Glycinebetaine mitigates drought stress-induced oxidative damage in pears

Abstract

Glycinebetaine (GB) is an osmoprotectant found in plants under environmental stresses that incorporates drought and is associated with drought tolerance in several plants, such as the woody pear. However, how GB improves drought tolerance in pears remains unclear. In the current study, we explored the mechanism by which GB enhances drought tolerance of whole pear plants (Pyrus bretschneideri Redh. cv. Suli) supplied with exogenous GB. The results showed that on the sixth day after withholding water, levels of O2·-, H2O2, malonaldehyde (MDA) and electrolyte leakage in the leaves were substantially increased by 143%, 38%, 134% and 155%, respectively. Exogenous GB treatment was substantially reduced O2·-, H2O2, MDA and electrolyte leakage (38%, 24%, 38% and 36%, respectively) in drought-stressed leaves. Furthermore, exogenous GB induced considerably higher antioxidant enzyme activity in dry-stressed leaves than drought-stressed treatment alone on the sixth day after withholding water, such as superoxide dismutase (SOD) (201%) and peroxidase (POD) (127%). In addition, these GB-induced phenomena led to increased endogenous GB levels in the leaves of the GB 100 + drought and GB 500 + drought treatment groups by 30% and 78%, respectively, compared to drought treatment alone. The findings obtained were confirmed by the results of the disconnected leaf tests, in which GB contributed to a substantial increase in SOD activity and parallel dose- and time-based decreases in MDA levels. These results demonstrate that GB-conferred drought resistance in pears may be due in part to minimizing symptoms of oxidative harm incurred in response to drought by the activities of antioxidants and by reducing the build-up of ROS and lipid peroxidation.

Fig 1

Impact of glycinebetaine (GB) spray application on levels of O₂·⁻ (A) and H₂O₂ (B) in the blood of pear planting under drought-related stress conditions. On the day of water preservation, the foliage of pear plants was sprayed with a GB solution of 0 (Drought), 100 (GB 100 + drought) or 500 mg L⁻¹ (GB 500 + Drought). The same volume of water was added to well-watered plants. On the third and sixth days of the GB foliar spray (or water retention), soil water levels and leaf water capacity culminated in both the "dryness" and the "GB + drought" classes undergoing mild and severe drought tension. Asterisks demonstrate considerable variations from watery plants (* P < 0.05, ** P < 0.01, Student′s t-test). Six replicates are shown as the mean ± SD.

Fig 2

Glycinebetaine (GB) foliar pellet effects in the leaves of pear seedlings under drought stress (MDA material (A) and electrolyte leakage (B)). The foliage was sprayed on the pear plants with GB solution of 0 (Drought), 100 (GB 100 + drought) or 500 mg L⁻¹ (GB 500 + drought). Well-watered plants with the same amount of water were also sprayed. Depending on the content of soil water and the water capacity, on the third and sixth days after foliar spraying (or withholding of the water), both the "Drought" and "GB + dryness" classes exhibited mild and severe drought stress characteristics. Important discrepancies are shown between asterisks and well-watered plants (* P < 0.05, ** P < 0.01, Student′s t-test). Six replicates of the data are shown as the mean ± SD.

Fig 3

Effects of the application of glycinebetaine (GB) to the leaves of pear seedlings under drought stress for SOD (A), POD (B) and CAT (C). The foliage was sprayed on pear plants with GB solution of 0 (Drought), 100 (GB 100 + drought) or 500 mg L⁻¹ (GB 500 + drought). Well-watered plants with the same volume of water were also sprayed. On the third and sixth days of GB foliar spray (or water retention), soil water levels and leaf water capacity culminated in both the "dryness" and the "GB + drought" classes undergoing mild and severe drought tension. Important discrepancies are shown by asterisks compared to well-watered plants (* P < 0.05, ** P < 0.01, Student′s t-test). Six replicates of the data are shown as the mean ± SD.

Fig 4. Foliar glycinebetaine (GB) spray on the leaves of pear seedlings under drought tension at the endogenous GB stage.

The foliage was sprayed on pear plants with a GB solution of 0 (Drought), 100 (GB 100 + drought) or 500 mg L−1 (GB 500 + drought). Well-watered plants with the same volume of water were also sprayed. On the third and sixth days of the GB foliar spray (or water retention), the soil water levels and leaf water capacity culminated in both the "dryness" and the "GB + drought" classes feeling mild and severe drought tension. Important discrepancies are shown between asterisks and well-watered plants (* P < 0.05, ** P < 0.01, Student′s t-test). Six replicates of the data are shown as the mean ± SD.

Fig 5

Glycinebetaine (GB) therapy’s dose-(A) and time-dependent (B) impact on the severed pear leaves and MDA material. Detached pear leaves were infiltrated with GB solution at varying concentrations for 10 min and permitted to lose water in natural fresh weight (A) or for a separate period (B) through up to 15% evaporation. MDA content was calculated as defined in the Materials and methods section. A was used as a control for nondehydrated leaves that had not been treated with GB (0’). Substantial variations in regulation (0’) were observed (** P < 0.01, Student′s t-test). Three replicates are shown as means ± SD.

Fig 6

Glycinebetaine (GB) treatment affects SOD activity in severed pear leaves in a dose- (A) and time-dependent manner (B). Detached pear leaves were treated with varying amounts with a GB solution for 10 min, and their water was then spontaneously lost through up to 15% evaporation or for a different duration (B) of the initial fresh weight (A). As described in the Materials and methods section, SOD activity was determined. In A, nondehydrated, non-GB-treated leaves were used as controls (0’). Important contrast is shown by the asterisks compared to the controls (0’) (** P < 0.01, Student′s t-test). Three replicates are shown as means ± SD.