非生物逆境下亞托敏及硒處理對小麥幼苗生理之影響

Abstract

本研究的目的主要在評估亞托敏（azoxystrobin, AZ）和硒（Selenium, Se）處理對小麥品種台中選2號（Triticum aestivum L. variety Taichung No. 2, TCS2）在高溫和鹽逆境下的作用機制。在亞托敏實驗中，探討殺真菌劑亞托敏前處理對小麥幼苗於突然來襲的熱逆境下（Heat stress, HT, 46℃）的生理機制影響。本試驗分別以0.4, 4, 40, 80和120 mg L-1的AZ預處理4天，再針對有經過AZ預處理和未處理AZ的幼苗施以46 oC 1小時的高溫逆境，緊接著進行1000 μmol m-2 s-1 之高光處理20分鐘。 高溫誘導的氧化逆境導致未處理亞托敏幼苗葉片中的還原力降低及丙二醛含量增加，抗壞血酸過氧化物酶（ascorbate peroxidase, APX）和過氧化氫酶（catalase, CAT）酶活性增強。然而在高溫逆境下的AZ預處理卻導致葉綠素螢光，APX和CAT活性以及清除DPPH能力的降低，並且隨著AZ處理濃度的增加，熱逆境所引起的生理損傷亦加劇。AZ預處理雖可增加光合色素的含量，然而綜合上述生理指標的結果表明AZ無法為小麥台中選2號在熱逆境下提供保護作用。在硒與鹽害實驗中，主要探討22 μM之硒處理在不同濃度（0, 100, 200, 300和400 mM NaCl）的鹽逆境下對台中選2號幼苗的保護作用。研究結果顯示，經過硒處理之小麥在葉綠素螢光參數，抗氧化酵素 (過氧化氫酶CAT)，抗氧化物質(總酚，類黃酮及黃青素含量)，抗氧化能力 (清除DPPH自由基能力、還原力分析)，光合作用色素 (總葉綠素及類胡蘿蔔素)，株高及根長皆有較佳之表現，顯示22 μM 的硒處理確實對台中選2號幼苗在鹽脅迫下具有保護效果。在硒及鹽害下之滲透逆境及離子逆境實驗之研究中，旨在區分鹽逆境引起的滲透和離子脅迫對台中選2號的影響，並評估22 μM Se處理對此二種脅迫之調節效果。我們假設耐鹽性較強的台中選2號較易受到滲透脅迫的影響，而22 μM 的Se處理對鹽害逆境所導致之滲透脅迫及離子脅迫皆發揮保護作用。為了驗證此一假設，本實驗將聚乙二醇（PEG）和鹽 (NaCl) 調成3種等滲濃度，最終滲透勢分別為 -1.05 MPa（24％（w / v）PEG和200 mM NaCl ）， - 1.33 MPa（26.5％（w / v）PEG和250 mM NaCl）和-1.57 MPa（29％（w / v）PEG和300 mM NaCl）。研究結果顯示，相較於PEG所造成之滲透逆境，鹽處理所造成的之離子逆境可使葉綠素螢光（ChlF）參數有較佳之表現，光合色素（總葉綠素和類胡蘿蔔素） 之降解速度較慢，抗壞血酸過氧化物酶（APX）活性較好，且丙二醛 （MDA）累積也較少。顯示在鹽害逆境下的滲透脅迫比離子脅迫對台中選二號造成更大之生理影響。同時，我們觀察到22 μM Se處理對鹽害逆境下之滲透脅迫及離子脅迫均無法提供保護效果，顯示硒的有效處理濃度還需要更進一步的實驗加以闡明。整體而言，本研究結果分別為亞托敏及硒處理下對台中選2號之小麥品種在熱逆境和鹽脅迫下之生理機制提供了更好的理解。

The objective of this study was to evaluate the effect of azoxystrobin (AZ) and Selenium (Se) on wheat (Triticum aestivum L.) variety Taichung No. 2 'Taichung SEL.2' (TCS2) in high temperature and salt stress. In the AZ exp., the physiological mechanism of the fungicide AZ in protecting against heat (HT, 46 °C) stress in wheat TCS2 seedlings was investigated. Seedlings were pretreated with 0.4, 4, 40, 80, and 120 mg L-1 of AZ for 4 d. Next, AZ-pretreated and untreated seedlings were subjected to HT for 1 h followed by 1000 μmol m-2 s-1 lighting for 20 min. HT induced oxidant stress which resulted in a decrease in the reducing power, an increase in malondialdehyde, and enhanced enzyme activities of ascorbate peroxidase (APX) and catalase (CAT) in leaves of untreated seedlings. However, AZ-pretreated seedlings under HT displayed reductions in chlorophyll fluorescence, APX and CAT activities, and the 1,1-diphenyl-2-picryl-hydrazyl scavenging capacity. Physiological damage caused by HT was aggravated by an increase in the AZ concentration. In addition, increased photosynthetic pigments were also observed in leaves of AZ-pretreated and HT-exposed seedlings. The results suggest that AZ does not provide a protective effect against HT stress. In the Se & salt exp., the mitigative effects of 22 μM Se on TCS2 were investigated under different salt stress levels (0, 100, 200, 300, and 400 mM NaCl). Results of the antioxidative capacity showed that catalase (CAT) activity, non-enzymatic antioxidants (total phenols, total flavonoids, and anthocyanins), 1,1-Diphenyl-2-Picryl-Hydrazyl (DPPH) radical-scavenging activity, and the reducing power of Se-treated seedlings were enhanced under saline conditions. The more-stabilized chlorophyll fluorescence parameters (maximal quantum yield of photosystem II (Fv/Fm), minimal chlorophyll fluorescence (F0), effective quantum yield of photosystem II (ΦPSII), quantum yield of regulated energy dissipation of photosystem II (Y(NPQ)), and quantum yield of non-regulated energy dissipation of photosystem II (Y(NO)) and the less-extensive degradation of photosynthetic pigments (total chlorophyll and carotenoids) in Se-treated seedlings were also observed under salt stress. The elongation of shoots and roots of Se-treated seedling was also preserved under salt stress. Protection of these physiological traits in Se-treated seedlings might have contributed to stable growth observed under salt stress. The present study showed the protective effect of Se on the growth and physiological traits of wheat seedlings under salt stress. In the Se and salt/PEG exp., the aim was to distinguish the effects of osmotic and ionic stress induced by salt stress on TCS2 and evaluate the effect of 22 μM Se treatment on these two stresses. We hypothesized that TCS2 is more susceptible to osmotic stress, and 22 μM Se treatment protects against osmotic stress and ionic stress caused by salt stress. In order to verify this hypothesis, this experiment adjusted polyethylene glycol (PEG) and salt (NaCl) to three isotonic concentrations, and the final osmotic potential was -1.05 MPa (24% (w / v) PEG and 200 mM NaCl), - 1.33 MPa (26.5% (w / v) PEG and 250 mM NaCl) and -1.57 MPa (29% (w / v) PEG and 300 mM NaCl). According to the results of chlorophyll fluorescence parameters, APX activity, photosynthetic pigments (total chlorophyll and carotenoids), malondialdehyde (MDA), and shoot height. The osmotic stress caused by PEG was more harmful than the ionic stress caused by salt stress to TCS2. Also, we observed that 22μM Se treatment could not protect against osmotic stress and ionic stress under salt stress. The effective treatment concentration of Se required furthering experimentation. Overall, the results of this study provide a better understanding of the physiological mechanisms of TCS2 under thermal and salt stress with the treatment of AZ and Se.