以L-system探討三種水生植物異形葉之形態發生

Abstract

有些水生植物在挺水及沉水時會產生不同形狀之葉片，稱為異形葉。與幼年葉、成熟葉不同的是水生植物之異形葉是因環境改變而導致葉形產生變化而非株齡因素，目的是為了適應空氣及水中兩種差異甚大的環境。在水中其氣體交換比空氣中較難進行，所以需要特化的葉片幫助植物生存在水中。前人研究發現某些特定因素會使水生植物產生異形葉，如乙烯、藍光 、ABA等，但影響因子與水生植物異形葉之間存在著劑量關係，而每種植物的劑量關係也不完全相同。有些植物在水中的異形葉較挺水葉細長，如紅宮庭。有些沉水葉缺刻深達主脈，挺水葉葉緣卻呈鋸齒狀，如紅雨傘。有些甚至連葉序也不相同，如大寶塔。在不同光強度及光週期，植物之生長速度因種類而有差異，可能是因原棲地環境不同導致，使水生植物對水族箱中的環境有不同的適應力。利用L-system模擬水生植物在水族箱環境中的生長情形，將植株之生長狀況分類，可利用於預測水族造景生長情形之上。L-system為一種以數學規則描述生物生長情形的理論，以起始字串及疊代重寫規則並以烏龜爬行軌跡來描述生物形態及生長過程。由於近年來分子生物學之進步，學者對遺傳及發生 (從受精卵到成長為個體的過程) 已有相當程度的瞭解，更有許多物種之遺傳基因已被解序。各種生物之間其遺傳基因各不相同，但生物之生長過程就是以這些遺傳訊息表達出的各種需要的蛋白或分化各個細胞 (依生物部位之不同而有不同分化結果) 。本研究提出以L-system的觀點模擬生物，其器官生長在同一種植物基本構形為相似的，只是因環境改變造成L-system參數改變以致最終外形不相同。如能找出DNA序列與L-system中參數改變的關係，甚至知曉L-system之基本構形，將能以各種DNA序列模擬出各個物種的外表形態。

Heterophylly observed in some aquatic plants which have different shapes of leaves while emerged or submerged. The shapes of the heterophyll of aquatic plants change when they encounter different environments but not age of plants. The purpose of aquatic plants heterophylly is to adapt the environments from air to water and the opposite direction. The exchange of gas is harder in water than in air, so plants need special leaves to survive in water. Some researches show that there are some factors leading the aquatic plants to form the heterophyll, including ethylene, blue light and ABA. The factors have different dosage relationships with heterophyll in different species. The heterophyll of submerged is thinner than emerged in some aquatic plants, Rotala rotundifolia for example. The notch of submerged heterophyll is deeper than emerged one, Proserpinaca palustris for example. Some heterophylly even changes the phyllotaxy, such as Limnophila aquatic. The reason that the plants have different growth rates in different light density and photoperiodism is because their original nature habitats are different. And the reason can lead aquatic plants to have different adaptability in aquarium. We can use L-system to simulate the growth situations of aquatic plants in aquarium, and it can also predict the view of aquarium. L-system is a theory about describing the growth situations of organism by mathematic, including axioms, rewriting rules, turtle graphics. Due to the progress of molecular biology, we have known a lot of DNA sequences of organism. The DNA between different organisms are different, it produces different genetics messages, and shapes the organism. From the view point of L-system, we propose that the basic form of plant organ is similar, and the different appearances are due to the parameters’ changes in different environment. If we can find the relationship between DNA sequences and the parameters of L-system, as well as the basic form of organism by L-system. We can simulate the shapes of organism by DNA sequences.