Abstract

Heavy metal contamination in soil is increasing rapidly due to increasing anthropogenic activities. Despite the importance of rose-scented geranium as a medicinal plant, little attention was paid to enhancing its productivity in heavy metal-polluted soil. In this regard, endophytes improve plant resistance to heavy metal toxicity and enhance its tissue quality. Here, the impact of the three endophytic fungi Talaromyces versatilis (E6651), Emericella nidulans (E6658), and Aspergillus niger (E6657) on geranium growth, tolerance, and tissue quality under cadmium (Cd) stress was investigated. In contrast to E. nidulans, T. versatilis and A. niger enhanced geranium growth and the stimulatory effect was more pronounced under Cd-stress. The three endophytes significantly alleviated Cd accumulation and increased mineral content in geranium leaves. In addition, endophytic fungi successfully alleviated Cd-induced membrane damage and reinforced the antioxidant defenses in geranium leaves. Inoculation with endophytes stimulated all the antioxidant enzymes under Cd-stress, and the response was more obvious in the case of T. versatilis and A. niger. To reduce the toxicity of tissue-Cd levels, T. versatilis and A. niger upregulated the detoxification mechanisms; glutathione-S-transferase, phytochelatin, and metallothionein levels. Moreover, endophytic fungi improved the medicinal value and quality of geranium by increasing total antioxidant capacity (TAC), phenolic compound biosynthesis (phenylalanine ammonia-lyase), and vitamin content as well as the quantity and quality of essential oil, particularly under Cd-stress conditions. The variation in the mechanisms modulated by the different endophytic fungi was supported by Principal Component Analysis (PCA). Overall, this study provided fundamental insights into endophytes’ impact as a feasible strategy to mitigate the phytotoxicity hazards of Cd-stress in geranium and enhance its quality, based on the growth and biochemical investigations.

Highlights

  • The three endophytic fungi were isolated from different organs of the medicinal plant Pelargonium graveolens according to our previous article [31]

  • DNA was extracted from a single spore of each fungal isolate and subjected to molecular identification where the nuclear DNA region containing the internal transcribed spacer 1 and 2 (ITS1 and ITS2) and two regions of the rRNA gene cluster, was amplified by PCR

  • Since fresh leaves are the main bulk of biomass yield and the main source of geranium oil extracted from the plant [53], we studied the growth in terms of the fresh weight of leaves

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Summary

Introduction

Rose-scented geranium (Pelargonium graveolens) is an important medicinal aromatic plant. The plant is commonly utilized for the extraction of essential oil (geranium oil). The essential oil is produced as 70–170 kg ha−1 geranium [1]. The price of geranium oil is expensive and reaches $120 kg−1 [2]. Egypt is in the second grade after

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