PLANT PHYSIOLOGY , Vol 106, Issue 3 1033-1039, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Sensitivity of Superoxide Dismutase Transcript Levels and Activities to Oxidative Stress Is Lower in Mature-Senescent Than in Young Barley Leaves
L. M. Casano, M. Martin and B. Sabater
Departamento de Biologia Vegetal, Universidad de Alcala de Henares, Alcala de Henares, 28871-Madrid, Spain
Antioxidant enzyme activities are inducible by oxidative stress and
decrease during senescence. To determine if the age-dependent decrease of
superoxide dismutase (SOD) activities is due to decreased sensitivity to
oxidative stress, we have investigated the changes in steady-state levels
of transcripts and activities of mitochondrial Mn-SOD (SOD1), chloroplastic
Fe-SOD (SOD2), and cytoplasmic Cu-Zn-SOD (SOD3) in young and
mature-senescent detached barley (Hordeum vulgare L.) leaves in response to
incubation in darkness, growth light (20 W m-2), and photooxidative stress
conditions (100 W m-2 with 21 or 100% O2). For a comparison, changes in the
mRNA for ribulose bisphosphate carboxylase were also measured. After leaf
detachment, the abundance of all three SOD mRNAs increased, then decreased
and eventually stabilized after 6 h of incubation. After 20 h of incubation
under darkness SOD transcripts decreased in both young and mature-senescent
leaves. While under strong photooxidative stress the levels of the three
SOD transcripts significantly increased in young leaves; in
mature-senescent leaves SOD2 and, to lesser extent, SOD1 and SOD3
transcripts decreased. Generally, SOD activity changes were similar to
those of mRNAs. It is proposed that oxidative damage during senescence
could be favored by the inability of senescing leaves to modulate the
steady-state level of SOD mRNA, and probably those of other antioxidant
enzymes, concomitant with the rate of oxyradical formation.
