In this study, we have evaluated the role of karrikin (KAR¹) against the absorption and translocation of a persistent organic pollutant (POP), 2,4,4'-Tribromodiphenyl ether (BDE-28) in plants, in the presence of two other stressors, cadmium (Cd) and high temperature. Furthermore, it correlates the physiological damages of Brassica alboglabra with the three stresssors separately. The results revealed that the post-germination application of KAR¹ successfully augmented the growth (200%) and pertinent physiochemical parameters of B. alboglabra. KAR¹ hindered air absorption of BDE-28 in plant tissues, and reduced its translocation coefficient (TF). Moreover, BDE-28 was the most negatively correlated (-0.9) stressor with chlorophyll contents, while the maximum mitigation by KAR¹ was also achieved agaist BDE-28. The effect of temperature was more severe on soluble sugars (0.51), antioxidative machinery (-0.43), and osmoregulators (0.24). Cd exhibited a stronger inverse interrelation with the enzymatic antioxidant cascade. Application of KAR¹ mitigated the deleterious effects of Cd and temperature stress on plant physiological parameters along with reduced aero-concentration factor, TF, and metal tolerance index. The phytohormone reduced lipid peroxidation by decreasing synthesis of ROS and persuading its breakdown. The stability of cellular membranes was perhaps due to the commotion of KAR¹ as a growth-promoting phytohormone. In the same way, KAR¹ supplementation augmented the membrane stability index, antioxidant defense factors, and removal efficiency of the pollutants. Consequently, the exogenously applied KAR¹ can efficiently alleviate Cd stress, heat stress, and POP toxicity.

Xu, X., Wang, R., Chao, J., Lin, Y., Jin, Q., He, X., Luo, S. and Wu, T. 2015. The expression patterns of Cucumis sativus WRKY (CsWRKY) family under the condition of inoculation with Phytophthora melonis in disease resistant and susceptible cucumber cultivars. Can. J. Plant Sci. 95: 1121–1131. Based on RNA-seq, we analyzed expression patterns of 55 CsWRKYs in the disease-resistant cultivar (JSH) and the disease-susceptible cucumber cultivar (B80) at 0 and 40 h post-inoculation with Phytophthora melonis. After inoculation with P. melonis, in JSH and B80, the number of up-regulated CsWRKY genes was both 25 with 22 commonly up-regulated genes, and there were 22 CsWRKY genes down-regulated in JSH and 23 in B80 with 18 commonly down-regulated genes, and there were eight CsWRKY genes with no or little change in transcript expression in JSH and seven in B80 with four common genes. Among the 55 CsWRKY genes, 17 genes showed significant differences (differences > twofold) in the degree of change of gene transcription level between JSH and B80 from RNA-seq data analysis, and the results validated using real-time PCR showed that there were only six genes (CsWRKY2, 20, 26, 35, 44, 52) out of the 17 that exhibited significant differences (differences > twofold) with four genes (CsWRKY2, 20, 26, 52) consistent with the data from RNA-seq and two genes (CsWRKY 35, 44) inconsistent with the data from RNA-seq. In addition, the six genes were strongly up-regulated after salicylic acid (SA) treatment with five genes (CsWRKY2, 20, 26, 35, 44) up to peak at 12 h and one gene (CsWRKY52) up to peak at 24 h in expression and that four CsWRKY genes (CsWRKY2, 20, 44, 52) out of six were strongly up-regulated with three genes (CsWRKY2, 20, 44) up to the highest point at 24 h and one gene (CsWRKY52) up after methyl jasmonate (MeJA) treatment. Based on the results above, we predicted CsWRKY2, 20, 26, 35, 44 and 52 may be involved in disease resistance of JSH against Phytophthora melonis by SA and (or) JA signaling pathway(s).