Senescence of plant leaves

The senescence process allows for the termination of cells, tissues, organs or even organisms in a controlled process. Senescence is age dependent and under the control by hormonal, molecular, and genetical processes. Most people are familiar with the senescence process in plants through the colour changes and removal of tree leaves in the autumn, or the decay of leaves and transfer of nutrients to seeds in crop species such as Maize.

Leaf Senescence

The last stage in leaf development is senescence, this involves both leaf decay and a removal of the nutrients that are stored in the leaves to other parts of the plant. Although overall leaf senescence occurs at the organ level but is heavily influenced by cellular and organismal fate. Although it may look like leaf senescence just happens and has little regulation it is a controlled altruistic process that requires changes in gene expression, metabolism and ultimately cell structure.

Changes that occur during leaf senescence

Leaf senescence involves age dependent programmed cell death. One of the major changes that occur during senescence of the leaf involves the breakdown of the chloroplast; this results in a major change in the cell structure. As the chloroplast is rich in protein it is important this source is not lost but utilised by other parts of the plant. In addition to changes in cell structure major metabolic changes occur during leaf cell senescence; the normal processes that occur in the leaf involving carbon assimilation are stopped, and new metabolic processes that involve the catabolism of proteins, chlorophyll, and lipids occurs. This allows the nutrients of the leaf to be broke down and exported out of the leaf and used to further the development of the plant in other areas.

Leaf Senescence is beneficial to plants

Although one may think of cell death as being a non beneficial process it is not. It leads to better control of the nutrients that are available to the plant, and allows these to be used at the correct time (such as a transfer of effort to seed development), to give the plant an evolutionary advantage.

The next section on leaf senescence takes a look at the control of leaf senescence and its coordination.