Three-dimensional formation of corolla shapes in relation to the developmental distortion of petals in Eustoma grandiflorum

Associations between petal growth patterns and the formation of three-dimensional corolla shapes were investigated using five cultivars of Eustoma grandiflorum with different corolla shapes. The cultivars showing outward curvature in the distal regions of petals exhibited rapid distal petal widening during the later stages of flower opening, whereas the cup-shaped cultivars exhibited rapid widening in the basal to middle regions of petals during earlier stages of flower development. In a funnel-shaped cultivar showing no apparent curvature, no regional differences in petal expansion were found. Distal petal widening was not due to cell widening but was the result of the rapid expansion both in width and length of petal cells, whereas basal expansion was partly due to cell widening. The data obtained suggested that non-uniform cell expansion within a petal resulted in petal distortion, and this played a central role in corolla curvature of E. grandiflorum.

► Petal expansion patterns were compared among cultivars with different corolla shapes.
► Bell-shaped cultivars showed a rapid widening in distal petal regions.
► Cup-shaped cultivars showed a rapid widening in the basal to middle region.
► Non-uniform cell expansion within a petal resulted in petal distortion.
► Petal distortion played a central role in corolla curvature formation.