颱風草葉片皺摺與葉子對光環境的反應

The cross-markings and the responses of leaves of Setaria palmifolia to contrasting light environment

廖顯淳(Hsien-Chun Liao)

指導教授 ： 高文媛

國立臺灣大學/生命科學院/生態學與演化生物學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.00048

摘要

颱風草 (Setaria palmifolia) 為台灣常見之大型禾草，因原住民會利用颱風草上的皺摺數量預測颱風侵襲次數與時間，俗名為颱風草。有別於其他C4植物多生長於高溫、高光度的環境中，觀察發現野外颱風草可以生長於多樣的光度環境下。本研究比較生長在不同光環境下的植株其葉片上的皺摺數量與分布的差異。並探討皺摺形成的原因以及颱風草如何適應不同的光環境。根據前人對陰性植物的報導，將檢驗下列假設：颱風草具有調整形態或光合作用生理的能力，使其得以在不同的環境下生長。實驗中發現颱風草葉片在不同強度的光照射下，其照光的部位會發生顏色的變化，推測應該是葉綠體排列的位置發生改變。因此本研究亦探討葉綠體移動現象對颱風草適應不同光環境的重要性。藉由野外植株調查與溫室種植實驗，比較不同光度環境下生長之颱風草葉片的皺摺數量分布、形態特徵、解剖構造、光學性質以及生理表現上的差異，並觀察颱風草葉片發育時皺摺生成的過程。
觀察發現颱風草葉上的皺摺可分為摺痕與皺紋兩種類型，且每片葉只有一條摺痕但有不同數量之皺紋。而野外測量與溫室光度處理實驗發現，颱風草摺痕至葉身近軸端的距離與葉身長度具顯著的正相關，而摺痕的相對位置(與葉身近軸端的距離除以葉長度)則具有負相關。而皺紋出現數量不定且其分布情形較為複雜，可能和光環境以外其他環境因子有關。
而觀察葉片解剖橫切面構造發現，摺痕與皺紋處的組織和葉面沒有皺摺處組織相類似；在平行葉脈切面發現摺痕為葉組織向上拱起，而皺紋為葉組織向下凹陷，推測造成兩種皺摺的成因應該不同。由不同葉片發育時期的解剖構造推測，摺痕的形成應該是較早生成的葉片上葉舌對新生葉片包裹擠壓而成；而在葉片發育的早期並沒有觀察到皺紋，因此皺紋形成無法從解剖上的觀察得知。
野外植株測量與溫室光度處理顯示，生長在遮陰的植株比全光照下的植株具有顯著較高之單位乾重葉面積比 (SLA) 以及比較薄的葉片，可增加對光的截取面積，有利於其在低光下生長。不同光環境下生長的植株其葉片單位面積葉綠素含量相同，也具有相似的對光的吸收率。相對於遮陰處理植株的葉片，全光照處理植株葉片因具有較多的單位面積氮含量，因此具有顯著較高的光飽合點光合作用速率以及光飽和點。在光度高於700 μmol m-2 s-1的光照射下，颱風草葉肉細胞葉綠體移動出現避光反應（導致葉片對光的穿透率增加），而照射低於300 μmol m-2 s-1的光時會出現聚集反應（導致葉片對光的穿透率減少）；推測颱風草葉綠體移動可提昇其光合作用對光的使用效率，並減少強光對葉綠體產生光傷害。綜合上述結果颱風草具有形態和光合作用生理表現的表型可塑性，配合快速的葉綠體移動反應，使颱風草得以在不同的光環境下生長。

關鍵字

颱風草 ； C4植物 ； 皺摺 ； 葉綠體移動 ； 表型可塑性

並列摘要

Setaria palmifolia (Poaceae) is a common tall grass in Taiwan. Because aborigines believed that cross-markings on its leaves can be used to forecast occurrence of typhoons of the year, it is locally called “tai feng cao”. This plant is recorded as a C4 plant, which is commonly adapted to high light and high temperature environment, growing in varied light environment at field. In this thesis, the number and distribution pattern of cross-markings on the leaves of S. palmifolia plants in different environments, and the formation of cross-markings were studied. The shade-tolerant mechanisms of the plant were also investigated. During the experiment, that leaves showed changing of brightness after illuminating with different intensities of light. This phenomenon was also explored.
Morphological and anatomical features, optical properties and physiological performance of field growing and greenhouse grown plants were analyzed. The cross-markings on leaves of S. palmifolia can be classified into two types, folding and wrinkles. Each leaf had only one folding but numerous wrinkles. Measurements on field growing and greenhouse grown plants revealed that S. palmifolia plants under different environment grew different length of leaf blade. The distance between the folding and proximal end of the leaf blade was significantly positive correlated with the length of leaf blade, while the relative location of folding was negatively correlated with the length of leaf blade. However, the number and distribution pattern of wrinkles were more complex than those of foldings.
No difference was found in cross sections between the part of folding (or wrinkles) and other part of leaves. Paraveinal sections revealed that the formation of folding was due to leaf tissues being compressed upward, while that of wrinkles being pressed concavely. Therefore, the formation of the two types of cross-markings might be induced by different forces. After investigating developing leaves, the formation of folding on developing leaf was caused by wrapping and compressing of ligule of the previous leaf. While the formation of wrinkles can’t be telled from current observation.
Phenotypic plasticity was found in S. palmifolia plants grown in different light environment. Plants in shady treatment had significantly larger leaf area per dry mass (SLA) and thiner leaves than those received full sun light treatment. An increased in SLA would increase light intercepting area with the same amount of biomass allocating which might benefit S. palmifolia growing under low-light condition. Significantly higher photosaturated photosynthetic rate and higher light saturation point were measured on plants received full sun light treatment than shady treatment. Mesophyll chloroplasts of S. palmifolia showed avoidance response (resulting in increment of transmittance) under illumination of light intensities higher than 700 μmol m-2 s-1, while showed accumulation response (resulting in reduction of transmittance) at light intensities lower than 300 μmol m-2 s-1. The behavior of chloroplast movements may optimize photosynthetical light use efficiency of leaves under low-light conditions while reduce the risk of photodamage of leaves under high light stress. Phenotypic plasticity and chloroplast movement response confer S. palmifolia ability to grow under varied light environment.

並列關鍵字

Setaria palmifolia ； C4 plant ； cross-marking ； chloroplast movement ； phenotypic plasticity

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