Wheat genotypes often differ significantly in their response to low and high boron (B) supply, although the underlying mechanisms for such differences are poorly understood. The stable isotopes 10B and 11B were used to investigate the contribution of root retention, uptake rates, translocation and allocation of B within wheat (Triticum aestivum L.) genotypes known to differ in B response. At high B supply, the tolerant GREEK had reduced B concentrations in main shoot leaves associated with lower uptake rates and increased allocation of B to tillers. The equally tolerant BT-SCHOMBURGK exhibited high uptake rates, but accumulation was low because of rapid development, lower concentrations of soluble B in the cell sap and lower B translocation to the shoot. In WlMMC, high uptake rates, slow development, high translocation and allocation to main shoots resulted in high B accumulation and poor tolerance. Retention in roots was not substantial in any of the genotypes. The results suggest that B tolerance is multi-faceted and genotype specific. Mechanisms contributing to B tolerance include reduced uptake rates and differential translocation and allocation within plants. Additionally, plant growth rate and leaf morphology can influence B response by affecting tissue concentrations and allowing completion of plant maturation before B accumulation impairs growth. These mechanisms are expressed to different extents depending on the genotype.

ABSTRACTSalinity aggravates B toxicity symptoms in several plant species. In the present study the interactive effects of B toxicity and salinity stresses on the subcellular distribution of boron, cations and proteins in basal and apical leaf sections of wheat were investigated. High B supply increased total B concentrations in all leaf parts, but values remained below 25 mg B kg−1 dry weight (DW) in basal sections, whereas they reached more than 600 mg B kg−1 DW in leaf tips. In basal leaf sections intercellular soluble B concentrations closely reflected the external supply, whereas intracellular soluble B concentrations remained lower by a factor of two, indicating some retention of excess B in the apoplast. Combined salinity and B toxicity stresses significantly increased soluble B concentrations in inter‐ and intracellular compartments of basal leaf sections in comparison with either stress alone, probably related to salinity‐induced changes in water status. The combined stresses also induced quantitative and qualitative changes in inter‐, but not intracellular protein composition. Most obvious was the induction of a 25 kDa protein and an increase in amount of a 33 kDa protein. It is suggested that these changes might be due to structural modifications of the cell wall. The concentration of soluble boron in cells is proposed to be an indicator of boron toxicity.

Plant BiologyVolume 4, Issue 2 p. 190-192 Functions of Boron in Higher Plants: Recent Advances and Open Questions A. Läuchli, Corresponding Author A. Läuchli Department of Land, Air, and Water Resources, University of California, Davis, California, USA9 Department of Land, Air and Water ResourcesUniversity of California One Shields AvenueDavis, CA 95616-8627USA aelauchli@ucdavis.eduSearch for more papers by this author A. Läuchli, Corresponding Author A. Läuchli Department of Land, Air, and Water Resources, University of California, Davis, California, USA9 Department of Land, Air and Water ResourcesUniversity of California One Shields AvenueDavis, CA 95616-8627USA aelauchli@ucdavis.eduSearch for more papers by this author First published: 28 June 2008 https://doi.org/10.1055/s-2002-25741Citations: 15AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume4, Issue2March 2002Pages 190-192 RelatedInformation

Salinity can cause toxic symptoms, especially in mature leaves after long-term exposure. Thus, Na(+) accumulation in leaves could be responsible for salt toxicity. The infiltration-centrifugation technique was employed for the isolation of apoplastic washing fluids (AWF) from leaves and the detection of Na(+), K(+) and Ca(2+) was carried out by ion chromatography. The Na(+) concentrations in the leaf apoplast of salt-sensitive corn and salt-tolerant cotton plants significantly increased with higher Na(+) supply. Nevertheless, the apoplastic Na(+) concentration did not exceed 10 and 30 mmol/L, respectively, after salt exposure up to 150mmol/L in the medium in short- and long-term salt treatments. Higher Na(+) concentrations were found in the leaf apoplast of salt-tolerant cotton in comparison to those of salt-sensitive corn, particularly in fully expanded leaves. No bound Na(+) was found in the leaf apoplast. The Na(+) concentration in the leaf apoplast did not reach high enough concentrations to be responsible for the decline in leaf growth under salinity. Supplemental Ca(2+) did not affect Na(+) concentration in the leaf apoplast under salinity. Apoplastic Ca(2+) concentration remained constant, while K(+) concentrations increased in the leaf apoplast under salinity. Our results do not support the hypothesis by Oertli (1968) who proposed that salt accumulation in the leaf apoplast could be responsible for the death of leaves in plants exposed to salinity.

Upon addition of nitrate and ammonium, respectively, to the bath of intact 'low salt' maize plants, the cortical membrane potential and the trans-root potential changed in a similar and synchronous way as revealed by applying conventional microelectrode techniques and the xylem pressure-potential probe (Wegner & Zimmermann 1998), Upon addition of nitrate, a hyperpolarization response was observed which was frequently preceded by a short depolarization phase. In contrast, addition of ammonium resulted in an overall depolarization response both of the cortical membrane potential and the trans-root potential. The nitrate-induced hyperpolarization response and the depolarization following the addition of ammonium were concentration-dependent.The data suggest that a tight electrical coupling exists between the cellular and tissue level in the root of the intact plant and that the resistance of the cellular (symplastic) space is much less than the resistance of the apoplast.

Glycinebetaine, proline, asparagine, sucrose, glucose, and dimethylsulphoniopropionate (DMSP) were the major organic solutes in Spartina alterniflora leaf blades. To investigate the physiological role(s) of these solutes, the effects of salinity, nitrogen, and sulphur treatments on leaf blade solute levels were examined. Glycinebetaine was the major organic solute accumulated in leaf blades grown at 500 mol m -3 NaCl, although asparagine and proline also accumulated when the supply of nitrogen was sufficient. These solutes may play a role in osmotic adjustment. In contrast, DMSP levels either did not change or were reduced in response to the 500 mol m -3 NaCl treatment. Furthermore, elevated nitrogen supply decreased leaf blade DMSP levels, which was opposite to the response of glycinebetaine, proline, and asparagine. A 1000-fold increase in external sulphate concentration had no effect on the leaf blade levels of DMSP, glycinebetaine, proline, or asparagine. These findings suggest that the major physiological role of DMSP in S. alterniflora leaf blades is not for osmotic adjustment, even under conditions of nitrogen deficit and excess sulphur. Instead, DMSP which was present at 45-130 μmol g -1 dry weight, may play a role as a constitutive organic osmoticum.

Experiments with labeled phosphorus (32P) were carried out to study the effect of NaCl (80 mM) on transport of inorganic phosphorus (P1) in the salt sensitive lettuce plant (Lactuca sativa L. cv. Black‐seeded Simpson). The concentration of P1 used in all experiments was 0.1 mM. Salinity inhibited 32P uptake by the roots as well as translocation of 32P1 from root to shoot. When the plants were exposed for 3 h to a nutrient solution containing 32P, 80 mM NaCl reduced 32P, translocation from root to shoot by 21%. This inhibition increased to 85% during a subsequent 3‐h period in unlabeled solution.‐ The concentration of 32P in leaves increased with decreasing leaf age regardless of the salinity level and leaf size. Indirect evidence supports the proposal that NaCl inhibits the retranslocation of P1 from old to young leaves. It is hypothesized that high levels of NaCl decrease the mobility of P1 stored in vacuoles and, as a result, inhibit export from this storage compartment to other parts of the plant.

The effects of supplemental Ca2+ supply and NaCl salinity on the ionic relations and levels of proline and other amino acids in the primary root of Sorghum bicolor (cv. Hegari) seedlings were investigated. Two days of exposure to 150 mM NaCl resulted in a 50‐fold increase in the proline level in the 0–10 mm root tips of seedlings supplied with 5.0 mM Ca2+, but only a 4‐fold increase in seedlings with 0.5 mM Ca2+. In contrast to the high levels of proline in the root tip, proline accumulation was only modest in the expanded tissues of the root. The enhancement of proline accumulation in the root tip of salinized seedlings with the Ca2+ supplement may be related to their more favorable tissue K to Na ratio. Thus, elevated Ca2+ may mitigate the NaCl‐induced inhibition of S. bicolor root growth via the maintenance of net K to Na selectivity and the enhancement of proline accumulation in the root tip.

SUMMARYRadio‐labelled phosphate (32P) was used to study the effect of 150 mM NaCl on P1 uptake and P distribution in the roots of cotton plants (Gossypium hirsutum L. cv Alcala SJ‐2), Salinity inhibited P, uptake more severely at low P1 concentration (30μM) than at high P, concentration (1 niM). Data of 32P1 uptake at low P1 concentration μM range) in the nutrient solution showed a typical Michaelis‐Menten hyperbolic curve (uptake rate VSmax concentration). NaCl increased the apparent Km (from 2.23 to 4.73 μM and decreased the apparent Vmax (from 1.18 to 0.87 μmol g−1f. wt h−1). High NaCl inhibited P, uptake in the mature root zone. However, salinity enhanced P, uptake in the root tips. We speculate that salinity may induce alkalinization of the cytoplasm in root tips cells, increasing the transmembrane pH gradient and therefore P, uptake. Our results showed an inhibition of 32P transport within the roots and from the roots to the shoots m the salt treatment.

In many salt-sensitive species, elevated concentrations of Ca in the root growth media ameliorate part of the shoot growth reduction caused by NaCl stress. The physiological mechanisms by which Ca exerts protective effects on leaf growth are still not understood. Understanding growth inhibition caused by a stress necessitates locating the leaf expansion region and quantifying the profile of the growth reduction. This will enable comparisons and correlations with spatial gradients of probable physiologically inhibiting factors. In this work we applied the methods of growth kinematics to analyze the effects of elevated Ca concentrations on the spatial and temporal distributions of growth within the intercalary expanding region of salinized sorghum (Sorghum bicolor [L.] Moench, cv NK 265) leaves. NaCl (100 mM) caused a decrease in leaf elongation rate by shortening the leaf growing zone by 20%, as well as reducing the peak value of the longitudinal relative elemental growth rate (REG rate). Increasing the Ca concentrations from 1 to 10 mM restored the length of the growing zone of both emerged and unemerged salinized leaves and increased the peak value of the REG rate. The beneficial effects of supplemental Ca were, however, more pronounced in leaves after their appearance above the whorl of encircling older leaf sheaths. Elevated Ca then resulted in a peak value of REG rate higher than in the salinized leaves. The peak value of unemerged leaves was not increased, although it was maintained over a longer distance. The duration of elongation growth associated with a cell during its displacement from the leaf base was longer in salinized than control leaves, despite the fact that the elongation zone was shorter in salinity. Although partially restoring the length of the elongation region, supplemental Ca had no effect on the age of cessation of growth. Elongation of a tissue element, therefore, ceased when a cellular element reached a certain age and not a specific distance from the leaf base.

Seedlings of cotton (Gossypium hirsutum L. cv. Acala SJ-2) were grown in modified Hoagland nutrient solution with various combinations of NaCl and CaCl2. Marking experiments and numerical analysis were conducted to characterize the spatial and temporal patterns of cotton root growth at varied Na/Ca ratios. At 1 mol m-3 Ca, 150 mol m-3 NaCl reduced overall root elongation rate to 60% of the control, while increasing Ca to 10 mol m-3 at the same NaCl concentration restored the elongation rate to 80% of the control. Analysis of the spatial distribution of elongation revealed that the presence of 150 mol m-3 NaCl in the medium shortened the growth zone by about 2 mm from the approximate 10 mm in the control and also reduced the relative elemental elongation rate (i.e. the longitudinal strain rate, defined as the derivatives of displacement velocity of a cellular particle with respect to position on root axis). Supply of 10 mol m - 3 Ca at the high salt condition restored partially the relative elemental elongation rate, but not the length of the growth zone. Compared to the control, the growth trajectories showed that at 1 mol m-3 CaCl 2 it took more time for a cellular particle to move through the growth zone at 150 mol m-3 NaCl, while at 10 mol m-3 CaCl it took less time and there was no difference between the NaCl treatments.

The aim of this study was to investigate changes in cell wall chemical composition and polymer size in the root tip of intact cotton seedlings (Gossypium hirsutum L. cv. Acala SJ-2) grown in saline environments, in order to relate the interaction between high salinity and root growth to possible changes in cell wall metabolism.Cotton seedlings were grown in modified Hoagland nutrient solution with various combinations of NaCl and CaCl2. Cell walls were fractionated into four fractions (pectin, hemicellulose 1 and 2, cellulose), and analysed for their total sugar content, neutral sugar composition and size of polysaccharides. At 1 mol m-3 Ca, 150 mol m-3 NaCl resulted in a significant increase in the cell wall uronic acid content, but a reduction in cellulose content on a per unit dry weight basis. Supplemental Ca overcame the inhibitory effect of high Na on cellulose content. The neutral sugar composition of the cell wall fractions showed no major changes caused by varied Na/Ca ratios. Determinations of polysaccharide polymer size showed that high Na at 1 mol m-3 Ca led to an increase in the amount of polysaccharides of intermediate molecular size and a decrease in that of small size in the hemicellulose 1 fraction, indicating a possible inhibition of polysaccharide degradation by high Na. This change was not observed in the 10 mol m-3 Ca treatments. The results reveal a relationship between the effects of high salinity on root growth and cell wall metabolism, particularly in regard to cellulose biosynthesis.

Beetroot storage tissue that had been aged in an aerated solution was particularly suited for studies of solute losses during anoxia; retention of betacyanin being a good indicator of tonoplast integrity.During anoxia, loss of K+ was nearly always greater than that of Na+, while Cl- loss was intermediate. Supply of glucose during ageing increased the tolerance of beetroot tissue to anoxia. In these tolerant tissues, there were three phases of solute loss. During the first phase, losses of K+ and amino acids were rapid, presumably due to membrane depolarization from -156 to -95 mV. In contrast, losses of Na+ and Cl- were slow. During the second phase, K+ loss had decreased to a low rate, while losses of Na+ and Cl- remained slow. Furthermore, the membrane potential remained at -95 to -90 mV, which was consistent with the diffusion potential estimated from the modified Goldman equation. In the third and final phase, loss of K+, Na+, Cl-, sugars, and amino acids began to increase, soon followed by loss of betacyanin.Tissues that had lost their betacyanin during anoxia were irreversibly injured, as shown by rapid uptake of Evans Blue and a failure to take up K+, Na+, and Cl- during re-aeration. In contrast, tissues which had retained their betacyanin did not take up Evans Blue, but took up substantial amounts of K+, Na+, and Cl- after re-aeration. After return to air for 1.5 h, tissue that had retained its betacyanin had a membrane potential of -154 mV.

Spatial distributions of growth and of the concentration of some inorganic nutrient elements were analyzed in developing leaves of maize (Zea mays L.). Growth was analyzed by pinprick experiments with numerical analysis to characterize fields of velocity and relative elemental elongation rate. Inductively coupled plasma and atomic emission spectroscopy were used to measure nutrients extracted from segments of leaf tissue collected by position. Leaves 7 and 8, both elongating 3 millimeters per hour had maximum relative elemental growth rates of 0.06 to 0.08 millimeters per hour with maximum rates 20 to 50 millimeters from the node and cessation of growth by 90 millimeters from the node. Spatial distribution of dry weight density revealed that the rate of biomass deposition was maximum in the most rapidly expanding region and continued beyond the elongation zone. The nutrient elements K, Cl, Ca, Mg, and P showed different distribution patterns of ion density (on a dry weight basis). K and Cl had minimal density in the leaf tips; K density was maximum in the growing region, whereas Cl density was maximum at the region of growth cessation. Ca, Mg, and P had relatively high densities at the base of the elongation zone near the node and also in the tip regions. Near the node, P and Mg densities were higher in the young, growing leaves, whereas Ca density near the node was higher in older leaves that had completed elongation. Deposition rates of all nutrients were greatest in the region of maximum elongation rate.

ABSTRACTHigh phosphorus status (High‐P) Azolla mexicana plants (P content 15.5 μmoles g fr wt−1, doubling time ca. 2.2 d) and Low‐P plants with early signs of P‐deficiency (P content 6.2 μmoles g fr wt−1, doubling time ca. 3.2 d) were used to study Pi uptake, efflux and deficiency. When High‐P plants were transferred to medium lacking Pi, uptake capacity increased 1.5‐fold within 12 h and before any detectable change in growth rate (24–48 h). When High‐P and Low‐P plants were compared, uptake rates from 0.3–10000 mmoles m−3 Pi were 2.6–1.7 times higher in Low‐P than High‐P plants (18–1150 vs 7–665 μmoles g fr wt−1 h−1). The relationship of uptake rate to concentration was interpreted as arising from a combined operation of a high‐ and a low‐affinity uptake system. Higher uptake in Low‐P plants involved a 3.4‐fold increase in Vmax (high affinity), no change in Km (high affinity), and a 1.5 to two‐fold increase in both Vmax (low affinity) and Km (low affinity). Rates of P efflux into 1–1000 mmoles m−3 Pi were 1.7 to two times higher from High‐P than Low‐P plants (12–22 vs 7–11 μmoles g fr wt−1 h−1). Below 1 mmole m−3 Pi, uptake and efflux rates were similar: the equilibrium concentration, at which net uptake was zero, was 0.22 mmoles m−3 for High‐P plants and 0.05 mmoles m−3 for Low‐P plants. Similar results were obtained with A. filiculoides. P transport characteristics of Azolla, a fern, are closely comparable with those of higher plants. Its high P requirement in the field arises from its ecological rather than physiological behaviour. We interpret the field behaviour by exploring the relationship between Azolla growth rate in the field, plant P concentration in the field, Pi transport rates required to support such growth, and Pi concentrations in pond waters. The transport characteristics which must operate in the field match those of Low‐P plants in the laboratory, not High‐P plants. Thus, Pi uptake in High‐P plants should be interpreted as repressed from the normal state, instead of that in Low‐P plants being induced.

We grew barley (Hordeum vulgare L. CM 72) for a 28‐day period and sequentially harvested plants every 3 or 4 days. Plants were salt‐stressed with either NaCl or KCl (125 mM) with or without supplemental Ca (10 or 0.4 mM final concentration, respectively). We determined tissue concentrations of Na, Ca, Mg, K. S, P, Fe, Mn, Cu and Zn for each harvest date by inductively coupled plasma spectrometry. Uptake (specific absorption rate) was calculated from the element content and growth rates. Salinity had significant effects on the uptake and concentrations of most elements. Mg and Mn concentrations declined with time. The concentrations of all other elements determined increased over time. Element uptake on a root dry weight basis declined with time. Three variables were significantly affected by salinity and correlated with growth; 1) the Ca concentration, 2) the total sum of the cation concentration (TC), and 3) the Mn concentration of the shoot. Salinity reduced Ca uptake and concentrations. Supplemental Ca increased Ca concentrations and was positively correlated with growth during salt stress. Salinity doubled TC, which was negatively correlated with relative growth rate (RGR). Relative growth rate declined at TC values above 150 mM. Salinity reduced the uptake and concentration of Mn. Manganese concentrations in the shoot were highly correlated with RGR. Relative growth rate declined at Mn concentrations below 50 nmol (g fresh weight)−1.

The effect of salinization on development of the whole shoot and individual leaves of Lactuca sativa L. cv Black-seeded Simpson was studied nondestructively. Salinization by 80 mol m-3 NaCl (from the 10 mol m-3 control concentration) slowed shoot development. The lengthening of the plastochron because of salinization was evident in rates of leaf expansion, frequency of leaf emergence, and growth rate of the whole shoot. The plastochron effect on shoot development was sufficient to account for a 33% reduction in biomass of the shoot, equaling the entire growth inhibition measured during the first week following salinization. A second effect, reduction in maximum leaf size, could be measured after 2 more wk of plant growth. A 50% reduction in fresh weight of fully mature leaves of salinized plants was evident in leaves already beyond the most rapid phase of expansion at the time of salinization. Curtailment of the slow phase of leaf expansion seems, therefore, to reduce maximum leaf size. This cultivar lends itself to nondestructive growth study because of its rapid growth, high rate of leaf emergence, the open access to its leaves, and the absence of a significant contribution by the stem to shoot biomass. Mathematical reconstruction of the shoot allows comparison with results from destructive studies measuring growth of the bulked shoot.