Young Sunflower Plants Research Articles

Effect of the Pătârlagele Diatomite on Seed Germination and Growth of Sunflower Plants

Sunflower (Helianthus annuus L.) is the third largest agricultural crop in Romania, after corn and wheat. In 2021 Romania cultivated 1112 thousand ha of sunflower with a production of 2818 thousand tons, ranking first among EU countries both in terms of production and cultivated area. Diatomite, also called diatomaceous earth or kieselguhr, is a natural sedimentary rock with a high content of silicon dioxide and clay minerals, widely used in agriculture for its insecticidal and fungicidal properties, stimulating the process of seed germination and plant growth, as well as the ability to absorb and retain nutrients and water. The paper presents preliminary results regarding the effect of diatomite from Pătârlagele deposit (Buzău County) on seed germination and growth of young sunflower plants in laboratory conditions and on seeds production in the field at three sowing dates as well. A semi-early hybrid P64LE99 was used in experiments. Our data showed that the Pătârlagele diatomite improves sunflower seed performances both in laboratory and field conditions. In the laboratory, an increase in seed germination and stimulation of plant growth and development were observed in the diatomite treated samples compared to the untreated control. In the field under climatic and soil conditions of the Moara Domnească area (Southern Romania), the diatomite treated samples performed better than the control, both in terms of plant growth and development as well as production elements, in three sowing dates, middle and late April and early May. The highest yields were when sowing was in the first week of May for both variants.

Поиск и анализ нуклеотидных последовательностей в геноме подсолнечника, ассоциированных с генами устойчивости к расам заразихи Orobanche cumana Wallr.

Studying of sunflower lines resistant to broomrape race G, bred in V.S. Pustovoit All-Russian Research Institute of Oil Crops (VNIIMK), Krasnodar showed the genetic control of resistance is monogenic with incomplete dominance. The purpose of the research was to seek and analyze molecular markers for the genes of resistance to broomrape race G using PCRmethods. In our research we used six developed in VNIIMK lines-donors resistant to broomrape race G: RGP1, RGP2, RGB, RGL1, RGL2, RGA, and susceptible lines VK 101, VK 678, VK 680. We extracted DNA from the leaves of young sunflower plants using STAB-buffer. For PCR-analysis we used 17 pairs of primers of two types: SCAR (sequence characterized amplified region) and SSR (simple sequence repeat). Conditions of amplification are as recommended by authors of markers with experimental selection of a temperature for primers hybridization. Within the research we balanced involved into work SSR- and 12 SCAR-loci using BLAST and a set of HanXRQr1.0. Due to these data we composed a physical map of loci location. After assessment of six resistant and three susceptible parental lines, seven markers demonstrated polymorphism by a length of locus DNA and two ones – by presence/absence of amplified fragment. For markers ORS 683 and ORS 1112 we observed a relation between loci polymorphism and susceptibility of parental lines to broomrape. This was certified with a presence of an allele of 364 n.p. length in ORS 683 and an absence of an allele of 375 n.p. length in ORS 1112. These markers were noted as primary ones for hybridological analysis in F1 и F2 with selected pairs for crossing. Additional markers will be selected individually using obtained data on loci polymorphism. Thus, as a result of the research we created a physical map for the further markers selection, found hybrid combinations and markers from the studied ones for hybridological analysis.

Assessment of phenol compound removal from olive oil mill wastewater by using peroxidases extracted from radish and nettle leaves

The aim of this work is to evaluate the degree of degradation phenolic compounds in olive mill wastewater (OMW), using crude plant peroxidases. In fact, OMW was treated with crude peroxidases extracted from radish (Raphanus sativus L.) and nettle (Urtica urens L.) leaves. A significant reduction of more than 60% of total phenols was observed in OMW incubated with peroxidase crude extract during seven days. The present chromatographic data obtained by high performance liquid chromatography (HPLC) show that enzymatic treatment may change the composition of the polyphenols contained in the OMW. Thus, we observed a significant decrease in some phenolic acid levels, such as gallic acid, p-coumaric acid and hydroxytyrosol, and the disappearance of vanillic acid, compared to the non-treated OMW. Finally, phytotoxicity of the treated and non-treated OMW was tested by means of young sunflower plants (Helianthus annuus) grown in hydroponic medium. Our results showed that sunflower plants grow normally when the nutrient medium contains treated OMW; whereas they fade rapidly in the presence of non-treated OMW. We conclude that treatment of OMW with radish and nettle crude extracts could attenuate OMW phytotoxicity considerably.

The effect of freezing temperature on physiological traits in sunflower

This study was conducted to identify the physiological mechanisms associated with the resistance and tolerance of young sunflower plants to freezing temperatures. The effect of overnight temperature –3°C on the maximal quantum efficiency of PSII (F<sub>v</sub>/F<sub>m</sub>), the relative electrolyte leakage (REL) and the osmotic potential (Ψ<sub>π</sub>) was determined in five genotypes of sunflower: C33, C98, C124 and C148 were chosen from the population of recombinant inbred lines (RILs) based on contrasted responses to low temperature, and a wild genotype 2603 that was chosen for its ability to maintain activities in cold conditions. The night temperature –3°C over the course of 10 h caused an immediate significant decrease of F<sub>v</sub>/F<sub>m</sub> in C33, C98, C124 and C148. In the case of genotype C98, the effect of this freezing temperature was manifested by a significant increase of REL. Significant changes of Ψ<sub>π</sub>, as a reaction to the effect of freezing temperatures, were not found in any of the monitored genotypes. The measurements of the physiological traits after 5 days of regeneration indicated the renewal of integrity of cellular structures and an increase of PSII reaction centre efficiency in all monitored genotypes. From the point of view of tolerance or sensitivity, the wild genotype 2603 showed itself as tolerant towards the tested freezing temperature, displaying insignificant differences with control plants in all monitored traits. Genotype C98 appears to be the most sensitive from the monitored set, with evident changes in two traits signalling frost damage.

Circadian regulation of sunflower heliotropism, floral orientation, and pollinator visits.

Young sunflower plants track the Sun from east to west during the day and then reorient during the night to face east in anticipation of dawn. In contrast, mature plants cease movement with their flower heads facing east. We show that circadian regulation of directional growth pathways accounts for both phenomena and leads to increased vegetative biomass and enhanced pollinator visits to flowers. Solar tracking movements are driven by antiphasic patterns of elongation on the east and west sides of the stem. Genes implicated in control of phototropic growth, but not clock genes, are differentially expressed on the opposite sides of solar tracking stems. Thus, interactions between environmental response pathways and the internal circadian oscillator coordinate physiological processes with predictable changes in the environment to influence growth and reproduction.

Antimony (SbIII) reduces growth, declines photosynthesis, and modifies leaf tissue anatomy in sunflower (Helianthus annuus L.).

The role of antimony (Sb)--a non-essential trace metalloid--in physiological processes running in crops is still poorly understood. Present paper describes the effect of Sb tartrate (SbIII) on growth, Sb uptake, photosynthesis, photosynthetic pigments, and leaf tissue organization in young sunflower plants grown in hydroponics. We found that growth of below- and aboveground part was reduced with increasing concentration of Sb in the medium. Although Sb was mostly taken up by sunflower roots and only small part (1-2%) was translocated to the shoots, decline in photosynthesis, transpiration, and decreased content of photosynthetic pigments were observed. This indicates that despite relatively low mobility of Sb in root-shoot system, Sb in shoot noticeably modifies physiological status and reduced plant growth. Additionally, leaf anatomical changes indicated that Sb reduced the size of intercellular spaces and made leaf tissue more compact.

Effect of limited supply of assimilates on the relationships between their sources and acceptors

Sink activity in young sunflower and bean plants was determined mainly by their growth rate. The organ with higher RGR (stem in sunflower and apical part with expanded trifoliate leaf- in bean plant) was the dominant acceptor even in conditions of limited supply of assimilates.Specific activity of root - donor of phosphorus, depends on the roofs metabolic and physiological activity only in the case, when supply of P to the aerial parts is not a factor limiting photosynthesis. If the activity of the whole root system is relatively low (like in preshaded series of sunflower) the photosynthetic compensation observed in plants replaced into better conditions coincides with compensation of P-absorption (both calculated per g of dry matter). It may explain the existence of a functional balance between shoot and root activity in the case of a changed proportion between their sizes.

Physiological responses as influenced by night freeze stress at the beginning of vegetative growth of sunflower

Physiological changes on leaves of young sunflower plants (genotypes C120, C124, C148 and PAC2) were evaluated in a growth chamber after exposure to night frost of -3 and -5°C for a period of 12 h. Net CO2 assimilation rate (PN), potential photochemical efficiency of electron transport PS2 (FV/FM), relative electrolyte leakage (REL%) and osmotic potential (ψπ) were monitored in the plants. Stressed plants were evaluated immediately (2 h) after the effect of the freezing temperature (var. S1), after 2-day recovery (var. S2) and after 6-day recovery (var. S3). The PN was determined as the most sensitive of the evaluated parameters of the sunflower. In genotypes C120, C148 and PAC2, a statistically evident decrease of PN in all variants S1-S3 was found during a temperature of -3°C. To the contrary, the results have proved minor sensitivity or, more precisely, a high stability of FV/FM, ψπ a REL% at the freezing temperature of -3°C. The results showed that physiological parameters were more sensitive to a freeze temperature at −5°C. It was also possible to determine the differences between genotypes. Statistically evident changes were found there in comparison to control plants: decrease of PN in genotypes C120 and C148 in all variants S1-S3, in genotype C124 in variant S1 and in genotype PAC2 in variant S3. There was also the decrease of FV/FM in genotypes C120, C124 and C148 in variant S1; increased REL% in genotype C120 in variants S1 and S3 and in genotypes C124 and C148 in variant S1; decreased ψπ in genotype C124 in variants S1-S3 and in genotypes C120 and C148 in variant S2. As apparent from the above, the PAC2 genotype may be considered relatively resistant to freeze stress, while genotypes C120, C124 and C148 rather sensitive to freeze stress.

Effect of Sodium Chloride Levels on Growth, Water Status, Uptake, Transport, and Accumulation Pattern of Sodium and Chloride Ions in Young Sunflower Plants

There is a paucity of information on the critical content, threshold levels, uptake, transport, and accumulation of sodium (Na+) and chloride (Cl−) ions in young sunflower plants. Effect of salinity was analyzed in root, stem, leaves, and buds by raising plants in fine sand irrigated with Hoagland's solution and supplemented with 10–160 mM sodium chloride (NaCl) for 30 days. Maximum sensitivity index, reduction in growth, and water content were observed in buds. Maximum Na+ and Cl− contents were obtained in old leaves and stems under low salinity but in roots at high salinity. Uptake, transport, and accumulation rate of Cl− were more than those of Na+, and for both ions they increased with increasing NaCl concentration but decreased with increasing exposure time. Growth reduction at low salinity seems to be because of Cl− toxicity, but Na+ toxicity and water deficiency could also be the causes at high salinity.

Dehydrocostus lactone is exuded from sunflower roots and stimulates germination of the root parasite Orobanche cumana

The germination of the obligate root parasites of the Orobanchaceae depends on the perception of chemical stimuli from host roots. Several compounds, collectively termed strigolactones, stimulate the germination of the various Orobanche species, but do not significantly elicit germination of Orobanche cumana, a specific parasite of sunflower. Phosphate starvation markedly decreased the stimulatory activity of sunflower root exudates toward O. cumana, and fluridone – an inhibitor of the carotenoid biosynthesis pathway – did not inhibit the production of the germination stimulant in both shoots and roots of young sunflower plants, indicating that the stimulant is not a strigolactone. We identified the natural germination stimulant from sunflower root exudates by bioassay-driven purification. Its chemical structure was elucidated as the guaianolide sesquiterpene lactone dehydrocostus lactone (DCL). Low DCL concentrations effectively stimulate the germination of O. cumana seeds but not of Phelipanche aegyptiaca (syn. Orobanche aegyptiaca). DCL and other sesquiterpene lactones were found in various plant organs, but were previously not known to be exuded to the rhizosphere where they can interact with other organisms.

Influence of pre-emergence herbicides on the early growth of sunflower hybrids

Introduction Beside cereals and maize, sunflower occupies the largest area on the arable fields in Hungary. Its economical production necessitates an effective weed regulation, of which determining element is the pre-emergent weed control, since weeds mean one of the most important problems in sunflower fields. Broad-leaved weeds (dicotyledons) cause serious problems. The agro-ecological and agricultural engineering requires different genotypes, and their stress resistance shows significant differences (Szabo and Pepo 2005, Hunyadi and Borbely 2006). In the last 20 years just a few herbicide with new action type came to the market. There are considerable differences among the new sunflower hybrids with respect to their herbicide-sensitivity, and it has an importance in their productivity and in the results of their production (Lehoczky et al. 2002, Lehoczky and Buzsaki 2005). The selectivity of a herbicide has to be taken into consideration. There are many herbicides, which have site selectivity only. On a permeable soil with poor organic matter content young sunflower plants may be damaged in consequence of heavy rain. The phytotoxic effects may directly endanger the yield otherwise they may promote early presence of stem diseases because of growing depression (Benecsne, 2005). The aim of our study was testing the sensitivity of sunflower hybrids to pre-emergent herbicides and analysing the changes of different growth parameters. For this reason a pot experiment with in the practice widely known pre-emergent herbicides were used.

Internal Boron Requirement of Young Sunflower Plants: Proposed Diagnostic Criteria

In a greenhouse study, a significant increase in sunflower (Helianthus annuus L., cv. Hysun 33) dry matter yield was observed with boron (B) application to a B-deficient (hot water-extractable, 0.23 mg B kg−1) calcareous soil of Missa series (Typic Ustochrept). Six rates of B, ranging from 0 to 8 mg B kg−1 soil, were applied as H3BO3 along with adequate basal fertilization of nitrogen (N), phosphorus (P), potassium (K), and zinc (Zn). Four plants of sunflower were grown in each pot; two were harvested after 4 weeks of germination and the other two after 8 weeks. Maximum crop biomass was produced with 1.0 mg B kg −1, and application of ≥2.0 mg B kg−1 proved toxic, resulting in drastic yield suppressions. Critical B concentration range for deficiency diagnosis in 4‐week‐old sunflower whole shoots appears to be 46–63 mg B kg−1. However, critical concentration in 8‐week‐old plants was much less (i.e., 36 mg B kg−l), presumably due to a dilution effect. As plant's internal B requirement can vary, in fact manifold, depending on the species, plant part, and plant age, only a relevant criterion can help in diagnosing the deficiency effectively.

Effect of airborne bromoxynil–octanoate and metribuzin on non-target plants

The present study was conducted to determine the effects of airborne herbicides on the photosynthesis and growth of non-target plants. Sunflowers at different growth stages were used as test plants and exposed for 24 h in a wind tunnel to a range of concentrations of bromoxynil–octanoate and metribuzin. The quantum yield (φPSII) and the dry weight were used as response parameters. Results indicate that young sunflower plants are affected by sublethal concentrations of both herbicides, whereas metribuzin proved to be more phytotoxic. Bromoxynil–octanoate and metribuzin concentrations >0.265 and >0.135 μg/m3 impair the photosynthetic activity of exposed leaves and concentrations >0.780 and >0.641 μg/m3 of leaves developed after exposure. Effects on dry weight indicate that younger plants were more susceptible, whereby the response to metribuzin proved to be more dependent on growth stage. Based on these results and considering herbicide concentrations in ambient air, there is a reasonable probability that non-target plants are temporarily at risk of being affected.

COMPARISON OF EXTRACTANTS USED FOR EVALUATING THE BIOAVAILABILITY OF SOIL P AND K

Numerous extractants including strong and weak acids and their salts, alkaline solutions, water etc. are used to evaluate the phosphorus and potassium status of soils. In our study, two weak extractants, hot water[1] and ammonium lactate[2] were used for the analyses. Hot water percolation (HWP) procedure developed in Hungary, seems to be a promising extraction methodology for rapid soil tests. The main objective of our study was to compare the results obtained with the two extraction procedures and to evaluate their use in estimating the bioavailability of soil P (Hw-P and AL-P mg kg−1) and K (Hw-K and AL-K mg kg−1) in different soil types. Soil samples were collected from experiments carried out with several NPK fertilizer sources applied in different treatment combinations. Four soil types (an Eutric cambisol in FAO taxonomy and Ortic Eutrochrept in USA taxonomy), a Haplic luvisol (FAO), Typic Hapludalf, a Stagnic Luvisol (FAO), Typic Endoaqualf and a Chromic Luvisol (FAO), Arenic Hapludalf, respectively, were used in the study. Main characteristics of experimental soils showed considerable differences. Results obtained with the two extractants were compared to each other as well as to amounts of P and K (Pup and Kup, respectively) removed by young corn and sunflower plants. Nutrient uptake of plants showed a dramatic increase compared to the control with the application of fertilizer sources not causing acid forming reactions in soils. From the results of statistical analyses, it was evident that a good correlation was found between the values of soil P and K obtained with the two extractants (“r” values ranged between 0.974 and 0.612 for P and between 0.761 and 0.04 for K, respectively). Generally, a better relationship could be observed between Hw-P and AL-P values than Hw-K and AL-K values. Similar tendencies were found when plant P and K removal was correlated with soil P and K contents extracted either with hot water or AL solution. Plant removal of P showed a better correlation with AL-extractable phosphorus. Among soils, closest relationships were observed between plant removal and soil P contents using the two extractants on the Orthic Eutrochrept (r=0.925 and 0.932, respectively). On the other hand, a better correlation was obtained between Hw-K values and K removal for the Typic Hapludalf as well as for the Arenic Hapludalf than between the soil P extracted by AL solution and P removal by young plants. For the wider understanding of dominant factors influencing the effectiveness of these extractants, especially for HWP, and their relationships with plant removal in a variety of soil types in Hungary, further studies are needed.

Effects of Nitrogen Nutrition on Photosynthesis in Cd-treated Sunflower Plants

Increased nitrogen supply stimulates plant growth and photosynthesis. Since it was shown that heavy metals may cause deficiencies of essential nutrients in plants the potential reversal of cadmium toxicity by increased N nutrition was investigated. The effects on photosynthesis of low Cd (0, 0.5, 2 or 5mmol m−3) combined with three N treatments (2, 7.5 or 10mol m−3) were examined in young sunflower plants. Chlorophyll fluorescence quenching parameters were determined at ambient CO2and at 100 or 800μmol quanta m−2s−1. The vitality index (Rfd) decreased approx. three-times in response to 5mmol m−3Cd, at 2 and 10mol m−3N. The maximum photochemical efficiency of PSII reaction centres (Fv/ Fm) was not influenced by Cd or N treatment. The highest Cd concentration decreased quantum efficiency of PSII electron transport (ΦII) by 30%, at 2 and 10mol m−3N, mostly due to increased closure of PSII reaction centres (qP). Photosynthetic oxygen evolution rates at saturating CO2were decreased in plants treated with 5mmol m−3Cd, at all N concentrations. The results indicate that Cd treatment affected the ribulose-1,5-bisphosphate (RuBP) regeneration capacity of the Calvin cycle more than other processes. At the same time, the amounts of soluble and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein increased with Cd treatment. Decreased photosynthesis, but substantially increased Rubisco content, in sunflower leaves under Cd stress indicate that a significant amount of Rubisco protein is not active in photosynthesis and could have another function. It is shown that optimal nitrogen nutrition decreases the inhibitory effects of Cd in young sunflower plants.

Are there two Mechanisms for Boron Uptake in Sunflower?

Summary Uptake mechanisms for B have been characterized in young sunflower plants ( Helianthus annuus L. cv. Frankasol), precultured with either low B supply (1 μmol L -1 ) or high B supply (100 gmol L -1 ), by investigating the distribution of B between cell sap and water insoluble residue in roots and the fluxes of B to the shoots in response to short term changes in B supply. Complementary studies were carried out on soluble B complexes in roots and xylem sap and on the effect of inhibition of metabolic processes in the roots on B uptake. Two mechanisms seem to bring about B uptake into the roots, dependent on B supply during plant culture. When B supply is high, passive diffusion is responsible. With low B supply, a concentration mechanism for B is established, which can be turned off by increasing B supply as well as by the inhibition of metabolic processes by low root zone temperature or 2,4-Dinitrophenol. For building up and maintaining the concentration gradient between the root and the external solution, the formation of B complexes within the cell seems at least partially to be involved. The uptake of B from the external medium into the root is likely to be the key step for translocation of B to the shoot, whereas the mechanism of xylem loading is still unclear.

Cadmium accumulation and distribution in sunflower plant

Cadmium (Cd) accumulation and distribution was studied in sunflower (Helianthus annuus L., public line HA‐89) plant. From an uncontaminated sandy loam brown forest soil with 162 μg kg‐1 HNO3/H2O2 extractable Cd the HA‐89 sunflower public line accumulated 114 ug kg‐1 Cd in its kernels under open field conditions. This value is rather low as compared to data found by others. Sandy loam brown forest soil was treated with 0, 1 or 10 mg kg‐1 of Cd to study the interaction of this heavy metal with young sunflower plants in a greenhouse pot experiment. The fresh weight and dry matter accumulation of sunflower plant organs (roots, shoots, leaves or heads) was unaffected by cadmium treatment of soil. The nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), or zinc (Zn) uptake of sunflower plant organs was not influenced by lower or higher Cd‐doses, except sunflower heads where 10 mg kg‐1 of Cd treatment of soil significantly reduced the uptake of Ca, Fe, and Mn. Although Cd reduced the Zn uptake of roots, its rate was statistically not significant. Cadmium was accumulated prevalently in roots (1.21 mg kg‐1,4.97 mg kg‐1, or 13.69 mg kg‐1 depending on Cd‐dose), and its concentration increased also in shoots or leaves. In spite of the short interaction time, elevated concentrations of cadmium (0.78 mg kg‐1, 1.34 mg kg‐1, or 3.02 mg kg‐1 depending on Cd‐dose) were detected in just emerged generative organs (heads) of young sunflower plants.

Effect of excess lead on sunflower growth and photosynthesis

The effect of different lead (Pb) concentrations in the nutrient solution on the growth, Pb and chlorophyll a+b content, chlorophyll fluorescence and quenching parameters in the leaves of young sunflower (Helianthus annuas L.) plants was studied. The content of Pb in the analyzed plant parts increased following the increase in Pb content in the nutrient medium. This increase was expressed to a higher extent in the roots than in the stems and leaves. In the presence of high concentration of Pb in the leaf area, the dry mass and the height of plants were reduced. Lead treatment of sunflower plants led to a pronounced reduction of chlorophyll (a+b) content, accompanied by much smaller decrease of photosynthetic O evaluation rate and PSll efficiency at low light intensity. Hence, Pb effect2did not result in the destruction of the photosynthetic apparatus, but in its reduction. The highest Pb concentration in the nutrient solution induced, however, at saturating photon flux density (PFD) a decrease in photochemical quenching and in the efficiency of PSll electron transport and significantly affected nonphotochemical fluorescence quenching, indicating an increase in proton gradient across the thylakoid membrane and a decrease of photophosphorylation.

Photosynthesis, chlorophyll fluorescence and soluble carbohydrates in sunflower leaves as affected by boron deficiency

Abstract The effect of various boron levels in the nutrient solution on the growth, boron and chlorophyll content, photosynthesis and chlorophyll fluorescence in the leaves of young sunflower (Helianthus annuus L.) plants was studied under greenhouse conditions. Deficiency of boron decreased the dry matter yield of the roots, shoots and leaves. The content of boron in all analyzed plant parts increased with the increase of boron levels in the nutrient solution, more so in the shoots than in the roots. Leaf area was reduced under boron deficiency as well as the content of chlorophyll in the leaves. The content of analyzed sugars was increased in boron deficient plants, glucose content exhibited the highest increase under boron deficiency. Boron deficiency appreciably decreased photosynthetic oxygen evolution by leaves, the apparent quantum yield and quantum efficiency of photosystem two electron transport. The diminished rate of photosynthesis in boron deficient sunflower leaves could be correlated to the ...

Regulation of K+ and NO3− fluxes in roots of sunflower (Helianthus annuus) after changes in light intensity

Shoot activity has been reported to affect rates of ion uptake by plant roots in other ways than merely through supply of assimilates. To elucidate the mechanisms by which a signal from the upper part of the plant controls the rate of K+ and NO3− uptake by roots, both uptake of K+ and NO3− and secretion into the xylem of young sunflower plants (Helianthus annuus L.) were measured after changes in light intensity.No close correlation was observed between the uptake of NO3− and that of K+; an increase in light intensity produced a much greater stimulation of NO3− uptake than of K+ uptake. On the other hand, secretion of NO3− into the xylem was tightly coupled to that of K+, and this coupling was strongly disturbed by excision of the root. The results suggest the involvement of the K2‐malate shuttle on the regulation by the shoot of K+ and NO3− secretion in the xylem, which is linked to NO3− uptake, while K+ uptake is independent of this regulation mechanism.