Changes to Intracellular Ca 2+ and Its Sensors Triggered by NaCl Stress in Pears
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Changes to Intracellular Ca2+ and Its Sensors Triggered by NaCl Stress in Pears J. Lia, *, B. Xiea, Y. Liua, N. Lia, and L. Lia, ** a
College of Horticulture, Shanxi Agricultural University, Taigu, Shanxi, 030801 China *e-mail: [email protected] **e-mail: [email protected] Received August 1, 2019; revised February 18, 2020; accepted April 24, 2020
Abstract—The responses of Ca2+ signaling mechanism to salt stress in pears are poorly understood. In this study, we investigated the difference in the Ca2+ signal responses to NaCl stress in two pear species (Pyrus betulaefolia Bunge. and P. bretschneideri Rehd. cv. ‘Xuehua’). Pear protoplasts were treated with 100 mM NaCl alone and NaCl combined with various chemical agents before changes in intracellular Ca2+ levels and the expression of Ca2+ sensor-related genes were analyzed. NaCl stress caused elevated Ca2+ levels in protoplasts labeled with the calcium indicator Fluo-3/AM. The Ca2+ signal increased earlier in P. betulaefolia than in the ‘Xuehua’ cultivar. The cytoplasmic Ca2+ bursts induced by NaCl stress were significantly constrained by the chemical agents supplied to both species. The plasma-membrane Ca2+ channel inhibitor LaCl3 and extracellular Ca2+ chelator EGTA had greater inhibitory effects than the intracellular Ca2+ chelator BAPTA/AM. Under NaCl stress, upregulation of PbCBL10 and genes in the classes PbCDPK and PbCIPK occurred more quickly in P. betulaefolia than the ‘Xuehua’ cultivar. In conclusion, NaCl stress stimulates Ca2+ signaling in pear cells, the ions for which are taken from extracellular and intracellular Ca2+ stores. Furthermore, the accumulation of cytoplasmic Ca2+ mediates early expression of Ca2+ sensor-related genes, especially PbCDPK1. Thus the response of Ca2+ signal plays pivotal roles, which enhance the salt tolerance of pear. Keywords: Pyrus betulaefolia, Pyrus bretschneideri, NaCl stress, cytoplasmic Ca2+, Ca2+ sensor -related genes DOI: 10.1134/S1021443720060126
INTRODUCTION In recent years, due to deterioration in the global environment, the problem of soil salinization has intensified [1]. NaCl, the salt most commonly found in soil, elicits two primary effects in plants, osmotic stress and ionic toxicity, both of which inhibit normal growth and development [2]. Calcium ion (Ca2+) is an important secondary messenger in eukaryotic cells and it plays an important role in plants’ responses to biotic and abiotic stresses. Ca supplementation strengthen the indigenous tolerance mechanisms like the synthesis of compatible solutes and upregulation of antioxidant system for preventing damage to cellular macromolecules [3]. And when plants are subjected to salt or drought stress, Ca2+ concentration in plant cells increases [4, 5]. The influx of extracellular Ca2+ via Ca2+ channels through the cell membrane and/or the Abbreviations: 6-BA—6-benzylaminopurine; CaM—calmodulin, CBL—calcineurin B-like protein; CDPK—calcium-dependent protein kinase; CIPK—CBL-interacting protein kinase; CPW— cell protoplast wash; FDA—fluorescein diace
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