Physiological Analysis.

Germination assays were performed in the presence of various ABA levels, as reported (44). Grafting experiments were conducted as described (44). Gas exchange measurements were carried out for analysis of carbon assimilation rates, intercellular CO₂ levels (c_i), and stomatal conductance (g_s) in the whole plant configuration and at single leaf level using the GFS-3000 gas exchange system equipped with custom-built cuvettes and the provided software (Heinz Walz). Mesophyll conductance (g_m) and CO₂ concentration in plastids of leaves of comparable developmental stage and age (leaf number 16 ± 3, 2 wk after leaf emergence) were determined by using a 2-cm² cuvette and applying the constant J method at saturating light condition (photosynthetic photon flux density: 1,500 µmol⋅m⁻²⋅s⁻¹) as described (45). The energy content was determined for each Arabidopsis line by combusting aliquots of dried plant material (four biological replicates, two technical repetitions) under high oxygen atmosphere using a Calorimeter C2000 (IKA) calibrated with benzoic acid provided by the supplier. Thermal imaging (InfraTec) was carried out on whole plant trays containing 24 pots at randomized positions and within the environmentally controlled plant growth cabinets.