Agriculture Reference
In-Depth Information
Table 5.1
Comparison of signaling and possible mechanisms of PCD in floral organs
Floral organ
Intercellular signals
Mechanism for PCD
References
Sex organ abortion
GA and brassinosteroids
?
Wu and Cheung (2000)
Tapetum in cytoplasmic
male sterility lines
Mitochondrial
dysfunction
Cytochrome C release
followed by loss of
mitochondrial function
Balk and Leaver (2001)
Synergids
Pollination in some
species
Requires mitochondrial
function
Christenson et al. (2002)
Petal senescence
Ethylene in some species
Calcium/phosphate
signaling, ROS
increases
Porat and Halevy (1993),
Kinoshita et al. (1999)
Jasmonate (via ethylene)
Activation of vacuolar
lytic enzymes through
vacuolar-processing
enzyme (caspase 1
activity)
Orzaez et al. (1999),
Schmid et al. (1999)
Cytokinin (via sugar
transport)
Activation of vesicle
bound proteases,
vacuolar leakage
Wagstaff et al. (2003),
Lara et al. (2004)
Pollen tube
During self-
incompatibility
Increased calcium,
cytochrome C release
and caspase-3 activity
Thomas and Franklin
(2004)
can be developed. Table 5.1 shows the comparison of signaling and possible mechanisms
of PCD in various floral organs.
5.16 A proteomic analysis of plant PCD
Despite the fundamental importance of PCD in plants, comparatively little is known about
the molecular mechanisms of plant PCD. Plant genomes do not contain obvious homologs
to the key animal cell death proteins such as the Bcl-2 family proteins (Arabidopsis Genome
Initiative, 2000), although a family of genes related to mammalian caspases has been iden-
tified in plants (Uren et al., 2000). Biochemical studies of plants have been able to establish
a causal role for events such as the translocation of cytochrome C from the mitochondria
to the cytosol (Balk et al., 1999; Sun et al., 1999; Zhao et al., 1999; Xu and Hanson, 2000).
In an attempt to identify key plant PCD genes that may function universally during dif-
ferent types of plant PCD, Swidzinski et al. (2002) have previously undertaken a custom
microarray analysis of gene expression during PCD in an Arabidopsis cell suspension cul-
ture. By identifying mRNA transcripts that changed in abundance following two unrelated
PCD-inducing treatments (a brief, mild heat treatment for 10 min at 55 C and culture senes-
cence), they have been able to discriminate between genes that may be common to a core
plant cell death program and those that are specifically related to the inducing stimulus it-
self. While this study was successful in identifying several candidate genes whose common
up- or downregulation during PCD may indicate a role for their products in plant PCD, it
was restricted to elements of the PCD process that are transcriptionally regulated and ig-
nored posttranscriptional and posttranslational regulation. Indeed, posttranslational events
such as proteolytic cleavage and activation and modifications such as phosphorylation are
key regulatory events in animal PCD (Reed, 2000). As a first step toward identifying such
Search WWH ::




Custom Search