Senescence in the life-cycle

Plants deploy the programmed senescence and elimination of cells throughout growth, differentiation and responses to the environment, from germination through vegetative and reproductive development. Amongst the developmental and adaptive events in which programmed senescence and death are decisive are:

• Selective deletion of cells destined to form male or female parts during development of unisexual flowers.
• Cell elimination during pollen and egg cell production, post-meiotic development of the micro- and mega-sporophye and degeneration of suspensor cells during embryo differentiation.
• ”Mummification” of starchy endosperm cells in maturing cereal grains and death of aleurone cells during germination.
• Lysigenic elimination of cell contents and groups of cells during formation of xylem, sclerenchyma, periderm, epidermal hairs, spines, oil glands, latex canals and so forth.
• Generation of complex organ forms by localised cell death as seen in, for example, Monstera and lace plant leaves.
• Senescence of laterals, including leaves, roots, flower parts and the tissues of ripening fruits, and schizogenous shedding of parts by cell death and separation in abscission layers.
• Abiotic stress responses such as formation of aerenchyma under anaerobic conditions.
• Hypersensitive and other senescence and death responses in hosts subject to biotic challenge.