兩種滿江紅花青素生成與PSⅡ光化學效能之研究

Abstract

滿江紅是水生蕨類，在冬天或夏天時葉面常累積花青素而呈現紅色。台灣有兩種滿江紅，分別為日本滿江紅（Azolla japonica Fr. et Sav）與羽葉滿江紅（Azolla pinnata R. brown），前者較常見呈現紅色，後者偶而也會形成紅色。本研究比較此兩種滿江紅在不同溫度與光度下其花青素合成能力，並使用葉綠素螢光儀測定其在不同溫度和光度下葉綠體PSⅡ之最大光使用效率（Fv/Fm值），以檢驗以下假設：一、強光、低溫的環境會造成滿江紅光合作用系統受到光抑制（Fv/Fm值下降）；二、在強光、低溫環境下綠色的A. japonica植株較A. pinnata容易受到光抑制；三、在強光、低溫環境下A. japonica較A. pinnata容易生成花青素；四、花青素含量增加可降低A. japonica植株受到光抑制的危險性。 比較含低量花青素的滿江紅在短期溫度（15/13℃、25/20℃、35/30℃）或光度（全光照、遮光）變化時的Fv/Fm值發現：兩種滿江紅在高光照下皆受到明顯的光抑制，並且在15/13℃時其正午Fv/Fm值下降最多並且恢復最慢。當曝露在高光照下時，A. japonica植株的Fv/Fm值顯著低於或等於A. pinnata植株的Fv/Fm值，顯示在某些情況下A. japonica植株比A. pinnata植株易受到光抑制。 將滿江紅培養在不同光度、溫度環境時，在高光照、低溫環境下的植株容易累積花青素，代表高光照以及低溫確實會誘導滿江紅合成花青素；又結果顯示在高光照、低溫環境下A. japonica花青素累積量及累積速率都比A. pinnata高（或快）。相較於花青素含量低的植株，花青素含量較高的植株其正午Fv/Fm值下降幅度較小，這樣的現象A. japonica較A. pinnata明顯。將具不同花青素含量的滿江紅放置在相同光度溫度環境中，同一種滿江紅，尤其是A. japonica，其花青素含量高的植株Fv/Fm值顯著高於花青素含量低的植株；隨著光度減弱，花青素含量越高的植株其Fv/Fm值恢復程度越高。 因此花青素合成可以降低滿江紅在高光、低溫環境下所受的光抑制程度，並且幫助植株在低溫環境中受到光抑制後快速恢復其光合作用效率，此現象A. japonica尤其明顯。比較種間差異時，即使A. japonica比A. pinnata有顯著較多的花青素，但放置在光度高於800 μmolm-2s-1時，其所受到的光抑制程度仍比A. pinnata高或沒有顯著差異，不同的結果可能跟兩種滿江紅葉綠素含量以及花青素總量的多寡有關。

Azolla, a genus of aquatic fern, often turn reddish in winter or in hot summer due to the accumulation of anthocyanin. There are two species of Azolla in Taiwan, Azolla pinnata R. brown and Azolla japonica Fr. et Sav. A. japonica is often found turning red while reddish A. pinnata is not that common. In this study, I compared the ability of accumulating anthocyanin in these two species of Azolla under different light and temperature treatments. The ratio of variable to maximum fluorescence (Fv/Fm) was also measured to quantify the maximum PSⅡ quantum use efficiency. Under light illumination, reduction in Fv/Fm indicates photoinhibition. Following hypotheses were tested. (1) Azolla is susceptible to photoinhibition under high light and low temperature conditions. (2) Without anthocyanin accumulation, A. japonica exhibits greater photoinhibition than A. pinnata under high light and low temperature environments. (3) A. japonica accumulates more anthocyanin than A. pinnata under high light and low temperature conditions. (4) Anthocyanin accumulation can reduce the risk of photoinhibition in A. japonica. The result revealed that both species had greater reduction in Fv/Fm values under high light environments than under shading conditions. The reduction in Fv/Fm was significantly higher at noon and the recovery of Fv/Fm was slower when plants were at lower air temperature (15/13℃) than at 25/20℃ and 35/30℃. A. japonica had equal or significantly lower Fv/Fm values than A. pinnata under high light environment. It indicates that A. japonica was more susceptible to photoinhibition than A. pinnata under some conditions. High light and low temperature environments did induce Azolla to accumulate anthocyanin. The rate and content of anthocyanin accumulation was significantly faster or higher in A. japonica than in A. pinnata. Exposed Azolla with different amounts of anthocyanin to low temperature and high light, I found that Azolla with more anthocyanin had less reduction in Fv/Fm at noon and the recovery of Fv/Fm was faster than Azolla with less anthocyanin accumulation. This pattern was more apparent in A. japonica than in A. pinnata. The results indicate that the accumulation of anthocyanin in Azolla, especially in A. japonica, can reduce the risk of plant being photoinhibited under high light and low temperature environment. Anthocyanin can also help Azolla’s photosynthetic efficiency to recover faster after being photoinhibited under low temperature. In comparison between two species, although A. japonica had higher anthocyanin content, it still suffered equal or higher photoinhibition level than A. pinnata under same light environment. The content of chlorophyll and anthocyanin are important factors determine the differential extent of photoinhibition between both species.