Effects of cuticular wax content and specific leaf area on accumulation and partition of PAHs in different tissues of wheat leaf.

An indoor simulation experiment was conducted to explore the effects of cuticular wax content and specific leaf area (SLA) on accumulation and distribution of PAHs in different tissues of wheat leaf. Three levels (0, 1.25, 6.0 mg L) of mixed solution of five PAHs (ΣPAHs) including phenanthrene (PHE), anthracene (ANT), pyrene (PYR), benz[a]anthracene (BaA), and benzo[a]pyrene (BaP) were sprayed on leaves of seven varieties of winter wheat for every other day during 20 consecutive days. Shoot and root biomass of wheat under 6.0 mg L ΣPAHs exposure were 5.87 and 0.33 g, which were significantly (p < 0.05) lower than those (7.14 and 0.65 g) without spraying ΣPAHs solution, respectively. Elevated ΣPAHs concentration in spraying solution significantly (p < 0.0001) decreased cuticular wax content (59.1 and 65.1 vs. 67.8 mg g) in leaves of wheat but exerted slight effects on SLA. Regardless of spraying ΣPAHs or not, SLA in leaves of Jiaomai (269-276 cm g) and Zhengmai (265-285 cm g) and cuticular wax content (104-118 mg g) in leaves of Zhengmai were significantly higher than other varieties of wheat, respectively. ΣPAHs concentration in cuticular waxes ranged from 24,616 to 106,353 μg kg, which was 23 orders and 12 orders of magnitude higher than that in mesophylls (46.0-535 μg kg) and leaves (785-5366 μg kg). There was a significant (r = 0.46, p < 0.05, n = 28) positive correlation between SLA and ΣPAHs concentration in wheat leaves when spraying 1.25 mg L of ΣPAHs. The present study indicated that cuticular wax content was significantly (p < 0.01) positive correlated with ΣPAHs concentration in the leaves and the translocation factor (TF) of PHE, ANT, PYR, and ΣPAHs from cuticular wax to mesophyll. Based on principal component analysis (PCA), cuticular wax content was the main limiting factor for folia uptake of PAHs in winter wheat. The present study suggested that cuticular wax could play significant roles in foliar uptake of PAHs of wheat via affecting their accumulation in cuticular wax and translocation to mesophyll.