Phenotypic analysis of Arabidopsis mutants: germination rate under salt/hormone-induced stress

Abiotic stress, such as high salt or low temperature, adversely affects plant growth and development. Salt stress inhibits seed germination, retards plant growth, and accelerates senescence. Freezing or drought stress can cause cell damage and plant death. The following parameters can be used to evaluate plant tolerance to salt, drought, or freezing stress: root elongation, fresh weight gain, seed germination (described here), electrolyte leakage, or water loss measurement. Several stress mutants have been characterized using these tests, including hos1 and hos2, which show higher expression of some stress-regulated genes when exposed to low-temperature stress; hos5, which shows higher expression of some stress-regulated genes under abscisic acid (ABA) and salt treatments; sfr mutants, which are deficient in freezing tolerance; and eskimo1, which is constitutively freezing-tolerant. This protocol describes a germination assay that can be carried out on seeds subjected to osmotic or hormone-induced stress. The seeds are plated on filter paper saturated with ABA (for hormonal stress) or with NaCl or mannitol (for osmotic stress). The germination rate can be scored on different days; germination is considered to have occurred when the radicles have penetrated the seed coats. The levels of stress suggested in this protocol may need to be adjusted, depending on the ecotype and growth conditions used.