Volume 60 - Tomato Genetics Cooperative - University of Florida

flowers have smaller and lighter green petals and anthers and longer filaments (Fig 1;
Petrova et al 1998). In addition to tomato nuclear male sterility mutants (reviewed in
Gorman and McCormick 1997) ), similar changes of flower structures have been
reported for tomato plants grown at low temperatures (Lozano et al. 1998) and in lossof-function
transgenic plants for the B-class genes required for petal and stamen
identity (De Martino et al. 2006).
The size of plant organs is determined by cell division and cell expansion and
elongation. Our investigation of the size of epidermal cells shows that the smaller size of
the anthers in the CMS line (Fig. 1; Stoeva-Popova et al., unpublished) can be
explained largely by the reduction in the size of the cells. The epidermal cells on both
surfaces of the CMS anther were significantly smaller in comparison to S. pennellii:
respectively 51% smaller on the adaxial side, and 42.3% on the abaxial surface. On
the other hand, no corresponding effect of cytoplasmic male sterility on cell size in the
petals was observed On the abaxial surface of the petals of CMS line, the cells were
81.5% larger than in S. pennellii, while on the adaxial side, they were 32.2 % smaller.
According to our measurements (Stoeva et al., unpublished data) the CMS-pennellii
filaments are several magnitudes longer than the filaments of S. pennellii (Fig. 1). This
is not merely a consequence of increased cells size, as the filament epidermal cells of
CMS are statistically larger than those of S. pennellii only on the abaxial side. CMSpennellii
and S. pennellii share the same nuclear genome and cytoplasmic male sterility
affects expression of nuclear genes ( reviewed in Linke, Börner 2005, Chase 2006). Our
results above show that cytoplasmic male sterility does not equally affect the
development of petals, stamens and filaments.
Our study has shown that there are significant differences in the size of
epidermal cells between the two species: the red-fruited cultivated tomato and the
green-fruited S. pennellii. Significant differences were determined for the epidermal cells
of the anthers and petals. The epidermal cells of the anthers of the cultivated tomato
were larger, which is an indication that the anthers of S. pennellii have greater number
of epidermal cells. The same conclusion could be drawn from the study of the abaxial
epidermal cells of the petals and the filaments. Since the two species are not closely
related it will be interesting to investigate other representatives of the tomato clade and
to determine if the size of epidermal cells of flower structures can be indicative of
species relatedness.
Although no statistical analysis was carried out, our data show one consistent
feature across all genotypes: the largest epidermal cells were observed on anthers,
while the ones with the smallest surface area were epidermal cells of petals.
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