MECHANISMS OF ALUMINUM TOLERANCE IN TRITICUM AESTIVUM L. (WHEAT). I. DIFFERENTIAL PH INDUCED BY WINTER CULTIVARS IN NUTRIENT SOLUTIONS

Twenty winter cultivars of Triticum aestivum L. (wheat) were grown in solution culture with and without aluminum (Al) (74 μM, 2.0 mg L^-1) for 14 days. Exposure to Al increased root growth of the most tolerant cultivar, while both root and shoot growth were depressed in all other cultivars. On the basis of a root tolerance index (RTI = weight of roots grown with Al/weight of roots grown without Al), cultivar tolerance to Al ranged 9-fold, from 0.13 ± 0.01 to 1.16 ± 0.10. Symptoms of Al toxicity were most evident on roots. Aluminum-affected roots were relatively short and thick and had numerous undeveloped laterals. Leaves of some cultivars showed chlorosis resembling iron deficiency, and others showed purple stems typical of phosphate deficiency. Plants of all cultivars grown with and without Al depressed the pH of nutrient solutions, presumably until NH₄⁺ was depleted, at which point the pH increased. Cultivar tolerance, expressed both as the root tolerance index and a shoot tolerance index, was negatively correlated with the negative log of the mean hydrogen ion (H⁺) concentration, the minimum pH, and the slope of the pH decline, each calculated from pH data collected during the first 9 days of the experimental period before any sharp rises in pH occurred. These results are consistent with the hypothesis that the Al tolerance of a given cultivar is a function of its ability to resist acidification of the nutrient solution and hence to limit the solubility and toxicity of Al.     

Salt tolerance of rice cultivars

Summary The dry matter production and the concentration of nutrients in rice (Oryza sativa L.) cultivars from soil adjusted to different levels of salinity were evaluated under a greenhouse conditions. Soil salinity levels were produced by applying 0.34 mol l^–1 solution of NaCl which resulted in the following levels, control (0.29), 5, 10 and 15 dS m^–1 conductivity of saturation extract. The effect of salinity on dry matter production varied from cultivar to cultivar.The concentrations of P and K in the tops of rice cultivars decreased with increasing soil salinity. But the concentrations of Na, Zn, Cu and Mn increased.Significant varietal differences were found in relation to salinity tolerance. Based on dry matter yield reduction, rice cultivars were classified as tolerant, moderately tolerant, moderately susceptible or susceptible.     

Differences in the tolerance of potato cultivars to potato cyst nematodes (Globodera rostochiensis and G. pallida) in field trials with and without nematicides

In field trials Cara, Brio, Maris Piper and Pentland Javelin were consistently more tolerant of damage by Globodera rostochiensis yielding more than Corsair, Pentland Dell, Maris Anchor and Maris Peer, in untreated, heavily infested soil and giving the smallest increases to nematicide treatment. No yield or growth differences were found between plants in untreated and nematicide treated plots at a nematode-free site. The most tolerant cultivars all had a gene (H₁) for resistance to G. rostochiensis derived from Solanum tuberosum ssp. andigena and in soil infested with G. pallida the tolerance of at least one resistant cultivar (Maris Piper) appeared to be lessened. However, some resistant cultivars were comparatively intolerant, even to G. rostochiensis. Early cultivars were generally less tolerant than late maturing cultivars but there were exceptions. Amongst cultivars with resistance derived from Solanum vernei the early cultivar Guardian was more tolerant than the main crop cultivar Corsair. The effect on the yield of several cultivars of a range of densities of G. rostochiensis, produced either by applying different rates of a nematicide or by cropping in the previous year, was examined at two sites. The results indicated that the slope of the regression for yield in relation to nematode density was less for tolerant than intolerant cultivars. At sites infested with G. rostochiensis Maris Piper was found to be consistently more tolerant than Pentland Crown.     

Morphological indicators of salinity stress and their relation with osmolyte associated redox regulation in mango cultivars

Soil salinization is a global issue impeding horticulture production and is approaching an alarming status due to climate change and urbanization. Breeding salt-tolerant rootstock varieties is an ideal strategy to mitigate stress due to salinity in mango and other perennial fruit species. Stress combating strategies employed by seedlings of 7 mango were studied under saline conditions (200 mM NaCl, EC: > 4.0 dSm⁻¹, pH 8.5) in pot experiments. Significantly high accumulation of proline (19.07 µg g⁻¹ FW in Bappakai), glycine betaine (55.11 µg g⁻¹ FW in 13–1), and total sugars (17.33 mg g⁻¹ FW in Kurukkan) were found to be the common mechanism employed by the tolerant cultivars to counter the osmotic stress, under suboptimal conditions. Non-enzymatic antioxidants viz., tannins (17.18 mg g⁻¹), phenols (18.68 mg g⁻¹), and anthocyanins (1.59 mg g⁻¹) were increased in seedling of "13–1", the salt-resistant cultivar from Israel. Reactive oxygen species (ROS) regulation by increased activity of superoxide dismutase and catalase in the two polyembryonic cultivars of Indian origin (Kurukkan and Nekkare) suggests their potential use as rootstocks to combat oxidative stress. The tolerance index of various cultivars was calculated by averaging the scores of morphological stress indicators, and its correlation with studied parameters suggests that salinity resilience is more tightly linked to enhanced catalase accumulation (r² = 0.8361) that is reduced ionic stress. This evidence assign the role of osmotic stress alleviation and redox regulation in salt tolerance mechanism operational in native Indian cultivars, Nekkare and Kurukkan at par with known salt tolerant rootstocks.

     

Root Respiration,Photosynthesis and Grain Yield of Two Spring Wheat in Response to Soil Drying

The effects of soil water regime and wheat cultivar, differing in drought tolerance with respect to root respiration and grain yield, were investigated in a greenhouse experiment. Two spring wheat (Triticum aestivum) cultivars, a drought sensitive (Longchun 8139-2) and drought tolerant (Dingxi 24) were grown in PVC tubes (120 cm in length and 10 cm in diameter) under an automatic rain-shelter. Plants were subjected to three soil moisture regimes: (1) well-watered control (85% field water capacity, FWC); (2) moderate drought stress (50% FWC) and (3) severe drought stress (30% FWC). The aim was to study the influence of root respiration on grain yield under soil drying conditions. In the experiment, severe drought stress significantly (p < 0.05) reduced shoot and root biomass, photosynthesis and root respiration rate for both cultivars, but the extent of the decreases was greater for Dingxi 24 compared to that for Longchun 8139-2. Compared with Dingxi 24, 0.04 and 0.07 mg glucose m⁻² s⁻¹ of additional energy, equivalent to 0.78 and 1.43 J m⁻² s⁻¹, was used for water absorption by Longchun 8139-2 under moderate and severe drought stress, respectively. Although the grain yield of both cultivars decreased with declining soil moisture, loss was greater in Longchun 8139-2 than in Dingxi 24, especially under severe drought stress. The drought tolerance cultivar (Dingxi 24), had a higher biomass and metabolic activity under severe drought stress compared to the sensitive cultivar (Longchun 8139-2), which resulted in further limitation of grain yield. Results show that root respiration, carbohydrates allocation (root:shoot ratio) and grain yield were closely related to soil water status and wheat cultivar. Reductions in root respiration and root biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions.     

Differential cadmium stress tolerance in five indian mustard (Brassica juncea L.) cultivars: An evaluation of the role of antioxidant machinery

The presence of Cadmium (Cd) in the agricultural soils affects horticultural cultivars and constrains the crop productivity. A pot experiment was performed using five cultivars of mustard (Brassica juncea L.) to evaluate the difference in their response to Cd toxicity under greenhouse conditions. The pots containing reconstituted soil were supplied with different concentration of CdCl₂ (0, 25, 50, 100 or 150 mg Cd kg⁻¹ soil). Increasing concentration of Cd in the soil resulted in decreased growth, photosynthesis and yield. Maximum significant reduction in growth, photosynthesis and yield were observed with 150 mg Cd kg⁻¹ soil in all the cultivars. Our results indicate that the cultivar Alankar is found to be more tolerant to Cd stress, recording higher plant dry mass, net photosynthesis rate, associated with high antioxidant activity and low Cd content in the plant leaves and thus less oxidative damage. Cultivar RH30 experienced maximum damage in terms of reduction in growth, photosynthesis, yield characteristics and oxidative damage and emerged as sensitive cultivar. The data of tolerance index of Alankar were found to be higher among all tested mustard cultivars which indicate its higher tolerance to Cd. Better coordination of antioxidants protected Alankar from Cd toxicity, whereas lesser antioxidant activity in RH30 resulted in maximum damage. Cultivars of mustard were ranked with respect to their tolerance to Cd: Alankar > Varuna > Pusa Bold > Sakha > RH30, respectively.Key words: antioxidants, cadmium, growth, mustard cultivars, photosynthesis, stress, yield     

A method for screening copper-tolerant rice (Oryza sativa L.) cultivars based on hydroponic experiments and cluster analysis

A method for screening copper (Cu)-tolerant rice cultivars was studied by combining hydroponic experiments and cluster analysis, and the classification of cultivars in Cu stress tolerance was done. In the first hydroponic experiment, seedlings of Jiahe991 and Xiushui114 were planted in nutrient solution with different Cu²⁺ concentrations from 10 to 1800 μg/L. Results indicated that the toxic threshold of Cu concentration in solution ranged from 900 to 1200 μg/L, since SPAD (Soil and Plant Analyzer Development, SPAD-502, a portable chlorophyll meter, Minolta Camera Co. Ltd., Japan) values of leaves and seedlings biomass of the treatments with ≥900 and/or 1200 µg/L were significantly lower than the control. The second experiment was conducted with 16 local rice cultivars under three Cu treatments (10, 1000, and 1500 μg/L). The 16 cultivars were well classified into tolerant, normal, and sensitive groups as a result of cluster analysis based on the relative SPAD (Soil and Plant Analyzer Development, SPAD-502, a portable chlorophyll meter, Minolta Camera Co. Ltd., Japan) value, shoot and root dry weights, root length and root dehydrogenase activity, and oxidizing capacity and shoot Cu concentration. Xiushui123, Xiushui134, Jiahe991, and Xianghu301 belonged to the tolerant group; Xiushui137 belonged to the sensitive group. The cluster analysis based on hydroponic experiments is an effective method for identifying rice cultivars that are tolerant to Cu stress. In addition, four cultivars (Xiushui123, Xiushui134, Jiahe991, and Xianghu301) are recommended in local practice.     

Differential response of Brassica juncea cultivars to Al; consequences for chlorophyll a fluorescence,antioxidants and psb A gene

The present study was undertaken to identify the aluminum (Al) tolerant cultivar of Brassica juncea. We examined the changes in antioxidant enzymes, proline level, chlorophyll a fluorescence and psb A gene expression at vegetative and reproductive growth stages of B. juncea cultivars (Bio-902, CS-14, Pusa-Tarak and Laxmi). The selected cultivars were exposed to soil (pH 5.2) supplemented with Al (0, 50, 100 and 150?mg?kg^?1). We observed the lowest decline in photosynthetic efficiency (ΔF/Fm′), ETR, PPFD values and psb A expression to Al stress in the cultivar Bio-902 (tolerant cultivar) followed by CS-14 and Pusa-Tarak whereas the highest decline was observed in the cultivar Laxmi (sensitive cultivar). The improved performance of the cultivar Bio-902 under Al stress was accompanied by an increase in proline level, CAT and APX activities but without any increase in SOD activity. However, significant increase in SOD activity was observed in Laxmi.     

Influence of host cultivars and Bradyrhizobium strains on the growth and symbiotic performance of soybean under salt stress

This paper examines the importance of salt tolerance of host cultivars, Bradyrhizobium strains, and host-Bradyrhizobium combinations on the symbiotic nitrogen fixation potential of soybean under NaCl and KCl salt stress. Plants were grown in a soil medium, and the experiments were conducted under controlled environment growth room conditions. Bradyrhizobium growth was examined in yeast-mannitol broth andB. japonicum strains tolerant of NaCl and KCl (80 mM) stress were identified. Soybean cultivar Williams, which was sensitive to salt stress, performed poorly both in growth and symbiotic nitrogen fixation, irrespective of whether it was matched with a tolerant or sensitive Bradyrhizobium strain. Tolerant cultivar Manchu sustained nodulation and nitrogen fixation, irrespective of whether it was matched with a tolerant or sensitive Bradyrhizobium strain. Evidence presented here suggests a need, first to select soybean cultivars that are tolerant to salt stress, and then to match them with tolerant and effective Bradyrhizobium strains.     

Correlation of cytological and biochemical parameters with resistance and tolerance to Mycosphaerella graminicola in wheat

This study investigated the infection process of Mycosphaerella graminicola and enzyme activities related to reactive oxygen species (ROS) or oxylipin biosynthesis in four French wheat cultivars with variable resistance to M.?graminicola infection. At field level, cultivars Caphorn, Maxyl and Gen11 were susceptible, whereas Capnor showed high levels of quantitative resistance. Moreover, Capnor and Gen11 were tolerant, i.e., their yield was less affected by infection compared to non-tolerant Maxyl and Caphorn. These four cultivars were inoculated under laboratory conditions with the M.?graminicola IPO323 reference strain. Cytological and biochemical responses were studied on collected first plantlet leaves and several features discriminated between cultivars. However, resistance and tolerance had no impact on the fungal infection process. Levels of lipoxygenase (LOX), peroxidase (PO) and glutathione-S-transferase (GST) activities were also compared with regard to cultivar resistance or tolerance to M.?graminicola. LOX, PO and GST activities did not discriminate resistance and tolerance profiles, although a low level of PO in inoculated and non-inoculated plants could be associated with tolerance. In addition, cell necrosis correlated positively with LOX in non-tolerant cultivars, while mycelia surrounding stomata were positively correlated with PO in the resistant cultivar. GST activity presented correlations between cytological and biochemical parameters only for susceptible cultivars. Stomatal and direct penetration were positively correlated with GST activity in the susceptible non-tolerant cultivars, while these correlations were negative in the tolerant cultivar. When combining cytological and biochemical observations with resistance and tolerance profiles, for each cultivar and at each time point, cultivars could be classified in tight accordance with their previous field characterisation. Moreover, tolerance allowed us to distinguish susceptible cultivars when both biochemical and cytological parameters were considered together.     

Cultivar Differences in Photosynthetic Tolerance to Photooxidation and Shading in Rice (Oryza Sativa L.)

Forty-four genotypes from the rice germplasm were identified under photoinhibition/photooxidation and shade conditions and divided into four basic types: (1) cultivars tolerant to both photooxidation and shading, (2) cultivars tolerant to photooxidation but sensitive to shading, (3) cultivars tolerant to shading but sensitive to photooxidation, and (4) cultivars sensitive to both photooxidation and shading. Photosynthetic characteristics of a cultivar tolerant (cv. Wuyugeng 3) and a cultivar sensitive (cv. Xiangxian) to photooxidation and shading were compared. The photochemical efficiency (F_v/F_m) of photosystem 2 (PS2) and the content of PS2-D1 protein in the tolerant cultivar Wuyugeng 3 decreased less under photooxidative conditions as compared with Xiangxian. Under similar conditions, superoxide dismutase was induced rapidly to a higher activity and the active oxygen (O^–) built up to a lower level in Wuyugeng 3 than in Xiangxian. Net photosynthetic rate (P _N) decreased by 23 % in Wuyugeng 3 vs. 64 % in Xiangxian. Shading (80 %) during the booting stage caused only small decreases (7–13 %) in ribulose-1,5-bisphosphate carboxylase activity and P _N in Wuyugeng 3 but severe decreases (57–64 %) were observed in Xiangxian which corresponded to the decreases in grain yield of the two cultivars (38 and 73 %, respectively). We described a simple and effective screening method and physiological basis for breeding crops for enhanced tolerance to both high and low irradiance.     

Responses of maize grain yield to changes in acid soil characteristics after soil amendments

An experiment was conducted from 1997 to 2000 on an acid soil in Cameroon to assess the effectiveness of cultivating acid tolerant maize (Zea mays L.) cultivar and the use of organic and inorganic fertilizers as options for the management of soil acidity. The factors investigated were: phosphorus (0 and 60 kg ha^?1), dolomitic lime (0 and 2 t ha^?1), organic manure (no manure, 4 t ha^?1 poultry manure, and 4 t ha^?1 of leaves of Senna spectabilis), and maize cultivars (ATP-SR-Y – an acid soil-tolerant, and Tuxpeño sequia – an acid susceptible). On acid soil, maize grain yield of ATP-SR-Y was 61% higher than the grain yield of Tuxpeño sequia. Continuous maize cultivation on acid soil further increased soil acidity, which was manifested by a decrease in pH (0.23 unit), exchangeable Ca (31%) and Mg (36%) and by an increase in exchangeable Al (20%). Yearly application of 60 kg ha^?1 of P for 3 years increased soil acidity through increases in exchangeable Al (8%) and H (16%) and a decrease in exchangeable Ca (30%), Mg (11%) and pH (0.07 unit). Lime application increased grain yield of the tolerant (82%) and susceptible (208%) cultivars. The grain yield increases were associated with a mean decrease of 43% in exchangeable Al, and 51% in H, a mean increase of 0.27 unit in pH, 5% in CEC, 154% in exchangeable Ca, and 481% in Mg contents of the soil. Poultry manure was more efficient than leaves of Senna producing 38% higher grain yield. This yield was associated with increases in pH, Ca, Mg and P, and a decrease in Al. The highest mean grain yields were obtained with lime added to poultry manure (4.70 t ha^?1) or leaves of Senna (4.72 t ha^?1). Grain yield increase was more related to the decrease in exchangeable Al (r = ?0.86 to ?0.95, P<0.01) and increase in Ca (r = 0.78–0.94, P<0.01), than to pH (r = ?0.57 (non-significant) to ?0.58 (P<0.05)). Exchangeable Al was the main factor determining pH (r = ?0.88 to ?0.92, P<0.01). The yield advantage of the acid tolerant cultivar was evident even after correcting for soil acidity. Acid soil-tolerant cultivars are capable of bringing unproductive acid soils into cultivation on the short run. The integration of soil amendments together with acid soil-tolerant cultivar offers a sustainable and comprehensive strategy for the management of acid soils in the tropics.     

Differences in responses to iron deficiency among various cultivars of mungbean (Vigna radiata (L.) Wilczek)

Ten mungbean cultivars were evaluated for their resistance to iron deficiency in view of chlorosis symptoms, plant growth and seed yield under field conditions on a calcareous soil in Thailand. The KPS2 cultivar was highly susceptible; the KPS1, PSU1 and Pag-asa 1 cultivars were somewhat susceptible; the VC1163B cultivar was moderately tolerant; the CN36, CN60, UT1 and CNM-I cultivars were tolerant; and the CNM8509B cultivar was very tolerant to iron deficiency. Foliar application of a solution of 5 g L^-1 ferrous sulphate was effective in correcting chlorosis that was induced by iron deficiency, and it enhanced both the growth and the yield of susceptible cultivars. Compared with the susceptible cultivar KPS2, the tolerant cultivar UT1 had a greater ability to lower the pH of the nutrient solution in response to iron deficiency. The root-associated Fe³⁺-reduction activity of UT1 that had been grown in -Fe medium was similar to that of the plants grown in +Fe medium when the acidification of the medium occurred. Acidification of the medium in response to iron deficiency might contribute to the efficient solubilization of iron from calcareous soils, and it related more closely to the resistance to iron deficiency than Fe³⁺ reduction by roots in mungbean cultivars.     

Reactive oxygen species, ascorbate–glutathione pool, and enzymes of their metabolism in drought-sensitive and tolerant indica rice (Oryza sativa L.) seedlings subjected to progressing levels of water deficit

Water deficit for rice is a worldwide concern, and to produce drought-tolerant varieties, it is essential to elucidate molecular mechanisms associated with water deficit tolerance. In the present study, we investigated the differential responses of nonenzymatic antioxidants ascorbate (AsA), glutathione (GSH), and their redox pool as well as activity levels of enzymes of ascorbate–glutathione cycle in seedlings of drought-sensitive rice (Oryza sativa L.) cv. Malviya-36 and drought-tolerant cv. Brown Gora subjected to water deficit treatment of ?1.0 and ?2.1 MPa for 24–72 h using PEG-6000 in sand cultures. Water deficit caused increased production of reactive oxygen species such as O₂?^?, H₂O₂, and HO? in the tissues, and the level of production was higher in the sensitive than the tolerant cultivar. Water deficit caused reduction in AsA and GSH and decline in their redox ratios (AsA/DHA and GSH/GSSG) with lesser decline in tolerant than the sensitive seedlings. With progressive level of water deficit, the activities of monodehydroascorbate reductase, dehydroascorbate reductase, ascorbate peroxidase (APX), and glutathione transferase increased in the seedlings of both rice cultivars, but the increased activity levels were higher in the seedlings of drought-tolerant cv. Brown Gora compared to the sensitive cv. Malviya-36. Greater accumulation of proline was observed in stressed seedlings of tolerant than the sensitive cultivar. In-gel activity staining of APX revealed varying numbers of their isoforms and their differential expression in sensitive and tolerant seedlings under water deficit. Results suggest that an enhanced oxidative stress tolerance by a well-coordinated cellular redox state of ascorbate and glutathione in reduced forms and induction of antioxidant defense system by elevated activity levels of enzymes of ascorbate–glutathione cycle is associated with water deficit tolerance in rice.     

22Na influx is significantly lower in salt tolerant groundnut (Arachis hypogaea) varieties

Distinct varieties differing in salt tolerance were initially identified from two separate green house experiments using two systems; solution as well as soil culture. The first screening involved a diverse group of 27 cultivars. Several physiological traits; Chlorophyll Stability Index (CSI), Salt Tolerance Index (STI) and ion content were determined to screen the cultivars for differences in salt tolerance using solution culture in the first experiment. A set of six varieties (three tolerant and three susceptible) were selected from this experiment and then subjected again to salt stress adopting a natural soil system in the second experiment which involved a screening approach essentially similar to that of the first experiment. In the third experiment using two distinct cultivars differing in salt tolerance selected from experiment II, ²²Na influx rate was determined in the root and shoot at the end of a 24 h salt imposition in Hoagland’s nutrient system containing 180 KBq of ²²Na. The results suggested that there were distinct differences in ²²Na influx rate into root and concurrently in the shoot. The salt tolerant Spanish improved and one of the moderately tolerant Trombay variety TAG 24, showed good regulation of ²²Na influx resulting in low ²²Na concentration. The salt susceptible variety JSP39 had nearly 7–8 fold higher root ²²Na content as compared to the tolerant and moderately tolerant cultivars. The results have highlighted the importance of Na exclusion as an important determinant of salt tolerance in groundnut.     

Effect of Salt Stress on Growth,Na+ Accumulation and Proline Metabolism in Potato (Solanum tuberosum) Cultivars

Potato (Solanum tuberosum) is a major crop world-wide and the productivity of currently used cultivars is strongly reduced at high soil salt levels. We compared the response of six potato cultivars to increased root NaCl concentrations. Cuttings were grown hydroponically and treated with 0 mM, 60 mM and 180 mM NaCl for one week. Growth reduction on salt was strongest for the cultivars Mozart and Mona Lisa with a severe senescence response at 180 mM NaCl and Mozart barely survived the treatment. The cultivars Desiree and Russett Burbank were more tolerant showing no senescence after salt treatment. A clear difference in Na⁺ homeostasis was observed between sensitive and tolerant cultivars. The salt sensitive cultivar Mozart combined low Na⁺ levels in root and stem with the highest leaf Na⁺ concentration of all cultivars, resulting in a high Na⁺ shoot distribution index (SDI) for Mozart as compared to Desiree. Overall, a positive correlation between salt tolerance and stem Na⁺ accumulation was found and the SDI for Na⁺ points to a role of stem Na⁺ accumulation in tolerance. In stem tissue, Mozart accumulated more H₂O₂ and less proline compared to the tolerant cultivars. Analysis of the expression of proline biosynthesis genes in Mozart and Desiree showed a clear reduction in proline dehydrogenase (PDH) expression in both cultivars and an increase in pyrroline-5-carboxylate synthetase 1 (P5CS1) gene expression in Desiree, but not in Mozart. Taken together, current day commercial cultivars show promising differences in salt tolerance and the results suggest that mechanisms of tolerance reside in the capacity of Na⁺ accumulation in stem tissue, resulting in reduced Na⁺ transport to the leaves.     

Differential growth, physiological and biochemical responses of niger (Guizotia abyssinica Cass.) cultivars to water-deficit (drought) stress

The present study demonstrates the effect of polyethylene glycol-8000 (PEG) and percent field capacity (FC%)-induced water-deficit stress on growth, water status, productivity and various biochemical parameters in Guizotia abyssinica Cass. cultivars (IGP 76, GA 10, No. 71 and IGPN 2004) at seedling and maturity stages of the plant. Cultivar GA 10 showed higher, IGP 76 and No. 71 moderate, and IGPN 2004 least reduction in percent seed germination given PEG stress treatments (0, 10 and 20%). A similar pattern was observed for decreased growth and water content of the seedlings and plants of the cultivars exposed to both kinds of water-deficit stresses. The productivity (number of capitula per plant, number of seeds per capitula and 1,000-seed weight) and total chlorophyll content of cultivar IGPN 2004 was significantly higher in comparison to other cultivars given different FC% treatments (100, 80 and 60%). Significantly higher accumulation of proline, glycine betaine and total soluble sugars and lower damage to membrane lipids under increased water-deficit stress (i.e., at 80 and 60% FC) conditions in cultivar IGPN 2004 suggested its more tolerance capacity to water-deficit stress in comparison to other cultivars. Besides, antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase and guaiacol peroxidase) partially demonstrated variations in the tolerance of the cultivars to water-deficit stress. The results suggest that cultivar IGPN 2004 could be considered as more tolerant, and IGP 76 and No. 71 as moderately tolerant, whereas GA 10 was more sensitive to water-deficit stress.     

Relative abundance of Δ5-sterols in plasma membrane lipids of root-tip cells correlates with aluminum tolerance of rice

We investigated variations in aluminum (Al) tolerance among rice plants, using ancestor cultivars from the family line of the Al-tolerant and widely cultivated Japonica cultivar, Sasanishiki. The cultivar Rikuu-20 was Al sensitive, whereas a closely related cultivar that is a descendant of Rikuu-20, Rikuu-132, was Al tolerant. These two cultivars were compared to determine mechanisms underlying variations in Al tolerance. The sensitive cultivar Rikuu-20 showed increased permeability of the plasma membrane (PM) and greater Al uptake within 1 h of Al treatment. This could not be explained by organic acid release. Lipid composition of the PM differed between these cultivars, and may account for the difference in Al tolerance. The tolerant cultivar Rikuu-132 had a lower ratio of phospholipids to Δ⁵-sterols than the sensitive cultivar Rikuu-20, suggesting that the PM of Rikuu-132 is less negatively charged and less permeabilized than that of Rikuu-20. We used inhibitors of Δ⁵-sterol synthesis to alter the ratio of phospholipids to Δ⁵-sterols in both cultivars. These inhibitors reduced Al tolerance in Rikuu-132 and its Al-tolerant ancestor cultivars Kamenoo and Kyoku. In addition, Rikuu-132 showed a similar level of Al sensitivity when the ratio of phospholipids to Δ⁵-sterols was increased to match that of Rikuu-20 after treatment with uniconazole-P, an inhibitor of obtusifoliol-14α-demethylase. These results indicate that PM lipid composition is a factor underlying variations in Al tolerance among rice cultivars.