Plant Senescence and Organ Abscission

Abstract Senescence is a complex, genetically regulated, and inevitable program. During senescence, biochemical and physiological changes occur that result in nutrient deficiency in a plant's organs or the whole plant and ultimately lead to death of the affected tissue. However, nutrients can be relocalized to other parts of the plant if senescence is going on in a particular organ, such as leaves and fruits. Abiotic stresses such as drought, salinity, waterlogging, high and low temperature, air pollutants, and nutrient deficiencies negatively regulate senescence. All these stresses results in disturbances of highly complex and endogenously regulated systems of the plants, thereby promoting senescence. Shedding of plant leaves, petals of the flower, the whole flower, and fruitlets are the characteristics of abscission. This separation of plant organs from the main plant body occurs when either there is an injury due to biotic/abiotic stress or as a regular process in plant growth and development. It occurs in a specialized zone called the abscission zone ( AZ ) at the junction of plant body and the organ. The cells in the AZ can be morphologically, physiologically, and cytologically different from the adjacent cells. Abscission starts with the breakdown of the middle lamella of the cells in the AZ, which results in the separation of organs from the plant body. The pattern and type of organ abscission differ among plant species, which may be due to adaptation to a specific environment or evolutionary pressure. Plant hormones such as ethylene, auxin, cytokinin (CK), abscisic acid (ABA), and jasmonic acid (JA) play pivotal roles in the mechanism and regulation of senescence and abscission. In this chapter, general aspects, mechanisms, and roles of plant hormones play in the regulation of senescence and abscission has been described.