Floral development of Dieffenbachia and the occurrence of atypical flowers in Araceae.

BACKGROUND: The floral development of Dieffenbachia seguine (N. J. Jacquin) Schott is analysed in relation to the molecular phylogeny of the Spathicarpae by Cusimano et al. (Am J Bot 98:654-668, 2011). RESULTS: The initiation of discoid floral primordia occurs acropetally on the surface of the spadix. Female flowers, atypical bisexual flowers, sterile male flowers, and male flowers share the same phyllotactic spirals on the spadix. Four or five stamen primordia are initiated simultaneously on the periphery of the male floral meristem. During early stages of stamen initiation, individual stamen primordia are connate at their base. In a synandrium, stamen fusion occurs very early during their developmental cycle with the stamens being already united laterally when longitudinal elongation occurs. The staminodes are also initiated on the periphery of the discoid floral primordium, and their number varies from four to six. The development of the fused staminodes will eventually form a longitudinal cavity in the center of the mature synandrode. The atypical flowers located in the intermediate zone range in morphology from aborted female flowers to rudimentary sterile male flowers with incomplete staminodes. CONCLUSIONS: The development of the female flower of Dieffenbachia Schott presents some similarities with atypical bisexual flowers of Cercestis Schott representing one of three types of aberrant flower forms in the family. From a developmental point of view and in the context of a phylogeny of the group, we believe that the presence of staminodes in the female zone constitutes a plesiomorphy in the tribe Spathicarpeae.

Quantitative developmental analysis of homeotic changes in the inflorescence of Philodendron (Araceae).

BACKGROUND AND AIMS: The inflorescence of Philodendron constitutes an interesting morphological model to analyse the phenomenon of homeosis quantitatively at the floral level. The specific goals of this study were (1) to characterize and quantify the range of homeotic transformation in Philodendron billietiae, and (2) to test the hypothesis that the nature of flowers surrounding atypical bisexual flowers (ABFs) channel the morphological potentialities of atypical bisexual flowers. METHODS: Inflorescences of P. billietiae at different stages of development were observed using SEM. The number of appendices in male, female and sterile flowers were counted on 11 young inflorescences (5-6 flowers per inflorescence). The number of staminodes and carpels on ABFs were counted on 19 inflorescences (n = 143). These data were used for regression and ANOVA analyses. RESULTS: There was an average of 4.1 stamens per male flower, 9.8 carpels per female flower and 6.8 staminodes per sterile male flower. There was an average of 7.3 floral appendices per atypical flower. Staminodes and carpels are inserted on the same whorl in ABFs. A negative exponential relationship was found between the average number of staminodes and the number of carpels in ABFs. If only the ABFs consisting of less than six carpels are considered, there is a linear relationship between the number of carpels and the average number of staminodes. The value of the slope of the regression equation indicates that on average, in P. billietiae, 1.36 carpels are replaced by one staminode. CONCLUSIONS: In P. billietiae, the number of appendages in female flowers imposes a constraint on the maximum total number of appendages (carpels and staminodes) that can develop on ABFs. The quantitative analyses indicate that the average number of different types of floral appendages on an ABF and the number of organs involved in a homeotic transformation are two independent phenomena.

Following the initiation and development of individual leaf primordia at the level of the shoot apical meristem: the case of distichous phyllotaxis in Begonia.

BACKGROUND AND AIMS: By using the technique of replicas of a developing apex it is possible to obtain a direct measure of phyllotactic parameters (plastochrone and platochronic ratio) involved in the initiation of two successive primordia at the level of the SAM. The goal of this study is to compare, in a real time setting, the value of phyllotactic parameters in distichous systems using Begonia as a case study, with the value of the same parameters in spiral phyllotactic systems. METHODS: To determine the real-time sequence of events at the level of the SAM, replicas were made of the developing apex at different intervals using previously described techniques. Impression moulds were made at 24-h intervals. The following phyllotactic parameters were measured: plastochrone, angle of divergence, plastochrone ratio and ratio between the diameter of the leaf and the apex. RESULTS: The time between the appearance of two successive leaves is 15-20 d. The average value of the plastochrone ratio (R) is 1.3, and the ratio of the leaf to the diameter of the apex (Gamma) is 2.5. The angle of divergence varies from 165 masculine to 180 masculine. The speed of advection of the primordium from the apex, varies from 0.28 to 0.37 microm d(-1). CONCLUSIONS: The speed of advection of primordia in Begonia is lower than that of Anagalis. This is not in accordance with theoretical simulations that predict the opposite. In Begonia, the plastochrone ratio does not reflect the real time of appearance of two successive primordia. The time separating the appearance of two primordia is not directly related to the distance of these two primordia from the centre of the apex but is related instead to the enlargement of leaves.

Complexity and information in regular and random phyllotactic patterns.

In biology, the theory of information has been used to study the degree of order of many living systems. Different concepts of entropy have been applied to the analysis of phyllotaxis. In the present paper we will determine the degree of order of disorganized patterns by using informational entropy concepts deduced from the work of Brillouin, Shannon, and Yagil. As case studies, we will apply these concepts of entropy to the disorganized patterns found in mutants of Arabidopsis. The calculation of entropy gives a precise idea of the degree of order of a phyllotactic system.

A stochastic approach to phyllotactic patterns analysis.

A statistical method is presented to characterize the degree of order in phyllotactic systems. We developed equations allowing the theoretical estimation of the number of leaves regularly distributed (spiral or verticillate) in a partially random phyllotactic system. The equations are simple and accurate enough to make quantitative predictions concerning the organization of different phyllotactic patterns (verticillate, distichous, spiral and random). This method can bring out patterns that are not visible a priori on a planar representation of the shoot apex. As a case study, the method was applied to the quantitative analysis of the sho mutants recently produced by Itoh et al. [2000. SHOOT ORGANIZATION genes regulate shoot apical meristem organization and the pattern of leaf primordium initiation in Rice. Plant Cell 12, 2161-2174]. By using our method, it was possible to predict the number of leaves distributed in distichous or random patterns on these phyllotactic mutants.

Classical and dynamic morphology: toward a synthesis through the space of forms.

In plant morphology, most structures of vascular plants can easily be assigned to pre-established organ categories. However, there are also intermediate structures that do not fit those categories associated with a classical approach to morphology. To integrate the diversity of forms in the same general framework, we constructed a theoretical morphospace based on a variety of modalities where it is possible to calculate the morphological distance between plant organs. This paper gives emphasis on shoot, leaf, leaflet and trichomes while ignoring the root. This will allow us to test the hypothesis that classical morphology (typology) and dynamic morphology occupy the same theoretical morphospace and the relationship between the two approaches remains a question of weighting of criteria. Our approach considers the shoot (i.e. leafy stem) as the basic morphological structural unit. A theoretical data table consisting of as many lines as there are possible combinations between different modalities of characters of a typical shoot was generated. By applying a principal components analysis (PCA) to these data it is possible to define a theoretical morphospace of shoots. Typical morphological elements (shoots, leaves, trichomes) and atypical structures (phylloclades, cladodes) including particular cases representing 'exotic' structures such as the epiphyllous appendages of Begonia and 'water shoot' and 'leaf' of aquatic Utricularia were placed in the morphospace. The more an organ differs from a typical shoot, the further away it will be from the barycentre of shoots. By giving a higher weight to variables used in classical typology, the different organ categories appear to be separate, as expected. If we do not make any particular arbitrary choice in terms of character weighting, as it is the case in the context of dynamic morphology, the clear separation between organs is replaced by a continuum. Contrary to typical structures, "intermediate" structures are only compatible with a dynamic morphology approach whether they are placed in the morphospace based on a ponderation compatible with typology or dynamic morphology. The difference in points of view between typology and continuum leads to a particular mode of weighting. By using an equal weighting of characters, contradictions due to the ponderation of characters are avoided, and the morphological concepts of continuum' and 'typology' appear as sub-classes of 'process' or 'dynamic morphology'.

Physical constraints on temperature difference in some thermogenic aroid inflorescences.

BACKGROUNDS AND AIMS: Thermogenesis in reproductive organs is known from several plant families, including the Araceae. A study was made of the relationship between temperature increase and spadix size in the subfamily Aroideae in order to determine whether the quantitative variation of heat production among species and inflorescences of different sizes follows a physical law of heat transfer. * METHODS: Spadix temperature was measured in 18 species from eight genera of tropical Araceae from the basal clade of Aroideae, both in French Guiana and in the glasshouses of the Montreal Botanical Garden. * KEY RESULTS: A significant logarithmic relationship was found between the volume of the thermogenic spadix zone and the maximum temperature difference between the spadix and ambient air. Four heat transfer models were applied to the data (conductive heat transfer alone, convective heat transfer alone, radiative heat transfer alone, and convective and radiative heat transfers) to test if physical (geometric and thermic) constraints apply. Which heat transfer model was the most probable was determined by using the criterion of a classical minimization process represented by the least-squares method. Two heat transfer models appeared to fit the data well and were equivalent: conductive heat transfer alone, and convective plus radiative heat transfers. * CONCLUSIONS: The increase in the temperature difference between the spadix and ambient air appears to be physically constrained and corresponds to the value of a thermal model of heat conduction in an insulated cylinder with an internal heat source. In the models, a heat metabolic rate of 29.5 mW g(-1) was used, which was an acceptable value for an overall metabolic heat rate in aroid inflorescences.

Statistical recognition of random and regular phyllotactic patterns.

AIMS: A statistical method used in ecology is adapted to characterize the degree of order in phyllotactic systems. SCOPE: The test consists of subdividing a planar projection of the stem apical meristem into 16 sectors and counting the number of primordia appearing in each. By dividing the sum of squared deviations by the mean number of primordia per sector the chi-square (chi2) is obtained. When there are a total number of 20 primordia, if the chi2 is less than 6.26, the phyllotaxis is spiral; if it is between 6.26 and 27.5 the phyllotaxis is random; and if it is greater than 27.5, the phyllotaxis is distichous or whorled (level of significance alpha = 5 %). It is also possible to remove one or more sectors. If there are k sectors, the two critical values delimiting the random zone will be found in a chi2 table for k - 1 degrees of freedom. CONCLUSIONS: The method is applied to the analysis of sho mutants described by Itoh et al. in 2000 (Plant Cell 12: 2161-2174). The results obtained are in agreement with the theoretical analysis showing that a whorled or spiral phyllotactic system may contain a certain number of randomly distributed elements without losing its regular global structure.

Intergeneric and infrafamilial phylogeny of subfamily Monsteroideae (Araceae) revealed by chloroplast trnL-F sequences.

The chloroplast trnL-F region was used as an independent data set for phylogenetic analysis of 118 aroid taxa. We investigated the intergeneric relationships of subfamily Monsteroideae (Araceae) and used this as a basis for an interspecific phylogenetic study of Rhaphidophora Hassk., the largest genus of the Monsteroideae. Results of the molecular tree were useful for inferring subfamilial and tribal circumscription and evolution in Araceae. Our results show that family Araceae consists of five clades that correspond to the subfamilies traditionally recognized. Starting from the most basal clade, these correspond to subfamilies Gymnostachydoideae and Orontioideae (proto aroids), with Lemna sp. (Lemnaceae) embedded in the Araceae and sister to the true aroids consisting of Pothoideae sister to Monsteroideae, immediately sister to Lasioideae and Aroideae. There is less agreement with existing tribal classifications. Complex relationships exist between members of the Monsteroideae. Our results show that Rhaphidophora and Epipremnum are paraphyletic with species of Rhaphidophora sampled, forming three informal groups with other genera of the Monstereae. Phylogenetic results may be used to suggest taxonomic changes to the current systematics of the monsteroids.

Study of homeosis in the flower of Philodendron (araceae): a qualitative and quantitative approach.

This study deals specifically with floral organogenesis and the development of the inflorescence of Philodendron squamiferum and P. pedatum. Pistillate flowers are initiated on the lower portion of the inflorescence and staminate flowers are initiated on the distal portion. An intermediate zone consisting of sterile male flowers and atypical bisexual flowers with fused or free carpels and staminodes is also present. This zone is located between the sterile male and female floral zones. In general, the portion of bisexual flowers facing the male zone forms staminodes, and the portion facing the female zone develops an incomplete gynoecium with few carpels. The incomplete separation of some staminodes from the gynoecial portion of the whorl shows that they belong to the same whorl as the carpels. There are two levels of aberrant floral structures in Philodendron: The first one is represented by the presence of atypical bisexual flowers, which are intermediates between typical female flowers and typical sterile male flowers. The second one is the presence of intermediate structures between typical carpels and typical staminodes on a single atypical bisexual flower. The atypical bisexual flowers of P. squamiferum and P. pedatum are believed to be a case of homeosis where carpels have been replaced by sterile stamens on the same whorl. A quantitative analysis indicates that in both species, on average, one staminode replaces one carpel.