Industrial Sector) Version 4 published by United Nations Framework Convention on Climate Change (UNFCC). The results from the studies showed that the introduction of CDM in the palm oil mill through conversion of the captured biogas from palm oil mill effluent (POME) treatment into power generation were able to reduce approximate 0.12 tonnes CO2 equivalent concentration (tCO2e) emission and 30 kW x hr power generation per 1 tonne of fresh fruit bunch processed. Thus, the application of CDM methodology on palm oil mill wastewater treatment was able to reduce up to 1/4 of the overall environment impact generated in palm oil mill.     

Decolorization of palm oil mill effluent using growing cultures of Curvularia clavata

Agricultural wastewater that produces color are of environmental and health concern as colored effluent can produce toxic and carcinogenic by-products. From this study, batch culture optimization using response surface methods indicated that the fungus isolated from the pineapple solid waste, Curvularia clavata was able to decolorize sterile palm oil mill effluent (POME) which is mainly associated with polyphenol and lignin. Results showed successful decolorization of POME up to 80 % (initial ADMI [American Dye Manufacturing Index] of 3,793) with 54 % contributed by biosorption and 46 % by biodegradation after 5 days of treatment. Analysis using HPLC and GC-MS showed the degradation of color causing compound such as 3-methoxyphenyl isothiocynate and the production of new metabolites. Ecotoxicity test indicated that the decolorized effluent is safe for discharge. To determine the longevity of the fungus for a prolonged decolorization period, sequential batch decolorization studies were carried out. The results showed that lignin peroxidase and laccase were the main ligninolytic enzymes involved in the degradation of color. Carboxymethyl cellulase (CMCase) and xylanase activities were also detected suggesting possible roles of the enzymes in promoting growth of the fungus which consequently contributed to improved decolorization of POME. In conclusion, the ability of C. clavata in treating color of POME indicated that C. clavata is of potential use for decolorization and degradation of agricultural wastewater containing polyphenolic compounds.     

Physiological and biochemical mechanisms of spermine-induced cadmium stress tolerance in mung bean (<Emphasis Type="Italic">Vigna radiata</Emphasis> L.) seedlings

The role of exogenous spermine (0.25 mM Spm, a type of polyamine (PA) in reducing Cd uptake and alleviating Cd toxicity (containing 1 and 1.5 mM CdCl₂ in the growing media) effects was studied in the mung bean (Vigna radiata L. cv. BARI Mung-2) plant. Exogenously applied Spm reduced Cd content, accumulation, and translocation in different plant parts. Increasing phytochelatin content, exogenous Spm reduced Cd accumulation and translocation. Spm application reduced the Cd-induced oxidative damage which was reflected from the reduction of H₂O₂ content, O₂ ^?– generation rate, lipoxygenase (LOX) activity, and lipid peroxidation level and also reflected from the reduction of spots of H₂O₂ and O₂ ^?– from mung bean leaves (compared to control treatment). Spm pretreatment increased non-enzymatic antioxidant contents (ascorbate, AsA, and glutathione, GSH) and activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) which reduced oxidative stress. The cytotoxicity of methylglyoxal (MG) is also reduced by exogenous Spm because it enhanced glyoxalase system enzymes and components. Through osmoregulation, Spm maintained a better water status of Cd-affected mung bean seedlings. Spm prevented the chl damage and increased its content. Exogenous Spm also modulated the endogenous free PAs level which might have the roles in improving physiological processes including antioxidant capacity, osmoregulation, and Cd and MG detoxification capacity. The overall Spm-induced tolerance of mung bean seedlings to Cd toxicity was reflected through improved growth of mung bean seedlings.     

Baseline study of methane emission from open digesting tanks of palm oil mill effluent treatment

Anthropogenic release of greenhouse gases, especially CO₂ and CH₄ has been recognized as one of the main causes of global warming. Several measures under the Kyoto Protocol 1997 have been drawn up to reduce the greenhouse gases emission. One of the measures is Clean Development Mechanisms (CDM) that was created to enable developed countries to cooperate with developing countries in emission reduction activities. In Malaysia, palm oil industry particularly from palm oil mill effluent (POME) anaerobic treatment has been identified as an important source of CH₄. However, there is no study to quantify the actual CH₄ emission from the commercial scale wastewater treatment facility. Hence, this paper shall address the CH₄ emission from the open digesting tanks in Felda Serting Hilir Palm Oil Mill. CH₄ emission pattern was recorded for 52 weeks from 3600 m³ open digesting tanks. The findings indicated that the CH₄ content was between 13.5% and 49.0% which was lower than the value of 65% reported earlier. The biogas flow rate ranged between 0.8 l min⁻¹ m⁻² and 9.8 l min⁻¹ m⁻². Total CH₄ emission per open digesting tank was 518.9 kg day⁻¹. Relationships between CH₄ emission and total carbon removal and POME discharged were also discussed. Fluctuation of biogas production was observed throughout the studies as a result of seasonal oil palm cropping, mill activities, variation of POME quality and quantity discharged from the mill. Thus only through long-term field measurement CH₄ emission can be accurately estimated.     

Evaluation of olive oil mill wastewater toxicity on spinach

Background, aim, and scope

Olive oil mill wastewater (OMW), a by-product of the olive oil extraction process, is annually produced in huge amounts in olive-growing areas and represents a significant environmental problem in Mediterranean areas. We studied the impact of OMW dilutions (1:20 and 1:10) on spinach plants in order to evaluate OMW dilutions as a low-cost alternative method for the disposal of this waste.

Materials and methods

The effects of OMW dilutions were evaluated on seed germination, shoot and root elongation, biomass production, nutrient uptake and translocation, ascorbic acid content, polyphenols, photosynthetic pigments, and photosynthetic performance of spinach.

Results

Plant biomass was more affected than plant height and total chlorophyll; carotenoid and ascorbic acid content progressively decreased with decreasing OMW dilution. Exposure to both OMW dilutions resulted in overaccumulation of total polyphenols, which were negatively correlated to plant biomass and nutrients. Nutrient (Fe, Ca, and Mg) content was insufficient leading to reduced growth. Water use efficiency decreased mainly due to decreased CO₂ assimilation rate rather than to a decline of transpiration rate. Disturbances in photosystem II (PSII) photochemical efficiency could be better envisaged by the ratio between variable fluorescence and initial fluorescence (Fv/Fo), which showed much greater amplitude than the maximal photochemical efficiency of PSII photochemistry (Fv/Fm).

Conclusions

From the data obtained, it is suggested that 1:20 OMW dilutions are still phytotoxic and that higher OMW dilutions should be used in order to use this waste for the irrigation of spinach plants.     

Effect of vermicast generated from an allelopathic weed lantana (Lantana camara) on seed germination,plant growth,and yield of cluster bean (Cyamopsis tetragonoloba)

In perhaps the first-ever study of its kind, the effect of vermicompost, derived solely from an allelopathic weed, on the germination, growth, and yield of a botanical species, has been carried out. In test plots, the soil was treated with the vermicompost of lantana (Lantana camara) at the rates of 5, 7.5, and 10 t ha^?1, and cluster bean (Cyamopsis tetragonoloba) was grown on it. The performance of these systems was compared with the systems in which the soil was fortified with inorganic fertilizers (IFs) in concentrations equivalent to those present in the respective vermicompost (VC) treatments. Additionally, a set of control was studied in which the soil was used without fortification by either VC or IF. It was seen that up to 51.5 % greater germination success occurred in the VC treatments compared to controls. VC also supported better plant growth in terms of stem diameter, shoot length, shoot mass, number of leaves, and leaf pigments. The positive impact extended up to fruit yield. In addition, vermicast application enhanced root nodule formation, reduced disease incidence, and allowed for a smaller number of stunted plants. The results indicate that allelopathic ingredients of lantana seem to have been totally eliminated during the course of its vermicomposting and that lantana vermicompost has the potential to support germination, growth, and fruit yield better than equivalent quantities of IFs.     

Evaluation and refinement of a continuous seed germination and early seedling growth test for the use in the ecotoxicological assessment of soils.

Four higher plant species (Avena sativa L., oat; Lepidium sativum L., cress; Brassica rapa Metzg., turnip; and Phaseolus vulgaris L., bush bean) and 15 soils including five mineral oil-contaminated soils were tested to assess a soil-based continuous seed germination and early seedling growth bioassay. Seed germination was recorded and the shoot biomass of 14-day seedlings measured. An automatic self-watering system was compared with the daily hand watering. Results obtained from this study show that the self-watering system had minor effects on both seed germination and early seedling growth, and that soil nutrient status rather than soil texture significantly affected both seedling emergence and shoot biomass. Proportional dilution of suspicious samples from primary tests with an appropriate control soil is recommended for secondary tests. Shoot biomass is a more sensitive measurement endpoint than seed germination. Bush bean should not be recommended for use due to its low sensitivity to mineral oil and poor germination in soil.     

Optimization of decolorization of palm oil mill effluent (POME) by growing cultures of Aspergillus fumigatus using response surface methodology

The conventional treatment process of palm oil mill effluent (POME) produces a highly colored effluent. Colored compounds in POME cause reduction in photosynthetic activities, produce carcinogenic by-products in drinking water, chelate with metal ions, and are toxic to aquatic biota. Thus, failure of conventional treatment methods to decolorize POME has become an important problem to be addressed as color has emerged as a critical water quality parameter for many countries such as Malaysia. Aspergillus fumigatus isolated from POME sludge was successfully grown in POME supplemented with glucose. Statistical optimization studies were conducted to evaluate the effects of the types and concentrations of carbon and nitrogen sources, pH, temperature, and size of the inoculum. Characterization of the fungus was performed using scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, and Brunauer, Emmet, and Teller surface area analysis. Optimum conditions using response surface methods at pH 5.7, 35 °C, and 0.57 % w/v glucose with 2.5 % v/v inoculum size resulted in a successful removal of 71 % of the color (initial ADMI of 3,260); chemical oxygen demand, 71 %; ammoniacal nitrogen, 35 %; total polyphenolic compounds, 50 %; and lignin, 54 % after 5 days of treatment. The decolorization process was contributed mainly by biosorption involving pseudo-first-order kinetics. FTIR analysis revealed that the presence of hydroxyl, C–H alkane, amide carbonyl, nitro, and amine groups could combine intensively with the colored compounds in POME. This is the first reported work on the application of A. fumigatus for the decolorization of POME. The present investigation suggested that growing cultures of A. fumigatus has potential applications for the decolorization of POME through the biosorption and biodegradation processes.     

Determination of optimum polymeric coagulant in palm oil mill effluent coagulation using multiple-objective optimisation on the basis of ratio analysis (MOORA)

The main limitation of a conventional palm oil mill effluent (POME) ponding system lies in its inability to completely decolourise effluent. Decolourisation of effluent is aesthetically and environmentally crucial. However, determination of the optimum process parameters is becoming more complex with the increase of the number of coagulants and responses. The primary objective of this study is to determine the optimum polymeric coagulant in the coagulation–flocculation process of palm oil mill effluent by considering all output responses, namely lignin–tannin, low molecular mass coloured compounds (LMMCC), chemical oxygen demand (COD), ammonia nitrogen (NH₃-N), pH and conductivity. Here, multiple-objective optimisation on the basis of ratio analysis (MOORA) is employed to discretely measure multiple response characteristics of five different types of coagulants as a function of assessment value. The optimum coagulant is determined based on the highest assessment value and was identified as QF25610 (cationic polyacrylamide). On the other hand, the lowest assessment value was represented by AN1800 (anionic polyacrylamide). This study highlights the simplicity of MOORA approach in handling various input and output parameters, and it may be useful in other wastewater treatment processes as well.     

Effects of DDT on the growth of crop plants

The effects of DDT on the germination and growth of plants were studied using many crop species. Of the species tested, oil-rich seeds of plants, such as peanut (Arachis hypogaea) and mustard (Brassica juncea), were more prone to DDT induced inhibition of germination and subsequent plant growth than cereals, pulses and fibre crops, like rice (Oryza sativa), barley (Hordeum vulgare), mung bean Vigna radiata), pigeon pea (Cajanus cajan) and cotton (Gossypium hirsutum). Studies with (14)C labelled DDT showed that insecticide uptake by seeds was directly proportional to seed size. However, there was no direct relationship between DDT uptake by the seeds and its subsequent translocation to the growing regions or the degree of growth inhibition. Data suggest that oil content of the seeds per se has a bearing on the susceptibility or tolerance of a plant to DDT. It is suggested that lipids of the plant cell solubilize and disperse DDT in the cytoplasm, which, in turn, affects normal metabolism within the cell.     

Comparative mesophilic and thermophilic anaerobic digestion of palm oil mill effluent using upflow anaerobic sludge blanket

The effects of organic loading rate and operating temperature on the microbial diversity and performances of upflow anaerobic sludge blanket (UASB) reactors treating palm oil mill effluent (POME) were investigated. The following two UASB reactors were run in parallel for comparison: (1) under a mesophilic condition (37 degrees C) and (2) under a mesophilic condition in transition to a thermophilic condition (57 degrees C). A polymerase chain reaction (PCR)-based denaturing gradient gel electrophoresis (DGGE) analysis showed that the microbial population profiles significantly changed with the organic loading rate (OLR) and the temperature transition from the mesophilic to the thermophilic condition. Significant biomass washout was observed for the mesophilic UASB when operating at a high organic loading rate (OLR) of 9.5 g chemical oxygen demand (COD)/L.d. In contrast, the thermophilic UASB can be operated at this OLR and at a temperature of 57 degrees C with satisfactory COD removal and biogas production. The PCR-based DGGE analysis suggested that the thermophilic temperature of 57 degrees C was suitable for a number of hydrolytic, acidogenic, and acetogenic bacteria.     

Environmental effects of nanosilver: impact on castor seed germination, seedling growth, and plant physiology

Increasing use of nanoparticles in daily products is of great concern today, especially when their positive and negative impact on environment is not known. Hence, in current research, we have studied the impact of silver nanoparticle (AgNPs) and silver nitrate (AgNO₃) application on seed germination, root, and shoot length of castor bean, Ricinus communis L. plant. Silver nanoparticles had no significant effects on seedling growth even at higher concentration of 4,000 mg L^?1, while the silver in bulk form as AgNO₃ applied on the castor bean seeds inhibited the seed germination. Silver uptake in seedlings of the castor seeds on treatment with both the forms of silver was confirmed through atomic absorption spectroscopy studies. The silver nanoparticle and silver nitrate application to castor seeds also caused an enhanced enzymatic activity of ROS enzymes and phenolic content in castor seedlings. High-performance liquid chromatography analysis of individual phenols indicated enhanced content of parahydroxy benzoic acid. These kinds of studies are of great interest in order to unveil the movement and accumulation of nanoparticles in plant tissues for assessing future applications in the field or laboratory.     

28-Homobrassinolide mitigates boron induced toxicity through enhanced antioxidant system in Vigna radiata plants

The objective of this study was to establish relationship between boron induced oxidative stress and antioxidant system in Vigna radiata plants and also to investigate whether brassinosteroids will enhance the level of antioxidant system that could confer tolerance to the plants from the boron induced oxidative stress. The mung bean (V. radiata cv. T-44) plants were administered with 0.50, 1.0 and 2.0 mM boron at 6 d stage for 7 d along with nutrient solution. At 13 d stage, the seedlings were sprayed with deionized water (control) or 10⁻⁸ M of 28-homobrassinolide and plants were harvested at 21 d stage to assess growth, leaf gas-exchange traits and biochemical parameters. The boron treatments diminished growth, water relations and photosynthetic attributes along with nitrate reductase and carbonic anhydrase activity in the concentration dependent manner whereas, it enhanced lipid peroxidation, electrolyte leakage, accumulation of H₂O₂ as well as proline, and various antioxidant enzymes in the leaves of mung bean which were more pronounced at higher concentrations of boron. However, the follow-up application of 28-homobrassinolide to the boron stressed plants improved growth, water relations and photosynthesis and further enhanced the various antioxidant enzymes viz. catalase, peroxidase and superoxide dismutase and content of proline. The elevated level of antioxidant enzymes as well as proline could have conferred tolerance to the B-stressed plants resulting in improved growth, water relations and photosynthetic attributes.     

Characteristics of granular sludge developed in an upflow anaerobic sludge fixed-film bioreactor treating palm oil mill effluent.

In the present study, characteristics of the granular sludge (including physical characteristics under stable conditions and process shocks arising from suspended solid overload, soluble organic overload, and high temperature; biological activity; and sludge kinetic evaluation in a batch experiment) developed in an upflow anaerobic sludge blanket fixed-film reactor for palm oil mill effluent (POME) treatment was investigated. The main aim of this work was to provide suitable understanding of POME anaerobic digestion using such a granular sludge reactor, particularly with respect to granule structure at various operating conditions. The morphological changes in granular sludge resulting from various operational conditions was studied using scanning electron microscopy and transmission electron microscopy images. It was shown that the developed granules consisted of densely packed rod- (Methanosaeta-like microorganism; predominant) and cocci- (Methanosarsina) shaped microorganisms. Methanosaeta aggregates functioned as nucleation centers that initiated granule development of POME-degrading granules. Under the suspended solid overload condition, most of the granules were covered with a thin layer of fiberlike suspended solids, so that the granule color changed to brown and the sludge volume index also increased to 24.5 from 12 to 15 mL/g, which caused a large amount of sludge washout. Some of the granules were disintegrated because of an acidified environment, which originated from acidogenesis of high influent organic load (29 g chemical oxygen demand [COD]/L d). At 60 degrees C, the rate of biomass washout increased, as a result of disintegration of the outer layer of the granules. In the biological activity test, approximately 95% COD removal was achieved within 72 hours, with an initial COD removal rate of 3.5 g COD/L d. During POME digestion, 275 mg calcium carbonate/L bicarbonate alkalinity was produced per 1000 mg COD(removed)/ L. A consecutive reaction kinetic model was used to simulate the data obtained from the sludge activity in the batch experiment. The mathematical model gave a good fit with the experimental results (R2 > 0.93). The slowest step was modeled to be the acidification step, with a rate constant between 0.015 and 0.083 hours(-1), while the rate constant for the methanogenic step was obtained to be between 0.218 and 0.361 hours(-1).     

Enhanced reduction of phenol content and toxicity in olive mill wastewaters by a newly isolated strain of Coriolopsis gallica

The search for novel microorganisms able to degrade olive mill wastewaters (OMW) and withstand the toxic effects of the initially high phenolic concentrations is of great scientific and industrial interest. In this work, the possibility of reducing the phenolic content of OMW using new isolates of fungal strains (Coriolopsis gallica, Bjerkandera adusta, Trametes versicolor, Trichoderma citrinoviride, Phanerochaete chrysosporium, Gloeophyllum trabeum, Trametes trogii, and Fusarium solani) was investigated. In vitro, all fungal isolates tested caused an outstanding decolorization of OMW. However, C. gallica gave the highest decolorization and dephenolization rates at 30 % v/v OMW dilution in water. Fungal growth in OMW medium was affected by several parameters including phenolic compound concentration, nitrogen source, and inoculum size. The optimal OMW medium for the removal of phenolics and color was with the OMW concentration (in percent)/[(NH₄)₂SO₄]/inoculum ratio of 30:6:3. Under these conditions, 90 and 85 % of the initial phenolic compounds and color were removed, respectively. High-pressure liquid chromatography analysis of extracts from treated and untreated OMW showed a clear and substantial reduction in phenolic compound concentrations. Phytotoxicity, assessed using radish (Raphanus sativus) seeds, indicated an increase in germination index of 23–92 % when a 30 % OMW concentration was treated with C. gallica in different dilutions (1/2, 1/4, and 1/8).

Palm oil mill effluent treatment and CO<Subscript>2</Subscript> sequestration by using microalgae—sustainable strategies for environmental protection

In this era of globalization, various products and technologies are being developed by the industries. While resources and energy are utilized from processes, wastes are being excreted through water streams, air, and ground. Without realizing it, environmental pollutions increase as the country develops. Effective technology is desired to create green factories that are able to overcome these issues. Wastewater is classified as the water coming from domestic or industrial sources. Wastewater treatment includes physical, chemical, and biological treatment processes. Aerobic and anaerobic processes are utilized in biological treatment approach. However, the current biological approaches emit greenhouse gases (GHGs), methane, and carbon dioxide that contribute to global warming. Microalgae can be the alternative to treating wastewater as it is able to consume nutrients from wastewater loading and fix CO₂ as it undergoes photosynthesis. The utilization of microalgae in the system will directly reduce GHG emissions with low operating cost within a short period of time. The aim of this review is to discuss the uses of native microalgae species in palm oil mill effluent (POME) and flue gas remediation. In addition, the discussion on the optimal microalgae cultivation parameter selection is included as this is significant for effective microalgae-based treatment operations.     

Protective role of a methanolic extract of spinach (Spinacia oleracea L.) against Pb toxicity in wheat (Triticum aestivum L.) seedlings: beneficial effects for a plant of a nutraceutical used with animals

Spinach extracts contain powerful natural antioxidants and have been used to improve the response of animal cells to various stress factors. The aim of the present study was to assess the effects of a methanolic extract of spinach (SE) used at two concentrations (21.7 and 217 ppm) on the growth, certain enzymes and antioxidant systems in wheat seedlings under lead stress. When wheat seedlings were grown for 7 days in a solution containing Pb(NO₃)₂ (3 mM), germination and growth were impaired, while signs of oxidative stress were observed. SE (217 ppm) pretreatment was able to protect seedlings from Pb toxicity by both reducing Pb uptake and Pb-induced oxidative stress. As a consequence, almost normal germination, elongation, biomass and α-amylase activity were restored by SE (217 ppm) pretreatment of wheat seedlings, in spite of the presence of Pb. Our results support the protective role and the antioxidant effect of SE against Pb. These results show an amazing similarity to the effects of SE in animals, which suggests that providing “nutraceuticals” to plants could improve their “health” status.     

Germination, growth and gas exchange of selected boreal forest seedlings in soil containing oil sands tailings

Greenhouse experiments were conducted to determine the effects of soil enriched in fine tailings (FT), produced by the oil sands extraction, on germination, seedling growth and physiology of several plant species of the boreal forest. The germination of seeds was initially delayed by 15% FT in dogwood (Cornus stolonifera Michx) and jack pine (Pinus banksiana Lamb) but not in white spruce [Picea glauca (Moench) Voss]. In the second set of experiments we showed that all dogwood seedlings survived 6 months of treatment with 15% FT while the survival rates of raspberry, jack pine and white spruce seedlings were reduced to 44, 55 and 94%, respectively. FT reduced root and shoot dry weights in raspberry seedlings and the number of lateral shoots in jack pine and white spruce seedlings. In raspberry and jack pine seedlings, reductions of gas exchange were recorded. The results of our study suggest that the modifications of soil chemistry, texture and structure by FT may all contribute to the observed phytotoxic effects.     

Reusing colored industrial wastewaters in a photofermentation for enhancing biohydrogen production by using ultrasound stimulated <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis>

One-time ultrasonication pre-treatment of Rhodobacter sphaeroides was evaluated for improving biohydrogen production via photofermentation. Batch experiments were performed by varying ultrasonication amplitude (15, 30, and 45%) and duration (5, 10, and 15 min) using combined effluents from palm oil as well as pulp and paper mill as a single substrate. Experimental data showed that ultrasonication at amplitude 30% for 10 min (256.33 J/mL) achieved the highest biohydrogen yield of 9.982 mL H₂/mL_medium with 5.125% of light efficiency. A maximum COD_total removal of 44.7% was also obtained. However, when higher ultrasonication energy inputs (>256.33 J/mL) were transmitted to the cells, biohydrogen production did not improve further. In fact, 20.6% decrease of biohydrogen yield (as compared to the highest biohydrogen yield) was observed using the most intense ultrasonicated inoculum (472.59 J/mL). Field emission scanning electron microscope images revealed the occurrence of cell damages and biomass losses if ultrasonication at 472.59 J/mL was used. The present results suggested that moderate ultrasonication pre-treatment was an effective technique to improve biohydrogen production performances of R. sphaeroides.     

Seeds’ physicochemical traits and mucilage protection against aluminum effect during germination and root elongation as important factors in a biofuel seed crop (Ricinus communis)

We determined the length, volume, dry biomass, and density in seeds of five castor bean cultivars and verified notable physicochemical trait differences. Seeds were then subjected to different toxic aluminum (Al) concentrations to evaluate germination, relative root elongation, and the role of root apices’ rhizosphere mucilage layer. Seeds’ physicochemical traits were associated with Al toxicity responses, and the absence of Al in cotyledons near to the embryo was revealed by Al-hematoxylin staining, indicating that Al did not induce significant germination reduction rates between cultivars. However, in the more sensitive cultivar, Al was found around the embryo, contributing to subsequent growth inhibition. After this, to investigate the role of mucilage in Al tolerance, an assay was conducted using NH₄Cl to remove root mucilage before or after exposure to different Al concentrations. Sequentially, the roots were stained with hematoxylin and a quantitative analysis of staining intensity was obtained. These results revealed the significant contribution of the mucilage layer to Al toxicity responses in castor bean seedlings. Root growth elongation under Al toxicity confirmed the role of the mucilage layer, which jointly indicated the differential Al tolerance between cultivars and an efficient Al-exclusion mechanism in the tolerant cultivar.