24-Epibrassinolide Ameliorates Endogenous Hormone Levels to Enhance Low-Temperature Stress Tolerance in Cucumber Seedlings.

Ali Anwar,Yumei Liu,Li Miao,Xianchang Yu,Shuzhen Li,Longqiang Bai,Yansu Li

doi:10.3390/ijms19092497

Abstract

Phytohormone biosynthesis and accumulation are essential for plant growth and development and stress responses. Here, we investigated the effects of 24-epibrassinolide (EBR) on physiological and biochemical mechanisms in cucumber leaves under low-temperature stress. The cucumber seedlings were exposed to treatments as follows: NT (normal temperature, 26 °C/18 °C day/night), and three low-temperature (12 °C/8 °C day/night) treatments: CK (low-temperature stress); EBR (low-temperature and 0.1 μM EBR); and BZR (low-temperature and 4 μM BZR, a specific EBR biosynthesis inhibitor). The results indicated that low-temperature stress proportionately decreased cucumber seedling growth and the strong seedling index, chlorophyll (Chl) content, photosynthetic capacity, and antioxidant enzyme activities, while increasing reactive oxygen species (ROS) and malondialdehyde (MDA) contents, hormone levels, and EBR biosynthesis gene expression level. However, EBR treatments significantly enhanced cucumber seedling growth and the strong seedling index, chlorophyll content, photosynthetic capacity, activities of antioxidant enzymes, the cell membrane stability, and endogenous hormones, and upregulated EBR biosynthesis gene expression level, while decreasing ROS and the MDA content. Based on these results, it can be concluded that exogenous EBR regulates endogenous hormones by activating at the transcript level EBR biosynthetic genes, which increases antioxidant enzyme capacity levels and reduces the overproduction of ROS and MDA, protecting chlorophyll and photosynthetic machinery, thus improving cucumber seedling growth.

Highlights

During their life cycles, plants are challenged by many kinds of biotic and abiotic stresses, which influence their growth and productivity
The results of the present study suggest that low-temperature stress caused oxidative stress by overproduction of reactive oxygen species (ROS) and MDA, and decreased antioxidant enzyme activity which would otherwise damage membrane stability, reduce chlorophyll, and limit photosynthetic capacity, all of which result a significant reduction in cucumber seedling growth
Application of exogenous EBR alleviated this inhibition by improving the chlorophyll content and photosynthetic capacity levels, enhancing tolerance to low-temperature stress

Summary

Introduction

Plants are challenged by many kinds of biotic and abiotic stresses, which influence their growth and productivity. Low-temperature stress hampers plant growth and development, resulting in yield reductions, especially in vegetable crops, such as cucumber, tomato, and pepper [2,3,4]. Greenhouse vegetable production is very common in the world during winter cultivation, though frequent sudden temperature drops occur, which can lead to serious plant damage. Low temperatures lead to reduced plant growth, flower drop, reduced yield, and economic losses in vegetable crops. Previous studies reported that chilling stress hampers plant growth and development by decreasing enzymatic activities, increasing the accumulation of reactive oxygen species (ROS), damaging membrane stability, reducing chlorophyll (Chl) biosynthesis, and impairing the photosynthetic machinery [5,6]

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