Figure 1.
The analysis of Arabidopsis pedicel growth over time.
A. Comparison of wild type and er pedicel length over time demonstrates that while growth occurs for the same total time, er pedicels grow more slowly. During early pedicel development the length was determined by DIC microscopy of fixed samples (FS) and the age was decided based on the flower stage; n = 5–12. Starting from 1 mm for wt and 0.95 mm for er the length was measured in real time (RT) and averaged for 9 samples. The yellow star represents the time when fertilization occurred in the wild type. B. Pedicel elongation is exponential for the first 16 days. The best fit exponential growth curve is shown: l = 0.036e0.0132t for wt and l = 0.035e0.0106t for er. The y axis is a logarithmic scale. C. Pedicel growth depends on fertilization of flower; n = 6–7. D. Pedicel growth after 300 hours does not depend on the presence of SAM; n = 7–8. A–D Error bars were added to all data points and are ± SD. A–D Time zero is when a flower buttress arises on a meristem.
Table 1.
Characteristics of the three stages of pedicel growth in the wild type.
Figure 2.
Formation of meristemoids, guard mother cells, and stomata in the wild type and er pedicels.
Formation of meristemoids, guard mother cells and stomata in the wild type (A) and in er (B) over time. Comparison of stomata formation in the wild type and er suggests an early onset of differentiation but slower rate in er (C). Data points represent the fraction of a cell type in an individual pedicel. The pedicel age (h) was determined based on pedicel length as described in the text. The decrease in the number of meristemoids in er after 350 h (B) is due to cell elongation and not cell differentiation into GMCs.
Figure 3.
Changes of epidermal cell length in er pedicels versus the wild type over time.
A. The average size of epidermal cells in the wild type during pedicel growth. The insert demonstrates an increase of cell size at 250 h. B–D. Comparisons of epidermal cell sizes in er and the wild type during pedicel growth: the average cell size (B); the average size of 10% of the shortest cells (C); the average size of 10% of the longest cells (D). A–D. Every data point represents an average cell size in an individual pedicel. N = 35–125. Error bars are ± SD in A, C, D and SE in B. The pedicel age (h) was determined based on pedicel length as described in the text. The length of meristemoids, guard mother cells and stomata is excluded from the presented data.
Figure 4.
Analysis of epidermal cell size distribution in pedicels of different ages.
Data points represent the percentage of cells of a specified length with bins at 4 µm representing cells that are 4 µm or smaller, bin at 6 µm representing cells 4 to 6 µm long, etc. Bin widths for A and B are 2 mm. Bin widths for C and D are 4 µm. Data series represent pedicels of different ages and are color coded. Age of pedicels is given in hours (e.g. 100–190 h). The wild type cell size distribution is in A and C and er cell size distribution is in B and D. Number of cells in distributions 100–190 h and 190–240 h are between 479 and 983; 240–300 h and 300–340 h are between 964 and 1224; 340–400 h 2043 and 2681; >440 h 790 and 1364. The length of meristemoids, guard mother cells and stomata is excluded from the presented data.
Figure 5.
Average cell length along proximodistal axis and on abaxial and adaxial sides in wt pedicels.
In older pedicels (>4 mm) elongation of epidermal (A) and cortex (B) cells at the distal end of the pedicel significantly exceeds elongation at the proximal end. The difference in cell elongation along the proximodistal axis in pedicels attached to unfertilized flowers (labeled with a star) is dramatically reduced. Epidermal (C) and cortex (D) cells typically are slightly longer on the abaxial side of pedicels compared to the adaxial side. This difference in length is independent of pedicel age. A–D. n = 50–60 Error bars are ± SE.
Figure 6.
Changes of cortex cell length in pedicels over time.
A. The average size of cortex cells in the wild type. B. The average size of 10% of the shortest and 10% of the longest cortex cells in the wild type. C. The average size of cortex cells in er compared to the wild type. D. The average size of 10% of the shortest and 10% of the longest cortex cells in er over time. A–D. Every data point represents an average cell size in an individual pedicel. N = 35–125. Error bars are added to all data points except the wild type on C and they are ± SD. The pedicel age (h) was determined based on pedicel length as described in the text.
Figure 7.
Cortex cell size distribution in pedicels of different ages in the wild type and er.
Data points represent percentage of cells of specified length range, e.g. data point at 6 µm represents the percentage of cells 5 to 6 µm long. All bins are equal of 1 µm. The last bin on C, D and G represent cells >40 µm long. Data series represent pedicels of different ages and are color coded. Age of pedicels is given in hours (e.g. 100–190 h). The wild type cell size distribution is given in A and C and the er cell size distribution in B and D. Cortex cells from the wild type and er pedicels of the same age are compared in E, F and G. Number of cells in distributions: 100–190 h and 190–240 h between 327 and 757; 240–300 h and 300–340 h between 929 and 1020; 340–400 h 2098and 2856; >440 h 790 and 1364.
Figure 8.
Simulation of Arabidopsis pedicel cell size distributions over time.
Experimental data (symbols) and simulations (solid lines) of cortex and epidermal cell size distributions. The data for wild type cortex cells is in the left column, for er cortex cells in the middle column, for the wild type epidermal cells is in the top two graphs of right column, and for er epidermal cells is in the lower graph of the right column. Vertical lines at 10 µm are guides to the eye. Later times for epidermis were not simulated.
Table 2.
Best-fit simulation parameters: mean (μ) and sigma (σ) of the normal distribution specifying the length (mm) at which cells divide.
Figure 9.
Model of cell behavior in the cortex and epidermis during pedicel growth.
The model depicts timing of the events occurring in different layers with the horizontal axis representing time (h). Model for the wild type is in A and for er in B. Time zero corresponds to a flower buttress formation on a meristem. The darkness of blue coloring on symmetric cell division tag represents the rate of the cell cycle with darker color representing the faster rate. The narrowing of that tag represents gradual reduction in number of cell divisions. The three stage of pedicel growth are proposed based on observed cell behavior. The timing of all events is based on experimental data except the end of asymmetric cell divisions in the wild type that was inferred and the end of asymmetric cell divisions and GMC differentiation in er that are a rough approximation.