Crynodeb
Leaf senescence has an important role in the plant’s
nitrogen economy. Chlorophyll catabolism is a visible
symptom of protein mobilization. Genetic and environmental
factors that interfere with yellowing tend to
modify protein degradation as well. The chlorophyll–
protein relationship is much closer for membrane
proteins than it is for soluble or total leaf proteins.
In stay-greens, genotypes with a specific defect in
the chlorophyll catabolism pathway, soluble protein
degradation during senescence may be close to
normal, but light-harvesting and reaction centre
thylakoid membrane proteins are much more stable.
Genes for the chlorophyll catabolism pathway and its
control are important in the regulation of protein
mobilization. Genes for three steps in the pathway
are reported to have been isolated. The gene
responsible for the stay-green phenotype in grasses
and legumes has not yet been cloned but a fair
amount is known about it. Pigment metabolism in
senescing leaves of the Festuca–Lolium stay-green
mutant is clearly disturbed and is consistent with a
blockage at the ring-opening (PaO) step in chlorophyll
breakdown. PaO is de novo synthesized in
senescence and thought to be the key enzyme in the
chlorophyll a catabolic pathway. The stay-green
mutation is likely to be located in the PaO gene, or
a specific regulator of it. These genes may well be in
the various senescence-enhanced cDNA collections
that have been generated, but functional handles
on them are currently lacking. When the stay-green
locus from Festuca pratensis was introgressed into
Lolium temulentum, a gene encoding F. pratensis
UDPG-pyrophosphorylase was shown to have been
transferred on the same chromosome segment.
A strategy is described for cloning the stay-green
gene, based on subtractive PCR-based analyses of
intergeneric introgressions and map-based cloning.
Iaith wreiddiol | Saesneg |
---|---|
Tudalennau (o-i) | 801-808 |
Nifer y tudalennau | 8 |
Cyfnodolyn | Journal of Experimental Botany |
Statws | Cyhoeddwyd - 2002 |