Plant materials and growth conditions
Seedlings of two tomato genotypes (JZ34 [low K+tolerant] and JZ18 [low K+ sensitive]) (Zhao et al. 2019) were grown under standard greenhouse conditions at 26/18℃ (day/night) with a photoperiod of 16 h light/8 h dark. Seedlings at the vegetative growing stage (25 days) were cleaned with water, washed three times with distilled water, and transferred to a pot (50 cm length, 30 cm width, 10 cm height) containing 12 L nutrient solution composed of 1.5 mM Ca(NO3)2· 4H2O, 4 mM KNO3, 0.67 mM NH4H2PO4, 2 mM MgSO4· 7H2O, 0.05 mM H3BO3, 0.009 mM MnSO4· 4H2O, 0.7 mM ZnSO4· 7H2O, 0.32 mM CuSO4· 5H2O, 0.1 mM
(NH4)2MoO4, 0.05 mM FeSO4· 7H2O, and 0.04 mM Na2-EDTA. The pH was adjusted to 5.8 ± 0.1 as required. The nutrient solution was replaced once every 3 days. At the vegetative growing stage (30 days), K+ deficiency treatment was applied by reducing the concentration of KNO3 from 4 mM (normal K+ ) to 0.5 mM (K+ deficiency) in the nutrient solution. A concentration of 4 mM KNO3 was used as a control. After 7 days of K+ deficiency stress, different parts of the plant were sampled and dried to assess plant root configuration, dry weight, and K+ content.