Down-regulation of catalase activity contributes to senescence induction in wheat leaves exposed to shading stress

HF CAUSIN; CL MARCHETTI; LB PENA; SM GALLEGO; AJ BARNEIX

BIOLOGIA PLANTARUM

SPRINGER

Lugar: Berlin; Año: 2014

0006-3134

In shaded wheat leaves, suppression of blue light (BL) triggers senescence. This phenomenon is correlated to an increase in oxidative stress symptoms and a decrease of catalase (CAT) activity, among other traits. Previous data suggest that the light signal transduction pathway may involve changes in Ca2+ and H2O2 homeostasis. To For better understanding of the interaction among light quality, Ca2+ availability and the antioxidant metabolism in the regulation of shade-induced senescence, detached wheat leaves were placed in a growth chamber, and exposed to either blue (B, high BL transmittance) and/or green (G, very low BL transmittance) Lee® filters, in absence or presence of 0.8 mM of verapamil (a Ca2+ channels blocker), 4.0 mM EGTA (a Ca2+chelator) or 8.0 mM 3-AT (a CAT inhibitor). At defined time points, leaf samples were analyzed for changes in chlorophyll concentration; in CAT, ascorbate peroxidase and guaiacol peroxidase specific activities; in CAT isozymes performance; and for gene expression profiles of CAT1, CAT2 and two senescence markers (TaSAG1 and TaSAG3). BL transmittance decreased chlorophyll degradation rate and SAG genes expression levels either in leaves continuously exposed to the B filter, as well as in leaves previously exposed to the G filter. The effect of BL was associated to the maintenance of a high CAT (but not peroxidase) activity, and it was suppressed when CAT activityeither in the presence of 3-AT or when Ca2+ availability were was pharmacologically decreased. BL altered the activity of CAT activity isozymes as well as the expression patterns of CAT1 and CAT2 genes, indicating that its regulatory effect is exerted both at the transcriptional and the post-transcriptional levels. Nevertheless, differential responses of CAT isozymes and CAT genes expression profiles to specific treatment combinations indicate that they differ in their regulatory pathways. Interactions between BL, Ca2+ fluxes and the antioxidant metabolism in leaves exposed to shading-stress are discussed.