Osmotic adjustment, gas exchanges and chlorophyll fluorescence of a hexaploid triticale and its parental species under salt stress

J. Plant Physiol. 161. 25 – 33 (2004) http://www.elsevier-deutschland.de/jplhp

Osmotic adjustment, gas exchanges and chlorophyll fluorescence of a hexaploid triticale and its parental species under salt stress Annick Morant-Manceau*, Elisabeth Pradier, Gérard Tremblin Laboratoire de Physiologie et Biochimie Végétales, Faculté des Sciences et Techniques, Université du Maine, Avenue Olivier Messiaen, 72085 Le Mans cedex 9, France

Received October 28, 2002 · Accepted March 24, 2003

Summary The effect of salt stress (NaCl 85.7 or 110 mmol/L) was investigated in the triticale T300 and its parental species, Triticum dicoccum farrum (Triticum df ) and Secale cereale cv. Petkus. Triticum df and T300 were more salt-tolerant than the rye (110 mmol/L NaCl was the highest concentration allowing rye growth to the three-leaf stage). Na + , K + and Cl – ions accounted for almost half of the osmotic adjustment in Triticum df and T300, and up to 90 % in rye. Salinity decreased the net photosynthesis and transpiration rates of the three cereals as compared to control plants, but induced no significant change in chlorophyll a fluorescence parameters. Water-use efficiency (WUE) increased with salinity. In the presence of 110 mmol/L NaCl, the K + /Na + ratio decreased markedly in rye as compared to the other two cereals. Proline concentration, which increased in Triticum df and T300, could have protected membrane selectivity in favour of K + . Proline content remained low in rye, and increasing soluble sugar content did not appear to prevent competition between Na + and K + . The salt sensitivity of rye could be due to low K + uptake in the presence of a high NaCl concentration. Key words: chlorophyll fluorescence – NaCl – osmotic potential – photosynthesis – proline – Secale cereale cv. Petkus – soluble sugars – transpiration – triticale – Triticum dicoccum farrum – water-use efficiency Abbreviations: chl a = chlorophyll a. – cv. = cultivar. – π = osmotic potential. – PS II = photosystem II. – RETR = relative electron transport rate. – RWC = relative water content. – Triticum df = Triticum dicoccum farrum. – TSS = total soluble sugars. – WUE = water-use efficiency

Introduction Hexaploid triticale is regarded as a cereal with considerable potential, particularly in marginal agricultural areas (Vermorel and Bernard 1979). Trials have shown that some triticales per* E-mail corresponding author: [email protected]

form well compared to their parental species, but many hybrids have failed to give the expected results (Lelley 1992). Except in Poland, no net increase of growing area has occurred since 1986. The basic genetic potential of the wheat/rye hybrid may have been overestimated. An amphidiploid hybrid such as triticale T300 represents a simple addition of the two parental genotypes. The performance of the hybrid may 0176-1617/04/161/01-25 $ 30.00/0

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Annick Morant-Manceau, Elisabeth Pradier, Gérard Tremblin

therefore be directly related to that of the parental wheat and rye components. On a yield basis, Lelley (1992) found a very close correlation between wheat and triticale genotypes, whereas no additive effect was exerted by the rye genome. Comparative studies concerning water stress have given conflicting results. According to Anderson (1984), only triticales with a short period of grain filling can have a complete cycle. Giunta et al. (1993) determined that some triticales are more drought-tolerant than durum wheat in a Mediterranean environment, whereas Josephides (1993) considered that triticale could not replace durum wheat in semi-arid areas. Few comparative investigations of triticales, wheat and rye under salt stress have been published (Jensen and Jönsson 1981, Gorham 1990). However, comparative studies have been reported for several cultivars of bread-wheat (Salam et al. 1999), or durum wheat (Gorham et al. 1997, Almansouri et al. 1999), or triticales (Haddad and Coudret 1989, Salim 1989, Karim et al. 1992, Morant-Avice et al. 1998). Plants under salinity stress reduce their solute potential by accumulating inorganic and/or organic solutes to maintain continuous water absorption at low soil water potential. Sodium and chloride ions contribute to osmotic adjustment as well as salt toxicity (Martin and Koebner 1995). In salt stressed plants, K + concentration decreases with increasing Na + (Weimberg 1987) affecting several aspects of plant metabolism (Passera and Albuzio 1977). Triticale T300 is an original hybrid of the tetraploid wheat, Triticum dicoccum farrum and the rye, Secale cereale cv. Petkus. In a previous investigation (Morant-Avice et al. 1994), the behaviour of triticale T300 and its parental species was compared under polyethylene glycol-induced drought. Under controlled conditions, T300 water-use efficiency (WUE) was higher than that of its genitors, while under water stress tetraploid wheat had a higher WUE than T300 and the rye Petkus. In the present study, the three cereals were subjected to salt treatments in order to compare their salt resistance. According to Gorham (1990), the effect of enhanced K + /Na + discrimination is most pronounced at low salinity, as shown in bread-wheat and the rye genome (RR). The highest NaCl level allowing cereal growth to the three-leaf stage was found to be 110 mmol/L. As drought and salt tolerance are not necessarily linked (Nagy and Galiba 1995), our study compared the salinity response of triticale T300 and its genitors. Plant growth, relative water content (RWC), osmotic potential (π), ionic and organic compound content, transpiration and net photosynthesis rates, and chlorophyll a fluorescence were measured under controlled conditions. Flower and Ludlow (1986) consider RWC as an alternative measure of plant water status, reflecting the metabolic activity in plant tissues. Chlorophyll a (Chl a) fluorescence is an analytical non-intrusive tool for investigation of stress damage on in vivo photosynthesis (Schreiber et al. 1994). The use of Chl a fluorescence to detect tolerance to abiotic stress in plants has given varying results. Changes in Chl a fluorescence were measured in salt-stressed durum wheat (El Mekkaoui et al. 1989)

and water-stressed potato (Basu et al. 1998), but no change was detected when roses were only salt-stressed (Jimenez et al. 1997).

Materials and Methods Plant material and growth conditions The hexaploid triticale T300 (2n = 42, genomes AABBRR) is an amphiploid issued from hybridization between Triticum dicoccum farrum (2n = 28, genomes AABB) and Secale cereale cv. Petkus (2n = 14, genomes RR). Seeds were germinated in Petri dishes in the presence of distilled water before being transferred to hydroponic culture in a home-made phytotron. Seedlings were grown either on a nutrient solution containing 0.2 mmol/L NaCl (Coic and Lesaint 1973) or on this medium supplemented with NaCl to a total NaCl concentration of 85.7 or 110 mmol/L. The osmotic potential of these media was respectively – 0.07, – 0.46 and – 0.55 MPa. Plants were illuminated with 400 W Phytoclaude lamps, providing 280 µmol m – 2 s –1 photosynthetic photon flux (Quantum meter Li-Cor, Lincoln, NE, USA) at the collar level. The photoperiod was 16 h, and air temperature and the vapour pressure deficit were 22 ˚C and 17.68 hPa during the light period and 18 ˚C and 10.30 hPa during the dark period. Analyses were performed on 18day-old plants.

Plant growth Leaves and roots of six plants of each species were weighed quickly and separately before being dried in an oven at 110 ˚C for 2 days. Leaf areas were calculated using a scanner and a home-made area programme.

Water relations Relative water content (RWC) was calculated on the basis of known fresh and dry weights and the water-saturated weight (SW) of shoots: RWC = (FW – DW) 100/(SW – DW). Osmotic potential (π) was measured on expressed sap of frozen/thawed leaves and roots using a microosmometer (Roebling, Berlin, Germany).

Ionic analysis Na + and K + were assayed by flame photometry (Eppendorf Gerätebau, Hamburg, Germany), and Cl – by potentiometric titration with AgNO3 (Metrohm, Heriseau, Switzerland) in aqueous extracts of aerial parts and roots, according to Férard and Coudret (1982).

Organic solute analysis Total soluble sugars, extracted from fresh matter with boiling water (Bourgeais-Chaillou and Guerrier 1992) were estimated by the anthrone reagent method using glucose as standard (Yemm and Willis 1954). The concentration of soluble sugars was thus expressed as mmol/L of glucose equivalent. Free proline was quantified using ninhydrin reagent (Bates et al. 1973).

A triticale and its parents under salt stress

Calculation of osmotic contribution The estimated osmotic contribution of mineral and organic solutes to leaf and root π was obtained by the van’t Hoff equation, using total tissue water and ionic and sugar content.

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rye growth was more affected (only 23 % of control values) than that of Triticum df and T300 (Table 1). With increasing salinization, leaf area decrease was 56 and 65 % for Triticum df, 36 and 69 % for rye, and 32 and 32.4 % for T300 (Table 1). Salt stress had no effect on stomatal density (Table 1).

Leaf gas exchanges and WUE calculation The experimental setting (Lascève and Couchat 1980) allowed continuous measurement of the transpiration rate with a dewpoint hygrometer (General Eastern, Woburn, MA, USA), and CO2 exchanges with an infrared gas analyser (Li-Cor, Lincoln, NE, USA) in an open system. WUE was the ratio of net photosynthesis to transpiration.

Chlorophyll fluorescence After a 30-min dark period in ambient conditions in the laboratory, chlorophyll a fluorescence was measured using a pulse-amplitudemodulated fluorometer (Teaching-PAM, Walz, Effeltrich, Germany), according to Schreiber et al. (1994). Measurements of minimal (F0) and maximal (Fm) fluorescence yields allowed determination of the optimal quantum yield (Fv/Fm), the ratio (Fm – F0)/Fm being used to calculate the maximal potential efficiency of PS II of dark adapted leaves. Leaves were then irradiated by actinic radiation (110 µmol m – 2 s –1), and saturation pulses of 3,500 µmol m – 2 s –1 were also triggered repeatedly (every 20 s) during approximately 6 min. For assessment of light use efficiency, leaves harvested on illuminated plants were gradually exposed to higher irradiance (2 min at each intensity: 50 to 1,850 µmol m – 2 s –1). The operational PS II quantum yield (Y) and relative electron transport rate (RETR) were calculated using, respectively, the following formulas according to Genty et al. (1989): Y = (F′m – Ft)/F′m and RETR = Y. PAR

Results Cereal growth The dry weight of roots and shoots decreased upon exposure to NaCl 85.7 and 110 mmol/L. Under 110 mmol/L NaCl stress,

Water relations The leaf RWC of the three species decreased as a result of salt stress (Table 1). The three cereals showed a similar reduction of RWC (4.48 to 4.65 %) in the presence of 85.7mmol/ L NaCl. However, in the presence of 110 mmol/L NaCl, T300 was less dehydrated ( – 8.9 %) than rye ( – 9.3 %) and Triticum df (–10.9 %). Salinity reduced the leaf and root π of the three cereals (Table 2). Regardless of culture medium and species, leaf π was lower than root π.

Ionic relations and osmotic adjustment Figure 1 shows the concentrations of Na + , Cl – and K + in leaves and roots. In control plants, K + concentration was higher than Na + and Cl – concentrations. The salinization of root medium increased Na + concentration considerably in leaves and roots of Triticum df and rye, but to a lesser extent in leaves of T300. In salt-stressed plants, K + concentration decreased in relation to salinity and was higher in leaves than roots of rye and triticale. Chloride accumulation was higher in leaves of rye than of Triticum df and T300. Chloride and K + were transported to leaves in salt-stressed cereals, whereas Na + was distributed more uniformly in stressed plants. Consequently, on a molecular basis, K + /Na + discrimination (Table 2) in leaves, as in roots, of control plants was considerably higher than in salt-stressed ones. This K + /Na + discrimination decreased in leaves and roots in relation to salinity. In the presence of salt, T300 leaves had a higher K + /Na + discrimination than those of rye and Triticum df.

Table 1. Shoot and root dry matter (DM, mg/plant), abaxial and adaxial stomatal density (mm – 2), leaf area (cm2/plant) and relative water content (RWC, %) of Triticum dicoccum farrum (Triticum df), rye and T300 grown with 0.2 (control), 85.7 or 110 mmol/L NaCl. Values represent the mean of 6 experiments with SE. Parameter

Triticum df control

Shoot DM Root DM Abaxial stomatal density Adaxial stomatal density Leaf area RWC

85.7 mmol/L

Rye 110 mmol/L control

T300

85.7 mmol/L 110 mmol/L control

85.7 mmol/L 110 mmol/L

148.0 ± 28.0 76.80 ± 13.10 51.66 ± 6.94 129.80 ± 9.60 55.70 ± 7.90 30.75 ± 1.25 166.40 ± 2.00 78.00 ± 7.00 60.66 ± 11.09 64.30 ± 10.30 41.00 ± 9.00 18.00 ± 2.45 32.80 ± 4.00 18.60 ± 3.00 7.50 ± 3.87 51.80 ± 13.20 35.00 ± 6.00 27.66 ± 6.53 43 ± 8

43 ± 5

75 ± 10 73 ± 19 51.03 ± 10.27 22.37 ± 3.67 98.36 ± 1.70 93.79 ± 4.69

46 ± 4

46 ± 3

76 ± 10 58 ± 5 17.93 ± 2.70 21.73 ± 4.94 87.57 ± 1.56 93.08 ± 1.33

45 ± 5

48 ± 7

30 ± 6

59 ± 18 56 ± 6 53 ± 5 13.79 ± 2.44 6.70 ± 1.55 35.35 ± 5.37 88.75 ± 3.58 84.42 ± 6.63 91.48 ± 1.36

40 ± 6

39 ± 7

50 ± 6 56 ± 4 24.01 ± 4.79 23.92 ± 4.05 87.38 ± 2.62 83.34 ± 1.48

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Annick Morant-Manceau, Elisabeth Pradier, Gérard Tremblin

Table 2. Osmotic potential (π) (- MPa), ionic (Na + , K + and Cl – ) and total soluble sugars contribution (%) to osmotic potential, and K + /Na + discrimination (mol mol –1) in leaves and in roots of Triticum dicoccum farrum (Triticum df), rye and T300 grown with 0.2 (control), 85.7 or 110 mmol/L NaCl. Values represent the mean of 6 experiments with SE. Parameter

Triticum df control

85.7 mmol/L

Rye 110 mmol/L

control

85.7 mmol/L

T300 110 mmol/L

control

85.7 mmol/L

110 mmol/L

Leaf π 1.120 ± 0.005 1.703 ± 0.202 1.508 ± 0.062 1.313 ± 0.118 1.722 ± 0.188 1.534 ± 0.132 1.167 ± 0.059 1.668 ± 0.014 1.569 ± 0.147 Ions contribution 36.96 47.38 59.54 42.27 89.14 90.35 26.36 54.88 57.56 Soluble sugars contribution 1.35 3.54 3.93 2.65 2.92 3.62 1.98 2.34 2.61 Root π 0.554 ± 0.050 0.873 ± 0.062 0.950 ± 0.053 0.613 ± 0.015 0.963 ± 0.022 0.799 ± 0.111 0.686 ± 0.007 0.879 ± 0.056 0.914 ± 0.016 Ions contribution 42.96 47.86 54.80 46.33 55.69 72.46 42.80 54.41 47.46 Soluble sugars contribution 2.54 4.15 2.70 6.21 5.87 7.96 1.78 5.18 2.12 K + /Na + in leaves 31.77 K + /Na + in roots 18.66

0.41 0.54

0.39 0.62

48.70 18.72

1.07 0.33

0.24 0.08

22.80 12.50

2.81 0.75

2.01 0.22

Figure 1. Na + , Cl – and K + content in leaves and roots of Triticum dicoccum farrum (Tdf), Secale cereale cv. Petkus (rye) and triticale T300 grown on nutrient medium with 0.2, 85.7, or 110 mmol/L NaCl. Values are the mean of 6 replications; vertical bars indicate standard errors.

A triticale and its parents under salt stress

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Figure 2. Total soluble sugar content in leaves and roots of Triticum dicoccum farrum (Tdf), Secale cereale cv. Petkus (rye) and triticale T300 grown on nutrient medium with 0.2, 85.7, or 110 mmol/L NaCl. Other indications are the same as for Fig. 1.

Figure 3. Proline content in leaves and roots of Triticum dicoccum farrum (Tdf), Secale cereale cv. Petkus (rye) and triticale T300 grown on nutrient medium with 0.2, 85.7, or 110 mmol/L NaCl. Other indications are the same as for Fig. 1.

Ion absorption contributed significantly to osmotic adjustment (Table 2) in salt-stressed plants. In the three cereals, osmotic adjustment was higher in leaves than roots and reached 90 % in rye leaves in the presence of 110 mmol/L NaCl.

ticular transpiration rates, measured during the dark period, increased and decreased respectively in relation to salt stress. Under saline conditions, the WUE of the three species (Fig. 5) was similar, but increased compared to control plants. The WUE of Triticum df was higher than that of T300 and rye in the presence of 110 mmol/L NaCl.

Organic solutes and osmotic adjustment Total soluble sugar (TSS) concentration increased in saltstressed plants, but was higher in the presence of 85.7 than of 110 mmol/L NaCl (Fig. 2). Under salt stress, TSS concentration in the leaves of Triticum df was higher than in rye and T300. Conversely, in the three media, TSS accumulated more in rye roots than in the roots of the other two cereals. TSS contribution to osmotic adjustment (Table 2) was higher in saltstressed plants. Free proline content (Fig. 3) was higher in leaves than roots and increased in relation to salinity. Proline contribution to osmotic adjustment (not shown) was very low (0.42 % for T300 leaves under 110 mmol/L NaCl), considering its low concentration in plant tissues.

Leaf gas exchanges and WUE Salinization of the root medium decreased the net photosynthesis and transpiration rates of the three species as compared to control plants. The transpiration rates of the three cereals decreased progressively during the photoperiod (Fig. 4) under salt stress. In the presence of 110 mmol/L NaCl, the photosynthesis and transpiration rates of T300 were less affected than those of its parental species. Respiration and cu-

Chlorophyll fluorescence Maximal quantum yield of PS II (Fv/Fm) showed no significant difference for control plants and salt-treated Triticum df and T300 (values close to 0.76). This ratio decreased slightly when rye was in the presence of 110 mmol/L NaCl (0.743) as compared to control rye (0.768). RETR in relation to irradiance and salinity (Fig. 6) showed no clear differences between saltstressed and control plants. High irradiance (above 750 µmol m – 2 s –1) induced photoinhibition of electron transport in PS II in both control and salt-stressed leaves.

Discussion This study showed that the growth of rye under saline conditions was more limited by a water deficit (osmotic stress) and salt toxicity than that of Triticum df and the triticale T300. Dry matter production and leaf area were more affected in the presence of 110 than 85.7 mmol/L NaCl. These results are consistent with changes in photosynthesis and transpiration rates under salt treatment. The WUE of the three cereals increased with salinity, as in the case of spinach (Downton et al. 1985). High Na + and Cl – concentrations in leaves disadvan-

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Annick Morant-Manceau, Elisabeth Pradier, Gérard Tremblin

Figure 4. Net H2O and CO2 exchanges for shoots of Triticum dicoccum farrum (Tdf), Secale cereale cv. Petkus (rye) and triticale T300 grown on nutrient medium with 0.2 (A, B, C), 85.7 (D, E, F), or 110 mmol/L NaCl (G, H, I). Positive values for CO2 exchange indicate uptake, while positive values for H2O exchange indicate loss. Light was switched on at 9 a.m. and switched off at 1a.m.

Figure 5. Water-use efficiency (WUE) of Triticum dicoccum farrum (Tdf), Secale cereale cv. Petkus (rye) and triticale T300 grown on nutrient medium with 0.2 (A), 85.7 (B), or 110 mmol/L NaCl (C).

taged K + and probably disturbed stomatal movements. In previous results, Morant-Avice et al. (1994) showed that the stomatal aperture of these three cereals decreases under water stress. In salt-stressed plants, a decrease of guard cell turgor could be induced by hydric stress (reduced RWC), decreased K + content, and probably increased abscissic acid synthesis (Lehmann et al. 1995). In our study, cuticular transpiration, as measured during the dark period, was lower in salt-stressed than control plants. It has been reported that NaCl, which increases cell wall thickness (Cutler et al. 1977, Harvey et al. 1985), reduced cell wall elasticity in salt-treated Acacia nilotica (Nabil and Coudret 1995). However, Willmer and Mansfield (1969) found that Na + ions had a greater effect than K + on stomatal opening in detached leaves of Commelina communis. On the other hand, Ridolfi et al. (1994) deter-

mined that sugars contribute to the increase of osmotic pressure in stomata when K + content is low, thus allowing stomatal aperture. Bethke and Drew (1992) have shown that partial stomatal closure occurs with salinisation, but that reductions in photosynthesis are primarily non-stomatal in origin. Analysis of chlorophyll fluorescence parameters allows insights into the state of PS II. In fact, this study confirms that PS II physiological functions were preserved up to a high level of stress. Downton et al. (1985) also showed that photosynthetic capacity in salt-stressed spinach leaves (200 mmol/L NaCl) is maintained at the chloroplast level, but that stomatal conductance and chlorophyll content decrease. Likewise, Jimenez et al. (1997) found no changes in fluorescence parameters in saltstressed roses. However, when the roses were subjected to

A triticale and its parents under salt stress

Figure 6. Values for the relative electron transport rate (RETR) with increasing irradiance of detached leaves of Triticum dicoccum farrum (Tdf), Secale cereale cv. Petkus (rye) and triticale T300 grown on nutrient medium with 0.2, 85.7, or 110 mmol/L NaCl.

both salt, and irradiation stress, chlorophyll fluorescence was affected. On the other hand, the decrease of fluorescence at high irradiance in water-stressed potato was restored after rewatering (Basu et al. 1998). A reduction of the photosynthesis rate of the three cereals in our study also seemed to be due to increased maintenance energy, because the respiration rate (measured during the dark period) increased under salt treatment. The stomatal density of the three cereals did not differ as a function of salinity, whereas that of Plantago lanceolata and P. maritima, increased in the presence of NaCl (Coudret and Louguet 1980). Analysis of plant extracts determined the factors involved in the salt tolerance of Triticum df and T300 and the salt sensitivity of the rye. In salt-stressed Triticum df, the concentrations of Na + , Cl – , total soluble sugars and proline increased in roots and shoots as compared to reference plants, but remained almost at the

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same levels in the presence of 85.7 mmol/L or 110 mmol/L NaCl. Thus, membrane ionic selectivity appeared to be the same for both salt-stressed Triticum df. Proline and glycinebetaine, which are usually synthesised in stressed plants, can stabilise the cell membrane under salt stress. Proline can also act as an osmoprotector of cytosolic enzymes and cellular structures (Mansour 1998). In wheat, polyamines are also considered to play a protective role in response to osmotic or saline stress (Erdei et al. 1990). Nevertheless, Renard and Guerrier (1997) questioned themselves on the cytocompatibility of proline in the salt-stressed calli of tomatoes. In Triticum df, K + , Na + and Cl – accounted for almost half of the osmotic adjustment, and the contribution of soluble sugars was less than 4 %. Proline content was too low to have a significant osmotic role. Similarly, proline did not play an appreciable role in osmotic adjustment under water stress in the pea (Sanchez et al. 1998), or under salt stress in hexaploid triticales (Morant-Avice et al. 1998). The triticale T300, with wheat cytoplasm, and Triticum df behaved similarly under salt treatment. However, the K + /Na + ratio in the leaves of salt-stressed T300 was 5 to 8 times higher than for the other two cereals. This higher K + selectivity might allow better regulation of stomatal movement and metabolism. Moreover, in the presence of 110 mmol/L NaCl, T300 was less dehydrated than rye and Triticum df. Rascio et al. (2001) obtained similar results with a wheat mutant, whose leaf water content increased linearly in relation to leaf K + concentration. The three ions (Na + , K + and Cl – ) have made a higher contribution (about 70 %) to osmotic adjustment in other hexaploid triticales under salt stress (Morant-Avice et al. 1998) than in T300 (about 50 %). The contribution of soluble sugars did not exceed 8 %, as previously obtained with hexaploid triticales (Morant-Avice et al. 1998). In terms of WUE, the rye Petkus performed less well than Triticum df and T300 under control conditions and salt treatments. Contrary to Triticum df and T300, Na + , K + and Cl – transport to the rye shoot increased as a function of salt concentration. Gorham (1990) reported that rye and hexaploid triticales display the same cation transport characteristics in saline conditions, i.e. K + /Na + discrimination is much better than for tetraploid wheat. This was confirmed under low salinity in this study, but only the triticale maintained a high K + /Na + ratio in the presence of 110 mmol/L NaCl. The incapacity of the rye Petkus to absorb enough K + when NaCl concentration is high might be due to low proline concentration, which could be the main reason for its salt sensitivity. K + , but not Na + , is an essential co-factor for many enzymes (Hasegawa et al. 2000). The contribution of all three ions to osmotic potential reached 89 – 90 % in the leaves of the salt-treated rye. Soluble sugars made a higher contribution to osmotic adjustment in the roots of rye than in those of the other two cereals, but did not seem to play a role in membrane protection. Generally speaking, the metabolism of the rye Petkus was less active than that of the other two cereals. Under saline conditions, Triticum df and T300 resisted better than rye,

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Annick Morant-Manceau, Elisabeth Pradier, Gérard Tremblin

which had low K + /Na + discrimination in the presence of NaCl. Increased proline concentration in Triticum df and T300 could have maintained membrane K + selectivity, but soluble sugars did not appear to play this role in roots of the rye Petkus. This study confirms that the K + /Na + ratio can be considered as a salt tolerance index in cereals. Studies of chlorophyll fluorescence showed that thylakoid physiological functions were preserved against NaCl damage in salt-stress conditions. Acknowledgements. The authors are grateful to E. Clergeau and M. Chartrain for technical assistance, and to the INRA (Guyancourt, France) and GIP-GEVES (Surgères, France) for providing seeds.

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