Cold-induced changes affect survival after exposure to vitrification solution during cryopreservation in the south-west Australian Mediterranean climate species Lomandra sonderi (Asparagaceae)

Abstract

There is limited knowledge of the effects of exposure to low temperatures in the unique Mediterranean climate plant species of Western Australia. We have thus investigated the effect of low temperature on cryogenic tolerance in Lomandra sonderi, an endemic perennial species of southwest Western Australia. Lomandra sonderi plants were preconditioned in tissue culture at constant 23 °C (12 h light/dark cycle) or alternating 20/-1 °C (16 h light and 8 h dark cycle). Shoot tips from both conditions were analysed for their phospholipid, sterol and soluble sugar compositions. Shoot tips were also cryoexposed via a droplet-vitrification protocol. Survival in both preconditioning regimes for cryoexposed and non-cryoexposed samples was the same, but plants from the 20/-1 °C regime displayed an improved tolerance to the overall cryopreservation process in both cryoexposed and non-cryoexposed samples, thereby eliminating exposure to liquid nitrogen as a primary cause of reduced post-cryogenic viability. Preconditioning of in vitro shoots of L. sonderi at 20/-1 °C induced significant increases in phosphatidylcholine (from 7.30 ± 3.46 to 22.2 ± 7.80 ng mg-1 FW) and increases in several soluble sugars (fructose, galactose, glucose, sucrose) compared to shoots incubated at 23 °C—changes consistent with known cold acclimation responses in plant species generally—but sterol content remained largely unchanged. Analysis of electrolyte leakage in shoot tips from both preconditioning regimes generated a significantly lower LT50 value in the 20/-1 °C samples (-5.45 ± 0.53 °C) over the 23 °C samples (-2.5 ± 0.08 °C). Increased tolerance to cryoexposure in L. sonderi appears to lie mainly with acclimation-induced changes in membrane composition and promotion of membrane stability and hence increased resistance to freeze damage.