*3.4. Compatible Solutes*

Concerning TSS content, the pretreatments with gamma radiation resulted in dramatic decrements (*p* < 0.05) in total soluble sugar (TSS) in wheat plants. Similarly, TSS decreased with increasing concentrations of stigmasterol in non-irradiated and irradiated plants. The control plants had the highest values of TSS compared to the other treatments.

Total soluble phenols showed no significant response to gamma radiation at 25 but were significantly stimulated (*p* < 0.05) with 50 Gy compared with the control value (Figure 3). In addition, stigmasterol at 100 and 200 ppm increased significantly the soluble phenol content in non-irradiated and 25 Gy-irradiated wheat plants over the control values. However, 100 ppm stigmasterol showed no significant effect on total phenols in 50 Gyirradiated plants compared to the corresponding control. The interaction between 50 Gy and 200 ppm stigmasterol achieved the highest value of total phenols compared to the other treatments.

**Figure 3.** Effect of stigmasterol treatments on compatible solutes; (**A**) soluble sugars, (**B**) soluble phenols, and (**C**) proline of wheat plants grown from grain irradiated with gamma rays. The different letters (a–e) show statistical significance at *p* < 0.05; vertical bars indicate ±SD.

Gamma radiation dramatically decreased proline content compared to the control value. The effect of foliar application of stigmasterol on the proline content depended on the applied concentration. Stigmasterol at 100 ppm significantly increased the proline content in wheat plants over the corresponding control values. However, the maximum increase (108%) in proline content was in 50 Gy-irradiated plants treated with 100 ppm stigmasterol compared to the control value. Stigmasterol at 200 ppm shifted the proline content to the minimum value below the control value.

## *3.5. Antioxidant Enzymes*

The data in Figure 4 indicated that irradiated grain with gamma radiation at 25 Gy and 50 Gy significantly (*p* < 0.05) increased the activity of the catalase (CAT) enzyme. Stigmasterol at 100 ppm and 200 ppm significantly (*p* < 0.05) increased the activity of CAT enzyme in wheat plants originating from irradiated and un-irradiated grains. Irradiated plants with 50 Gy and treated with 200 ppm stigmasterol increased the CAT activity by 13.0 (U/g) over the control 3.6 (U/g).

Peroxidase (POX) induced a significant decrease (*p* < 0.05) in response to the tested dose of gamma radiation in wheat plants. Radiation at 25 Gy and 50 Gy significantly decreased POX activity by 25.0% and 50.7%, respectively, compared to control values. On the other hand, stigmasterol increased POX activity compared to untreated wheat plants. Stigmasterol at 100 ppm resulted in the highest increase percentage, reaching 49.73, 84.43, and 173.0% in the 0 Gy-, 25 Gy-, and 50 Gy-irradiated plants, respectively, compared to the corresponding untreated plants.

**Figure 4.** Effect of stigmasterol treatments on the activities of antioxidant enzymes; (**A**) CAT and (**B**) POD, and (**C**) lipid peroxidation of wheat plants grown from grain irradiated with gamma rays. The different letters (a–f) show statistical significance at *p* < 0.05; vertical bars indicate ±SD.
