How is leaf senescence assayed?

Leaf senescence is advantageous to plants as it allows nutrients to be passed from an area where they are no longer required to areas where nutrients are required, such as in the development of seeds. The process of senescence is age related and coordinated by both internal and external stimuli. The senescence process consists of a programmed cell death the cell to keep functioning until the last possible moment, and therefore allowing the maximum amount of nutrients to be removed possible. There are many molecular and genetic processes that are involved in the senescence process and these have both similarities and differences with other programmed cell processes. To further understand the processes behind senescence many assays have been developed.

Assaying Leaf Senescence

When molecularly and genetically assaying the differences between senescence and other cell processes it is important to consider two main points.

1. Many parameters must be assayed when looking at leaf senescence as many processes are known to be involved.
2. Only single leaves can be measured, as senescence is age related; different leaves on the same plant will be of different ages.

Understanding senescence requires the use of many biological markers, these include:

1. Leaf Yellowing, a sign of mesophyll cell senescence
2. Photochemical efficiency
3. Ion leakage
4. Chlorophyll content
5. Protein levels
6. Expression of known senescence stimulated genes
7. Expression of senescence stimulated enzymes

Some common methods (linked to the above) used in measuring senescence include assaying the activation of RNAase and peroxidase; measuring decrease in chlorophyll levels; measuring ion linkage from membranes; measuring the expression level of the genes CAB2, RBC and SAG. The changes in gene expression levels that occur during senescence can be measured by Northern blotting, qRT-PCR or by use of microarrays. These methods help senescence to be better understood both at the genetic and molecular levels.