Stable osmotica in Eucalyptus spathulata - responses to salt and water deficit stress

Salt and water deficit stress elicited contrasting responses in seedlings of Eucalyptus spathulata (Hook.). Under salt stress, seedlings reduced osmotic potential by accumulating large quantities of inorganic ions in leaf tissues. Sodium concentrations reached 350 mm on a leaf water basis and total cellular osmolality reached ∼2000 mm. Under water deficit stress, maximum sodium concentrations were around 50 mm in leaf water and seedlings reduced osmotic potential through increasing concentrations of a range of constitutive solutes up to a total cellular osmolality of ∼1200 mm. We postulate that measured concentrations of the cyclic polyol, quercitol, of up to 200 mm leaf water, are the likely means of balancing accumulation of inorganic ions. Under the common assumption of localisation of inorganic ions to the vacuole and organic balancing solutes to the cytoplasm, the concentrations of cyclitol, and other carbohydrates were more than sufficient to balance osmotic potential across the tonoplast membrane. Results confirm other recent studies that suggest a range of putative roles for cyclitols in tissues and these are discussed in the larger context of plant responses to salt and water deficit stress.