Báo cáo lâm nghiệp: "Contribution of different solutes to the cell osmotic pressure in tap and lateral roots of maritime pine seedlings: effects of a potassium deficiency and of an all-macronutrient deficienc"

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Original article Contribution of different solutes to the cell osmotic pressure in tap and lateral roots of maritime pine seedlings: effects of a potassium deficiency and of an all-macronutrient deficiency Marie-Béatrice Gérard Bogeat-Triboulot* Lévy Équipe sol et nutrition, unité d’écophysiologie forestière, Institut national de la recherche agronomique (Inra), 54280 Champenoux, France (received 7 April 1997; accepted 4 September 1997) Abstract - Seedlings of maritime pine (Pinus pinaster Ait.) were grown in hydroponics and submitted either to a potassium deficiency or to an all-macronutrient deficiency. In response to both nutrient stresses, tap root elongation was maintained while lateral root elongation was severely reduced. In both treatments, K content was decreased to 0.85 % of dry weight in roots and in shoots. Other minerals were little affected by the single deficiency except nitrogen, whose content increased significantly in roots. Measurements of the concentrations of inorganic ions, sol- uble sugars and amino acids on a tissue water basis revealed that, in unstressed plants, potassium, phosphate, choride, glucose, fructose and glutamine accounted for about two thirds of cell osmotic pressure with relative contributions depending on location in the root system. In seedlings subjected to deficiency, K was more or less efficiently replaced by soluble sugars, glutamine and/or sodium according to location in the root system. Osmotic pressure was better maintained in younger tissues but also in tap root tip as compared to lateral root tip. potassium deficiency / osmotic pressure / ion / glutamine / inorganic soluble sugar / root growth Résumé - Contribution de différents solutés à la pression osmotique cellulaire dans le pivot et les racines latérales de semis de pin maritime. Effets d’une carence en potassium et d’une carence en tous macroéléments. Des plantules de pin maritime (Pinus pinaster Ait.) cultivées en hydroponie ont été soumises à une carence en potassium et à une carence en tous macroélé- ments. En réponse aux deux stress nutritifs, l’élongation du pivot a été maintenue alors que celle des racines latérales a été fortement réduite. Le contenu en K a été réduit à 0,85 % du poids sec dans les racines et les parties aériennes. Les autres minéraux ont été peu affectés par la mono- carence excepté l’azote, dont la teneur a augmenté significativement dans les racines. La mesure * Correspondence and reprints E-mail: triboulo@nancy.inra.fr
des concentrations en ions inorganiques, sucres solubles et acides aminés (par rapport à la teneur en eau) a montré que, chez les témoins, les solutés potassium, phosphate, chlorure, glucose, fructose et glutamine représentaient environ deux tiers de la pression osmotique cellulaire. Cependant, la contribution de ces éléments variait d’un endroit à l’autre du système racinaire. Dans les plantules carencées, le potassium a été plus ou moins efficacement remplacé par les sucres solubles, la glutamine et/ou le sodium en fonction de la position dans le système racinaire. La pres- sion osmotique a été mieux maintenue dans les tissus jeunes mais aussi dans l’apex du pivot par rapport à l’apex des racines latérales. potassium / pression osmotique / ion inorganique / glutamine / sucre soluble / carence en croissance racinaire Abbreviations: Solute charges were not and reduced ity during drought growth expressed in the text or in figures and tables: K, [13]. In contrast to nitrogen or phos- rate Na, Mg, Ca, Cl, PO and SO were used 4 4 phorus deficiencies, K deficiency induces instead of K Na Mg Ca Cl (PO , , , , , 3- + + 2+ 2+ - 4 , decrease of the root/shoot biomass ratio, a ,) 2- - 44 HPO H2PO and SO Moreover, [K] . 2- 4 which is due to a stronger reduction of written instead of ’potassium concentra- was root expansion [6]. A recent study con- tion’ and similarly for other solutes. ducted on maritime pine seedlings showed K, potassium; MD, all-macronutrient defi- that a potassium deficiency (KD) affected ciency; KD, potassium deficiency; TR, tap root; LR, lateral roots; TRA, tap root apex; differently the elongation of the different TRPA, tap root post-apex; LRA, lateral root types of roots [23]. The elongation rate of apices; LRPA, lateral root post-apices; P, tur- the tap root (TR) was not affected while gor pressure; π, osmotic pressure; PAR, pho- that of lateral roots (LR) was severely tosynthetically active radiation. reduced. Furthermore, the effects on osmotic and turgor pressures (π and P) varied with location in the root system. In 1. INTRODUCTION particular, π was significantly reduced in the mature cells next to the expanding Potassium (K) is the most abundant zone of LR but not of TR. This suggested cation in plant tissues and plays both bio- heterogeneous capacities of the root sys- chemical and biophysical roles in cells. In tem to maintain π. These differences high- the cytoplasm, although it is not part of light the variability of behaviour existing the structure of any plant molecule, it is within a root system, even at an early stage required for the activation of several of development. Several studies have enzymes, for protein synthesis and pho- already shown that responses varied with tosynthesis. It also plays an important role the stimulus and with the type of roots. in the vacuole where it contributes largely For instance, growth of LR of cotton to the osmotic pressure and thus to the tur- seedlings was more inhibited by salinity gor pressure [11, 13; and references than was primary root growth [19]. TR therein]. K deficiency may occur in trees growth of Phaseolus remained almost con- growing on peaty or sandy soils [5, 20]. stant during the night (as compared to the It has also been shown that, in nurseries, K day) while LR growth was reduced [27]. deficiency, aggravated by an excess of On the other hand, temperature inhibited nitrogen fertilization, caused injuries to TR growth of soybean seedlings but did Picea pungens glauca [2]. not affect LR growth [22]. In a recent study the osmotically active solutes in the The most important consequences of K maize root tip were mapped [17]. How- shortage are a higher sensitivity to frost damage, lower osmotic adjustment capac- ever, little information is available about
their distribution in various parts of the the nutrient solution,1 mM KH was4 PO 2 replaced with [1mM (NH + 25 μM PO 2 )H 4 root system. KH and NH supply was reduced ] 4 PO 2 3 4 O The aims of the present investigation from 4 to 3 mM in order to keep the NH con- + 4 to answer several questions raised centration at the level of controls. This treat- were ment is referred to as KD. The second con- by the different growth and water relation straint consisted of a deficiency of all responses of pine roots to a K deficiency macronutrients (referred to as MD). Supplies of [23]. i) What are the osmotically active Ca, Cl, Mg, S, K, P and N were reduced to compounds in pine root tissues? ii) Are 1/40th of the control levels. their respective contributions to the osmotic pressure similar everywhere in the root system? iii) What are the effects of 2.2. Harvest a potassium deficiency on the distribution of the solutes in the different parts of the Seedlings were harvested 30 days after ger- root system? iv) Which solute(s) replace mination. Lengths of the shoots (consisting potassium? only of a bunch of primary leaves), of the tap of Pinus pinaster Ait. were Seedlings root (TR) and of the three longest lateral roots (LR; as an assessment of the length of the lat- grown in conditions similar to those in our eral roots) of each plant were measured just previous work [23] and concentrations of before harvest. After these measurements, plant inorganic ions, soluble sugars and amino root systems were rinsed by a rapid immersion acids were determined on a water basis in in deionized water and quickly blotted dry. different parts of the root system and To determine the mineral content as a frac- related to cell osmotic pressure. More- tion of dry weight, the whole root system and over, the potassium deficiency was com- primary leaves were separated and dried at pared with an all-macronutrient deficiency. 60 °C for 48 h. To determine solute concen- In order to compare their effects with other trations on a water basis, several parts of the data, the mineral contents of the seedlings root systems were collected: a) the apical in above- and below-ground parts were 15 mm of the TR tip, referred to as TR apex (TRA); b) the following 30 mm of the TR, also determined on a dry matter basis. referred to as TR post-apex (TRPA); c) the apical 10 mm of the LR, referred to as LR apex (LRA); and d) the remaining part of the LR, 2. MATERIAL AND METHODS referred to as LR post-apex (LRPA). For the KD stressed plants, no part d) could be col- 2.1. Plant material lected since LR were usually shorter than 10 mm. Anatomical observations showed that and growth conditions parts a) and c) contained the expanding tissues but also some mature tissues [23]. Pinus pinaster Ait. seeds (provenance ’Lan- des’, southwestern France) grown in were The tissue samples were placed either in hydroponics as described previously [23]. The insulin-type syringes (for the inorganic ion composition of the control nutrient solution analysis) or in 1.5 mL microtubes (for the sol- was: CaCl 0.5 mM, MgSO 0.5 mM, KH 2 4 4 PO 2 uble sugar and amino acid analysis), immedi- 1 mM, NH 4 mM and micronutrients 3 4 O ately frozen in liquid nitrogen and stored at [21]In the growth chamber, temperature was - 20 °C until analysis. Corresponding tissue 22/19 °C, humidity 70/90 % (day/night), pho- samples of three to four plants were pooled in 16 h and the PAR toperiod was was a single syringe (or microtube) in order to μmol msThe nutrient solution -2-1 . 500-600 obtain enough material to carry out the analy- was changed once a week and pH was adjusted sis. Analyses were conducted on samples of daily to 4.5-5.0 with NH OH. 4 35-150 mg (15 mm of TR corresponded to Seedlings were subjected to two different about 12 mg fresh weight). All lateral roots of mineral constraints. The first was a reduction of one plant were pooled together or split into the K supply to 1/40th of the control level. In two samples.
injector (Gilson 222 XL, Villiers le Bel, In order to increase the number of samples, France). Guard column AG12A and column the whole experiment was replicated twice. No used with an (Na 2.7 mM / AS 12A differences appeared between the two repli- 3 CO 2 were 0.3 mM) eluant and a flow rate of cates and therefore data were pooled together. 3 NaHCO 1.5 mL min Injection volume was 50 μL. . -1 In total, 56, 58 and 42 seedlings were used for the control, KD and MD treatments, respec- We noticed that P concentrations measured tively. by inductively coupled plasma were correlated with the PO concentrations measured by 3- 4 ionic chromatography over the whole range of concentrations ([P04 ] 3- 1.02[P] - 2.24, 2.3. Mineral content as fraction = 2 r 0.94, data not shown). A similar correlation of dry weight = was observed between S and SO indicat- , 2- 4 ing that soluble P and S in the tissue extracts Dry samples were ground to powder in were present in inorganic form. liquid nitrogen. An aliquot of each sample (5 mg) was used to measure the total nitrogen 2.4.2. Soluble sugar analyses a C.H.N. (Carlo Erba Instru- content with ments). Following the combustion of the sam- ple at 950 °C, nitrogen oxides were reduced crushed in tube con- Frozen tissues were a detected by a thermal N and this gas was 2 to taining 0.5 mL of 80 % ethanol at 80 °C. These To determine K, Na, conductivity detector. conditions neutralized invertase before it could Mg, Ca and P contents, 20 mg of each sample decompose sucrose into fructose and glucose. were dry-ashed at 500 °C and ashes dissolved Microtubes were rinsed with 0.5 mL 80 % in 5 mL HCl I N. Concentrations of S, P, Mg, ethanol. After 30 min extraction, supernatants Ca, Na and K were determined with a sequen- were collected and residues rinsed twice with tial ICP-OES (JY 38+, Jobin Yvon, 0.5 mL 80 % ethanol. After drying, the extracts Longjumeau, France) and expressed relative were dissolved in 1 mL ultrapure water, puri- to dry weight (g g DW). Because of the small -1 fied with micro-columns filled with ion- volume of samples, we used the ’direct-pick- exchange resins (0.5 mL cationic resin, Amber- ing’ method with three replicates for each ele- lite, IRN77, Prolabo; 0.5 mL anionic resin, ment. Ag1×8, formate, Biorad) and dried again. Before analysis, the extracts were dissolved in 400 μL ultra-pure water and filtered (0.45 p, Acrodisc, Gelman). Next 20-40 μL were analysis in tissue extracts 2.4. Solute injected in a HPLC equipped with a Poly- sphere Pb column (Merck) and ultrapure water Inorganic ion analysis 2.4.1. as eluant. a very small Insulin-type syringes (with 2.4.3. Amino-acid analysis used to extract tissue sap. dead volume) were Glasswool, previously cleaned with HCl 1N, rinsed with ultra-pure water and dried, was Extraction was carried out at 4 °C. 40 μL of placed at the bottom of each syringe. Severed internal standard (α-butyric acid) were an tissue was inserted into the syringe tube and added to samples which were crushed with a the piston put back into it. After thawing, tissue pinch of pure quartz sand in 150-300 μL of sap was collected by pushing the piston back 70 % methanol. After a 15-min incubation, and diluted with ultra-pure water about 100 microtubes were centrifuged for 10 min at times (determined by weighing). This brought 14 000 r/min. Supernatants were collected and ion concentrations into the range of the best the residues rinsed with 150 μL 70 % methanol. accuracy of the methods of analysis. The extracts were filtered (0.45 μm) and, 90 s before the injection in HPLC, 10 μL ortoph- Concentrations of K, Na, Mg, Ca and P taldialdehyd (OPA) were added to 40 μL sam- then measured with ICP-OES as were described above, and of Cl NO PO and , - 3- -34 ple. The fluorescent derivatives of the amino , acids were detected at 340 nm. The HPLC was 2- 4 SO with ionic chromatography with a con- fitted with a RP18 column and a (20 % ductimetric detection and an autosuppression methanol-80 % sodium acetate)-100 % recycle mode (Dionex DX 300, Sunnyvale, methanol gradient was used as eluant. USA). This was associated with an automatic
needles. As compared to KD, the all- 2.5. Calculation of the cellular concentration of the solutes macronutrient deficiency (MD) inhibited LR elongation less and shoot growth more In a side experiment on unstressed plants, but did not induce any deficiency symp- measured the osmotic pressure of single we toms. cells of the different parts of the root (TRA, In control plants, K content was larger TRPA and LRA) with a cryoscopic picolitre osmometer [12] and the osmotic pressure of in roots than in primary leaves, 2.4 and the sap of these tissue parts with a vapour pres- 1.7 %DW, respectively (figure 2). K con- sure osmometer (Wescor 5500). The ratio tent decreased uniformly to 0.85 %DW in between cell osmotic pressure and tissue sap response to both mineral constraints. Na osmotic pressure yielded a coefficient corre- content increased significantly but sponding to the dilution of cell sap by apoplas- remained below 0.3 %DW since this ele- mic sap or by water remaining on the surface of ment was only supplied with the micronu- the roots. The dilution coefficients were 1.15, 1.28 and 1.75 for TRA, TRPA and LRA, trient solution (0.1mM FeNaEDTA). respectively. The large dilution coefficient for Roots accumulated more Na than shoots. LRA was probably due to the drying technique Ca, Mg and P contents were little affected used for these sections (several roots dry-blot- by KD and N content remained unchanged ted together, in order to limit root dehydration at about 4.5 %DW in primary leaves but before storage). The coefficient determined for was significantly increased from 3.9 to LRA was also used for LRPA sections. 4.8 %DW in roots. MD decreased signif- Cellular solute concentrations were calcu- icantly Ca, Mg, P and N contents both in lated by multiplying the concentrations mea- sured in tissue sap by the dilution coefficient of roots and primary leaves. the corresponding root section. In order to cal- culate the contribution of each solute to the cell osmotic pressures (π), these concentra- 3.2. Solute contribution to cell tions were related to π measured in the corre- osmotic pressure in sponding tissue sections in plants grown in same conditions as described above [23]. Cell unstressed plants π was measured by cryoscopy and converted from MPa to osmol L using the Van t’Hoff -1 In all parts of the roots, K was the main relation [9]. When calculating the contribu- cation (62-107 mM) and Cl and PO the 4 tions of solutes to cell π, we neglected the main inorganic anions with a Cl/PO ratio 4 osmotic coefficients and thus obtained semi- quantitative contributions of solutes to π. of about two (figure 3). [Na] remained below 5 mM. [Ca], [Mg], [NO and [SO ] 4 ] 3 were less than 2 mM, contributing very 3. RESULTS weakly to cell osmotic pressure (n), and thus were not presented in, figure 3. K, Na, 3.1. Effect of deficiencies growth on Cl and PO contributed approximatively , 4 and mineral content half of cell π (table I). Osmotically active organic compounds were glucose and fruc- The potassium deficiency (KD) did not tose, with a 1:1ratio, and glutamine, pre- affect tap root (TR) elongation but reduced sent in much larger concentration than the significantly lateral roots (LR) elongation other amino acids. Sucrose was present in of the maritime pine seedlings (figure 1B these tissues as traces only although sig- and C), as found in our previous experi- nificant concentrations were found in older ment [23]. Moreover, growth of shoots, (data not shown). roots displaying only a bunch of primary leaves, was significantly decreased (figure 1A) Solute concentrations differed slightly and symptoms of K deficiency, such as between the parts of the roots. Most impor- tant points were: higher [soluble sugars] in yellowing and necrotic rings, appeared on
apices than in more mature tissues (figure tion of π due to the identified solutes 3 and table I); higher [glutamine] in TR remained also constant (figure 4A and than in LR; lower [organic solutes] and table I). However, KD reduced [K] from higher [inorganic ions] in LR than in TR. 83 to 28 mM and, more surprisingly, this Globally, solutes analysed in this study was associated with a decrease of [Cl] contributed to 65-84 % of cell n (table I). although its supply was not modified. An increase of [glucose], [fructose] and [glu- tamine] fully compensated for the deficit 3.3. Effect of deficiencies on of inorganic solutes. MD reduced [K] less the contribution of solutes severely than did KD (to 50 mM) although to the osmotic pressure limitation of K supply was similar in both treatments (figure 2). The concommitant [Cl], [PO and [glutamine] decreases were of the deficiencies In TRA, ] 4 none changed the osmotic pressure and the frac- compensated for by an increase of [soluble
compensated for by an increase of [soluble which was 1 for all samples in the control and KD treatments, was 1.6 in MD. sugars]. In TRPA, KD reduced [K] from 62 to 9 LRA, the KD treatment dramatically In mM, that is to a level similar to that in reduced [K] from 107 to 10 mM and also LRA (figure 4C). There were increases in affected significantly [Cl] (figure 4B). By [glucose], [fructose] and, more impor- contrast to what happened in TRA, [solu- tantly, [glutamine] which compensated sugars] and [glutamine] were not sig- ble for than the decreases in [K] and more nificantly modified and [Na] increased MD plants, the deficit of K was [Cl].In from 4 to 16 mM. Although cell π was compensated for by Na and soluble sugars, reduced, the ’explained’ fraction of π as in LRA. In response to both treatments, decreased (table I). This means that solutes π was slightly decreased and the fraction other than those analysed here contributed of πdue to the solutes analysed remained to π maintenance. In response to MD, [K] increased unchanged slightly or was was reduced to 25 mM, which is less than (table I). by KD as also happened in TRA (figure 4A). [Cl] and [PO were reduced as com- ] 4 pared with control plants and [soluble sug- 4. DISCUSSION ars] and [Na] increased largely. Cell π decreased and the fraction of ’explained’ π remained almost constant (table I). Sur- In Pinus pinaster seedlings, potassium prisingly, the ratio [glucose]/[fructose], concentrations ([K]) found in root cells
of a large peak with the same reten- were close to those mea- (62-107 mM) ence tion time as shikimate on the anions chro- sured in the same species (80 mM, [15]), matograms. However, identification tests in maize roots (60-97 mM, [16]; 75 mM, were not made and no conclusion could [17]) and slightly lower than in barley be drawn. roots (about 160 mM, [28]). The calcula- tion of cell [K] from tissue [K] gave results In the control and MD treatments, the similar to those measured directly in cells charge balance was close to unity or pre- dispersive X-ray microanaly- by energy sented a slight deficit in negative charges sis [16, 17] or by microelectrodes [28]. (data not shown). Organic anions may The good correlation between the range carry the missing negative charges. In con- of [K] found in the present study and those trast, in the KD treatment, there was a found in the other studies suggests that strong deficit in positive charges, show- the cation exchange capacity of the cell ing that one or several cations were not wall was probably low. taken into account. One of them may be ammonium which cannot accumulate in Major inorganic solutes, K, PO and 4 the cytosol but could be present in the vac- Cl, accounted for approximately half the uole at high concentration (50 mM) as cell osmotic pressure (π). In comparison, found by Lee and Ratcliffe [10] in maize they accounted for 57 % in maize roots root tissue. [16] and for only 20 % in tissue extracts of Potassium deficiency (KD) reduced the white apices of oak roots [25]. It seems K content of roots and shoots by a factor of that the fraction of π due to inorganic about 3 to 0.85 %DW and induced visi- solutes is higher in leaves than in roots: ble symptoms of deficiency. In birch 45 % in oak [25] and above 90 % in barley seedlings, the minimal K content still [8]. As in maize roots [16], glucose and allowing maximal growth was about fructose were found at appreciable con- 1.2 %DW [7]. In Scots pine needles, it centrations and sucrose only as traces. In was lower, close to 0.5 %DW, but was a control experiment, known quantities of measured in an adult stand [5, 20]. By con- sucrose were added to samples and were trast to what happened in the observations recovered, showing that it was not hydrol- on birch, KD significantly increased total ysed during the extraction and purifica- N content in maritime pine roots. Although tion steps and thus that the 1:1glucose/ the mineral contents in MD were similar to fructose ratio was not an artefact. The or lower than those in KD plants, no visual higher soluble sugar concentration in the deficiency symptoms could be seen on apices is probably related to the intense MD plants. This may be due to a better cell division and expansion in the growing balance between minerals. zone. The other important solute, glu- Although most nutritionists express tamine, reached high concentrations mineral contents on a dry matter basis, (35 mM). This solute plays a role in nitro- Barraclough and Leigh [4] underlined the gen storage and transport and here con- importance of expressing them on a tis- tributed to cell π, especially in the mature sue water basis, especially for K because zone of the tap root. Inorganic ions, solu- of its importance in plant-water relations. ble sugars and glutamine accounted for Furthermore, [K] (in mM) changes less about two third of cell π. The remaining during plant development than K in %DW part of π could be due to ammonium, other and has been shown to be independent of amino acids [17, 26] or organic acids. the N and P supplies. However, caution Indeed, quinate, succinate and malate are should be taken since tissue water content present in leaves and roots of oak [24]. varies with water availability and also This hypothesis is supported by the pres-
differently affected. The biophysical anal- depends on K content [4, 7]. In the pre- sent study, expressing solute concentra- ysis conducted in the previous study sug- water basis allowed us to tions gested that a reduction of wall extensibil- on a their contribution to π. Osmotic analyse ity was involved in the inhibition of LR coefficients were ignored when calculating growth. However, turgor pressure (P) and the contribution of solutes to π since, con- π in cells next to the expansion zone were sidering the inherent inaccuracies in the more sensitive to the mineral constraints in measurements of concentrations, the cor- LR than in TR. This could have had effects rections would not have been significant. additive to the reduction of wall extensi- Moreover, osmotic coefficients are more bility. Indeed, Mengel and Arneke [14] or less unknown for such complicated related the reduction of leaf expansion of solutions. Phaseolus in response to a K deficiency to a reduction of cell P and π. Similarly, In response to KD and MD, K was inhibition of ryegrass growth induced by soluble sugars and/or glu- replaced by K deficiency was associated with a reduc- tamine and/or Na. No other cations, e.g. tion of π [4]. Ca or Mg, played a role as alternative osmoticum. This is in contrast to what In pine seedlings, the different compo- happened in leaves of Phaseolus [14] but sition of cell sap in TR and LR and the in agreement with results of Barraclough modifications induced by the mineral con- and Leigh [4] where Na was more effi- straints may be related to different func- cient than Ca and Mg in replacing K and tions of these two types of roots. Many maintaining yield of ryegrass. In response studies have reported heterogeneous to KD, mainly organic substitutes were behaviour or different functions of indi- involved. According to Leigh and Wyn Jones [11; and references therein], the glu- vidual roots within a root system, even in tamine accumulation may have been due the absence of evident morphological dif- to an inhibition of protein synthesis. When ferences [27; and references therein]. In all macronutrients were reduced, π main- several cases, for instance considering the tenance involved accumulation of soluble responses to temperature [22] or to light sugars and Na. [27], it was suggested that differences in carbon allocation to TR and to LR could The maintenance of π occurred more be involved. Moreover, it has been estab- less efficiently and involved different or lished that root elongation is tightly depen- solutes, depending on the part of the root dent on carbon assimilation [1] and that considered. By contrast to the post-apex of potassium deficiency inhibits photosyn- the tap root (TRPA) and to the apex of the thesis and reduces carbon availability in lateral roots (LRA), the apex of the tap roots [6]. According to Atzmon et al. [3], root (TRA) seemed to be protected: [K] in case of a shortage of assimilates in the decreased less, π was perfectly maintained root system, the apical dominance of TR and there was no Na accumulation. Logi- becomes more significant at the expense of cally, younger and more active tissues LR. The growth response of TR and LR to appeared to be favoured over more mature KD seems to confirm that TR presents a ones. This has also been noticed in poplar stronger carbon sink. Moreover, solute where, following K deficiency, [K] was distribution between LR and TR following better maintained in root apices [18]. More KD indicates that sink strength for K was surprisingly, but in agreement with the similar to sink strength for carbon. The growth and water relation parameter question whether these are independently responses [23], solute concentrations in regulated remains unanswered. the root apices (TRA and LRA) were very
Ericsson T., Growth and shoot:root ratio of Solutes contributing to cell osmotic [6] seedlings in relation to nutrient availability, pressure were heterogeneously distributed Plant Soil 168/169 (1995) 205-214. in the root system of maritime pine Ericsson T., Kähr M., Growth and nutrition of [7] seedlings. Moreover, potassium and all- birch seedlings in relation to potassium sup- macronutrient deficiencies induced dif- ply rate, Trees 7 (1993) 78-85. ferent responses in tap and lateral roots in Fricke W., Leigh R., Tomos A.D., Epider- [8] mal solute concentrations and osmoiality in terms of growth, solutes involved in K barley leaves studied at the single cell level, replacement and efficiency in maintenance Planta 192 (1994) 317-323. of turgor and osmotic pressures. This illus- Kramer P.J., Boyer J.S., Water Relations of [9] trates that the morphological differences Plants and Soils, Academic Press, San Diego, between TR and LR are associated to 1995. physiological differences. The complexity Lee R.B., Ratcliffe R.G., Observations on the [10] subcellular distribution of the ammonium ion of the root system is still poorly under- in maize root tissue using in-vivo 14 N-nuclear stood and further studies on the variability magnetic resonance spectroscopy, Planta 183 of the responses to various constraints (1991) 359-367. within the root system are needed. Leigh R.A., Wyn Jones R.G., A hypothesis [11] relating critical potassium concentrations for growth to the distribution and functions of this ion in the plant cell, New Phytol. 97 ACKNOWLEDGEMENTS (1984) 1-13. Malone M., Leigh R.A., Tomos A.D., Extrac- [12] tion and analysis of sap from individual wheat We thank Claude Brechet and Maryse Bitch leaf cells: the effect of sampling speed on the for expert technical assistance in the minerals osmotic pressure of extracted sap, Plant Cell and soluble sugars analyses. We wish also to Environ. 12 (1989) 919-926 thank Erwin Dreyer for useful comments on Marschner H., Mineral Nutrition of Higher [13] the manuscript. Plants, Academic Press, London, 1995. Mengel K., Arneke W.W., Effect of potas- [14] sium on the water potential, the pressure REFERENCES potential, the osmotic potential and cell elon- gation in leaves of Phaseolus vulgaris, Phys- iol. Plant 54 (1982) 402-408. Aguirrezabal L.A.N., Deleens E., Tardieu F., [1] Root elongation rate is accounted for by inter- N’Guyen A., Effets d’une contrainte hydrique [15] cepted PPFD and source-sink relations in racinaire de jeunes plants de pin maritime sur field and laboratory-grown sunflower. Plant (Pinus pinaster Ait.), Ph. D. thesis, Université Cell Environ. 17 (1994) 443-450. de Bordeaux I. 1986, France. Alt D., Rau J.N., Wirth R., Potassium defi- [2] Pritchard J., Tomos A.D., Correlating bio- [16] ciency causes injuries to Picea pungens physical and biochemical control of root cell glauca in nurseries, Plant Soil 155/156 ( 1993) expansion, in: Smith J.A.C., Griffiths H., 427-429 (Eds.),Water Deficits, Plant Responses from Cell to Community, Bios Scientific Publish- Atzmon N., Salomon E., Reuveni O., Riov [3] UK, Oxford, 1993, pp. 53-72. ers, J., Lateral root formation in pine seedlings. I. Sources of stimulating and inhibitory sub- Pritchard J., Fricke W., Tomos A.D., Turgor- [17] stances, Trees 8 (1994) 268-272. regulation during extension growth and osmotic stress of maize roots. An example Barraclough P.B., Leigh R., Critical plant K [4] of single-cell mapping, Plant Soil 187 (1996) concentrations for growth and problems in 1I-21. the diagnosis of nutrient deficiencies by plant analysis, Plant Soil 155/156 (1993)219-222. Qi L., Fritz E., Tianqing L., Hüttermann A., [18] X-ray microanalysis of ion contents in roots Bonneau M., Need of K fertilizers in tropi- [5] of Populus maximowiczii grown under potas- cal and temperate forests, in: Potassium in sium and phosphorus deficiency, J. Plant Ecosystems: Biogeochemical Fluxes of Physiol. 138 (1991) 180-185. Cations in Agro- and Forest-systems, Pro- ceeding of the 23rd colloquium of the Inter- Reinhardt D.H., Rost T.L., Primary and lateral [19] national Potash Institute held at Prague, Inter- root development of dark- and light- grown national Potash Institute, Basel, 1992, pp. cotton seedlings under salinity, Bot. Acta 108 309-324. (1995) 457-465.
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