Nuclear Instruments and Methods in Physics Research A 424 (1999) 129—135

A distribution pattern of cadmium, gadolinium andsamarium in Phaseolus vulgaris (L) plants as assessed

by dynamic neutron radiography

Ferenc Ko? rosi!, Marton Balasko", Erzsebet Svab#,*

! Agricultural University, Go( do( lloL , H-2100 Go( do( llo, Hungary" KFKI Atomic Energy Research Institute, POB 49, 1525 Budapest, Hungary

# KFKI Research Institute for Solid State Physics, POB 49, 1525 Budapest, Hungary

Abstract

The qualitative and semi-quantitative distributions, presumably apoplast transport patterns for the Gd, Sm and Cdwere investigated in the primordial leaf tissues of the bean using dynamic neutron radiography. According to the applied3D, 2D images and the pixel count distribution histograms of the considered gray levels, peculiar distribution patternswere postulated for the elements. Main and lateral vascular systems for Gd, the cell walls as well as intercellular spaces forSm and the main leaf vein for Cd assumed to be the apoplast transport spaces and volumes. ( 1999 Elsevier ScienceB.V. All rights reserved.

Keywords: Dynamic radiography; Apoplast transport; Cadmium distribution; Dicotyledons; Gadolinium distribution;Phaseolus vulgaris (L); Samarium distribution

1. Introduction

The visualization of the uptake, long distancetranslocation and accumulation pattern of ele-ments in plants are important to clarify their func-tion in a plant’s life.

The cadmium uptake, translocation and distri-bution are influenced by the pH, ionic strength,metal concentration of the nutrient medium and

*Corresponding author. Tel.: #36 1 3959220; fax:#36 1 3959220; e-mail: svab@power.szfki.kfki.hu.

quantity of available organic compounds as wellas plant species and phenological stages [1—4].For the Cd uptake a model was set up [5]. Theuptake, translocation and distribution of gado-linium and samarium and related physiologicalpurposes have been far less studied in com-parison with those of cadmium. The samariumand gadolinium concentrations in fruit and otherplant tissues correlate with those determined in thesoil [6,7]. The involved physiological functionsseem to be the interaction with Ca2`, and othersignaling pathways as well as with gene expressions[8—11].

0168-9002/99/$ — see front matter ( 1999 Elsevier Science B.V. All rights reserved.PII: S 0 1 6 8 - 9 0 0 2 ( 9 8 ) 0 1 2 8 0 - 7 VII. APPLICATIONS III

&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&"Fig. 1. The gadolinium apolast transport pattern as assessed by 3D and 2D diagrams of the DNR images at a time scale on the leaf ofthe bean at primordial phenological stage (a) & (d) t"0 min, (b) and (e) t"30 min, (c) and (f) t"60 min.

To our knowledge qualitative picture imageson the distribution patterns of Cd, Gd and Smhave not yet been recorded. It would be ofgreat help to further clarify the roles and functionof these elements in plant systems. In this studyusing dynamic neutron radiography (DNR)distribution patterns of these element in the pri-mordial leaf of bean, in tissue level, at a time scalehas been imaged, recorded and analysed in vivoand in situ.

2. Material and method

Bean plants (Echo Elit variety) were grown ina specially designed aluminum cassette which wasfilled with D

2O (heavy water) during the measure-

ment. Then 1 cm3 D2O containing 1.6 mg Gd and

Sm and 2.6 mg Cd, respectively, was dropped witha syringe on the adaxial surface of the main vein.The high neutron absorption of Gd, Sm and Cdenables the DNR imaging of the distribution pat-terns of these elements in the neutron transparentD

2O. During the DNR imaging process the plants

at primordial phenological stage were being kept ina plant rearing unit placed in the neutron beam andreceived photosynthetically active light radiationintensity of 200 lE m~2 s~1.

The experiments were performed at the 10 MWVVR-SM research reactor in Budapest (Hungary).The used DNR installation facility and the arrange-ment of the imaging system in detail were outlinedin our earlier works [12,13].

The thermal neutron flux U4at the sample posi-

tion was 108 cm~2 s~1 with a beam diameter of150 mm. The radiography images were convertedinto light by NE 426 converter screen and detectedby a 10~4 lux TV 1122 type television cameramaking a 40 ms imaging cycle with a &100 lmresolution. The DNR images were displayed ona monitor, recorded and stored by a S-VHS re-corder. In order to explore the information on theelemental distribution revealed by neutrons, trans-mitted through the plants, the image analysis pro-

grams, Sapphire 5.05, made by Quantel and Imane1.4, made by KFKI were used. For image analysis800 images were integrated and beam shading cor-rection was applied.

3. Results

3.1. Gadolinium distribution

A solution of Gd in D2O (1.6 mg Gd in D

2O) was

prepared and dropped onto the surface of themain vein of the adaxial surface of the primordialbean leaf. This point of time was designated ast"0 and is clearly visible in Fig. 1a in 3D dia-grams and in Fig. 1d in 2 D diagrams obtainedfrom the DNR images. Then the apoplast move-ment was observed at the 30th minute (Fig. 1b, ande) and the 60th minute (Fig. 1c and Fig. 1f). The Gdapoplast transport mainly took place in the mainvein and then in the lateral vascular systems. Thesimultaneous and uneven penetration frontier ofthe Gd into the intercostal mesophyllum tissuesfrom the 30th minute was clearly observable(Fig. 1b, and Fig. 1e). This type of Gd movementeven more manifested itself at t"60 min (Fig. 1c,and f).

The images were quantified using pixel countdistribution histograms (areas) of the gray levels in50—110 intensity range. The results are summarizedin Fig. 2. The areas in the interval of 50—70 graylevels pixels can only be observed at t"0 min.These areas of lower gay levels agree with theinformation based on neutron-beam attenuationpattern caused by the Gd drop, and converted intoa characteristic light photon pattern. For the 60thminute observation, within the confines of 70—88gray levels, the number of pixels exceeded thosemeasured for t"0 min. Then in the range of88—110 gray level intensities, the pixel count distri-bution both for 60 and 30 min surpassed thosedetected at 0 min. These phenomena represent andfeature an enhanced Gd movement.

130 F. Ko? ro( si et al. /Nuclear Instruments and Methods in Physics Research A 424 (1999) 129—135

F. Ko? ro( si et al. /Nuclear Instruments and Methods in Physics Research A 424 (1999) 129—135 131

Fig. 2. Pixel count distribution histograms of gray levels after Gd dropping.

&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&"Fig. 3. Samarium and cadmium apoplast transport pattern as depicted by 3 D diagrams of the DNR images (a) Sm at t"15 min; (b) Smat t"60 min; (c) Cd at t"0 min; (d) Cd at t"30 min.

3.2. Samarium distribution

Fig. 3a and b show the 3D diagrams of the DNRimages. Here for technical reasons the DNR imagesare observed at t"15 and 60 min. In the case ofSm a lateral apoplast transport from the mainvascular system towards intercostal tissue canbe appraised, presumably involving cell walls andintercellullar spaces of mesophyllum cells. Thesemi-quantitative transport may be reckoned fromthe distribution of pixel counts observed in theinterval of 130—155 multigray levels as is evidentfrom Fig. 4.

3.3. Cadmium distribution

In order to estimate the Cd distribution, 2.6 mgCd dissolved in 1 cm3 D

2O was added to the

adaxial surface of the main vein of the primordialleaf which can be exactly identified in 2D projectionof the 3D diagram of the DNR image. During

30 min period the distribution of the Cd on/in theleaf tissues was being studied. At the 30th minute(Fig. 3d) from the declination of the composition ofthe plan perceived at t"0 min (Fig. 3c) a main veinmovement can be presumed and put forth. Thispostulation is advocated by the characteristic pixelcount distribution. This differed from those notedfor either Gd or Sm distribution pattern wherelateral translocation was also implicated.

4. Conclusion

In the plant’s nutritional research the in vivo andin situ qualitative and quantitative images on thetransport and distribution processes are helpful inrevealing the role of the elements. This statementare especially valid for those elements whose biolo-gical importance are either less studied or notyet revealed. The Gd, Sm and Cd are included tothis group. Till now, according to our knowledge,

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Fig. 4. Pixel count distribution histograms of gray levels after Sm dropping.

Fig. 5. The pixel count histograms observed during 30 min Cd-transport.

distribution patterns in organ and tissues werestudied only for Cd. Recently, with X-ray micro-probe analysis it was revealed that the cadmiumpreferably locates in the inner compartment of rootcortex cells [14].

In our present study using DNR technique withSapphire and Iman image processing and analyzingprograms in the primordial leaf of the bean distri-

bution patterns for Gd, Sm, Cd from D2O dripfeed

were laid open. The following postulations, regard-ing qualitative distribution and a semi-quantitativeanalysis, were applied:

1. The &100 lm resolution of the DNR techniqueused made it possible only to follow the longdistance apoplast transport of the investigated

134 F. Ko? ro( si et al. /Nuclear Instruments and Methods in Physics Research A 424 (1999) 129—135

elements. These implicated vascular systems, cellwalls and intercellular spaces.

2. The findings obtained are positive affirmable forthe leaves.

3. The semi-quantitative analysis of the time kinet-ics of apoplast transport was based on pixelcount distribution histograms of the pertinentgray levels represented areas.

The initial drops of Gd, Sm and that of Cd underour experimental conditions were clearly observed(Figs. 1 and 1d and 3a and c). This observationproves and accentuates the sensitivity and efficacyof our experimental set-up and method.

From the 3D and their 2D projections for theinvestigated elements and time intervals, the fol-lowing apoplast transport patterns can be estab-lished:

1. The Gd during 60th minute was transported inthe main and lateral vascular systems, then therewas penetration into the intercostal tissues.

2. The Sm at the same time interval was trans-ported from the initial drop in the direction oflateral tissues possibly involving cell walls andintercellular space.

3. As regards Cd movement, in the course of30 min, it occurred longitudinally in the mainvein Fig. 5.

Acknowledgement

We wish to thank Karoly Szasz, the programmerof IMAN, for kindly providing the A version.

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VII. APPLICATIONS III