毛豆採收前乾旱逆境對產量與γ-胺基丁酸含量影響之研究

Abstract

毛豆(Glycine max L. Merr)富含植物性蛋白質、油脂及礦物質，營養價值高。毛豆生育期間對水分需求高，若於生殖生長期遭遇乾旱逆境會導致生理變化及產量下降，但乾旱逆境可促使大豆葉片、根部及根瘤中γ-胺基丁酸(γ-aminobutyric acid, GABA)累積。本試驗於溫室栽培毛豆‘高雄9號’及‘高雄11號’，探討採收前乾旱處理及復水、以及儲藏溫度對產量與莢殼、豆仁GABA含量之影響，期能提升毛豆之機能性物質含量。 春作與秋作毛豆‘高雄9號’與‘高雄11號’，於生殖生長達R6種子發育階段且80%以上豆莢可銷售時，以土壤持續斷水方式分別乾旱17及10天，期間測定介質體積含水量(volumetric water content, VWC)。春秋作兩品種於採收前進行乾旱處理，乾旱延長時，介質VWC顯著下降，且其與葉片氣孔導度及葉綠素計讀值之間皆呈顯著正相關，R2分別高於0.90 和0.76。秋作介質VWC與兩品種葉片Fv/Fm之間亦呈顯著正相關，R2高於0.73，但春作‘高雄11號’則二者間不具相關性。春秋作兩品種豆莢L與a*值皆隨介質VWC降低而提高，‘高雄9號’之L、a*值分別增加了13.3%與19.1%，‘高雄11號’分別增加了14.1%與44.5%。春秋作介質VWC與兩品種黃化豆莢率則皆呈顯著負相關，R2高於0.77。秋作兩品種單株總莢數皆高於其春作，秋作‘高雄9號’可達44莢；秋作‘高雄9號’及‘高雄11號’生育期亦分別較其春作短48及23天。 秋作毛豆兩品種於採收之前進行乾旱處理後復水，可以減緩乾旱對‘高雄9號’葉片氣孔導度、葉綠素計讀值及黃化豆莢率之影響，其分別較乾旱組顯著提高22.2%、40.7%及57.2%；而‘高雄11號’之葉片氣孔導度、葉綠素計讀值及葉綠素螢光Fv/Fm則分別較乾旱組顯著提高69.7%、2.3倍及5.1倍。毛豆適當的採收期為豆仁為七至八分飽滿且80%豆莢達綠熟階段；‘高雄9號’及‘高雄11號’在50%可銷售成熟度時進行乾旱處理，其對於氣孔導度、葉綠素計讀值、Fv/Fm及黃化豆莢率之影響，與在80%可銷售成熟度時處理乾旱者相同，但單株總莢重及十粒重較於80%可銷售成熟度時處理乾旱者少，‘高雄9號’分別少11.4%及34.3%，而‘高雄11號’分別少25.4%及11.7%。兩品種豆莢於-20 oC儲藏三個月，其豆仁之十粒重、長、寬、含水量及外觀色彩仍與採收當天無顯著差異，而於7 oC及常溫儲藏三個月之毛豆不具銷售價值。 毛豆各部位GABA含量方面，秋作毛豆兩品種於採收前進行乾旱處理，隨著乾旱天數增加，豆仁GABA含量逐漸增加，莢殼與葉片之GABA含量則逐漸減少，但乾旱組豆仁與莢殼之GABA含量皆高於對照組，‘高雄9號’分別可達107.3及140.3 mg·100g-1、‘高雄11號’分別可達152.8及132.9 mg·100g-1。毛豆不同部位對於乾旱後復水之反應有差異，兩品種皆僅豆仁於乾旱3天後復水組比連續乾旱組有較高的GABA含量。毛豆於50%可銷售成熟度處理乾旱組之莢殼及豆仁GABA含量皆較於80%可銷售成熟度處理乾旱者高，‘高雄9號’及‘高雄11號’於50%可銷售成熟度處理乾旱組之豆仁GABA含量最高，分別可達425.8及284.1 mg·100 g-1，顯示乾旱逆境下植株不同生殖生長階段也是影響GABA含量的因子。兩品種豆莢於-20 oC儲藏三個月也可大量增加莢殼及豆仁之GABA含量，‘高雄9號’及‘高雄11號’莢殼最高分別可達278.2及229.7 mg·100 g-1，而豆仁最高分別可達583.4及290.4 mg·100 g-1。

Vegetable soybean (Glycine max L. Merr), rich in protein, oil and mineral, is a crop with high healthcare value. The water requirement during growth and development of vegetable soybean is relatively high. Water stress during reproductive stages leads to physiological change and poor yield. But water stress can enhance γ-aminobutyric acid (GABA) levels in leaf, root and nodule of soybean. This research aimed on the effect of drought stress and rewatering before harvest, and the storage temperature on yield and GABA content of pod shell and seed of vegetable soybean ‘Kaohsiung no.9’ and ‘Kaohsiung no.11’cultivated in greenhouse. Enhancing functional component in vegetable soybean was expected. Vegetable soybean ‘Kaohsiung no.9’ and ‘Kaohsiung no.11’ were exposed to drought for 17 and 10 days by progressive transpiration before harvest with more than 80% pods at marketable maturity during R6 seed development stage in spring and autumn. The substrate volumetric water content (VWC) was measured periodically during the treatment. In both seasons, two cultivars were treated with drought before harvest. As the drought was prolonged, substrate VWC declined significantly. Substrate VWC were significantly positively correlated with leaf stomatal conductance and SPAD value with R2 higher than 0.90 and 0.76 respectively. There was also a significantly positive correlation between VWC and Fv/Fm of two cultivars in autumn with R2 higher than 0.73. However, VWC and Fv/Fm in ‘Kaohsiung no. 11’ showed no correlation in spring. In two seasons, the L and a* values of pods in two cultivars increased with the decrease of substrate VWC. The L and a* values in ‘Kaohsiung 9’ increased by 13.3% and 19.1% respectively, and ‘Kaohsiung 11’ increased by 14.1% and 44.5% respectively. In two seasons, substrate VWC and yellow pods of two cultivars showed significantly negative correlation with R2 higher than 0.77. Both cultivars also produced more pods per plant in autumn than that in spring. ‘Kaohsiung no.9’ had 44 pods per plant in autumn. Growth period of both cultivars was shorter in autumn than that in spring, with 48 d and 23 d less in ‘Kaohsiung no. 9’ and ‘Kaohsiung no. 11’, respectively. In both cultivars in autumn, drought followed by rewatering before harvest could alleviate leaf stomatal conductance, SPAD value and yellowing pod ratio in ‘Kaohsiung no. 9’ with significantly increase by 22.2%, 40.7% and 57.2% respectively, when comparing to the drought treatment. Leaf stomatal conductance, SPAD value and fluorescence Fv/Fm of ‘Kaohsiung no.11’ were significantly increased by 69.7%, 2.3-fold and 5.1-fold respectively, when comparing to the drought treatment. The appropriate harvest timing of vegetable soybean was up to 80% pods of marketable maturity and seeds of 70~80% fullness in green ripe stage. For ‘Kaohsiung no. 9’ and ‘Kaohsiung no. 11’, leaf stomatal conductance, SPAD value, fluorescence Fv/Fm and yellow pod ratio in drought treatment at 50% pods of marketable maturity before harvest, were not significantly different with those in drought treatment at 80% pods of marketable maturity. But total pod weight per plant and 10 grains weight in drought treatment at 50% pods of marketable maturity were less than those treated drought at 80% of marketable maturity. The total pod weight and 10 grains weight of ‘Kaohsiung no. 9’ were decreased for 11.4% and 34.3% respectively, while ‘Kaohsiung no. 11’ decreased for 25.4% and 11.7% respectively. Pods of two cultivars were stored at -20 oC for three months maintained 10 grain weight, and length, width, moisture content and color of seeds were non-significantly different with those on the harvest day. However, Pods stored at 7 oC and room temperature for three months did not have sale value. Concerning GABA contents in different parts of vegetable soybean, in both season, the longer drought treatment was, the higher GABA content in seed of both cultivars was. While the GABA contents in the pod shell and leaf gradually decreased. GABA contents in seed and pod shell in drought treatment were higher than those of control. GABA content in seed and pod shell of ‘Kaohsiung no.9’ were 107.3 and 140.3 mg·100 g-1 respectively, and ‘Kaohsiung no.11’ were 152.8 and 132.9 mg·100 g-1 respectively. The responses of different tissues to drought followed by rewatering were different. Treatment of rewatering after drought for three days in both cultivars showed higher seed GABA content than continuous drought treatment. The GABA contents in pod shell and seed of drought treatment at 50% pods of marketable maturity were higher than those of drought treatment at 80% marketable maturity. The seed GABA contents in ‘Kaohsiung no.9’ and ‘Kaohsiung no.11’ of drought treatment at 50% pods of marketable maturity reached up to 425.8 and 284.1 mg·100 g-1 respectively. Different reproductive growth stage of the plants under drought stress also affected the GABA content. In addition, pods of both cultivars stored at -20oC for three months showed substantial increased GABA content in pod shell and seeds. Pod shell GABA contents in ‘Kaohsiung no. 9’ and ‘Kaohsiung no.11’ were increased up to 278.2 and 229.7 mg·100 g-1 respectively, while seed GABA content were increased ut to 583.4 and 290.4 mg·100 g-1.