ГЕНЕТИКА, 2012, том 48, № 4, с. 556-560
КРАТКИЕ СООБЩЕНИЯ
УДК 577.22:582.579.2
ONTOGENY OF FLOWER PARTS ON NATURALLY GROWING Iris pumila CLONES: IMPLICATIONS FOR POPULATION DIFFERENTIATION AND PHENOTYPIC PLASTICITY STUDIES
© 2012 N. Barisic Klisaric, S. Avramov, D. Miljkovic, U. Zivkovic, A. Tarasjev
Institute for Biological Research,University of Belgrade, 11000 Belgrade, Serbia e-mail: tarasjev@yandex.ru, tarasjev@ibiss.bg.ac.rs Received June 09, 2011
Previous studies revealed significant phenotypic plasticity, genetic variability and population differentiation of flower morphometric traits on dwarf bearded iris Iris pumila. Also, study of I. pumila flowering phenology revealed significant impact of habitat type as well as population differentiation for flowering time. Since the flowering time can influence other flower traits, we performed this analysis of flower morphometric traits in three time points during the flower bud ontogenic development in two habitat types (open vs. shaded). Analysis revealed that for most of the traits greater trait values were recorded for open habitat but only on latter time points. For most of the analyzed traits direction of differences in bud stage was the opposite to the direction of differences in mature flower stage detected in previous studies. However, length of the stem, a trait that showed the greatest variability between habitats and populations and therefore greatest genetic differentiation and phenotypic plasticity, was significantly greater in the samples from the late flowering shaded habitat in all time samples, indicating that in case of this trait different mechanisms were involved. Those findings have implications for design of the future studies on I. pumila.
Evolution of adaptations depends not only on genetic variation that leads to between population differentiation for traits in question but also on their phenotypic plasticity [1—4] so choice of appropriate model system on which all those aspects can be studied simultaneously is extremely important. On the other hand ontogenic aspect must also be covered since plasticity in plants can be a result of direct response of a trait to environmental cues during the development, or a passive result of changes of plant growth rate due to various factors [1, 5, 6] with phenological response influencing other traits being a significant one [7, 8].
In dwarf bearded iris — Iris pumila L. existence of both clonal and sexual reproduction enables implementation of various experimental designs including various crossings (full-sib, half-sib) as well as transplantation ones. Coupled with huge flower color polymorphism that enables identification of genetically distinct clones even on the small distances and significant amount of genetic variability both within and among populations, they represent main advantages of this model system [9, 10]. These characteristics enabled various studies of phenotypic plasticity and developmental instability, genetic variability and between population differentiation, on a range of I. pumila traits, including floral ones. Several studies on morphology at flowering dwarf bearded iris I. pumila L. were previously conducted on plants and populations of this perennial monocot from open and shaded localities in Natural Protected Reserve of Deliblato Sand [9—15] as well as on plants in different flowering
seasons [10, 11, 15]. Results of comparison of plants occupying open and shade habitats were mostly consistent with responses expected in the case of so called "shade avoidance syndrome" [10, 16—18]. On the other hand, previous study of I. pumila phenology revealed significant phenotypic plasticity as well as differentiation for flowering time in populations occupying those contrast habitats [12] so possible influence of flowering time on detected differences in flower traits in previous studies must also be examined.
Therefore, goals of this study were to analyze mor-phometric flower traits in different time periods of flower ontogeny on naturally growing clones of I. pumila occupying contrasting light habitats (open vs shade) in order to:
analyze traits at different time points during the flower bud ontogenetic development in order to detect time when significant differences between clones occupying different habitats occur;
compare detected differences in flower bud stages between clones from two habitats with differences detected in previous studies that used plants in flowering stage;
evaluate those findings to differentiate between passive plasticity that is result of difference in flowering time and plasticity as an active shade avoidance response.
This study was conducted in Deliblato Sand, a protected sandy area 40 km NE from Belgrade, Serbia (44°48' N, 20°58' E), on naturally growing clones in two I. pumila populations. Chosen populations occupy
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contrasting natural habitats (Dune and Woodland) that were utilized in previous studies. First one is open habitat with plants exposed to direct sunlight, while the second is shaded habitat (forest) created under anthropogenic influence. The Dune and the Woodland sites are located in the northwestern part of Deliblato Sand and the distance between them is approximately 0.5 km (estimated by GPS Personal Navigator eTrex Vista™, Garmin Ltd.).They differ in many ecological indices [19], foremost in quality and intensity of light. In sand-steppe habitat, radiation intensity is 666.1 ^mol m-2 s-1 and red/far red ratio (R/FR) is 1.16 ((E) estimated with LiCor 1000 (D) adata logger and Li190SA and Skye SKR-110 sensors). On Woodland site, clones of I. pumila grow in the vegetation shade (radiation intensity of 170.9 ^mol m-2 s-1 and R/FR ratio of 0.96).
On three dates before I. pumila flowering onset, the ramets with flower buds were collected on naturally growing clones (3 ramets per date from the 30 clones in each habitat). Collection dates were separated by three-day periods with no flower bud collections. All measurements on vegetative and floral parts were made to the nearest millimeter using fresh material. Following traits were utilized in this analysis: leaf length (LL), leaf width (LW), length of the first spathe (LIS), length of the second spathe (LIIS), stem length (LS), ovary length (OL), ovary width (OW), tube length (TL), tube radius (TR), fall length (FL), fall width (FW), beard length (BL), standard length (SL), standard width (SW), stigma length (SML), crest length (CL), crest width (CW), stamen length (STL) and anther length (AL). Detailed descriptions of parts of I. pumila flower as well as their graphical representation are given in Tarasjev et al., 2009 [10]. Morpho-metric data were transformed to natural logarithms as the appropriate transformation determined by the method given by Box et al. [20] and SAS programme given by Fernandez [21]. Since 19 traits were utilized in single analysis and the Type I statistical error can be inflated, the sequential Bonferroni test was applied [22]. In order to compare differences detected in this study with trait contribution to overall variability detected in previous studies, scores on first two canonical components form Canonical Discriminant Analysis on the data from Tarasjev et al. study (details on sample and procedure can be found in [10]) of morpho-metric variability in flowering stage between open vs. shade habitats, populations and flowering seasons was utilized. All statistical analyses were performed by the SAS statistical package [23] with PROC MEANS, PROC GLM and PROC CANDISC procedures.
Results of analysis of morphometric traits in flower bud stage are presented in Table 1. Fifteen out of nineteen analyzed traits showed significant differences between localities, while for LW, OL, OW, and TL showed no significant differences at any analyzed time point prior to flowering. Almost all significant differences turned to be a consequence of higher trait values
in the open habitat (the only exception being the stem length). This direction (higher trait values in open habitat) was opposite to the direction detected in studies on open flowers, where morphometric traits had higher values in shade habitat [10] where they flower later [12]. Most of the traits showed significant differences only in the latter phases of flower bud development (LL, LIS, LIIS, FL, STL, CL, CW, SML, and AL) while for couple of them difference was detected in all three points in time (LS, FW and SW)
These results indicate that significant differences previously detected in open flower phase [10] must include reversal of the direction of the difference (higher values in open habitat in bud stage to higher trait values in shaded habitat in open flower stage) for most of the analyzed traits. This reversal must occur within short period of time - according to Tarasjev study [12] difference between those two habitats in flowering onset ranged from eight to fifteen days in three analyzed flowering seasons. In case of those traits environmental or genetic variation may differ depending on whether comparisons are conducted among individuals of the different stages [24]. However, their response is reasonably similar (Table 1). Moreover, positive and high loadings on first component for analyzed traits in the previous study [10] presented in Table 2 also suggest that their response was mostly similar and connected with general size, with some exception for flower part widths (high loadings on the second axis). In future evolutionary ecology and ecological genetics studies on I. pumila, this set of traits therefore can be reduced to a set with much fewer traits (that will include at least one trait measuring length and at least one measuring width of flower parts) and should include flowering time as the important variable. On the other hand, length ofthe stem was showing the same pattern of difference in all flower bud stages and i
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