Stages Of Primordium Development Research Articles

The GLV6/RGF8/CLEL2 peptide regulates early pericycle divisions during lateral root initiation.

Small peptides of the Arabidopsis GLV/RGF/CLEL family are involved in different developmental programmes, including meristem maintenance and gravitropic responses. In addition, our previous report suggested that they also participate in the formation of lateral roots. Specifically, GLV6 is transcribed during the first stages of primordium development and GLV6 overexpression results in a strong reduction of emerged lateral roots. To investigate the cause of this phenotype we analysed primordium development in gain-of-function (gof) mutants and found that GLV6 induces supernumerary pericycle divisions, hindering the formation of a dome-shaped primordium, a prerequisite for successful emergence. The GLV6 phenotype could be reproduced by ectopic expression of the gene only in xylem-pole pericycle cells. Furthermore, GLV6 seems to function at the very beginning of lateral root initiation because GLV6 excess—either gene overexpression or peptide treatment—disrupts the first asymmetric cell divisions required for proper primordium formation. Our results suggest that GLV6 acts during lateral root initiation controlling the patterning of the first pericycle divisions.

Influence of clavata3-2 mutation on early flower development in Arabidopsis thaliana: quantitative analysis of changing geometry.

Early development of the flower primordium has been studied in Arabidopsis thaliana clavata3-2 (clv3-2) plants with the aid of sequential in vivo replicas and longitudinal microtome sections. Sequential replicas show that, although there is no regular phyllotaxis in the clv3-2 inflorescence shoot apex, the sites of new primordium formation are, to a large extent, predictable. The primordium always appears in a wedge-like region of the meristem periphery flanked by two older primordia. In general, stages of primordium development in clv3-2 are similar to the wild type, but quantitative geometry analysis shows that the clv3-2 primordium shape is affected even before the CLAVATA/WUSCHEL regulatory network would start to operate in the wild-type primordium. The shape of the youngest primordium in the mutant is more variable than in the wild type. In particular, the shape of the adaxial primordium boundary varies and seems to be related to the shape of the space available for the given primordium formation, suggesting that physical constraints play a significant role in primordium shape determination. The role of physical constraints is also manifested in that the shape of the primordium in the later stages, as well as the number and position of sepals, are adjusted to the available space. Longitudinal sections of clv3-2 apices show that the shape of surface cells of the meristem and young primordium is different from the wild type. Moreover, there is only one tunica layer in both the meristem and in the primordium until it becomes a bulge that is distinctly separated from the meristem. Starting from this stage, the anticlinal divisions predominate in subprotodermal cells, suggesting that the distribution of periclinal and anticlinal cell divisions in the early development of the flower primordium is not directly affected by the clv3-2 mutation.

Patterns of Auxin Transport and Gene Expression during Primordium Development Revealed by Live Imaging of the Arabidopsis Inflorescence Meristem

Plants produce leaf and flower primordia from a specialized tissue called the shoot apical meristem (SAM). Genetic studies have identified a large number of genes that affect various aspects of primordium development including positioning, growth, and differentiation. So far, however, a detailed understanding of the spatio-temporal sequence of events leading to primordium development has not been established. We use confocal imaging of green fluorescent protein (GFP) reporter genes in living plants to monitor the expression patterns of multiple proteins and genes involved in flower primordial developmental processes. By monitoring the expression and polarity of PINFORMED1 (PIN1), the auxin efflux facilitator, and the expression of the auxin-responsive reporter DR5, we reveal stereotypical PIN1 polarity changes which, together with auxin induction experiments, suggest that cycles of auxin build-up and depletion accompany, and may direct, different stages of primordium development. Imaging of multiple GFP-protein fusions shows that these dynamics also correlate with the specification of primordial boundary domains, organ polarity axes, and the sites of floral meristem initiation. These results provide new insight into auxin transport dynamics during primordial positioning and suggest a role for auxin transport in influencing primordial cell type.

Cell population dynamics in Coprinus cinereus: co-ordination of cell inflation throughout the maturing basidiome

Cell sizes were measured in microscope sections of fruit bodies of Coprinus cinereus whose temporal development was defined by the stage they had reached in meiosis and sporulation. Comparison of length/width ratios suggested that in pre-meiotic stages of primordium development, stipe elongation was more due to cell proliferation than inflation. Major inflation was a post-meiotic event and could account for all the basidiome expansion involved in maturation. Inflation of cells in the pileus was closely correlated with inflation of cells in the stipe. These studies provide new data about the spatiotemporal co-ordination of basidiome tissue development and indicate that some form of long range signalling system exists.

Scanning Electron Microscope Studies on Fruitbody Primordium Formation inAgaricus Bisporus

To obtain specimens suitable for viewing the early stages of development in Agaricus bisporus, we modified the Halbschalentest method. A plastic foam, impregnated with peat moss, enabled examination ofthe mycelium throughout its entire depth by scanning electron microscopy. Early in the developmental sequence, single hyphae with infrequent branches appeared. As development progressed, the hyphae were consolidated into strands by adhesive, mucilaginous substances. These substances formed electronlucent sheets which were especially obvious after the mycelium was watered. The initial stage of primordium formation was marked by appearance of hyphae which were turgid and tended to curve sharply and branch frequently. These hyphae were found in both initial and later stages of primordium development. Primordia that continued to increase in size appeared to recruit hyphae and strands from surrounding mycelium.