Exogenously Supplemented Proline and Phenylalanine Improve Growth, Productivity, and Oil Composition of Salted Moringa by Up-Regulating Osmoprotectants and Stimulating Antioxidant Machinery

Abstract

Salinity is linked to poor plant growth and a reduction in global food output. Therefore, there is an essential need for plant adaptation and mitigation of salinity stress conditions. Plants combat salinity stress influences by promoting a set of physiological, biochemical, and molecular actions. Tremendous mechanisms are being applied to induce plant stress tolerance, involving amino acid application. For evaluating the growth and productivity of Moringa oleifera trees grown under salt stress conditions, moringa has been cultivated under different levels of salinity and subjected to a foliar spray of proline (Pro) and phenylalanine (Phe) amino acids. Moringa plants positively responded to the lowest level of salinity as the leaves, inflorescences, seeds, and oil yields have been increased, but the growth and productivity slightly declined with increasing salinity levels after that. However, Pro and Phe applications significantly ameliorate these effects, particularly, Pro-treatments which decelerated chlorophyll and protein degradation and enhanced vitamin C, polyphenols, and antioxidant activity. A slight reduction in mineral content was observed under the high levels of salinity. Higher osmoprotectants (proline, protein, and total soluble sugars) content was given following Pro treatment in salted and unsalted plants. A significant reduction in oil yield was obtained as affected by salinity stress. Additionally, salinity exhibited a reduction in oleic acid (C18:1), linoleic (C18:2), and linolenic (C18:3) acids, and an increase in stearic (C18:0), palmitic (C16:0), eicosenoic (C20:2), and behenic (C22:0) acids. Generally, Pro and Phe treatments overcome the harmful effects of salinity in moringa trees by stimulating the osmoprotectants, polyphenols, and antioxidant activity, causing higher dry matter accumulation and better defense against salinity stress.

Keywords: abiotic stress; fatty acids; linoleic acids; moringa; oleic acid; proline; salinity.

Figure 1

Influence of exogenous spray treatments of proline (Pro) or phenylalanine (Phe) on (A) plant height and (B) stem diameter of moringa trees cultivated under different levels of salinity. Data are mean value ± SE. Bars with different letters are significantly different at p ≤ 0.05 level.

Figure 2

Influence of exogenous spray treatments of proline (Pro) or phenylalanine (Phe) on (A) leaves number, (B) leaves fresh weight, and (C) leaves dry weight tree⁻¹ of moringa trees cultivated under different levels of salinity. Data are mean value ± SE. Bars with different letters are significantly different at p ≤ 0.05 level.

Figure 3

Influence of exogenous spray treatments of proline (Pro) or phenylalanine (Phe) on (A) inflorescences number tree⁻¹, (B) pods number inflorescence⁻¹, (C) pods number tree⁻¹, and (D) pod weight of moringa trees cultivated under different levels of salinity. Data are mean value ± SE. Bars with different letters are significantly different at p ≤ 0.05 level.

Figure 4

Influence of exogenous spray treatments of proline (Pro) or phenylalanine (Phe) on (A) yield of mature pods tree⁻¹, (B) seeds number pod⁻¹, (C) seed weight, and (D) seed yield tree⁻¹ of moringa trees cultivated under different levels of salinity. Data are mean value ± SE. Bars with different letters are significantly different at p ≤ 0.05 level.

Figure 5

Influence of exogenous spray treatments of proline (Pro) or phenylalanine (Phe) on (A) total chlorophyll, (B) total phenols, and (C) flavonoids content of moringa leaves cultivated under different levels of salinity. Data are mean value ± SE. Bars with different letters are significantly different at p ≤ 0.05 level.

Figure 6

Influence of exogenous spray treatments of proline (Pro) or phenylalanine (Phe) on (A) proline, (B) protein, and (C) total soluble solids (TSS) of moringa leaves cultivated under different levels of salinity. Data are mean value ± SE. Bars with different letters are significantly different at p ≤ 0.05 level.

Figure 7

Influence of exogenous spray treatments of proline (Pro) or phenylalanine (Phe) on (A) antioxidant activity and (B) vitamin C of moringa trees cultivated under different levels of salinity. Data are mean value ± SE. Bars with different letters are significantly different at p ≤ 0.05 level.

Figure 8

Influence of exogenous spray treatments of proline (Pro) or phenylalanine (Phe) on (A) phosphorus (P) and (B) potassium (K) content of moringa leaves cultivated under different levels of salinity. Data are mean value ± SE. Bars with different letters are significantly different at p ≤ 0.05 level.

Figure 9

Influence of exogenous spray treatments of proline (Pro) or phenylalanine (Phe) on (A) oil % and (B) oil yield of moringa trees cultivated under different levels of salinity. Data are mean value ± SE. Bars with different letters are significantly different at p ≤ 0.05 level.