Toward a 3D model of phyllotaxis based on a biochemically plausible auxin-transport mechanism

AbstractPolar auxin transport lies at the core of many self-organizing phenomena sustaining continuous plant organogenesis. In angiosperms, the shoot apical meristem is a potentially unique system in which the two main modes of auxin-driven patterning— convergence and canalization—co-occur in a coordinated manner and in a fully three-dimensional geometry. In the epidermal layer, convergence points form, from which auxin is canalized towards inner tissue. Each of these two patterning processes has been extensively investigated separately, but the integration of both in the shoot apical meristem remains poorly understood. We present here a first attempt of a three-dimensional model of auxin-driven patterning during phyllotaxis. We base our simulations on a biochemically plausible mechanism of auxin transport proposed by Cieslak et al. (2015) which generates both convergence and canalization patterns. We are able to reproduce most of the dynamics of PIN1 polarization in the meristem, and we explore how the epidermal and inner cell layers act in concert during phyllotaxis. In addition, we discuss the mechanism by which initiating veins connect to the already existing vascular system.Author summaryThe regularity of leaf arrangement around stems has long puzzled scientists. The key role played by the plant hormone auxin is now well established. On the surface of the tissue responsible for leaf formation, auxin accumulates at several points, from which new leaves eventually emerge. Auxin also guides the progression of new veins from the nascent leaves to the vascular system of the plant. Models of auxin transport have been developed to explain either auxin accumulation or auxin-driven venation. We propose the first three-dimensional model embracing both phenomena using a unifying mechanism of auxin transport. This integrative approach allows an assessment of our present knowledge on how auxin contributes to the early development of leaves. Our model reproduces many observations of auxin dynamics. It highlights how the inner and epidermal tissues act together to position new leaves. We also show that an additional, yet unknown, mechanism is required to attract new developing veins towards the main vasculature of the plant.

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Ontogenetic Changes in Auxin Biosynthesis and Distribution Determine the Organogenic Activity of the Shoot Apical Meristem in pin1 Mutants

International Journal of Molecular Sciences ◽

10.3390/ijms20010180 ◽

2019 ◽

Vol 20 (1) ◽

pp. 180 ◽

Cited By ~ 3

Author(s):

Alicja Banasiak ◽

Magdalena Biedroń ◽

Alicja Dolzblasz ◽

Mateusz Adam Berezowski

Keyword(s):

Shoot Apical Meristem ◽

Apical Meristem ◽

Auxin Transport ◽

Vascular System ◽

Auxin Biosynthesis ◽

Wild Type ◽

Ontogenetic Changes ◽

Auxin Distribution ◽

Stem Development ◽

Knockout Mutation

In the shoot apical meristem (SAM) of Arabidopsis, PIN1-dependent polar auxin transport (PAT) regulates two crucial developmental processes: organogenesis and vascular system formation. However, the knockout mutation in the PIN1 gene does not fully inhibit these two processes. Therefore, we investigated a potential source of auxin for organogenesis and vascularization during inflorescence stem development. We analyzed auxin distribution in wild-type (WT) and pin1 mutant plants using a refined protocol of auxin immunolocalization; auxin activity, with the response reporter pDR5:GFP; and expression of auxin biosynthesis genes YUC1 and YUC4. Our results revealed that regardless of the functionality of PIN1-mediated PAT, auxin is present in the SAM and vascular strands. In WT plants, auxin always accumulates in all cells of the SAM, whereas in pin1 mutants, its localization within the SAM changes ontogenetically and is related to changes in the structure of the vascular system, organogenic activity of SAM, and expression levels of YUC1 and YUC4 genes. Our findings indicate that the presence of auxin in the meristem of pin1 mutants is an outcome of at least two PIN1-independent mechanisms: acropetal auxin transport from differentiated tissues with the use of vascular strands and auxin biosynthesis within the SAM.

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The shoot apical meristem and development of vascular architectureThis review is one of a selection of papers published on the Special Theme of Shoot Apical Meristems.

Canadian Journal of Botany ◽

10.1139/b06-126 ◽

2006 ◽

Vol 84 (11) ◽

pp. 1660-1671 ◽

Cited By ~ 33

Author(s):

Nancy G. Dengler

Keyword(s):

Arabidopsis Thaliana ◽

Shoot Apical Meristem ◽

Apical Meristem ◽

Leucine Zipper ◽

Vascular Tissue ◽

Vascular System ◽

Expression Patterns ◽

Three Dimensional ◽

Integrative Model ◽

Class Iii

The shoot apical meristem (SAM) functions to generate external architecture and internal tissue pattern as well as to maintain a self-perpetuating population of stem-cell-like cells. The internal three-dimensional architecture of the vascular system corresponds closely to the external arrangement of lateral organs, or phyllotaxis. This paper reviews this correspondence for dicotyledonous plants in general and in Arabidopsis thaliana (L.) Heynh., specifically. Analysis is partly based on the expression patterns of the class III homeodomain-leucine zipper transcription factor ARABIDOPSIS THALIANA HOMEOBOX GENE 8 (ATHB8), a marker of the procambial and preprocambial stages of vascular development, and on the anatomical criteria for recognizing vascular tissue pattern. The close correspondence between phyllotaxis and vascular pattern present in mature tissues arises at early stages of development, at least by the first plastochron of leaf primordium outgrowth. Current literature provides an integrative model in which local variation in auxin concentration regulates both primordium formation on the SAM and the first indications of a procambial prepattern in the position of primordium leaf trace as well as in the elaboration of leaf vein pattern. The prospects for extending this model to the development of the complex three-dimensional vascular architecture of the shoot are promising.

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Imagens meméticas e a comunic(ação) na web: um experimento analítico, reflexões e aplicabilidades acerca do discurso multimodal do Facebook

Texto Livre Linguagem e Tecnologia ◽

10.17851/1983-3652.8.2.54-68 ◽

2015 ◽

Vol 8 (2) ◽

pp. 54-68

Author(s):

Claudia dos Santos Gomes

Keyword(s):

Social Networks ◽

Political Discourse ◽

Presidential Elections ◽

Three Dimensional ◽

Integrative Approach ◽

Dimensional Model ◽

Three Dimensional Model ◽

Political Messages ◽

The Relationship ◽

The Web

RESUMO:Ampliando-se nosso foco de estudo sobre a relação entre História e imagens, passa-se, a partir deste trabalho, a observar como as imagens vêm se prestando a externar mensagens de cunho político, desde as eleições presidenciais de 2014 no Brasil, quando se nota o aumento das mensagens de caráter dicotômico entre “direita e esquerda”. Tendo em vista a importância das imagens para a comunicação, busca-se analisar essa manifestação do discurso político imagético nas redes sociais, mais especificamente no Facebook, no âmbito de um evento digital disseminado na Web, a partir de uma proposta de análise de orientação linguística (SOUZA JÚNIOR, 2015a; 2015b; 2015c; 2015d). Nesse sentido, a partir do estudo de duas unidades de propagação (imagens disseminadas), este artigo propõe a análise desse tipo de mensagem dentro dos eventos digitais identificados por nós como “Coxinha” e “Petralha”. Utilizou-se o Modelo Tridimensional de Análise (FAIRCLOUGH, 2003; SOUZA JÚNIOR, 2013; 2015c) como metodologia, associado à Abordagem Integradora (SOUZA JÚNIOR, 2015a; 2015b). Os resultados da análise das imagens evidenciaram disputas político-ideológicas como uma prática propagada por meio de recursos tecnológicos e discursivo-imagéticos.PALAVRAS-CHAVE: discurso; política e propagação digital; imagens meméticas e multimodalidade; ensino de História e imagens meméticas. ABSTRACT:Expanding our focus of study on the relationship between History and images, this article observes how images have been expressed political messages since the 2014 Brazilian presidential elections, when it is possible to observe the increase of dichotomous messages between "right” and “left". Given the importance of images for communication, this article analyzes this pictorial way of manifesting political discourse on social networks, specifically on Facebook, regarding the spread of such manifestations as a digital event disseminated on the Web. This study makes use of a Linguistics-oriented proposal of analysis (SOUZA JUNIOR, 2015a; 2015b; 2015c; 2015d). Accordingly, by examining two units of propagation (disseminated images), the article suggests the study of this type of message within the scope of the digital events identified as "Coxinha” and “Petralha". This investigation uses the Three-dimensional Model of Analysis (FAIRCLOUGH, 2003; SOUZA JUNIOR, 2013; 2015c) as a methodology in association with the Integrative Approach (SOUZA JUNIOR, 2015a; 2015b). Results of analysis revealed political-ideological dispute as a propagated practice through technological and discursive-pictorial resources.KEYWORDS: discourse; politics and digital propagation; memetic images and multimodality; teaching of History and memetic images.

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