270 S. Afr. J. Bot. 1996,62(5): 270-276

Salinity. induced changes in anatomy, stomatal counts and photosynthetic rate of AtripZex semibaccata R. Br.

A.J. de Villiers,* I. von Te ichman, M.W. van Rooyen and G.K. Theron Department of Botany. University of Pretoria, Pretoria, 0002 Republic of South Africa

Reaived J April 1996: reviJed 2 Jul.\' /996

Anatomical changes in the roots and of semibaccata R. Br., induced by stress, as well as photosynthetic and stomatal response to salinity. were investigated. As salinity increased, decreases were observed in rool diameter and size, as well as in the number of in the chlorenchyma and bundle sheath cells. Development of these two cell types was also inhibited. Net leaf photosynthetic rate and leaf stomatal conductance

decreased with increasing salinity, while the interceJlular CO 2 concentration increased. 80th stomatal closure and inhibition of biochemical processes probably caused the reduced leaf photosynthetic rates. The stomatal indices suggest that the trend towards an increase in number of stomata per unit leaf area with an increase in salinity was not due to decreased epidermal cell size.

Keywords: Anatomy, Atriplex semibaccata, Chenopodiaceae, photosynthetic rate, salinity, stomatal counts.

"To whom correspondence should be addressed

Introduction des. This knowledge could aid the selection of species suited for Atriptex semibaccata R. Br. is a ruderal perennial glycophytc and reclamation purposes on saline . The aim of this study was a member of the Chenopodiac~ae (Shomer-Ilan et at. 1981), a to determine the changes in root and leaf anatomy, photosyn­ family including many species which have a high sah wierancc thetic rate and stomatal counlS of Atriplex semibaccata, induced and many members of which, although growing on salt-laden by increased salinity. Differences in photosynthetic response soils. are useful forage species (Aslam et al. 1986). might help explain the reduction in of these species at It is widely accepted that , especially that caused different soil (de Villiers 1993). by sodium chloride, adversely afTects growth and yield (Greenway & Munns 1980; Chow el al. 1990; Myers el al. 1990; Methods de Villicrs 1993). Morphology, anatomy, ultrastructure and meta­ Arripiex semibaccata R. Br. was chosen because it acts as a pioneer bolism of plant species (Werker et 01. 1983; Solomon et al. 1986; species in surrounding mined areas (Ie Raux. pers. commun.). Serrato Valenti et at. 1991) as well as their mineral and organic of a natural population of Atriplex semibaccata were col­ compound and water contents are affected by salinity (Prat & lected near Brand 5e Baai (31 °18'S, 17°54'E). The seeds were sown Fathi-Etlai 1990). Jeschke and Wolf (1988) stated that the salt in I O-cm l pots containing fine and irrigated daily with tap tolerance of the plant depends on the salt tolerance of the root. water. under free-draining conditions. for a period of two weeks. Several aspects of rool anatomy may be of importance in a saline Thereafter the were irri gated tw ice a week under free-draining environment, but the endodermis plays a major role, since it conditions with 250 em1 soluti on of a specific sa li nity. forms the barrier to the apoplastic flow of ions (Hajibagheri et (II. A stock sea-water solu ti on (B rujewicz sea-water solution cited in 1985), Interspecific anatomical differences in response to salinity Uhlig 1948) was diluted to attain three saline solutions, namely full stress may therefore provide useful criteria for sell!cting species strength, 2/~ strength and iI, strength sea-water. Equal amounts of best suited to withstand the desertification process (Serrato Val­ half-s trength Arnon and Hoagland's complete nutrient so lution enti et al. 1991). (Hewitt 1952) were added [Q all treatments during application of the Reductions in photosynthetic rate due to high salinity have saline solutions. Salts that might have accumulated in the soil were been reported for both glycophytes (Gale et al. 1967; Downton leached from it by giv ing t!ach pot 500 em·' rap water fortnightly 1977; Seemann & Critchley 1985; Zekri & Parsons 1990) and before the saline solution was applied. halophytes (Gale & Poljakoff-Mayber 1970; Kannan & Ramani One plant was grown per pot for all treatments. After approxi­ 1988; Myers el al. 1990). Salinity-induced limitations to photo­ mately five to six months, when the plants of one of the treatments synthesis may be separated into two major categories: (I) limita­ reached peak tlowering stage, plant material was fixed for the ana­ tions due to reduced stomatal conductance, and (2) limitations tomical study. A portion of root taken close to the soil surface was due to inhibition of biochemical processes (Gale et ai. 1967; Cllt into small pieces. and small sections, including the main vein. Downton 1977; Seemann & Critchley 1985; Flanagan & Jeffer­ were cut from the middle portion of the mature leaves. Before the ies 1988; Plaut et al. 1990). An increase in soil salinity can result plants were cut. the photosynthetic rate of both surfaces of two in a reduced biochemical capacity for because of leaves per plant (leaves 4 and 8 from the boltom) was determined interference with mineral uptake or the toxic effect of excess ions se paratel y and stomatal counts of five leaves per plant were made for (Flanagan & Jefferies 1988). each of five plants per treatment. Along the west of South Africa, the sandy soils are rich The material was fixed in 25 kg m·' glutaraldehyde in a \OO~moI in heavy minerals. The process whereby these heavy minerals are m·' buffer, consisting of Na2HP04 and NaH 2P04 (Coetzee & van de! extracted involves the use of sea-water, causing the salinity of the Merwe 1985). To fix the tannins, 5 kg m·' caffeine was added to the mined soil to be so high that plants find it difficult to grow under fixative (Mueller & Greenwood 1978). For the dehydration, the these extremely adverse conditions (Environmental Evaluation material was transferred to 2-methoxyethanol, ethanol, "-propanol Unit 1990). Anatomi cal studies of plants could provide info rma­ and n-butanol, according to Feder & O'Brien (1968), however, fixa­ tion all the nature of the salt tolerance ex hi bited by different spe- tion was done at room tcmperaturl!. The material was then infiltrated S. Afr. 1. Bot. 1996,62(5) 271

in a monomer mixture consisting of 94% (v/v) hydroxyethyJ mcth~ In sea-water-treated plants (Figure Id), less secondary xylem acrylate. 50 kg m· l polyethylene glycol 200, and 6 kg m" benzoyl nnd secondary phloem were produced by the consecutive vascu­ peroxide. Embedding was done in the monomer mixture at 60°C for lar cambia when compared to those of the control (Figure 1a). 24 h. Glycomethacryiate (GMA) sections. 3-5 ~m thick. Wt.!fC cut on The secondary tissues wh ich were formed by the first and second a Rei chert·lung 2040 uil ramicrOlome. The Periodic acid-Schiff vascular cambia were arranged morc or less in a spiral (Figure (PAS) reaction was used to stain the sections (Feder & O 'Brien Id), similar Lo that of the II, sea-water-treated plants (Figure lb). 1968). which were then counterstained for about 2-3 min in 0.5 kg Only a small portion of the derivates of the third cambium, which l m· toluidine blue 0 in a benzoate buffer, pH 4.4 (Sidman et al. comprised only about a half of the circumference. had differenti­ 1961). and mounted in cntellan. To tcst for cUlin and suberin. sec· ated into tracheary elements. lions were stained with a saturated solution of sudan black B in 7 volumes ethanol :3 volumes water, for 10 min. These sections were mounted in liqut!fied glycerine jelly. Crystals could also be observed Leaf anatomy in thest! sections, under crossed polarizing filters . Leaf material tixed The leaves of Atriplex semibaccaw were amphistomatic and the in formalin - acetic acid - alcohol (FM) was examined under a light guard cells of the stomata were situated at the level of the inner microscope to study the trichomes. tangential cell wall of the subsidiary cells (Figure 2a-d). Adaxial Ali-Cor LI-6200 Portable Photosynthesis System (open system and abaxial epidermal cells did not have strongly thickened outer infra-red gas analyser) (LI-COR, P.O. Box 4425, Lincoln, NE tangential cell walls. Lobed extensions of the hypodermal paren­ 68504, USA) was used to determine the leaf photosynt heti c rate. leaf chyma often projected into the inner tangential cell walls of both stomatal conductivity and internal e0 concentration of plants 2 epidermal layers (Figore 2e). grown under different saline soi l conditions. The mean photosyn­ Bladder-like salt trichomes, which were sparsely distributed thetic pholon flux density reaching the chamber was 1220.88 ± on the adaxial surface, bUl which occured in a dense cover on the 135.3 ~tmol m-2 S-I while the mean leaf temperature and mean cham­ abaxial surface (as seen under a stereomicroscope), were mostly be r air temperature were 30.1 ± 1.9°e and 31.6 ± O.3°e respectively. collapsed in the mature leaf. Only shrunken remnants of these The mean relative hum idity (RH) within the chamber was 3.21 ± 1.75%. Leaf areas were determined with aLi-Cor 3100 area meter. bladders (salt trichomes) could be seen in the cross sections For stomatal counts and stomatal indices. nail polish was applied (Figure 2e). to both the adaxial and abaxial surfaces of the leaves. This was Superficially, the transverse section of the Atriplex semibac­ removed when it had hardened, and the epidermal peels were cata leaf resembled an isobilateral leaf. however, the hypodermal mounted on microscope slides. A light microscope fitted with an thin-walled parenchyma should rather be described as spongy eye-piece with a 10 mm x lO-mm grid was used for counting the parenchyma. This hypodermal layer was further characterized by number of stomata as well as the number of other epidermal cells a small number of chloroplasts in the cells and especially by the within a specific area. Although it consists of two cells, each stoma lobed nature oflhe cell walls (Figure 2e). It could be described as was counted as one unit for determining the stomatal index. a uniseriate, sometimes biseriate, hypodermic which resembled a Results were analysed statistically using the one-way and water-storage tissue. In , the presence of hypo­ muhi-factor analysis of variance and LSD (least-significant differ­ dermal uniseriate water-storage tissue has been reported (Napp­ ence) multiple range test of the Statgraphic s 5.0 computer program Zinn 1973). (S til tgraphics 5.0, 1989; STSe.lnc.. USA) to test fo r signifi ca nl dif­ ferences at a = 0.05. Adaxially, the hypodermal tissue of the mid-vein did not differ from the rest of the lamina. while on the abaxial side. very thin Results walled parenchyma (probably representing a water-storage ti s­ sue) occurred and the hypodermal layer was weakly collenchy­ Root anatomy matous. The roots of Atripfex semibaccata exhibited a diarch structure, The centrally situated, multi-seriate chlorenchyma was pali­ which is typical of the Chenopodiaceae (von Guttenberg 1968). sade like and surrounded the collateral mid-vein partially and the In the control plants, two distinct primary xylem groups abutted lateral veins completely (Figure 2f). A 'Kranz' -type assimilation on the innermost secondary xylem. However, the primary tissue (Metcalfe 1979; Ray & Black 1979) in the form of phloem groups were difficult to distinguish from the innermost sheath-like chlorenchyma, which is 'open' on the abaxial side of secondary phloem. Four consecutive vascular cambia and their the mid- and lateral veins, surrounded the vascular bundles. bands of secondary xylem and secondary phloem could be distin­ Chloroplasts, which were more conspicuous and abundant (Met­ guished in the vascular cylinder (Figure la). Most of the 'inner' calfe 1979) in these sheath cells than in the other chlorenchyma, dcrivatcs of the fourth vascular cambium had not yet fully differ­ contained various starch grains which coloured dark red during entiated into secondary tracheids, vessel members, fibres and the PAS reaction. Several other halophytic and glycophytic plant parenchyma, although secondary walls and a slight lignin species have an open bundle sheath structure (Shomer-I1an e/ al. impregnation were visible within this zone of secondary xy lem 1981; Fahn 1990). (Figure I a). This differentiation had taken place only in certain parts of the root circumference. The outer portion of the root, i.e. The transverse section of leaves of the 1/ "J sea-water-treated the cortex, consisted of thi n-walled parenchyma (Figure I a). plants (Figure 2b) did not differ notably from that of the control Some of Ihese cells had divided periclinally or anticlinally. plants (Figure 2a), although the number of chl oroplasts in the Sudan black B-stained sections showed a suberin impregnation bundle sheath cells decreased. of the cell walls of the outermost cortex cells. Comparing the leaf anatomy of the plants treated with 2/1 In the roots of the III sea-waler-treated plants, the four consec­ sea-water with that of the control plants, the reduction in both utive vascular cambia formed a continuous spiral (Figure Ib). leaf size and thickness can be explained by the overall reduction Compared with the control plants, there was no reduction in the in cell size (Figure 2a & c). Furthermore, the chlorenchyma was root diameter and the amount of secondary tissues formed. less well developed and discontinuous between the veins. The The secondary xylem and phloem of roots of the 2./1 sea-water­ bundle sheaths were also less prominent, and a reduction in the treated plants (Figure Ic) had not differentiated to the same number of chloroplasts in the sheath ceBs was apparent. In the degree as those of the control plants (Figure 1a), especially in the outer-most (peripheral) chloroplasts of the bond Ie sheath cells fourth zone of the second ary xylem. the absence of starch-grains was remarkable. Uphof (1941) 272 S. Afr. l. Bot. 1996.62(5)

reported that plants growing under saline conditions often exhibit Leaf photosynthetic rate a reduction in the number of chloroplasts. The leaves of the 2/. sea-water- and full-strength sea-water­ Differences in leaf size were also evident when comparing treated plants were too small for measurements of photosynthesis plants of the sea-water tremment (Figure 2d) with those of the to be made with the Li-6200. With an increase in salinity From control and Il, sea-water treatment. Leaf thickness of the sea­ the control to 1/, sea-water, the leaf photosynthetic rate decreased water and conlrol plants was not signiticantly different, however, significantly from 29.49 ).lmoJ CO, m·l s" to 5.01 ).lmol CO, m·' the differentiation of various tissues, especially sheath cells and S·I (Table J). palisade-like chlorenchyma, was considerably inhibited. The Concomitant with the decrease in photosynthetic rate. the leaf number of starch grains in the chloroplasts of the sheath cells stomatal conductance decreased in the 11:.. sea-water salinity treat­ was greatly reduced. ment (Table 1). Stomatal closure is generally associated with

d

Figure 1 Transverse section of the root of Alriplex semibaccala plants grown under different saline so il condirions: a, control; b, 11.1 sea-water treatment; c .. 2/1 sea-water treatment and ; d, Full-strength sea-water treatment. Scale bar:::; 100 Jjm. s. Afr. J. Bot. 1996.62(5) 273

salinization in salt-sensitive species (Gale et al. 1967: Downlon few and small for measurements to be made. Significantly more 1977; Scemann & Critchley 1985). stomata occurred on the adaxial than on the abaxial leaf surface of the comrol and the l/~ and 2/, sea-water treatments (Table 2). Stomatal counts With an increase in salinity From the control to l/~ sea-water, the The leaves o f the full- strength sea-watcr-tn:atcd plants were too number o f adaxial stomata on the leaves (Table 2) increased sig-

- -

Figure 2 Transverse secti on of the leaf of Atripfex semibaccata plants grown under different saline soil conditions: a, control; h, I/~ sea-water treatment; c. 2/, sea-w ater treatment and; d. full-strength sea-water treatment; e, higher magnification of a part of the abaxial epider­ mis; f. higher magnification of a . E - abaxial epidermis, L - lobed hypodermal cell wall. S - salt hair (shrunken), C - bundle sheath cell , P - phloem. and X - xylem. Scale bar = 50 J.un . 274 S. Afr. J. Bot. 1996,62(5)

Table 1 Leaf photosynthetic rate, leaf stomatal conduc­ Table 2 The mean number of stomata per unit leaf area tivity and intercellular CO, concentration of Atriplex semi­ (mm') and stomatal indices, of Atriplex semibaccata grown baccata grown under different saline soil conditions under different saline soil conditions Leaf Treatment photosyn- Lea f II, sea-water 2/1 sea-water thetlc stomatal Intcr Leaf surface COnlrol rale conduc- cellular Stomata per Adaxial 75.63 h 94.76 c 100.69 c (j.lmol lanCe{moI CO2 con- unit leaf area CO m-2 CO m_2 Treal- 2 Standard 2 Standard central ian Standard (mm2) men! 5-') deviation 5-1) devIation (~I I · I) deviation Abaxial 50.00 a 52.83 a 47.07 a Control 29.49* 7.60 0.153* 0.05 108.19' 43.6 Stomatal Adaxial 0.138cd 0.162 e 0.152 de 1/, sea- indi ces water 5.01 1.87 0.058 0.01 318.24 57.5 Abaxial 0.124 be 0.119 b 0.095 a *Denotes a statisticall y Significant difference (P ~ 0.05) between the a-e: Values followed by the same letter (within a parameter) do not dif- conlrol and 1/1 sea-waler treatment fe r significan tl y at a ::: 0.05

nificantly. but no significant increase occurred in the number of epidermaltrichomes, including reduction of intense illumination.

adaxial stomata between '/1 and 21, sea-water treatments. Salinity insu lation against excessive heat to reduce transpiration, wa ter treatments had no effect on the number of abaxial stomata. storage. and water absorption (Karimi & Ungar 1989). The stomatal index showed no distinct pattern with increased Blumenthal-Goldschmi dt and Poijakoff-Mayber (1968) found salinity. but suggested that the trend towards an increase in that salinity damage (i.e. decreased number of chloroplasts, number of stomata, wit h an increase in salinity, was not the result structural changes of the cells) in the leaves of Atrip/ex halimus of dec reases in epidermal cell size (Table 2). St. Orner and progressed gradually from the outside inwards. First. the palisade Schlesinger (1980), on the other hand, reported that due to a cells showed signs of structural change. and only when they were decrease in the stomatal ratio with increased salinity, the greater rather extensively damaged, did the structure of the bundle number of stomata per unit leaf area at a very high Nael concen­ sheath cell become affected. tration was the result of decreases in epidermal cell size. In some species, leaf succulence is induced by increasing the concentration of chloride in the external medium, while in other Discussion species, particularly those of Atriplex. it is induced by sodium Root anatomy (Black 1954, 1956, 1958; Jennings 1976; Handley & Jennings With increasing salinity, the relative amount of conducting tissue 1977). In A/riplex semibaccara. no increase in leaf thickness is decreased noticably, and a disruption in the arrangement of these observed, although leaf succulence increases as the relative tissues occurred. As conducting tissues are of vital importance amount of water storage tissue increases. Salt tolerance would for the survival of plants, their redu ction might explain the also be accomplished by storage of salts in salt hairs and di sposal decrease in the total growth in this species with increasing salin­ at maturity. ity (de Villiers 1993). A decrease in the size of the vascular cylin­ For the plants of all treatments in our study, the leaf cuticle der of Prosopis tamarugo, due to increased salinity, was reported was observed to be thicker abaxialJy than adaxially, but no differ­ by Serrato Valenti er af. (1991), while Hajibagheri er al. (1985) ences in cuticle thickness occurred between treatment s. In found an increase in the root stelar diameter of the halophyte Suaeda maritima, the appearance of the epicuticuiar wax layer Suaeda maritime (L.) Dum. with increasing salinity. Greenway differed considerably between plants grown in the presence or (in Jennings 1976), on the olher hand, reported that salinity had absence of sodium chloride, i.e. wax plates appeared generally little effect on the roots of the halophyte Atriplex l1ummularia thkker, wider, and more upright after growth with sodium chlor­ Lindl. ide (Hajibagheri er al. 1983). Moser (1935) was able to distinguish two groups within the Leaf anatomy genus Atriplex L. on the basis of leaf anatomy. Group one Hill and Hill (1976) described the salt hairs of Arriplex spp. as showed the normal dicotyledonous dorsiventral arrangement two~celled structures on the epidermis. The whole salt hair is (adaxial palisade and abaxial spongy parenchyma) of chloren­ covered with a waxy material which reduces transpiration. The chyma, while group two displayed the 'Kranz'~type, where, as stalk cell is connected by plasmodesmata to the epidermal cell described above, the -rich sheath cells more or less and the bladder cell. Salt, mainly NaCI (As lam er al. 1986), is surrounded the veins while the palisade-like parenchyma radi­ accumulated in the vacuole of the bladder cell. and moves from aled from the bundle sheaths outwards. Moser (1935) examined the stalk cell to Ihe bladder cell Ihrough the plasmodesmata. 98 speci es of Arriplex, 19 of which belonged to the first group, Eventually the hair dies. depositing its salt as a scale or scurf and 79 exhibited the 'Kranz' -type assimilation tissue (among (Osmond er al. 1980) on the surface. The accumulated salt is thus them was Atriplex semibaccatn). The 'Kranz' -type mesophyll shed with the hair, which functioned during its life as a reservoir occurs almost exclusively in certain leaf succulents and 'malako­ for salt excretion from the leaf tissues. As a consequence. many phyllen' plants of hot, periodically dry (Napp-Zinn plants with such hairs colonize both arid and saline regions (Hill 1984). Wilhin Ihe Chenopodiaceae, Napp-Zinn (1984) reported & Hill 1976). Salt storage and excretion by bladder cells is con­ on two main types. i.e. the 'malakophylJ' C4 plants (including sidered to be especially critical for the salt tolerance of young those with a leaf anatomy as exhibited by Atripiex semihaccara) deve loping Arriplex spp. leaves (Karimi & Ungar 1989). and secondly. Col leaf succulents, in which a water storage tissue Other functions, besides salt excretion, have been ascribed to is also present. S. Arr. J. Bol. 1996,62(5) 275

Leaf photosynthetic rate phyte. A more correct term, however, would be a facultative The reduction in photosynthetic rate with increased salinity cor­ halophyte. responds with ohservations on hoth halophytic (Gale & Poljakoff-Mayber 1970: Kannan & Ramani 1988: Drake 1989: Acknowledgements Warren & Brockelman 1989; Myers et al. 1990) and glycophylic The authors would like to express their appreciation to Hester species (Gale et ([/. 1967: Downton 1977; Robin.son et af. 1983: Steyn for her assistance during this study and preparation of this Seemann & Critchley J 985; Munns & Te rmaat 1986; Khavari­ article, M . Potgieter for his assistance during the preparation of Ncjad 1988: Heuer & Plaul 1989: Gorham & Hardy 1990; Onk· the plates. Anglo American Corporation and the Foundation for ware 1990; Plaut et al. 1990; Zekri & Parsons 1990; Zerbi et ai. Research Development for linancial support, and the University 1990; Ziska ef af. 1990). Leidi et (/f. (1991), however, found no of Pretoria for tinancial support and facilities. significant response of leaf photosymhetic rate to salinity in wheat, although the photosynthetic rate of the entire plant was References lower in the presence of salt. because of limited leaf expansion. ASLAM, Z .. JESCHKE W.D .. BARRETT· LENNARD E.G., SETTER The cause of salinity-induced reduction in photosynthetic capa­ T.L., WATKIN E. & GREENWAY H. 1986. Effects of external NaCl city is, however, difficult to ascertain. on the growth of and the ion relatIOns and carbohy­ A reduction in leaf s[Omatal conductance is usually associated drate status of the leaves. Pl. Ceil Envir. 9: 571 - 580. with increased stomatal limitation of photosynthesis, due to a BLACK, R.F. 1954. The leaf anatomy of Australian members of the reduction in intercellular CO;: concentration (Seemann & Critch­ genus Atriplex. I. Atriplex ve.l'icaria Hcwach. and Amplex nummu­ ley 1985: Flanagan & Jefferies 1988: Gorham & Hardy 1990; laria Lind!.. AI/Sf. J. Bot. 2: 269- 286. Myers el al. 1990; Plaut et a1. 1990; Zerbi et al. 1990). In this BLACK, R.E 1956. Effect of NaCI in watcr cullUre on the ion uptake study however, the intercellular COz concemration increased and growth of Atrip lex hosIata L. Au.H. 1. bioI. Sci. 9: 67-80. with increasing salinity (Table I), which corresponds with the BLACK. R.E 1958. Effect of sodium chloride on leaf succulence and results of Gorham and Hardy (I (90). The intercellular CO2 con­ area of Atriplex hastata L. Aust. 1. Bot. 6: 306- 321. centration can be maintained by primary modification of either a BLUMENTHAL·GOLDSCHMIDT. S. & POLJAKOFF·MAYBER. A. reduction in stomatal conductance, or a reduction in the hio­ 1968. Effect of substrate salinity on growth and on submicroscopIc chemical activity of photosynthesis (Yeo et al. 1985). An inhibi­ structure of leaf cells of Alriplex halimus L. Au<~t. 1. Bot. 16: 469-478. tion of biochemical processes would lead to a rise in intercellular CHOW, W.S., BALL, M.e. & ANDERSON, J.M. 1990. Growth and CO2 concentration, which could cause partial stomatal closure, photosynthetic responses of spinach to salinity: Implications of K+ and this, in turn, could prevent changes in intercellular CO2 con­ nutrition for salt to lerance. Aust. J. Pl. Physiol. 17: 563- 578. centration. On the other hand, a more ma'tked decrease in sto­ COETZEE, J. & VAN DER MERWE, C.F. 1985. Penetration rate of glu­ matal conductance than in biochemical activity would result in a taraldehyde in various buffers IOto plant tissue and gelatin gels. I.

drop in intercellular CO2 concentration. This could result in Micros/:. 137: 129- 136. decreased fixation rates and, finally, in a new steady state of DE VILLIERS. A.J. 1993. Ecophysiologlcal studies on several Nama­ qualand pioneer speCies, with special reference to the of unchanged intercellular CO2 concentrations (Plaut et al. 1990). saline mined soil. M.Sc. thesis. University of Pretoria, Pretoria. Stomatal counts DOWNTON, W.J .S . 1977. Photosynthesis in salt-stressed grapevines. Aust.1. PI. Physiol. 4: 183- 192. In the case of several halophytes, SI. Orner and Schlesinger DRAKE, B.G . 1989. Photosynthesis of salt marsh species. Aq!WI. BOl (1980) and Flowers ef al. (1986) reported a significant decrease 34: 167-180. in number of stomata per unit leaf area with an increase in salin­ ENVIRONMENTAL EVALUATION UNIT 1990. Anglo American Cor­ ity. In A triplex semibaccata, however. the number of stomata per poration: West coast heavy mineral project. Unpublished report. unit leaf area increased with an increase in salinity from the con­ University of Cape Town. Cape Town. trol to II, sea-water; therefore the number of stomata per unit leaf FAHN, A. 1990. Plant anatomy. Pergamon Press, Oxford. area did not contribute towards the reduction in leaf photosyn­ FEDER. N. & O'BRIEN, T.P. 1968. Plant microtechnique: some princi­ thetic rate at increasing salinity. ples and new methods. Am. 1. Bot. 55: 123-\42. For plants grown at high salinity, the decrease in the develop­ FLANAGAN, L.B. & JEFFERIES. R.L. 1988. Stomatal limitation of ment of the vascular cylinder might explain the overall decrease photosynthesis and reduced growth of the halophyte. Plantago mari­ in plant size. as found by de Villiers ([993). Arriplex semibac­ tima L.. at high salinity. Pl. CeLl Envir. 11: 239- 245. cata tolerated high salinities, mainly hy storing the salts in salt FLOWERS, T.J., HAJIBAGHERI, M.A. & CLIPSON, NJ.W. 1986. hairs or bladders on the leaf surface. A marked decrease in leaf Halophytes. Q. Rev. BioI. 61: 15313-337. size, but not in leaf thickness, occurred. The development of the GALE. J .• KOHL, H.C. & HAGAN. R.M. 1967 . Changes in the water chlorenchymatous tissue and that of the bundle sheath cells was balance and photosynthesis of oman, bean and colton plants under inhibited. Another response to the increased salinity was a saline conditions. Physiologia Pl. 20: 408-420. decrease in the number of chloroplasts present in the chloren­ GALE. J. & POLJAKOFF-MAYBER, A. 1970. Interrelations between chyma and bundle sheath cells. growth and photosynthesis of salt bush (Atrip/ex halimus L.) grown in A reduction in the number of stomata per unit leaf area of saline media. Aun 1. bioi. Sci. 23: 937-945. plants grown under saline conditions. as reported by St. Orner GORHAM. J. & HARDY, C.A. 1990. Response of Eragrostis tef to and Schlesinger (1980) and Flowers et al. (1986), mighl explain salinity and acute water shortage. Pl. Physiol. 135: 641 - 645. the reduction in their leaf photosynthetic rates. Because Atriplex GREENWAY, H. & MUNNS, R. 1980. Mechanisms of salt tolerance in semibaccata did not behave in this manner, the reduction in leaf nonhalophytes. A. Rev. Pl. Physiol. 31: 149- 190. photosynthetic rates of this species could be attributed rather to HAJIBAGHERI, M.A .. HALL, J.L. & FLOWERS, TJ. 1983. The slrue· an inhibition of the biochemical processes, as is evident from the ture of the cuticle in relation to cuticular transpIration in leaves of the reduction in the number of chloroplasts with increasing salinity. halophyte Suaeda marilima (L.l Dum. Nev',,' Phytol. 94: 125-13 1. This characteristic of the species might therefore be of benetit for HAJIBAGHERL M.A .. YEO, A.R. & FLOWERS, T.J. 1985. Sail loler· survival under saline soil conditions, even though A. semihaccafa ance in SU(leda maritima (L.l Dum. Fine structure and ion concentra­ is considered, according to scientific terminology, to be a glyco- tions in the apical region of roots. New Phylol. 99: 331 - 343. 276 s. Afr. J. Bot. 1996.62(5)

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