Silicon and Iron Differently Alleviate Copper Toxicity in Cucumber Leaves

Copper (Cu) toxicity in plants may lead to iron (Fe), zinc (Zn) and manganese (Mn) deficiencies. Here, we investigated the effect of Si and Fe supply on the concentrations of micronutrients and metal-chelating amino acids nicotianamine (NA) and histidine (His) in leaves of cucumber plants exposed to Cu in excess. Cucumber (Cucumis sativus L.) was treated with 10 mu M Cu, and additional 100 mu M Fe or/and 1.5 mM Si for five days. High Cu and decreased Zn, Fe and Mn concentrations were found in Cu treatment. Additional Fe supply had a more pronounced effect in decreasing Cu accumulation and improving the molar ratio between micronutrients as compared to the Si supply. However, the simultaneous supply of Fe and Si was the most effective treatment in alleviation of Cu-induced deficiency of Fe, Zn and Mn. Additional Fe supply increased the His but not NA concentration, while Si supply significantly increased both NA and His whereby the NA:Cu and His:Cu molar ratios exceeded the control values indicating that Si recruits Cu-chelation to achieve Cu tolerance. In conclusion, Si-mediated alleviation of Cu toxicity was directed toward Cu tolerance while Fe-alleviative effect was due to a dramatic decrease in Cu accumulation

Silicon and Iron Differently Alleviate Copper Toxicity in Cucumber Leaves

Copper (Cu) toxicity in plants may lead to iron (Fe), zinc (Zn) and manganese (Mn) deficiencies. Here, we investigated the effect of Si and Fe supply on the concentrations of micronutrients and metal-chelating amino acids nicotianamine (NA) and histidine (His) in leaves of cucumber plants exposed to Cu in excess. Cucumber (Cucumis sativus L.) was treated with 10 mu M Cu, and additional 100 mu M Fe or/and 1.5 mM Si for five days. High Cu and decreased Zn, Fe and Mn concentrations were found in Cu treatment. Additional Fe supply had a more pronounced effect in decreasing Cu accumulation and improving the molar ratio between micronutrients as compared to the Si supply. However, the simultaneous supply of Fe and Si was the most effective treatment in alleviation of Cu-induced deficiency of Fe, Zn and Mn. Additional Fe supply increased the His but not NA concentration, while Si supply significantly increased both NA and His whereby the NA:Cu and His:Cu molar ratios exceeded the control values indicating that Si recruits Cu-chelation to achieve Cu tolerance. In conclusion, Si-mediated alleviation of Cu toxicity was directed toward Cu tolerance while Fe-alleviative effect was due to a dramatic decrease in Cu accumulation

Silicon mediates ion uptake, transport and homeostasis in plants under mineral stress

Silicon is the only known mineral element that effectively alleviates multiple environmental stress in many plant species. Over the past decade rapid progress has been made in understanding the mechanisms through which Si mediates mineral excess and/or toxicity stress. It has been demonstrated that Si mediates uptake and transport of mineral elements at excess by regulating expression of various transporter genes (e.g. Kim et al., 2014; Akcay and Erkan, 2016; Che et al., 2016); however, the role of Si in nutrient uptake and transport under nutrient deficiency conditions is still insufficiently understood. In this presentation, I will talk about Si influence on (a) root P- starvation responses for rhizosphere mobilization and uptake of Pi in wheat (Triticum aestivum) and (b) acquisition and long-distance transport of Fe in cucumber (Cucumis sativus) under low Fe conditions; our recent unpublished work on (c) Si-regulated expression of the transporters involved in Na homeostasis in maize (Zea mays) subjected to NaCl stress will also be discussed

Selekcija i RAPD analiza izolata Pseudomonas spp. koji poboljšavaju biološku sposobnost krtola krompira

Indoleacetic acid (IAA) producing Pseudomonas isolates from the rhizosphere of maize (Q4 and Q20), alfalfa (Q1 and Q16) and wild red clover (B25) were selected for the investigation of their effect on the biological vitality of the potato seed tubers. The production of IAA ranged from 4.09 to 15.9 µ gmL- 1 after 24h of cultivation and 4.08 to 26.4 µ gmL-1 after 48h of cultivation. The molecular comparison by RAPD analysis also was done. RAPD patterns of selected Pseudomonas spp. isolates obtained by BC318, AF14, SPH 1 and AP 10 primers demonstrated the suitability of RAPD method in distinguishing a high variability among the four isolates (44 to 68%). The effect on the biological viability of potato (industrially important variety Pirol) was observed during the seven weeks of sprouting at the temperature of 18-20°C. Potato tubers treated by the selected isolates formed slightly lower number of sprouts, but statistically higher mean length - up to 129.9% higher than the control. The mean sprouting capacity was 64.5% higher than a control. Obtained results suggested positive effects of selected IAA producing Pseudomonas isolates on the length of potato tubers and sprouting capacity as the parameters which define biological viability.Izolati Pseudomonas iz rizosfere kukuruza (Q4 i Q20), lucerke (Q1 i Q16) i divlje bele deteline (B25) selektovani su na osnovu produkcije indolsirćetne kiseline (IAA) radi ispitivanja efekta na biološku sposobnosti semenskih krtola krompira. Produkcija IAA iznosila je 4.09 do 15.9 µ gmL-1 posle 24h i 4.08 do 26.4 µ gmL-1 posle 48h kultivacije. Upoređivanje izolata izvršeno je na osnovu RAPD analize. Na osnovu RAPD profila selektovanih Pseudomonas spp. izolata, dobijenih amplifikacijom BC318, AF14, SPH1 i AP10 prajmerima, ustanovljen je visok stepen različitosti između 4 izolata (44 do 68%), što je potvrdilo efikasnost RAPD metode pri upoređivanju izolata. Efekat na biološku sposobnosti semenskih krtola krompira (industrijski važnu sortu Pirol) ispitivan je tokom sedam nedelja naklijavanja na temperaturi 18-20°C. Krtole tretirane selektovanim izolatima bakterija formirale su nešto manji broj klica, ali je dužina klica statistički značajno veća i do 129,9% u odnosu na kontrolu. Ostvaren je kapacitet klijanja veći do 64,6% u odnosu na kontrolu. Dobijeni rezultati ukazuju na pozitivan efekat selektovanih Pseudomonas izolata koji produkuju IAA na dužinu klica i kapacitet klijanja kao parametara koji određuju biološku sposobnosti semenskih krtola krompira

Silicon influence on plant ionome and mineral element transporters

The plant ionomics is the study of essential and nonessential mineral element composition of plants (the ionom) at cellular, tissue or organismal level. The plant ionomic profile is affected by various factors, including plant (e.g. species, genotypes, organ, developmental change) and environment (e.g. soil, fertilizers, stress conditions). Over the past decade rapid progress has been made in understanding the mechanisms through which silicon (Si) mediates mineral excess and/or toxicity stress. However, the effect of Si on the mineral element uptake and consequently the plant ionome is still unclear, in particular under conditions of limited nutrient availability. Firstly, I will present recent results of my research group demonstrating that Si application modulates the ionomic profile of various plant species (e.g. rice, barley, wheat, maize, cucumber, sunflower, soybean, grapevine and tomato) grown under both normal and stress conditions. In the second part of my talk I will review the current knowledge of Si influence on the expression of (a) root and shoot metal transporter genes under excess of cadmium (Cd), manganese (Mn) and copper (Cu) (Li et al., 2018; Kim et al. 2014; Che et al., 2016; Farooq et al., 2016); (b) transporter genes involved in the uptake, long-distance transport and homeostasis of iron (Fe) under low Fe conditions (Pavlovic et al., 2013, 2016); (c) transporter genes for inorganic phosphorus (Pi) root uptake under low P conditions (Kostic et al., manuscript submitted); and (d) transporter genes involved in shoot homeostasis of sodium (Na+) (see Bosnic et al., this proceedings) and B (Akcay & Erkan, 2016) under saline stress. In conclusion, the role of Si in modulation of plant ionome, including also nutrient and other mineral element uptake and utilization, appears to be more indirect by transcriptional regulation of genes responsible for both root acquisition and tissue homeostasis. Further understanding of how exactly Si regulates the expression of mineral element transporter genes will help to improve crop productivity, yield quality and food safety in stress conditions

Phosphorus Deficiency Induced Silicon Mobilization in Grapevine Rhizosphere: A Field Study

Silicon (Si) uptake by crops is well studied and Si transporters have been characterized in various crop species, including grapevine. However, information on the rhizosphere mobilization of Si is still lacking and virtually no information is available on grapevine. Our previous study showed that grapevine is a phosphorus (P)-efficient species with a high root capacity to mobilize P from the rhizosphere by the released of organic anions (mainly citrate). The field experiment was established in 12-y-old vineyard with the cultivar ‘Chardonnay’, grafted on 5BB rootstock under extremely low P conditions (Olsen P < 3 mg kg-1). Four own-designed rhizotrons (80 cm depth) were installed in a vineyard enabling easy access to the new intact roots. The following treatments were performed: –P/–Si, +P/–Si, –P/+Si (soil application) and –P/+Si (foliar application). The samples of rhizosphere and bulk soils, root exudates from intact root tips and vine tissues (root and leaves) were collected at different growth stages according to Eichhorn-Lorentz (E-L) system: flowering (E-L stage 23), berries pea-size (E-L stage 31), and veraison (E-L stage 35). In addition to Si and P concentrations in the tissues, the expressions of VvALMT, VvMATE (encoding efflux transporters for malate and citrate, respectively), and VvNIP2.1 (encoding Si influx transporter) were also determined. Phosphate fertilization decreased, while low soil P and Si fertilization increased Si availability in the rhizosphere. At the flowering stage, –P plants accumulated more Si than the P-fertilized ones and was comparable to the Si-fertilized plants. Foliar application of Si was less effective in comparison with soil application unless at the veraison stage. The leaf Si concentrations showed a clear seasonal pattern being the highest at the veraison stage. Exudation rate of citrate also showed a clear seasonal pattern and was significantly higher in the –P/–Si than in +P/–Si plants, which was followed by an increased Si availability in the vine rhizosphere. Overall, low P conditions induced Si accumulation in the leaves due to increased exudation of organic anions that can also mobilize Si in the rhizosphere, thereby increasing Si uptake by grapevine

Silicon modulates root phenomics and leaf ionomics in oak under Phytophthora infection and low phosphorus conditions

Pedunculate oak (Quercus robur L.) is the most abundant deciduous tree species in Europe with high economical and ecological importance. Different species of Phytophthora are considered as one of the most important factors responsible for deterioration of oak forest, causing serious root damage not only in the forest trees, but also in the nurseries. Oak seedlings were grown in plastic pots with extremely low phosphorus (P) soil (1.5 mg kg-1 total P; no available Olsen-P detected). Silicon (Si) and P were supplied as Na2SiO3 (300 mg Si kg-1 dry soil) and KH2PO4 (180 mg P kg-1 dry soil), respectively. Four treatments (-P/-Si, -P+/Si, +P/-Si, and +P/+Si) were used in the experiment. After two months of experiment, a half of the plants in each treatment were root-inoculated with Phytophthora plurivora. After further four weeks, the first symptoms of P. plurivora infection appeared in leaves (e.g., leaf necrosis and wilting). Plants were then carefully removed from the pots, divided into roots and shoots, and the roots were scanned and analyzed by the WinRHIZO® software. Foliar concentrations of Si, P, K, Ca, Mg, B, Cu, Fe, Mn, and Zn were determined by ICP-OES, while the concentrations of N and S were determined by CHNS Analyzer. The addition of Si obviously improved root health status (e.g., decreasing de number of lesions and necrosis intensity) in the infected plants grown under -P conditions, which was followed by an increased foliar P concentration. The Si supply significantly increased the root variables (e.g., total root volume, root length, and area of thin roots) in both -P and +P plants inoculated with P. plurivora. Therefore, P. plurivora infection and supply of P and Si modulated the nutrient uptake and thereby changed the leaf ionomics, especially for infected -P plants supplied with Si (e.g., significantly increased B, Cu, and Si foliar concentrations and decreased Fe, Mn, Ca, Mg, K, and S foliar concentrations). Furthermore, Si fertilization significantly declined loses in plant dry biomass caused by P. plurivora infection and/or P deficiency, showing biomass comparable to non-infected +P plants

Silicon Differently Affects Apoplastic Binding of Excess Boron in Wheat and Sunflower Leaves

Monocots and dicots differ in their boron (B) requirement, but also in their capacity to accumulate silicon (Si). Although an ameliorative effect of Si on B toxicity has been reported in various crops, differences among monocots and dicots are not clear, in particular in light of their ability to retain B in the leaf apoplast. In hydroponic experiments under controlled conditions, we studied the role of Si in the compartmentation of B within the leaves of wheat (Triticum vulgare L.) as a model of a high-Si monocot and sunflower (Helianthus annuus L.) as a model of a low-Si dicot, with the focus on the leaf apoplast. The stable isotopes 10B and 11B were used to investigate the dynamics of cell wall B binding capacity. In both crops, the application of Si did not affect B concentration in the root, but significantly decreased the B concentration in the leaves. However, the application of Si differently influenced the binding capacity of the leaf apoplast for excess B in wheat and sunflower. In wheat, whose capacity to retain B in the leaf cell walls is lower than in sunflower, the continuous supply of Si is crucial for an enhancement of high B tolerance in the shoot. On the other hand, the supply of Si did not contribute significantly in the extension of the B binding sites in sunflower leaves

Duration of priming with silicon modulates antioxidative response of wheat to salinity stress

Priming with silicon (Si) may increase plant resistance to biotic and abiotic stresses, in particular in conjunction with its subsequent application. Yet, the very effect of the duration of priming with Si is less understood. Here, we investigated the effect of the duration of priming with Si on components of the antioxidative response of wheat exposed to a gradient of salinity stress. After priming with 1.5 mM Si(OH)4 (0, 1, and 3 days), wheat seedlings were exposed to different NaCl levels (0, 30, and 60 mM) without (-Si) or with (+Si) supply of 1.5 mM Si(OH)4. The activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), and the concentration of malondialdehyde (MDA) were measured in shoots and roots after 1 and 5 days of NaCl treatments. Interaction of priming duration and addition of Si on antioxidative variables were analyzed using general regression model. Overall, priming had no influence on -Si plants under salt stress. On the day 1 of NaCl exposure, priming duration did not affect SOD and APX activities neither in roots nor in shoots. However, on the day 5 of NaCl exposure longer priming with Si significantly increased the activities of APX and SOD in both roots and shoots. The activity of CAT showed no response to priming with Si and subsequent Si supply in both plant organs irrespectively of the duration of NaCl exposure. Interestingly, in both organs the concentrations of MDA as a proxy for oxidative damage of plant membranes were very clearly and consistently lower after 3 days of priming with Si (compared to 1 day or no priming) during the whole period of NaCl exposure. This study demonstrated that longer priming with Si can enhance the ameliorative effect of Si supply on the antioxidative response of wheat plants to a gradient of salinity stress

Zn concentrations in wheat grains along the gradient of native Zn soil availability in Serbia

Zinc (Zn) is an essential microelement for plants and also an important nutritional and health factor in humans. As a consequence of low Zn availability in soils, nearly half of the world's population suffers from Zn malnutrition. Zn deficiency has serious implications for human health (e.g. impairments in physical development, immune system, brain function and learning ability) and thus for the overall economy of a country; it is most severe in nations who depend on cereals as the main staple food. A critical Zn concentration in the whole grain for humans that depend on cereal based diets is 24 mg kg-1 dry matter. Research focused on increase of Zn content in cereals (biofortification), is the strategic priority in many countries. In Serbia however, the awareness of this problem is lacking, and no systematic survey of Zn availability in soi ls and concentrations in cereal grains has been undertaken so far. Our study included 156 grain samples of the two major bread wheat varieties (Simonida and NS 40S) collected at 89 localities throughout Serbia. We analyzed soil pH, available Zn and grain Zn concentration together by principle component analysis and multiple linear regression. Wheat varieties did not differ in ability to accumulate Zn in grains. Both soil pH and available Zn concentration were the nominally significant predictors for grain Zn concentration and explained about 12 and 9% of the encountered variation, respectively. Zn concentration below the critical limit (24 mg kg-1) was found in 58% of grain samples (values in the range 11-61 mg kg-1, median only 21.3 mg kg-1), while in only 14% of soil samples the available Zn was below the critical value (05 mg kg-1). The most severe lack of Zn in grains (below 18 mg kg-1) was observed in samples from the major production regions of bread wheat (e.g. Pancevo, Vrbas and Sremska Mitrovica). The alarming results of this survey indicate that Serbia urgently needs a strategy for Zn biofortification, primarily through a breeding program to enhance Zn efficiency as a sustainable alternative to application of Zn fertilizers