Spatial-Temporal Response of Reactive Oxygen Species and Salicylic Acid Suggest Their Interaction in Pumpkin Rootstock-Induced Chilling Tolerance in Watermelon Plants.

Fei Cheng,Min Gao,Junyang Lu,Yuan Huang,Zhilong Bie

doi:10.3390/antiox10122024

Fei Cheng, Min Gao + Show 3 more

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https://doi.org/10.3390/antiox10122024

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Abstract

Grafting with pumpkin rootstock could improve chilling tolerance in watermelon, and salicylic acid (SA) as a signal molecule is involved in regulating plant tolerance to chilling and other abiotic stresses. To clarify the mechanism in pumpkin rootstock-induced systemic acquired acclimation in grafted watermelon under chilling stress, we used self-grafted (Cl/Cl) and pumpkin rootstock-grafted (Cl/Cm) watermelon seedlings to study the changes in lipid peroxidation, photosystem II (PSII) activity and antioxidant metabolism, the spatio–temporal response of SA biosynthesis and H2O2 accumulation to chilling, and the role of H2O2 signal in SA-induced chilling tolerance in grafted watermelon. The results showed that pumpkin rootstock grafting promoted SA biosynthesis in the watermelon scions. Chilling induced hydrolysis of conjugated SA into free SA in the roots and accumulation of free SA in the leaves in Cl/Cm plants. Further, pumpkin rootstock grafting induced early response of antioxidant enzyme system in the roots and increased activities of ascorbate peroxidase and glutathione reductase in the leaves, thus maintaining cellular redox homeostasis. Exogenous SA improved while the inhibition of SA biosynthesis reduced chilling tolerance in Cl/Cl seedlings. The application of diphenyleneiodonium (DPI, inhibitor of NADPH oxidase) and dimethylthiourea (DMTU, H2O2 scavenger) decreased, while exogenous H2O2 improved the PSII activity in Cl/Cl plants under chilling stress. Additionally, the decrease of the net photosynthetic rate in DMTU- and DPI-pretreated Cl/Cl plants under chilling conditions could be alleviated by subsequent application of H2O2 but not SA. In conclusion, pumpkin rootstock grafting induces SA biosynthesis and redistribution in the leaves and roots and participates in the regulation of antioxidant metabolism probably through interaction with the H2O2 signal, thus improving chilling tolerance in watermelon.

Highlights

Watermelon (Citrullus lanatus) is a warmth-loving plant originating from tropicalAfrica
In order to clarify the mechanism of pumpkin rootstock grafting in improving chilling tolerance of watermelon, we investigated the spatio–temporal response of chlorophyll fluorescence, membrane lipid peroxidation, antioxidant enzyme activities, cellular redox status, salicylic acid (SA) biosynthesis, and H2 O2 accumulation to chilling stress in self-grafted and pumpkin rootstock-grafted watermelon plants
The ΦPSII showed constant decrease in Cl/Cl seedlings within seven days of chilling stress, while that in Cl/Cm seedlings decreased slightly in comparison with control (Figure 1D). These results indicated that pumpkin rootstock alleviated the oxidative damage of chilling stress in grafted watermelon seedlings

Summary

Introduction

It requires a higher temperature in the whole process of growth and development, being not resistant to temperatures below 15 ◦ C. Watermelon plants usually suffer from chilling (0~15 ◦ C) or freezing (

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