非洲菊耐熱相關之形態適應與生理特性

Morphological Adaptation and Physiological Characteristics Associated with Heat Tolerance in Gerbera

非洲菊（Gerbera jamesonii H. Bolus. ex Hook. f.）於高溫地區生產亟需選育耐熱品種，本研究探討日／夜溫35／30℃、30／25℃及25／20℃對四個非洲菊品種生長之影響，評估與耐熱性有關之形態適應與生理特性。結果於高溫35／30℃栽培之‘Monte Crysto　’植株分枝數、花序形成數、花序直徑及花序乾、鮮重未因高溫而下降；而‘Ching Shin Huang　’及‘Lisa　’分枝數及花序形成數皆未下降，但花徑及花序乾、鮮重顯著下降。高溫35／30℃使‘Monte Crysto　’、‘Ching Shin Huang　’和‘Lisa　’之花梗長、花梗粗及花梗乾、鮮重及花瓣彩度皆顯著下降，而‘Rosalin　’則分枝數減少且無花序形成。由高溫栽培之分枝性及花序特性顯示‘Monte Crysto　’最耐熱，其次為‘Ching Shin Huang　’及‘Lisa　’，‘Rosalin　’為熱敏感品種。相較於30／25℃或25／20℃處理，於高溫35／30℃栽培之耐熱非洲菊‘Monte Crysto　’葉片下表皮氣孔密度增加、葉肉組織增厚；而熱敏感品種‘Rosalin　’之氣孔密度與葉肉解剖在溫度處理間無顯著差異，且35／30℃處理之葉綠素計讀值下降。測量各參試品種於23℃與33℃處理14天內之葉綠素螢光變化（Fv／Fm）及葉片電解質滲漏（electrolyte leakage）以判別細胞膜熱穩定性，結果顯示耐熱之‘Monte Crysto　’苗株於33℃及23℃處理之葉片Fv／Fm值無顯著差異；‘Lisa　’於33℃處理之葉片Fv／Fm值略低於23℃處理者，而不耐熱的‘Rosalin　’於33℃生長7天後其葉片Fv／Fm即顯著下降。將非洲菊四個品種葉圓片置於45－48℃水浴溫度處理15 min後，計算其相對熱傷害值（relative injury, RI），結果各品種之RI值與其水浴溫度呈S曲線變化。各品種達到50% RI的溫度，分別為‘Monte Crysto　’（54.1℃）、‘Rosella　’（53.2℃）、‘Lisa　’（53.1℃）及‘Rosalin　’（52.2℃）。本研究顯示耐熱之非洲菊品種在高溫（≈33℃）下，具葉片下表皮氣孔密度增加、葉肉組織增厚之形態適應特性，且其Fv／Fm值不受高溫影響，葉片細胞膜熱穩定性高。 It is crucial to select heat-tolerant gerbera (Gerbera jamesonii H. Bolus. ex Hook. f.) cultivars for hot climate production. Morphological adaptations and physiological characteristics associated with heat-tolerance were evaluated in four gerbera cultivars grown at day/night temperatures of 35/30, 30/25, and 25/20℃. Results showed branch number, and inflorescence number, diameter, and fresh and dry weights of 'Monte Crysto' did not decrease with increasing temperature. Increased temperature resulted in decreased inflorescence diameter, and fresh and dry weights of 'Ching Shin Huang' and 'Lisa', but not for shoot and inflorescence number. Scape length, diameter, fresh and dry weights, and ray floret chroma decreased with increasing temperature in 'Monte Crysto', 'Ching Shin Huang', and 'Lisa'. Shoot number decreased with increasing temperature and no inflorescence was recorded in 'Rosalin' at 35/30℃. Based on shoot and inflorescence growth at high temperatures, heat tolerance ranked as 'Monte Crysto' ＞ 'Ching Hsin Huang' ≈ 'Lisa' ＞ 'Rosalin'. Leaf abaxial stomatal density and mesophyll thickness of 'Monte Crysto' increased at 35/30℃ compared to 30/25 and 25/20℃. High temperature at 35/30℃ did not alter leaf abaxial stomatal density and mesophyll thickness but decreased leaf SPAD-502 value in heat-sensitive 'Rosalin'. Cell membrane thermostability was evaluated by measuring the changes of leaf Fv/Fm value and electrolyte leakage at 23 and 33℃ treatments for 14 days. Results showed that Fv/Fm of heat-tolerant 'Monte Crysto' did not change significantly, and Fv/Fm of 'Lisa' was slightly lower at 33℃ than 23℃, whereas Fv/Fm of heat-intolerant 'Rosalin' was significantly lower since 7 d after 33℃ treatment. Leaf discs of each cultivar were treated at water bath of 45-48℃ for 15 min, measured the electrolyte leakage, and then calculated their relative injury (RI) values. The relationship between the RI occurring in leaf tissue discs and water bath temperature was sigmoidal. The 50% RI value of the sigmoid response curve occurred at 54.1, 53.2, 53.1, and 52.2℃ for 'Monte Crysto', 'Rosella', 'Lisa', and 'Rosalin', respectively. We conclude that heat-tolerant gerbera cultivar such as 'Monte Crysto' had morphological adaptations through increased abaxial stomatal density and mesophyll thickness, and physiological characteristics such as unaffected Fv/Fm value and high cell membrane thermostability under high temperature (≈33℃) conditions.