A pivotal role for starch in the reconfiguration of 14C-partitioning and allocation in Arabidopsis thaliana under short-term abiotic stress

Abstract

Plant carbon status is optimized for normal growth but is affected by abiotic stress. Here, we used 14C-labeling to provide the first holistic picture of carbon use changes during short-term osmotic, salinity, and cold stress in Arabidopsis thaliana. This could inform on the early mechanisms plants use to survive adverse environment, which is important for efficient agricultural production. We found that carbon allocation from source to sinks, and partitioning into major metabolite pools in the source leaf, sink leaves and roots showed both conserved and divergent responses to the stresses examined. Carbohydrates changed under all abiotic stresses applied; plants re-partitioned 14C to maintain sugar levels under stress, primarily by reducing 14C into the storage compounds in the source leaf, and decreasing 14C into the pools used for growth processes in the roots. Salinity and cold increased 14C-flux into protein, but as the stress progressed, protein degradation increased to produce amino acids, presumably for osmoprotection. Our work also emphasized that stress regulated the carbon channeled into starch, and its metabolic turnover. These stress-induced changes in starch metabolism and sugar export in the source were partly accompanied by transcriptional alteration in the T6P/SnRK1 regulatory pathway that are normally activated by carbon starvation.

A Cytosolic Protein Kinase STY46 in Arabidopsis thaliana Is Involved in Plant Growth and Abiotic Stress Response

“…Previous studies in Arabidopsis showed that 150 mM salt stress results in increased sugar accumulation and reduced starch content [51], highlighting that STY46, is necessary for this physiological process. Our work suggests the activation of a regulatory mechanism, whereby carbon is preferentially partitioned into osmoprotectants (sugars, amino acids, organic acids) at the expense of storage compounds (starch or protein) as a positive way to respond to salinity stress [34]. The 14 CO 2 labeling experiment reinforced this and showed that OE-25 partitioned more 14 C into amino acids (AA) and sugars, while it partitioned less into starch and protein in source leaf, which suggested that OE-25 is more responsive to salinity stress than the wild type.…”

“…The idea that STY46 may be part of a biological pathway integrating carbon availability and abiotic stress was directly tested. The STY46 genotypes were exposed to 150 mM mannitol and 100 mM NaCl stress, and carbohydrates were assayed in rosettes and harvested at the end of the light period, when carbohydrate content was highest [34]. There were no differences in starch and reducing sugar contents among genotypes under non-stressed conditions ( Figure 6B,C).…”

“…The data mined from Genevestigator ® suggested that STY46 was responsive to abiotic stress, but there was no data for salinity or osmotic stress (the latter used as a proxy for water-deficiency), which are major factors limiting plant productivity [33]. Therefore, changes in STY46 transcript levels were measured in the rosette of three-week-old Arabidopsis exposed to 200 mM NaCl and 300 mM mannitol, conditions that our previous work indicates, trigger the most dynamic changes in the carbon flux [34]. As Figure 1 shows, the transcript level of STY46 was induced 12 h post exposure to 300 mM mannitol.…”

“…Carbon partitioning into major metabolite pools changes dynamically in response to various abiotic stresses [34]. To further investigate if STY46 could regulate carbon partitioning and allocation under abiotic stress, four-week-old Arabidopsis seedlings were exposed to 100 mM NaCl for one week, and a single mature source leaf was fed with 14 CO 2 at the beginning of the day for 30 min, as previously described [34]. The labeled source leaf, unlabeled sink leaves, and the silique were harvested separately at the middle of the day.…”

“…RNA extraction was done as described [34]. Arabidopsis tissue (100 mg) was ground into a fine powder with liquid nitrogen in a 2 mL Eppendorf tube, and 1 mL TRIzol ® reagent (Invitrogen, Carlsbad, CA, USA) was added.…”