Senescence is an important developmental process in plants. It is also an important factor in agriculturally important plants, limiting their biomass and altering their nutritional value, thus affecting yields. It is a regulated physiological process that can take place at different levels of the biological system: cells, tissues, organs and the whole plant. Leaf senescence involves programmed cell death and transport of nutrients from ageing and dying tissues to storage and overwintering tissues. The used substances accumulate in the dead cells. The most visible sign of leaf senescence is yellowing of the leaves, which is a result of the breakdown of pigment-protein complexes in the chloroplasts. Leaf senescence is stimulated or inhibited by various biotic (viruses, fungi, bacteria, herbivores (insects)) and abiotic factors (change in temperature, nutrient deficiency, drought, heavy metals, light intensity). Leaf senescence allows pathogenic organisms to easier exploit plant nutrients therefore infections by pathogens are often associated with delayed senescence, nutrient accumulation at the infection sites and growth changes. The entire course, initiation and even termination of senescence is governed by complex regulatory pathways and mechanisms influenced by both internal and external factors. Functional and transcriptomic genetic studies report that the expression of many ageing-related genes is altered during the ageing process by genetic reprogramming. NAC, WRKY, MYB and AP2/ERF are known as key transcription factors that activate and regulate senescence gene expression in response to abiotic and biotic stresses affecting the plant.
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