BackgroundCoccinia grandis is a dioecious species of Cucurbitaceae having heteromorphic sex chromosomes. The chromosome constitution of male and female plants is 22 + XY and 22 + XX respectively. Y chromosome of male sex is conspicuously large and plays a decisive role in determining maleness. Sex modification has been studied in hypogynous Silene latifolia (Caryophyllaceae) but there is no such report in epigynous Coccinia grandis. Moreover, the role of organ identity genes during sex expression in Coccinia has not been evaluated earlier. Investigations on sexual phenotypes of C. grandis including a rare gynomonoecious (GyM) form and AgNO3 mediated sex modification have added a new dimension to the understanding of sex expression in dioecious flowering plants.ResultsMorphometric analysis showed the presence of staminodes in pistillate flowers and histological study revealed the absence of carpel initials in male flowers. Though GyM plant had XX sex chromosomes, the development of stamens occurred in hermaphrodite flowers but the pollens were not fertile. Silver nitrate (AgNO3) application enhanced stamen growth in wild type female flowers like that of GyM plant but here also the pollens were sterile. Differential expression of CgPI could be involved in the development of different floral phenotypes.ConclusionsThe three principle factors, Gynoecium Suppression (SuF), Stamen Promoting Factor (SPF) and Male Fertility (mF) that control sex expression in dioecious C. grandis assumed to be located on Y chromosome, play a decisive role in determining maleness. However, the characteristic development of stamens in hermaphrodite flowers of GyM plant having XX sex chromosomes indicates that Y-linked SPF regulatory pathway is somehow bypassed. Our experimental findings together with all other previous chromosomal and molecular cytogenetical data strongly support the view that C. grandis could be used as a potential model system to study sex expression in dioecious flowering plant.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0325-0) contains supplementary material, which is available to authorized users.

Chromosome studies and soluble protein profiles, fractionated by reducing and non-reducing SDS-PAGE, were carried out in dioecious Trichosanthes bracteata. Somatic chromosome no. 2n = 22 was recorded in both sexes. The karyotype of male and female plant shows high homogeneity and the absence of any heteromorphic pair of chromosomes negates the possibility of XY mechanism. Soluble protein profiles from the tuberous roots of the male and female plants, fractionated by reducing SDS-PAGE, did not show any qualitative distinction. Whereas the protein profile in non-reducing SDS-PAGE reveals a clear distinction when compared on a single gel. The difference is marked by the presence of a disulphide linked tertiary or folded protein at 19 k D region detected in male sex. However, at the level of primary structure the qualitative expression is similar indicating a common ancestry.

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