niaterial of apple {Mahis) cultivars; from their peroxidase patterns ..... Martin SS.S7()473 (1); Hollow Brook, Martinhoe S.S667496 670494 (.3); \Vood\- Bay.
Nezi- Phytol.
(1989), 112, 569 575
Evidence from peroxidase polymorphism on the taxonomy and reproduction of some Sorbus populations in south-west England BY MICHAEL C F . PROCTOR, MARGARET E. PROCTOR AND ANDREW C.GROENHOF Department of Biological Sciences, University of Exeter, UK {Received 4 March 1988; accepted 5 May 1989) SUMMARY
Peroxidase isoenzymes in stem tissue w-ere invt-stigated by polyacrylatiiide gel eleetrophoresis it-i Sorbtis populations maitily from Devoti, south-west England. A total of 16 bands were recognized, of which 10 were variable between indi\-iduals or populations. The sexual diploid species i \ atutiparia, S. aria and S. torniiitalis showed individual variation within populations. Six polyploid microspecies, 5. anglica, S. porrigeittijortitis, S. rupicula, S. vexans, S. subciiiicata and .S\ dcx'Dinetisi.-:, and an extensive unnamed rupicola-Vxke population on the coast of north De\-ot-i and west Son-iersct, consisted of individuals of essentially identical phenotype (with a few recognizable minor variant.s). Every tnicrospecies hiid a distinctive peroxidase plienotype but S. porrigentiforntis from Devon was not idetitical with a specimen from Leigh Woods, Bristol. Microspecies of the S. aria group ha\-e various combinations of seven bands which occur in diploid 5. aria popuhitions. 5. attglica cotnbines '.S'. aria' bands with a prominet-it b.and from S. atictiparia. S. stihciineiita and S. dei-onieitsis possess fotir or fi\-o of the ' S. aria' batids, together with two bands whtch are apparetltly constant it-\ S. t(>rniiiialis\ S. intermedia also has a peroxidase phenotype related to these species. Key words: Sorhtis, isoenzyn-ies, peroxidase, apomixis, taxotiomy.
I N T R ( ) D I I C -r I ( ) N
The British species of Sorhiis comprise three widespread sexually reproducing diploids, 5. atictiparia, S. aria and S. torminali.s, and dnumber of poWpUiids all of yvhich are probably normally apomictic. The polyploids typically form localized and often disjunct populations of essentially identical individuals recognizable as distinct microspecies (Warburg, 1957, 1962; Herring & Sell, 1968). The microspecies that haye been distinguished in the British Isles fall into three groups. The largest number appear to be derivatives of diploid S. aria, and with it make the 5 . ar?a aggregate. The members of a group including S. anglica show characters intermediate between S. aucuparia and 5. aria sensu lato; those ot the 5./a- of .S. porrigentiformis, and Wilmott and Warburg refer specifically to the 'Devon form' of 'S. porrigens Hedl.' (Martin &• Eraser, 1939), whose distinctness is borne out by our results. Our data pro\ ide additional e\ idence that the 'No Parking' tree (mentioned above) and its neighbours near Watersmeet in in)rth Devon show small but constant genetic differences from 5. suhcuneata and S. devoniensis. and support the inclusion of them as a minor variant within the latter species by Sell
F i g u r e 2. F^^lectroplioretic pattcrn.s of peroxidases from some representative samples of Sorhi/s s p p . ; for loiation of sites see Appendix. Only bands of groups C - F are shown, (c;) Five individuals of .S. aria (Box Hill). (/;) Five individuals of 5 . aucuparia (Watersmeet); one Box 11 ill.?, aria-AKleft for comparison, (r) (f.eft to right; n u m b e r of individuals in parentheses if more than one.) S. aiifflica (N. Whilhorough C o m m o n (2), Dainion Hill, Woody Bay (2), C o m b e M a r t i n ) ; 5 . aria (Box Plill); S. aucuparia ('Peignmouth Golf Course, (Jreat H a l d o n ) ; 5 . arranensis (Arran (CambridKe liotanic Garden)), (d) S. dcfouiensis (Woody Bay, W a t e r s m e e t ) ; "Paxon D ' (Countisbury Cove to G l e n t h o r n e (8)). (e) S. rupicola (Brixham, Babbaeombe (3)); S. porrigeiitiformis (.Anstey's Cove). (/) 5 . vexans (Oxen 'For (2), Woody Bay (2)); "Faxon D ' (Woody Bay), (g) S. anglica (Woody Ba>); 5 . porrigentifnrmis (Anstey's Cove), Leigh Woods (Cambridge Botanic Garden), Woody Bay (2)). (//) S. anglica (Lee Bay); S. subcuneata ( M a r t i n h o e ) ; S. dcfnuicnsis (Martinhoe, Watersmeet (2)).
574
M. C. F. Proctor, M. E. Proctor and A. C. Groenhof
(1989). Our results from 5. an/jtica and '"Paxon D ' suggest that such local minor variants within microspecies may be not uncommon. The peroxidase phenotype patterns also provide useful additional evidence on the reproductive status and origins of Sorbus populations. Sexually reproducing diploid populations are apparent from even small samples of individuals by their variability. Apomictic populations would be expected to show constant isoenzyme patterns. In polyploids, amphimixis will generally result in less pbenotypic variation than in diploids (Gottlieb, 1981), so substantial phenotypic constancy may not in itself be conclusive evidence of apomixis. However, the way in which electrophoretic patterns retnain apparently constant and distinct for each mierospecies within mixed populations does suggest a high degree of apomixis. The phenotypes ot the polyploids give clear indications of the diploids from which they are derived. For the most part they confirm generally accepted taxonomic opinion, but S. intermedia shows a pattern quite unlike that of S. angtica and its allies, to which it has been thought to be related (Warburg, 1962; Richards, 1975; Clapham, Tutin & Moore, 1987), and more indicative of an origin from 5. aria and 5. torminatis. This is consistent with the conclusions of Liljefors (1955) and the flavone glycoside evidence of Challice & Kovanda (1978). Whether outcrossing occurs in the polyploid mierospecies, and if so, with what frequency, is of interest in relation to both their origin and their present-day biology. A number of examples of apparent hybridization are listed by Richards (1975), and the results of Hull & Smart (1984) suggest some gene flow into populations of S. arranensis and 5. pseudofennica. Gustafsson (1947) concluded from the limited available cytological evidence and Hedlund's (unpublished) crossing experiments that some gene exchange between the apomiets is possible (see also Hedlund, 1948). Our results neither confirm nor exclude this possibility, but they suggest a potentially fruitful basis for future experimental work. Liljefors (1953, 1955) found that most of the Scandinavian polyploid mierospecies normally show aposporic embryo-sac development and pseudogamy. In his scheme for the origin of the Scandinavian microspecies, he envisaged possible occasional sexual function of unreduced embryo-sacs in triploids, and of reduced pollen and embryo-sacs in tetraploids. Along with known partial apomiets in other genera, Sorhus mierospecies may perhaps be seen as part of a continuum of variation within which one may seek to understand the selection pressures leading to breeding systems with various levels of apomixis (Clausen, 1954; Proctor & Yeo, 1973; Richards, 1986). In a genus where for much of the time the morphological phenotype offers only a small range of (often variable) eharacters, isoenzyme patterns pro^
vide valuable additional taxonomic evidence, with the particular advantage that they are available at any time of year. For this limited purpose the peroxidases are a very useful system to work with. They are robust enzymes, and typically produce complex electrophoretic patterns, so they are easy to handle and yield plenty of phenotypic evidence. Other enzyme systems could undoubtedly contribute to both taxonomic and genetic knowledge of Sorbtis and might be more suitable for genetic analysis; isoenzyme studies in general could be of major value in advancing our understanding of this genus. A C K N O W L E n G K M !•: N T S
The original impetus for this work came from rare-species recording carried out by M.E.P, under contract for the Nature Conservancy Council. We are indebted to the National Trust for permission to collect material on their properties in north Devon, to Mr W. Singleton for help with tieldwork in the East Lyn valley and on the north Devon coast, to Dr R. M. Hodgson for material of S. devonierisis from Yelverton, to Mr P. D. Sell for help with identification of Sortyti.': specimens, to the Director, Dr C. D. Pigott and Mr C. Birkenshaw tor Sortnis material from the University Botanic Garden, Cambridge, and to Dr M. R. Macnair for helpful discussion.
R E F KR E N C E S Ci.APHAM, A. R., TuTlN, T . G . & MOORF,, D . M , (19H7). Flora of
ttie liritisti htcs, 3rd Edn. Cambridge. CHAI.I.ICI-, J . & KOVANDA, M . (1978). Chemotaxonomic survey of the g e n u s Sorbus in E u r o p e . Niiturwisseiisctiaften 6 5 , 111 1 1 2 .
CJ.AlsiiN, J. (1954). Partial apomixis as an equilibrium .system in e\c)lution. Atti det IX Coiigresso hitermixionate (ti Genetiia. I. Ciirylogia 6 (suppl.), 469 479. GoTTLJEn, L. D. (1981). Electrophoretic evidence and plant populations. Progress in Ptiyloclwmislry 7, I 46. Cji'SiAFSSON, A. (1947). Apomixis in higher plants, l i . T h e causal aspect of apcimixis. III. Hiotypc and species formation. Lunds
Vnivcrsiicis Arsstuift, N.I'\, Avd. 2. 43, 71 .170. llr.Di.iiNi), T. (1948). ()m uppkoni.sten av nya li\stypcr inom slaktet Sorhiis. Bntaiiistia Nnliscr. l.uiid 1948, .181 .192. lIovi.E, M. C. (1978). Ittustrated tiandbooht for tiigti resotiitioii of lAA oxidase-peroxidase i.soenzynic's by isoetectru focussing in slitbs of potyacrvlcimide gel. Forest Service (icncral Technical Report NE-37. Forest service, USDA, Broomhall, Pa. HUM., P . & SMART, G . J. B. (1984). Variation in two Sorbus species endemic to the Isle of .Arran, Scotland. Annats of Botany S3, 641 648. LAEMMI.I, U . K . (1970). Cleavage of structural proteins during the assembly of the head of Bacteriophage T4. Nature 227. 680-685. Lii.jrn-'OKS, A. (1953). Studies on propagation, embryology' and pollination in Sorbus. Acta liorti Begiani 16, 227 329. LlI.JEFORS, A. (1955). Cytological studies in Sorbus. .4cUi Horti Bergiani 17, 47 113. ' MARTIN,
W . K . & FRASI-R,
G . T . (1939).
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Devon.
T. Buncle, Arbroath. MlSlC, P. D., VlNTliRIlAI.TER, D. & T(JRI)OVK\ R. (1980). Polymorphism of apple isoperoxidases. Genetitta (Betgradc) 12, 263-269. PERRING, F . H . & SELL, P. D. (1968). Critical Supl>temcnt to the
Attas of ttie Britisti Ftora. B.S.B.I, and Nelson, London. PROCTOR, M . & YEO, P. (1973). Ttie Pollination of Floivers. Collins, London. RICHARDS, A. J. (1975). 232. Sorbus L. Hybridization and ttie Flora of ttie Britisti Istes (Ed. by C. A. Stace), pp. 233-238. Academic Press, London.
Peroxidase polymorphism in Sorbus RiCHAHD.s, .\. J. (19S6). Plinit Hreet/ing .Switcms. .Allen &• Unwin. London. SELL, P. D. (1989). The .VoiV);/.? latifolia (Lam.) Pers. aKKrcgate in the British Isles. Wataoiiia 17, 385 349. V'lNTERH.-M.TEK, D. V. & J.-\ME.s, D. J. (1983). The use of peroxidase polymorphism in the identification of apple scion cultivars. Scientin holinitliirai' 18, 2.S3 261. \V.\RBLRG, E. V. (1957). [Original descriptions of .'iorhus pscudofennica. S. efnint'iis. S. hihcrnica. S. porrigentiformis.
575 S. liuiiastriciisis, S. vtwaiis and S. lievonii'iisis.] Watsonin 4, 43-46. W.\i!iirKO, Ii. F. (1962). .S'o)7;».v L. In Flora of the British Isles (By .\. R. Claphani, T. G. Tutin &: R. 1-. Warburg), pp. 423-437. Cambridge. Wni-DEN, N. F. iv GOTTLIEB, L . D . (1979). Distinguishing alloz\nies and isoz\nies of phosphoglucoisomerases b\' eleetrophoretie comparisons of pollen and somatic tissues. Biochenucal (ienelics 17, 287-296.
APPENDIX Summarv of Sorbus material examined [Species are numbered in the sequence of Clapham, Tutin & Moore (1987). Localities are in Devon unless otherwise stated, with National Grid references. Numbers of individuals exatnined from each site are given in parentheses; CBG indicates material of known wild origin from the University Botanic Garden, Cambridge. Herbarium specimens of representative trees have beeti deposited in the Herbarium of the Botany School, Cambridge (CGE). 1. 5. aucuparia
T e i g n m o u t h Golf Course, SX915752 (1); Great Haldon, SX9067S7 (1); Whitestone Wood, SX857957 (5); Morchard Bishop, SS771064 (1); Watersmeet, SS745487 (5); Oxen T o r , SS729490 (1); nr Martinhoe SS674485 (1); Rufus Stone, Hants. SZ27O122 (1).
6. S. intermedia 7. S. anglica
Iloopern Fields, Exeter SX92()937 ( I ) ; above W o o d y Hay SS674484 (1). N. W h i l b o r o u g h C o m m o n , SX86.S673 (2); Dainton Hill SXS.S967\ ( 1 ) ; C o m b e Martin SS.S7()473 (1); Hollow Brook, M a r t i n h o e S.S667496 670494 (.3); \Vood\- Bay SS674487-679489 (2); Lee Bay SS692492 (3); Leigh W o o d s , Bristol, .Avon ST.S7 ( C B G : 1); Llangollen, Clwyd SJ24 ( C B G : 1). Rufus Stone, H a n t s . SZ270122 ( 5 ) ; Box Hill, Surrey c. T Q 1 7 6 5 2 0 ( 5 ) ; T i d e n h a m , Glos. S T 5 4 1 9 9 0 - 5 4 8 9 8 0 (5); Weston Big Wood, Avon ( N . Somerset) c S T 4 5 5 7 4 0 (5). Anstey's Cove SX934648-935650 (3); Babbacombe SX927656-928654 (6); W o o d y Bay SS679489 (2); L y n m o u t h SS73349O (1); Leigh W o o d s , Bristol, Avon S T 5 7 ( C B G : 1). Churston Coye, Brixham SX916570-920569 (15); Babbacome SX927656 (3); Neck Wood, T r e n t i s h o e SS633485 (2); Malham Cove, N . Yorks. SD897641-898641 (2). Culbone, Somerset SS823486-841485 (10); Black Gate SS789490 (1); C o u n t i s b u r y Cove to G l e n t h o r n e S S 7 6 7 5 0 I - 7 9 1 498 (13); Woody Bay SS673487 (1); Neck Wood, T r e n t i s h o e SS633484 633485 (4); C o m b e Martin SS548476 (2). Culbone, Somerset SS837486-839485 (8); Dogsworthy C o m b e SS777498 (2); L y n m o u t h SS729490-734489 (5); Woody Bay SS675486~679489 (3); Neck Wood, T r e n t i s h o e SS633485 (1). Minehead, Somer.set c. SS961478 (3); Watersmeet SS744490-745488 ( I S ) ; Woody Bay SS676486 (1); nr M a r t i n h o e SS669494 (4); Neck Wood, T r e n t i s h o e SS633484-633485 (4). Near Yelverton SX5196(i4 (1); Little Haldon SX912750 920753 (5); W a t e r s m e e t SS745490-744488 ( I I ) ; Woody Bay SS67249(M)74486 (3); Hollow l'irook, M a r t i n h o e SS666496-669494 (4); Neck Wood, T r e n t i s h o e SS633484 (1). Stoke Woods, Exeter SX916957 (6); Whitestone Wood SX857957 (5); Weston Big W o o d , Avon ( N . Somerset) c. ST45575O (1).
8. S. aria
13. S. porrigeiitiforniis
15. S. rupicola
[1 5a.] ' Taxon D ' 16. 5. vexans 18. S. subcuneata 19. S. devoniensis
20. 5. torminalis
