5-Aminolevulinic Acid and 24-Epibrassinolide Improve the Drought Stress Resilience and Productivity of Banana Plants

Abstract

Plant growth, development, and productivity are adversely affected under drought conditions. Previous findings indicated that 5-aminolevulinic acid (ALA) and 24-epibrassinolide (EBL) play an important role in the plant response to adverse environmental conditions. This study demonstrated the role of ALA and EBL on oxidative stress and photosynthetic capacity of drought-stressed 'Williams' banana grown under the Egyptian semi-arid conditions. Exogenous application of either ALA or EBL at concentrations of 15, 30, and 45 mg·L^-1 significantly restored plant photosynthetic activity and increased productivity under reduced irrigation; this was equivalent to 75% of the plant's total water requirements. Both compounds significantly reduced drought-induced oxidative damages by increasing antioxidant enzyme activities (superoxide dismutase 'SOD', catalase 'CAT', and peroxidase 'POD') and preserving chloroplast structure. Lipid peroxidation, electrolyte loss and free non-radical H₂O₂ formation in the chloroplast were noticeably reduced compared to the control, but chlorophyll content and photosynthetic oxygen evolution were increased. Nutrient uptake, auxin and cytokinin levels were also improved with the reduced abscisic acid levels. The results indicated that ALA and EBL could reduce the accumulation of reactive oxygen species and maintain the stability of the chloroplast membrane structure under drought stress. This study suggests that the use of ALA or EBL at 30 mg·L^-1 can promote the growth, productivity and fruit quality of drought-stressed banana plants.

Keywords: 5-aminolevulinic acid; antioxidants; brassinosteroids; chloroplast degeneration; drought; malondialdehyde; photosynthesis.

Figure 1

Effect of foliar spray with 5-aminolevulinic acid (ALA) or 24-Epibrassinolide (EBL) on the leaf nitrogen (N), phosphorus (P), and potassium (K) contents of drought-stressed “Williams” banana plants during the 2018/2019 and 2019/2020 seasons (n = 5). The results are the averages of both seasons, and Duncan’s multiple range test (DMRT) was used for mean comparisons of treatments under each water requirement (WR) level (p ≤ 0.05).

Figure 2

Effect of foliar spray with ALA or EBL on the leaf total chlorophyll content, photosynthetic oxygen evolution, and H₂O₂ generation of drought-stressed “Williams” banana plants during the 2018/2019 and 2019/2020 seasons (n = 5). The results are the averages of both seasons, and DMRT was used for mean comparisons of treatments under each WR level (p ≤ 0.05).

Figure 3

Effect of foliar spray with ALA or EBL on the activity of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) in drought-stressed “Williams” banana plants during the 2018/2019 and 2019/2020 seasons (n = 5). The results are the averages of both seasons, and DMRT was used for mean comparisons of treatments under each WR level (p ≤ 0.05).

Figure 4

Effect of foliar spray with ALA or EBL on the fruit weight, length, and diameter of drought-stressed “Williams” banana plants during the 2018/2019 and 2019/2020 seasons (n = 5). The results are the averages of both seasons, and DMRT was used for mean comparisons of treatments under each WR level (p ≤ 0.05).

Figure 5

Effect of foliar spray with ALA or EBL on the percentage of total soluble solids (TSS), total acidity (TA) and total sugars in the fruit of drought-stressed “Williams” banana plants during the 2018/2019 and 2019/2020 seasons (n = 5). The results are the averages of both seasons, and DMRT was used for mean comparisons of treatments under each WR level (p ≤ 0.05).