臭氧對阿拉伯芥花粉、花藥和葉片之影響

Abstract

本研究利用光學與電子顯微鏡觀察臭氣對阿拉伯芥花粉活性、花粉萌發、花粉管生長、花粉超微細構造、花藥內壁細胞葉綠體和葉片的影響，並研究臭氣對阿拉伯芥成熟花藥中脯氨酸組成的影響。 以濃度800 ppb的臭氣連續處理五週大阿拉伯芥植株8小時復，在掃描式電子顯微鏡下發現成熟葉片的外部形態並無明顯可見的傷害，但氣孔張開比例增加，此可能為植株成熟葉片2至3天復逐漸凋萎的原因之一。在穿透式電子顯微鏡下發現成熟花藥內壁細胞的葉綠體之類囊膜瓦解，推測葉肉細胞的葉綠體之類囊膜亦會瓦解，此可能為植株成熟葉片凋萎的另一原因。 臭氧處理後，花藥始原細胞、花粉母細胞或較早期的小抱子對臭氣不敏感，因此對於將來成熟花粉粒的萌發影響較小。但晚期的小孢子容易受臭氣影響，因而影響了將來成熟花粉的活性與萌發。此外成熟花粉粒的活性、萌發率和花粉管的長度皆明顯下降，花粉管會發生彎曲、膨大、粗細不均等現象，管壁外觀呈網紋狀，顯示臭氣對阿拉伯芥的成熟花粉活性與萌發有明顯的抑制作用。但以穿透式電子顯微鏡觀察經臭氣處理復成熟花粉的超微細構造，和未受臭氣處理植株之花粉無明顯差異，顯示臭氣對阿拉伯芥花粉的影響可能是生理性的，而不是構造性的。本研究亦首次發現阿拉伯芥的精細胞為兩型性。經臭氧熏氣處理後花藥脯氨酸含量下降，此可能為影響花粉管生長的原因之一。 綜合上述結果可知，阿拉伯芥在花藥始原細胞時期、花粉母細胞時期或發育早期的小孢子對臭氧不敏感，而在小孢子發育晚期正進行有絲分裂時期的小孢子對臭氧最為敏感。

Arabidopsis thaliana (L.) Heynh. was used to study the effects of ozone on pollen viability, pollen germination rate, pollen tube growth and the intracellular level of proline. After treating the five week-old Arabidopsis thaliana plants with 800 ppb ozone for 8 hours, there was no visible damage on leaf surface observed under SEM. However, the ratio of opening stomata increased, which was considered one of the reasons making treated plant shriveled. Under TEM, it was observed that the thylakoids of chioroplast in endothecium degraded, possibly the other reason of leaf withering. After exposing to ozone, the germination rate of pollen grain was lowered. Also the length of pollen tube was decreased obviously. In addition, the pollen tubes became uneven or aberrant in shape with slight swelling at the tip region and striated reticulate on the cell wall. The sensitivity to ozone was dependent of developing stages of microspores. Archesporial cells and pollen mother cells are less sensitive to ozone than those cells at late development stages. Also the germination of mature pollen and the growth of pollen tube were affected by ozone to certain degree. It was observed that there was a dimorphism in sperm cell of Arabidopsis thaliana: one of the sperm cell has a cellular projection and the other not. The treatment with ozone did not cause significant change in ultrastructure of mature pollen grain. Analysis of free proline in mature anthers showed that intracellular proline level was lowered when treated with ozone. Alteration in intracellular prolme level was considered an indicator of the disturbance in physiological processes. It was likely that the effect of ozone might be related more to physiological processes rather than to morphological change. It was concluded that the microspores of Arabidopsis thaliana at archesporial cells stage, pollen mother cells stage, and early development stage were less sensitive to ozone than at the stages of the first and second mitotic divisions of the microspore. Because microspores are very sensitive to ozone, it is possible to use it as a bioindicator of cell damage to ozone pollution.