Effect of drought on nutrient uptake and the levels of nutrient-uptake proteins in roots of drought-sensitive and –tolerant grasses

Authors: BISTA, DEEPESH - University Of Toledo; HECKATHORN, SCOTT - University Of Toledo; JAYAWARDENA, DILEEPA - University Of Toledo; MISHRA, SASMITA - Kean University; Boldt, Jennifer

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2018
Publication Date: 3/30/2018
Publication URL: http://handle.nal.usda.gov/10113/6472474
Citation: Bista, D.R., Heckathorn, S.A., Jayawardena, D.M., Mishra, S., Boldt, J.K. 2018. Effect of drought on nutrient uptake and the levels of nutrient-uptake proteins in roots of drought-sensitive and –tolerant grasses. Plants. 7(2):28-44. http://doi:10.3390/plants7020028.
DOI: https://doi.org/10.3390/plants7020028

Interpretive Summary: Predicted increases in the frequency, intensity, and duration of drought are expected with global climate change. Drought tends to decrease plant growth, as well as decrease the concentration of nutrients in plant tissue. Therefore, increases in drought will affect food production, both yield and quality, in natural ecosystems and agricultural systems. Plants use nutrient-uptake proteins to take up most of their nutrients from the soil. We investigated the effects of drought on the concentration of nitrogen (N) and phosphorus (P) nutrient-uptake proteins in roots, and how this relates to effects on nutrient-uptake rate and tissue nutrient concentration. We used three grass species (barley, corn, and big bluestem) encompassing a range of drought tolerance. Drought-related decreases in the levels of N- and P-uptake proteins per gram root occurred despite increases in levels per unit total root protein, because of larger decreases in the concentration of total protein per gram root. Our results indicate that (1) decreases in plant nutrient concentration with drought are likely caused, at least in part, by decreases in the concentration or activity of nutrient-uptake proteins in roots; (2) decreases in the concentration of nutrient-uptake proteins per g root can be driven by decreases in the concentration of total root protein; and (3) these effects of drought occur in both drought-sensitive and -tolerant species and often become more severe as drought stress progresses. Efforts to improve the tolerance of crops to drought should include adaptations which help roots maintain bulk protein levels or increase their expression of nutrient-uptake proteins, both of which will minimize decreases in root nutrient uptake and tissue nutrient concentration.

Technical Abstract: Climate models predict a reduction in precipitation and an increase in evapotranspiration rates in many regions of the world in coming decades, resulting in increased drought. In addition to decreasing plant growth and reproduction, drought also decreases the concentration (%) of nitrogen (N) and phosphorous (P) in plant tissues, but the reasons for this decrease are not fully understood. We investigated if decreases in the nutrient status of plant tissues during drought may be associated with decreases in the concentration of nutrient-uptake proteins in roots, which has never been quantified. Barley (Hordeum vulgare), corn (Zea mays), and big bluestem (Andropogon gerardii), drought-sensitive to -tolerant grasses, respectively, were subjected to a gradual dry-down lasting up to 30 days. Plants were harvested at mid and/or late drought (26-37% and 71-94% stomatal closure), at which times we measured biomass, tissue nutrient concentrations, nutrient uptake rates, and the concentration of nutrient-uptake proteins in roots (NRT1 for NO3, AMT1 for NH4, PHT1 for P). Drought reduced the concentration of N and P in plants, indicating that (1) drought reduced the acquisition of nutrients more than it did plant growth, and (2) decreases in nutrient acquisition cannot be explained simply by decreases in water uptake. The rate of nutrient uptake per gram of root decreased with drought, providing an explanation for decreases in nutrient concentration. For P, decreases in nutrient-uptake rate were associated with decreases in both the concentration and activity of the major P-uptake proteins in roots; for N, decreases in N-uptake protein concentration occurred only in big bluestem during late drought, indicating that decreases in the activities of N-uptake proteins was the main cause of decreases in N-uptake rate. Drought-related decreases in the levels of nutrient-uptake proteins per gram root occurred despite compensatory increases in levels per unit total root protein, because of larger decreases in the concentration of total protein per gram root. The negative effects of drought on nutrient concentration, uptake, and uptake proteins were often greater for late vs. mid drought. Thus, decreases in plant nutrient concentration, and hence food quality, with drought are likely caused, at least in part, by decreases in the concentration or activity of nutrient-uptake proteins in roots, and this will increase with climate-change-related increases in drought frequency and severity.