Comparative assessment of metabolic responses to cold acclimation and deacclimation in annual bluegrass and creeping bentgrass

Abstract

The level of freezing tolerance achieved by perennial grasses and their capacity to remain cold acclimated throughout winter is critical for their winter survival. Research is necessary to better understand the metabolic processes associated with cold acclimation and deacclimation. This study was conducted to assess the response of creeping bentgrass (Agrostis stolonifera L.) (CB) and two ecotypes of annual bluegrass (Poa annua L.), one freezing-tolerant (AB-T) and one freezing-sensitive (AB-S), to cold acclimation and deacclimation. Following cold acclimation, plants were exposed to 8°C for 0.5, 1, 3, and 5 d to induce deacclimation. Plants were assessed for their freezing tolerance (lethal temperature resulting in 50% mortality, LT50), their concentrations in soluble sugars and amino acids, and for changes in dehydrin-like proteins. Fully acclimated CB achieved higher level of LT50 (−21.5°C) than AB-T (−19.8°C), followed by AB-S (−15.3°C). Total soluble sugars, mainly high molecular weight (HMW) fructans, accumulated in each species/ecotypes during cold acclimation with higher levels measured in CB. Dehydrin-like proteins were present in each species but they were mostly constitutive in AB while they were cold-inducible and linked with the LT50 in CB. Freezing tolerance decreased during deacclimation in each species. However, at each step of deacclimation, CB maintained higher freezing tolerance than AB in which the LT50 reached the low level of non-acclimated plants after five days at 8°C. The depletion of HMW fructans observed during deacclimation followed a similar trend, with higher levels remaining at the end in CB, followed by AB-T and then by AB-S. The higher susceptibility of AB to winter injury is associated with both its lower cold acclimation capacity and deacclimation sensitivity.