Abstract
Drought tolerance is a complex trait controlled by many metabolic pathways and genes and identifying a solution to increase the resilience of plants to drought stress is one of the grand challenges in plant biology. This study provided compelling evidence of increased drought stress tolerance in two sugar beet genotypes when treated with exogenous putrescine (Put) at the seedling stage. Morpho-physiological and biochemical traits and gene expression were assessed in thirty-day-old sugar beet seedlings subjected to drought stress with or without Put (0.3, 0.6, and 0.9 mM) application. Sugar beet plants exposed to drought stress exhibited a significant decline in growth and development as evidenced by root and shoot growth characteristics, photosynthetic pigments, antioxidant enzyme activities, and gene expression. Drought stress resulted in a sharp increase in hydrogen peroxide (H2O2) (89.4 and 118% in SBT-010 and BSRI Sugar beet 2, respectively) and malondialdehyde (MDA) (35.6 and 27.1% in SBT-010 and BSRI Sugar beet 2, respectively). These changes were strongly linked to growth retardation as evidenced by principal component analysis (PCA) and heatmap clustering. Importantly, Put-sprayed plants suffered from less oxidative stress as indicated by lower H2O2 and MDA accumulation. They better regulated the physiological processes supporting growth, dry matter accumulation, photosynthetic pigmentation and gas exchange, relative water content; modulated biochemical changes including proline, total soluble carbohydrate, total soluble sugar, and ascorbic acid; and enhanced the activities of antioxidant enzymes and gene expression. PCA results strongly suggested that Put conferred drought tolerance mostly by enhancing antioxidant enzymes activities that regulated homeostasis of reactive oxygen species. These findings collectively provide an important illustration of the use of Put in modulating drought tolerance in sugar beet plants.
Highlights
Abiotic stresses created by a range of hostile environments are considered a prime limiting factor for plant growth, development, and productivity worldwide [1, 2]
A significant (P 0.05) reduction in plant growth rate (PGR), shoot dry weight (SDW), and root dry weight (RDW) (39.44, 50, and 77.42%, respectively) was found in Bangladesh Sugarcrop Research Institute (BSRI) Sugar beet 2 in response to drought stress compared to the control (Table 2)
The reduction in leaf area (LA), leaf relative water content (LRWC), and root-shoot ratio (RSR) were not significant under drought stress, LRWC increased significantly (37.78%) in the seedlings treated with 0.3 mM Put compared to the drought
Summary
Abiotic stresses created by a range of hostile environments are considered a prime limiting factor for plant growth, development, and productivity worldwide [1, 2]. Plants grown under drought stress produce a pool of reactive oxygen species (ROS) through physiological, biochemical, morphological, and molecular changes [5], causing an imbalance in component quantities and dysfunction of their typical defensive system [12]. This interruption of the defensive system provokes the overproduction of ROS consisting of both non-radical (hydrogen peroxide, H2O2) and free radical species (superoxide, O2−; hydroxyl radical, OH) that are highly detrimental to plant cells [13]
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