Abstract
BackgroundSuboptimal root zone temperature (RZT) causes a remarkable reduction in growth of horticultural crops during winter cultivation under greenhouse production. However, limited information is available on the effects of suboptimal RZT on nitrogen (N) metabolism in cucumber seedlings. The aim of this study is to investigate the effects of 24-Epibrassinolide (EBR) on nitrate and ammonium flux rate, N metabolism, and transcript levels of NRT1 family genes under suboptimal RZT in cucumber seedlings.ResultsSuboptimal RZT (LT) negatively affected on cucumber growth and proportionately decreased EBR contents, bleeding rate, root activity, enzyme activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT), nitrate (NO3−) influx rate, ammonium (NH4+) efflux rate, and transcript levels of nitrate transporter (NRT1) encoding genes. However, exogenous EBR reduced the harmful effects of suboptimal RZT and increased endogenous EBR contents, bleeding rate, root activity, enzyme activities of NR, NiR, GS, and GOGAT, NH4+ and NO3− flux rates and contents, and N accumulation. EBR-treated seedlings also upregulated the transcript levels of nitrate transporters CsNRT1.1, CsNRT1.2A, CsNRT1.2B, CsNRT1.2C, CsNRT1.3, CsNRT1.4A, CsNRT1.5B, CsNRT1.5C, CsNRT1.9, and CsNRT1.10, and downregulated CsNRT1.5A and CsNRT1.8. LT treatment upregulated the expression level of CsNRT1.5A, while exogenous BZR application downregulated the expression level of NRT1 genes.ConclusionThese results indicate that exogenous application of EBR alleviated the harmful effects of suboptimal RZT through changes in N metabolism, NH4+ and NO3− flux rates, and NRT1 gene expression, leading to improved cucumber seedlings growth. Our study provides the first evidence of the role of EBR in the response to suboptimal RZT in cucumber, and can be used to improve vegetable production.
Highlights
Suboptimal root zone temperature (RZT) causes a remarkable reduction in growth of horticultural crops during winter cultivation under greenhouse production
The plant height, root fresh weight, shoot fresh weight, and total fresh weight of cucumber seedlings in the EBR treatment were significantly higher than in the LT and BZR treatments. These results suggest that EBR alleviated the harmful effects of suboptimal RZT temperature, leading to improved cucumber seedlings growth
Our results suggested that the nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS) and Glutamate Synthase (GOGAT) enzymes activities, and assimilation of nitrate and ammonium were promoted after EBR application in cucumber, as exposed to stress
Summary
Suboptimal root zone temperature (RZT) causes a remarkable reduction in growth of horticultural crops during winter cultivation under greenhouse production. Temperature and light intensity are key factors affecting plant growth and development [2], which are influenced by humidity and nutrient availability [3, 4]. Among these factors temperature is very important, Anwar et al BMC Plant Biology (2019) 19:225 and can alter ion balance and nitrogen metabolism [8]; a small increase in RZT could induce large changes in plant growth and development [6]. Earlier studies reported that RZT severely affected nitrogen metabolism in cucumber and reduced growth and yield [2] These studies demonstrated the importance of RZT on plant growth and development. The potential mechanisms of growth inhibition at ambient RZT may involve water and nutrient uptake rates but are largely unknown
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