The different fates of mitochondria and chloroplasts during dark‐induced senescence in Arabidopsis leaves

Abstract

Senescence is an active process allowing the reallocation of valuable nutrients from the senescing organ towards storage and/or growing tissues. Using Arabidopsis thaliana leaves from both whole darkened plants (DPs) and individually darkened leaves (IDLs), we investigated the fate of mitochondria and chloroplasts during dark-induced leaf senescence. Combining in vivo visualization of fates of the two organelles by three-dimensional reconstructions of abaxial parts of leaves with functional measurements of photosynthesis and respiration, we showed that the two experimental systems displayed major differences during 6 d of dark treatment. In whole DPs, organelles were largely retained in both epidermal and mesophyll cells. However, while the photosynthetic capacity was maintained, the capacity of mitochondrial respiration decreased. In contrast, IDLs showed a rapid decline in photosynthetic capacity while maintaining a high capacity for mitochondrial respiration throughout the treatment. In addition, we noticed an unequal degradation of organelles in the different cell types of the senescing leaf. From these data, we suggest that metabolism in leaves of the whole DPs enters a 'stand-by mode' to preserve the photosynthetic machinery for as long as possible. However, in IDLs, mitochondria actively provide energy and carbon skeletons for the degradation of cell constituents, facilitating the retrieval of nutrients. Finally, the heterogeneity of the degradation processes involved during senescence is discussed with regard to the fate of mitochondria and chloroplasts in the different cell types.

WRKY22 Transcription Factor Mediates Dark-Induced Leaf Senescence in Arabidopsis

“…Besides the change of AtWRKY22 expression and translation, no other obvious differences in morphology or growth were observed between the wild-type and two mutant plants under normal growth conditions (data not shown). Earlier work demonstrated that both H 2 O 2 (David, 1995) and dark (Keench et al, 2007) could induce plant senescence. At-WRKY22 transcription increased continuously with 3% H 2 O 2 treatment (Fig.…”

“…2C). Both of dark (Keench et al, 2007) and H 2 O 2 (David, 1995) treatment can induce plant senescence, thus AtWRKY22 might participate in senescence-induced signal transduction pathways.…”

The conserved mobility of mitochondria during leaf senescence reflects differential regulation of the cytoskeletal components inArabidopsis thaliana

“…This is in line with our previous work, where an important diminution of the number of mitochondria was observed in leaves subjected to darkinduced senescence. 3 However, although the MT network was highly altered in leaves having lost 75% to 85% of their chlorophyll content, 1 a distinct motility of mitochondria could still be observed (estimated during 40 seconds as shown in Fig. 1C and D), suggesting a conservation of cytoplasmic streaming until the last stage of leaf senescence.…”

Triphosphate Tunnel Metalloenzyme Function in Senescence Highlights a Biological Diversification of This Protein Superfamily

“…Other organelles, such as mitochondria and peroxisomes, remain active much longer and provide energy for the cell as well as take over a number of metabolic tasks during this process (Keech et al, 2007;Chrobok et al, 2016). While yeast and animals possess mitochondrial PPases (Lundin et al, 1991;Curbo et al, 2006), so far no mitochondrial PPase has been identified in plants.…”

“…Usually a carefully orchestrated dismantling of the chloroplast is one of the first events in the senescence process (Keech et al, 2007). Other organelles, such as mitochondria and peroxisomes, remain active much longer and provide energy for the cell as well as take over a number of metabolic tasks during this process (Keech et al, 2007;Chrobok et al, 2016).…”