Biochem. Physiol. Pflanzen 188, 1-12 (1992) Gustav Fischer Verlag lena

Effect of Sodium Chloride on Primary Photochemical Activities in Cotyledonary Leaves of Brassica juncea

ALIAl), PRASANNA MOHANTy2) and P. PARDHA SARADHIl)

1) Centre for Biosciences, lamia Millia Islamia, New Delhi, India, and 2) School of Life Sciences, lawaharlal Nehru University, New Delhi, India

Key Term Index : Chlorophyll , cotyledonary leaves , photosystem, salt stress , sodium chloride, uncoupler ; Brassica juncea

Summary

The effect of varying concentrations of sodium chloride (NaCl) (0, 100, 150 and 200 roM) on seedling growth, pigment composition and the primary photochemical activities in cotyledonary leaves of Brassica juncea cv. DIRA 367 was investigated. NaCl-stress resulted in a considerable decrease in growth of the seedlings without causing any significant change in dry weight. While, chlorophyll a content was higher in cotyledonary leaves of seedlings raised in high salt containing media, chlorophyll b content did not show any significant variation till 11th day of growth. Thus the high ChI a/Chi b ratio in NaCI treatments reflects changes in the photosynthetic antenna size. The carotenoid content in II day old cotyledonary leaves, on the other hand, was much reduced at high concentrations of NaCl. NaCI treatments caused an increase in water oxidation capacity, as measured through H20 ~ MV (whole chain) or H20 -+ PDox (PS II) photoreactions, by 1.2 to 2.0 fold . But, PS I mediated photochemical activities showed no or only a minor increase by NaCI treatment. The enhancement in photochemical activities noted even in presence of uncouplers (NH4CI and methyl amine) suggest that the NaCI induced enhancement of primary photochemical activity is not linked to the uncoupling of electron transport from photophosphorylation.

Also, the studies on the interactive effect of in vivo ageing and salinity on the pigment composition and primary photochemical activities suggest that ageing and NaCl-stress result in partly independent and partly interactive changes in the pigment composition and photochemical activities.

Introduction

Salt stress has been known to retard plant growth and development by interfering with a wide range of physiological processes including photosynthesis (see BLACQUIRE and LAMBERS 1981; BALL and FARQUHAR 1984; STAPLES and TOENNIESSEN 1984; LEOPOLD and WILLING 1985; SEEMANN and CRITCHLEY 1985; AHMED et al. 1989; NEALE and ME LIS 1989; MUNNS 1990).

A decline in rate of photosynthesis as measured by rate of CO2 assimilation has been reported" to accompany the decline in growth under stress conditions as 90 per cent of

Abbreviations: ChI, chlorophyll ; DCMU, 3-(3,4-dichlorophenyl)-I, I-dimethyl urea; DCPIP, 2,6-dichlorophenol indophenol ; FeCN, Ferricyanide; HEPES, 4-(2-hydroxyethyl)-I-piperazine­ethanesulphonic acid; LHC, light harvesting chlorophyll protein complex; PD, phenylenediamine; PS I, photosystem I; PS II, photosystem II; TMPD, N ,N ,N' ,N' -tetramethyl-p-phenylenediamine; TRICINE, N-[2-hydroxy-l, l-bis(hydroxymethyl)ethyIJ glycine; MV, methyl viologen.

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plant dry matter comes from photosynthetically fixed CO2 (TRIPATHY et al. 1982). The

photosynthetic CO2 fixation of plants subjected to salt stress has been reported to be affected drastically under in vivo conditions by several workers (HEUER and PLAUT 1981;

ROBINSON et al. 1983; NEALE and MELIS 1989; PLAUT et al. 1989). Although there are

several reports on the influence of salt stress on primary photochemical reactions under in vitro conditions (BAKER 1978; DOMINY and BAKER 1980; KAISER et al. 1981), the investigations on the effect of salinity stress on primary photochemical processes under in vivo conditions is highly meagre.

In this study we attempt to identify the way(s) in which sodium chloride stress influences the pigment composition and primary photochemical processes in cotyledonary

leaves of Brassica juncea (one of the major oil yielding plants of India) under in vivo conditions. Since in vivo ageing of the cotyledonary leaves could influence primary photochemical processes, it was felt worthwhile to study in vivo ageing simultaneously while examining the effect of salt stress. In this paper, we report an increase in whole chain and PS II mediated photoreactions and this increase is possibly associated with an

increase in chlorophyll content under NaCI stress.

Material and Methods

Material and Growth conditions

Seeds of Brassica juncea cv. Dira 367 were procured from Dr. S. C. GULATI, Cummings, Laboratory, Indian Agricultural Research Institute (New Delhi, India). Modified B5 (GAMBORG et al. 1968) media without sucrose supplemented with NaCl (0, 100, 150 or 200 mM) was used for germinating and maintaining the cultures. B5 liquid medium has been used to reduce hannful effects due to lack/deficiency of essential elements. Seeds were surface sterilised with 0.1 % mercuric chloride and placed on cotton in 20 x 10 cm glass bottles containing 100 ml of test solutions under sterile conditions. These were then incubated at 25 DC under continuous light (~16 Wm- 2

) for 10 days.

For investigation of NaCl effect on the photochemical activities and pigment composition as a function of age, the seedlings were raised on B5 medium in the absence and the presence of 200 mM NaCl and observations were recorded during different stages of development (i.e. on 6th, 9th, 12th, and 15th day after the inoculation of seeds).

Fresh and Dry weight determination

Cotyledonary leaves from the seedlings were excised and their fresh weight was determined and after oven drying at 80 DC for 48 h the dry weight was taken.

Estimation of Chlorophylls and Carotenoids

Photosynthetic pigments chlorophylls (Chi) and carotenoids were estimated by following the procedures of PORRA et al. (1989) and WELLBURN and LICHTENTHALER (1984), respectively.

Chloroplast Isolation

The cotyledonary leaves from the seedlings grown at different concentrations of sodium chloride were used for isolation of thylakoid membranes. Freshly harvested leaves were dipped in ice cold isolation buffer (PH 7.8) containing 400 mM sucrose, 10 mM NaCI and 20 mM Tricine. After 30 min the leaves were taken out and homogenized in the prechilled mortar and pestle in ice cold isolation buffer in dark. The homogenate was filtered through 4 layers of miracloth and the

2 BPP 188 (1992) 1

filtrate was centrifuged at 5000 X g for 5 min at 4°C. The pellet was washed and resuspended in a small volume of suspension buffer (PH 7.5) containing 100 ruM sucrose, 10 mM NaCl, 2 ruM MgClz and 20 mM Hepes. ChI content of the chloroplast preparations was determined according to the method of ARNON (1949).

Assay of photochemical activities

Photochemical activities of the thylakoid membranes were assayed polarographically with a Clark-type oxygen electrode (SABAT et al. 1989b). For the assay of whole chain (HzO-..MY) electron transport the reaction mixture contained in addition to the suspension buffer, 0.5 ruM MY and 1 ruM Na-azide. The reaction mixture for assay of the electron transport catalyzed by PS II, contained suspension buffer, I mM FeCN and 0.1 mM PD. The thylakoid membranes equivalent to 20 fA,g ChI were used for each assay. The assay mixture for PS I contained 0.6 mM ascorbate, 1 ruM Na-azide, 0.5 mM MY, 5 fA,M DCMU and 100 fA,M DC PIP or 50 fA,m TMPD. The thylakoid membranes equivalent to 10 fA,g ChI were used for assaying PS I activity. All the measurements were carried out at 25 ± 1°C at saturating white light intensity (900 fA,Em-zS- I ).

Absorption spectra of chloroplasts

Room temperature absorption spectra of the thylakoid membranes isolated from cotyledonary leaves of plants grown at different concentrations of NaCI were recorded on a Hitachi 557 spectrophotometer operated in split beam mode. To minimize scattering, Shibata technique was followed (SHIBATA et al. 1954).

Results and Discussion

Growth parameters

The presence of NaCI in the medium in general delayed seed germination, reduced elongation of the hypocotyl and fresh weight of hypocotyl and cotyledons. The retarda­tion of all the above parameters was more prominent at high concentrations of NaCI

Table 1. Length of hypocotyl, fresh weight and dry weight of cotyledonary leaves and hypocotyl of seedlings obtained in varying concentrations of NaCI on day 11 after inoculation of seeds.

Treatment Length of Fresh weight (mg) Dry weight (mg) Hypocotyl

cotyledons hypocotyl cotyledons

control 8.2 ± 0.18 43.0 ± 1.0 38.0 ± 0.9 2.5 ± 0.2 100 ruM NaCl 6.5 ± 0.13 36.0 ± 1.3 28.0 ± 1.1 2.5 ± 0.2 150 ruM NaCl 5.7 ± 0.20 32.0 ± 2.0 25.0 ± 2.0 2.6 ± 0.3 200 ruM NaCl 4.9 ± 0.20 29.0 ± 2.1 20.0 ± 2.2 2.7 ± 0.2

The experiments were carried at least 3 times with five replicates each time. The data represent mean ± standard error.

hypocotyl

1.12 ± 0.01 1.12 ± 0.04 1.13 ± 0.10 1.13 ± 0.10

(Table 1). The NaCl induced delay in seed germination and reduction in growth is well documented (see KAISER et al. 1983; BALL and FARQUHAR 1984; SEEMANN and

CRITCHLEY 1985; BLISS et al. 1986; LI and NOTHNAGEL 1989). Although analysis of

solute (including ionic) composition of cotyledonary leaves and hypocotyls is essential for ascertaining the nature of the increase in the dry weight to fresh weight ratio, the observed enhancement in the ratio by NaCI treatment may arise due to the presence of higher solute

1* BPP 188 (1992) I 3

concentration and/or smaller cell volume as suggested by QUISENBERRY et al. (1981) for

osmotic stress.

Content of chlorophyll and carotenoids

The total ChI content on fresh weight basis was found to be higher in cotyledonary leaves obtained from plants grown in the presence of NaCI compared to those r~ised in the absence of NaCI and this increase in Chi content was more significant at high concentra­tions of NaCI (see Table 2) . No significant difference in Chi b levels was observed with

Table 2. Effect of NaCl on contents of chlorophyll and carotenoid in cotyledonary leaves.

Treatment Chi a Chlb Chi a + b Chi alb Carotenoids

control 709.6 ± 28 268.5 ± 16 987.1 ± 45 2.6 ± 0.Q7 147.4 ± 9.1 100 mM NaCl 749.9 ± 34 270.8 ± 18 1018.7±52 2.7 ± 0.04 124.6 ± 12.0 150 mM NaCI 779.8 ± 27 275.6 ± 9 1055.5 ± 37 2.8 ± 0.03 108.5 ± 10.0 200 roM NaCI 802.4 ± 19 265 .0 ± 14 1067.5 ± 33 3.0 ± 0.09 85.7 ± 13.0

The pigment contents are expressed as Ilg g - I fresh weight. All the experiments were carried at least 3 times . The data represent mean ± standard error.

increase in the concentration of NaCI. A similar increase in Chi content in leaves of Panicum miliaceum grown at low concentrations of NaCI (up to 60 ruM) has been documented earlier (LI and NOTHNAGEL 1989). The observed increase in the Chi levels may be associated with the increase in the PS II unit size (FORK and GOVINDJEE 1980; LI and NOTHNAGEL 1989). A greater Chi a/ChI b ratio in cotyledonary leaves of seedlings in

NaCI media compared to control suggests an increase in antenna size of photosystems

Table 3. Age dependent change in the chlorophyll and carotenoid contents in cotyledonary leaves of seedlings raised in absence and presence of 200 mM NaCI.

Treatment Age ChI a Chlb ChI a + b Chi alb Carotenoids

Control 6 558.0 ± 10 22l.0 ± 2 779.2 ± 13 2.50 ± 0.10 116.5 ± 8.2 200 mM NaCI 6 421.0± 2 141.3 ± 0 562.5 ± 2 2.98 ± 0.01 38.8 ± 3.2

Control 9 698.6 ± 17 207.0 ± 7 905.2 ± 20 3.35 ± 0.12 117.1 ± 5.4 200 mM NaCI 9 608 .2 ± 30 160.9 ± 7 769.0 ± 37 3.74 ± 0.02 67.3 ± 2.8

Control 12 564.6 ± 62 177.2 ± 20 728 .8 ± 80 3.11 ± 0.06 160.4 ± 14.5 200 mM NaCI 12 655.2 ± 65 169.7 ± 16 825 .0 ± 81 3.85 ± 0.01 104.3 ± 8.6

Control 15 392.0 ± 24 159.7 ± 7 552.0 ± 32 2.44 ± 0.03 142.2 ± 14.0 200 mM NaCI 15 722.0 ± 6 193.6 ± 8 915.6 ± 2 3.73 ± 0.01 150.5 ± 7 .3

The pigment contents are expressed as Ilg' g-I fresh weight and age is expressed in days. All the experiments were carried at least 3 times. The data represent mean ± standard error. Chloroplast preparation equivalent to 20 Ilg ChI were used for this purpose.

4 BPP 188 (1992) 1

c: o

1·0 ,----------------,

0·75 :' I , ,

440 ~ (1 1\ I ,

I I I

'.470 ' ... i"

--Control

----·200mM Noel

678 + " " 1\ 1\ I I

i 0·5

\ \ \ \ \ \ I

... o 11\ .0

<l

0·25

400 450 500 550 600 650 700 750

Wavelength (nm)

Fig. 1. Change in the absorption spectrum of chloroplasts isolated from cotyledonary leaves of Brassica juncea grown in B5 medium in the absence and the presence of NaCl (200 mM). Chloroplasts equivalent to 20 lig Chi were used and scattering effect was minimised by SHIBATA' S

technique (SHIBATA et al. 1954).

relative to LHC under the influence of NaCI. However, a decline in chlorophyll content has been reported by many workers (PETOLINO and LEONE 1980; GRANT and SOMERS 1981; CHAVAN and KARADGE 1986; BALL et a1. 1987) under salt stress. In contrast, WALKER (1989) reported a reduction in Chi content under NaCI stress specially at concentrations above 100 mM in Santalum acuminatum but an increase in mature clover leaves. On the other hand, SCHROPPEL-MEIER and KAISER (1988) did not find any change in the total chlorophyll content and photosynthetic capacity of leaves by NaCI treatments even at concentrations as high as 300 mM in spinach . These investigators concluded that the influx of salt into chloroplasts was very slow to impair photosynthesis even after a massive salt shock as most of NaCl gets sequestered in vacuoles. In the present study, the carotenoid content on the other hand was found to be low in presence of NaC1. The

difference was more prominent at high concentrations of NaCI (Table 2). The cause for the reduction of carotenoid content by salt stress needs further investigation.

The Chi content of cotyledonary leaves of seedlings raised in presence of NaCI,

increased with age (till day 15) while the plants raised in absence of NaCI showed a decline in Chi after day 9 (Table 3). The change in Chi a content was more prominent as compared to Chi b content leading to a significant change in Chi a/ChI b ratio with time in

both presence and absence of NaCI (Table 3). A similar change in chlorophyll content has been reported earlier during leaf ageing in absence of NaCI (see SABAT et al. 1989a). An increase in carotenoid content was recorded in cotyledonary leaves with age both in the

BPP 188 (1992) 1 5

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t t 0 NN 0 :rI N

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E 0 0 <:> 0 ~ 0 ~ ~ N

1 I 0 0

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~<:> c: 0 0 <II .....

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o 0 0 0 II'> 0 II'>

("!oj Al!"q:>O IISd u c: L_4 14:> L~6w paAloAa lO lOW rI 0

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6 BPP 188 (1992) 1

..... H20~MV I I

....... -NH4CI ~

::c 150 O-O+ NH4C1 u u .....

~ I 0'1 J: E 120 3 Z

I

'U ...... Q) u E 90 ~

~ 2 J: III Z C + 0 60 u 0 N ....

0 C

0 30 0:

E :t

0 0 100 150 200

NoCI (mM)

Fig. 3. Effect of uncoupler (NH4CI) on whole chain electron transport activity of thylakoids isolated from cotyledonary leaves of Brassica juncea raised in B 5 medium with varying concentra­tions of NaCI. (11 days old plants were used) . The details of assay procedure were as described in Material and Methods . The extent of uncoupling has been presented as the ratio of rates obtained with and without 5 rnM NH4Cl (6 - 6). The vertical bars represent standard error of the mean value of three separate experiments.

presence (till day 15) and the absence (till day 12) of NaCI. Although carotenoid content

was less in NaCl-treated plants as compared to controls, there was a higher increase in

carotenoid content with age in seedlings raised in presence of NaCI compared to those in

its absence (Table 3).

Chloroplast absorption characteristics

A comparison of absorption spectra of chloroplast preparations obtained from coty­

ledonary leaves of plants raised in the absence and the presence of varying concentrations

Fig. 2. Primary photochemical actlvltles of thylakoids isolated from cotyledonary leaves of Brassicajuncea raised in B5 medium with varying concentrations ofNaCI. (11 days old plants were used.) The details of assay procedure were as described in Material and Methods . 100 % activity for (A) whole chain, (B) PS II mediated and (C) PS I mediated photoreactions were 47, 83 and 300 I-tmol O2 evolved or consumed mg- 1 Chi h- 1

, respectively. The vertical bars represent standard error of the mean value of three independent experiments.

Fig. 4. Age dependent changes in (A) whole chain (H20 ........ MV); (B) PS II (H20 ---+ PDo,,) ; and (C) PS I (DCPlP2 ---+ MV) mediated photochemical activities of thylakoids isolated from cotyledonary leaves of Brassica juncea raised in B5 medium with in the absence and the presence of 200 mM NaCI. The details of assay conditions were as described in Materials and Methods. The vertical bars represent standard error of the mean value of three independent experiments.

BPP 188 (1992) 1 7

Table 4. Relative absorption of chloroplast preparations from cotyledonary leaves of plants raised in various concentrations of NaCI.

Treatment

Control 100 mM NaCl 150 mM NaCl 200 mM NaCl

Absorption

678/650

2.259 ± 0.052 2.326 ± 0.064 2.341 ± 0.033 2.356 ± 0.031

438/470

1.490 ± 0.029 1.590 ± 0.043 1.520 ± 0.019 1.570 ± 0.033

The experiments were carried at least 3 times. The data represent mean ± standard error.

of NaCI showed no spectral shifts between 400 and 750 nm (Fig. 1). However, with increase in concentration of NaCI significant changes in absorption profile were observed

(Fig. I) . The spectrum quite clearly showed a decrease in carotenoid and Chi b relative to

Chi a revealing an alteration in Chi alb ratio by salt stress (see Table 4).

Photochemical activities

The structure and function of the chloroplast have been shown to be influenced by the ionic environment (lZAWA and GOOD 1966; MURAKAMI and PACKER 1971). KAISER et al. (1983) have reported that salinity does not affect the photosynthetic capacity as measured in terms of relative rates of O2 evolution from leaf discs of spinach plants (grown in

presence and absence of NaCl) at saturated CO2 concentration, probably by effectively excluding the salt from the chloroplast compartment (see also SCHROPPEL-MEIER and KAISER 1988). In the present investigations the presence of sodium chloride, in the medium in which plants were raised, enhanced water oxidation capacity of chloroplasts. Broken chloroplast (thylakoids) preparations obtained from cotyledonary leaves of plants raised in NaCl containing media showed significant enhancement in water oxidation capacity as measured through H20 ->- MV (whole chain) (Fig.2A) as well as H20 ->- PDox (PS II mediated) photoreactions (Fig. 2B) . At 200 mM NaCI , approximately 200 per cent enhancement in PS II mediated and 170 per cent in whole chain electron transport activity over control was recorded. Salt stress induced stimulation of PS II

activity has been reported earlier in intact chloroplasts (IZAWA and GOOD 1966; MURAKAMI and PACKER 1971; DOMINY and BAKER 1980) and in cyanobacterial sphero­plasts (WAVARE and MOHANTY 1983). The work of WAVARE and MOHANTY (1983)

suggests that cations including Na+ enhance the accessibility of the electron acceptors or

donors to photosystems due to screening of charges. Our results on PS I mediated photochemical activity with TMPDH2 or DCPIPH2 as donor showed no or minor increase in activity due to NaCl treatment (Fig. 2C). Under in vitro conditions NaCI has been

shown to stabilize PS I by HUNER and REYNOLD (1989). These authors further emphas­ised that sodium effect involves a site close to PS I. An enhancement in PS II mediated photochemical reactions with no significant change in PS I mediated reactions and a high

8 BPP 188 (1992) 1

ChI a/ChI b ratio in cotyledonary leaves of plants raised in NaCI containing media compared to controls suggests a probable increase in the core antenna size of PS II and not of PS I under the influence of NaCl. In order to ascertain if the increase in photochemical reactions by NaCl treatment is linked to uncoupling of electron transport from photophos­phorylation, uncouplers- NH4Cl and methylamine were used. The isolated thylakoid membrane preparations from cotyledonary leaves of seedlings raised in media both without and with NaCl showed an enhanced whole chain activity in presence of either NH4Cl (Fig. 3) or methylamine (data not shown). The ratio of the whole chain activity obtained in presence of NH4CI to the activities obtained in absence of NH4Cl was slightly more in presence of NaCI as compared to control (Fig. 3). Thus, stimulation of electron transport activities due to uncoupling of electron transport from photophosphorylation appears quite unlikely (SABAT et al. 1985). Photochemical reactions measured in terms of fluorescence induction kinetics made by earlier workers (FORK and GOVINDJEE 1980; LI and NOTHNAGEL 1989) also suggested a probable increase in size of PS II in salt treated plants. However, according to NEAL and MELIS (1989) chloride salinity exerts no appreciable change in the photosystem stoichiometry and/or antenna size, but it increases the susceptibility of photochemical apparatus to photoinhibition. Elevated concentrations of salt in the medium have long been known to promote thylakoid stacking in isolated chloroplasts (MURAKAMI and PACKER 1971). Our results, with cotyledonary leaves, however, favour the possibilities of a change in PS II units and/or antenna size as well as structural changes associated with the thylakoid stacking.

In vitro leaf ageing induces alteration in chloroplast structure and functions (STOD­DART and THOMAS 1982) including photochemical activities (BISWAL and MOHANTY 1976; SABAT et al. 1989a, b). The high extent of photochemical activity in thylakoids isolated from cotyledonary leaves of plants raised in 200 mM NaCl than the thylakoids from control cotyledonary leaves was seen at all stages during the growth period (Fig. 4). However, the maximal increase was seen in cotyledonary leaves between 9 and 12 days of growth. The control plant cotyledonary thylakoid activity declined at a faster rate than the NaCl treated ones (Fig. 4). A considerable increase in the above mentioned photochemi­cal reactions was recorded with ageing of cotyledonary leaves until day 9 in controls and till day 15 in presence of NaCl (Fig. 4). Treatment of isolated thylakoids with NaCI delayed ageing effect by controlling the degree of energy coupling between light harvesting ChI alb complex and the two photosystems, I and II, and not by regulation of coupling between PS I and PS II (DOMINY and BAKER 1980).

It is difficult at this stage to state exactly the mechanism by which NaCl alters the functioning of photochemical apparatus in the cotyledonary leaves. Since, thylakoids are sensitive to change in cation concentration (BAKER 1978; WAVARE and MOHANTY 1983), the osmotic potential of the environment might also induce some changes. The present study clearly suggests an alteration involving antenna size of PS II. However, further studies are required to ascertain this possibility.

Acknowledgement One of us (ALIA) is thankful to University Grants Commission (New Delhi) for providing

financial assistance.

BPP 188 (1992) 1 9

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WELLBURN, A. R., and LICHTENTHALER, H.: Formulate and program to determine total carotenoids and chlorophyll a and b of leaf extracts in different solvents. In: Advances in Photosynthesis Research, Vol. II, SEBESMA (Ed.) pp. 9-12, M. NijhofflDr. W. Junk Pub­lishers, The Hague 1984.

Received April 2, 1991; revised form accepted July 7, 1991

Authors' address: Dr. PRASANNA MOHANTY, School of Life Sciences, Jawaharlal Nehru University, New Delhi - 110 067, India.

Biochem. Physiol. Pflanzen 188, 12 (1992) Gustav Fischer Verlag Jena

Buchbesprechung

HEGNAUER, R.,: Chemotaxonomie der Pflanzen. Eine Ubersicht fiber die Verbreitung und die systematische Bedeutung der Pflanzenstotl'e. Band 9. Nachtriige zu Band 5 und 6 (Ma­gnoliaceae bis Zygophyllaceae). Chemische Reihe: Band 31. 786 S., zahlr. Abb. u. Tab. Birkhiiuser Verlag, Basel-Boston-Berlin 1990. Preis: SFR 580.

1m kurzen Zeitraum von nur vier Jahren brachte der Verfasser drei auBerordentlich umfang­reiche Ergiinzungsbiinde zu den Biinden 1-6 (1962-1973) seines Werkes heraus, von denen der letzte jetzt vorliegt. Die urspriinglich (s. Vorwort zu Bd. 7) als Band 9 vorgesehene Bearbeitung der Leguminosen wurde zuriickgestellt.

Neu aufgenommen in die Reihe der Familien von Magnoliaceae bis Zygophyllaceae wurden: Onagraceae, Oncotheaceae, Peridiscaceae, Pyrolaceae, Retziaceae und Roridulaceae. Die Elaeocarpaceae werden getrennt von den Tiliaceae, zu denen sie friiher gerechnet wurden, behandelt; nach DAHLGREN und BEHNKE geh6ren sie iiberhaupt nicht zu den Malvales. Ein Nachtrag iiber neueste biologisch interessante Ergebnisse auf dem Gebiet der Phytochemie bei verschiedenen Familien der Polycarpicae bildet den AbschluB.

In der chemotaxonomischen Auswertung der phytochemischen Merkmale der einzelnen Fami­lien stellt der Verfasser die Rolle der Sekundiirstoffe in der Chemotaxonomie heraus. Als besonders wichtig flir die Bewertung chemischer Inhaltsstoffe werden Zusammenhiinge bei ihrer Biogenese aufgezeigt. Auch auf die neuesten Systeme der Pflanzentaxonomie (CRONQUIST 1981; DAHLGREN 1983; TAKHTAJAN 1986; THORNE 1983) geht der Verfasser ein.

Der "Hegnauer" hat sich als unentbehrlich fUr Naturstoffchemiker, Pharmazeuten und Taxono­men erwiesen; er bietet tiber seinen informativen Charakter hinaus wertvolle Anregungen fUr weitere Forschung. A. ROMEIKE, Gatersleben

12 BPP 188 (1992) 1