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Studies on the enhancement of UV-B tolerance in rice seedlings
|關鍵字:||rice;水稻;UV-B tolerance;hardening;ascorbic acid;glutathione;salicylic acid;紫外線耐性;健化;抗壞血酸;榖胱苷;;水楊酸||出版社:||農藝學系||摘要:||
本試驗以台農67號水稻幼苗（三葉期為材料），試驗項目共分為：一、經健化處理之水稻幼苗對過量UV-B照射的反應；二、水稻幼苗施用活性氧族清除劑（ascorbic acid and glutathione）後對過量UV-B照射的反應；三、水稻幼苗施用水楊酸（salicylic acid，SA）後對過量UV-B照射的反應。調查分析植株形態及生理反應，前者包括植株生長高度與傷害等級，後者則有電解質滲漏、葉綠素含量、MDA含量以及抗氧化酵素活性和抗氧化物的含量，藉此了解前處理之效果，並進一步探討這些處理提高水稻耐過量UV-B之機制，作為研究日後有關植物與UV-B的參考。
對水稻進行健化處理後，再行過量UV-B照射，可緩和葉綠素含量下降。以UV-B 12.4 kJ m-2day-1健化8到10天可明顯緩和過量UV-B照射下幼苗葉片內MDA含量之上升，相對地可降低GSSG量並提高幼苗葉片ascorbic acid、GSH含量與GSH/GSH+GSSG值，另外在過量UV-B照射前所行之健化處理對兩個抗氧化酵素ascorbate peroxidase和glutathione reductase之活性，則沒有產生任何較為明顯的影響。
前處理以外加不同濃度的ascorbic acid或reduced glutathione，皆可略減緩過量UV-B照射下幼苗葉片MDA的增加，其中以濃度10-3 M前處理效果最為佳。以ascorbic acid前處理會提高的幼苗葉片的ascorbic acid含量與ascorbate peroxidase活性，以reduced glutathione前處理則是略為增加葉片GSH含量。兩種抗氧化物前處理對於水稻幼苗在過量UV-B照射下所造成之傷害勢、葉綠素量、GSH/GSH+GSSG值以及glutathione reductase活性並未有較明顯的影響。
水稻幼苗在外加SA後進行過量UV-B照射，發現SA處理並不能減緩幼苗在UV-B下之傷害，無法明顯緩和葉片葉綠素含量降低或MDA含量增加。抗氧化系統方面，外加SA可些微增加ascorbic acid以及GSH含量，但效果不大，對幼苗的ascorbate peroxidase與glutathione reductase活性則沒有影響。
由試驗結果綜合而知，數種人為處理以健化處理效果較佳，其中又以12.4 kJ m-2day-1 UV-B健化8到10天最能減緩水稻幼苗受到過量UV-B照射時之氧化傷害，而減緩的主要原因可能是由於健化處理誘導水稻幼苗ascorbic acid含量增加所致。
Plants exposed to the excess UV-B irradiation resulted in of peroxidation injury, decreased chlorophyll content, increased electrolyte conductivity and malondialdehyde (MDA) content. The purpose of this study is to explore the possibility of decreased injury of rice seedlings exposed to excess UV-B irradiation and enhanced excess UV-B tolerance by hardening or pretreatment with various chemical agents.
Rice cultivar TNG 67 V3-seedlings were used as materials and three experiments were performed in this study, the first part was a series injury and physiological responses conducted as hardened rice seedlings exposed to excess UV-B irradiation. Second part was injury and physiological responses of rice seedlings pretreated ascorbic acid and glutathione exposed to excess UV-B irradiation. Last was a series injury and physiological responses of rice seedlings pre-applied salicylic acid (SA) exposed to excess UV-B irradiation.
Experimental results indicated that decrease of chlorophyll content in rice seedlings exposed the excess UV-B irradiation was eased by hardening. The enhancement of malondialdehyde (MDA) content was reduced, decreased oxidized glutathione (GSSG) content, increased reduced glutathione (GSH), ascorbic acid (AsA), and GSH/GSH+GSSG in rice seedlings were hardened by 12.4 kJ m-2day-1 UV-B for 8 days to 10 days before excess UV-B treatment. Ascorbate peroxidase (APx) and glutathione reductase (GR) activities in hardened seedlings were not different.
The enhancement of MDA content was slightly reduced in rice seedlings that pretreated with 10-3 M AsA and GSH respectively. AsA content and Apx activity of rice seedlings were increased by pretreatment of AsA. GSH content was lightly increased by pretreatment of GSH.
In application of SA, the excess UV-B injury, decrease of chlorophyll content and increase of MDA content weren't reduce, but content of AsA and GSH were lightly increased.
The results indicated hardening was more effective than other pretreatments in this study. The effect of hardening by 12.4 kJ m-2day-1 UV-B for 8 to 10 days was the greatest and significantly reduced injury and peroxidation injury of rice seedlings exposed excess UV-B irradiation. It was suggested that increasing AsA content in rice seedlings by hardening could scavenged the production of active oxygen species, and lead to decreased damage of peroxidation.
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