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 ^-1 ) of mixed solution of five PAHs (Σ ₅ PAHs) 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 ^-1 Σ ₅ PAHs 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 Σ ₅ PAHs solution, respectively. Elevated Σ ₅ PAHs concentration in spraying solution significantly (p < 0.0001) decreased cuticular wax content (59.1 and 65.1 vs. 67.8 mg g ^-1 ) in leaves of wheat but exerted slight effects on SLA. Regardless of spraying Σ ₅ PAHs or not, SLA in leaves of Jiaomai (269-276 cm ²  g ^-1 ) and Zhengmai (265-285 cm ²  g ^-1 ) and cuticular wax content (104-118 mg g ^-1 ) in leaves of Zhengmai were significantly higher than other varieties of wheat, respectively. Σ ₅ PAHs concentration in cuticular waxes ranged from 24,616 to 106,353 μg kg ^-1 , which was 2~3 orders and 1~2 orders of magnitude higher than that in mesophylls (46.0-535 μg kg ^-1 ) and leaves (785-5366 μg kg ^-1 ). There was a significant (r = 0.46, p < 0.05, n = 28) positive correlation between SLA and Σ ₅ PAHs concentration in wheat leaves when spraying 1.25 mg L ^-1 of Σ ₅ PAHs. The present study indicated that cuticular wax content was significantly (p < 0.01) positive correlated with Σ ₅ PAHs concentration in the leaves and the translocation factor (TF _w-m ) of PHE, ANT, PYR, and Σ ₅ PAHs 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.