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In order to analyze the signaling function of hydrogen peroxide (H2O2) production in senescence in more detail, we manipulated intracellular H2O2 levels in Arabidopsis thaliala (L.) Heynh by using the hydrogen-peroxide-sensitive part of the Escherichia coli transcription regulator OxyR, which was directed to the cytoplasm as well as into the peroxisomes. H2O2 levels were lowered and senescence was delayed in both transgenic lines, but OxyR was found to be more effective in the cytoplasm. To transfer this knowledge to crop plants, we analyzed oilseed rape plants Brassica napus L. cv. Mozart for H2O2 and its scavenging enzymes catalase (CAT) and ascorbate peroxidase (APX) during leaf and plant development. H2O2 levels were found to increase during bolting and flowering time, but no increase could be observed in the very late stages of senescence. With increasing H2O2 levels, CAT and APX activities declined, so it is likely that similar mechanisms are used in oilseed rape and Arabidopsis to control H2O2 levels. Under elevated CO2 conditions, oilseed rape senescence was accelerated and coincided with an earlier increase in H2O2 levels, indicating that H2O2 may be one of the signals to inducing senescence in a broader range of Brassicaceae. [ABSTRACT FROM AUTHOR]

In general, yield and fruit quality strongly rely on efficient nutrient remobilization during plant development and senescence. Transcriptome changes associated with senescence in spring oilseed rape grown under optimal nitrogen supply or mild nitrogen deficiency revealed differences in senescence and nutrient mobilization in old lower canopy leaves and younger higher canopy leaves. Having a closer look at this transcriptome analyses, we identified the major classes of seed storage proteins (SSP) to be expressed in vegetative tissue, namely leaf and stem tissue. Expression of SSPs was not only dependent on the nitrogen supply but transcripts appeared to correlate with intracellular H2O2 contents, which functions as well-known signaling molecule in developmental senescence. The abundance of SSPs in leaf material transiently progressed from the oldest leaves to the youngest. Moreover, stems also exhibited short-term production of SSPs, which hints at an interim storage function. In order to decipher whether hydrogen peroxide also functions as a signaling molecule in nitrogen deficiency-induced senescence, we analyzed hydrogen peroxide contents after complete nitrogen depletion in oilseed rape and Arabidopsis plants. In both cases, hydrogen peroxide contents were lower in nitrogen deficient plants, indicating that at least parts of the developmental senescence program appear to be suppressed under nitrogen deficiency. [ABSTRACT FROM AUTHOR]