細胞內鈣離子含量提升可促進植物對逆境的耐受性，本試驗評估外施鈣離子前處理誘導葉用蘿蔔耐熱性之效益，並探討其在高溫逆境反應下所扮演之角色。結果顯示以200及500 mg • L-1 CaCl2前處理效果較佳，顯著減緩了40oC高溫下植株淨光合作用、葉綠素螢光值、總葉綠素濃度之降低及離子滲漏率增加的趨勢，並增加氣孔導度和蒸散速率，以有效的除去積熱；此外，藉由提高抗氧化酵素超氧歧化酶(superoxide dismutase, SOD)、過氧化氫酶(catalase, CAT)、抗壞血酸過氧化酶(ascorbate peroxidase, APX)和穀胱苷肽還原酶(glutathione reductase, GR)之活性，降低其氧化逆境傷害，植株可維持較低之H2O2和MDA含量。另植株前處理鈣離子螯合劑ethylene glycol bis(2-aminoethyl) tetraacetic acid(EGTA)，在高溫下對於抗氧化酵素活性有明顯抑制的效果，反向證明了鈣 離子誘導葉用蘿蔔抗氧化酵素活性以増進其耐熱性之機制。

The increase of cellular Ca2+ level can promote the stress tolerance in plants. This study aimed to evaluate the effect of calcium (Ca2+) pretreatment on the heat tolerance of leafy radish and analyze how Ca2+ played a role on plants under high temperatures. The results demonstrated that pre-application of 200 or 500 mg • L-1 CaCl2 improved the heat tolerance of leafy radish, significantly decreasing net photosynthetic rate (Pn), chlorophyll inflorescence (Fv/Fm), total chlorophyll content, and electrolyte leakage of the plants. The increase of stomata conductance (gs) and transpiration rate (E) for removing the accumulated heat was also noted. In addition, the increased activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) resulted in lower oxidative injury and lower H2O2 and MDA content in plants. Moreover, pre-treating Ca2+ chelator ethylene glycol bis(2-aminoethyl) tetraacetic acid (EGTA) indicated significant effect on the inhibition of the activities of antioxidant enzymes. This result inversely manifested the mechanism that Ca2+ induced heat tolerance of leafy radish by activating antioxidant enzymes.