光照誘導水稻種子根產生波動形態之生理機制

Abstract

光照是調控植物生長發育的重要環境訊息因子之一，本研究發現於水稻(Oryza sativa L.)種子發芽過程中，光照刺激會誘導秈型稻之台中在來1號(Taichung Native 1; TCN1)水稻種子根產生波動形態，而稉型稻之台農67號(Tainung 67; TNG67)則無此現象發生。幼苗局部照光之實驗結果指出，誘導根波動之光訊息主要是由根部組織直接接收及感應。由根部之切片觀察，發現光照會造成根部的中柱細胞兩側細胞產生不對稱生長，進而導致波動形態之發生。進一步觀察不同光質及光強度對TCN1水稻種子根之影響，結果發現不同光強度之紅光及白光處理下均會誘導TCN1水稻種子根產生捲曲及波動形態。另一方面，高光度之藍光(90 μmol m-2s-1)不會誘導根波動之現象發生，然而較低光度之藍光(30 μmol m-2s-1)則會誘導種子根波動；故不同藍光的光強度造成根部形態有明顯的差異。利用Aspirin抑制水稻內生茉莉酸之生合成，會降低TCN1水稻種子根於紅光(90 μmol m-2s-1)、低藍光(30 μmol m-2s-1)及白光(90 μmol m-2s-1)誘導下所產生的捲曲及波動百分比；進一步利用real-time RT-PCR分析TCN1水稻種子根中茉莉酸生合成及訊息傳導基因之表現，發現allene oxide synthase (OsAOS)家族基因、12-oxophytodienoic acid reductase 1 (OsOPR1)及root specific rice PR10 (RSOsPR10)均會受到紅光及白光處理而誘導其表現。N-1-naphthylphthalamic acid (NPA)會抑制生長素(Auxin)流出載體蛋白的功能，以破壞水稻之生長素極向運移，結果指出NPA會抑制白光誘導TCN1水稻種子根產生的波動形態且會影響根部之向地性反應。綜合以上實驗結果，推測茉莉酸生合成及生長素極向運移反應均為光照誘導TCN1水稻種子根產生捲曲及波動形態所必須之條件。

Light is an important environmental factor controlling plant growth and development. In this study, it was observed that continuous white light can induce the wavy growth pattern of seminal roots in germinating rice (Oryza sativa L. cv. Taichung Native 1; TCN1) seeds. However, the phenotype of light-induced wavy root was genetic diverse among rice cultivars; for example, the light-induced wavy root could be presented in seedlings of indica type rice (such as TCN1), but could not be presented in that of japonica type cultivars (such as Tainung 67; TNG67). According to the experiment with plants partially exposed to light, it was suggested that the light signal for inducing the wavy roots were directly sensed by root tissues. Analysis of longitudinal sections of wavy seminal roots indicated that light-induced root waving was caused by the asymmetric cell growth on both side of vascular cylinder cells in the root tips. In addition to white light, red light (90 μmol m-2s-1) could also induce root curling phenotype on seminal roots. However; the blue light with high intensity (90 μmol m-2s-1) presented no effect on inducing root waving/curling. On the other hand, other results in our laboratory showed that low intensity (30 μmol m-2s-1) of blue light could induce root waving. Using Aspirin to inhibit endogenous jasmonic acid (JA) biosynthesis in TCN1 seedlings conducted the light-induced curling/wavy root phenotypes were absent. Furthermore, light effects on expressions of the genes involved in JA biosynthesis, i.e., allene oxide synthase (OsAOS) gene family and 12-oxophytodienoic acid reductase (OsOPR1), and a root specific JA-responsive gene, root specific rice PR10 (RSOsPR10) were observed. The data showed that transcript levels of most JA biosynthesis-related and JA-responsive genes were increased in white- and red-light conditions. Moreover, N-1-naphthylphthalamic acid (NPA), an inhibitor of auxin efflux carriers, was used to interrupt auxin polar transport in roots, and then the morphology of light-induced wavy root was eliminated. Thus, the results suggested that JA biosynthesis and auxin polar transport were essential for light-induced seminal root waving in seedlings of indica type rice.