Physiological and Genetic Effects of Imazamox Treatment on Imidazolinone-Sensitive and Resistant Sunflower Hybrids

Use of herbicides is one of the most preferred options for crop protection against weeds. Imazamox is an imidazolinone (IMI)-group herbicide, and even low concentrations of imazamox might exhibit high biological activities on soil and plants. Therefore, in contrast to the conventional types of sunflowers that are sensitive to IMI-group herbicides, sunflowers that are resistive to IMI-group herbicides were also developed in recent years. In this study, the effect of imazamox on some physiological and genetic parameters of two types of sunflowers that are sensitive and resistant to IMI-group herbicides is comparatively investigated. For this purpose, three concentrations of imazamox (0.82, 1.64 and 2.45 mM, respectively) were applied on the two types of sunflower (i.e. SN:8 as IMI-sensitive type and SN:9 as IMI-resistant type, respectively). In addition, the physiological and molecular effects of IMI on antioxidant enzymes (such as superoxide dismutase (SOD), catalase, glutathione S-transferase (GST)), heat shock proteins (such as HSP26, HSP60, HSP70), phenolic contents (coumaric acid, caffeic acid, ferulic acid), phytohormone levels (indole-3-acetic acid, jasmonic acid (JA), salicylic acid (SA)) and accumulation of pesticides in the leaf tissue of sunflowers were analysed by qRT-PCR and LC MS/MS analysis. In this study, the pesticide concentration of resistant-type SN9 was significantly greater than that of SN8 with the application of 1.64–2.45 mM of imazamox, and the total pesticide amounts were 1.6 and 1.8 times significantly higher in leaf tissues, respectively. This pesticide accumulation led to an imbalance in the phytohormone and phenolic levels, increased levels of unfolded or misfolded proteins, and selective reduction of the GST, SA and JA levels in the two types of sunflowers. However, SN9 significantly responded to the pesticide accumulation via the overexpression of mitochondrial chaperone HSP60 (16.15-fold) and stress-specific HSP70 (54.46-fold), as well as higher SOD expression and SA and JA levels. In particular, by the application of high-dose IMI, our data revealed strong protein chaperone response, a high level of SOD expression, and finally the crosstalk of SA and JA, and these physiological and molecular phenomena can be indicative of pesticide-induced stress in SN9. The study suggested that high-concentration imazamox treatment induces some physiological and genetic changes at the phytotoxic level on not only IMI sensitive type but also resistant type.