The leaves are replaced by a whole new set at the end of dormancy in the spring. Sequential senescence is a feature of evergreen plants, particularly those that grow throughout the year. Leaves are continuously produced and shed in order of age. It then dies after setting seed However senescence occurs, the underlying changes are very similar. There is a switch from synthesis to breakdown of cell structure.
Photosynthesis declines as the chloroplast becomes a chromoplast .
Proteins and other polymers are broken down by digestive enzymes. In perennial plants some of the amino acids and other small molecules are withdrawn from the leaves before they are shed. In this way the plant recovers some of its investment. Senescing plant parts often produce ethylene and senescence is generally promoted by ethylene or ethylene-releasing compounds. One of the major uses of ethephon is to promote senescence of tobacco leaves prior to harvest.