Abstract
With increasing areas of direct sowing, low-temperature (LT) stress drastically affects global rice production. Exogenous applications of melatonin (MT) serve as one of the effective ways to improve seed germination under various stress conditions. In this study, we found that MT treatment greatly improved the LT stress-induced loss of germination percentage and the weak performance of seedlings under LT of constant 20°C (LT20). This was largely dependent on the activated antioxidant system and enhanced activities of storage substance utilization-associated enzymes. Moreover, we also detected that exogenous feeding of MT significantly increased the biosynthesis of gibberellin (GA) and endogenous MT but simultaneously inhibited the accumulation of abscisic acid (ABA) and hydrogen peroxide (H2O2) under LT20 stress. These results suggested that MT had antagonistic effects on ABA and H2O2. In addition, MT treatment also significantly enhanced the expression of CATALYSE 2 (OsCAT2), which was directly regulated by ABA-INSENSITIVE 5 (OsABI5), a core module of ABA-stressed signals, and thus promoting the H2O2 scavenging to reach reactive oxygen species (ROS) homeostasis, which consequently increased GA biosynthesis. However, in abi5 mutants, OsCAT2 failed in response to LT20 stress irrespective of MT treatment, indicating that OsABI5 is essential for MT-mediated seed germination under LT20 stress. Collectively, we now demonstrated that MT showed a synergistic interaction with an ABI5-mediated signal to mediate seed germination, partially through the direct regulation of OsCAT2.
Highlights
Seed germination is vital for the subsequent establishment of seedlings in higher plants (Bewley, 1997)
In abi5-1 and abi5-2, there were no significant differences in transcriptional abundance presented under low temperatures (LTs) of constant 20◦C (LT20) stress with or without MT (Figures 6B–E). All these results indicated that OsABI5 mutation affects the expression of genes for the biosynthesis of endogenous MT under LT20 stress even in the conditions of exogenous MT treatment
LT20 stress, irrespective of MT treatment (Figure 7F and Supplementary Figures 6A–D). These results suggested that MT had a synergistic interaction on GA biosynthesis, which was inhibited in OsABI5 mutants
Summary
Seed germination is vital for the subsequent establishment of seedlings in higher plants (Bewley, 1997). Some favorable environmental conditions, including at least optimal temperature, water, and oxygen, are required for the initiation of seed germination (Gutterman, 2002). Due to their sessile lifestyle, plants may encounter various abiotic stress conditions and are forced to delay seed germination during the sowing seasons (Baskin and Baskin, 1998; Ahmad et al, 2012). Melatonin Alleviates Low Temperature Stress makes negative effects on the metabolic process and water absorption, and leads to a huge loss of germination rates during seed germination (Lou et al, 2007). Seeds failed to germinate at low temperatures (LTs) in melon (Edelstein and Kigel, 1990) and Citrullus colocynthis (El-Keblawy et al, 2019)
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