Plant Physiology - Musienko M. M. 2001

Physiology of Plant Reproduction
Sex Determination

Sex determination in angiosperms is the onset of readiness for The formation of floral Organs or even plant individuals of a particular sex. It depends both on genetic factors localized in Chromosomes (genetic sex determination) and on environmental and internal conditions (Phenotypic Sex determination). The flower is the reproductive organ in angiosperms. It is a shortened, unbranched SHOOT with determinate growth, whose leaves are modified for sexual reproduction. As reproductive organs, flowers can be unisexual (possessing only a pistil — a female flower, or only stamens — a male flower) or bisexual (possessing both stamens and a pistil). Plants in which unisexual flowers are borne on separate individuals (willow, poplar, hemp, mulberry, aspen) are called dioecious, whereas those that produce both male and female flowers on the same individual are called monoecious. Sexual Dimorphism, when present in dioecious plants, typically manifests only during the period leading up to flowering. This dimorphism is evident not only in Anatomical and morphological traits but also in the physiological and Biochemical characteristics of individuals of different sexes.

In many monoecious plants with diclinous flowers, male and female flowers or inflorescences develop on different PARTS OF THE stem. For example, under normal conditions in maize, male inflorescences form at the apex of the shoot, whereas female inflorescences (ears) develop in the leaf axils of the middle section of the stem.

The degree of sex expression (sexualization) in dioecious plants and unisexual flowers is a highly labile parameter dependent on environmental factors (light intensity and spectral composition, photoperiod characteristics, mineral Nutrition, gas COMPOSITION OF THE air, etc.). In many plants, not only floral evocation itself but also The Development of individual reproductive organs is under photoperiodic control. For instance, short days or reduced light intensity generally accelerate reproductive development, while also promoting female sexualization. Long days produce the opposite effect, thereby enhancing masculinization.

Sex regulation in unisexual plants is controlled by Phytochrome and is closely linked to the plant's phytohormonal status. It has been established that male sexualization is promoted by Gibberellins, whereas Cytokinins, Auxins, and Ethylene enhance female sexualization. The Mechanism of phytohormone action on sex expression is associated with altered activity of the Gene apparatus. Overall, sex in plants is regulated by both genetic and hormonal systems.

Recently (Yin, Quinn, 1991), a novel synthetic model for the physiological and generative Determination of Sex in plants has been proposed. This model involves a regulatory system consisting of a single hormone and two receptors. The first receptor inhibits the development of one sex, while the second induces The Emergence of the other. These factors interact in regulating the formation of a specific sex. Each possible relationship among these three factors corresponds to a naturally occurring sexual form. Thus, all existing sexual forms can be accounted for by these interactions. This model can be used to predict the physiological and GENETIC BASIS OF natural breeding systems, as well as to interpret data obtained from studies on individual species. The proposed model has been validated by experiments involving hormone Treatment of reproductive organs and the analysis of their endogenous levels in cucumber. In maize, the authors suggest that sex genes can be viewed as altering the hormonal balance through various pathways, thereby ensuring the development of different sexual forms. The model provides precise predictions of sex that can be tested using physiological, genetic, and molecular Methods.