葉面施用甜菜鹼對於甘藍淹水與復氧期生理反應之影響

Abstract

台灣地處熱帶季風區與颱風帶，急降雨造成之淹水於台灣夏季甘藍(Brassica oleracea Linn. var. capitata) 栽培造成負面影響，而改善甘藍淹水耐受性可以通過基改作物、選育品種與噴施生長促進物質等達成。甜菜鹼為相容性溶質之季銨類化合物，相關研究證實基因轉殖甜菜鹼生合成酵素相關基因、外施或內生甜菜鹼能降低多種逆境對作物造成之傷害，然實際應用甜菜鹼以促進植物抗淹水能力之機制仍較缺乏，因此本研究探討預措甜菜鹼對甘藍‘Fuyudori’與‘228’淹水逆境後之反應，並從性狀調查、光合生理、抗氧化生理與相關基因表現量變化逐一測試，以評估甜菜鹼提高甘藍淹水耐受性之可行性，並探討其關鍵調控機制。 施用20 mM之甜菜鹼於‘228’可提高其受淹水逆境後之株高、莖徑、葉片數、地上部鮮重、過氧化物酶之活性、葉綠素含量與可溶性蛋白含量，亦能降低葉片傷害、過氧化氫、超氧陰離子與丙二醛累積量；反之施用20 mM之甜菜鹼於‘Fuyudori’時，其性狀表現、抗氧化與光合作用系統較對照組無明顯改善。推測造成兩品種反應性之差異主要為氣孔於復氧期之變化，且兩品種對於甜菜鹼吸收能力相異，其原因可能為兩品種甜菜鹼轉運蛋白ProT基因表現量之差異。對於厭氧呼吸相關基因如BoERF71、BoADH1、BoPDC1-L、BoSUS1-L與BoEIN3等，施用20 mM之甜菜鹼於‘228’能提高其淹水後期至復氧初期之表現量，推測施用20 mM之甜菜鹼於‘228’可提高其乙烯反應性；且其葉綠素生成基因如BoGSA1與BoCAO1在淹水期間表現量較對照組高，而葉綠素降解基因如BoCBR1在復氧期表現量較對照組低，因而有效保持葉綠素含量；然施用20 mM之甜菜鹼於‘228’於復氧期之ABA合成基因BoNCED9表現量較對照組低，而ABA降解基因BoCYP707A1表現量較對照組高，此結果與氣孔觀察結果相異。 整體而言，兩品種甘藍適合施用不同之甜菜鹼濃度以提高抗淹水能力，其原因可能為兩品種轉運蛋白表現差異；造成兩品種於復氧期之生理變化主要可能為氣孔所影響，然於復氧期之生理代謝變化除由離層素調控，乙烯亦扮演關鍵角色。

Taiwan is located in the tropical monsoon zone and typhoon zone, and the flooding caused by heavy rainfall would lead to a negative impact on the cultivation of summer cabbage (Brassica oleracea Linn. var. capitata). We can improve the submergence tolerance of crops by genetic modification technology, breeding and spraying growth promoting substances etc. Glycine betaine a quaternary ammonium compound which belongs to compatible solute. Relevant studies have confirmed that transfer of glycine betaine biosynthetic enzyme-related genes, external application or endogenous glycine betaine can reduce the damage of crops caused by various stresses. However, the mechanism about practical application of glycine betaine to improve the ability of plants to resist submergence is still lacking. Therefore, this study explored the response of foliar-application glycine betaine to ‘Fuyudori’ and ‘228’ after submergence, and measured the phenotypes, photosynthetic physiology, antioxidant physiology and related gene expression. Finally, the feasibility of glycine betaine to improve submergence tolerance of cabbage was evaluated, and its key regulatory mechanism would also be discussed. Applying 20 mM glycine betaine to ‘228’ not only could increase the plant height, stem diameter, number of leaves, fresh weight of shoots, peroxidase activity, chlorophyll content and soluble protein content after submergence, but also could decrease leaf damage, accumulation of hydrogen peroxide, superoxide anion and malondialdehyde. On the contrary, when 20 mM glycine betaine was applied to ‘Fuyudori’, its phenotypes, antioxidant and photosynthesis systems were not significantly improved compared with the control group. It is speculated that the different susceptibility between the two cultivars is mainly due to the change of stomatal conductance during the reoxygenation period, and the difference in the absorption capacity of glycine betaine between the two cultivars may cause by the expression of glycine betaine transporter ProT gene. For anaerobic respiration-related genes such as BoERF71, BoADH1, BoPDC1-L, BoSUS1-L and BoEIN3, application of 20 mM glycine betaine to ‘228’ can improve the expression level during the late submergence to the early reoxygenation period. It is evaluated that the application of 20 mM glycine betaine to ‘228’ can improve its ethylene reactivity. Moreover, its chlorophyll-producing genes such as BoGSA1 and BoCAO1 were expressed much than the control group during the submergence period, while the expression of chlorophyll-degrading genes such as BoCBR1 during the reoxygenation period was lower than that of the control group, which effectively maintaining the chlorophyll content. However, the expression level of the ABA biosynthesis gene BoNCED9 in the ‘228’ was lower than that of the control group, while the expression level of the ABA degradation gene BoCYP707A1 was higher than that of the control group during the reoxygenation period, which is aside from the stomata observations result. Taken together, the two cultivars of cabbage are suitable for application of different concentrations of glycine betaine to improve the submergence tolerance, the reason may be the difference in the expression of transporters between the two cultivars. The physiological changes of the two cultivars during the reoxygenation period may be mainly affected by the stomata aperture. Apart from the regulation of abscisic acid, ethylene also plays a key role in the physiological and metabolic changes during the reoxygenation period.