Awaiting better times: A quiescence response and adventitious root primordia formation prolong survival under cadmium stress in Tetradenia riparia (Hochst.) Codd

Plants survive stressful conditions by employing three main strategies: escape, tolerance, and survival. Experiments were conducted to pinpoint the response strategy adopted by Tetradenia riparia to cadmium (Cd) stress by monitoring several physiological parameters and plants' ability to recover once the stress receded. Cadmium (30 and 150 μM) strongly affected shoot and root growth in a dose dependent manner, with almost complete inhibition of shoot growth, stomatal opening and CO2 assimilation in plants exposed to 150 μM CdSO4. Independently of the CdSO4 concentrations, plants excluded Cd from the aboveground tissues, with concentrations in shoots remaining around 0.1 μmol g-1 dry mass. Furthermore, Cd stress was associated with a decline in methylation of Lys4 of histone H3, likely associated with the transition from an active to a quiescent state. Surprisingly, Cd also induced the initiation of root primordia in T. riparia stems, which, once placed in a Cd-free media, quickly (24 h) developed into adventitious roots, which were likely the driving factor of the rapid resumption of leaf elongation and photosynthetic activity, which increased almost 20-fold over the 3 weeks of recovery. Therefore T. riparia ability to survive Cd stress was mediated by quiescence, which associated with an excluder strategy and stem root primordia formation, enabled rapid resumption of growth under Cd-free conditions.