Response to additive stress: response quotients and volcano plots for the hypocotyl and root. Response quotients (RQ, left) and volcano plots (right) of the hypocotyl and root adaptations to dark-to-dark with water stress (−0.4 MPa, darkW). RQ response quotients are normalized to the respective wild-type response; a value of 1 (vertical red line) indicates that the response to a shift from dark to darkW is identical to that of the respective wild-type ecotype. Each replicate is represented by a dot. Mean RQ values are given on the right. Volcano plots show the mean RQ depicted on the X axis and the median P value of the response on the Y axis (negative log scale). (A) Hypocotyl responses to dark versus darkW conditions. Note that club-2 and trs120-4 had attenuated responses (RQ_hypocotyl < 0.8, magenta arrows). (B) Root responses to dark versus darkW conditions. Note that the triple bin2-3bil1bil2 knock out (from Kalbfuß et al., 2022) had the strongest attenuated RQ_root phenotype (mean RQ_root = 2.42, magenta arrow) with an insignificant root response. phyAphyBcry1cry2, club-2, trs120-4, and echidna mutants show also an attenuated root response (RQ_root > 1.2, magenta arrows). Quadruple pyrpyl mutants did not have a phenotype, possibly because only four genes are knocked out in a family with 14 members (Ma et al., 2009; Park et al., 2009). Due to the opposite adaptations of the hypocotyl and root under the additive stress conditions (decrease in hypocotyl and increase in root length from dark-to-darkW), the respective thresholds for attenuated responses are opposite (Fig. S8 A, compared to Fig. S8 B). Related to Fig. 5.