Melatonin Is Involved in Regulation of Bermudagrass Growth and Development and Response to Low K+ Stress.

Liang Chen,Ao Liu,Aoyue Bi,Jibiao Fan,Xuebing Huang,Zhengrong Hu,Ke Chen,Jinmin Fu,Yan Xie,Erick Amombo

doi:10.3389/fpls.2017.02038

Abstract

Melatonin (N-acetyl-5-methoxytryptamine) plays critical roles in plant growth and development and during the response to multiple abiotic stresses. However, the roles of melatonin in plant response to K+ deficiency remain largely unknown. In the present study, we observed that the endogenous melatonin contents in bermudagrass were remarkably increased by low K+ (LK) treatment, suggesting that melatonin was involved in bermudagrass response to LK stress. Further phenotype analysis revealed that exogenous melatonin application conferred Bermudagrass enhanced tolerance to LK stress. Interestingly, exogenous melatonin application also promoted bermudagrass growth and development at normal condition. Furthermore, the K+ contents measurement revealed that melatonin-treated plants accumulated more K+ in both shoot (under both control and LK condition) and root tissues (under LK condition) compared with those of melatonin non-treated plants. Expression analysis indicated that the transcripts of K+ transport genes were significantly induced by exogenous melatonin treatment in bermudagrass under both control and LK stress conditions, especially under a combined treatment of LK stress and melatonin, which may increase accumulation of K+ content profoundly under LK stress and thereby contributed to the LK-tolerant phenotype. In addition, we investigated the role of melatonin in the regulation of photosystem II (PSII) activities under LK stress. The chlorophyll fluorescence transient (OJIP) curves were obviously higher in plants grown in LK with melatonin (LK+Mel) than those of plants grown in LK medium without melatonin application for 1 or 2 weeks, suggesting that melatonin plays important roles in PSII against LK stress. After a combined treatment of LK stress and melatonin, the values for performance indexes (PIABS, PITotal, and PICS), flux ratios (φP0, ΨE0, and φE0) and specific energy fluxes (ETO/RC) were significantly improved compared with those of LK stress alone, suggesting that melatonin plays positive roles in protecting PSII activity under LK stress. Collectively, this study reveals an important role of melatonin in regulating bermudagrass response to LK stress.

Highlights

Potassium is an essential element for plant growth and development, and a vital determinant of crop yield and quality
The results revealed that the endogenous melatonin contents were remarkably increased for 2- to 4.7-fold during the 12–72 h of LK treatment (Figure 1)
The significant increase of endogenous melatonin content by LK stress suggests that melatonin may be involved in plant response to LK stress in bermudagrass

Summary

Introduction

Potassium is an essential element for plant growth and development, and a vital determinant of crop yield and quality. The K+ concentration is high in plant cells, it is limited in soils, typically within the micromolar range (0.1–1 mM) (Schroeder et al, 1994; Maathuis, 2009). Under low-K+ (LK) conditions, plants absorb K+ through the high-affinity K+ transporters and some K+ channels (Maathuis and Sanders, 1997; Véry et al, 2014). In Arabidopsis, the AtHAK5 transporter (Rubio et al, 2000; Nieves-Cordones et al, 2010) and AKT1 channel (Lagarde et al, 1996; Hirsch et al, 1998; Spalding et al, 1999; Ivashikina et al, 2001) expressed primarily in the roots, were identified as the two major K+ uptake components, which mediate K+ absorption in roots under LK conditions (Gierth et al, 2005; Pyo et al, 2010; Nieves-Cordones et al, 2014). AtHAK5 gene transcription was remarkably induced by K+ deficiency, while AKT1 was regulated mainly at the posttranslational level (Gierth et al, 2005; Xu et al, 2006)

Methods

Results

Discussion

Conclusion