Abstract

Individuals of Marsilea quadrifolia, an amphibious fern, experiencing xtreme variations in environment develop heterophyll with different morphological haracteristics. The objective of this study is to investigate if ethylene can induce floating type of leaves in his fern. To achieve this goal, ratio of stomatal density on abaxial and adaxial leaf surfaces (stomatal atio) and the mass per unit length of petiole (PML), on leaves of terrestrial shoots sprayed with an ethylene as releaser, Ethephon, were compared with those of leaves produced by submergence of terrestrial hoots. Leaves with different stomatal ratio and PML, corresponding to that of terrestrial type and loating type of leaves, were produced when terrestrial shoots of M. quadrifolia were submerged. The esult reveals that the plasticity of leaves to respond to submergence depends on leaf’s age. Application of thephon significantly altered the stomatal ratio of young leaves on terrestrial shoot but not their PML. eaves response to Ethephon treatment was also age dependent. These results indicate that ethylene ight be involved in the formation of floating leaves in M. quadrifolia.

中文摘要

田字草是一種水陸兩棲的蕨類，在不同環境下會長出異形葉，這些異形葉具不同的形態特徵。本研究目的在探討乙烯氣體是否可以誘導田字草浮水葉的形成。我們比較陸生植株經淹水後、以及噴灑Ethephon (會釋出乙烯氣體) 後，不同葉齡的葉片其上、下表皮氣孔密度比和葉柄單位長度重量比。結果發現陸生環境下長出的葉子經淹水後能否轉變成浮水葉特徵和其葉齡有關，較老的葉子維持陸生葉特徵(較高的下/上表皮氣孔比和較重的葉柄單位長度重量比)，幼葉則可以轉而形成浮水葉特徵(較低的下/上表皮氣孔比和較輕的葉柄單位長度重量比)，而淹水後才新長出的葉片具浮水葉特徵。陸生植株噴灑Ethephon 後有些原已形成的葉子其氣孔比是否會轉變成傾向浮水葉特徵也和其葉齡有關；葉柄單位長度重量比則不受Ethephon 噴灑的影響，仍維持陸生葉特徵。結果顯示乙烯氣體可以誘導田字草改變葉子的部份特徵，此可能和浮水葉的形成有關。

Keyword: amphibious fern, ethylene, floating leaves, heterophyll, M. quadrifolia, stomatal ratio. 水陸兩棲蕨類、乙烯、浮水葉、異形葉、田字草、氣孔比。