Browsing by Subject "Mucilage"

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Differences in mucilage properties and stomatal sensitivity of locally adapted Zea mays in relation with precipitation seasonality and vapour pressure deficit regime of their native environment
(2023) Berauer, Bernd J.; Akale, Asegidew; Schweiger, Andreas H.; Knott, Mathilde; Diehl, Dörte; Wolf, Marc‐Philip; Sawers, Ruairidh J. H.; Ahmed, Mutez A.
With ongoing climate change and the increase in extreme weather events, especially droughts, the challenge of maintaining food security is becoming ever greater. Locally adapted landraces of crops represent a valuable source of adaptation to stressful environments. In the light of future droughts—both by altered soil water supply and increasing atmospheric water demand (vapor pressure deficit [VPD])—plants need to improve their water efficiency. To do so, plants can enhance their access to soil water by improving rhizosphere hydraulic conductivity via the exudation of mucilage. Furthermore, plants can reduce transpirational water loss via stomatal regulation. Although the role of mucilage and stomata regulation on plant water management have been extensively studied, little is known about a possible coordination between root mucilage properties and stomatal sensitivity as well as abiotic drivers shaping the development of drought resistant trait suits within landraces. Mucilage properties and stomatal sensitivity of eight Mexican landraces of Zea mays in contrast with one inbred line were first quantified under controlled conditions and second related to water demand and supply at their respective site of origin. Mucilage physical properties—namely, viscosity, contact angle, and surface tension—differed between the investigated maize varieties. We found strong influences of precipitation seasonality, thus plant water availability, on mucilage production (R2 = .88, p < .01) and mucilage viscosity (R2 = .93, p < .01). Further, stomatal sensitivity to increased atmospheric water demand was related to mucilage viscosity and contact angle, both of which are crucial in determining mucilage's water repellent, thus maladaptive, behavior upon soil drying. The identification of landraces with pre‐adapted suitable trait sets with regard to drought resistance is of utmost importance, for example, trait combinations such as exhibited in one of the here investigated landraces. Our results suggest a strong environmental selective force of seasonality in plant water availability on mucilage properties as well as regulatory stomatal effects to avoid mucilage's maladaptive potential upon drying and likely delay critical levels of hydraulic dysfunction. By this, landraces from highly seasonal climates may exhibit beneficial mucilage and stomatal traits to prolong plant functioning under edaphic drought. These findings may help breeders to efficiently screen for local landraces with pre‐adaptations to drought to ultimately increase crop yield resistance under future climatic variability.
Drought-induced processes in the rhizosphere of maize (Zea mays L.)
(2023) Käsbauer, Lena; Zörb, Christian
Drought events are increasing due to climate change, resulting in significant yield losses. Many breeding strategies focus on drought resistance to avoid these yield losses or complete crop failure. Additionally, to improve drought resistance under soil desiccation, the soil and particularly rhizosphere processes are more and more in the focus of research. Specifically, linkages between the diverse and highly dynamic interactions of soil, plant, and microorganism community must be understood. This thesis thus aims to answer the following research questions: i) Are root hairs relevant for water uptake, and what role do they play under drought? ii) Does local drought in Zea mays result in distinguishable systemic and local metabolic and physiological responses, as well as compensatory water uptake? iii) Do the physico-chemical properties of Zea mays mucilage differ between two common collection systems? In the first part, published studies considering root hairs in nutrient and water uptake were summarized, and show a high plasticity of root hairs under different nutrient and water availability states. This plasticity was apparent through changes in root hair morphology and development. Furthermore, the role of root hairs in water uptake is under discussion due to variable results from different studies and crop species. Nevertheless, it seems that overall root hairs improve drought resilience. Furthermore, a better nutrient uptake and mucilage exudation by root hairs and thus an increased drought stability is discussed. This suggests a beneficial role of root hairs for drought stress robustness. In the second part, local and systemic drought responses of maize and their effect on rhizosphere processes were assessed in a split-root experiment. The root system of maize was separated into two differently watered (watered, drought stressed) rhizobox chambers. The local drought treatment was performed for 10 days. Under these conditions, the local drought led to a local and systemic response through osmotic adjustment. Osmolarity increased in the shoot, while increased proline concentrations and slight changes in root exudates indicated a local response in the drought stressed root compartment. This metabolic adjustment contributed to a hydraulic redistribution of water between the root halves and enhanced water availability. Comparing the physico-chemical properties of maize mucilage collected by two common collection systems emphasized the impact of mucilage collection when interpreting the role of mucilage in rhizosphere processes. The mucilage differed in terms of physico-chemical properties, which included contact angle, viscosity, surface tension (physical) and nutrient content, pH, polysaccharide polymer length, and neutral sugar composition (chemical). The mucilage was collected in two ways: 1) from primary and seminal roots of seedlings growing in a semi-sterile aeroponic system and 2) from airborne brace roots of maize growing on sandy soil. The two collection systems differed in terms of plant age, environment (sterility, light availability, air humidity), and root type. The higher viscosity of the brace root mucilage may have reflected the drier air humidity surrounding the root and therefore the need to enhance water holding capacity. Non-sterile conditions during brace root mucilage collection probably resulted in higher shares of hexoses, while semi-sterile conditions may explain the lack of mannose in the aeroponic mucilage. Brace root mucilage may therefore have a greater relevance during soil desiccation than aeroponic mucilage. In summary, this work helps to fill knowledge gaps in understanding and linking rhizosphere processes by i) providing a state-of-the-art summary of root hair plasticity related to nutrient and water availability and concluding a beneficial role of root hairs in drought robustness, ii) showing local and systemic osmotic adjustment and hydraulic redistribution under local drought, and iii) emphasizing the role of the mucilage collection systems when interpreting the role of mucilage in rhizosphere processes