Osmotic Adaptation in Panicum repens. Differences Between Organ, Cellular and Subcellular Levels

Physiol. Plant. 45:325-331. 1979 OSMOTIC ADAPTATION AT DIFFERENT LEVELS IN PANICUM 325

Osmotic Adaptation in Panicum repens.Differences Between Organ, Cellular and Subcellular Levels

B y - • ' • , ' ; .

A. RAMATI," NILI LIPHSCHITZ and Y. WAISEL

Department of Botany, Tel Aviv University, Tel Aviv, Israel

• , (Received 12 June, 1978; revised 30 September, 1978) " '

Abstract

Tbe process of osmotic adaptation was studied in leaves of•:• Panicum repens. Two phases were observed: the first phase, which';' continued for 2-4 days, was mainly characterized by dehydration

of leaves, a fast synthesis of organic acids and penetration ofsodium into leaf cells. Chloride becomes dominant in the leaves onlyfrom the third day of exposure and onwards. The second phase ofadaptation lasted for 4-6 days. During this phase, a decrease inorganic acid content and an increase in leaf-chloride content wasobserved. In spite of the fact that the osmotic potential of the leavesreached lower values than that of the external medium already after2 days, the rate of growth of the plants was hampered. Suchinhibition of growth disappeared 6-8 days after exposure to salinity.

,;, Ion content of the cell walls, chloroplasts and vacuoles of• Panicum leaf cells was investigated during the various stages ofosmotic adaptation. An increase in sodium and chloride content ofthe cell walls during the early period of adaptation probablyprevented the full osmotic adaptation ol" the protoplasts. It issuggested that a locally unbalanced distribution of ions may be oneof the reasons for the decrease in growth rate during the process ofosmotic adaptation and frequently after that.

Introduction

Some plants grow naturally in salty media and arecontinuously exposed to highly saline salt solutions. Suchplants, the halophytcs, must be osmotically adapted to theirsaline environment, and maintain high concentrations ofosmotically active substances, so that the osmotic potential(OP) differences between the tissues of halophytes and theirenvironment remains constant (cf. Gale and PoljakofF-Mayber 1970, Waisel 1972, etc.). Osmotic adjustment ispartially accomplished by accumulation of inorganic ionsand partially by accumulation of organic ions (Bernstein1961, Osmond 1963).

,' ' Present address: The Israeli Atomic Energy Commission, Tel-Aviv.

When the OP of the medium is decreased due to eithersalinization or loss of water, the difference in OP between themedium and the plants is changed and the plants aresubjected to a period of water stress. A consequent decreasein the OP of the tissue sap of the plants can be observed. Theprocess of maintaining the osmotic difference between theplant and its environment is usually called osmotic adap-tation. Such process might be incomplete in some plants,whereas in others full adaptation may be attained in duetime. However, the growth rate of many plants which aresubjected to saline media is hampered in spite of theirosmotic adaptation. Growth inhibition is caused by waterstress, mostly when osmotic adjustment is incomplete(Scholander et al. 1962, Greenway and Thomas 1965, Oertli1966).

Some investigators ascribe this growth inhibition to thefact that the adaptation process is only partial (Scholander etal. 1962, Greenway and Thomas 1965, Oertli 1966). Others(cf. Bernstein 1961, 1963) suggested two other alternativeexplanations to this phenomenon. (1) A penetration into thecells of large quantities of sodium and chloride which maydisturb the normal metabolism. (2) Diversion of some energywhich is needed for the growth of the plant to the osmoticadaptation process.

The main purposes of the present investigation were,firstly, to follow the subsequent changes in the ionic balancewithin the leaf during the osmotic adaptation process and,secondly, to find out the reasons for temporary growthretardation both in the leaf as a whole and at the subcellularlevels. Panicum repens L. (Graminae, Panicoideae) waschosen for this investigation. P. repens is a scmihalophyticgrass capable of growing under saline conditions. Plants ofthis species possess trichome-like salt glands, and excretesome of the absorbed salts (Liphschitz and Waisel, unpub-lished data). Nevertheless, when Panicutn plants are transfer-red from non-saline to saline conditions, their growth isinhibited for several days. Later on, presumably after

A. RAMATI, NILI LIPHSCHITZ AND Y. WAISEL Physiol. Plant. 45. 1979

completion of fheir osmotic adaptation, the plants overcomesuch inhibition and normal growth rates are resumed.Panicum repens was, therefore, used for the investigation ofthe osmotic adaptation process.

; OP, osmotic potential.

Material and Methods

Panicutn repens L. plants were grown for 2 weeks undercontrolled conditions (temperature, 25°C ± 1°C; daylength, 8 h of light; 60% relative humidity; light intensity 4.1W • cm^^ VHO lamps). The plants were grown on full-strength Hoagland's nutrient solution (Hoagland and Arnon1950). After such a period, sodium chloride was added fo thegrowth medium so as to give concentrations of 50 mM, 100mM or 200 mM NaCl. Ion content of the leaves wasmeasured before salinization and after the plants had beensubjected to the treatment for 2, 3, 6, 8 and 10 days. Leavestaken for analysis were rinsed for 60 s in deionized wafer,dried (90°C for 24 h) and extracted in 5 ml boiling acidicsolution (6.4 ml of concentrated HNOj -f 10 ml glacialacetic acid in 1 liter water). Their ion content was deter-mined either spectrophotometrically or by electro-titration.

Growth rates were expressed as the rates of elongation ofthe youngest leaf. The OP of the youngest leaf of each plantwas determined by measuring the freezing point of its sap, aswell as by the plasmolyfic method. Sucrose was used an anosmoticum for the plasmolysis studies.

Malic acid content of the leaves was measured spectro-photometrically by measuring the reduction rates of NAD toNADH, using malate dehydrogenase and NAD (Hohorst1963).

Electron probe x-ray microanalysis (EPMA) was used forlocalization of Na, K, Ca, Mg and CI in different cells anddifferent cell compartments (cf. Ramati et al. 1976). Ioncontent was calculated on a volume basis of 1 //m^

17

5

U

11

9

-

-

- /

I-

. / - •

^ ~

1 1

•*

1

' ' 1

ILSD

10

Days

Figure I. Changes in OP values during osmotic adaptation ofPanicum repens leaves. Plants subjected to (1) Hoagland's solution;(2) 50 mM NaCl; (3) 100 mM NaCl; (4) 200 mM NaCl inHoagland's solution.

%Water

Figure 2. Changes in leaf water percentage during osmotic adap-tation in Panicum repens plants subjected to 100 mM NaCl inHoagland. Vertical lines: SE.

Results

Effect of salt concentrations on the OP of leaf sap. Leavesof Panicum repens plants became osmotically adapted afterthe transfer of the plants to a saline environment (Figure 1).A decrease in the OP of the medium was shortly afterwardsfollowed by a decrease in the OP of whole-leaf extracts. Thefirst rapid decrease of OP was slowed down after 24, 48 and72 h in plants given 50, 100 and 200 mM NaCl solutionrespectively.

The decrease in the OP of the leaves as compared withthat of the growth medium, i.e., percentage of osmoticadaptation, was calculated for the 3rd, 6th and 10th days ofexposure (Table 1). Plants reached complete adaptation inthe 50 mM and 100 mM NaCl treatment only after 10 days.No adaptation was reached in the 200 mM NaCl treatment.

0.6

0,4

0,2

. . " • • • •

3

- J^y ""^/.X ,

t^ 1 1 1 1

TLSD

110

Days

Figure 3, Changes in content of sodium during osmotic adaptationof Panicum repens leaves. Plants subjected to ( I ) Hoagland'ssolution; (2) 50 mM NaCl; (3) 100 mM NaCl ; (4) 200 m M NaClin Hoagland's solution, dw = dry weight.

PhysioL Plant. 45. 1979 OSMOTIC ADAPTATION AT DIFFERENT LEVELS IN PANICUM 327

Table 1. Osmotic adaptation of Panicum repens leaves grown on 50, 100 and 200 mM NaCl for 3, 6 and 10 days. AOP values aregiven in -bars. T.S. = treatment solution. Representative experiment, d = days.

T.S.mM NaCl T.S. 3 d

%ofOP3d

zfOP6d

%ofOP6d

zlOPlOd

%ofOPlOd

50100200

2.24.38.7

1.02:36.1

506070

1,23.65.7

608070

2.04.S6.9

9110580

IVater percentage of the leaves. During the first 4 days ofsubjection of the plants to saline conditions, a decrease inwater content of the leaves was observed. Later on, theplants overcame this effect and their water percentageequalled that of the control plants (Figure 2).

Iort accumulation. The sodium content of plants grown on50 mM and 100 mM NaCl increased during the first 6 daysof the salt treatment, after which a steady state was reached(Figure 3). A steady state in Na content was not attained inplants which were subjected to 200 mM NaCl even after 10days of exposure. As for potassium content, it decreased inall treatments after the fourth day (Figure 4). Chlorideuptake showed a different pattern. A lag period of 2 dayscould be distinguished in plants which were subjected to 50mM and 100 mM NaCl treatments, and the equilibrationperiod for chloride content lasted between 6 and 8 days.Under the 200 mM NaCl treatment no equilibration wasattained (Figure 5).

Calcium and magnesium content did not change markedlythroughout the experiment.

Malic acid contettt. The malate content was comparedbetween P. repens plants grown on a non-saline solution andthose grown on a 100 mM NaCl solution (Figure 6). Anincrease in malate content was observed during the first 2days. Later on, the content of malate dropped sharply.

OP of sotne leaf cells. OP values of epidermal, mesophylland bundle-sheath cells were measured by the plasmolyticmethod. A decrease in OP values was detected in all tissues

0.9 -

-o

0.7 -

0)

O.5 -

O.3

• ' . • " ,

1 1

^»

• •

N

• • • • . .

N ••

^ ^

1

- - • •

S

1

3

T

TL S D

1

10

DaysFigure 4. Changes in content of potassium during osmotic adap-tation of Panicum repens leaves. Plants subjected to (1) Hoagland'ssolution; (2) 50 mM NaCl; (3) 100 mM NaCl; (4) 200 mM NaClin Hoagland's solution.

0,8 -

0,6 -

0.4 -

O 0,2 -

/

7 x^"Lt^—f r

....-•••/

/ •

1

L S D

1n^ L-

10Days

Figure 5. Changes in content of chloride during osmotic adaptationof Panicum repens leaves. Plants subjected to (I) Hoagland'ssolution; (2) 50 mM NaCl; (3) 100 mM NaCl in Hoagland'ssolution.

Figure 6. Changes in content of malate during osmotic adaptationof Panicum repens leaves. Plants subjected to (1) 100 mM NaCland (2) to Hoagland's solution.

Tahle 2. OP values (-bars) of Panicum repens leaves and percent-age of osmotic adaptation as measured by the cryoscopic andplasmolytic methods.

TreatmentOP ofT.S.

OP of leaves(osmometer)

OP in leaves(plasmolysis)

HoaglandHoagland -i-

100 m/W NaClDifference

% of osmoticadaptation

-4 .3

-4 .3

-8.0-12.3 .

-4 .3

100

-16.9-20.8

-3 .9

90.7

328 A, RAMATI, NILI LIPHSCHITZ AND Y, WAISEL Physiol. Plant. 45. 1979

during the first 4 days of saline conditions. Later on, stabili-zation of the OP was attained. The OP values for theepidermis and mesophyll cells were lower than the OP valuesfor the bundle-sheath cells. The OP values measured byplasmolysis in individual cells were almost double the valuesobtained by cryoscopic measurements of whole-leaf sap(Table 2).

Ion cotnparttnetttation duritig osmolic adaptation process.The ion content in various cell compartments was measuredby electron probe x-ray microanalysis (Table 3). Plants

grown on Hoagland's nutrient solution contained undetect-ablc quantities of sodium and chloride. Potassium contentwas higher than that of calcium or magnesium. The highestcontent of potassium was found in the buUiform leaf cells.Vacuoles of mesophyll and epidermal cells contained lowerquantities of ions than those of the bundle-sheath orbulliform cells.

Traces of sodium and chloride were found in leaf cells onlyafter a 2-day period of salt treatment. The content of thesetwo ions increased gradually during the period of osmotic

Table 3. CI, Na, Mg, Ca, and K content in Ivac, vacuole; Hoag., Hoagland's solution.

in various cell types and organelles ' eq.). +SE. c.w,, cell wall; chl, chloroplast;

Treatment Cell type Organelle CI Na Mg Ca

Hoag. sheath

Hoag.

Hoag.

Hoag.

Hoag. + 100 mMNaCl (2 days)

Hoag. -1- 100 mMNaCl (4 days)


• • , • • • . - ' • ' , ' , •

- ' . . - • " • • - • • ; ; - • - -


: ' : ' ' • ' • • "

btilliform

epidermis

mesophyll

sheath

bulliform

epidermis

mesophyll

sheath

bulliform

epidermis

mesophyll

sheath

bulliform

epidermis

mesophyll

sheath

bulliform

epidermis

mesophyll

c.w.chl.vac.c.w.vac.c.w.vac.c.w.vac.


c.w.chl. •vac.c.w.vac.c.w.vac.c.w.vac.



0.25 -H 0.070.01 ± 0.010.07 + 0,010.45 + 0.300.15 + 0.130.30 + 0.07

0.37 + 0.12

0.67 ±0.150.01 +0.010.45 + 0.221.18 + 0.170.94 ± 0.60

• 0.85 + 0.450.63 + 0,250.78 ± 0.50.61 ±0.30

2.18 ±0.520.01 + 0.012.48 + 0.922.14 + 0.473.06 ± 1.161.81 ±0.801.34 ±0.602.01 ±0.211.10 ±0.31

1.83 + 0.970.02 + 0.012.48 + 1.393.88 + 0.805.62 + 2.011.63 + 0.791.17 + 0.911.43 +0.711.00 + 0.58

-' "

. ^ ' i " . . " , • , • . • . . - ' . • - . .

0,41 ± 0,050,01 ±0.010,07 + 0,070.28 ± 0.050.11 + 0.071.35 ±0.07

0.15 ± 0.08

0,92 ± 0.080.01 ± 0.010.37 + 0.300.83 + 0.050.56 + 0.080.79 ±0.110.33 +0.150.59 + 0.100.37 ±0.15

2.0 +0.420.03 ± 0.013.10 ± 1.642.28 + 0.613.40+ 1.231.93 + 0.971,24 ±0.891.99 + 0.831.35 ±0.71

2.18 ±0.450.03 + 0.023.14+ 1.372.76 ± 3.53.94 + 1.842.93 ± 1.481.56 ± 0.883.00 ± 1.151.60 ±0.79

4.08 + 1,760.01 +0.002.54 + 0.991.60 ± 1.031.81 ± 9.042.08 ± 1.361.42 ± 0.622.13 + 1.191.55 ± 1.18

2.44 ± 1,500.01 ±0.011.48 + 1.491.90 ± 0.851.79 + 1.551.35 + 0.600,92 ±0.811.46 ±0.581.41 ± 0.76

1.99 ± 0.720.01 ±0.011.32 + 0.931.40 + 0.801.56 + 0.931.20 ±0.480.76 + 0.651.39 ±0.731.16 ±0.87

3.08 + 1.760.01 ±0.011.81 + 1.212.28 + 0.722.53 ± 1.432.65 ± 0.850.86 + 0.682.15 + 0.830.94 ± 0.57

3.14 ±0.940.01 + 0.011.83 + 1.372.06 + 0.792.39 + 1.532.35 + 0.970.93 ± 0.652.65 + 0.890.92 + 0.72

0.67 + 0,150.01 ± 0.011.01 +0.460,68 ±0,161.49 ± 2.130.55 ± 0.230.36 ± 0.240.58 + 0,290.60 ± 0.24

0.69 ±0.170.0! ±0.061.30 + 0.160.67 ±0.151.41 + 0.780.60 + 0.190.43 ± 0.200.73 ± 0.340.49 ± 0.50

0.70 ±0.150.01 ± 0.000.91 ± 2.280.69 + 0.131.39 + 0.220.51 ±0.19O.U ±0.020.57 + 0.230.13 ±0.04

0.8 +0.140.01 ±0.010.88 ± 1.210.73 +0.160.71 ±0.510.72 + 0.360.21 ± 0.050.60 ± 0.320.25 ± 0.03

0.71 ±0.160.01 +0.090.55 ± 0.470.76 ±0.161.03 ±0.500.64 + 0.290.22 + 0.030.56 + 0.370.27 + 0.04

5.26 + 1.100.10 + 0.043.78 ± 1.406.51 +0.386,84 ± 1.355.11 ± 2.061.03 ±0.655.30+ 1.901.01 ±0.63

5.53 + 2.380.13 ±0.043.83 ± 1.336.96 ± 0.338.11 ± 1.355.37 + 2.061.98 ± 1.375.11 ±2.091.97 ± 1,25

4,21 + 1.350.09 + 0.033.59 ± 1.586.60 + 1.706.09 ± 2.534,55 ± 1,381.10 ±0.675.06 + 2.571.09 ± 0.69

1.23 +0.440.03 + 0.011,24 ±0,882,42 + 0.442.51 ±1.031.95 +0.711.27 + 0.851.15 +0.901.12 ±0.60

1.92 ±0.650.04 ± 0.021.26 ±0.072.37 + 0.652.41 ± 1.141.72 ±0,971.05 ±0.661.80 + 1,001.28 + 0.62

Pbysiol. Plant. 45. 1979 OSMOTIC ADAPTATION AT DIFFERENT LEVELS IN PANICUM 329

Table 4. Ratios of ion content in cell walllchloroplast and cell wall/vacuole in various celt types during osmotic adaptation in Panicumrepens leaves. Hoag., Hoagland's solution.

Treatment

Hoag., Odays

-)- 100 mM NaCl,2 days

-t- 100 mM NaCl,4 days

-1- IOO mM NaCl,6 days

-I- 100 mM NaCl,8 days

Cell type

sheathsheathbulliform





Ratio ofcontent

c.w./chl.c.w./vac.c.w./vac.





K

52.61,51.0

42.51.40.8

47.51.21.0

41.01.01.0

48,01.51.0

Ca

67.00.70.6

69.00.50.5

70.00.80,5

86.0I.O1.0

71.01.20.7

Mg

408.01.60.9

244.01.61.0

199.01.50.9

308.01.70.9

314.01.70.9

Na

41.05.82.5

92.02.51.5

68.60.70.7

72.60.70.7

CI

25.03.63.0

67.01.51.2

218.00.80.7

91.50.70.7

adaptation of the plants. Saturation levels were reached after6 days. Concomitantly, potassium content decreased fromthe fourth day onward in all cell types and in all investigatedorganelles. There were no significant changes in the contentof calcium and magnesium during the experiments.

The ratio between ion content in the cell walls and in thechloroplasts, and between the cell walls and the vacuoles wascalculated in two cell types during osmotic adaptation (Table4). The ratios of calcium and magnesium distribution did notindicate any clear trend or changes. Sodium and chloridedistribution between the cell walls and the vacuoles de-creased gradually from the second day, through the sixth dayof exposure, till a steady state was achieved. Such a cleartrend could not be distinguished for the ratio cell wall/chloro-plasts.

Figure 7. Daily elongation of the first leaf of Panicum repens plantsduring osmotic adaptation. Plants subjected to (1) Hoagland'ssolution and (2) 100 mM NaCl in Hoagland.

Leaf elongation. Addition of salts to the growth mediumof Panicum repens plants reduced the elongation rates of theyoung leaves. Such retarded growth was most prominentwithin the first 24 h of exposure to the salty medium (Figure7). Plants overcame such inhibition after 5 days and the ratesof elongation in salt-treated plants reached those of thecontrols.

Discussion

Osmotic adaptation is obtained by gradual changes in theOP of the plant. In the reported investigation OP was firstachieved by accumulation of sodium, which started from thefirst day of the treatment. Chloride accumulation wasdelayed and started only 48 h later. Since the ionic balancemust always be maintained, sodium was probably balancedby organic ions during this lag period, a fact whichcontributed to the decrease in the OP (cf. lljin 1944,McDougal et al, 1960, Bernstein 1961, Osmond 1963,Strogonov 1964, Poljakoff-Mayber and Meiri 1969). Indeed,the content of malic acid was found to increase during thefirst 2 days of the experiments. The rapid increase in malicacid content was probably due to the enhanced activation ofPEP-carboxylase by the penetrating ions (cf. Shomer-Uanand Waisel 1973). Malate synthesis also demands thepresence of malic enzyme; the activation of which is likewiseenhanced by low levels of NaCl and is inhibited by high saltconcentrations (cf. von Willert 1974). Low levels of sodiumneeded for such activation were present in the leaves at thefirst 2 days of the experiments. The continued absorption ofsodium and of chloride may later on have inhibited theactivity of PEP-carboxylase and malate dehydrogenase. At

A, RAMATl, NILI LIPHSCHITZ AND Y. WAISEL Physiol. Plant. 45, 1979

this stage, the metabolic balance was probably turned towardsynthesis of amino acids (cf, Karmarkar and Joshi 1969).Chloride at this stage was rapidly accumulated in the leaves,taking the place of the malate as the main anion.

The loss of water which was observed during the firstdays, beside adding to the decrease of the OP, probablydisturbed the normal activities of the plant cells. Already 24h after exposure to saline treatment, growth rates reachedvalues as low as 50% of the rates of growth of the controlplants. Such inhibition was overcome only at the end of theosmotic adaptation, i.e. 6-8 days after the exposure tosalinity.

Growth inhibition due to osmotic stress was attributedfirstly to the poisonous effects of sodium and chloride, whichpenetrated into the subcellular organelles. Such penetrationinto organelles and changes in ionic balance might disturbthe normal metabolism of those cells, and this might befollowed by growth inhibition of the plants (Bernstein 1961,Heber and Santarius 1965, Isawa and Good 1966, Giles etal. 1974, e/c).

Another hypothesis indicates that growth inhibition mightbe caused by loss of the energy which is exploited during theosmotic adaptation process. Investigations made byLagerwerff (1969) with sugar beet show that part of theavailable energy is consumed by the plant for salt uptakeinstead of for producing sugar. Still another explanation ofgrowth inhibition by salinity was suggested by Oertli (1966).His hypothesis was that under saline conditions salts wereaccumulated outside the protoplasts, thus leaving themunadapted. Such inhibition by an uneven distribution of ionswas not limited to NaCI. In similar cases it was shown thatdamages which were originally attributed to the chemicaleffects of boron, were essentially osmotic effects. Growthinhibition under high boron treatments were caused by theaccumulation of boron in the cell walls rather than by itspenetration into the protoplast (Oertli 1963),

Data presented in the present paper, regarding locali-zation of ions in various cell compartments, strengthen thislast explanation for growth inhibition. Growth occurs only inturgid cells. Therefore, it is affected by the general state ofcell hydration as well as by the state of adaptation of eachcompartment. Cells may remain physiologically unadapted ifthe distribution of ions in their various compartments is notbalanced. An excess accumulation of ions in the cell wallfraction, such as observed during the first 4 days of exposureto salinity, will certainly lower the water potential in the cellwall region as compared to that of the protoplasts. Thus, aloss of water out of the protoplasts may occur, followed by a-drop in turgor and changes in the viscosity of the cytoplasm.This might happen in spite of a total increase in mineralcontent of the whole leaf. Such disturbance of the osmoticbalance between the apoplast (cell wall) and the symplast(cytoplasm, organelles, ete.) certainly would result in growthdisturbances and may explain the observed inhibition ofgrowth.

Appendix

Calibration of the EPMA (Electron Probe Miero-Analyzer)readitigsfor cell walls, chloroplasts and vacuoles

Calibration of the EPMA readings for various cellcompartments was achieved by correlating the x-ray yieldswith the concentrations of the investigated ions (sodium,potassium, calcium, magnesium and chloride) in the variouscell compartments investigated.

Tracheid xylem cells of Cupressus sempervirens L., ofwhich the lignin was extracted, were used for all wallcalibration. Isolated chloroplasts of Potatnogeton lueens L.were used for chloroplast calibration. Calibration of thevacuole was based on the assumption that the vacuole isnearly a true solution, Vacuoles were thus calibrated usingKCl, NaCl, MgClj and CaCl^ solutions.

The standards were prepared with different quantities ofthe various ions. The samples were then divided into two:ions were extracted from one-half of the sample and theextract was analysed spectrometrically. The concentrationper unit volume was calculated. The second half was placedon an aluminium plate, coated and analysed by x-ray micro-analysis.

The correlation between the counts obtained by theEPMA and ion content per unit volume was calculated andexpressed by regression equations for each of the ions ineach of the three cell compartments.

References

Bernstein, L. 1961. Osmotic adjustment of plants to saline media. I,Steady state. — Am. J. Bot. 48: 909-917.

— 1963. Idetn. 11. Dynamic phase. — Ibid. 50:360-370.Gale, J. & Poljakoff-Mayber, A. 1970. Interactions between grown

and photosynthesis of salt bush (Atriplex halimus L.) grown insaline media. — Aust. J. Biol. Sci. 23: 937-945.

Giles, K. L., Beardsell, N. F. & Cohen, D. 1974. Cellular and ultra-structural changes in mesophyli and bundle sheath cell of maizein response to water stress. — Plant Physiol. 54: 208-212.

Grecnway, H. & Thomas, D. A. 1965. Plant response to saline sub-strates. V. Chloride regulation in the individual organs ofHordeum vulgare during treatment with sodium chloride. —Aust. J. Biol. Sci. 18:505-524.

Heber, U. W. & Santarius, K. A. 1965. Compartmentation andreduction of pyridine nucleotides in relation to photosynthesis.— Biochiin. Biophys. Acta 109; 390-408.

Henkel, P. A. & Strogonov, B. P. 1961. Physiology of plantsconsuming saline water. — Uncsco Arid Zone Conf. SalinityProblems in the Arid Zones 14: 145-151.

Hoagland, D. R. & Arnon, D. I. 1950. The water-culture methodfor growing plants without soil. — Circ. Calif. Agric. Exp. Stn.347: 1.

Hohorst, J. H. 1963. Methods of Enzymatic Analysis. — pp.328-332. Academic Press, N.Y.

lljin, W. S. 1944. Salze und organische Sauren bei Kalkpflanzen. —Flora 37: 265-299.

Isawa, S. &. Good, N. E. 1966. Effects of salts and electrontransport on the conformation of isolated chloroplasts. — PlantPhysiol. 41: 535-543, 544-552.

Physiol. Plant. 45. 1979 OSMOTIC ADAPTATION AT DIFFERENT LEVELS IN PANICUM 331

Karmarkar, S. M. & Joshi, G. V. 1969. Effect of sand culture andsodium chloride on growth, physical structure and organic acidmetabolism in Bryophyllum pinnatum. — Plant Soil 30: 41—48.

Lagerwerff, J. V. 1969. Osmotic growth inhibition and electro-metric salt tolerance evaluation of plants. — Ibid. 3 1: 77-96.

MacDougal, I. R,, Dekoch, P. C. & Knight, A. H. 1960. Variationsin the mineral content of storage tissue disks maintained in tapwater. — Physiol. Plant. 13: 77-89.

Oertli, J. J. 1963. The influence of certain environmental conditionson water and nutrient distribution in barley seedling with specialreference to boron. — Adv. Frontiers Plant Sci. 6: 55—86.

— 1966. ElTect of external salt concentration on water relation inplants. HI. Concentration dependence of the osmotic differentialbetween xylem and external medium. — Soil Sci. 104: 56-62.

Osmond, B. 1963. Oxalates and ionic equilibrium in Australian saltbushes (Atriplex). — Nature 198: 503-504.

Poljakoff-Mayber, A. & Meiri, A. 1969. The responses of plants tochanging salinity. — Final Tech. Rep. U.S. Dep. Agric. Proj.AlO-SWC-7,

Ramati, A., Liphschitz, N. & Waisel, Y. 1976. Ion localization andsalt secretion in Sporobolus arenarius (Gou.) Duv.-Jouv. —New Phytol. 76: 289-294.

Richards, L. A. (ed.) 1954. Diagnosis and Improvement of Salineand Alkali Soils. — U.S. Dep. Agric. Handb. No. 60.

Scholander, P. F., Hammel, H. T., Hcmmingsen, E. & Garey, W.1962. Salt balance in mangroves. — Plant Physiol. 37: 722-729,

Shomer-llan, A. & Waisel, Y. 1973. The elTect of sodium chlorideon the balance between the Cj and C^ carbon fixation path-ways. — Physiol. Plant. 29: 190-193.

Strogonov, B. P. 1964. Physiological basis of salt tolerance ofplants (as affected by various types of salinity). — Akad. NaukS.S.S.R. Translated from Russian. Israel Progr. Sci. Transl.Jerusalem.

von Willert, D. J. 1974. Dor Einfluss von NaCl auf die Atmung undAktivitat der Malatdehydrogcnase bei cinigcn Halophyten undGlykophyten. — Oekologia 14: 127-137.

Waisel, Y. 1972. Biology of Halophytes. — Academic Press,New York,

Edited by A.K.

Documents

Osmotic Adaptation in Panicum repens. Differences Between Organ, Cellular and Subcellular Levels