Fruit Research (Jan 2021)
Nitrate application affects root morphology by altering hormonal status and gene expression patterns in B9 apple rootstock nursery plants
Abstract
Lateral roots (LRs) are critical for absorbing water, minerals, and nutrients. Nitrate is a vital signaling molecule for regulating LR growth. However, understanding how nitrate interacts with endogenous hormones and genes to coordinate LR development is a bottleneck. In this study, B9 apple rootstock nursery plants were cultured hydroponically and treated with different nitrate treatments (Control; T1, 2.25 mM L−1; T2, 9 mM L−1; T3, 18 mM L−1; T4, 36 mM L−1; and T5, 72 mM L−1), where T5 outperformed the other treatments. Nursery plants were subsequently treated with control and T5 to explore the underlying physiological and molecular mechanisms by which nitrate promoted LR growth. Plant height, stem diameter, root morphological parameters, endogenous hormones, and gene expression levels were measured. Results showed that T5 promoted LR growth by increasing the endogenous contents of indole-3-acetic acid (IAA) and gibberellic acid (GA), and by decreasing the contents of abscisic acid (ABA), jasmonic acid (JA), and zeatin riboside (ZR) at most time points. Furthermore, the relative expression levels of nitrate transporter genes were upregulated in the control group, and nitrate assimilation genes were upregulated in T5 nursery plants at various time points. In addition, the transcript abundances of auxin-related genes were higher in T5 nursery plants, which increased auxin contents. MdSHR, MdGATA1, and MdSCR1 expressions were induced, hence increasing LR growth. In contrast, higher auxin content raised MdWOX11 expression, which enhanced the MdLBD16 and MdLBD29 expression levels, thus prompting the transcripts of cell cycle-related genes: MdCYCD1;1 and MdCYCP4;1. Overall, the changes in hormonal content and gene expression levels followed superior LR growth by T5.
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