the fate of chlorophyll in degreening tissue

1. Fate of Chlorophyll in degreening tissue
Rubab Iqbal
2014-ag-834
Ph.D Scholar
Department of Botany
Assigment submitted to
Dr. Anjum Zia

2. Chlorophyll
Chlorophyll is a green photosynthetic pigment found
in plants, algae and cyanobacteria. It absorbs mostly
the blue and red portions of the electromagnetic
spectrum.
Degreening
Degreening is the process of removing the green
color (chlorophyll).
Chlorophyll degradation
When the chlorophyll breaks down, the green color disappears,
and the yellow to orange colors become visible.

3.  Introduction
 The loss of green color in senescent leaves and ripening fruits is a spectacular
natural phenomenon.
 Albert F. Woods addressed in the subject, “The destruction of chlorophyll by oxidizing
enzymes” that chlorophyll could be readily converted by oxidation, into a yellow coloring
matter, xanthophyll
 In the fall, because of changes in the length of daylight and changes in temperature, the leaves
stop their food-making process. The chlorophyll breaks down, the green color disappears, and
the yellow to orange colors become visible.

4. What enzyme breaks down chlorophyll?
Chlorophyllase
This is the enzyme that catalyzes chlorophyll by removing the phytol
group, which result in chlorophyllide formation. This enzyme is
present in chloroplast.
1912,Arthur Stoll discover this enzyme

5.  Chlorophyll degradation pathway
 The pathway can be divided into two parts:
 1. Early reactions with colored pigments as substrates, ending with the
synthesis of a ‘primary’ colorless, blue-fluorescing breakdown product,
termed as pFCC.
2. pFCC -modifying reactions, typically ending with the non-
enzymatic isomerization of modified FCCs to their respective NCCs inside the
vacuole. Transfer of catabolites from senescent chloroplast to the vacuole is
mediated by primary activated transport processes.

6. Reactions envolve in chlorophyll degradation
Chl b to Chl a
conversion
Phytol removel
Mg dechelation
Phorbide a
oxygenase
Red chlorophyll
catabolite
reductase
Demethylation
at C13
Malonylation
reaction at C8
FCC to NCC
isomerization
Localiztion of
catabolites

7.  Chlorophyll a and b differ in only one atom in a side-chain on the third
carbon. In A, the third carbon is attached to a methyl group whereas, in b the
third carbon is attached to an aldehyde group
 the conversion of Chl b to Chl a conversion are catalyzed by two
different enzymes NADPH-dependent Chl b reductase and ferredoxin-
dependent hydroxymethyl Chl reductase a.
Convertion of Chl b to a

8. Structural Differences Between Chlorophyll a and b

10. Chlorophyll Degradation Mechanism
Mg Dechelatase
Chlorophylase Mg Dechelatase
Chlorophyll Pheophorbide a
 Chlorophylase removes phytol side chain.
 Magnesium dechelatase removes the magnesium from the chlorin macrocycle
 The product of dechelation of chlorophyll a is pheophytin, Chlorophyll a with no
magnesium.

11.  pheophorbide oxygenase RCC Reductase
 Pheophorbide a RCC pFCC
 Pheophorbide oxygenase break the pi electron conjugation and change the emmision properties to
red, thus the red chlorophyll catabolite (RCC).
 RCC reductase reduces a double bond and the product is primary flourecent chlorophyll catabolite
formed

12.  FCC-to-NCC isomerization
 NCCs are the final catabolites
 pFCC are further modified by unidentified hydroxylating enzyme
 When carrying free propionic acid group, FCCs are transported in the vacoule
where they isomerize by a spontaneous acid catalyzed reaction to the
corresponding non flourecent chlorophyll catabolites.