Hydraulic conductivity and contribution of aquaporins to water uptake in roots of four sunflower genotypes

The sensitivity of root water uptake to cold root temperature follows species-specific upper elevational distribution limits of temperate tree species

Physiological water stress induced by low root temperatures might contribute to species-specific climatic limits of tree distribution. We investigated the low temperature sensitivity of root water uptake and transport in seedlings of 16 European tree species which reach their natural upper elevation distribution limits at different distances to the alpine treeline. We used 2H-H2O pulse-labelling to quantify the water uptake and transport velocity from roots to leaves in seedlings exposed to constant 15°C, 7°C or 2°C root temperature, but identical aboveground temperatures between 20°C and 25°C. In all species, low root temperatures reduced the water transport rate, accompanied by reduced stem water potentials and stomatal conductance. At 7°C root temperature, the relative water uptake rates among species correlated positively with the species-specific upper elevation limits, indicating an increasingly higher sensitivity to lower root zone temperatures, the lower a species' natural elevational distribution limit. Conversely, 2°C root temperature severely inhibited water uptake in all species, irrespective of the species' thermal elevational limits. We conclude that low temperature-induced hydraulic constraints contribute to the cold distribution limits of temperate tree species and are a potential physiological cause behind the low temperature limits of plant growth in general.

Exploring the role of HaTIPs genes in enhancing drought tolerance in sunflower

BACKGROUND

Activity of plant aquaporins (AQPs) is extremely sensitive to environmental variables such as temperature, drought, atmospheric vapor pressure deficit, cell water status and also appears to be closely associated with the expression of plant tolerance to various stresses. The spatial and temporal expression patterns of genes of Tonoplast Intrinsic Proteins (TIPs) in various crops indicate the complex and diverse regulation of these proteins and are important in understanding their key role in plant growth, development and stress responses.

METHODS AND RESULTS

Based on phylogenetic analysis, six distinct HaTIPs were selected for studying their spatial and temporal expression in sunflower (Helianthus annuus). In this study semi quantitative polymerase chain reaction (semi q-PCR) and real time polymerase chain reaction (q-PCR) analysis were used to study the spatial and temporal expression of HaTIPs in sunflower. The results indicated that all of HaTIPs showed differential expression specific to both the tissues and the accessions. Moreover, the expression of all HaTIPs was higher in cross compared to the parents. Results of semi q-PCR and real time PCR indicated an upregulation of expression of HaTIP-RB7 and HaTIP7 in drought tolerant entries at 12 h of 20% polyethylene glycol (PEG) treatment compared to 0 h.

CONCLUSION

Hence these genes can be utilized as potential target in improving water use efficiency and for further genetic manipulation for the development of drought tolerant sunflower. This study may further contribute to our better understanding regarding the precise role of HaTIPs through their spatial and temporal expression analysis and their application in sunflower drought stress responses.

Spatio-Temporal Variation in Water Uptake in Seminal and Nodal Root Systems of Barley Plants Grown in Soil

The spatial and temporal dynamics of root water uptake in nodal and seminal roots are poorly understood, especially in relation to root system development and aging. Here we non-destructively quantify 1) root water uptake and 2) root length of nodal and seminal roots of barley in three dimensions during 43 days of growth. We developed a concentric split root system to hydraulically and physically isolate the seminal and nodal root systems. Using magnetic resonance imaging (MRI), roots were visualized, root length was determined, and soil water depletion in both compartments was measured. From 19 days after germination and onwards, the nodal root system had greater water uptake compared to the seminal root system due to both greater root length and greater root conductivity. At 29 days after germination onwards, the average age of the seminal and nodal root systems was similar and no differences were observed in water uptake per root length between seminal and nodal root systems, indicating the importance of embryonic root systems for seedling establishment and nodal root systems in more mature plants. Since nodal roots perform the majority of water uptake at 29 days after germination and onwards, nodal root phenes merit consideration as a selection target to improve water capture in barley and possibly other crops.

Aquaporin regulation in roots controls plant hydraulic conductance, stomatal conductance, and leaf water potential in Pinus radiata under water stress

Stomatal regulation is crucial for forest species performance and survival on drought-prone sites. We investigated the regulation of root and shoot hydraulics in three Pinus radiata clones exposed to drought stress and its coordination with stomatal conductance (g_s ) and leaf water potential (Ψ_leaf ). All clones experienced a substantial decrease in root-specific root hydraulic conductance (K_root-r ) in response to the water stress, but leaf-specific shoot hydraulic conductance (K_shoot-l ) did not change in any of the clones. The reduction in K_root-r caused a decrease in leaf-specific whole-plant hydraulic conductance (K_plant-l ). Among clones, the larger the decrease in K_plant-l , the more stomata closed in response to drought. Rewatering resulted in a quick recovery of K_root-r and g_s . Our results demonstrated that the reduction in K_plant-l , attributed to a down regulation of aquaporin activity in roots, was linked to the isohydric stomatal behaviour, resulting in a nearly constant Ψ_leaf as water stress started. We concluded that higher K_plant-l is associated with water stress resistance by sustaining a less negative Ψ_leaf and delaying stomatal closure.

Heliaphen, an Outdoor High-Throughput Phenotyping Platform for Genetic Studies and Crop Modeling

Heliaphen is an outdoor platform designed for high-throughput phenotyping. It allows the automated management of drought scenarios and monitoring of plants throughout their lifecycles. A robot moving between plants growing in 15-L pots monitors the plant water status and phenotypes the leaf or whole-plant morphology. From these measurements, we can compute more complex traits, such as leaf expansion (LE) or transpiration rate (TR) in response to water deficit. Here, we illustrate the capabilities of the platform with two practical cases in sunflower (Helianthus annuus): a genetic and genomic study of the response of yield-related traits to drought, and a modeling study using measured parameters as inputs for a crop simulation. For the genetic study, classical measurements of thousand-kernel weight (TKW) were performed on a biparental population under automatically managed drought stress and control conditions. These data were used for an association study, which identified five genetic markers of the TKW drought response. A complementary transcriptomic analysis identified candidate genes associated with these markers that were differentially expressed in the parental backgrounds in drought conditions. For the simulation study, we used a crop simulation model to predict the impact on crop yield of two traits measured on the platform (LE and TR) for a large number of environments. We conducted simulations in 42 contrasting locations across Europe using 21 years of climate data. We defined the pattern of abiotic stresses occurring at the continental scale and identified ideotypes (i.e., genotypes with specific trait values) that are more adapted to specific environment types. This study exemplifies how phenotyping platforms can assist the identification of the genetic architecture controlling complex response traits and facilitate the estimation of ecophysiological model parameters to define ideotypes adapted to different environmental conditions.