To develop a growing root, cell division in the root meristem has to be properly regulated in order to generate or propagate new cells. How cell division is regulated in the root meristem remains largely unknown. Here, we report the identification and characterization of the Arabidopsis (Arabidopsis thaliana) RETARDED ROOT GROWTH (RRG) gene that plays a role in the regulation of root meristem c...

Cytokinins and gibberellins (GAs) play antagonistic roles in regulating reproductive meristem activity. Cytokinins have positive effects on meristem activity and maintenance. During inflorescence meristem development, cytokinin biosynthesis is activated via a KNOX-mediated pathway. Increased cytokinin activity leads to higher grain number, whereas GAs negatively affect meristem activity. The GA...

The process of organ positioning has been addressed, using the pin-formed 1 (pin1) mutant as a tool. PIN1 is a transmembrane protein involved in auxin transport in Arabidopsis. Loss of function severely affects organ initiation, and pin1 mutants are characterised by an inflorescence meristem that does not initiate any flowers, resulting in the formation of a naked inflorescence stem. This pheno...

BACKGROUND In all multicellular organisms, the links between patterning genes, cell growth, cell cycle, cell size homeostasis, and organ growth are poorly understood, partly due to the difficulty of dynamic, 3D analysis of cell behavior in growing organs. A crucial step in plant organogenesis is the emergence of organ primordia from the apical meristems. Here, we combined quantitative, 3D analy...

Maintenance of indeterminacy is fundamental to the generation of plant architecture and a central component of the plant life strategy. Indeterminacy in plants is a characteristic of shoot and root meristems, which must balance maintenance of indeterminacy with organogenesis. The Petunia hybrida HAIRY MERISTEM (HAM) gene, a member of the GRAS family of transcriptional regulators, promotes shoot...

Upon seed germination, apical meristems grow as cell division prevails over differentiation and reach their final size when division and differentiation reach a balance. In the Arabidopsis root meristem, this balance results from the interaction between cytokinin (promoting differentiation) and auxin (promoting division) through a regulatory circuit whereby the ARR1 cytokinin-responsive transcr...

The aerial architecture of plants is determined primarily by the pattern of shoot branching. Although shoot apical meristem initiation during embryogenesis has been extensively studied by molecular genetic approaches using Arabidopsis, little is known about the genetic mechanisms controlling axillary meristem initiation, mainly because of the insufficient number of mutants that specifically alt...

In order to separate the effects of size and meristem maturation on age-related changes in shoot growth behaviour, a reciprocal grafting experiment was conducted involving juvenile (J), mid-age (MA) and old-growth (OG) red spruce (Picea rubens Sarg.) trees as both scion donors and rootstock. The effects of rootstock and scion age on vegetative growth, foliar morphology and reproductive developm...

The tassel seed mutations ts4 and Ts6 of maize cause irregular branching in its inflorescences, tassels, and ears, in addition to feminization of the tassel due to the failure to abort pistils. A comparison of the development of mutant and wild-type tassels and ears using scanning electron microscopy reveals that at least four reproductive meristem types can be identified in maize: the inflores...

Regulating the transition of meristem identity is a critical step in reproductive development. After the shoot apical meristem (SAM) acquires inflorescence meristem identity, it goes through a sequential transition to second- and higher-order meristems that can eventually give rise to floral organs. Despite ample information on the molecular mechanisms that control the transition from SAM to in...