Plant senescence can be induced by various environmental stresses (darkness, cold, heat, drought, pathogen attack) and internal factors (age, reproduction process, phytohormones). It is a complex process over which cells undergo sequential changes in cellular structure, metabolism, and gene expression. Leaf senescence has been well studied, but little is known in root senescence. Moreover, diverse studies have investigated plant senescence in separate organs of leaf, flower (petal), seedling, and tuber; whereas whole plant senescence is poorly characterized. Here I used Arabidopsis thaliana as a model to elucidate the mechanisms promoting whole plant senescence in natural and artificial conditions. Transcriptome analyses revealed that jasmonic acid (JA), abscisic acid (ABA), salicylic acid (SA), and ethylene promoted senescence in leaf, while JA and ethylene trigger senescence in roots. The comparison between natural death (ND) and artificial death (AD) in leaf and root suggested that AD is similar to ND stage 1 in leaf (6th week after germination, ND1), closer to ND stage 2 (7th week after germination, ND2) in root. Several ROS/oxidants and antioxidants (peroxidase proteins and glutathione S-transferase) were detected in leaf and root, respectively. Three genes that were over-expressed in both AD and ND2 in the root, AT2G43570 (chitinase), AT3G04720 (pathogenesis-related 4), and AT2G18660 (plant natriuretic peptide A) were involved in SAR- systemic acquired resistance which has been known to be associated with ROS signaling. In which, AT2G43570 is a marker for SAR, AT3G04720 is an SAR-associated defense gene, and AT2G18660 functions as a signal via phloem. Taken together, during the whole plant senescence, plant hormones regulated the generation of ROS signals in leaves, while these signals are then transported to roots via long distance signaling factors and induced the increase of antioxidants.

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