Chlorophylls and their Degradation in Nature - Photobiogeochemistry of Organic Matter - page 731

1991 ; Janave 1997 ; Maeda et al. 1998 ; Ziegler et al. 1988 ). Pheophorbide a oxy-
genase is thought to catalyze the reaction that produces RCC in various leaves and
fruits (Fig. 4 ) (Hörtensteiner 2006 ; Kräutler et al. 1997 ; Mühlecker et al. 1997 ;
Hörtensteiner et al. 1998 ). Pheophytinase, a chloroplast-located and senescence-
induced hydrolase that is widely distributed in algae and land plants can also
specifically dephytylate the Mg-free Chl pigment, pheophytin (phein), yielding
pheophorbide (Schelbert et al. 2009 ).
In the second phase, p FCC-modifying reactions produce FCCs that are imported
into the vacuole by a primary active transport process. FCCs are further converted
to nonfluorescent Chl catabolites (NCCs) by an acid-catalyzed isomerization, tak-
ing place inside the vacuole (Fig. 4 ) (Hörtensteiner 2006 ; Moser et al. 2009 ;
Hörtensteiner and Kräutler 2011 ; Hinder et al. 1996 ; Kräutler 2003 ; Christ et al.
2012 ). Transfer of catabolites from senescent chloroplasts to the vacuole is mediated
by primary activated transport processes (Hörtensteiner and Kräutler 2011 ). Note
that the vacuole is a membrane-bound organelle within the cell cytoplasm. It occurs
in plant cells and other microorganisms and can store water, salts, minerals, nutri-
ents, proteins, pigments and enzymes. It is involved in growth, protection, waste
disposal and structural support and tends to be very large in mature plant cells.
Degradation products and enzymes involved in the described reactions have been
identified in leaves and fruits (Hörtensteiner and Kräutler 2011 ; Hörtensteiner et al.
1995 , 1998 ; Hinder et al. 1996 ; Christ et al. 2012 ; Kräutler et al. 1991 ; Matile et al.
1992 ; Ginsburg and Matile 1993 ; Mühlecker and Kräutler 1996 ; Matile et al. 1999 ).
A process that is closely coupled with the oxygenase reaction is a reduction
of the δ -methine bridge of the RCC by a stromal enzyme, termed RCC reductase
(RCCR). The reaction yields colorless fluorescent products (Fig. 4 ) (Hörtensteiner
2006 ; Rodoni et al. 1997 ; Wüthrich et al. 2000 ; Oberhuber and Kräutler 2002 ;
Oberhuber et al. 2008 ). RCCR has been purified and cloned recently in barley and
Arabidopsis (Wüthrich et al. 2000 ).
Spectroscopic analysis shows that p FCC has been identified from senescent
leaves of various plants (Matile et al. 1996 ; Mühlecker et al. 1997, 2000 ; Kräutler
and Matile 1999 ). The p FCC is converted to FCCs by several modifications
depending on the plants, such as demethylation and hydroxylation (Hörtensteiner
2006 ; Hörtensteiner and Kräutler 2011 ; Matile et al. 1992 ). Modified FCCs are
transported to the central vacuole by ATP-dependent translocator(s) in the tono-
plast. They are non-enzymatically converted to NCCs by rearrangement of double
bonds, in the pyrrole IV ring and adjacent g-methine bridge (Fig. 4 ) (Hörtensteiner
2006 ; Moser et al. 2009 ; Hörtensteiner and Kräutler 2011 ; Hinder et al. 1996 ;
Kräutler 2003 ; Christ et al. 2012 ; Matile et al. 1999 ). The p FCC and all fluores-
cent Chl catabolites have the same absorption spectrum, with a major peak at
around 320 nm and a shoulder at around 360 nm (Takamiya et al. 2000 ). In con-
trast, NCCs have an absorption maximum at 316 nm with no shoulder (Takamiya
et al. 2000 ). Finally, three degradation products of monopyrrole derivatives such
as hematinic acid, methyl ethyl maleimide and methyl vinyl maleimide aldehyde
have been detected in senescent leaves and cotyledons of barley, spinach, pea and
cucumber (Suzuki and Shioi 1999 ).