Abstract
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.
Highlights
Despite being a member of the glucosinolate producing Brassicaceae family, selection and breeding of oilseed rape (OSR, Brassica napus L.) has made it one of the most important oilseed crops after soybean and oil palm
Around 60% of this protein content are composed of seed storage proteins (SSPs), which in turn are mainly comprised of two protein families: 12S globulins (Cruciferins) and 2S albumins (Napins) [2,3]
reactive oxygen species (ROS), especially H2 O2, are well known signaling molecules in senescence and we have demonstrated that developmental senescence in Arabidopsis as well as in OSR is associated with the down-regulation of central components of the anti-oxidative systems and associated with a transient increase in intracellular H2 O2 contents [11,12]
Summary
Despite being a member of the glucosinolate producing Brassicaceae family, selection and breeding of oilseed rape (OSR, Brassica napus L.) has made it one of the most important oilseed crops after soybean and oil palm. The seed storage reserves deposited in the protein storage vacuoles and oil bodies in the endosperm and embryo tissue are degraded for energy supply and anabolic processes of seedling development. In Arabidopsis, differential regulation of more than 6000 genes during onset and progression of leaf senescence emphasizes the importance of this developmental program [10]. In this analysis, autophagy, transport and response to reactive oxygen species (ROS) are the first processes activated in the chronology of leaf senescence [10]. In a new growth experiment, we confirmed that the SSP genes CRUCIFERIN and NAPIN were expressed and that the corresponding proteins are produced in leaf tissue. This indicates that N-starvation induced senescence is driven by different signals compared to developmental senescence and that at least the hydrogen peroxide-driven parts of the developmental senescence processes appear to be suppressed in N-starvation induced senescence
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