The effects of mepiquat chloride (DPC) on the soluble protein content and the activities of protective enzymes in cotton in response to aphid feeding and on the activities of detoxifying enzymes in aphids

Abstract

Background Mepiquat chloride (DPC) enhances the resistance of cotton plants, and it is widely used as a growth regulator. DPC can stimulate photosynthesis, stabilize the structure of cotton leaves, and affect population reproduction and energy substances in Aphis gossypii Glover (cotton aphids), but interactions between DPC and cotton aphids remain unclear. In this study, we analyzed the physiological responses of cotton to DPC, and the toxicity of DPC toward cotton aphids, before and after feeding, to explore the DPC-induced defense mechanism against cotton aphids. Results Measurements of protective enzyme activity in cotton showed that the soluble protein contents, peroxidase (POD) activity, and catalase (CAT) activity in cotton treated with different concentrations of DPC were higher than in the control. Superoxide dismutase (SOD) activity was higher than that of the control when the concentration of DPC was < 0.1 g/L. Under aphid feeding stress, POD activity in cotton treated with a low insect population density was significantly lower than in the controls, but the reverse was true for cotton treated with a high insect population density, and SOD activity was positively correlated with population density. The activities of detoxification enzymes in field and laboratory experiments showed that DPC promoted the specific activity of glutathione S-transferase (GST) in cotton aphids, while the specific activities of carboxylesterase (CarE) and acetylcholinesterase (AchE) were decreased. Conclusions DPC enhanced the aphid resistance in cotton by increasing the soluble protein content and the activity of protective enzymes. It also had a toxic effect on cotton aphids by increasing GST activity (the main DPC target). DPC increased the soluble protein content and protective enzymes activity in cotton under aphid stress, and thereby enhanced tolerance to cotton aphids. It conclude that DPC interferes with cotton aphids through indirect (DPC induced cotton defense responses) and direct (DPC toxicity to cotton aphids) ways, which plays a positive role in interfering with cotton aphids.

Increasing the activities of protective enzymes is an important strategy to improve resistance in cucumber to powdery mildew disease and melon aphid under different infection/infestation patterns

“…When cucumber plants are damaged by the leaf miner Liriomyza huidobrensis, the can adapt to insect stress by regulating the main nutrients, secondary metabolites, chlorophyll content, and defensive enzyme activity (Sun et al, 2012(Sun et al, , 2013. In our previous studies, we found that cotton aphid feeding can also cause changes in the photosynthetic capacity, nutrient levels, metabolic pathways, protective enzyme activities, and other defense mechanisms in the host cotton plants (Zhang et al, 2020, Zhang Q. C. et al, 2022a. In this study, we found that when only infected with powdery mildew, the cucumber plants were able to resist the powdery mildew pathogen by increasing the soluble protein and soluble sugar contents, and regulation the activities of protective enzymes, but the response of protective enzymes is not so intense (Figures 1, 2A,B).…”

“…After applying pesticides, the desired outcome is to reduce the occurrence of pests and diseases and to alleviate the stress on the plants. However, our latest research shows that mepiquat chloride (DPC), a plant growth regulator, not only has toxic effects on cotton aphids ( A. gossypii ), but also enhances the defense response of cotton plants against cotton aphids ( Zhang Q. C. et al, 2022a ). In this study, we also found that both azoxystrobin and imidacloprid treatment increased chlorophyll ( Figures 9A , 11A ), soluble protein ( Figures 10A , 12A ), and free proline contents ( Figures 10C , 12C ), and increased SOD activity ( Figures 9B , 11B ) and decreased MDA content ( Figures 10D , 12D ) in cucumber leaves.…”

Protective enzyme activity regulation in cotton (Gossypium hirsutum L.) in response to Scirpus planiculmis stress

“…Therefore, we believe that when controlling S. planiculmis , application of low-dose selective herbicides may help cotton to resist stress caused by weeds. Our previous studies showed that application of low-dose insecticides, fungicides and plant growth regulators can increase protective enzyme activities of cotton, and help resist pest-associated stress ( Zhang et al., 2022c ; Zhang et al., 2022d ; Zhang et al., 2022e ). Clearly, a low-dose pesticide can stimulate the defence response of cotton.…”

Current views of drought research: experimental methods, adaptation mechanisms and regulatory strategies

“…These exogenous hormones can usually promote seed germination, seedling growth and development, increase the content of osmotic adjustment substances in leaves, antioxidant enzyme activity and chlorophyll content, reduce the relative conductivity and malondialdehyde content of seedling leaves, thereby improving the drought resistance of crops ( Arnao and Hernández-Ruiz, 2018 ; Ahmad et al., 2023 ; Liu et al., 2023 ). Some plant growth regulators, such as mepiquat chloride, are commonly used to regulate cotton plant type, but can also increase soluble protein content and antioxidant enzyme activity ( Zhang et al., 2022d ). It can also promote the accumulation of flavonoids in soybeans to enhance drought resistance ( Figure 3 ) ( Wang et al., 2023a ).…”