The combination of arbuscular mycorrhizal fungi inoculation (Glomus versiforme) and 28-homobrassinolide spraying intervals improves growth by enhancing photosynthesis, nutrient absorption, and antioxidant system in cucumber (Cucumis sativus L.) under salinity

Abstract

Salinity is one of the major obstacles in the agriculture industry causing huge losses in productivity. Several strategies such as plant growth regulators with arbuscular mycorrhizal fungi (AMF) have been used to decrease the negative effects of salt stress. In our experiment, 28-homobrassinolide (HBL) with spraying intervals was combined with AMF (Glomus versiforme) in cucumber cultivars Jinyou 1^# (salt sensitive) and (Changchun mici, in short, CCMC, salt tolerant) under NaCl (100 mmol/L). Studies have documented that the foliar application of HBL and AMF colonization can enhance tolerance to plants under stress conditions. However, the mechanism of the HBL spraying intervals after 15 and 30 days in combination with AMF in cucumber under salt stress is still unknown. Our results revealed that the HBL spraying interval after 15 days in combination with AMF resulted in improved growth, photosynthesis, and decreased sodium toxicity under NaCl. Moreover, the antioxidant enzymes SOD (superoxide dismutase; EC 1.15.1.1) and POD activity (peroxidase; EC 1.11.1.7) showed a gradual increase after every 10 days, while the CAT (catalase; EC 1.11.1.6) increased after 30 days of salt treatments in both cultivars. This research suggests that the enhanced tolerance to salinity was mainly related to elevated levels of antioxidant enzymes and lower uptake of Na⁺, which lowers the risk of ion toxicity and decreases cell membrane damage.

Keywords: 28‐homobrassinolide; NaCl stress; antioxidants; arbuscular mycorrhizal fungi; cucumber.

Figure 1

Effect of HBL spraying intervals, AMF, and their combination on electrolyte leakage and relative leaf water content of leaves after 25 and 45 days in cucumber cultivars Jinyou 1# and CCMC under NaCl (100 mmol/L), respectively. Data are means of three replicates ± standard error. Means followed by the same letters in a column are not significantly different at p = .05 using LSD

Figure 2

Effect of HBL spraying intervals, AMF, and their combination on photosynthesis [mmol/L(co₂)m⁻² s⁻¹], carbon dioxide (ppm), stomatal conductance (mol m⁻² s⁻¹), and transpiration rate (mmol/L m⁻² s⁻¹) on cucumber cultivars Jinyou 1^# and CCMC under NaCl (100 mmol/L), respectively. Data are means of three replicates ± standard error. Means followed by the same letters in a column are not significantly different at p = .05 using LSD

Figure 3

Effect of HBL spraying intervals, AMF, and their combination on AMF colonization in roots of cucumber cultivars Jinyou 1^# and CCMC under NaCl (100 mmol/L), respectively. Means followed by the same letters in a column are not significantly different at p = .05 using LSD

Figure 4

Effect of HBL spraying intervals, AMF, and their combination on antioxidant enzymes, superoxide dismutase (U g⁻¹ FW hr⁻¹), peroxidase (μg g⁻¹ FW min⁻¹), catalase (μg g⁻¹ FW min⁻¹), and malondialdehyde content (mmol/g FW) of cucumber cultivar Jinyou 1^# under NaCl (100 mmol/L). Data (means ± SD, n = 3) sharing the same letters above the bars are not significantly different at p = .05

Figure 5

Effect of HBL spraying intervals, AMF, and their combination on antioxidant enzymes, superoxide dismutase (U g⁻¹ FW hr⁻¹), peroxidase (μg g⁻¹ FW min⁻¹), catalase (μg g⁻¹ FW min⁻¹), and malondialdehyde content (mmol/g FW) of cucumber cultivar CCMC under NaCl (100 mmol/L). Data (means ± SD, n = 3) sharing the same letters above the bars are not significantly different at p = .05

Figure 6

The combination of 28‐homobrassinolide spraying intervals and AMF‐elevated photosynthesis, relative water content, and antioxidant system in leaves as well as AMF colonization in roots. Moreover, it decreased leaf electrolyte leakage and sodium ion concentration in shoots and roots, which resulted in improved growth of cucumber plants under NaCl