Interactive effect of drought and cadmium stress on soybean root morphology and gene expression

Recent climatic changes and low water availability due to unpredictable precipitation have reduced the productivity of soybean (Glycine max [L.] Merr.) cultivars. Limited information is available on how drought affects the accumulation and translocation of cadmium (Cd) by affecting soybean root. In this study, we investigated the effect of polyethylene glycol (PEG; 5% and 10%)-induced drought and Cd (0.2 and 0.5 mg L^-1) stresses on soybean root morphology, Cd uptake and gene expression; plants not exposed to these stress (0% PEG and 0 mg L^-1 Cd) served as a control. The results showed that drought affected roots morphology and Cd uptake. The reduction in root length, root area and root diameter and increase in catalase activity was less prominent in drought tolerant cultivars (Shennong20 and Liaodou32) than in drought sensitive cultivars (Liaodou3 and Liaodou10). Genes involved in abscisic acid (ABA) degradation, gibberellin and salicylic acid biosynthesis, hydrogen peroxide (H₂O₂) production and Cd transport were up-regulated, while those involved in zeatinriboside (ZR), indole 3-acetic acid (IAA) and methyl jasmonate (MeJA) biosynthesis were down-regulated under Cd and drought stress. Biosynthesis genes of gibberellin (Glyma03G019800.1), IAA (Glyma02G037600), ZR (XM_003550461.3) and MeJA (Glyma11G007600) were expressed to higher levels in drought tolerant cultivars than in drought sensitive cultivars. These genes represent potential candidates for the development of drought and Cd tolerant soybean cultivars.