Effect of increasing salinity on growth and mineral composition of wheat varieties and role of sodium exclusion capacity in salt tolerance mechanisms

A few wheat varieties including two Japanese wheat varieties were evaluated for their salt tolerance at seeding stage, their behavior to increasing salinity levels and role of Na exclusion capacity in salt tolerance mechanisms. The wheat varieties were grown in nutrient solution and subjected to 0 (control), 25,75 and 125 mM NaCl salinity levels for 7 days. Although the shoot growth was reduced while Na contents were increased progressively with increasing salinity in all varieties, the varieties were quite different in their response. Salt tolerant va rieties maintained less reduction in their root and shoot growth and better water relations in their shoots than salt sensitive varieties under saline conditions. The wheat varieties were quite different in their Na exclusion capacity. Poor growth in salt sensitive varieties might be due to higher accumulation of Na in their shoots resulting from low Na exclusion capacity of roots, higher Na transport to shoot and/or inferior compartmentation capability

Differences in Salt Tolerance within Strains of Cynodon dactylon

Nine strains of Cynodon dactylon grass were collected from various habitats as the seaside, the saline soil areas and the roadside. These strains were grown in sand culture under greenhouse at various NaCl treatments, and their growth, morphological variation, mineral contents and rooting were determined. The growth of most strains was increased by Cl concentrations of 1,000 ppm to 3,000 ppm, and addition of NaCl up to 5,000 ppm of Cl concentrations did not affect their growth. Furthermore all strains survived relatively well even when grown with Cl concentrations of 10,000 ppm. With increasing Cl concentrations, Na content in their tissues increased. Especially some strains which were collected from saline areas, had higher Na content in their tissues than those of other strains. It was also found that Cynodon dactylon may possess one mechanism for salt tolerance, which be related to restriction of Na translocation from root to top. Morphological characters of all strains at various NaCl treatments varied widely, and a relation between morphological variation and yield variation was found. In contrast, NaCl treatments significantly affected the rooting and the root growth of Cynodon dactylon.近年、乾燥地域、半乾燥地域、乾燥半湿潤地域における気候上の変動や人間活動を含む様々な要素に起因する土地の劣化が進んでいる。その劣化の中で、灌漑農地の土壌の塩類化が大きな問題となっている。これは、灌漑が行われる際に、過剰な灌漑や水路からの漏水等のために地下水位の上昇が起こったり、塩類濃度の高い地下水を用いることにより、水分が蒸発した後に水に含まれていた塩類が表層面に集積し、塩化によって農地が荒廃、劣化することである。とくに土壌の浸透圧を高め、植物の吸収わ妨げたり、植物体内のイオンバランスを崩すなど生理作用を阻害する塩化ナトリウム(NaCl)などの中性のナトリウムが問題であるといわれている。このような塩類集積土壌は世界の陸地面積の約10％、100カ国以上に及んでおり、早急な修復が望まれている。解決策の一つとして、生物生産性を高める土壌に改善するために、まず、耐塩性の高い植物好塩性の植物を緑化資材として導入することが考えられる。筆者は、タイ東北部の塩類集積土壌の植生調査をじっしするきかいがあり、ギョウギシバが自生しているのを確認した。また、国内においても海岸地帯に広く自生しているので、塩類集積土壌に自生する有用資源植物の候補種として選定した。ギョウギシバ(Cynodon dactylon (L.) Pers.)は寒帯を除く、ほとんど全世界の分布するイネ科多年生植物で、日本でも各地の路傍、原野、海浜に広く生育する。また、世界の畑地の強害草であると共に、飼料作物や芝生用にも活用される植物である。そこで、ギョウギシバにNaCl処理を行い耐塩性の程度を調査した結果、Cl濃度で5000ppm以上では乾物生産に影響が現れるが、比較的耐塩性の高い植物であることが把握された。従って、本実験では、海岸付近や塩類集積地などの影響のある土壌に自生していたギョウギシバの系統と、路傍など塩分の影響のない土壌に自生していた系統を供試し、NaCl処理を行うことにより、塩分濃度が生育と外部形態に及ぼす影響、及び、耐塩性の系統間差異を検討した。さらに、これらの結果を踏まえて塩類集積地や海浜における緑化被覆植物として活用する可能性を探った

The Outline of Totaling Result of The Class Evaluation Questionnaire by Students in 2001

The committee of academic affairs of the Faculty of Environmental Science and Technology in 2001 planned and carried out "the class evaluation questionnaire survey by students" with original one. The committee has announced the totaling result of this survey, especially concerning both of the class evaluation and the self-estimation of student by themselves, in this paper. It is expected that these contents become the aid of the class improvement in near future

Phosphorus and Biomass Distribution, and P-efficiency by Diverse Brassica Cultivars Exposed to Adequate and P-stress Environment

To acclimate under orthophosphate (Pi) starved environment, plant species and cultivars display an elegant myriad of Pi-adaptive and rescue responses via reprioritizing internal Pi use and maximizing external Pi acquisition by reprogramming metabolism and restructuring root system architecture.Exploitation of considerable genetic diversity both between and within crop species and harnessing of these genetic variations can lead us to develop smart plants with improved P-acquisition, growth and yield under P-deprivation. To elucidate the effect of P-stress on plant growth, and P-efficiency under Pstarvation, 14 diverse Brassica cultivars were grown hydroponically in a climatically controlled chamber using sufficient (200 and 400 μM) and stress (10 and 20 μM) P-levels using ammonium phosphate (NH4H2PO4) as a P source. Cultivars showed differential growth behaviour in terms of biomass accumulation (shoot and root dry matter partitioning), percent distribution of Pi-concentration ([P]) and P-contents in plant parts (roots and shoots), and P-efficiency ratio (% PER)(relative shoot growth) indicating considerable genetic diversity among the tested Brassica cultivars. PER and the proportional increases in shoot dry matter (SDM) accumulation (SDMmax/SDMmin) in response to the P levels assisted in categorizing the cultivars into efficient and inefficient utilizers of the absorbed P from an ambient environment. Cultivars were classified into efficient responsive (ER), efficient non-responsive (ENR), non-efficient responsive (NER) and non-efficient non-responsive (NENR) by plotting ordination plots between PER and SDMmax/SDMmin under P-stress environment. Differential PER values at stress P levels corresponds to high P levels suggest that P efficiency mechanisms can be different from one cultivar to another within a give plant species and cultivars exhibiting high PER values are better choice to thrive under P-starvation

Distribution of Mineral Ions in Root and Leaf Tissues and Their Role in Salt Tolerance of Wheat Varieties under Saline Conditions

The distribution on Ca, K, Na and Cl in root and leaves was studied in salt tolerant variety (Chikugo Izumi) and salt sensitive variety (PB-81) of wheat under saline conditions. The plants grown in 5% Hoagland's nutrient solution were subjected to 100 mM NaCl salinity for one week before observation with scanning electron microscope and analysis of selected samples with X-ray microanalyzer. Root growth was not affected in salt tolerant variety but reduced significantly in salt sensitive variety. Shoot growth was reduced in both varieties but much higher in salt sensitive variety. Salinity increased accumulation of Na and Cl in all root cells including vascular cells in salt sensitive variety. Salt tolerant variety not only reduced uptake of Na and Cl under saline conditions but also restricted their accumulation in cortex maintaining vascular cells relatively free of these ions. Salt sensitive variety failed to block transport of Na and Cl from root to leaves leading to much accumulation of these ions in leaves under salinity sterss

The separate or the combined effect of hypoxia and salinity on growth and ionic relations of four wheat varieties

To evaluate hypoxic-salinity tolerance in wheat varieties, three Japanese varieties (Nourin-61, Chikugo Izumi and Shirasagi Komugi, relatively salt tolerant) and one Pakistani variety (Blue Silver, relatively salt sensitive) were grown under control, hypoxia, saline and hypoxic-saline conditions. The results suggested that relatively hypoxia and salt tolerant variety Nourin-61 was capable of producing the highest relative shoot yield under combined stress conditions. On the other hand, relatively sensitive variety to both hypoxia and salinity conditions, could not withstand harmful effects of combined stress. A more close correlation of plant growth characters between salinity and hypoxic-salinity than hypoxia and hypoxic-salinity indicated that varieties with higher salt tolerance would suffer less than varieties with higher hypoxia tolerance under combined stress conditions. And the balance of Na/K ratio in shoot tissues seems to be the major evaluation factor as the tolerant variety when salinity and hypoxia stress occur together

From Fate to Faith and Soil to Cell: Estimation of Phosphate (Pi) Uptake Rate, Pi-Uptake Kinetics and Relative Growth Rate are Important Parameters to Scavenge Pi by Brassica Cultivars under P-Starved Environment

As a rule, ion uptake by plant cells and roots has features of saturation kinetics. This is in accordance with the assumption of control, as for example by the number of binding sites of ions (carriers, permeases), or the capacity of the proton efflux pumps, in the plasma membrane and tonoplast. Solute transport across membranes is carrier mediated transport. Protein macromolecules integrated into the membrane matrix seems to be the carriers. The carrier-mediated process is subject to kinetics assumig that the number of carriers (binding sites) in the membranes is limited. Kinetics of ion transport through a membrane is considered equivalent to relationship between an enzyme and its substrate. To obtain plants of different P status, two genetically diverse Brassica cultivars (P-tolerant 'Con-1' and P-sensitive 'Gold Rush') were grown for several weeks in nutrient solution culture media. P-uptake kinetics of the roots with intact plants in short-term experiments by monitoring P depletion in culture media revealed that P-tolerant 'Con-1' cultivar had favorable characteristics for P-uptake because of high I(max) or V(max) and low K(m) or 1/2 I(max) value than P-sensitive 'Gold Rush' cultivar. By plotting relative growth rate (RGR) and internal P-concentration (PNC) among P-tolerant (group I; Brown Raya, Con-1, Rainbow, Dunkled and Peela Raya) and P-sensitive (group II; Toria, Sultan Raya, B.S.A, Toria Selection and Gold Rush) cultivars revealed that group I cultivars showed large metabolic fraction and small structural fraction than group II cultivars which provided basis for P-stress tolerance

'Tailoring the Plant to Fit the Soil' in Stead of 'Tailoring the Soil to Fit the Plant' is an Alternate Environmental Sound Strategy to Acclimate Orthophosphate (Pi) Deprivation via Highly Coordinated Classical Pi-Starvation Induced Mechanisms

Acclimation to orthophosphate (Pi) deprivation via highly coordinated Pi-starvation induced (PSI) classical mechanisms such as copious quantities of H(+) and carboxylates (OAs) exudation, remodeling and modification of root architecture by increasing structural and functional plasticity, enhanced uptake rate and increased synthesis of Pi transporters would reduce or eliminate our current overreliance on expensive, polluting, and nonrenewable Pi-fertilizers. These complicated but elegant morphological, physiological, biochemical and molecular adjustments of Pi-starved plants provide an excellent example of how the unique flexibility of plant metabolism and energy transduction helps them to cope in a typically stressful environment. Pi-starved roots possess enhanced H(+)-ATPase and PEPCase which could result in increasing H(+) efflux and OAs exudations in the root vicinity. This would lead to the rhizosphere acidification, which thereby contribute to the solublization and assimilation of mineral Pi from environment. To visualize the dissolution of sparingly soluble Ca-phosphate and rhizospheric pH changes (in situ), genetically diverse Brassica cultivars were grown on agar media. Newly formed Ca-phosphate was suspended in agar containing other essential nutriens. With NH(4)(+) applied as the N source, the precipitate dissolved in the root vicinity and this was ascribed to acidification. No dissolution was occurred with No(3)(-)-nutrition. In order to observe the pH changes at the media-root interface (rhizosphere), an image analysis was carried out after embedding the roots in agar containing bromocresol purple as pH indicator. Efficient cultivar 'Brown Raya' showed greater decrease in pH than P-inefficient 'B.S.A' in the culture media. Hydroponically grown cultivars were compared with respect to P-utilization efficiency (PUE), P-stress factor (PSF), and Ca- and P-uptake at P-starvation. PUE, and Ca- and P-uptake correlated significantly (P<0.01) with biomass accumulation, indicating that higher P-uptake of efficient cultivars was because of their higher Ca-uptake, which in turn was related to their better P-acquisition and PUE. Remodelling of root architecture of efficient cultivars helped the cultivars to establish a better rooting system, which provided basis for tolerance under P-starvation