GENETIC AND HORMONAL REGULATION OF GROWTH, FLOWERING, AND SEX EXPRESSION IN PLANTS

Abstract

The interaction of the genetic and hormonal regulation of growth, flowering, and sex expression in plants is discussed. The genetic control of these processes is characterized, and data on their hormonal regulation are supplied. The interaction of genetic and hormonal regulation is considered with reference to tall‐growing and genetic dwarf forms of the pea and wheat plants. It is shown that in the dwarf forms of the pea plant and in many other varieties, growth stimulation in response to treatment with the phytohormone gibberellic acid is clearly manifested and the expression of genetic dwarfism is eliminated, whereas in dwarf wheats it is expressed only slightly, if at all. At the same time both tall‐growing and dwarf forms of both pea and wheat show a clearly defined growth retardation response to treatment with the growth inhibitor, abscisic acid, which causes the expression of physiological dwarfism. The short‐ and long‐day characteristics of the photoperiodic response of plants are described as genetically controlled features, and data are given on the induction of flowering of a long‐day variety coneflower grown under short‐day conditions with the aid of gibberellins extracted from leaves of long‐day vegetative plants of short‐day Mammoth tobacco. Data are also supplied on the induction of flowering of a short‐day variety, red‐leaved goosefoot, grown under continuous light with the aid of metabolites extracted from leaves of the same Mammoth tobacco plants flowering under short‐day conditions. This demonstrates the possibility of hormonal regulation of the genetically controlled long‐day and short‐day characteristics in photoperiodically sensitive plants. Genetic and hormonal regulation of sex expression in two dioecious plants, hemp and spinach, is discussed. It is shown that sex expression in these plants is regulated by gibberellins which are synthesized in leaves and cause male sex expression and by cytokinins which are synthesized in the roots and cause female sex expression. These data indicate that sex expression in dioecious plants is the result of interaction between the genetic apparatus and phytohormones.