台灣野生稻穗部各器官其解剖結構及光合作用角色之探討

Abstract

Oryza rufipogon為現行栽培稻之祖先，也為重要之育種資源。台灣野生稻亦屬於Oryza rufipogon 之一群，其學名為Oryza rufipogon Griff.，其生理特性值得深入探究。本研究針對具有長芒之台灣野生稻其穗部各光合器官(芒、內外穎、枝梗等）之解剖構造及色素組成進行觀察及比較，並輔以田間生育資料對其生理意義進行探討。結果顯示台灣野生稻芒僅有少量氣孔，其葉綠素含量極低，並非穗部主要之光合器官，剪芒處理則可能影響穗溫。其內外穎之氣孔主要分佈於內表皮，與栽培稻相同，且葉綠體之分佈靠近胚乳側，推論主要之生理功能為重新固定穀粒本身呼吸作用所釋放出之CO2。枝梗之氣孔密度及葉綠素含量最高，推測為穗部主要與外界進行氣體交換之器官，一次枝梗及穗軸其轉流能力高於二次枝梗及小枝梗。進一步於乳熟期觀察各器官之葉綠體超微結構，發現其光合作用效能之最大值出現於不同之穀粒充實期，且穗部各光合器官之葉綠體生命週期小於劍葉。比較芒中靠近維管束及近厚壁組織之葉綠體構造，則可判定芒中之光合作用較偏向C3路徑。 總結而言，穗部各光合器官具有不同之生理功能，其主要功能與麥穗器官亦不盡相同，再固定呼吸作用之CO2對產量及米質之影響，以及枝梗及穗部光合作用作為供源之能力在育種過程中是否改變，都需要進一步研究。

Oryza rufipogon is considered to be the direct wild ancestor of cultivated rice (Oryza sativa L.), and significant genetic resource as well. The wild rice in Taiwan, Oryza rufipogon Griff. , is a subfamily of Oryza rufipogon and worthy to explore its physiological and morphological significances. This study was focused on the anatomical structure and pigment composition of panicle organs (awn, lemma, palea, rachis branch, etc) of Oryza rufipogon Griff. . Combinding the datas in the field, we can elucidate the photosynthetic roles of these panicle organs. The results show that awn has low stomata density, low chlorophyll contents, interpreting it is not an important ‘source’ in panicle. Meanwhile, clipping awns probably affects the panicle temperature. Stomata on lemma and palea were found in inner epidermis, corresponding to the observation in cultivated rice. The position of green tissue (near the grain) also indicate that re-fixing respired CO2 is the fuction of rice glumes. Rachis branch, with highest stomata density and chlorophyll content, is the main site of gas exchange in rice panicle. The translocation capabilities of panicle axis and primary branch are larger than secondary branch and pedicel. Observation of the chloroplast ultrastructure in different organs reveals that maximum photosynthetic rate of these organs may appear in different grain-filling stages. Life span of chloroplast in panicle organs are shorter than flag leaf. Comparing the chloroplasts in awn showed that awn carries C3 photosynthesis characteristics. Every rice panicle organs has its own physiological role, not the same as the ear of wheat. How CO2 re-fixation affects yield and quality and the contribution of panicle photosynthesis change in breeding process need further researches.