Patterns of cell division and expansion in developing petals of Petunia hybrida

Abstract

The definition of the patterns of cell division and expansion in plant development is of fundamental importance in understanding the mechanics of morphogenesis. By studying cell division and expansion patterns, we have assembled a developmental map of Petunia hybrida petals. Cycling cells were labelled with in situ markers of the cell cycle, whereas cell expansion was followed by assessing cell size in representative regions of developing petals. The outlined cell division and expansion patterns were related to organ asymmetry. Initially, cell divisions are uniformly distributed throughout the petal and decline gradually, starting from the basal part, to form a striking gradient of acropetal polarity. Cell areas, in contrast, increased first in the basal portion and then gradually towards the petal tip. This growth strategy highlighted a cell size control model based on cell-cycle departure time. The dorso-ventral asymmetry can be explained in terms of differential regulation of cell expansion. Cells of the abaxial epidermis enlarged earlier to a higher final extent than those of the adaxial epidermis. Epidermal appendage differentiation contributed to the remaining asymmetry. On the whole our study provides a sound basis for mutant analyses and to investigate the impact of specific (environmental) factors on petal growth.

Cell Division and Expansion in Petals during Flower Development and Opening in <i>Eustoma grandiflorum</i>

“…Petunia petals are composed of limb and tube, which are equivalent to blade and claw, respectively, in Eustoma petals. Reale et al (2002) Abaxial epidermal cells were elongated in shape at all stages (Fig. 4), suggesting that cell shape is largely determined at a very early stage of floral development.…”

“…Thus, it is unclear whether cell division and expansion progress simultaneously at various petal parts. Reale et al (2002) investigated cell division of petals by in situ hybridization using two markers, cyclin and histone 4 genes, during flower development in petunia. They showed that cell divisions are uniformly distributed throughout the petal initially and decline gradually, starting from the basal part (Reale et al, 2002).…”

“…Reale et al (2002) investigated cell division of petals by in situ hybridization using two markers, cyclin and histone 4 genes, during flower development in petunia. They showed that cell divisions are uniformly distributed throughout the petal initially and decline gradually, starting from the basal part (Reale et al, 2002). By using their method, modes of cell division and expansion can be understood in detail in Eustoma petals.…”

Downregulation of the Petunia hybrida α-Expansin Gene PhEXP1 Reduces the Amount of Crystalline Cellulose in Cell Walls and Leads to Phenotypic Changes in Petal Limbs

“…In leaves, PhEXP1 mRNA levels were very low, and in anthers, the transcript levels were barely detectable ( Figure 1B). A developmental map of P. hybrida petals previously has been defined that describes the patterns of cell division and expansion throughout 14 different developmental stages (Reale et al, 2002). During the first three stages of petal development, growth is sustained by cell divisions that are uniformly distributed in the apical and basal portion of the petal.…”

“…In a previous study, we defined a developmental map of Petunia hybrida (petunia) petals by analyzing the expression of in situ cell cycle markers and by reconstructing the pattern of cell expansion through measurement of cell size (Reale et al, 2002). During flower development, floral organs typically assume their final shape long after the major mitotic activity has ceased, indicating that cell expansion plays an important role in determining organ shape (Pyke et al, 1991;Tsuge et al, 1996).…”