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dc.contributor.advisorSharp, Robert E.eng
dc.contributor.advisorFritschi, Felix B.eng
dc.contributor.authorGriffith, Amelia Elyseeng
dc.date.embargountil5/1/2024
dc.date.issued2023eng
dc.date.submitted2023 Springeng
dc.description.abstract[EMBARGOED UNTIL 5/1/2024] Maize (Zea mays L.) is one of the most produced cereal crops worldwide and is increasingly susceptible to yield limitations resulting from drought stress. The growth of roots is essential to plant adaptation to water-limiting conditions. In maize, the nodal roots, which are produced from the base of the stem, provide the framework of the mature root system and, with their lateral roots, are responsible for a large part of water and nutrient uptake. Under drought conditions, emerging nodal roots may need to grow through the upper layer of very dry soil to reach water in deeper soil layers. To do this, nodal roots must transport enough water from the stem down the root axis to the root tip in order to maintain cell expansion in the growth zone. A divided root chamber system was used to compare nodal root elongation and water status under different levels of soil water deficit conditions in two contrasting maize genotypes (B73 and FR697). Nodal roots grew into an outer chamber containing soil of precise, pre-adjusted water potentials while the primary and seminal root systems (collectively, the "seedling root system") grew in well-watered soil in the inner chamber. Results showed that when growing through very dry soil (water potential of -2.0 MPa), FR697 maintained nodal root elongation at 67 percent of well-watered rates, whereas B73 only maintained nodal root elongation at 38 percent of well-watered rates. The superior growth maintenance of FR697 was related to the maintenance of a relatively high water status of the root growth zone. Moreover, FR697 completely maintained both nodal root elongation and nodal root tip water potential between soil water potentials of -0.9 and -2.0 MPa. FR697 also completely maintained mature root water potential in both dry soil treatments compared to the well-watered control. In the same conditions, B73 showed greater inhibition of nodal root elongation and a larger decrease in growth zone water potential. The results indicate that FR697 is better able to avoid nodal root dehydration in dry soil via a greater ability to transport water to the growth zone and/or by preventing water loss to the soil, thereby allowing superior maintenance of root elongation. To better understand the mechanisms involved in the superior ability of FR697 to maintain nodal root tip water status in dry soil, a transcriptomic analysis was done using RNAseq to compare the responses to low soil water potentials in FR697 and B73 in different developmental regions of the nodal root. Five sequential root regions were analyzed, encompassing the root growth zone and adjoining maturation zone. This study was done using plants grown in the above-described divided root chamber system. The analysis revealed that the transcriptional responses to water stress differed significantly in different regions within the growth zone and became more similar in more mature root regions. This study also revealed significant differences in transcriptional responses between the genotypes in the same regions. Three major responses were highlighted that suggest mechanisms for FR697's nodal root tip dehydration avoidance phenotype. In regions closest to the root meristem, the results suggest that FR697 has enhanced cellular signaling responses via ROS and hormones like ABA and auxin. This increase in cell signaling and response likely allows for modification of DNA and changes to cell protein structures to avoid cell damage due to ROS. The results also strongly suggest that in the mature root regions further from the meristem, FR697 has more suberization and/or lignification of the exodermis and endodermis in response to water deficit conditions in comparison with B73. This could help FR697 maintain root water potential by preventing water loss to the surrounding dry soil. The transcriptome analysis also showed an increase in transmembrane transporters including aquaporins amino acid, and sugar transporters in FR697. This could suggest that FR697 may have a superior ability to transport water and osmolytes to the root tip to maintain growth and allow for osmotic adjustment. The results of this study provide guidance for more in-depth studies to explore FR697's ability to maintain nodal root elongation in dry soil.eng
dc.description.bibrefIncludes bibliographical references.eng
dc.format.extentxviii, 229 pages : illustrations (color)eng
dc.identifier.urihttps://hdl.handle.net/10355/96200
dc.identifier.urihttps://doi.org/10.32469/10355/96200eng
dc.languageEnglisheng
dc.publisherUniversity of Missouri--Columbiaeng
dc.relation.ispartofcommunityUniversity of Missouri--Columbia. Graduate School. Theses and Dissertationseng
dc.titleMaize nodal roots maintain elongation in dry soil by avoiding growth zone dehydrationeng
dc.typeThesiseng
thesis.degree.disciplinePlant Insect and Microbial Sciences (MU)eng
thesis.degree.grantorUniversity of Missouri--Columbiaeng
thesis.degree.levelMasterseng
thesis.degree.nameM.S.eng


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