Gender is the product of long-term biological evolution and an important symbol of higher biological evolution. In higher plants, the vegetative body itself rarely shows obvious female and male characteristics, but it has specialized female or male reproductive organs. The sex of hermaphroditic plants is difficult to determine, because they have pistils and stamens in the same flower, so the sex of higher plants is mainly aimed at hermaphroditic plants (also known as hermaphroditic plants) and hermaphroditic plants. The female and male reproductive processes of these plants are completed in different parts of the plant or on different individual plants, and the structure of female and male reproductive organs shows obvious differences. Studies in cytogenetics and molecular genetics show that sex determination in higher plants is not only influenced by sex-determining genes, but also related to sex chromosomes. The sex of some plants is also controlled by the ratio between sex chromosomes and autosomes possessed by recipient cells.
1, monoecious plants and their sex determination
Monogamous plants refer to plants that can produce unisexual female flowers and unisexual male flowers on the same plant, such as corn, with male inflorescence (male ear) at the top and female inflorescence (female ear) in the leaf axils. In this kind of plants, although the process of female reproduction and male reproduction is completed in different parts, because the female flowers and male flowers are born on the same plant at the same time, the gender difference is limited to the flower organs and still belongs to monoecious plants. The study on the sex determination mechanism of these plants shows that although these plants are monoecious like hermaphroditic plants, the formation mechanism of their reproductive organs is very different: the formation of female flowers and male flowers in monoecious plants is controlled by different genes, which are called sex determination genes, and the number of sex determination genes in different plants is different. The sex of some plants is controlled by a pair of sex-determining genes, such as Cucurbitaceae of Cucurbitaceae and spinach of Oryzaceae, that is, female, male or bisexual plants are determined by three alleles at a single locus.
The sex determination of some plant species is related to multiple gene loci, such as some plants in Cucurbitaceae. The sex of cucumber is regulated by multiple unlinked gene loci.
To sum up, the sex determination of monoecious plants is regulated by specific sex determination genes. Plants regulate the development process of their sexual organs through the expression of sex-determining genes at the development level, and then form functional specific sexual organ structures. The existence and expression of sex-determining genes in different plants are different, which leads to sex polymorphism in monoecious plants.
2. Sex determination of monoecious plants.
The male and female flowers of monoecious plants are planted on different plants, and there are female and male plants according to their flower organs. The results of cytogenetic research show that most dioecious plants have sex chromosomes, and the different combinations of sex chromosomes and the interaction between sex chromosomes and autosomes determine the sex of plants.
(1) Sex chromosomes determine sex.
The existing research data show that in most dioecious plants, males are usually heterozygous (XY) and females are homozygous (XX), that is, they belong to XY sex determination. In this mode of sex determination, the sex chromosomes of most plants are not equal in morphology. For example, Silene plants have sex chromosomes of different sizes and shapes. In Silene, the genetic composition of diploid plants is 2ndi (24, X Y), heterozygosity (XY) is male, resulting in unisexual male flowers, homozygosity (XX) is female, resulting in unisexual female flowers.
⑵, X-staining Hugh/autosomal ratio determines sex.
Although some dioecious plants also have sex chromosomes, their sex is not entirely determined by sex chromosomes. In the process of evolution, these plants adopted the sex determination system of X chromosome/autosome ratio to determine sex. The gene balance between X heterozygote and autosome determines the sex of plants, which is similar to that of Drosophila. Typical examples are Spartinaceae and Cannabiaceae, such as Rumex, Spiraea, Cannabis, Hops and so on. Hops of Humulus is strictly monoecious, 2n=( 20, X Y). But sometimes sterile male flowers are formed on female plants, and it is found that the reason is related to the ratio of X chromosome to autosome in plant somatic cells. When the value of X chromosome/autosome is 0.5 or lower, the individual phenotype of the plant is male; When the ratio is 1.0 or higher, the individual phenotype is female.
Some plants are strictly dioecious. Because of the small number of chromosomes in their somatic cells, it is difficult to distinguish sex chromosomes, so their sexual mechanism is still not clear.
Sex determination mechanism is the theoretical basis for human beings to control biological sex, which has important application value in agricultural production and people's life. For example, the breeding and utilization of crop male sterile lines are closely related to the sex formation of plants; In order to obtain the seeds and fruits of Ginkgo biloba, we hope to have all kinds of female plants. When Ginkgo biloba is used as a street tree, this male plant is more beautiful. In order to improve the quality of flax fiber, more flax male plants are needed. Therefore, in order to meet the needs of human production and life, it is necessary to study the sex determination mechanism at the molecular level and seek ways and methods to control plant sex.
Analysis from other angles is as follows:
(1) Chromosome Determination of Plant Sex
Since the discovery of plant chromosomes in 1923, more than 70 species of plants belonging to 25 families have contained sex chromosomes. Most plants that determine sex by sex chromosomes are dioecious, and their sex is determined by the combination of male and female gametes. The sex determination of such plants has the following forms.
1. This type of XX-XY plants with sex determination include hemp, hops, spinach, ginkgo, Cyclobalanopsis, etc. This type of sex determines that female plants are homozygous (XX) and male plants are heterozygous (XY). Most of the plants studied belong to the sex determination of XX-XY chromosome.
2.XX-XO, a sex-determined female plant, is homozygous (XX) and the male plant lacks matching (XO). Zanthoxylum bungeanum belongs to this type of sex determination. Male plants have two gametes: n=34+X and 34+O, while female plants have only one gamete: n = 34+x.
3.ZW-ZZ homozygous ZZ is male and ZW heterozygous ZW is female. Pineapple-shaped strawberries belong to this type of sex determination.
4.X/Y balance sex is determined by the x and y balance of sex chromosomes, but y plays a stronger role. Ruluo:
5.x/a balanced sex is determined by the balance between sex chromosome x and autosomal a, and y chromosome does not affect gender performance. Such as Rumex:
6. Decisive proof of sex chromosome 1948 Westergan proved the role of Y chromosome in determining men. According to the research, the X and Y chromosomes of plants in the genus Caesalpinia are obviously different in size. X is smaller than y, but both are larger than autosomes. Y chromosome has four regions: inhibition region, initiation region, fertility region and region homologous to X chromosome. Studies have shown that when the inhibitory region is missing, a complete flower will be produced; The promoter region is missing, and the original male plant becomes a female plant; When the fertility zone is missing, male sterile plants will be formed. Most of the genes that determine women are located on the X chromosome.
Kbhtko.K.B used hemp as experimental material to verify the homomorphism and heteromorphism of XX-XY sex-determined gametes. There are two methods for verification: one is self-pollination after sex conversion (that is, under certain conditions, male plants or female plants produce heterosexual flowers or bisexual flowers, and then self-pollination); The second is to cross monoecious plants and hermaphroditic plants respectively.
(2) Genetic determination of plant sex
Plant traits are controlled by genes, and gender is no exception. There are several ways in which sex genes control sex.
1. Single gene determination 1943. Rick and Hanna once proposed and proved that the sex of asparagus is controlled by a single gene. The male gene combination is M__, the female gene combination is mm, and M is dominant to M..
2. Double genes determine that the sex control of corn, grapes and other plants belongs to this category. The stable allele bsbs of maize can make the plant only have tassels, while Cheng Xiong plants; The spike allele tsts can make the male spike become a female spike and bear fruit, becoming a female plant. A new population of dioecious maize. Genotype bsbsTs__ and genotype bsbsTs (or BS _ _ TS) can form a new dioecious maize population. In the mixed population of genotypes BSBSBSBSBSSTS and BSBSBSBSBSSTS, the ratio of female to male plants in offspring can be kept stable at1:1.
3. Multiple alleles determine the sex of oriental strawberry and watermelon through three alleles.
4. Multiple genes determine the sex of cucumber, which is controlled by multiple genes. For example, genotype acr acrG__ determines monoecious plants, ACR-G _ _ determines female plants, ACR ACGG determines male plants, ACR-GG determines fully flowering plants, ACR-AA determines male plants, and Tr determines bisexual plants.
5. The gene balance determines the sex of papaya, which is determined by the gene balance of F, F and Fh. These genes are located on the homologous chromosomes of Hofemegr sex chromosome M 65438+M 65438+M 1 respectively, and the locus Fh is the repetition of F and F (see table). M 1M 1, M 1M2 and M2M2 are lethal gene combinations.
(3) Sex-linked inheritance of plants
There are few species of plants with sex-linked genetic characteristics, only plants of the genus Lysimachia, the male plant is XY and the female plant is XX. There are two leaf shapes of Loucai: broad leaf and thin leaf. The B and B alleles controlling leaf shape are located at the differentiation site of X chromosome, and the pollen with Xb is lethal.