Effects of NaCl and silicon on ion distribution in the roots,shoots and leaves of two alfalfa cultivars with different salt tolerance

Abstract

The effects of exogenous NaCl and silicon on ion distribution were investigated in two alfalfa (Medicago sativa. L.) cultivars: the high salt tolerant Zhongmu No. 1 and the low salt tolerant Defor. The cultivars were grown in a hydroponic system with a control (that had neither NaCl nor Si added), a Si treatment (1 mmol L^?1 Si), a NaCl treatment (120 mmol L^?1 NaCl), and a Si and NaCl treatment (120 mmol L^?1 NaCl + 1 mmol L^?1 Si). After 15 days of the NaCl and Si treatments, four plants of the cultivars were removed and divided into root, shoot and leaf parts for Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe³⁺, Mn²⁺, Cu²⁺ and Zn²⁺ content measurements. Compared with the NaCl treatment, the added Si significantly decreased Na⁺ content in the roots, but notably increased K⁺ contents in the shoots and leaves of the high salt tolerant Zhongmu No.1 cultivar. Applying Si to both cultivars under NaCl stress did not significantly affect the Fe³⁺, Mg²⁺ and Zn²⁺ contents in the roots, shoots and leaves of Defor and the roots and shoots of Zhongmu No.1, but increased the Ca²⁺ content in the roots of Zhongmu No.1 and the Mn²⁺ contents in the shoots and leaves of both cultivars, while it decreased the Ca²⁺ and Cu²⁺ contents of the shoots and leaves of both cultivars under salt stress. Salt stress decreased the K⁺, Ca²⁺, Mg²⁺ and Cu²⁺ contents in plants, but significantly increased Zn²⁺ content in the roots, shoots and leaves and Mn²⁺ content in the shoots of both cultivars when Si was not applied. Thus, salt affects not only the macronutrient distribution but also the micronutrient distribution in alfalfa plants, while silicon could alter the distributions of Na⁺ and some trophic ions in the roots, shoots and leaves of plants to improve the salt tolerance.     

不同铃重基因型棉花盛花期14C-同化物在"铃-叶系统"中的分配特征

以大铃、中铃和小铃3个不同铃重棉花基因型为材料,通过在盛花期测定棉株中部主茎和果枝叶面积及叶面积指数,并用^14CO2饲喂中部主茎叶,研究了^14CO2同化物在棉株不同层次“铃-叶系统”中的分配特征。结果表明,盛花期中部主茎和果枝单叶面积与铃重呈正相关。小铃基因型棉花群体盛花期叶面积指数最大;大铃基因型棉花蕾铃比中、小铃基因型表现出更强的库活性。主茎叶片产生的同化物除主要输送到对应的果枝外,还向上部、下部的库器官及主茎生长点输送;而流向其对应果枝的同化物,主要供应第一果节蕾铃。     

Effect of nitrogen supply on leaf traits related to photosynthesis during grain filling in two maize genotypes with different N efficiency

In the present study, plant traits related to the photosynthetic capacity at the whole plant level were compared during grain filling in two maize genotypes with different nitrogen (N) efficiency. The plants were grown in a greenhouse in large root containers and supplied either with suboptimal or optimal rates of N fertilizer. Suboptimal N supply reduced total plant biomass at maturity (47 days (d) after flowering) by 29 % for the efficient genotype and by 36 % for the inefficient genotype. Suboptimal N supply reduced leaf growth of both genotypes. The reduction of leaf area was less severe in the N‐efficient genotype, despite of lower N content in the leaves. This indicates lower sensitivity of leaf growth towards internal N limitation in the efficient genotype. At low N supply, the green leaf area per plant gradually decreased after flowering in both genotypes, because of loss of chlorophyll during leaf senescence. The rate of net photosynthesis per unit leaf area (A) was reduced at low in comparison with high N supply. The ratio of A/leaf N content or leaf chlorophyll content was higher in the efficient genotype, indicating more efficient utilization of internal N for photosynthesis. At the end of grain filling, low N supply led to enhanced intercelluar CO₂ concentrations (Ci) in the leaves, indicating limitation of CO₂ assimilation by carboxylation rather than by stomatal resistance. The N deficiency‐induced increase of Ci was less pronounced in the efficient genotype. Furthermore, higher photosynthetic rate of the efficient genotype at suboptimal N supply was associated with lower contents of reducing sugars and sucrose in the leaves, whereas starch content was higher than in the inefficient genotype. The ability to avoid excessive sugar accumulation in the leaves under N deficiency might be related to higher photosynthetic N efficiency.     

Comparative growth and physiological responses of two wheat (Triticum aestivum L.) cultivars differing in salt tolerance to salinity and cyclic drought stress

Two cultivars of wheat (Triticum aestivum L.) with differential salinity tolerance were compared by evaluating the growth attributes, pigment composition and accumulation of Na⁺, K⁺, Zn²⁺, Fe ²⁺, Mn ²⁺ and proline. Wheat cultivars Al-Moiaya (AM) (salt tolerant) and Habbe-Druma (HD) (salt sensitive) were subjected to four levels of salinity (1.21 dS m^?1, 4.4 dS m^?1, 8.8 dS m^?1 and 13.2 dS m^?1) in factorial combinations with three drought stress (FC 30%, FC 60% and FC 90%) treatments in a randomized complete block design. Plant dry weight, leaf area ratio (LAR), soluble protein and total chlorophyll (Chl) content were higher in AM than HD. Salt-tolerant AM maintains a higher K⁺/ Na⁺ ratio and thereby is able to grow better than the salt-sensitive HD under both the stresses. The lower foliar Na⁺ in AM resulted in retention of higher Chl content, reflected in the strong positive correlations between plant ion status and Chl contents (Na⁺-Chl r² = 0.83; Chl- Fe²⁺ r² = 0.76; Zn²⁺ r² = 0.93 and Mn²⁺ r² = 0.88). In conclusion, our results suggested that the K⁺/Na⁺ ratio, exclusion of Na⁺ and ion homeostasis play much more important roles in the tolerance to salinity and drought stress than the compatible osmolyte, proline.     

Assessment of variation in drought tolerance using some key physiological criteria in potential wheat (Triticum aestivum L.) cultivars of different geographic origins

The present experiment comprised seven wheat cultivars, two drought levels (0 and 17% PEG-8000) and four replicates. The seeds of six wheat cultivars (Al-lugaimi, Bonus, Kronos, Yecora-rojo, Irena and Sama) were supplied by the King Saud University, Riyaz, Saudi Arabia, whereas S-24 was obtained from the Department of Botany, University of Agriculture, Faisalabad. The seeds were allowed to germinate and grow for 20 days in medium having full-strength Hoagland's nutrient solution or Hoagland's solution with 17% PEG-8000. For the appraisal of drought tolerance, various physiological traits such as gas-exchange attributes (A, E, C_i, g_s , and A/E), leaf water relations (ψ_w, ψ_s and ψ_p) and the activities of key antioxidant enzymes (SOD, POD and CAT) were determined. On the basis of biomass and gas-exchange attributes (A, E, and g_s ), cultivars Al-lugaimi and Sama were found to be drought tolerant, cultivars Yecora-rojo and Irena moderately drought tolerant, and cultivars S-24, Bonus and Kronos drought sensitive. However, plant osmotic adjustment and the activities of potential antioxidant enzymes (SOD, POD and CAT) were not found to be associated with drought tolerance of the different wheat cultivars.     

Molecular confirmation of candidate Hsp70 gene associated with heat tolerance in BC3F2 advanced backcross lines and their phenotypic resemblance with recurrent chilli Kulai

ABSTRACT

Domestic production of chilli in Malaysia is insufficient which accounted for 52% self-sufficiency level. Poor performance of local varieties under high temperatures above 42°C is one of the major factors affecting chilli production. This study was conducted with the objective of introgress heat-tolerant gene (Hsps) from AVPP0702 donor into Kulai using marker-assisted backcrossing. A total of 68 SSR markers, including Hsp linked markers that showed polymorphism between the parents were used to assess the generation of backcrossing; BC1F1, BC2F1, BC3F1 and BC3F2 and the average RPG percentage of the recurrent parent was found to be 81, 90, 95 and 97%, respectively. The pattern of Hsp expression in the backcross generations was similar to the donor parent (upregulated with more than 4-fold increase). Twelve improved heat tolerant chilli lines were developed. Most of the morphological and agronomical traits were recovered in the selected improved heat-tolerant genotypes from Kulai such as plant height, number of days to 50% flowering, number of fruits, fruit length and total fruit yield per plant. Improved high-yielding heat-tolerant chilli lines showed tolerance to high temperature as well as did not express any negative effect on agronomic traits in comparison with Kulai variety.     

Diversity of rhizosphere bacteria associated with different soybean cultivars in two soil conditions

Aiming at learning the effects of soil conditions and cultivar on the bacterial diversity in the rhizosphere of soybean (Glycine max(L.) Merr.), bacterial communities associated with four soybean cultivars grown in two soils were revealed by terminal-restriction fragment length polymorphism (T-RFLP) combined with sequencing analysis of a 16S rDNA clone library. Lower bacteria diversity was found in soil A which has higher salinity and nutrient contents, while the highest bacterial diversity was found in the rhizosphere of cv. Jidou 12 in both soils. These results revealed that both the soil conditions and soybean cultivar affected the community composition of rhizosphere bacteria, but the effect of soil conditions was greater than that of soybean cultivar as demonstrated by the principal component analysis. It also revealed that the abundant rhizosphere bacteria may also the main symbiotic or non-symbiotic nodule endophytes.     

The effect of porosity and nutrient solution concentration on the cation composition and root cation exchange capacities of two cultivars of Fragaria

Abstract

Leaf content of Ca remained fairly constant over three dilutions of nutrient solution. K content of the leaves fell with dilution. Porosity of the rooting medium had no effect on Fe, Cu, Mg, K in leaves but Ca and Zn decreased linearly with increasing porosity. Cation exchange capacity of the roots was not affected by porosity but there was a nutrient effect.     

The effect of cobalt stress on growth and physiological traits and its association with cobalt accumulation in barley genotypes differing in cobalt tolerance

Cobalt (Co) is beneficial for legume plants and not an essential element for most plants. There is no sufficient information about the effect of Co stress on barley growth. The current experiment was carried out to investigate the effects of different Co levels (25, 50, 75, and 100 µM) on growth and physiological traits of three barley genotypes (B325, J36, and B340) differing in Co tolerance. The results showed that Co stress inhibited plant growth, decreased chlorophyll content and photosynthetic rate, and enhanced oxidative stress. However, the effects differed among genotypes, with B325 and B340 being the most and the least affected, respectively. Co stress caused decrease and increase of manganese (Mn) and phosphorus (P) concentrations in both roots and shoots, respectively; iron (Fe) concentration had little change in shoots and a significant decrease in roots. The current results showed a close association of Co tolerance and its accumulation in plant tissues.     

Effects of drought stress on the seedling growth,development, and metabolic activity in different cultivars of canola

ABSTRACT

The comparative effects of drought stress on seed performance, growth parameters, free proline content, lipid peroxidation, and several antioxidative enzymes activities were studied in both cultivars of Brassica napus L. Drought stress increased mean germination rate and mean of day germination in both cultivars, and its effect was more pronounced in RGS003. The length and dry weight of root increased significantly in both cultivars under drought. RGS003 was more tolerant and obtained more biomass under drought than that of Sarigol. Proline content and pyrroline-5-carboxylate synthetase expression increased in Sarigol under drought. Measurement of malondialdehyde content in seedlings showed that lipid peroxidation was lower in RGS003 than in Sarigol. Antioxidant enzyme activities showed different trends in the two cultivars under drought stress but were higher in RGS003 than in Sarigol. These results suggest that RGS003 is better protected against drought-induced oxidative damage. Lipoxygenase activity only induced under water deficit condition in RGS003. Changes of respiratory enzymes activities of RGS003 subjected to drought stress showed a pattern different with Sarigol. Drought stress induced aconitase activity in RGS003, but it reduced fumarase and succinate dehydrogenase activity in Sarigol. This study showed that RGS003 exhibits a better protection mechanism against oxidative damage and RGS003 is more drought-tolerant than Sarigol possibly by maintaining and/or increasing growth parameters, antioxidant enzyme activities, and respiratory enzymes activities.     

Delineating the drivers of waning wildlife habitat: The predominance of cotton farming on the fringe of protected areas in the Mid-Zambezi Valley, Zimbabwe

Zimbabwe’s Mid-Zambezi Valley is of global importance for the emblematic mega-fauna of Africa. Over the past 30 years rapid land use change in this area has substantially reduced wildlife habitat. Tsetse control operations are often blamed for this. In this study, we quantify this change for the Dande Communal Area, Mbire District, of the Mid-Zambezi Valley and analyse the contribution of three major potential drivers: (1) increase in human population; (2) increase in cattle population (and the expansion of associated plough-based agriculture), and; (3) expansion of cotton farming. Although direct effects of land use change on wildlife densities could not be proven, our study suggests that the consequences for elephant and buffalo numbers are negative. All three of the above drivers have contributed to the observed land use change. However, we found farmland to have expanded faster than the human population, and to have followed a similar rate of expansion in cattle sparse, tsetse infested areas as in tsetse free areas where cattle-drawn plough agriculture dominates. This implies the existence of a paramount driver, which we demonstrate to be cotton farming. Contrary to common belief, we argue that tsetse control was not the major trigger behind the dramatic land use change observed, but merely alleviated a constraint to cattle accumulation. We argue that without the presence of a cash crop (cotton), land use change would have been neither as extensive nor as rapid as has been observed. Therefore, conservation agencies should be as concerned by the way people farm as they are by population increase. Conserving biodiversity without jeopardising agricultural production will require the development of innovative technological and institutional options in association with policy and market interventions.     

Sodium exclusion is a reliable trait for the improvement of salinity tolerance in bread wheat

Identification of novel wheat (Triticum aestivum L.) germplasm is imperative to develop salt tolerant varieties. In the first phase, 400 accessions were screened against high salt stress (200 mM NaCl) on the basis of Na⁺ accumulation in leaf blade, and 40 genotypes with contrast reaction to salinity were selected. Salt tolerant group (25 genotypes) had higher leaf K⁺/Na⁺ ratio, maximum root and shoot lengths, leaf fresh/dry weights and chlorophyll content as compared to the salt sensitive group (15 genotypes). In second phase, physiologically based screening was performed on selected genotypes against varying salinity levels (0, 100 and 200 mM NaCl). GGE biplot analysis indicates that genotypes TURACO, V-03094, V0005, V-04178, Kharchia 65 and V-05121 were the most salt-tolerant and declared winners as depicted by more gaseous exchange relations and growth potential which was strongly correlated with proper Na⁺, K⁺ discrimination in leaf and root tissues. Genotypes PBW343*2, NING MAI 50, PGO, PFAU, V-04181, PUNJAB 85, KIRITATI, TAM200/TUI and TAM200 were poor performer due to more Na⁺ accumulation in leaf ultimately retarded growth. In conclusion, low Na⁺ accumulation in leaf can be used as the best screening criteria, employing a large set of genotypes in a breeding program.     

The influence of high salt stress on starch,sucrose and degradative enzymes of two glycine max varieties that differ in salt tolerance

Salt stress effects were investigated on growth, the carbohydrate levels and the activity of degradative enzymes amylases, phosphorylase and invertase of two soybean varieties, Jackson and the more salt tolerant Lee.

Stress depressed growth of Jackson more than of Lee. Salt stress increased leaf and root sucrose more in Jackson than it did in Lee. Root sucrose was higher in Lee. Stress reduced leaf starch in both. It decreased spec. invertase activity in close negative correlation with the sucrose. Independent from salt tolerance, increased spec. amylase activity was in some correlation with the declined starch level. Stress changed phosphorylase little in both varieties. It is concluded that salt stress‐induced restricted utilization of leaf sucrose, but not foliar starch, could partly be a result of ionic affected degradation, which may diminish survival value of soybean varieties.     

Nitrogen nutrition and changes in the chemical attributes of the soil for cultivars of Brachiaria brizantha intercropped with Stylosanthes in different forage systems

ABSTRACT

Nitrogen in the soil-plant system is extremely complex, and any change in soil management or cultivated species can modify its dynamics. To minimize environmental problems and sustainably optimize agricultural production, it is necessary to understand the dynamics of nitrogen in the soil-plant system. Thus, the objective of this study was to evaluate plant nitrogen nutrition and changes in the chemical attributes of the soil for cultivars of Brachiaria brizantha intercropped with Stylosanthes in different forage systems. The experimental design consisted of randomized block experimental design was used, with three replicates. The treatments consisted of forage systems: Piata palisadegrass, Paiaguas palisadegrass, Stylosanthes cv. Campo Grande, row intercropping of Piata palisadegrass with Stylosanthes, mixed intercropping of Piata palisadegrass and Stylosanthes, row intercropping of Paiaguas palisadegrass and Stylosanthes, and mixed intercropping of Paiaguas palisadegrass and Stylosanthes. Evaluations were performed in winter, spring, summer, and autumn in the same plots and over a 2-year period. The intercropping of grasses and legumes positively influences the chemical characteristics of the soil and the nutritional status of the forage by improving the concentration of nutrients. Overall the row seeding method provided better nutrient concentrations. The second year provided higher nitrogen absorption but resulted in greater soil acidification.     

Interaction of biological nitrogen fixation with sowing nitrogen fertilization on common bean in the two seasons of cultivation in Brazil

Sowing nitrogen (N) fertilization can limit biological nitrogen fixation (BNF) reducing common bean yield. The aim of this study was to evaluate the effect of sowing N fertilization plus inoculation on the growth and yield of plants in the two seasons of cultivation in Brazil. In the dry season, N fertilization and inoculation promoted a greater shoot dry weight and higher pod number and yield than only inoculated. In contrast, in the rainy season, this treatment promoted no increase in shoot dry weight and yield compared with the inoculated alone. The number of nodules was greater for the inoculated alone treatment, but nodule weight was not affected by N fertilization in either season. Therefore, sowing N fertilization and inoculation can be an agronomic practice to achieve a higher common bean yield in the dry season, while in the rainy season, the inoculation without N fertilization can support a high yield at a lower cost.     

Denitrification in the rhizosphere of plants with inherently different aerenchyma formation: Wheat (Triticum aestivum) and rice (Oryza sativa)

Summary Denitrification in the rhizosphere of wheat and rice was studied in relation to aerenchyma formation. Seedlings were grown in quartz silt amended with mineral nutrients at given bulk densities and water tensions. In adventitious wheat roots the formation of cortical lacunae was strongly dependent on soil aeration. Growing the wheat plants in dry (–20 kPa) and moist substrate (–2 kPa) established aerenchyma contents of 3% and 15%, respectively. Denitrification was measured after the introduction of equal moisture levels in the substrates of both treatments. The higher aerenchyma content of roots pregrown in the wetter substrate did not counteract denitrification in the rhizosphere which had doubled in this treatment. In contrast to the unspecific lysis of cortical cell walls, the well organized formation of aerenchyma in rice roots was independent of soil aeration. Root porosity averaged 14%. As in wheat, it was not related to denitrification. However, the level of denitrification per mg of root dry matter was about four times lower than that of wheat. The addition of decomposable organic matter (cellulose) to the substrate stimulated aerenchyma formation in rice and considerably increased denitrification. The results suggest that denitrification in the rhizosphere is independent of aerenchyma formation.     

The role of the external mycelium in early colonization for three arbuscular mycorrhizal fungal species with different colonization strategies

Arbuscular mycorrhizal fungi (AMF) differ in their rate and extent of colonization of both plant roots and soil but the mechanism responsible for these differences is unclear. We compared the external mycelium of three AMF isolates (Glomus intraradices, Glomus etunicatum and Gigaspora gigantea) during early colonization of plant roots. We investigated whether an AMF with the most rapid colonization would have higher numbers of infective structures (i.e., infection hyphae and contact points), an AMF with extensive root colonization would have more infection units, and (3) AMF with extensive soil colonization would have large numbers of all external features (including absorptive hyphae, runner hyphae and hyphal bridges). Using specially designed soil and root observation chambers, we followed the development of the external mycelium for 7 weeks. We found that rapid colonization rate was due, in part, to the presence of more infective structures, in particular more infection hyphae and root contact points. Second, the extensive root colonizer had more, larger infection units. Third, data did not support the hypothesis that the extensive soil colonizer had more external structures. These results show that differences in the architecture of the external mycelium are responsible, in part, for variation in the colonization strategy of AMF.