Cell Division and Expansion Growth during Rose Petal Development

Abstract

There have been few reports on the morphology of flower opening, despite its horticultural significance. It is not clear when cell division stops during rose petal development or what changes occur in cell morphology. This study aims to clarify the details of cell morphological changes during rose petal development. Rose (Rosa hybrida L. 'Sonia') petals were sampled in six flower bud stages. Cell morphological changes were observed by light microscopy, transmission and scanning electron microscopy using cross sections of the petals, and the number of epidermal cells was measured using Nomarski differential interference contrast microscopy. The number of epidermal cells increased with flower opening, but the rate of increase in the number of abaxial epidermal cells slowed down at an earlier stage than in adaxial epidermal cells. The increase in the epidermal cell area was much more rapid in later stages compared with the increase in cell number, suggesting that petal growth in later stages is mainly due to cell expansion. During flower opening, the unique expansion of spongy parenchyma cells produced large air spaces. Epidermal cells of the upper part showed obvious lateral expansion. In particular, marked expansion of adaxial epidermal cells with enlargement of the central vacuole was observed. Differences in the patterns of cell expansion among cell types and locations would contribute to the reflex of petals during rose flower opening.

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

“…In G. grandiflora (Koning, 1984) and T. caerulea (Norikoshi et al, 2013), only two phases have been observed: cell division and expansion, and cell expansion. In rose petals, similar findings have been reported, although cell division continues in the final stage of flower opening (Yamada et al, 2009b). It is unclear whether the presence of the four phases is specific to Eustoma.…”

“…This finding suggests that stored starch is degraded to soluble carbohydrates because large amounts of soluble carbohydrates are required for flower opening in Eustoma (Shimizu and Ichimura, 2005). The disappearance of plastids has also been observed in rose petals (Yamada et al, 2009b). Similarly, a decrease in starch content in petals has been reported in rose (Evans and Reid, 1988;Ho and Nichols, 1977) and gladiolus (Yamane et al, 1991).…”

“…Cell division of adaxial and abaxial epidermal cells terminates at the same stage in T. caerulea (Norikoshi et al, 2013). In contrast, the division of both adaxial and abaxial epidermal cells in rose continues even when flowers have opened completely (Yamada et al, 2009b). Thus, patterns of cell division and expansion during flower opening vary depending on the plant species.…”

“…4). In the petals of several other flowers, such as morning glory (Yoshida et al, 2003), rose (Yamada et al, 2009b), snapdragon (Jackson et al, 1992), and wallflower (Weston and Pyke, 1999), adaxial epidermal cells also show conical-papillate shapes at the open stage. Changes in cell shape during flower opening have also been reported in rose (Yamada et al, 2009b) and wallflower (Weston and Pyke, 1999).…”

“…In Gaillardia grandiflora (Koning, 1984) and Tweedia caerulea (Norikoshi et al, 2013), the division of petal cells stopped before flower opening and petal growth associated with flower opening was due to cell expansion. However, cell division in rose did not stop in open flowers, and petal growth during flower opening was due mainly to cell expansion (Yamada et al, 2009b).…”