Using iron-deprived (-Fe) chlorotic as well as green iron-deficient (5 μM Fe) and iron-sufficient supplied (50 μM Fe) leaves of young hydroponically reared Brassica napus plants, we explored iron deficiency effects on triggering programmed cell death (PCD) phenomena. Iron deficiency increased superoxide anion but decreased hydroxyl radical (•OH) formation (TBARS levels). Impaired photosystem II efficiency led to hydrogen peroxide accumulation in chloroplasts; NADPH oxidase activity, however, remained on the same level in all treatments. Non-autolytic PCD was observed especially in the chlorotic leaf of iron-deprived plants, to a lesser extent in iron-deficient plants. It correlated with higher DNAse-, alkaline protease- and caspase-3-like activities, DNA fragmentation and chromatin condensation, hydrogen peroxide accumulation and higher superoxide dismutase activity. A significant decrease in catalase activity together with rising levels of dehydroascorbic acid indicated a strong disturbance of the redox homeostasis, which, however, was not caused by •OH formation in concordance with the fact that iron is required to catalyse the Fenton reaction leading to •OH generation. This study documents the chain of events that contributes to the development of non-autolytic PCD in advanced stages of iron deficiency in B. napus leaves.
Keywords: AA, ascorbic acid; APX, ascorbate peroxidase; Brassica napus; CAT, catalase; Caspase; DAB, 3,3′-diaminobenzidine; DAPI, 4′,6-diamidino-2-phenylindole dihydrochloride; DHA, dehydroascorbic acid; DNAse, deoxyribonuclease; DTT, 1,4-dithio-dl-threitol; Deficiency; Deprivation; EDTA, ethylenediaminetetraacetic acid; ETR, electron transport rate; ETS, electron transport system; Iron; NBT, p-nitro-blue tetrazolium chloride; PCD, programmed cell death; POD, peroxidase; Programmed cell death; Reactive oxygen species; SOD, superoxide dismutase; TBARS, thiobarbituric acid reactive substances; Y(II), effective quantum yield.