Plants have various hydrophobic barriers that protect against environmental stresses. Suberin is one such extracellular lipid-based barrier that is deposited in various tissues in terrestrial plants. It is a complex aliphatic and aromatic heteropolymer that plays important roles in controlling water and ion movement. The precise mechanisms of suberin in defending against abiotic stresses (e.g. drought, salinity and heavy metals) are currently. In this thesis, I explore some of the specific roles of root suberin and seed coat suberin in the model plant Arabidopsis thaliana in relation to abiotic stress tolerance.

Physio-chemical responses and stress tolerance as a result of alterations in suberin were investigated using several suberin-altered mutants of Arabidopsis thaliana. Drought-induced suberin reduced water loss through the root periderm. The amount of water loss in roots was inversely correlated to the amount of total suberin. Suberin lamellae structure was important in reducing water loss under drought stress. Salt stress responses in suberin-altered mutants indicate suberin composition or lamellae structure are essential in barrier function of root suberin against uncontrolled Na uptake into the plant.

Mutants of Arabidopsis defective in various seed coat polymeric substances (suberin, cutin, mucilage, or proanthocyanidins) were tested for changes in germination and viability after stratification and imbibition in a range of mining environment-relevant chromium Cr(III) concentrations. Seeds reduced in total seed coat suberin were strongly affected by increasing Cr3+ concentrations, affecting both germination and embryo viability. This provides evidence for the effective barrier function of seed coat suberin on the imposition of impermeability to Cr3+. Although proanthocyanidin mutants displayed reduced germination in the presence of chromium, their embryo viability was only partially affected by higher levels of Cr3+. Overall, these results reveal the risks associated with Cr3+ toxicity on the existence of plants with reduced seed coat suberin content in environments contaminated with high levels of chromium.

The findings presented in this thesis helps to clarify how suberin content, composition, and lamellae structure relate to tolerance against drought, salinity, and chromium (Cr3+) toxicity. Further, these findings shed light on future directions in manipulating suberin genes for the development of stress-tolerant high-value crops.