Climate change will increase drought in many regions of the world. Besides decreasing productivity, drought also decreases the concentration (%) of nitrogen (N) and phosphorous (P) in plants. We investigated if decreases in nutrient status during drought are correlated with decreases in levels of nutrient-uptake proteins in roots, which has not been quantified. Drought-sensitive (Hordeum vulgare, Zea mays) and -tolerant grasses (Andropogon gerardii) were harvested at mid and late drought, when we measured biomass, plant %N and P, root N- and P-uptake rates, and concentrations of major nutrient-uptake proteins in roots (NRT1 for NO₃, AMT1 for NH₄, and PHT1 for P). Drought reduced %N and P, indicating that it reduced nutrient acquisition more than growth. Decreases in P uptake with drought were correlated with decreases in both concentration and activity of P-uptake proteins, but decreases in N uptake were weakly correlated with levels of N-uptake proteins. Nutrient-uptake proteins per gram root decreased despite increases per gram total protein, because of the larger decreases in total protein per gram. Thus, drought-related decreases in nutrient concentration, especially %P, were likely caused, at least partly, by decreases in the concentration of root nutrient-uptake proteins in both drought-sensitive and -tolerant species.

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 °C/20 °C (day/night) and then transferred some plants for six days to 35 °C /30 °C (moderate heat) or 42 °C/37 °C (severe heat) (maximum root temperature = 32 °C or 39 °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 °C/23 °C, 32 °C/27 °C, 36 °C/31 °C, and 40 °C/35 °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 °C–42 °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.

Chloroplast small (low-molecular-weight) heat-shock proteins (csHsps) can protect photosynthetic electron transport (Pet), and quantitative variation in csHsps is correlated with thermotolerance of net photosynthesis and Photosystem II. However, the functional (i.e. protective) consequence of natural variation in csHsps is unknown. To investigate this, we used an in vitro assay to determine the contribution of csHsps to the tolerance of Pet to high temperatures in five ecotypes of Chenopodium album collected from habitats ranging from cool to warm, and we partitioned total Pet thermotolerance into basal and induced Pet components (without and with a pre-heat treatment, respectively, to induce csHsps). The ecotypes varied in total Pet thermotolerance and this was correlated with habitat temperature. Variation in total Pet thermotolerance was associated primarily with variation in induced Pet thermotolerance, and not with basal Pet thermotolerance. Variation in induced Pet was highly correlated with csHsp protection of Pet. Variation in csHsp function was associated with variation in csHsp content among ecotypes. These results are the first to demonstrate the direct functional consequences for natural variation in Hsps in plants, and show that functional variation is associated with evolutionary adaptation to specific habitats among ecotypes.

Plants can accumulate heavy metals when exposed to them at high levels. These metals can interfere with photosynthesis. Limited evidence suggests that increased synthesis of some heat‐shock proteins (Hsps) may be a general plant response to metal stress, but the specific functions or structures protected by Hsps remain unidentified. Chloroplast small Hsps (smHsps) protect photosynthetic electron transport (Ph_et) during heat, oxidative, and photoinhibitory stress, but it is not known if chloroplast smHsps are synthesized during metal stress and protect photosynthesis. Zea mays (corn) plants were exposed to varying soil concentrations of Cu, Ni, Pb, and Zn to determine if chloroplast smHsps are induced by heavy metals, if smHsps protect Ph_et, and any effects on chloroplast smHsp and photosynthesis. Net photosynthesis (Ph_n) decreased with all metals—more so at higher levels and with longer exposures. Decreases in Ph_n resulted from damage to photosynthetic metabolism, including Ph_et. All metals increased chloroplast smHsp content, which increased with time of exposure. In vitro, Ph_et was protected from Pb (but not Ni) by purified chloroplast smHsp added to thylakoids. In vivo, Ph_n was protected from Ni and Pb by increases in smHsp in a heat‐tolerant Agrostis stolonifera selection genotype expressing additional chloroplast smHsps compared to a near‐isogenic heat‐sensitive genotype. These results are evidence that Hsps protect photosynthesis from heavy metals and are among the first to demonstrate specific functions protected by Hsps during metal stress.