**1. Introduction**

Wheat (*Triticum aestivum*, L.) is the main strategic cereal crop. It has high nutritional value as it is rich in carbohydrates, essential amino acids, fiber components, vitamins, and minerals [1]. Global wheat production amounted to around 778.6 million tons from 2020 to 2021 [2]. Wheat is used for making bread, starch, and wheat germ oil. The nutritional value of grains of bread-making quality depends mainly on the various protein constituents [3]. Wheat plants are exposed to numerous stressors, such as ionizing radiation stress, that seriously affect plant growth and productivity [4].

Ionizing radiation is a pollutant that could potentially lead to disturbances in ecosystems [5]. Gamma-radiation is an electromagnetic wave that results in ionizing radiation that impacts different biological macromolecules and induces variable biological effects [6,7]. The effects of gamma-rays on plant growth and development are diverse, ranging from stimulatory to inhibitory effects depending on the radiation dose, exposure duration, the

**Citation:** Hussein, H.-A.A.; Alshammari, S.O.; Elkady, F.M.; Ramadan, A.A.; Kenawy, S.K.M.; Abdelkawy, A.M. Radio-Protective Effects of Stigmasterol on Wheat (*Triticum aestivum* L.) Plants. *Antioxidants* **2022**, *11*, 1144. https://doi.org/10.3390/ antiox11061144

Academic Editor: Nafees A. Khan

Received: 9 May 2022 Accepted: 6 June 2022 Published: 10 June 2022

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response and sensitivity of different plant species and cultivars, and their interaction inside the cell, especially in water, to produce free radicals [8] that change the biochemical processes of plants [9]. Previous studies have investigated the effect of dose and exposure time of gamma-ray irradiation on seed germination and physiological parameters. Gamma rays at 100 Gy enhanced growth, yield characters, and certain biochemical constitutes of fenugreek [10] and wheat plants [11]. A recent study revealed that IS-Jarissa wheat varieties were able to live after exposure to radiation doses of 0 Gy, 100 Gy, 200 Gy, 300 Gy, and 400 Gy [12]. Additionally, gamma radiation at 200 Gy enhanced flavonoid compounds in 37 wheat lines [13], while ionizing radiation from 10 to 1000 Gy caused dramatic alterations in the composition of plant cells and induced cell death [14,15]. Mean germination time, root and shoot length, and seedling dry weight of wheat genotypes (Roshan and T-65-58-8) decreased with increasing radiation doses (100, 200, 300, and 400 Gy) [16]. Additionally, the radiation doses of 10, 15, 20, 25 and 30 kR caused different types of chromosomal anomalies in wheat plants, which increased with the increasing intensity of gamma radiation [17].

Plants produce mixtures of sterols, including stigmasterol, campesterol, and sitosterol. Stigmasterol belongs to the plant sterols and is a precursor of brassinosteroids, which act as growth regulators [18]. Additionally, Campesterol is the precursor of BR; the crucial role of BR in plant growth and development is well established [19], while sitosterol participates in cellulose synthesis [20]. Stigmasterol is implicated in the structure of phospholipid constituents, maintaining plasma membrane fluidity and permeability [19,21,22]. Moreover, foliar application of stigmasterol improved the growth characters, yield, anatomical structures, and percentage/composition of essential oil of basil plants [23]. Stigmasterol may be involved in gravitropism and tolerance to abiotic stress [19]. Indeed, stigmasterol application of germinating seeds enhanced the salt tolerance of faba beans and flax plants [24,25]. It is, however, unclear whether stigmasterol can overcome the harmful effects of ionizing radiation stress. As the cost of stigmasterol is brought down to affordable levels [24], the present research theme may contribute greatly to the usage of stigmasterol in agriculture production as well as to overcome the threat of ionizing radiation on crop plants around the world. Therefore, our purpose is to examine the role of stigmasterol in alleviating the adverse effects of γ-radiation on wheat plants and to understand the direct role of stigmasterol in plant growth and stress responses.
