Plant sex - Male, female and hermaphrodite plants: Sex determination by molecular methods (PCR and RAPD)

Most plants have both sexes in each specimen, but some have separate sexes, with male specimens, and other female specimens. The separation of sexes can occur between specimens of plants of some species, and also within specimens of the same species that can have male flowers and female flowers. In vertebrates (mammals, birds, reptiles, fish) there are X and Y sex chromosomes, but these chromosomes, although they have been searched in plants, have been in a few species where it has been possible to find XY chromosomes in male specimens and XX chromosomes in female specimens. (Silene latifolia, Asparragus Oficinalis, Humulus lupulus, Rumex acetosa, Cannabis sativa, among others). Likewise, some of the genetic loci that regulate the expression of masculinity and femininity in plants have been known.

The determination of the sex of the plants, to differentiate the masculine and the feminine ones, is important for their cultivation since, in some cases, only the feminine ones are of interest. In plants, the seeds are usually 50% male and 50% female, so only half of the seeds are of interest and those of one sex would have no interest, so it would be very useful to have methods that allow them to be differentiated. The advances in the genetic knowledge of the genes that participate in the determination of the sex of the plants offer methods to be able to know the sex when they have not yet expressed any characteristic of masculinity or femininity. In this way, in the species that only the female specimens are of interest, the male specimens can be discarded, with a sample as small as a leaf fragment.

In the development of plants, a vegetative phase and a flowering phase can be distinguished. In the vegetative phase the plant grows in size and height without differentiating sex, so they cannot be distinguished by their macroscopic phenotypic characteristics whether they are male or female. In some plants, after about 6 weeks of development, some phenotypic signs that orient towards the type of sex can begin to express themselves before the male or female flowers develop. In the flowering phase, the plant stops growing and devotes all the effort to the development of flowers giving rise to the sexual organs.

The male reproductive organs of the flowers are the pollen-loaded stamen, and the female reproductive organs are the carpels or egg-holding pistil). The insemination of plants is carried out using nature as an element of intercourse: the wind, animals like insects, water, which transport pollen to a female adherent stigma. Pollen grains germinate and grow progressively and slowly down towards the ovules.

There are two groups of plants, Gymnosperms and Angiosperms. The first, Gymnosperms, with naked ovules and of them there are with copies with both sexual organs, male and female, as occurs in 75% of all plants. The second, Angiosperms, flowering plants have the ovules inside an ovary. In these plants, the majority have in the same specimen the male sexual organs and the female sexual organs, while only a small number correspond to specimens with separate sexes in male and female specimens.

In general, most plants sprout bisexual flowers, with male and female parts, but sometimes they develop male flowers and separate female flowers. Others have both bisexual flowers and unisexual flowers. Plants with male flowers and bisexual flowers produce more seeds. The cause of this phenomenon is unknown, but it could be because male flowers consume less energy, which would be used to produce seeds.

When trying to classify plants according to their sex, it is usually spoken simply of male, female and hermaphrodite plants. However, the terminology, if we want to be more precise, must differentiate more complex situations, such as the following:

  • Monomorphic sexual plants (plants in which in the same specimen there are male and female sexual organs). These correspond to 75% of all plants. Within this group the following situations can be found:

Hermaphrodites. These plants have flowers with male and female sexual organs in the same flower. This situation is found in 90% of flowering plants (e.g. roses).

Monoecious: These plants have male flowers and female flowers. This situation is found in 5% of flowering plants, and in many gymnosperm plants (e.g. pines).

Gynomonoecious (male sterile). These plants have female flowers and hermaphrodite flowers (e.g. daisies).

Andromonoecious (female sterile). These plants have male flowers and hermaphrodite flowers.

This situation means that we should talk about co-sexual states for plants that have both sexual functions, either present in each flower (hermaphrodites), or in male and female (monoecious) flowers.

  • Sexual polymorphic plants (plants in which there are male and female specimens). These correspond to 25% of all plants.

Dioecious. These plants have specimens with separate sexes, that is, there are male and female plants. This situation is found in 5% of flowering plants and in some gymnosperms (e.g. nettle).

Ginodioecious. These plants have female specimens and hermaphrodite specimens (e.g. Plantago lanceolata, and Silene vulgaris).

Androdioecius. These plants have male specimens and hermaphrodite specimens. Very rare.

In plants the determination of sex depends on two loci, one of them responsible for the expression of the female organs, and others that participate in the activation of the development of the male organ. This means that in dioecious plants (specimens with different sexes), such as Silene latifolia, there are four whorls of reproductive organs, observing male and female floral meristems as occurs in any monolaic hermaphrodite species: sepals, petals, stamens and carpels. In the initial phase, meristems are similar in male plants and in female plants, that is, they are undifferentiated. When the primordia of the floral organs begin, the female organs of the meristem center are significantly smaller in the male plant, than in the female plant. In the male plant the male organs develop, while in the female plant the female organs develop and degenerate the beginnings of the male organs. The male genotype includes a female suppressor gene (SuF).

Molecular methods to determine the sex of plants

In the absence of clearly differentiated sex chromosomes in all plants, genetic differentiation of sex has had to be faced with other strategies, which can be applied to the study of any species of plant with sexual polymorphism (with sexes in different specimens; dioecious in general) before that express their phenotypic characteristics corresponding to each sex.

The general strategy to know the differential genetic markers is to perform a genetic test with random primers, in general, nucleotide decameters, by the RAPD method (Randomly Amplified Polymorphic DNA). With the random primers, genomic amplification of adult male and female specimens is performed. This genomic amplification will lead to multiple amplicons, which once electrophoretically separated in an agarose gel, will allow differentiating the patterns corresponding to male and female plants. With the RAPD method the SCAR (Sequence-Characterized Amplified Region) markers are obtained that allow one of the sexes to be identified. Once these regions of SCAR sequences have been identified, specific amplification procedures can be cloned, sequenced and procedures designed to identify the sex of the specimens.

There are markers of masculinity for several species: Silene latifolia, Humulus luoulus, Actinidia chinensis, Cannabis sativa, among others. In addition, there are femininity markers for several species: Pistacia vera, Actinidia sinensis, Salix viminalis, among others.

Tests performed in IVAMI

  • Determination of sex by molecular methods (PCR) for male sex genes (male plants), when the male MAD (Male-Associated DNA) sequences are known.
  • Sex determination of plants with sexual polymorphism (male and female) using RAPD (Random Amplified Polymorphic DNA) methods, for male or female sex genes, when they are not known.

Recommended samples:

  • Portion of leaf.

Sample submission:

  • Introduced in a sterile plastic container, and if possible refrigerated (polystyrene container –white cork-, with pack frozen), or frozen with dry ice.

Delivery of results:

  • Molecular methods: 48 to 72 hours.

Cost of the test:

  • Molecular detection (PCR): Consult to