| The impact of abrupt heat stress on plant nutrient uptake is unclear, since most past studies have examined uptake under highly-artificial conditions (e.g., detached roots), which likely yielded artifactual results. Heat stress often affects roots, roots are often more heat sensitive than shoots, and global warming and increasing heat waves mean more acute heat stress for roots in the future. Hence, we are investigating effects of abrupt high temperatures (=acute heat or a heat wave), on nutrient uptake by roots, using tomato as a model system. In the current study, we grew plants at 25/20 ° C (day/night) (= control conditions) and then transferred some plants to 35/30 ° C (moderate heat) or 42/37 ° C (severe heat) for 6 days, after which, plants were moved back to control conditions for 7 days to monitor recovery. Samples were harvested after 1 and 6 days of heat treatment, and after 7 days of recovery (day 13), and then the concentration of major nutrient uptake proteins in roots was determined using protein-specific antibodies and ELISA. Photosynthesis was reduced by severe heat, compared to controls, and recovered within 7 days of a return to control temperatures. Roots were negatively impacted by heat (severe > moderate), as indicated by decreases in respiration, protein concentration, membrane integrity, and root mass. Root mass decreased more than shoot mass with heat stress. Total plant nutrient content, root nutrient uptake rate, and the level and, in some cases, activity of nutrient uptake proteins were decreased by both moderate and severe heat. Importantly, for most measures of function, moderately-stressed plants were able to recover within 7 d after heat, but recovery was incomplete for severely-stressed plants. Together, our results indicate that abrupt severe heat events can damage roots and decrease root nutrient uptake, by decreasing root metabolic rate, levels or activities of nutrient uptake proteins, and/or root mass. |
