Proline (Pro) accumulation is a common physiological reaction in response to abiotic stresses in many plants. Accumulation of Pro is believed to play the important role in protecting cellular components from dehydrating effects due to such stresses. The study was performed to investigate the relationship between cold hardiness and Pro content or expression of related genes in peach cultivars during a constant experimental deacclimation. Changes in cold hardiness were determined using electrolyte leakage method in the shoots of 10 peach cultivars (Prunus persica ‘Aikawanakajima’, ‘Chiyomaru’, ‘Daewol’, ‘Janghowon Hwangdo’, ‘Kiraranokiwami’, ‘Mihong’, ‘Misshong’, ‘Soomee’, ‘Suhong’, and ‘Sun Gold’). Pro content was analyzed using the ninhydrin method and related gene expressions were examined using quantitative real-time RT-PCR. While cold hardiness of 10 peach cultivars decreased, Pro contents of those increased during the deacclimation. Notably, at the same time, expression of P5CS (Δ1-pyrroline-5-carboxylatesynthase) decreased in 10 peach cultivars, whereas expressions of P5CR (Δ1-pyrroline-5-carboxylatereductase) and OAT (ornithine-δ-aminotransferase) increased. Our results demonstrate that Pro responds positively to higher temperature in the shoots of 10 peach cultivars and expression of both P5CS and P5CR genes could show contrasting patterns during the deacclimation. Furthermore, our results suggest that ornithine pathway, which has been suggested to be important during seedling development, could serve as an alternative pathway in Pro synthesis process during the deacclimation in peach.

• Daeil Kim(Department of Horticulture, Chungbuk National University, Brain Korea 21 Center for Bio-Resource Chungbuk National University) Corresponding Author
• Hyeondae Han(Department of Horticulture, Chungbuk National University, Brain Korea 21 Center for Bio-Resource Chungbuk National University)
• Jungyeon Won(Department of Horticulture, Chungbuk National University, Brain Korea 21 Center for Bio-Resource Chungbuk National University)
• Youngjae Oh(Department of Horticulture, Chungbuk National University, Brain Korea 21 Center for Bio-Resource Chungbuk National University)
• Keumsun Kim(Department of Horticulture, Chungbuk National University, Brain Korea 21 Center for Bio-Resource Chungbuk National University)
• Sewon Oh(Department of Horticulture, Chungbuk National University, Brain Korea 21 Center for Bio-Resource Chungbuk National University)
• Hyunsuk Shin(Department of Horticulture, Chungbuk National University, Brain Korea 21 Center for Bio-Resource Chungbuk National University)