INFLUENCE OF THE TRANSPORT OF WATER IN PLANT CUTICLES ON THE PA SIGNAL

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INFLUENCE OF THE TRANSPORT OF WATER IN PLANT CUTICLES ON THE PA SIGNAL

B. Büchner, P. Korpiun, E. Lüscher, J. Schönherr

To cite this version:

B. Büchner, P. Korpiun, E. Lüscher, J. Schönherr. INFLUENCE OF THE TRANSPORT OF WATER

IN PLANT CUTICLES ON THE PA SIGNAL. Journal de Physique Colloques, 1983, 44 (C6), pp.C6-

125-C6-129. �10.1051/jphyscol:1983619�. �jpa-00223178�

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Colloque C6, suppl6ment au nD1O, Tome 44, octobre 1983 page C6- 125

INFLUENCE OF THE TRANSPORT OF WATER I N PLANT CUTICLES ON THE PA SIGNAL

B . ~ G c h n e r , P . Korpiun, E . ~ G s c h e r and J. ~chEnherr*

Technische UniversitEt Mnchen, Physik-Department, 0-8046 Garching, F.R.G.

*Technische U n i v e r s i t a t mnchen, LehrstuhZ ^fgir Botanik, 0-8000 Mllnchen, F.R. G.

ResumP - Le s i g n a l p h o t o a c o u s t i q u e des e c h a n t i l l o n s humides augmente ex- p o n e n t i e l l e m e n t avec l a temperature. En u t i l i s a n t c e phenomene on p e u t G t u d i e r l e t r a n s p o r t de 1 'eau t r a v e r s des c u t i c u l e s d e p l a n t e s . A b s t r a c t - The PA-signal o f wet samples i n c r e a s e s e x p o n e n t i a l l y w i t h temperature. T h i s enables t h e s t u d y o f t h e t r a n s p o r t o f w a t e r t h r o u g h p l a n t c u t i c l e s .

I - YATER PERMEABILITY OF CUTICULAR MEMBRANES

The a e r i a l p a r t s o f h i g h e r t e r r e s t r i a l p l a n t s a r e covered by t h e c u t i c u l a r membrane which has a v e r y l o w p e r m e a b i l i t y c o e f f i c i e n t o f about 10-10 m/s

( F i g . 1 ) /I/. T h a t means t h a t t h e p e r m e a b i l i t y o f t h e c u t i c l e s i s i n t h e o r - d e r o f magnitude o f t h e l e a s t permeable a r t i f i c i a l polymer membranes /2/.

\

Cuticle

Upper epidermis Chloroplasts

Fig. 1 - Arrangement o f t h e c u t i c l e on t h e upper p a r t o f a green l e a f ( t r a n s v e r s e s e c t i o n ) /5/.

The c u t i c u l a r membrane (CM) c o n s i s t s o f two components t h a t a r e c h a r a c t e r i z e d by t h e ~ r s o l u b i l i t y i n l i p i d s o l v e n t s . The polymer m a t r i x (MX) i s t h e b u l k o f t h e membranes, i n s o l u b l e i n l i p i d s o l v e n t s w i t h a c o n t e n t o f up t o 80 % c u t i n , a polymer formed by hydroxy f a t t y a c i d s . The second component a r e t h e s o l u b l e c u t i c u l a r l i p i d s (SCL), t h a t f o r example o f C i t r u s l e a v e s have an amount o f 3 % o f t h e weight. The c u t i c u l a r membranes a r e o b t a i n e d f r o m green l e a v e s b y an en- z y m a t i c process d e s c r i b e d by Schonherr e t a l . / 3 / . T r e a t i n g t h e CM w i t h methanol and c h l o r o f o r m removes t h e SCL and t h e polymer membran (MX) remains.

Because t h e p e r m e a b i l i t y c o e f f i c i e n t o f t h e polymer m a t r i x (MX) i s about t h r e e o r d e r s of magnitude h i g h e r t h a n t h a t o f t h e CM, i t i s proposed t h a t t h e SCL de- t e r m i n e t h e w a t e r p e r m e a b i l i t y /I/.

The p e r m e a b i l i t y o f CM and MX depends on t h e vapour p r e s s u r e o f t h e w a t e r i n t h e s u r r o u n d i n g a i r . T h i s r e s u l t was o b t a i n e d by Schonherr e t a l . /2/ ( F i g . 21, s t u d y - i n g t h e p e r m e a b i l i t y c o e f f i c i e n t o f t r a n s p i r a t i o n t h r o u g h t h e c u t i c l e , t h a t i s i n c o n t a c t w i t h w a t e r a t t h e i n n e r and w i t h a i r a t t h e o u t e r s i d e .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983619

JOURNAL DE PHYSIQUE

Fig. 2 - Dependency o f t h e p e r m e a b i l i t y c o e f f i c i e n t Ptr o f c u t i c u l a r membranes on t h e " w a t e r a c t i v i t y " expressed by t h e r e l a t i v e h u m i d i t y awv /2/. PT;X : Ptr a t aw, = 1.

Another method t o s t u d y t h e p e r m e a b i l i t y i s t o determine t h e p e r m e a b i l i t y c o e f f i - c i e n t f o r d i f f u s i o n . I n a system t r i t i a t e d w a t e r / c u t i c l e / water,the t r a c e r f l u x i s measured. T h i s was t h e way Schonherr e t a l . /3,4/ s t u d i e d t h e temperature de- pendence o f t h e p e r m e a b i l i t y .

They found an i n c r e a s e w i t h i n c r e a s i n g temperature. These r e s u l t s a r e shown i n F i g . 3 as an A r r h e n i u s - p l o t . There a r e two l i n e a r regimes i n t h e p e r m e a b i l i t y o f CM t h a t i n t e r s e c t a t about 44 OC. Above t h i s temperature t h e w a t e r p e r m e a b i l i t y i n c r e a s e s suddenly w h i l e i t does n o t change i n MX-membranes.

Schonherr e t a l . i n t e r p r e t e t h e t r a n s i t i o n as t h e s o l i d / l i q u i d c r y s t a l l i n e o f t h e SCL and a change i n t h e i r m o l e c u l a r o r i e n t a t i o n , so t h a t h o l e s a r e formed.

T h i s t r a n s i t i o n o n l y appears i n wet samples /4/.

- I 9 r

oscendlng 1 rnernbrone

F i g . 3 - A r r h e n i u s p l o t o f w a t e r p e r m e a b i l i t y Pd o v e r r e c i p r o c a l

L L C temperature o f CM and MX membranes

( C i t r u s l e a v e s ) /3/.

- 15

a "

d

- 1 . 4 -

MX - rnembront

- ^{I 1}

-10

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I 1 - EXPERIMENTAL TECHNIQUE

As f a r as we know, Rosencwaig and Pines / 6 / were t h e f i r s t who r e p o r t e d on t h e i n - f l u e n c e o f w a t e r c o n t e n t o f samples o v e r t h e PA-signal. We used a gas mircophone- c e l l , where t h e t e m p e r a t u r e i s v a r i e d by a h e a t i n g c o i l and measured by a thermo- element c l o s e t o t h e sample. A d e t a i l e d scheme o f t h e sample's arrangement i s shown i n F i g . 4. To a v o i d t h a t t h e samples d r y up d u r i n g t h e experiment, t h e i n n e r s i d e o f t h e c u t i c l e i s w e t t e d f r o m a " w a t e r r e s e r v o i r 1 ' t h a t c o n s i s t s o f wet p i e c e s o f c e l l u l o s e .

condensed w i n d o w

water / /

.cell top part g a s (air)

gasket and spacer s a m p l e

w a t e r reservoir (wet cellulose)

Fig. 4 - Arrangement o f t h e c u t i c l e sample i n PA-cell. Backside o f t h e sample i s w e t t e d f r o m t h e " w a t e r r e s e r v o i r " . Arrow: d i - r e c t i o n o f w a t e r t r a n s p o r t .

Because o f t h e a b s o r p t i o n o f t h e chopped w h i t e l i g h t , t h e sample has t h e h i g h e s t t e m p e r a t u r e i n t h e c e l l . To p r e v e n t t h a t t h e w a t e r condenses a t t h e window, i t i s surrounded by a c o o l e d m e t a l area t h a t a c t s as a c o o l i n g t r a p . A gasket o f s i l i c o n r u b b e r s e a l s t h e gas volume above t h e sample a g a i n s t t h e w a t e r r e s e r v o i r .

11.1 - P r i n c i p l e o f p e r m e a b i l i t y measurement w i t h PA

The temperature g r a d i e n t i n t h e c e l l causes a t r a n s p o r t o f w a t e r t h r o u g h t h e sample and o f w a t e r vapour i n t h e gas t h a t condenses a t t h e t o p p a r t o f t h e c e l l . The t r a n s p o r t mechanism o f w a t e r and t h e r e f o r e t h e vapour p r e s s u r e i n t h e a i r i s governed b y t h e p e r m e a b i l i t y o f t h e c u t i c l e .

From measurements on l i q u i d samples l i k e b l a c k i n k we know t h a t t h e PA-signal i n - creases w i t h i n c r e a s i n g temperature. F i g . 5 shows an e x p o n e n t i a l i n c r e a s e t h a t seems t o be p r o p o r t i o n a l t o t h e vapour pressure.

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.-

2 9"

I I

block ink

F i g . 5 - Temperature-dependency o f t h e PA-amplitude f o r a l i q u i d sample ( b l a c k i n k ) .

7 295 7 ^{MO T/K-}

The vapour p r e s s u r e depends a p p r o x i m a t e l y e x p o n e n t i a l l y on t h e temperature.

l o g Pvw ^a - Lo/RT , ( 1

C6-128 JOURNAL DE PHYSIQUE

where Lo i s the heat of vapouration, R the gas constant. Therefore a variation of the water permeability of the sample should vary the amplitude of the PA-signal.

I11 - _MEASUREMENTS AND RESULTS

The temperature was varied between 298 K and 330 K. For a dry porous sample the signal i s nearly independent of the ambient temperature To, Fig. 6. This i s ex- pected f o r an isochoric signal forming process in a closed c e l l / 7 / , where the signal i s proportional t o To/Po, where Po i s the average pressure in the c e l l . The r e s u l t s of the temperature dependent measurements of a wet c u t i c u l a r membrane and of a wet polymer matrix membrane are shown in Fig. 6 resp. Fig. 7. In the semi logarithmic plots there are two regimes increasing with increasing temperature characterized by a concave and convex shape.

- - -

Fig. 6 - Temperature dependency of the PA-amplitude.

A: Wet c u t i c u l a r membrane (CM). Intersection of the concave and convex regime a t 320 K. B: Dry carbon black sample on copper.

Fig. 7 - T-dependency of the PA-amp1 i tude f o r a wet polymer matrix membrane (MX). Inter- section a t 315 K.

300 310 320

TIK - ^B

I V - INTERPRETATION OF THE RESULTS

The i n t e r s e c t i o n o f t h e concave and convex regimes i n t h e p l o t s a t 320 K (CM) and a t 315 K (MX) can be e x p l a i n e d by t h e s o l i d / l i q u i d c r y s t a l l i n e phase t r a n s i t i o n o f t h e l i p i d s . A t t h a t t e m p e r a t u r e t h e w a t e r p e r m e a b i l i t y changes a b r u p t l y ( F i g . 3).

We f o u n d t h e t r a n s i t i o n n o t o n l y i n t h e CM b u t a l s o i n MX-membranes as E c k l and G r u l e r /4/ w i t h c a l o r i m e t r i c measurements.

CONCLUSION

The i n c r e a s i n g w a t e r p e r m e a b i l i t y o f b i o l o g i c a l membranes i s connected w i t h an i n c r e a s e i n PA-amplitude. There seems t o be a c o n n e c t i o n between t h e vapour p r e s s u r e o f t h e sample and t h e magnitude o f t h e PA-signal.

The magnitude o f t h e change i n t h e PA-amplitude c a n n o t be e x p l a i n e d o n l y by 1. The change o f thermal d i f f u s i v i t y o f t h e c u t i c l e by t h e w a t e r c o n t e n t ;

2. The thermal and o p t i c a l p r o p e r t i e s o f m o i s t a i r and t h e v a r i a t i o n o f t h e w a t e r vapour p r e s s u r e i n t h e c e l l gas.

The oDserved e f f e c t y e t cannot be e x p l a i n e d q u a n t i t a t i v e l y .

References

/ I / SCHONHERR J., P l a n t a - 131 (1976) 159

/2/ SCHONHERR J. i n : Encyclopedia o f P l a n t P h y s i o l o g y ; New S e r i e s , Vol.lZB, P h y s i o l o g i c a l P l a n t Ecology 11, p.154. Eds. O.L. Lange, P.S. Nobel, C.B.

Oswald, H. Z i e g l e r , S p r i n g e r - V e r l a g , B e r l i n - H e i d e l berg, 1982 /3/ SCHONHERR d., ECKL K. and GRULER H., P l a n t a 147 (1979) 21 /4/ ECKL K. and GRULER H., P l a n t a @ (1980) 102

/5/ NOBEL P.S., I n t r o d u c t i o n t o ~ i o ~ h ~ s i c a l P l a n t P h y s i o l o g y . W.H. Freeman and Company, San F r a n c i s c o , 1970

/6/ RDSENCWAIG A. and PINES E., Biochim.Biophys.Acta, 493 (1977) 10

/7/ KORPIUN P. and BUCHNER B., Appl.Phys. B 30 (1983) 121