PNL Volume 17 1985

RESEARCH REPORTS

A GENE FOR FLOWER DOUBLING IN PISUM

Gottschalk, W. Institute for Genetics

University of Bonn, Federal Republic of Germany

The flowers of the X-ray induced recessive mutant 175 of our

collection are doubled. Doubling is due both to an increase in the

number of petals in the corolla and to the formation of petal-like

organs in the staminate whorl. The later the flowers are formed the

higher is their degree of doubling. Most of the stamens have petal-like

appendices of varying size and shape. Sometimes these organs carry a

rudimentary anther with predominantly sterile pollen grains. The ovary

is mostly open; style and stigma are present but ovules are absent.

Thus, the mutant is both male and female sterile.

The gene causes an additional anomaly: from many growing points,

inflorescence-like organs develop instead of single flowers (Fig. 1).

Differentiation begins normally in the basal region of these growing

points, forming a normal calyx, a doubled corolla, and a corolla-like

staminate whorl. The pistil, however, shows a stronger reduction as

compared to the same organ in the single flowers of the mutant. It is

completely open and has a petal-like shape; only a narrow centrally lo-

cated sector consists of carpel tissue. In this way, the basic flower

of such an "inflorescence" is formed. A second t lower is produced from

the same growing point sitting on a short stalk, but there is no calyx

and no pistil in most of these apical flowers and the number of petals

and petal-like stamens is reduced.

More rarely even three�flowered inflorescences are produced from

such growing points. Their middle flower is strongly reduced, con-

sisting mostly of a single petal only. Calyx, staminate, and pistillate

cycles are lacking. Also the apical flower is reduced but not to such a

high degree. There is no calyx and the staminate and pistillate cycles

are mostly absent. The whole flower consists exclusively of petals the

number of which is somewhat higher than In normal pea flowers. In a few

cases, even five strongly reduced flowers were different Lated from a

single growing point. The uppermost two or three flowers of these "in-

florescences" were small, consisting only of a large number of scale

like leaflets without any specific characteristics.

The differentiation of the growing points of this mutant is a very

labile process resulting in flowers or even inflorescence-like organs

which differ from each other in many details even within the same plant.

This lability is interpreted as variable expressivity of the mutant

gene. In all those cases in which inflorescences are produced, distinct

regions of the growing points remain meristematic whereas other regions

undergo some degree of differentiation. Later these meristematic zones

produce somatic tissues in the form of small stalks. Finally, their

apical regions differentiate into flowers. As a consequence of this

"fractionated differentiation", not the usual single flowers but reduced

inflorescences arise from the respective growing points.

20 PNL Volume 17 1985 RESEARCH REPORTS

Fig. 1. Flowers of mutant 175

Left: Inflorescence with two flowers derived from

a single growing point. The calyx of the lower

flower was removed; the second flower, sitting

on a short stalk, comes from the central region

of that calyx.

Right: Inflorescence with three flowers derived

from a single growing point. Most of the lower

flower was removed. The middle flower consists

only of a single petal opposite to the leaf-

like carpel of the lowest flower. Between these

two organs, the stalk is discernible carrying

theapical flower inside the petal of the middle

flower.



PNL Volume 17 1985	RESEARCH REPORTS	19

A GENE FOR FLOWER DOUBLING IN PISUM Gottschalk, W. Institute for Genetics University of Bonn, Federal Republic of Germany The flowers of the X-ray induced recessive mutant 175 of our collection are doubled. Doubling is due both to an increase in the number of petals in the corolla and to the formation of petal-like organs in the staminate whorl. The later the flowers are formed the higher is their degree of doubling. Most of the stamens have petal-like appendices of varying size and shape. Sometimes these organs carry a rudimentary anther with predominantly sterile pollen grains. The ovary is mostly open; style and stigma are present but ovules are absent. Thus, the mutant is both male and female sterile. The gene causes an additional anomaly: from many growing points, inflorescence-like organs develop instead of single flowers (Fig. 1). Differentiation begins normally in the basal region of these growing points, forming a normal calyx, a doubled corolla, and a corolla-like staminate whorl. The pistil, however, shows a stronger reduction as compared to the same organ in the single flowers of the mutant. It is completely open and has a petal-like shape; only a narrow centrally lo- cated sector consists of carpel tissue. In this way, the basic flower of such an "inflorescence" is formed. A second t lower is produced from the same growing point sitting on a short stalk, but there is no calyx and no pistil in most of these apical flowers and the number of petals and petal-like stamens is reduced. More rarely even three�flowered inflorescences are produced from such growing points. Their middle flower is strongly reduced, con- sisting mostly of a single petal only. Calyx, staminate, and pistillate cycles are lacking. Also the apical flower is reduced but not to such a high degree. There is no calyx and the staminate and pistillate cycles are mostly absent. The whole flower consists exclusively of petals the number of which is somewhat higher than In normal pea flowers. In a few cases, even five strongly reduced flowers were different Lated from a single growing point. The uppermost two or three flowers of these "in- florescences" were small, consisting only of a large number of scale like leaflets without any specific characteristics. The differentiation of the growing points of this mutant is a very labile process resulting in flowers or even inflorescence-like organs which differ from each other in many details even within the same plant. This lability is interpreted as variable expressivity of the mutant gene. In all those cases in which inflorescences are produced, distinct regions of the growing points remain meristematic whereas other regions undergo some degree of differentiation. Later these meristematic zones produce somatic tissues in the form of small stalks. Finally, their apical regions differentiate into flowers. As a consequence of this "fractionated differentiation", not the usual single flowers but reduced inflorescences arise from the respective growing points.