Natural Biostimulant Attenuates Salinity Stress Effects in Chili Pepper by Remodeling Antioxidant, Ion, and Phytohormone Balances, and Augments Gene Expression.

Clara R. Azzam,Atef A. S. Abdel-Kader,Khaled A. M. Khaled,Mostafa M. Rady,Sudad K. Al-Taweel,Ali Majrashi,Alaa I. B. Abou-Sreea,Ranya M. Abdel-Aziz,Hussein E. E. Belal

doi:10.3390/plants10112316

Abstract

A biostimulant is any microorganism or substance used to enhance the efficiency of nutrition, tolerance to abiotic stress and/or quality traits of crops, depending on its contents from nutrients. Plant biostimulants like honey bee (HB) and silymarin (Sm) are a strategic trend for managing stressed crops by promoting nutritional and hormonal balance, regulating osmotic protectors, antioxidants, and genetic potential, reflecting plant growth and productivity. We applied diluted honey bee (HB) and silymarin-enriched honey bee (HB- Sm) as foliar nourishment to investigate their improving influences on growth, yield, nutritional and hormonal balance, various osmoprotectant levels, different components of antioxidant system, and genetic potential of chili pepper plants grown under NaCl-salinity stress (10 dS m‒1). HB significantly promoted the examined attributes and HB-Sm conferred optimal values, including growth, productivity, K+/Na+ ratio, capsaicin, and Sm contents. The antioxidative defense components were significantly better than those obtained with HB alone. Conversely, levels of oxidative stress markers (superoxide ions and hydrogen peroxide) and parameters related to membrane damage (malondialdehyde level, stability index, ionic leakage, Na+, and Cl− contents) were significantly reduced. HB-Sm significantly affects inactive gene expression, as a natural biostimulator silencing active gene expression. SCoT primers were used as proof in salt-treated or untreated chili pepper plants. There were 41 cDNA amplicons selected by SCoT-primers. Twenty of them were EcDNA amplicons (cDNA-amplicons that enhanced their genes by one or more treatments) representing 49% of all cDNA amplicons, whereas 7 amplicons for ScDNA (whose genes were silenced in one or more treatments) represented 17%, and 14 McDNA (monomorphic cDNA-amplicons with control) amplicons were represented by 34% from all cDNA amplicons. This indicates the high effect of BH-Sm treatments in expression enhancement of some inactive genes and their silenced effect for expression of some active genes, also confirming that cDNA-SCoT markers succeeded in detection of variable gene expression patterns between the untreated and treated plants. In conclusion, HB-Sm as a natural multi-biostimulator can attenuate salt stress effects in chili pepper plants by remodeling the antioxidant defense system and ameliorating plant productivity.

Highlights

Peppers (Capsicum spp.), including chili pepper (Capsicum frutescens L.) of the Solanaceae family that grow worldwide, have the most significant and common medicinal properties
Under normal or stress conditions, growth parameters and fruit yield of chili pepper plants were improved by foliar spraying with honey bee (HB) and further improved with honey bee enriched with silymarin (HB-Sm), compared to the corresponding control (Table 3)
Under normal or stress conditions, except for the reduced choline content, relative water content (RWC) and levels of proline, total soluble sugars (TS sugar), and glycine betaine (GB) of the chili pepper plant were significantly increased by foliar spraying with HB and further increased with

Summary

Introduction

Peppers (Capsicum spp.), including chili pepper (Capsicum frutescens L.) of the Solanaceae family that grow worldwide, have the most significant and common medicinal properties. It is mainly cultivated in warm climates, including in Egypt. The spread of chili pepper should be encouraged to obtain more antioxidants related to human health [2,3,4]. Chili peppers are susceptible or moderately susceptible to salinity, which poisons plant cells due to the formation of reactive oxygen species (ROS) [5]. To overcome osmotic and ionic stress, plants alter their biochemical mechanisms and stimulate defense mechanisms by synthesizing more compounds ranging from low-molecular-mass antioxidants to compatible solutes [11,12]. Plants increase ROS-eliminating enzymes like superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), etc., as defense mechanisms under salt stress [16,17]

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