3.7 Al and P are co-localized in roots of Al-tolerant XZ29
Since Morin dye may not be able to detect Al bound to cell wall (Eticha, Stass, & Horst, 2005), further examination of the Al uptake and distribution over 72 h was applied using the SIMS technique. In the elongation zone, SIMS-detected Al accumulation increased gradually throughout the experiment (Figure S11a-h). Initial Al accumulation in the epidermal cells with XZ9 exhibited greater accumulation than that in XZ29 (Figure S11a,e). After 24 h, Al was largely accumulated in the apoplast of the cortex (Figure S11c,d,g,h). In the mature zone of XZ29, more Al was accumulated at the inner epidermal layer than the cortex (Figure 8a). We also detected the distribution of P in the mature tissues after 72 h and P levels were generally higher in XZ29 than in XZ9, especially in the stele and epidermis (Figure 8c,d). Interestingly, a strong P signal co-localized with Al at the inner layer of the epidermis (Figure 8a,c). Moreover, the same co-localization between P and Al was not detected for XZ9 despite this accession accumulating more Al in the cortex (Figure 8b,d).