Abstract
BackgroundThe Arabidopsis outer ovule integument is a simple two-cell layered structure that grows around the developing embryo and develops into the outer layer of the seed coat. As one of the functions of the seed coat is the protection of the plant embryo, the outer ovule integument is an example for a plant organ whose morphogenesis has to be precisely regulated.ResultsTo better characterise outer ovule integument morphogenesis, we have isolated some marker lines that show GFP expression in this organ. We have used those lines to identify distinct cell types in the outer integument and to demonstrate similarities between leaves and the outer integument. Using confocal microscopy, we showed that cell sizes and shapes differ between the two cell layers of the outer integument. Expression of KNAT1 in the integuments leads to extra cell divisions specifically in the outer layer of the outer integument. This is being compensated for by a decrease of cell volume in this layer, thus showing that mechanisms exist to control proper ovule integument morphogenesis.ConclusionThe Arabidopsis outer ovule integument can be used as a good model system to study the basic principles of plant organ morphogenesis. This work provides new insights into its development and opens new possibilities for the identification of factors involved in the regulation of cell division and elongation during plant organ growth.
Highlights
The Arabidopsis outer ovule integument is a simple two-cell layered structure that grows around the developing embryo and develops into the outer layer of the seed coat
In seed coats of seeds that contained walking stick stage embryos, green fluorescent protein (GFP) expression in three of the lines (KS059, KS110, KS151) was seen throughout the outer layer of the outer integument, one line (KS149) showed expression in both outer integument cell layers, and two lines (M214, M237) showed GFP expression that was restricted to the micropylar end of the outer layer of the outer integument
To describe GFP expression patterns in those four lines we will follow a recent suggestion by Skinner et al [15]
Summary
The Arabidopsis outer ovule integument is a simple two-cell layered structure that grows around the developing embryo and develops into the outer layer of the seed coat. As one of the functions of the seed coat is the protection of the plant embryo, the outer ovule integument is an example for a plant organ whose morphogenesis has to be precisely regulated. The two integuments grow around the nucellus and, after fertilization, develop into the seed coat that encloses the embryo (Figure 1). Whereas the inner integument initially develops as a radially symmetrical structure that surrounds the nucellus, the outer integument grows only from the side of the ovule primordium that faces the basal end of the carpel (gynobasal side) [1,2]. At later stages of seed development, cells of the abaxial (outer) layer of the outer integument differentiate termi-
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