Plant Molecular Biology 37: 455–469, 1998.
1998 Kluwer Academic Publishers. Printed in Belgium.
A comparison of the expression patterns of several senescence-associated
genes in response to stress and hormone treatment
Louis M. Weaver, Susheng Gan
, Betania Quirino and Richard M. Amasino
Dept. of Biochemistry, University of Wisconsin at Madison, 420 Henry Mall, Madison, WI 53706, USA (
current address: Tobacco and Health Research Institute and Dept. of Agronomy, University
of Kentucky, Lexington, KY 40546, USA
Received 10 September 1997; accepted in revised form 6 January 1998
Key words: gene expression, phytohormone, Lea, leaf senescence, senescence-associated gene, stress
The expression of several Arabidopsis thaliana senescence-associated genes (SAGs) in attached and/or detached
leaves was compared in response to age, dehydration, darkness, abscisic acid, cytokinin, and ethylene treatments.
Most of the SAGs responded to most of the treatments in a similar fashion. Detachment in darkness and ethylene
were the strongest inducers of both SAGs and visible yellowing. Detachment in light was also a strong inducer
of SAGs, but not of visible yellowing. The other treatments varied more in their effects on individual SAGs.
Responses were examined in both older and younger leaves, and generally were much stronger in the older ones.
Individual SAGs differed from the norms in different ways, however, suggesting that their gene products play a role
in overlapping but not identical circumstances. Some SAGs responded quickly to treatments, which may indicate
a direct response. Others responded more slowly, which may indicate an indirect response via treatment-induced
senescence. Four new SAGs were isolated as part of this work, one of which shows strong similarity to late
embryogenesis-abundant (Lea) genes.
Leaf senescence is an orderly, active process in which
nutrients in a leaf are reclaimed and mobilized to other
parts of the plant. It is often referred to as the ﬁnal stage
of leaf development, to emphasize that it is both highly
regulated and genetically programmed. The changes
most closely associated with senescence are declines
in total protein and RNA levels and chloroplast break-
down. Its most visible symptom is chlorophyll loss
and concomitant leaf yellowing. It has been known for
some time that transcription and translation are neces-
sary for senescence to progress , and in the past
few years many genes have been cloned for which the
corresponding messenger RNAs are upregulated dur-
ing the process (for recent reviews see [5, 8, 32, 35,
The Nucleotidesequence data reported will appear inthe EMBL
and GenBank Nucleotide Sequence Databases under the accession
numbers AF053063, AF053064, AF053065.
44]). Such genes are often referred to as senescence-
associated genes, or SAGs.
Senescence occurs in response to aging, and under
constant environmental conditions is relatively con-
stant and predictable . Certain stresses and hor-
mones, however, are able to hasten or repress sen-
escence. Drought, darkness, detachment, and the hor-
mones abscisic acid (ABA) and ethylene can all induce
visible yellowing (see for example [4, 29, 34, 36]). The
hormone cytokinin is generally regarded as an inhibit-
or of senescence (e.g. [14, 34]). It is also known that
certain stresses and hormones are able to induce genes
directly responsiveto those stresses and hormones. For
instance, several genes are known to be inducible by
ABA (e.g. [37, 45]) , drought (e.g. [3, 23, 47]), and
darkness (e.g. ).
What is less clear is the overlap between the SAGs
and the stress-and hormone-response genes.That there
is such an overlap is clear from the fact that ﬁve of the
11 genes cloned as SAGs and examined in this paper