Abstract
Glycerol metabolism has been well studied biochemically. However, the means by which glycerol functions in plant development is not well understood. This study aimed to investigate the mechanism underlying the effects of glycerol on root development in Arabidopsis thaliana. Exogenous glycerol inhibited primary root growth and altered lateral root development in wild-type plants. These phenotypes appeared concurrently with increased endogenous glycerol-3-phosphate (G3P) and H2O2 contents in seedlings, and decreased phosphate levels in roots. Upon glycerol treatment, G3P level and root development did not change in glycerol kinase mutant gli1, but G3P level increased in gpdhc1 and fad-gpdh mutants, which resulted in more severely impaired root development. Overexpression of the FAD-GPDH gene attenuated the alterations in G3P, phosphate and H2O2 levels, leading to increased tolerance to exogenous glycerol, which suggested that FAD-GPDH plays an important role in modulating this response. Free indole-3-acetic acid (IAA) content increased by 46%, and DR5pro::GUS staining increased in the stele cells of the root meristem under glycerol treatment, suggesting that glycerol likely alters normal auxin distribution. Decreases in PIN1 and PIN7 expression, β-glucuronidase (GUS) staining in plants expressing PIN7pro::GUS and green fluorescent protein (GFP) fluorescence in plants expressing PIN7pro::PIN7-GFP were observed, indicating that polar auxin transport in the root was downregulated under glycerol treatment. Analyses with auxin-related mutants showed that TIR1 and ARF7 were involved in regulating root growth under glycerol treatment. Glycerol-treated plants showed significant reductions in root meristem size and cell number as revealed by CYCB1;1pro::GUS staining. Furthermore, the expression of CDKA and CYCB1 decreased significantly in treated plants compared with control plants, implying possible alterations in cell cycle progression. Our data demonstrated that glycerol treatment altered endogenous levels of G3P, phosphate and ROS, affected auxin distribution and cell division in the root meristem, and eventually resulted in modifications of root development.
Highlights
Terrestrial plants have evolved effective and intricate mechanisms to survive biotic and abiotic stress in soil
When wild-type Arabidopsis plants were grown on 0.56Murashige and Skoog (MS) media containing various concentrations of glycerol ranging from 0 to 20 mM, the primary root (PR) length of the plants grown on media containing less than 100 mM glycerol was not significantly different from the root length on the control medium; the PR length of plants grown on medium containing 1 mM glycerol was significantly shorter than the root length on the control medium (Figure S1)
The effect of glycerol treatment on the number of lateral root primordium (LRP) was examined at the same time points used for PR length observations, following the four developmental stages proposed by Zhang et al [50]: Stage A includes primordia of up to three cell layers; Stage B includes unemerged LRs that have more than three cell layers; Stage C includes emerged LRs,0.5 mm in length; and Stage D includes LRs longer than 0.5 mm
Summary
Terrestrial plants have evolved effective and intricate mechanisms to survive biotic and abiotic stress in soil. One good example of such a mechanism is the plasticity of plant root development. Root development involves cell division and elongation at the root meristem, lateral root primordium (LRP) initiation and lateral root (LR) formation. Asymmetric auxin distribution, which involves dynamic changes in the auxin gradient [2], play a crucial role in root development. Maintaining the correct auxin gradient is necessary for major root developmental events, such as apical-basal axis formation and LR development [3,4,5]. Asymmetric auxin distribution can be modulated by intercellular polar auxin transport, which is a specialized delivery system whereby plants transport indole-3acetic acid (IAA) from auxin sources in the shoot to sink tissues such as roots. Environmental and/or genetic interference with auxin transport can alter root meristem activity, affecting root development [6,9,10]
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