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High CO₂ Triggers Preferential Root Growth of Arabidopsis thaliana Via Two Distinct Systems Under Low pH and Low N Stresses

Hachiya, Takushi, Sugiura, Daisuke, Kojima, Mikiko, Sato, Shigeru, Yanagisawa, Shuichi, Sakakibara, Hitoshi, Terashima, Ichiro, Noguchi, Ko
Plant & cell physiology 2014 v.55 no.2 pp. 269-280
Arabidopsis thaliana, abiotic stress, auxins, carbon, carbon dioxide, carbon nitrogen ratio, cytokinins, dry matter partitioning, genes, metabolites, mutants, nitrogen, pH, plant hormones, root growth, roots, shoots, sugars
Biomass allocation between shoots and roots is an important strategy used by plants to optimize growth in various environments. Root to shoot mass ratios typically increase in response to high CO ₂, a trend particularly evident under abiotic stress. We investigated this preferential root growth (PRG) in Arabidopsis thaliana plants cultivated under low pH/high CO ₂ or low nitrogen (N)/high CO ₂ conditions. Previous studies have suggested that changes in plant hormone, carbon (C) and N status may be related to PRG. We therefore examined the mechanisms underlying PRG by genetically modifying cytokinin (CK) levels, C and N status, and sugar signaling, performing sugar application experiments and determining primary metabolites, plant hormones and expression of related genes. Both low pH/high CO ₂ and low N/high CO ₂ stresses induced increases in lateral root (LR) number and led to high C/N ratios; however, under low pH/high CO ₂ conditions, large quantities of C were accumulated, whereas under low N/high CO ₂ conditions, N was severely depleted. Analyses of a CK-deficient mutant and a starchless mutant, in conjunction with sugar application experiments, revealed that these stresses induce PRG via different mechanisms. Metabolite and hormone profile analysis indicated that under low pH/high CO ₂ conditions, excess C accumulation may enhance LR number through the dual actions of increased auxin and decreased CKs.