Dwarf Shoots Research Articles

MtESN2 is a subgroup II sulphate transporter required for symbiotic nitrogen fixation and prevention of nodule early senescence in Medicagotruncatula.

Adequate distribution of mineral sulphur (S) nutrition to nodules mediated by sulphate transporters is crucial for nitrogen fixation in symbiosis establishment process. However, the molecular mechanisms underlying this process remain largely unknown. In this study, we characterized the function of Early Senescent Nodule 2 (MtESN2), a gene crucial to nitrogen fixation in Medicago truncatula. Mutations in MtESN2 resulted in severe developmental and functional defects including dwarf shoots, early senescent nodules, and lower nitrogenase activity under symbiotic conditions compared to wild-typeplants. MtESN2 encodes an M. truncatula sulphate transporter that is expressed only in roots and nodules, with the highest expression levels in the transition zone and nitrogen-fixing zone of nodules. MtESN2 exhibited sulphate transport activitywhen expressed in yeast. Immunolocalization analysis showed that MtESN2-yellow fluorescent protein fusion protein was localized to the plasma membranes of both uninfected and infected cells of nodules, where it might transport sulphate into both rhizobia-infected and uninfected cells within the nodules. Our results reveal an unreported sulphate transporter that contributes to effective symbiosis and prevents nodule early senescence in M. truncatula.

NODULE INCEPTION: a direct regulator of gibberellin biosynthesis during symbiotic nodulation.

This article is a Commentary on Gao et al. (2023), 239: 459–465.

Conifer Cone and Dwarf Shoot Diversity in the Anisian (Middle Triassic) of Kühwiesenkopf/Monte Prà della Vacca (Dolomites, Northeastern Italy)

Conifer Cone and Dwarf Shoot Diversity in the Anisian (Middle Triassic) of Kühwiesenkopf/Monte Prà della Vacca (Dolomites, Northeastern Italy)

Comparative analysis of differential gene expression indicates divergence in ontogenetic strategies of leaves in two conifer genera.

In land plants, heteroblasty broadly refers to a drastic change in morphology during growth through ontogeny. Juniperus flaccida and Pinus cembroides are conifers of independent lineages known to exhibit leaf heteroblasty between the juvenile and adult life stage of development. Juvenile leaves of P. cembroides develop spirally on the main stem and appear decurrent, flattened, and needle‐like; whereas adult photosynthetic leaves are triangular or semi‐circular needle‐like, and grow in whorls on secondary or tertiary compact dwarf shoots. By comparison, J. flaccida juvenile leaves are decurrent and needle‐like, and adult leaves are compact, short, and scale‐like. Comparative analyses were performed to evaluate differences in anatomy and gene expression patterns between developmental phases in both species. RNA from 12 samples was sequenced and analyzed with available software. They were assembled de novo from the RNA‐Seq reads. Following assembly, 63,741 high‐quality transcripts were functionally annotated in P. cembroides and 69,448 in J. flaccida. Evaluation of the orthologous groups yielded 4140 shared gene families among the four references (adult and juvenile from each species). Activities related to cell division and development were more abundant in juveniles than adults in P. cembroides, and more abundant in adults than juveniles in J. flaccida. Overall, there were 509 up‐regulated and 81 down‐regulated genes in the juvenile condition of P. cembroides and 14 up‐regulated and 22 down‐regulated genes in J. flaccida. Gene interaction network analysis showed evidence of co‐expression and co‐localization of up‐regulated genes involved in cell wall and cuticle formation, development, and phenylpropanoid pathway, in juvenile P. cembroides leaves. Whereas in J. flaccida, differential expression and gene interaction patterns were detected in genes involved in photosynthesis and chloroplast biogenesis. Although J. flaccida and P. cembroides both exhibit leaf heteroblastic development, little overlap was detected, and unique genes and pathways were highlighted in this study.

MICROPROPAGATION AND PLOIDY STABILITY OF Lippia lacunosa Mart. & Schauer: AN ENDANGERED BRAZILIAN MEDICINAL PLANT

Lippia lacunosa is a Brazilian savanna plant that belongs to the Verbenaceae family. It has been used in folk medicine as a treatment for different diseases. This species represents an endangered Brazilian medicinal plant, and this is the first report documenting a reliable protocol for the in vitro propagation and regeneration of L. lacunosa. Axenic explants were cultivated in MS medium containing different concentrations of naphthalene acetic acid (NAA) to induce root growth. The mean shoot length and the number of roots were highest with 0.06 mg·L-1 NAA. The highest number of buds in shoot regeneration was induced with 2 mg·L-1 6-benzylaminopurine (BA). To obtain a long-term culture, the dwarf shoots were elongated on MS media containing 0.5 mg·L-1 BA alternated with MS containing 2 mg·L-1 BA every 40 days. In the present protocol, the long-term shoots retained the ability to root even after long periods of BA treatment. In addition, we evaluated the nuclear DNA content and ploidy levels, including the occurrence of endopolyploidy, in long-term micropropagated plant leaves using flow cytometry analysis. The plants propagated in vitro over several years possessed nuclear DNA contents ranging from 2.940 to 3.095 pg, and no differences in DNA content were found among in vitro plants or between these plants and the control (L. lacunosa from a greenhouse with a DNA content of 3.08 pg). The flow cytometry analysis also demonstrated that there was no polyploidization. The present study will be useful for biotechnological approaches and provides the first estimate of the nuclear DNA content of this species using flow cytometry.

Waterlogging and soil freezing during dormancy affected root and shoot phenology and growth of Scots pine saplings.

Soil waterlogging is predicted to increase in the future climate in boreal regions due to increased precipitation. Snowmelt periods in winter may also become more common and further increase the amount of water in soil. It is not well known how waterlogging and soil freezing during winter affect the physiology, phenology and growth of trees. Our aim was to study the below- and aboveground responses of Scots pine (Pinus sylvestris L.) saplings to waterlogging (WL) in frozen (Fr) and unfrozen (NoFr) soils in a growth chamber experiment. The soil was either -2 °C or +2 °C and either waterlogged or not in a split-plot design for 6 weeks during dormancy, with similar air conditions in all treatments, which were Fr + WL, NoFr + WL, Fr + NoWL and NoFr + NoWL. Needles showed a shift towards a deeper dormancy in frozen than unfrozen soil in terms of chlorophyll fluorescence (Fv/Fm), water potential and apoplastic electrical resistance. In spring, initiation of shoot elongation started earlier if the soil was frozen during dormancy. In Fr + WL, initiation of root growth was delayed by 20 days compared with other treatments; after that, the root growth peaked at the same time as needle elongation. Needles remained smaller in Fr + WL than in the other treatments, indicating that roots formed a strong sink for carbon. Shoot and root biomass were not negatively affected by waterlogging if the soil remained unfrozen. In Fr + WL, survival and growth capacity of new terminal and whorl buds, the number of bud scales and the number of dwarf shoots were reduced. We conclude that soil freezing on sites prone to waterlogging should be considered in management of boreal forests, especially in the face of predicted climate change.

Towards improved comparability of studies addressing atmospheric concentrations of semivolatile organic compounds based on their sequestration in pine needles

Coniferous needles can be used as a passive air sampler of semivolatile organic compounds (SVOC) and an indicator of atmospheric pollution patterns and trends. There is limited information on whether different parts of the plant (e.g., foliage leaves, dwarf shoots, twig, etc.) contain different levels of SVOC. Only few studies have compared levels of SVOC surface layer of wax and to their total content in all needle tissues and what affects an uptake and distribution of SVOC. It is important to have better understanding of the extent to which sampling and sample preparation procedures affect measured levels of SVOC in pine needles and reduce comparability of data from samples processed in different ways. In the present study, we assessed an impact of various sampling and sample preparation techniques on the levels of SVOC in Pinus sylvestris needles. While the impact of various storing, washing and drying methods was not significant, presence of dwarf shoots in the sample or structural damage of needles affected the results significantly. Results show that levels of SVOC in dwarf shoots are 2–8 times higher than those in foliage leaves. Therefore, dwarf shoots must be carefully removed before foliage leaves extraction to improve comparability of results. There were different patterns in SVOC on the surface of the foliage leaves compared to the whole leaves. An uptake of these substances by the surface wax as well as their occurrence in the internal structure was of function of the physico-chemical properties of the substances (log Kow, molar weight).

Agrobacterium T-DNA insertion in the rice DWARF SHOOT AND DEFECTIVE PANICLE1 (DSDP1) gene causes a severe dwarf phenotype, reduces plant vigour, and affects seed germination

We report a new T-DNA-tagged rice plant chi7, which displays a severe dwarf phenotype, reduced plant vigour, and impaired panicle development in the homozygous state. By chromosome walking, T-DNA integration was mapped in chromosome 2, 1054-bp upstream of the translation start site of a gene (Os02g0820400), which we designate as DWARF SHOOT AND DEFECTIVE PANICLE1 (DSDP1). DSDP1 expression was unexpectedly higher in the homozygous mutant leaves than in the hemizygous mutant and control plant leaves. Mutant dsdp1 seeds, stored for 24 weeks, failed to germinate in soil. The growth vigour of the dsdp1 mutant reduced with increasing seed storage period. The dsdp1 mutant plants, grown in vitro on MS medium, formed short, stout, and ageotropic roots with lesser number of root hairs. The findings suggest that DSDP1 may function as a negative regulator of many developmental processes in rice.

Conifer diversity in the Kungurian of Europe—Evidence from dwarf-shoot morphology

A major global change, the transition from an icehouse to a greenhouse world, took place during the Permian. In the equatorial Euramerican floral realm this resulted in stepwise changes from sub-humid climates in the early Cisuralian to semi-arid/arid climate by the late Cisuralian. During the same time interval we see a change from spore plant-dominated lowland floras, to increasingly drought-tolerant floras dominated by conifers and other seed plants. A recently discovered Kungurian (late Cisuralian) flora from the “Le Fraine” section near the village of Tregiovo (Trento Province, NE-Italy), is characterized by several types of conifers, callipterids, sphenopterids, and sphenopsids. The conifer fossils included both vegetative and reproductive organs. Five different ovuliferous dwarf shoot types were found, ranging from forms with many scales and interspersed sporophylls, that typically resemble late Pennsylvanian and early Permian walchian conifers, to stalked forms with largely fused sterile scales and sporophylls, comparable to early and late Permian voltzian conifers. One of the voltzian-type dwarf shoots belongs to the genus Dolomitia, extending the range of this genus back to the late Cisuralian. Another form strongly resembles those of the voltzian conifer Pseudovoltzia. The other three dwarf shoot types show a wide morphological variation, but cannot be assigned to any known genus due to the imperfect preservation. In western Euramerica, the transition from walchian- to voltzian-conifer-dominated floras took place during the late Cisuralian. This study shows that this change occurred across the entire equatorial Euramerican realm. The well-dated Tregiovo flora is one of the very few late Cisuralian floras of Euramerica. As such, this flora documents an important step in the evolution of Permian terrestrial biotas.

The Mutation of Glu at Amino Acid 3838 of AtMDN1 Provokes Pleiotropic Developmental Phenotypes in Arabidopsis.

MDN1/Rea1, as an AAA-type ATPase, is predicted to be the largest protein involved in pre-ribosome maturation in most organisms. However, its function in plant growth and development is poorly understood. Here, we characterized a novel Arabidopsis mutant, dwarf & short root (dsr) 1, which shows pleiotropic developmental phenotypes, such as slow germination, short root, dwarf shoot, and reduced seed set under normal growth conditions. Using positional cloning, we revealed that the AtMDN1 function is impaired by a ‘glutamic acid’ to ‘lysine’ change at position 3838 of the amino acid sequence in dsr1. Multiple sequence alignment analysis revealed that the mutated Glu residue, which located in the linker domain of AtMDN1, is extremely conserved among organisms. AtMDN1 is expressed in various tissues, particularly in the shoot apex and root tip. Moreover, the results of transcript profile analyses showed that the dysfunction of AtMDN1 in dsr1 impairs the expression of genes related to plant growth and development, which is tightly associated with the pleiotropic phenotypes of dsr1. Thus, we concluded that the Glu residue plays a vital role in maintaining AtMDN1 functions, which are essential for plant growth and development.

Pinus remains from the Pitsidia plant assemblage document coastal pine forests in southern Crete during the late Miocene

The fossil remains of the genus Pinus are common in the European Paleogene and Neogene record. Apart from seed cones, most of the vegetative remains are difficult or even impossible to accurately classify in the modern systematic schemes of the genus. In the late Miocene assemblage of Pitsidia (Messara Basin, southern Crete) Pinus and Myrica remains dominate with thousands of vegetative and fertile specimens. The outcrop comprises a 4.5 to 5.0m thick sequence of silts and sands, rich in plant fossils. The exceptional preservation of some specimens provides significant micro-morphological and anatomical details of taxonomic value. The Pitsidia pine remains include dwarf shoots, long shoots, isolated needles, fascicle bracts, bud scales, male cones, isolated scales of male cones, seeds and ovulate cone scales. We were able to classify the material to at least subgenus and in some cases section. Both subgenera Pinus and Strobus occur in the assemblage. Concerning the dwarf shoots, three different pine species were identified, Pinus sp. – two-needled fascicles (subgen. Pinus), Pinus sp. – five-needled fascicles (subgen. Strobus) and the proposed new species Pinus pitsidiensis (subgen. Pinus) for the abundant three-needled fascicles. Lastly, we reconstruct the whole plant of P. pitsidiensis sp. nov. and discuss its paleoecology.

Biological and physical evidence for extreme seasonality in central Permian Pangea

Climate models indicate increased desertification in the continental interior of Pangea during the Permian, which would have affected the composition of the flora and fauna. We present a multi-proxy paleoenvironmental reconstruction of a terrestrial ecosystem in central Pangea of Lopingian age. The reconstruction is based on biological and physical data from the Moradi Formation, located in the Tim Mersoi sub-Basin, northern Niger. Paleosols and sedimentological evidence indicate that the prevailing climate was semi-arid to very arid with marked intervals of high water availability. Carbon stable isotope data from organic matter and paleosols suggest that both the soil productivity and actual evapotranspiration were very low, corresponding to arid conditions. Histological analysis of pareiasaur bones shows evidence of active metabolism and reveals distinct growth marks. These interruptions of bone formation are indicative of growth rhythms, and are considered as markers for contrasting seasonality or episodic climate events. The macrofossil floras have low diversity and represent gymnosperm-dominated woodlands. Most notable are ovuliferous dwarf shoots of voltzian conifers, and a 25-m long tree trunk with irregularly positioned branch scars. The combined biological and physical evidence suggests that the Moradi Formation was deposited under a generally arid climate with recurring periods of water abundance, allowing for a well-established ground water-dependent ecosystem. With respect to its environment, this system is comparable with modern ecosystems such as the southern African Namib Desert and the Lake Eyre Basin in Australia, which are discussed as modern analogues.

Earliest Occurrence of Autorotating Seeds in Conifers: The Permian (Kungurian-Roadian)Manifera talarisgen. et sp. nov.

We describe the conifer genus Manifera (Majonicaceae, voltzian Voltziales) from the Lower Pease River flora (Early Permian, north central Texas) on the basis of dispersed ovuliferous dwarf shoots and seeds and compare it with coeval and Late Permian taxa. Manifera talaris gen. et sp. nov. is exceptional for two reasons. First, it is the earliest known conifer with winged seeds adapted for autorotating wind dispersal; second, its seeds had variable wing configurations. The ovuliferous dwarf shoots of M. talaris were stalked and bilaterally symmetrical and were composed of five partially fused sporophylls and sterile scales. The sporophylls were in median and lateral positions, and the sterile scales were in intermediate positions. The seeds bore two integument-derived wings on the chalazal end of the seed, with the secondary wing ranging in size from rudimentary to a small stub to almost equal to that of the primary wing. Single-winged seeds are the most common morphology among extant anemochorous conifer seeds. When falling, such seeds autorotate about their center of mass, which significantly slows down their descent and increases the probability of longer-distance dispersal. The discovery of M. talaris seeds with these morphological traits shows that this mechanism of wind dispersal had already evolved in conifers by the Early Permian.

Production of triploid plants from endosperm cultures of Phlox drummondii

Triploid plants of ornamental Phlox drummondii Hook. were raised from cultures of endosperm excised from immature fruits having zygotic embryo at early dicotyledonous stage. Endosperm tissue was firstly cultured with the embryo on the Murashige and Skoog's (MS) medium supplemented with 5 μM 6-benzylaminopurine (BAP) + 10 μM α-napthaleneacetic acid (NAA) for 7 d and recultured after the embryo was removed. A friable callus appeared two weeks after removal of the embryo and it became compact callus mass in another three weeks. Upon transfer of this 5-week-old callus to the MS medium with 10 μM BAP + 2.5 μM indole-3-acetic acid (IAA), maximum percentage of green nodular shoot buds appeared from which regenerated dwarf shoots. Elongation of the dwarf shoots, however, required transfer of the individual dwarf shoots excised from the callus on the fresh medium and best results achieved on medium with low concentration of IAA (0.5 μM) in presence of 10 μM BAP. The shoots were then rooted in vitro and plants subsequently established in pots containing soil. Over 70 % of plants were triploid with a chromosome number of 2n=3x=21. Size of stem, leaves, flowers, pollen, and stomata of these triploid plants were higher and the plants were more vigorous as compared to naturally occurring diploid plants. In particular, flowers showed bright colour with enlarged central eye adding to their ornamental value.

Enhanced drought and heat stress tolerance of tobacco plants with ectopically enhanced cytokinin oxidase/dehydrogenase gene expression

Responses to drought, heat, and combined stress were compared in tobacco (Nicotiana tabacum L.) plants ectopically expressing the cytokinin oxidase/dehydrogenase CKX1 gene of Arabidopsis thaliana L. under the control of either the predominantly root-expressed WRKY6 promoter or the constitutive 35S promoter, and in the wild type. WRKY6:CKX1 plants exhibited high CKX activity in the roots under control conditions. Under stress, the activity of the WRKY6 promoter was down-regulated and the concomitantly reduced cytokinin degradation coincided with raised bioactive cytokinin levels during the early phase of the stress response, which might contribute to enhanced stress tolerance of this genotype. Constitutive expression of CKX1 resulted in an enlarged root system, a stunted, dwarf shoot phenotype, and a low basal level of expression of the dehydration marker gene ERD10B. The high drought tolerance of this genotype was associated with a relatively moderate drop in leaf water potential and a significant decrease in leaf osmotic potential. Basal expression of the proline biosynthetic gene P5CSA was raised. Both wild-type and WRKY6:CKX1 plants responded to heat stress by transient elevation of stomatal conductance, which correlated with an enhanced abscisic acid catabolism. 35S:CKX1 transgenic plants exhibited a small and delayed stomatal response. Nevertheless, they maintained a lower leaf temperature than the other genotypes. Heat shock applied to drought-stressed plants exaggerated the negative stress effects, probably due to the additional water loss caused by a transient stimulation of transpiration. The results indicate that modulation of cytokinin levels may positively affect plant responses to abiotic stress through a variety of physiological mechanisms.

Performance of jack pine (Pinus banksiana) rooted cuttings from proliferated dwarf shoots versus seedlings 8 years after planting

Growth and tree form characteristics of jack pine (Pinus banksiana Lamb.) rooted cuttings propagated from proliferated dwarf shoots (PDS) were compared with seedlings in two field trials 8 years after establishment. Results indicated that jack pine rooted cuttings from PDS can grow as well as seedlings and maintain acceptable tree form. Rooted cuttings of progeny from the 22 top-ranking open-pollinated families in a seedling seed orchard of jack pine were 4.2% taller and 10% larger in diameter at breast height than commercial seedlings tested on the same sites, which indicates that rooted cuttings have potential in realizing genetic gains in jack pine tree improvement programs. Rooted cuttings increased the proportion of trees with normal branching characteristics and reduced the percentage of trees with excessive heavy branches in the Sault St. Marie trial, which had larger tree sizes. However, longer term monitoring (20 to 25 years) is needed to determine stability of jack pine rooted cuttings planted on sandy soil where wind throw may become a problem as tree size increases.

A bizarre Palissya ovulate organ from Upper Triassic strata of the Zixing coal field, Hunan Province, China

Palissya, a little-known reproductive organ with a long history, is recorded from China and Asia for the first time. A new species, Palissya hunanensis (sp. nov.), is described from the Upper Triassic Rhaetican strata of the Zixing coal field of Hunan Province. The ovulate cone has a compound shoot system that consists of a main axis and many helically-arranged axillary structures referred to as female dwarf shoots, each of which is subtended by a bract. Despite a superficial similarity, P. hunanensis differs from the typical species P. sphenolepis (Braun) Nathorst in a number of subtle but consistent features: the cone is much smaller and narrower, the bracts are much thinner, there are fewer pairs of cup-like seed scales, and the seed scales are adaxially attached to a thick axis rather than to bracts. These traits are all distinctly different from other species of the genus. Moreover, SEM observation of the new species reveals morphological features of the seed scales and seeds and details of the female dwarf shoot; significantly increases our knowledge of Palissya; and provides new evidence that it is a conifer. Palissya is related to the Lower Permian Lebowskia, a voltzian conifer bearing ovuliferous structures similar to the bract plus dwarf-shoot organization of Palissya. Palissya-type conifers probably grew in specialized marine-continent habitats, unlike most other extant and extinct conifers that grow in drier upland environments.

Anomalous needle numbers on dwarf shoots of Pinus mugo and P. uncinata (Pinaceae)

The frequency of occurrence of abnormal, three- (or more) needle dwarf shoots of most southern and central European two-needle pine (<em>Pinus</em>) species were studied. No specimens with more than two-needle dwarf shoots were found in a population of <em>P. nigra </em>Arnold subsp. <em>salzmannii </em>(Dunal) Franco from the Iberian Peninsula and in two populations of <em>P. uliginosa</em> Neumann from the Sudeten Mountains in Central Europe. Single specimens were found within one population of <em>P. pinaster </em>Aiton from the Iberian Peninsula and among six populations of <em>P. sylvestris </em>L. from the Iberian Peninsula and Central Europe. Abnormal dwarf shoots mostly with three, but also four, five or six needles were found among 24 of 25 surveyed populations of <em>P. mugo </em>Turra and <em>P. uncinata </em>Ramond. The average frequency of specimens with at least one three-needle dwarf shoot was 24% for <em>P. mugo</em> and 20% for <em>P. uncinata</em>. The frequencies of occurrence varied significantly among studied populations and were highest in samples collected from the upper elevational range limits of the species in the mountains and near the northern limits of their ranges. The frequency of abnormal dwarf shoots in the same populations was significantly high in 2-3 consecutive years. Needles from three-needle dwarf shoots were not significantly shorter than those of two-needle shoots.

Relationship between gibberellin, ethylene and nodulation in Pisum sativum.

• Gibberellin (GA) deficiency resulting from the na mutation in pea (Pisum sativum) causes a reduction in nodulation. Nodules that do form are aberrant, having poorly developed meristems and a lack of enlarged cells. Studies using additional GA-biosynthesis double mutants indicate that this results from severe GA deficiency of the roots rather than simply dwarf shoot stature. • Double mutants isolated from crosses between na and three supernodulating pea mutants exhibit a supernodulation phenotype, but the nodule structures are aberrant. This suggests that severely reduced GA concentrations are not entirely inhibitory to nodule initiation, but that higher GA concentrations are required for proper nodule development. • na mutants evolve more than double the amount of ethylene produced by wild-type plants, indicating that low GA concentrations can promote ethylene production. The excess ethylene may contribute to the reduced nodulation of na plants, as application of an ethylene biosynthesis inhibitor increased na nodule numbers. However, these nodules were still aberrant in structure. • Constitutive GA signalling mutants also form significantly fewer nodules than wild-type plants. This suggests that there is an optimum degree of GA signalling required for nodule formation and that the GA signal, and not the concentration of bioactive GA per se, is important for nodulation.

Intraspecific variation in growth and allocation patterns in seedlings of Pinus pinaster Ait. submitted to contrasting watering regimes: can water availability explain regional variation?

• Interpopulation variation in key functional traits of Pinus pinaster Ait. is well recognized. However, the relative importance of drought tolerance to explain this regional variation in the species remains elusive. • Here, we raise the question whether water availability constitutes a likely driver of regional variation in biomass allocation, growth and morphological traits of ten populations that cover the distribution range of P. pinaster. We carried out an experiment where seedlings of five families per population were submitted to two contrasting watering treatments. • The effects of water availability and population were significant for relative diameter and height growth rate, biomass allocation and number of lateral stems and dwarf shoots. Total dry mass significantly differed between watering treatments but it did not among populations. Populations could be clustered into four main groups. Root mass fraction explained most of the variation and significantly correlated to altitude but not to aridity. • The geographical pattern of genetic variation found in morphology and biomass allocation did not translate into population differences in drought tolerance or phenotypic plasticity to water availability, indicating that water availability is not a likely driver of the regional variation observed in the studied traits of P. pinaster at the seedling stage. Mots-cles : altitude / tolerance a la secheresse / Bassin mediterraneen / modeles mixtes / performance du plant entier