Protein Dynamics in Young Maize Root Hairs in Response to Macro- and Micronutrient Deprivation

Plants
increase their root surface with root hairs to improve the
acquisition of nutrients from the soil. The unicellular character
of root hairs and their position at the root surface make them an
attractive system to investigate adaptive processes of rhizodermal
cells that are in direct contact with the soil solution. In young
maize seedlings, roots are densely covered with root hairs, although
nutrient reserves in the seed are sufficient to support seedling growth
rates for a few days. We used a label-free quantitative proteomics
approach to study protein abundance adjustments in 4 day old root
hairs grown in aeroponic culture in the presence and absence of several
macro- and micronutrients. Compared to the proteome of root hairs
developed under full nutrition, protein abundance changes were observed
in pathways related to macronutrient (N, P, K, and Mg) deficiencies.
For example, lack of N in the medium repressed the primary N metabolism
pathway, increased amino acid synthesis, but repressed their degradation,
and affected the primary carbon metabolism, such as glycolysis. Glycolysis
was similarly affected by K and P deprivation, but the glycolytic
pathway was negatively regulated by the absence of the micronutrients
Fe and Zn. In contrast, the deprivation of Mn had almost no affect
on the root hair proteome. Our results indicate either that the metabolism
of very young root hairs adjusts to cellular nutrient deficiencies
that have been already experienced or that root hairs sense the external
lack of specific nutrients in the nutrient solution and adjust their
metabolism accordingly.