Normal and Abnormal Development in the Arabidopsis Vegetative Shoot Apex

Abstract

Vegetative development in the Arabidopsis shoot apex follows both sequential and repetitive steps. Early in development, the young vegetative meristem is flat and has a rectangular shape with bilateral symmetry. The first pair of leaf primordia is radially symmetrical and is initiated on opposite sides of the meristem. As development proceeds, the meristem changes first to a bilaterally symmetrical trapezoid and then to a radially symmetrical dome. Vegetative development from the domed meristem continues as leaves are initiated in a repetitive manner. Abnormal development of the vegetative shoot apex is described for a number of mutants. The mutants we describe fall into at least three classes: (1) lesions in the shoot apex that do not show an apparent alteration in the shoot apical meristem, (2) lesions in the apical meristem that also (directly or indirectly) alter leaf primordia, and (3) lesions in the apical meristem that alter meristem size and leaf number but not leaf morphology. These mutations provide tools both to genetically analyze vegetative development of the shoot apex and to learn how vegetative development influences floral development.

Complexity in Differential Peptide–Receptor Signaling: Response to Segonzac et al. and Mueller et al. Commentaries

“…We tested the growth conditions described in their Commentary, which involve the use of 24-well plates, and found that the seedlings were stressed and exhibited delayed development compared with ours, which might explain the severely retarded shoot development in their CLV3p-treated seedlings and the relatively flat SAM they observed even in clv3 seedlings. Furthermore, our seedlings were grown in liquid medium at higher temperature (27˚C compared with 22˚C) and constant light (compared with 16-h light) during bacterial infection, which likely explains the more advanced SAM development in wild-type and clv3 seedlings that we observe (Medford et al, 1992;Bowman, 1993;Fiers et al, 2006;Kinoshita et al, 2010;Lee et al, 2011) but was not observed by Segonzac et al (2012).…”

“…In their Commentary, Segonzac et al (2012) report that they were not able to observe the characteristically enlarged vegetative SAM and Pseudomonas syringae pv tomato (Pst) DC3000-GFP (for green fluorescent protein) infection in the clv3 seedlings (Medford et al, 1992;Bowman, 1993;Fiers et al, 2006;Kinoshita et al, 2010;Lee et al, 2011) and argue from first principles that it would not be possible for P. syringae to infect the SAM. However, Segonzac et al (2012) used very different conditions for growing seedlings when they attempted to repeat our bacterial infection experiments.…”

The Argonaute family: tentacles that reach into RNAi, developmental control, stem cell maintenance, and tumorigenesis

“…ago1 mutants exhibit numerous phenotypic abnormalities such as radialized leaves, abnormal infertile flowers with filamentous structures resembling small squid (thus the name Argonaute), and in some cases shoot apical meristem defects (Bohmert et al 1998;Lynn et al 1999). It should be noted that mutants affecting the shoot apical meristem, around which leaves are initiated and patterned, are known to produce abnormal leaf phenotypes (Medford et al 1992). AGO1 was subsequently shown to be necessary for post-transcriptional silencing of transgenes as well as for cosuppression of transgenes and their corresponding homologous endogenous genes (Fagard et al 2000).…”

Developmental and age-related processes that influence the longevity and senescence of photosynthetic tissues in arabidopsis.

“…The fifth and sixth leaves of the rosette represent the first consistently adult leaves of the Ler strain (as defined for the Wassilewskija strain by Medford et al, 1992). Under the culture conditions used, individual leaves progressed through full expansion to maturity followed by a period of progressive leaf yellowing and, finally, a degeneration and complete desiccation of the tissue.…”