Fig. 5. Osmotic support abolishes constitutive JA production in kor1, while hypoosmotic treatment triggers JA-Ile signaling in WT.

(A) Constitutive JAZ10p:GUS activity in kor1-4 seedlings (orange arrowhead) is abolished following growth in 3% mannitol-supplemented media (empty arrowhead). (B) qRT-PCR of basal JAZ10 root expression of indicated genotypes grown without (mock) or with mannitol. JAZ10 levels were normalized to UBC21. Bars represent the means of three biological replicates (±SD), each containing pools of ~60 5-do roots. (C) Root length box plots of 7-do WT and kor1-4 grown without or with mannitol. Medians are solid lines inside the boxes, and circles depict n = 59 to 61. Mannitol reduced WT root length by −0.78 cm, whereas it increased kor1-4’s by +0.35 cm (linear model, P = 2 × 10⁻⁶). (D) Representative split images from kor1-4 root cross sections (left) and respective cell segmentations (right) grown without or with mannitol. (E) Total and cell-specific area fold change from segmented transversal root sections of WT and kor1-4 grown without or with mannitol. Bars represent mean fold changes of individual cellular areas from 10 roots (±SD), normalized to mock-treated WT indicated by a dashed line (individual measurements are in fig. S6). (F) JAZ10p:GUS expression in WT seedlings submerged in isotonic solution (liquid MS, mock) or deionized water (H₂O) for the indicated time. (G to J) JAZ10p:NLS-3xVEN expression in WT roots submerged in (G) mock solution or (H) H₂O for 24 hours and counterstained with PI. (I) Orthogonal and (J) longitudinal view from the root early differentiation zone in (H). co, cortex; en, endodermis; pe, pericycle. Letters in (B), (C), and (E) denote statistically significant differences among samples as determined by ANOVA followed by Tukey’s HSD test (P < 0.05). Scale bars, 0.5 mm (A and F), 50 μm (D and J), 200 μm (G and H), and 30 μm (I).