Al-tolerant Variety Research Articles

Development of ammonium nitrate free nutrient media for aluminium toxicity tolerance screening of rice genotypes from North-Eastern India

North-Eastern India is blessed with a vast diversity of rice genotypes with varying yielding abilities. However, the predominant strong soil acidity induced nutrient stresses from the toxicity of aluminum (Al3+) ions often causes sub-optimal rice productivity. The lack of suitable nutrient media for the screening of aluminum (Al) toxicity tolerance of rice genotypes is one of the limiting factors in Al tolerant varieties' development. Modified Magnavaca's solution has been the most recommended nutrient solution for this purpose where ammonium nitrate is the primary nitrogen source. However, strict regulations related to the handling and storage of ammonium nitrate in India limit the preparation of Modified Magnavaca’s solution for laboratory use. Here, a modified ammonium nitrate-free formulation based upon the Magnavaca's solution has been proposed. The modified formulation was found to have 160.9 µM of active Al3+ concentration when 550 µM of aluminum chloride hexahydrate (AlCl3.6H2O) was added at pH 4.1 to the solution. Through a plant growth screening experiment using ten diverse rice genotypes a significant difference in the response of various genotypes to differential Al toxicity levels on root growth performance indicators was observed. Based on the response, we could able to categorize the genotypes into tolerant and sensitive in relative terms. Thus, the present experiment provided an important nutrient formulation suitable for screening rice genotypes under Al toxicity conditions. Moreover, the selected tolerant and sensitive genotypes can further pave the way for studying the molecular mechanism of Al toxicity response in rice and their use in the breeding program.

Metabolome Analysis under Aluminum Toxicity between Aluminum-Tolerant and -Sensitive Rice (Oryza sativa L.).

Aluminum (Al) solubilizes into trivalent ions (Al3+) on acidic soils, inhibiting root growth. Since about 13% of global rice cultivation is grown on acidic soils, improving Al tolerance in rice may significantly increase yields. In the present study, metabolome analysis under Al toxicity between the Al-tolerant variety Nipponbare and the Al-sensitive variety H570 were performed. There were 45 and 83 differential metabolites which were specifically detected in Nipponbare and H570 under Al toxicity, respectively. Furthermore, the results showed that 16 lipids out of 45 total metabolites were down-regulated, and 7 phenolic acids as well as 4 alkaloids of 45 metabolites were up-regulated in Nipponbare, while 12 amino acids and their derivatives were specifically detected in H570, of which 11 amino acids increased, including L-homoserine and L-methionine, which are involved in cysteine synthesis, L-ornithine and L-proline, which are associated with putrescine synthesis, and 1-aminocyclopropane-1-carboxylate, which is associated with ethylene synthesis. The contents of cysteine and s-(methyl) glutathione, which were reported to be related to Al detoxification in rice, decreased significantly. Meanwhile, putrescine was accumulated in H570, while there was no significant change in Nipponbare, so we speculated that it might be an intermediate product of Al detoxification in rice. The differential metabolites detected between Al-tolerant and -sensitive rice variants in the present study might play important roles in Al tolerance. These results provide new insights in the mechanisms of Al tolerance in rice.

Integration of GWAS and transcriptome analyses to identify SNPs and candidate genes for aluminum tolerance in rapeseed (Brassica napus L.)

BackgroundThe exchangeable aluminum (Al), released from the acid soils, is another addition to the environmental stress factors in the form of Al toxicity stress. Al stress affects the normal crop development and reduces the overall yield of rapeseed (Brassica napus L.). The response mechanism of plants to Al toxicity is complicated and difficult to understand with few QTL related studies in rapeseed under Al toxicity stress.ResultUsing 200,510 SNPs developed by SLAF-seq (specific-locus amplified fragment sequencing) technology, we carried out the genome-wide association analysis (GWAS) in a population of 254 inbred lines of B. napus with large genetic variation and Al-tolerance differences. There were 43 SNPs significantly associated with eight Al-tolerance traits in the seedling stage were detected on 14 chromosomes, and 777 candidate genes were screened at the flanking 100 kb region of these SNPs. Moreover, RNA-seq detected 8291 and 5341 DEGs (the differentially expressed gene) in the Al -tolerant line (ATL) and -sensitive line (ASL), respectively. Based on integration of GWAS and RNA-seq analysis, 64 candidate genes from GWAS analysis differentially expressed at least once in 6 h vs 0 h or 24 h vs 0 h conditions in ATL or ASL. Moreover, four out of sixty-four candidate genes (BnaA03g30320D, BnaA10g11500D, BnaC03g38360D and BnaC06g30030D) were differentially expressed in both 6 h and 24 h compared to 0 h (control) conditions in both lines. The proposed model based on the candidate genes excavated in this study highlighted that Al stress disturb the oxidation-redox balance, causing abnormal synthesis and repair of cell wall and ABA signal transduction, ultimately resulting in inhibition of root elongation.ConclusionsThe integration of GWAS and transcriptome analysis provide an effective strategy to explore the SNPs and candidate genes, which has a potential to develop molecular markers for breeding Al tolerant rapeseed varieties along with theoretical basis of molecular mechanisms for Al toxicity response of Brassica napus plants.

Morpho-physiological responses of indica rice (Oryza sativa sub. indica) to aluminum toxicity at seedling stage.

Aluminum (Al) toxicity in acidic soils is a major problem in rice crop production, especially in the acid sulfate soil (pH < 4.0). Selecting Al-tolerant varieties of rice with low toxicity is one of the most appropriate strategies to overcome this problem. In the present study, we investigated the Al content in different rice genotypes, IR64 (high yielding), RD35 (local acidic-tolerant), and Azucena (AZU, positive-check Al-tolerant), and their physiological and morphological adaptations under a wide range Al (10, 25, 50 mM [Al2(SO4)3]) treatments in the greenhouse conditions. Under 50-mM Al treatment, Al levels in the root tissues of rice seedlings cvs. AZU and IR64 were increased by 2.74- and 2.10-fold over control. Interestingly, Al contents in the roots of cv. RD35 were also exhibited by 2.04-fold over control. Similarly, Al contents in the leaves trend to increase in relation to a degree of Al treatments, leading to increase leaf temperature, chlorophyll degradation, limited CO2 assimilation, and negative effect on root traits under 50 mM Al were evidently observed. Therefore, leaf temperature was considered a sensitive parameter regulated by high concentration of Al (50 mM), leading to increase in crop water stress index (CWSI > 0.6) and decrease in stomata conductance. Net photosynthetic rate (Pn) and transpiration rate (E) in rice seedlings of cv. RD35 subjected to 50 mM Al were significantly dropped by 74.76% and 47.71% over the control, respectively, resulting in reduced growth performances in terms of root length (26.57% reduction) and shoot fresh weight (46.15% reduction). An enrichment of Al in the root tissues without toxicity in rice cv. AZU may further help in discovering the Al homeostasis. In summary, Al enrichment in rice genotypes grown under Al-treatments was evidently observed in the root, leading to the limited root growth, root length, and root dry weight, especially in cv. RD35. Al restriction in the root tissues of cv. AZU (Al-tolerant) may play a key role as defense mechanisms to avoid translocation to other organs and the stomata closure was an alternative key factor to limit H2O transpiration.

Genome-wide association analysis of aluminum tolerance related traits in rapeseed (Brassica napus L.) during germination

With the increasing acidification of soil, aluminum (Al) toxicity has become one of the most important stress factors affecting seed germination quality and crop yield. To investigate the Al tolerance on seed germination, genome-wide association analysis (GWAS) of 19,949 SNPs with genome-wide coverage was used to identify the candidate genes, which were potentially related to germinate traits of rapeseed (Brassica napus L.) under Al stress. In the experiment, 169 rapeseed cultivars (lines) were treated with AlCl3 solution of 90 ppm, and distilled water was added to the control. At the 7th day, the phenotype data, including root length and dry weight, were measured and calculated. Using the TASSEL software, Al tolerance related traits were explored in rapeseed under germination with a 60 K Brassica Illumina® Infinium SNP array. Then, the structure of the population was analyzed with the STRUCTURE software, and the genetic relationship and LD attenuation were analyzed with the software TASSEL, respectively. The GWAS of relative root length (RRL) and relative dry weight (RDW) with SNP markers were carried out under the optimal model. Meanwhile, the candidate genes were predicted based on the LD interval sequence of the associated SNP locus. Subsequently, the homologous genes of rapeseed related to Al tolerance in the target genome region were screened in Arabidopsis thaliana (L.) Heynh. The results showed that 13 SNPs were significantly associated with these two traits. Among them, 8 SNPs were significantly associated with RRL and located on chromosomes A03, A07, A09, A10, C05, C06, and C09, respectively. Five SNPs were significantly associated with RDW and located on chromosomes A03, A04, A10, C05, and C07, respectively. Afterward, fifty-nine candidate genes related to Al tolerance were identified in the LD region of these SNP loci. Four of these genes were involved in the growth regulation about organic acid, ten were involved in growth-regulating substance, eleven were related to oxidative stress, and nineteen were involved in carbon and nitrogen metabolism. The results of this study provided a theoretical basis for Al tolerance in rapeseed and laid out a foundation for further functional verification of genes and cultivation of new Al tolerant rapeseed varieties.

Cluster Analysis and SSR (Simple Sequence Repeats) Primers Selection for Aluminium Tolerance on Hot Pepper

Perakitan varietas unggul cabai merah toleran Al (Aluminium) merupakan solusi terbaik untuk mengatasi persoalan rendahnya produkvitas cabai di lahan kering masam. Identifikasi tetua toleran dan marka SSR (Simple Sequence Repeats) sangat bermanfaat dalam meningkatkan efektifitas program pemuliaan tanaman untuk merakit varietas toleran terhadap cekaman aluminium. Seleksi primer SSR adalah bagian awal yang penting dalam pengembangan marka molekuler tersebut. Penelitian bertujuan untuk menentukan kelompok genotipe toleran alumunium dan menentukan primer prospektif dalam pengembangan marka SSR untuk sifat toleran terhadap Al pada tanaman cabai. Evaluasi tingkat toleransi 27 genotipe cabai terhadap cekaman aluminium dilakukan menggunakan hidroponik sistem sumbu dengan larutan hara AB mix ditambah 500 ppm AlCl3.6H2O. Tahap selanjutnya adalah menguji 20 primer SSR dalam mengamplifikasi DNA genom cabai toleran dan peka yang mewakili. Hasil analisis cluster sifat toleransi terhadap 27 genotipe cabai menghasilkan 7 kelompok tingkat toleransi terhadap aluminium. Individu PBC396 dan PBC518 adalah genotipe yang sangat toleran terhadap cekaman aluminium yang unik sehingga keduanya sangat baik digunakan sebagai tetua dalam pengembangan cabai toleran aluminium. Primer SSR yang potensial menghasilkan marka polimorfik untuk sifat toleran terhadap cekaman aluminium pada cabai adalah TMS7 dan CAMS358. Primer tersebut selanjutnya harus diuji pada mapping population untuk menentukan pita yang dapat digunakan sebagai penanda toleransi terhadap aluminium.&#x0D; Kata kunci: Capsicum annuum, NTSYS, sidik gerombol, tenggang masam

Transcriptomic Analysis for Indica and Japonica Rice Varieties under Aluminum Toxicity.

Aluminum (Al) at high concentrations inhibits root growth, damage root systems, and causes significant reductions in rice yields. Indica and Japonica rice have been cultivated in distinctly different ecological environments with different soil acidity levels; thus, they might have different mechanisms of Al-tolerance. In the present study, transcriptomic analysis in the root apex for Al-tolerance in the seedling stage was carried out within Al-tolerant and -sensitive varieties belonging to different subpopulations (i.e., Indica, Japonica, and mixed). We found that there were significant differences between the gene expression patterns of Indica Al-tolerant and Japonica Al-tolerant varieties, while the gene expression patterns of the Al-tolerant varieties in the mixed subgroup, which was inclined to Japonica, were similar to the Al-tolerant varieties in Japonica. Moreover, after further GO (gene ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analyses of the transcriptomic data, we found that eight pathways, i.e., “Terpenoid backbone biosynthesis”, “Ribosome”, “Amino sugar and nucleotide sugar metabolism”, “Plant hormone signal transduction”, “TCA cycle”, “Synthesis and degradation of ketone bodies”, and “Butanoate metabolism” were found uniquely for Indica Al-tolerant varieties, while only one pathway (i.e., “Sulfur metabolism”) was found uniquely for Japonica Al-tolerant varieties. For Al-sensitive varieties, one identical pathway was found, both in Indica and Japonica. Three pathways were found uniquely in “Starch and sucrose metabolism”, “Metabolic pathway”, and “Amino sugar and nucleotide sugar metabolism”.

Identifying aluminum tolerance in rice with a molecular marker

Improving rice aluminum (Al) tolerance in acid soils is highly significant to rice production. So far, no molecular marker which can efficiently identify rice Al tolerance has been developed. In this study, Art1, a primer specific for the ART1 gene was designed to study whether some natural variations exist in ART1 between Al tolerant and sensitive varieties. The results showed that two Al tolerant varieties had identical nucleotides and amino acids, while three Al sensitive varieties had the same nucleotides and amino acids differing from the two Al tolerant varieties. The same results were discovered within 150 rice varieties of Ting’s core collection. Art1 could be used to judge rice Al tolerance.

MECHANISM OF ALUMINUM TOXICITY AVOIDANCE IN TROPICAL RICE (Oryza sativa), MAIZE (Zea mays), AND SOYBEAN (Glycine max)

Planting Al tolerant crops is an economically justifiable approach in crop production on acid soils. Experiments were conducted to study the mechanisms of Al tolerance among species and varieties of tropical rice, maize, and soybean with previously known levels of Al tolerance. These varieties were hydroponically cultured in 0, 5, 10, and 30 mg l-1 Al with complete nutrient solution at pH 4. The results show that root/shoot ratio of dry weight at 10 mg l-1 Al treatment was an important parameter to indicate differential Al tolerance in maize. Oxalic acid exudation from roots cannot always explain the Al tolerance. Total organic acid concentration in roots at 10 mg l-1 Al treatment indicated a difference of Al tolerance in soybean and lowland rice. Aluminum translocation from roots to shoots was lower in tolerant varieties than in sensitive varieties of soybean. Increased Al concentration in shoots with increased Al level in the solution was larger in soybean and maize than in lowland or upland rice. Among varieties of soybean, the Al concentration in shoots increased drastically in Wilis (Al-sensitive variety) with increase Al level, while in Kitamusume (Al-tolerant variety) it did not.

MECHANISM OF ALUMINUM TOXICITY AVOIDANCE IN TROPICAL RICE (Oryza sativa), MAIZE (Zea mays), AND SOYBEAN (Glycine max)

Planting Al tolerant crops is an economically justifiable approach in crop production on acid soils. Experiments were conducted to study the mechanisms of Al tolerance among species and varieties of tropical rice, maize, and soybean with previously known levels of Al tolerance. These varieties were hydroponically cultured in 0, 5, 10, and 30 mg l-1 Al with complete nutrient solution at pH 4. The results show that root/shoot ratio of dry weight at 10 mg l-1 Al treatment was an important parameter to indicate differential Al tolerance in maize. Oxalic acid exudation from roots cannot always explain the Al tolerance. Total organic acid concentration in roots at 10 mg l-1 Al treatment indicated a difference of Al tolerance in soybean and lowland rice. Aluminum translocation from roots to shoots was lower in tolerant varieties than in sensitive varieties of soybean. Increased Al concentration in shoots with increased Al level in the solution was larger in soybean and maize than in lowland or upland rice. Among varieties of soybean, the Al concentration in shoots increased drastically in Wilis (Al-sensitive variety) with increase Al level, while in Kitamusume (Al-tolerant variety) it did not.

Pengujian Nomor-nomor Harapan Padi Tahan Al dan pH Rendah Hasil Seleksi In Vitro dengan Kultur Hara

&lt;p&gt;Rice productivity in acid soil is very low because of low pH,&lt;br /&gt;low availability of N, P, K, Ca, Mg, Mo, toxicity of Al and Mn.&lt;br /&gt;Development of Al tolerant varieties could increase rice&lt;br /&gt;productivity in acid soil. Somaclonal variation and in vitro&lt;br /&gt;selection method can be used to develop new Al tolerance&lt;br /&gt;varieties. A rapid screening method is needed to select a&lt;br /&gt;large number of new genotypes or new inbred lines in plant&lt;br /&gt;breeding, such as solution culture methods to evalu-ate Altolerant&lt;br /&gt;rice. This methods was used to know the response&lt;br /&gt;to Al in the seedling stage, root development, and pH&lt;br /&gt;changing. In this experiment solution culture method was&lt;br /&gt;used to evaluate the new genotypes derived from somaclonal&lt;br /&gt;variation and in vitro selection methods. These new&lt;br /&gt;genotypes have been tested the tolerance characteristic by&lt;br /&gt;using AlCl36H2O at 6 concentrations (0, 100, 200, 300, 400,&lt;br /&gt;and 500 ppm). Yoshida solution with two Al concentration&lt;br /&gt;were used to tested these genotypes. Measurement of Al&lt;br /&gt;tolerance was based on root development by using Relative&lt;br /&gt;Root Length (RRL), the relativity of root length at 45 ppm and&lt;br /&gt;0 ppm. Almost all of the genotypes have RRLs higher than&lt;br /&gt;0.7, which means that there was a positive correlation&lt;br /&gt;between the in vitro method and solution culture method. In&lt;br /&gt;this experiment pH changes were not applicable to measure&lt;br /&gt;the tolerance of the rice genotypes to Al and low pH.&lt;/p&gt;

The effects of root surface charge and nitrogen forms on the adsorption of aluminum ions by the roots of rice with different aluminum tolerances

Our objectives were to compare effects of root charge properties on Al adsorption by the roots of rice that differed in Al-tolerance, and to examine effects of different nitrogen forms on charge properties of rice roots and Al adsorption. Streaming potential and chemical methods were used to measure root zeta potential and investigate Al chemical forms adsorbed on the roots of rice obtained from solution culture experiments. Rice roots of the Al-sensitive variety Yangdao-6 carried greater negative charge than the Al-tolerant variety Wuyunjing-7, which meant the roots of Yangdao-6 adsorbed more exchangeable and complexed Al. When both rice varieties were grown in NH4 +-containing nutrient solutions, there were less functional groups and lower negative surface charge on their roots, which reduced Al adsorption compared to the rice grown in NO3 − containing nutrient solutions. The decline in nutrient solution pH due to NH4 + uptake by rice roots was responsible for the reduced numbers of functional groups and the lower negative surface charge on the roots compared to the rice grown in NO3 − containing solutions. Integrated root surface charge, as expressed by zeta potential, played an important role in Al adsorption by the roots of rice with different Al-tolerance.

A new allele of acid soil tolerance gene from a malting barley variety.

BackgroundAcid soil is a serious limitation to crop production all over the world. Toxic aluminium (Al) cations in acid soil inhibit root growth and reduce yield. Although a gene tolerant to acid soil has been identified, it has not been used in malting barley breeding, which is partly due to the acid soil tolerance gene being linked to unfavorable malting quality traits.ResultsA Brazilian malting barley variety Br2 was identified as tolerant to acid soil. A doubled haploid (DH) population was developed from a cross between Br2 and the Australian acid-sensitive cultivar Hamelin. The DH population was tested for acid soil tolerance in native acid soil and a hydroponic system with pH 4.2, pH 4.2 + Al or pH 6.5, and genotyped using SSR, DArT and gene-specific markers. A single QTL was detected for all parameters related to acid soil tolerance. The QTL was mapped to the known HvMATE location on chromosome 4H. Sequence alignment of the HvMATE gene identified 13 INDELs and 87 SNPs, where one SNP coded for a single amino acid difference between the two varieties. A gene-specific marker was developed to detect the single nucleotide polymorphism between Hamelin and Br2. This marker co-segregated with aluminium tolerance and accounted for 79 % of phenotypic variation for acid soil tolerance.ConclusionThe present study identified a novel source of acid soil/Al tolerance from a Brazilian malting barley cultivar Br2. This variety tolerated Al toxicity but was sensitive to low pH which is similar to most other Al-tolerant varieties. A gene-specific marker Cit7 was developed based on the HvMATE gene sequence. Cit7 will improve the efficiency of molecular-assisted selection of new barley varieties with tolerance to acid soil. Multiple alleles exist for the acid soil tolerance gene on chromosome 4H, so a malting barley variety that tolerates acid soil could be developed by selecting suitable tolerant alleles. Tolerance to low pH may play an important role for barley to adapt to acid soils.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-015-0254-4) contains supplementary material, which is available to authorized users.

Interactive regulation of nitrogen and aluminum in rice

Despite many studies on the high aluminum (Al) tolerance of rice (Oryza sativa), its exact mechanisms remain largely unknown. It is also unclear why Al improves growth of some plants. Our research on interactions between nitrogen (N) and Al may help to understand these phenomena. Previously, we found that ammonium-supplemented rice was more Al tolerant than nitrate-supplemented rice. Furthermore, Al-tolerant rice varieties preferred ammonium, while Al-sensitive ones preferred nitrate; in fact, Al tolerance was significantly correlated with the ammonium/nitrate preference among rice varieties. Al even enhanced growth of ammonium-supplemented rice, while it inhibited growth of nitrate-supplemented rice. Based on our own and other reports on N-Al interactions, we propose that intermediate products of N metabolism may play a role in rice Al tolerance. Al-enhanced ammonium utilization may explain why Al promotes growth of some plants, since Al often coexists with higher levels of ammonium than nitrate in acid soils.

Sensitivity of Barley Varieties to Aluminum Ions: Separately Effects and Combine with Iron Ions

Differences in the barley varieties have been revealed from tolerance to iron (Fe) and aluminum (Al) ions as well as to their combined effect. Received results allowed to separate barley variety into some (three) groups: the first—Al-tolerant varieties, the second—Al-sensitive ones and third—moderately resistant variety. The increased concentration of Fe had practically no effect on biometric (seed germination energy) and cytogenetics (frequency of chromosome aberrations and mitotic index) parameters as compared to the reference values. At the same time, iron ion significantly reduces the phytotoxic effect for Al-tolerant varieties in case of these elements jointly presented in solution.

Effect of aluminum toxicity on flowering time and grain yield on rice genotypes differing in Al-tolerance

Aluminum is a major phytotoxic mineral in the soil at low pH conditions. The effect of aluminum (Al) on root length, flowering time, dry matter production, and grain yield was examined using two tolerant, Pungsan (PS) and Geumgang (GG), and one susceptible, IR36, rice varieties to acid soil. Rice seedlings were subjected to two Al treatments (+Al, 150 μM of Al; −Al, 0 μM of Al) in solution culture, where pH was always adjusted at 3.5. PS and GG showed significantly larger root length than IR36 in +Al at 2 and 8 weeks after the treatment (WAT). Flowering time was delayed 9 days in +Al compared to −Al in GG and PS and 27 days in IR36. Dry matter weight and grain yield of GG and PS were also significantly higher than those of IR36 under +Al. The inhibition of such agronomic traits by Al toxicity was less in Al-tolerant varieties than in a susceptible variety.

Aluminium-induced alteration of ion homeostasis in root tip vacuoles of two maize varieties differing in Al tolerance

Root elongation is a primary target of Al toxicity in plants. The objective of this study was to see whether Al-induced disturbance of ion homeostasis is related to the inhibition of root elongation. For this purpose, root growth rate, free cytoplasmic calcium (Ca 2+) and vacuolar content of phosphate (P i), potassium (K +), nitrate (NO 3 −) and malate, as well as malate and citrate exudation and nitrate reductase activity were analysed in tips of two Zea mays L. varieties differing in Al resistance. Aluminium treatment affected root growth and cytoplasmic Ca 2+ in the Al sensitive variety Bakero, but not in the Al tolerant variety Sikuani. However, both varieties suffered Al-induced decrease of vacuolar K +, and phosphate concentrations. Vacuolar malate concentrations were more affected by Al in Bakero than in Sikuani. Vacuolar nitrate concentrations increased upon Al exposure in both varieties. Only in Sikuani rhizosphere, pH slightly increased upon Al exposure. Our data are consistent with the hypothesis that disturbance of Ca 2+ homeostasis is an early event in the Al toxicity syndrome. However, Al-induced alterations of the root tip homeostasis of major ions seem unrelated to Al-induced inhibition of root elongation.

Constitutive and aluminium-induced patterns of phenolic compounds in two maize varieties differing in aluminium tolerance

Aluminium tolerance in maize is mainly due to more efficient Al exclusion. Nonetheless, even in tolerant varieties Al can gain access into the cells. Detoxification by binding to strong organic ligands should therefore play a role also in plants with high Al exclusion capacity. To test this hypothesis in this study the concentrations of soluble, free and bound, phenolics were analyzed in roots of two maize varieties differing in Al tolerance. Exposure for 24 h to 50 microM Al in nutrient solution strongly inhibited root elongation in the sensitive variety 16 x 36, but not in the Al-tolerant variety Cateto. Cateto accumulated about half the concentration of Al in roots than 16 x 36 (analysis performed after root desorption with citrate). Roots of Al-tolerant Cateto contained higher concentrations of caffeic acid, catechol and catechin than roots of the sensitive variety. Exposure to Al induced the accumulation of taxifolin in roots of both varieties. However, Al-tolerant Cateto accumulated about twice the concentration than Al-sensitive 16 x 36 of this pentahydroxyfavonol. The molar ratio for phenolics with catecholate groups to Al was about unity in roots of Cateto, while in those of 16 x 36 the ratio was ten times lower. Both the fact that these phenolics are strong ligands for Al and their high antioxidant and antiradical activity suggest that these compounds may provide protection against the Al fraction that is able to surpass the exclusion mechanisms operating in the tolerant maize variety.

Different Effects of Aluminum on the Actin Cytoskeleton and Brefeldin A-Sensitive Vesicle Recycling in Root Apex Cells of Two Maize Varieties Differing in Root Elongation Rate and Aluminum Tolerance

A relationship between aluminum (Al) toxicity, endocytosis, endosomes and vesicle recycling in the root transition zone has recently been demonstrated. Here the importance of filamentous actin (F-actin)-based vesicle trafficking for Al tolerance has been investigating in maize varieties differing in their Al sensitivities. More Al was internalized into root tip cells of the Al-sensitive variety 16x36 than in the Al-tolerant variety Cateto. The actin cytoskeleton and vesicle trafficking were primary targets for Al toxicity in the root tips of the sensitive variety. Visualization of boron-cross-linked rhamnogalacturonan II (RGII)-containing brefeldin A (BFA) compartments revealed that Al inhibited the formation of these compartments, especially in variety 16x36. The time sequence of Al effects on pectin recycling matches the growth effects of Al in this sensitive variety. These results support the hypothesis that Al binding to pectin-rich cell walls can contribute to reversible inhibition of root elongation. Al-induced alterations on F-actin were most evident in the central part of the transition zone of Al-sensitive 16x36, where Al was localized inside the nucleoli. In relation to this observation, a role for symplastic Al in both irreversible growth inhibition and amelioration of BFA-induced inhibition of root elongation is discussed.

Uptake and Distribution of Aluminum in Root Apices of Two Rice Varieties under Aluminum Stress

Aluminum (Al) toxicity is the major limiting factor of plant growth and production in acid soils. The target of Al toxicity is the root tip, which affects mainly on root growth inhibition. The aim of this research was to study the uptake and distribution of Al in root apices of two rice varieties IR64 (Al-sensitive) and Krowal (Al-tolerant), which were grown on nutrient solution containing 0, 15, 30, 45, and 60 ppm of Al. The root growth was significantly inhibited in both rice varieties at as low as 15 ppm Al concentration. The adventive roots of both varieties showed stunted growth in respons to Al stress. There was no difference in root growth inhibition between both rice varieties as well as among Al concentrations. Al uptake on root apices was qualitatively and quantitatively analyzed. Histochemical staining of roots using hematoxylin showed dark purple color on 1 mm region of Al-treated root apices. Rice var. IR 64 tended to take up more Al in root tip than Krowal did. However, there was no statistically significant difference (p = 0.176) in root Al content of both varieties in response to different concentration and period of Al treatments. Al distribution in root apices was found in the epidermal and subepidermal region in both rice varieties. Based on those results, rice var. Krowal that was previously grouped as Al-tolerant variety has similar root growth and physiological response to Al stress as compared to Al-sensitive variety IR64.