Conditions In Nutrient Solution Research Articles

Nitrogen-utilization efficiency during early deficiency after a luxury consumption is improved by sustaining nitrate reductase activity and photosynthesis in cotton plants

Understanding mechanisms underlying N use efficiency (NUE) after luxury consumption and nitrate deprivation is crucial to crop productivity. The aim was to elucidate the importance of photosynthesis, assimilatory nitrate reduction and N-reserve remobilization to NUE in cotton. Plants were exposed to three conditions in nutrient solution: (a) previous exposure to high nitrate supply (10 mM) for long-term (8 days); (b) nitrate deprivation (NO3− withdrawal) for 8 days followed by (c) an early N-deficiency for 4 days. Plants supplied with nitrate excess were able to display increment in shoot NUE related to dry matter gain, whereas photosynthetic N use efficiency did not change, evidencing that excess N per se was not able to improve CO2 assimilation. Nitrate reductase (NR) activity was crucial to remobilize stored nitrate through deprivation phase and free amino acids, total proteins, and chlorophylls were also essential to N-remobilization. High NUE was important to kept high root growth rates throughout deprivation and early deficiency phases. Despite the great decrease in chlorophyll content, PSII and PSI activities were kept stable until the onset of early N-deficiency, when cotton plants displayed high shoot NUE. These responses are closely associated with high NR activity and sustaining of photosynthesis, which contribute to N-homeostasis in different nutritional regimes.

Effect of nutrient omission and pH on the biomass and concentration and content of steviol glycosides in stevia (Stevia rebaudiana (Bertoni) Bertoni) under hydroponic conditions

Steviol glycosides (SGs), have recently been approved in western countries as sources of intense natural sweeteners. SGs are found in Stevia rebaudiana, mainly in the leaves, and industry prefers rebaudioside A (Reb-A) over other steviol glycosides for its superior flavour profile. Hence leaf biomass and concentration of SGs (and their product, SG content) are of primary agronomic interest. Experiments were conducted under controlled conditions in nutrient solution to assess the effects of nutrient deficiencies and pH on biomass production, and concentration and plant content of SGs. Total SG content was low in plants deficient in the macronutrients N, P, S, Mg or Ca because of reduced photosynthesis and because of the decreased leaf yield, even though lack of N resulted in greater concentration of stevioside in the leaves. Lack of N or P reduced the proportion of Reb-A to total SGs. Plants deficient in K had less yield than in the nutrient-complete control, but not significantly so and SG concentration in the leaves was similar to that of the control. Deficiency of the micronutrients Cu and Fe led to low SG yield, because of reduced SG concentration in leaves, and because of reduced leaf yield, respectively. Lack of other micronutrients did not influence SG content. Neutral to alkali conditions reduced plant growth and leaf yield, most likely due to deficit of P, but pH had no effect on SG concentration. Our results are indicative, but preliminary, and require confirmation in open field trials over several years.

Responses of Selected Indonesian Rice Varieties under Excess Iron Condition in Media Culture at Seedling Stage

Iron toxicity could limit rice productivity on irrigated lowland acid and swampy soil. The use of iron toxicity tolerant rice is an alternative strategy to improve rice productivity in these areas. We studied the phenotypic variation of twenty-four rice genotypes and characterized the fate of Fe2+ along its path between the roots and shoot of rice plant. Twenty-four rice genotypes form different agro-ecosystem were grown under agar nutrient solution conditions with 400 mg. L-1 iron stress and under normal condition. We found variation in the biomass accumulation of rice seedling during stress of iron namely, high accumulated biomass tolerant type and low accumulate biomass tolerant type. The relative biomass weight was highly correlated with the leaf bronzing scores (LBS) under excess iron. Based on these categorizations, we chose six genotypes to observe the present of Fe in root and shoot using invivo-staining 2,2 bypiridine. The result indicated that some genotypes were able to develop root and shoot aerenchym during iron stress. This was related to the development on root iron plaque and the iron content of the shoot of the rice seedling. In this present study, rice genotypes could be classified as the includer tolerant type (Inpara 2) and some others were the excluder tolerant type (Mahsuri, Pokkali and Siam Saba). This information on tolerance strategies is important for rice breeder to develop physiological-based breeding program of iron-toxicity tolerant in rice.

Root morphology and phosphorus uptake by potato cultivars grown under deficient and sufficient phosphorus supply

Information regarding the characteristics that affect P-uptake capacity may assist in the selection of more adapted potato (Solanum tuberosum L.) cultivars and more adequate fertilization management for each cultivar. This study evaluated the P-uptake capacity of potato cultivars (Agata, Asterix, Atlantic, Markies, and Mondial) grown under P-deficient (2mgL−1) or P-sufficient (31mgL−1) conditions in nutrient solution and related it to physiological parameters of uptake and morphological root characteristics. When the plants were 24 days old, they were subjected to a P-uptake kinetics study. The length and surface area of roots and the uptake kinetic parameters (Imax, Km, and Cmin) varied among potato cultivars. Phosphorus-deficient potato plants had an approximately 60% smaller root surface area and an increase of 86% in the Imax and net P influx compared with the plants in P-sufficient conditions. However, these modifications in P uptake kinetics can do not influence P acquisition in the soil environment due to very limited P diffusion. The amount of P accumulated by plants grown under P-deficient conditions was directly related to the root length and surface area; a greater root surface, as demonstrated by the Asterix cultivar, is the most important factor for achieving a greater P-uptake capacity. Under P-sufficient conditions, potato cultivars such as Markies and Mondial showed a balance between morphological root characteristics (medium/large length and surface area) and physiological parameters (medium/high Imax values and net P influx) and had a greater P-uptake capacity. However, under field conditions, the responses to P deficiency may be different due to the very limited diffusion of P in the soil and because plants can use additional mechanisms to improve their P uptake from the soil.

Maintaining elevated Fe2+ concentration in solution culture for the development of a rapid and repeatable screening technique for iron toxicity tolerance in rice (Oryza sativa L.)

Iron toxicity decreases rice (Oryza sativa) grain yield especially in acid soils after flooding. Our aim was to establish a high-throughput screening technique using nutrient solution culture for identifying Fe-toxicity-tolerant genotypes. Varying levels of Fe, pH, and chelators in Yoshida nutrient solution culture were tested to maintain sufficient Fe2+ concentration over time to optimize the severity of Fe toxicity stress for distinguishing between a tolerant (Azucena) and sensitive (IR64) genotype. The optimized solution was tested on 20 diverse genotypes in the greenhouse, with measurement of leaf bronzing scores and plant growth characteristics at the seedling stage. The same 20 genotypes were grown to maturity in a field with natural Fe toxicity stress, with measurement of seedling-stage leaf bronzing scores and grain yield to determine their inter-relationship. Optimized nutrient solution conditions were 300 mg L−1 Fe supplied as Fe2+ at pH 4.0 with a 1:2 molar ratio of Fe:EDTA, which maintained sufficient Fe2+ stress over 5 days. The highest correlation of nutrient solution phenotypic data with field grain yield was found with leaf bronzing scores at 4 weeks, with a Pearson r of 0.628 for simple association and a Spearman corrected r of 0.610 for rank association (P < 0.01) using 20 diverse rice genotypes with proven Fe toxicity tolerance reaction. The Leaf bronzing scores at 4 weeks in nutrient culture solution were also found highly correlated with LBS under natural field stress after 8 weeks that had highest correlation with grain yield under stress. This culture solution-based standardized screening technique can be used in plant breeding programs as a high-throughput technique to identify genotypes tolerant to Fe toxicity.

Transcript expression of Mg-chelatase and H+-ATPase isogenes in Vicia faba leaves as influenced by root and foliar magnesium supply

Magnesium deficiency results in a loss of yield and quality of crop plants. Foliar application of magnesium is under discussion with regard to the amelioration of magnesium deficiency. We have tested the effect of magnesium foliar application on the leaf photosynthesis rate and on the transcript abundance of two enzymes that depend upon the supply of magnesium. Vicia faba L. were grown under controlled environmental conditions in nutrient solution. Plants growing in low-magnesium solution were treated with foliar applications of 0, 50 or 200 mM MgSO4. Photosynthesis rate and chlorophyll concentration increased following magnesium leaf application in magnesium-deficient plants but did not reach the levels of plants sufficiently supplied with magnesium via the roots. Under magnesium deficiency, foliar application had its greatest effect on magnesium concentration, photosynthesis and chlorophyll concentration in older leaves but had only minor effects on younger leaves. However, foliar application increased the transcript levels of plasma-membrane ATPase in younger leaves but not in older leaves. The transcript levels of Mg-chelatase remained unchanged. The appearance of chlorosis is associated to aggravated loss of magnesium, in contrast a reduction in Mg chelatase transcript abundance is already measurable before the occurrence of visible symptoms as in the young leaves and might therefore represent a sensitive indicator of Mg deficiency.

Physiological Responses to N-NO&lt;sub&gt;3&lt;/sub&gt; and N-NH&lt;sub&gt;4&lt;/sub&gt; of Triazine Resistant and Susceptible Plants of Horseweed (Erigeron canadensis L.)

Triazine resistant and susceptible biotypes of horseweed (&lt;i&gt;Erigeron canadensis&lt;/i&gt; L.) were grown under controlled conditions in nutrient solution with NH&lt;sub&gt;4&lt;/sub&gt; or NO&lt;sub&gt;3&lt;/sub&gt; ions as nitrogen source. Indicators such as: dry matter, CO&lt;sub&gt;2&lt;/sub&gt; assimilation, chloroplasts activity, dark respiration and the content of K, Ca, Mg in the above ground parts displayed lower levels when plants were fed with NH&lt;sub&gt;4&lt;/sub&gt; than with NO ions. Reduction of these indicators was stronger for the triazine susceptible plants which grew better than their resistant counterparts when fed with N-NO&lt;sub&gt;3&lt;/sub&gt;. The triazine resistant plants grown with N-NH&lt;sub&gt;4&lt;/sub&gt; contained more protein-N and K than the susceptible ones. Chloroplasts of the resistant plants were also less sensitive to NH&lt;sub&gt;4&lt;/sub&gt;CL treatment. It is concluded that the resistant plants appear to be more tolerant to NH&lt;sub&gt;4&lt;/sub&gt; ions as compared with their susceptible counterparts. For this reason application of ammonium forms of nitrogen fertilization in horticultural practice could favour spreading of triazine resistant horseweed.

Effect of silicon on sunflower growth and nutrient accumulation under low boron supply

Study was focused on effect of silicon (Si) on growth and nutritional status of sunflower (Helianthus annuus L.) under low boron (B) external supply. Plants were grown under controlled environmental conditions in nutrient solutions with two low B treatments (0.2 μM B and 0.5 μM B) with or without addition of Si and control treatment containing sufficient B supply. Shoots growth was only slightly affected by Si supply while accumulation of B in fully developed leaves was significantly higher only at 0.5 μM B. In roots, nutrients contents were relatively constant, while accumulation of all nutrients in leaves was affected by addition of Si. Differences were significant only in K, Fe and Mo between treatments 0.5 μM B and 0.5 μM B with Si added and in Zn between both treatments. In comparison with other studies, results confirmed that plant species show different response to Si application. Interaction of B and Si should be involved in further research in B deficiency in sunflower. [Projekat Ministarstva nauke Republike Srbije, br. ON 173028]

Potential of Arundo donax to treat chromium contamination

The ability of Arundo donax against chromium pollution was tested. A. donax plants were grown under greenhouse conditions in nutrient solution having Cr (0, 50, 100, 200, 400, 600, and 900μgL−1) for three weeks. Shoots and roots dry matter production, growth parameters, plant physiological and morphological characters were measured. The maximum Cr content in roots was 206.33μgg−1. Likewise, Cr concentration in stem was 262.6μgg−1 at 900μgL−1 supplied Cr. In case of leaves, the maximum Cr concentration was 206.33μgg−1 at 900μgL−1 supplied Cr. The IC50 values of antioxidants using ABTS and DPHH standards showed that both time and increasing Cr concentrations affected the production of antioxidants indicated by lower IC50 value on 21st day. A. donax may be used in remediation of Cr contaminated wastewaters.

Stable Isotopes of Cu and Zn in Higher Plants: Evidence for Cu Reduction at the Root Surface and Two Conceptual Models for Isotopic Fractionation Processes

Recent reports suggest that significant fractionation of stable metal isotopes occurs during biogeochemical cycling and that the uptake into higher plants is an important process. To test isotopic fractionation of copper (Cu) and zinc (Zn) during plant uptake and constrain its controls, we grew lettuce, tomato, rice and durum wheat under controlled conditions in nutrient solutions with variable metal speciation and iron (Fe) supply. The results show that the fractionation patterns of these two micronutrients are decoupled during the transport from nutrient solution to root. In roots, we found an enrichment of the heavier isotopes for Zn, in agreement with previous studies, but an enrichment of isotopically light Cu, suggesting a reduction of Cu(II) possibly at the surfaces of the root cell plasma membranes. This observation holds for both graminaceous and nongraminaceaous species and confirms that reduction is a predominant and ubiquitous mechanism for the acquisition of Cu into plants similar to the mechanism for the acquisition of iron (Fe) by the strategy I plant species. We propose two preliminary models of isotope fractionation processes of Cu and Zn in plants with different uptake strategies.

Anatomical characteristics and nutrient uptake and distribution associated with the Cd-phytoremediation capacity of Eucalyptus camaldulenses Dehnh

Cadmium (Cd) is a hazardous heavy metal whose concentrations have been increasing in Brazilian soils, largely due to mining activities. Eucalyptus species are widely planted in Brazil to produce raw materials, and the confirmation of their phytoreme diation potential would link their economic and environmental roles. We examined the Cd-tolerance of Eucaliptus camaldulenses Dehnh and the anatomical and physiological features associated with that capacity. Plants were grown under greenhouse conditions in nutrient solutions with increasing concentrations of Cd (0, 15, 25, 45, 90 μmol m -3 ). Shoot biomass production was less sensitive to the phytotoxic effects of cadmium than root biomass production due to low Cd transport rates from roots to shoots. Increases in epidermal and endodermal thickness, changes in the vascular conductive elements of the roots, as well as differential nutrient distributions between roots and shoots are features of Cd tolerance in this species. The Cd tolerance of E. camaldulenses and its high biomass production support its potential use in Cd phytoremediation programs.

A comparative study on the potential of oxygen release by roots of selected wetland plants

The capacity of root oxygen release by selected wetland plants pre-grown under both nutrient solution and artificial wastewater conditions were determined. The results indicated that the significant differences of root oxygen release by the tested wetland plants existed, and the biochemical process was the main source of root oxygen release as oxygen released by Vetiveria zizanioides L. Nash roots through biochemical process was contributed to 77% and 74% of total root oxygen release under nutrient solution conditions and artificial wastewater conditions, respectively, and that was 72% and 71% of total root oxygen release for Cyperus alternifolius L. It was found that the formation of root plaque with iron oxide was a function of root oxygen release as iron oxide concentration in root plaque was positively correlated to the potential of oxygen released by wetland plant roots with the regression coefficients as 0.874 *( p < 0.05) under nutrient solution conditions and 0.944 **( p < 0.01) under artificial wastewater conditions, which could be regarded as an important mechanism of wetland plants being tolerant to anoxia during wastewater treatment. It was suggested that the potential of root oxygen release could be used as a parameter for selecting wetland plants that can increase oxygen supply to soil or substrate of constructed wetlands and enhance nutrient transformation and removal, and V. zizanioides L. Nash with the highest potential of root oxygen release and higher tolerance to wastewater could be recommended to establish vegetated wetlands for treating nutrient-rich wastewater such as domestic wastewater.

Nitrogen Redistribution Characteristics of Oilseed Rape (Brassica napus L.). Varieties with Different Nitrogen-Use Efficiencies during Later Growth Period

To determine the relationship between nitrogen (N) redistribution of oilseed rape (Brassica napus L.) varieties and N-use efficiency during later growth stages, the differences in N-use efficiency between two varieties (X-36 and X-50) were studied using the 15N labeling method with sand culture under complete nutrient solution conditions. Results showed that X-36 had greater grain yield not because of greater N uptake but because of greater grain yield per unit N in the plant and N-harvesting index. The average proportion of N in the two varieties that was redistributed from the vegetative organs to the grain was 65.1%. The redistribution amount and the proportion of N absorbed at the stem elongation stage and redistributed into the grain of two varieties were the greatest; the least were amounts absorbed at the siliquing stage. The high-N-use-efficiency variety (X-36), when compared with the low-N-use-efficiency variety (X-50), had slower redistribution speed of N before the siliquing stage, which then became faster after the siliquing stage. The amount of N redistributed to the grains and its proportion were larger, whereas those toward the silique husk were smaller. The amount of N loss from the plant and its proportion were smaller, and the velocity of N loss was also slower. This explains why varieties with high N efficiency have high N-harvesting index. At the later growth stages, N redistribution in the vegetative organs will significantly affect N-use efficiency.

Absorption, Distribution, and Translocation of Nitrogen at Growth Stages in Oilseed Rape Plant

The differences of concentration and distribution of nitrogen in crop depend on organs and growth stages, and nitrogen redistribution in different organs will be occurred at different stages; these differences are related to the transfer of growth center. Consequently, the high crop yield depends not only on the high amount of nitrogen absorption, but also on the high efficiency of nitrogen redistribution. The objective of this study was to reveal the law of nitrogen absorption, distribution, and translocation in oilseed rape plant at different growth stages using two winter oilseed rape cultivars with the 15N labeling method in sand culture under Hoagland complete nutrient solution conditions. The results (average value from the two cultivars) indicated that 83.5% of nitrogen absorbed at the seedling stage, and 67.3% of nitrogen absorbed at the stem elongation stage, were distributed to leaves; 79.1% of the nitrogen absorbed at flowering stage was contained in leaves and stems, with 42.8% of it in the leaves. However, 42% of the nitrogen absorbed at siliquing stage was distributed to siliquae which is just the organ directly distributed the highest proportion of nitrogen absorbed at this stage. The nitrogen absorbed at four growth stages (seedling, stem elongation, flowering, and siliquing) translocated from the vegetative to the reproductive organs at 34.4%, 44.3%, 41.2%, and 31.7%, i.e. 203.2, 325.8, 218.0, and 82.0 mg plant-1, respectively. The translocated nitrogen from vegetative organs to the total nitrogen in seed accounted for 65.1%; among with 25.8% absorbed at the stem elongation stage, 16.9% absorbed at flowering stage, 15.9% absorbed at seedling stage, and 6.4% absorbed at siliquing stage, respectively. The proportion of nitrogen loss, after being absorbed at the four growth stages, was 24.0%, 10.5%, 11.7%, and 7.3 %, i.e. 141.6, 79.2, 43.2, and 16.2 mg plant-1, respectively. To sum up, nitrogen absorbed by roots at the earlier growth stages in oilseed rape was mainly translocated to leaves first, and then to the reproductive organ at the later growth stages.

Different Eucalyptus Species Show Different Mechanisms of Tolerance to Salinity and Salinity × Hypoxia

ABSTRACT We studied the effect of sodium chloride (NaCl) salinity and oxygen deficiency stress on growth and leaf ionic composition of three Eucalyptus species [E. tereticornis, E. camaldulensis (Silverton), and E. camaldulensis (Local)]. Species were grown with control (no NaCl) and salinity (150 mol m−3 NaCl) under hypoxic and non-hypoxic conditions in nutrient solution with five replications following CRD. Species differed significantly in their response to salinity and hypoxia. Absolute shoot dry matter was significantly better in E. camaldulensis (Silverton) in salinity and in E. camaldulensis (Local) in saline hypoxic treatment. E. tereticornis was the most sensitive species to salinity and salinity × hypoxia in the root environment. Sodium (Na+) and chloride (Cl−) concentrations were significantly lower in E. camaldulensis (Local) in non-hypoxic saline treatment compared to the other two species. E. camaldulensis (Silverton) seems to have better tissue compartmentalization, whereas E. camaldulensis (local) seems to have better exclusion of Na+ at the root level.

Differential tolerance to Mn toxicity in perennial ryegrass genotypes: involvement of antioxidative enzymes and root exudation of carboxylates

Mechanisms underlying differential tolerance to Manganese (Mn) toxicity in perennial ryegrass (Lolium perenne L.) cultivars are poorly understood. We evaluated activity of antioxidative enzymes and root exudation of carboxylates in four ryegrass cultivars subjected to increasing Mn supply under nutrient solution conditions. A growth reduction caused by Mn toxicity was smaller in Jumbo and Kingston than Nui and Aries cultivars. Shoot Mn accumulation varied in the order Nui > Aries > Kingston > Jumbo. Ascorbate peroxidase and guaiacol peroxidase activities increased with Mn excess. Mn-tolerant Jumbo and Kingston had high activity of these enzymes and relatively low lipid peroxidation. Kingston was most tolerant to high tissue Mn concentrations and had the highest superoxide dismutase activity. Increased activity of antioxidative enzymes in Mn-tolerant cultivars could protect their tissues against oxidative stress triggered by Mn excess. Mn toxicity induced root exudation of carboxylates; oxalate and citrate may decrease Mn availability in the rhizosphere, thus enhancing Mn tolerance in ryegrass.

Effects of nutrition and Bacillus amyloliquefaciens on tomato (Solanum lycopersicum, L.) growing in perlite

Plant growth-promoting rhizobacteria (PGPR) are free-living bacteria that, as their name suggests, promote plant growth. However, they can also be of help in the biological control of plant diseases. This study reports the effects of two different commercially available strains of Bacillus amyloliquefaciens (FZB24 and FZB42) on tomato production in open and closed systems in the presence of different amounts of nutrients. Three factors were tested: (1) the type of nutrition system (open or closed), (2) the concentration of the nutrient solution (full or half strength), and (3) the PGPR applied (either B. amyloliquefaciens FZB24 or B. amyloliquefaciens FZB42, or a no-PGPR control). Perlite was used as the growth medium. Variables related to water use efficiency, yield and fruit quality were assessed. The use of half strength nutrient solution was sufficient for full growth in the open system in both spring and autumn seasons. However, the same strength nutrient solution was associated with reduced yields in the closed system during the autumn season. The application of either strain of B. amyloliquefaciens increased the yield of the tomato plants by 8-9% in the open system in the spring, whereas they had an adverse effect on yield in the closed system under half strength nutrient solution conditions during the autumn.

Evaluation the efficiency of some Egyptian wheat Triticum aestivum L. cultivars to Zn deficiency through peroxidase activity and protein profile techniques.

Zinc (Zn) is an essential micronutrient for plants. The ability of plants to maintain significant yields under low zinc is called Zn efficiency (ZE). Eleven wheat ( Triticum aestivum L.) (Banisuef 1, Gemiza 10, Gemiza 7, Giza 170, Giza 168, Sohag 3, Sids 7, Sids 5, Sids 1, Sakha 94, and Sakha 93) cultivars were grown under controlled environmental conditions in nutrient solution for 30 days to study the effect of varied supply of Zn (0 and 1 micro M ) on shoots, root dry production, shoot and root Zn efficiency, peroxidase activity. Also the peroxidase isozyme and protein on gel electrophoresis were investigated. Among all wheat cultivars Banisuef 1, Sohag 3 and Sakha 93 were less affected by Zn deficiency. Banisuef 1 showed the lowest value for shoot/root ratio under Zn deficiency. Peroxidase activity increased in Sohage 3 and Sakha 93. A new polypeptide with molecular weight 34 Kda was expressed in Banisuef 1, Gemiza 10, Gemiza 7 and Giza -170 under Zn deficiency. It can be concluded based on the experimental results that, for assessing wheat cultivars for resistance to Zn deficiency the POD enzyme activity together with protein profile could be considered as a better reliable techniques to select the resistance cultivars for zinc deficiency stress.

The effect of nitrate and plant size on nitrate uptake and in vitro nitrate reductase activity in strawberry ( Fragaria × ananassa cv. Selva)

Nitrogen plays a major role in the growth and yield of strawberry. For optimizing nitrogen fertilizer application, it is necessary to understand the response of strawberry to nitrogen supply. The objective of this study was to determine the effect of nitrate supply and plant size on strawberry nitrate uptake and nitrate reductase activity (NRA). Strawberry plants cv. Selva were grown under growth chamber conditions in nutrient solutions containing 0, 0.1, 0.25, 0.7 or 4 mM nitrate. Cumulative nitrate uptake increased with the increase in nitrate supply. Increasing nitrate concentrations from 0 to 0.25 mM decreased leaf NRA; however, further increases to 4 mM nitrate restored NRA to activities observed at 0 mM nitrate. The activity of NADH- and NADPH-dependent NR was similar at every external nitrate concentration. Activity of NR was greater in the smallest plants and decreased as plant size increased. However, increasing external nitrate concentration increased nitrate uptake, but had not the same effect on nitrate reductase activity, showing that NRA and nitrate uptake are not necessarily correlated.

Silicon nutrition of tomato and bitter gourd with special emphasis on silicon distribution in root fractions

AbstractTwo plant species, tomato (Lycopersicon esculentum Mill.) and bitter gourd (Momordica charantia), were used for in‐depth studies on the dynamics of silicon (Si) uptake and translocation to the shoots and compartmentation of Si in the roots. The experiments were conducted under controlled environmental conditions in nutrient solutions, which were partly amended with 1 mM Si in the form of silicic acid. At harvest, xylem exudates were collected, and Si concentrations and biomass of roots and shoots were determined. Mass flow of Si was calculated based on the Si concentration of the nutrient solution and transpiration determined in a parallel experiment. Plant roots were subjected to a fractionated Si analysis, allowing attributing Si to different root compartments. Silicon concentrations in the roots compared to the shoots were higher in tomato but lower in bitter gourd. A more ready translocation from the roots to the shoots in bitter gourd was in agreement with Si concentrations in the xylem exudates which were higher than in the external solution. In tomato, the xylem‐sap Si concentration was lower than in the nutrient solution. Calculated Si mass flow to the root exceeded Si uptake in tomato, which was consistent with the measured accumulation of Si in the root water‐free space (WFS). In contrast, Si concentration in the root WFS was lower than in the nutrient solution in bitter gourd, reflecting the calculated Si depletion at the root surface based on the comparison of Si mass flow and Si uptake. Within the roots, more than 80% of the total Si was located in the cell wall and less than 10% in the cytoplasmic fractions in tomato. In bitter gourd, between 60% and 70% of the total root Si was attributed to the cell‐wall fraction whereas the proportion of the cytoplasmic fraction reached more than 30%. Our results clearly confirm that tomato belongs to the Si excluders and bitter gourd to the Si‐accumulator plant species for which high Si concentrations in the cytoplasmic root fraction appear to be characteristic.