Heat Stress Decreases Levels of Nutrient-Uptake and -Assimilation Proteins in Tomato Roots

Global warming will increase root heat stress, which is already common under certain conditions. Effects of heat stress on root nutrient uptake have rarely been examined in intact plants, but the limited results indicate that heat stress will decrease it; no studies have examined heat-stress effects on the concentration of nutrient-uptake proteins. We grew Solanum lycopersicum (tomato) at 25 degrees C/20 degrees C (day/night) and then transferred some plants for six days to 35 degrees C /30 degrees C (moderate heat) or 42 degrees C/37 degrees C (severe heat) (maximum root temperature = 32 degrees C or 39 degrees C, respectively); plants were then moved back to control conditions for seven days to monitor recovery. In a second experiment, plants were grown for 15 days at 28 degrees C/23 degrees C, 32 degrees C/27 degrees C, 36 degrees C/31 degrees C, and 40 degrees C/35 degrees C (day/night). Concentrations of nutrient-uptake and -assimilation proteins in roots were determined using protein-specific antibodies and ELISA (enzyme-linked immunosorbent assay). In general, (1) roots were affected by heat more than shoots, as indicated by decreased root:shoot mass ratio, shoot vs. root %N and C, and the level of nutrient metabolism proteins vs. less sensitive photosynthesis and stomatal conductance; and (2) negative effects on roots were large and slow-to-recover only with severe heat stress (40 degrees C-42 degrees C). Thus, short-term heat stress, if severe, can decrease total protein concentration and levels of nutrient-uptake and -assimilation proteins in roots. Hence, increases in heat stress with global warming may decrease crop production, as well as nutritional quality, partly via effects on root nutrient relations.