Biochemistry of senescence
 

Biochemical pathways in leaf senescence

We know new biochemistry is happening during senescence because our eyes tell us as much.  The changing colours of autumn leaves and ripening fruits are symptoms of big chemical changes inside senescing cells.

As well as the alterations we can see, analysis and measurement reveal extensive modifications of chemical composition and physiological function.

These changes occur where the influences of senescence-associated genes, developmental signals from elsewhere in the whole plant and environmental cues and constraints come together to make senescence happen.

Although probably every nook and cranny of metabolism will show some kind of response to the onset and progress of senescence, we can identify a few biochemical events that are of particular significance because of their scale and impact on the whole plant.
 

Chlorophyll

 		 <  In the senescence of green tissues and organs, the loss of Chlorophyll is the definitive event.  The story of pigment catabolism is continues to spring surprises on researchers.
 

Proteins

 		 <  After light, water and air, nitrogen is the plant’s major nutritional need, and senescence is the principal way in which nitrogen is recycled from old tissues to new.  Most of this nitrogen is salvaged from Proteins; but although we can measure (and, in agriculture, control) nitrogen recycling in detail, the cellular mechanisms remain quite mysterious.
 

Photosynthesis

 

 <  Green tissues are there to carry out Photosynthesis, of course.  And when the green colour is lost, photosynthesis decreases.  But it turns out that this relationship is more complicated, and interesting, than first appears.
 

Oxidation

 		 <  In a sense respiration is the converse of photosynthesis, because it consumes oxygen (which photosynthesis produces) and emits CO2 (which is assimilated by photosynthesis).  Respiration is one of the processes of Oxidation that are modulated in distinctive ways during senescence.
 
Hormones <  Hormones are the chemical messengers that ensure the semi-independent structures that make up an individual plant work together in a coordinated way.  Senescence is sensitive to different kinds of plant hormone and full understanding how it’s regulated will ultimately require the mechanism of action of the major hormone types to be worked out.