Báo cáo khoa học: "Proanthocyanic polymorphism in holm oak (Quercus ilex L) in the Mediterranean region of France"

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Original article Proanthocyanic polymorphism in holm oak (Quercus ilex L) in the Mediterranean region of France S Nader P Lebreton M Barbero 2 1 Laboratoire de biochimie Université Lyon-1, 43, boulevard du 11 novembre 1918, végétale, F-69622 Villeurbanne Cedex; 2 Laboratoire de botanique et d’écologie Méditerranéenne, faculté des sciences de Saint-Jérôme, rue H Poincaré, 13397 Marseille Cedex, France Summary — We studied the proanthocyanic diversity of holm oak in France. The percentage of pro- delphinidin remains constant for each individual tree, independent of age or location of the leaves. By contrast, this content can be significantly different between trees within the same population. An in-depth analysis of a Languedocian population showed a good relationship between observed and predicted sample structure, according to the hypothesis of 2 alleles, prodelphinidin ’weak’ and ’strong’, respectively, governing the biosynthesis of this polyphenol. We have probably observed a biochemical polymorphism comparable to that previously demonstrated for several coniferous spe- cies. holm oak / prodelphinidin / polymorphism Résumé — Polymorphisme proanthocyanique du chêne vert Quercus ilex L dans la région méditerranéenne française. La diversité proanthocyanique d’une population languedocienne de chêne vert Quercus ilex a été étudiée. La teneur foliaire relative en prodelphinidine est constante pour un individu, indépendamment de son âge et de la situation des feuilles; elle peut par contre dif- férer significativement entre arbres de la même population. Une analyse détaillée montre une bonne corrélation entre effectifs observés, et ceux calculés conformément à l’hypothèse de l’existence de 2 allèles, respectivement «faible» et «fort», gouvernant la synthèse de la prodelphinidine. Il s’agit donc probablement ici de polymorphisme biochimique, analogue à celui déjà mis en évidence chez plu- sieurs conifères à l’aide du même marqueur phénolique. chêne vert / prodelphinidine / polymorphisme
INTRODUCTION part of the area, and Quercus ilex ss in the eastern part, between Italy and Turkey. Because of the above ecological and The holm oak Quercus ilex L is the most of holm oak, we biological particularities prevalent and characteristic preforest and considered it of interest to investigate to forest species in the western Mediterrane- what extent proanthocyanic ’marking’ - the an basin. The species has a large geo- systematic use of which has thrown light graphical range from Morocco (where it is on several conifers - was able to help clar- very widespread) to Turkey (where its ify such a complex situation, through a presence is more fragmentary). The holm more objective expression of the biological oak in France has penetrated northwards diversity of this species. The data present- to above the 45th parallel, to the Vendée ed here are taken from Nader (1990). and the southern extremity of the Dombes (Ain). Its ecological adaptability is also note- MATERIALS AND METHODS worthy, as the species can be found from the edge of the sea, on the northern side of the Mediterranean, up to an altitude of Sampling strategy 2 500-2 600 m in the Atlas Mountains (Barbero et al, 1992). It grows in temper- Forty-four specimens were taken from 1 popula- ate to very cold Mediterranean bioclimates Valliguières (Gard) in the French Mediter- tion at between the semi-arid and the damp, one. ranean zone of holm oak. The sampling strategy The species grows equally well on lime- was based on spatial and temporal parameters. stone or siliceous soils, though this adapt- ability cannot be clearly linked to any Spatial parameters ecophysiological or morphological charac- teristics of the populations concerned. Bioclimatic parameters were evaluated indirectly Q ilex participates in the structure of nu- by analyzing the significant floristic complex merous potential vegetational series repre- growing alongside the holm oak. The Valli- sented by pre-steppe or forest structures. guières population is located at the top of the meso Mediterranean level and can even reach By contrast, the numerous preforest land- the base of the upper Mediterranean; Buxus scapes composed of holm oak are an ex- sempervirens and Coronilla emerus are com- pression of the anthropogenic constraints mon here. Edaphic parameters revealed com- of the agro-sylvo-pasture systems in which pact and dolomitic limestone. Analyses were it is involved. Moreover, this species pos- performed on samples from neighboring individ- sesses considerable morphological vari- uals (A, B and C); the samples were taken at dif- ferent heights of the same tree or taken in isola- ability as regards its leaves, to such an ex- tion in relatively clear or densely wooded areas. tent that there are occasionally more The effects of the organization and spatial- differences within a given individual than temporal evolution of populations on the bio- between close neighbors or even between chemical structure of individuals is described distinctpopulations. elsewhere (Barbero et al, 1991). Such variability has an obvious impact on the systematics of holm oak, consid- Temporal parameters ered by some authors as a specific large taxon and by others as being organized The hypothesis that the biochemical structure of into several entities, the 2 most important adult leaves varies with the season was also being Quercus rotundifolia in the western tested by taking samples from 3 individuals: A,
I). The difference noted between high and low B and C, during different seasons from the sum- mer of 1985 to the autumn of 1986 inclusive. In leaves for a given individual was virtually zero, less than the deviation of the biochemical assay addition, young and old leaves were compared in 16 individuals, to evaluate any differences in technique (A: + 0.04 ± 0.23 mg/g; B: +0.08 ± 0.20 mg/g; C: +0.01 ± 0.20 mg/g). proanthocyanic composition. Total levels of proanthocyanins in adult leaves (> 5 months) from these same individuals were also found to be practically constant (< ± Biochemical aspects 10%), as shown by the mean values of 11 sam- ples taken between 5 August, 1985 and 24 De- The leaves of holm oak always contain the 2 cember, 1986 (A: 3.30 ± 0.32 mg/g; B: 3.22 ± proanthocyanidins: procyanidin and prodelphini- 0.27 mg/g; C: 3.40 ± 0.21 mg/g). The results din, but in variable absolute (mg/g) and relative were even more demonstrative as regards rela- (%) quantities depending on the specimen (the tive prodelphinidin content (A: 41 ± 2%; B: 52 ± second molecule differs from the first only by the 2%; C: 20 ± 1%). presence of a supplementary vicinal hydroxyl However, when data were grouped for each group on the lateral phenyl ring. The analytical season, absolute values were seen to be slightly technique, based on treatment with hot hydro- lower in winter (table II, fig 1). In addition, more chloric acid followed by visible photometry then pronounced differences were noted between high-performance liquid chromatography, is de- young (< 4 months) and adult leaves from the scribed in detail elsewhere (Nader, 1990)). Stud- same individual. The former were shown to con- ied separately at other French sites, this vari- tain markedly lower levels of total proanthocya- ability was shown to be comparable in all cases, nin and a little more relative prodelphinidin, re- and therefore characterizes the Q ilex species sulting from active biosynthesis during foliar considered globally in the biogeographic zone ontogenesis (table III, fig 2). concerned. In the Valliguières population, mean values were 3.88 mg/g (n 41 individuals; stan- = In conclusion, the proanthocyanic composi- dard deviation 0.48 mg/g) for the proanthocyan- tion of holm oak leaves is an individual charac- ic pool, and 39% (standard deviation 14%) for teristic which is dependent, to a secondary de- relative prodelphinidin content; extreme values gree, on seasonal ontogenesis. Nevertheless, were 2.30 and 4.25 mg/g, 20 and 68%, respec- the relative level of prodelphinidin (LD %) ap- tively. pears to be a particularly reliable and sensitive marker in adult leaves, where it has been shown The in-depth investigation of 3 individuals, A, B and C, showed that proanthocyanic composi- to be independent of the morphological height tion was quite independent of the height at and the date the sample was taken. It is there- which leaf samples were taken in the tree (table fore quite possible to describe each individual
polymorphism. The study of the 38 other by a small number, even a single biochemical individuals in the same population has con- analysis, independent of the weight and dryness of the sample. firmed the diagnosis and yielded further details. It would seem permissible to subdi- vide the population into 3 subsets: I, II and POPULATION ANALYSIS III, with limits of 31, 31-46, and > 47% < prodelphinidin content. The frequency his- Values for the LD% marker in the 3 individ- togram (fig 3) and the proanthocyanic uals A, B and C, at Valliguières (see table plane LD/LC (mg/g) (fig 4) illustrate this II) enable us to differentiate between the 3 point. The number of individuals within the individuals without any ambiguity, and are limits of each subset is 10, 19 and 12 (24, probably the expression of biochemical 46 and 29% of the total, respectively).
Proanthocyanic polymorphism of the types dd, dD and DD whose numbers holm oak therefore appears to be struc- should conform with the well known Har- tured, and we can put forward the hypothe- dy-Weinberg binomial formula. sis of a genetic model in conformity with The conformity between observed and that demonstrated for the same prodel- calculated sample structures (table IV) phinidin marker in Juniperus thurifera seems sufficiently good to accept the im- (Gauquelin et al, 1988) and in J oxycedrus plicit genetic model. The allelic frequency (Lebreton et al, 1991).The results suggest obtained (p(d) 0.48) suggests a process = that the gene(s) governing the synthesis of of hybridization, virtually equilibrated in this this molecule is present as 2 alleles, pro- population. It should be noted that this bio- delphinidin ’weak’ d (< 31%) and ’strong’ D chemical polymorphism cannot be directly (> 47%), explaining the appearance - in linked to the morphological ’polymorphism’ the panmictic hypothesis - of 3 pheno- of the leaves of the same individuals.
GENERAL DISCUSSION The ubiquitous nature and variability of the holm oak are such that considerable research has been performed in the hope of establishing a realistic and convenient taxonomy. The populations in France are even more interesting in that, for biogeo- graphers and ecologists, they are derived from the hybridization of the 2 eastern (Q ilex ss) and western (Q rotundifolia) taxa, which only accentuates the biologi- cal and systematic complexity of the question.
Madjidieh (1982) used morphological ed) to show a possible distinction between data (including foliar surface indices), col- Spanish and Italian populations; the latter lected from the whole western Mediterra- appear to be more homogeneous from a nean area, to establish that the popula- foliar biometrics point of view. The lipid tions of holm oak present notable composition of the acorns has also been envisaged as an aid in the systematics of differences, though no abrupt discontinui- ties are apparent. The south of France is holm oak (Pelleau, 1984; Rafii et al, 1991). the site of extreme types: Q ilex and Q ro- Already demonstrated by Touati (1985), tundifolia, but with a continuum of interme- the variability of holm oak polyphenols diary types. Q ilex ss is more frequently completes the picture, especially since it found on siliceous soils (north-facing seems to be the expression of genetically slopes, deep soil), whereas Q rotundifolia determined polymorphism. Moreover, this type seems to be dominant on limestone variability can be brought to light using substrates (zones of summer hydric very simple methods of sampling and bio- stress) (Madjidieh, 1987). chemical analysis, which could, therefore, From a biochemical point of view, Ya- be applied in a large ecogeographic cine (1987) used alloenzyme frequencies sweep. As with other lignous species to show the differentiation (unsuspected by whose prolonged period of immaturity ren- biometrics) between Italian and Spanish ders classical genetic experiments very dif- populations. Similarly, Afzal-Rafii (1988) ficult, early biochemical diagnosis can be used electrophoretic analysis of isoen- considered a particularly realistic alterna- zymes (13 peroxidase bands demonstrat- tive.
ecosystems in Mediterranean region. Vegeta- Our results, however, are currently limit- tio 99-100, 14-19 ed to French sites, and therefore possess a preliminary character that should prelude Gauquelin T, Idrissi Hassani M, Lebreton P (1988) Le Genévrier thurifère Juniperus thu- further research in an attempt to: 1) test the rifera L (Cupressacées) : analyse biomé- biochemical and genetic model proposed trique et biochimique; propositions systéma- here on other populations; 2) test the useful- tiques. Ecol Mediterr XIV, 31-42 ness of the prodelphinidin marker (very ef- Lebreton P, Bayet C, Muracciole M (1991) Le fective in conifers) in biogeographical stud- statut systématique du Genévrier oxycèdre ies throughout the whole area of the species Juniperus oxycedrus L (Cupressacées) : une considered; 3) search for correlations be- contribution d’ordre biochimique et biomé- tween other biochemical and/or morphologi- trique. Lazaroa (Spain) 12, 21-42 cal characteristics, in order to establish a Madjidieh H (1982) Contributionà l’étude taxo- synthetic expression describing the general nomique du chêne vert (Q ilex L) dans le polymorphism of this taxon; 4) describe in sud-est de la France. Doctoral dissert, 3 cy- e systematic terms the reality of this polymor- cle, Univ Aix-Marseille III phism in order to define reliable taxonomic (1987) Caractéristiques biomé- H Madjidieh entities which could be used for biogeo- optiques de Quercus ilex L dans triques et graphical and phytoecological purposes les différentes stations écologiques du sud- est méditerranéen français (Var). Doctoral and, in general, contribute to the establish- thesis, Univ Aix-Marseille III ment of a modern biosystematic of oaks. Nader S (1990) Contribution à l’étude structurale Again, very generally, these approaches des phytocénoses ligneuses méditerra- should contribute to a reduction in the diffi- néennes : aspects écologiques et biochi- culties met in characterizing polymorphic miques. Thesis Univ Aix-Marseille III species within the entire Quercus genus. Pelleau Y (1984) Contribution à l’étude chimio- taxonomique du complexe Quercus ilex L et Quercus rotundifolia Lamk. DEA thesis, Univ REFERENCES Aix-Marseille III Rafii AZ, Zavarin E, Pelleau Y (1991) Chemo- systematic differentiation of Quercus ilex L Afzal-Rafii Z (1988) Caractéristiques taxono- and Q rotundifolia Lam based on acorn fatty miques, morphologiques et isoenzymatiques acids. Biochem Syst Ecol 19, 163-166 du complexe chêne vert. Bull Soc Bot Fr Lett Bot 135, 343-352 Touati D (1985) Contribution à la connaissance du profil biochimique des dicotylédones buis- M, Hubert B, Lebreton P, Nader S, Barbero sonnantes et arbustives de Méditerranée. Quezel P (1991) Phenological and ecological Doctoral thesis, 3 cycle, Univ Lyon-I e variations in the biochemical composition of some Mediterranean woody species. Com- Yacine A (1987) Une étude d’organisation de la 266, IVth International Rangeland mun no diversité génétique inter- et intra- 22-26 Apr 1991 Congress. Montpellier, populationnelle chez le chêne vert (Quercus ilex L). Doctoral thesis, 3 cycle, Univ Sci e Barbero M, Loisel R, Quezel P (1992) Biogeo- graphy, ecology and history of Quercus ilex Tech, Languedoc