http://www.nchu.edu.tw/~giab/giabchy/yang/ygoal2.htm
分生組織分裂及分化
高等植物的發育過程中之所以會有界面的轉移，完全是因為植物在成熟的過程中能不停的
分裂產生新的細胞，這些細胞接著就分化成地上部的莖葉花，或地下部的根等組織與器官
。植物具有這個分裂能力的區域叫作分生組織(meristem)，在地上部莖頂端上的叫頂芽分
生組織(shoot apical meristem, 簡稱SAM)，在地下部根尖處的叫作根尖分生組織(root
apical meristem, 簡稱RAM)，這兩處分生組織理論上都具有無限制分裂的能力，而若分
裂出的細胞能正確的發育並執行分化的功能則就會形成正常的植株形態，故對分生組織的
研究已成一個重要的領域。為了深入暸解植物在發育過程中，分生組織如何正確的調控細
胞的分裂與後續的分化，本實驗室選用分子遺傳(molecular genetic)的策略來進行影響
分裂分化的突變植株如之篩選，及進行後續相關基因如Abnormal Root and Shoot
(ARS), Lily Protein Kinase 1(LPK1), p70 ribosomal S6 kinase (p70s6k),及40S
ribosomal protein S6等基因之選殖分析，基因之表現及功能的探討，及轉殖基因植物之
分析等工作，以期能深入了解分生組織調控植物生長發育之機制。
Meristematic Activity And Cell Differentiation
In plants, the regions harboring the ability to generate new cells, named the
meristem, are established in the tips of embryonic shoot and root, named
shoot apical meristem (SAM) and root apical meristem (RAM) respectively,
during embryogenesis. The mature embryo in seeds germinated once the
environment is favorable for growth. Both SAM and RAM divide indefinitely and
result in the growth of the plant. Meristematic activity specifies the fate
of the shoot and root, and initiates different developmental programs which
are subsequently responsible for specific organ differentiation. To explore
how meristem controls cell division and differentiation, molecular genetic
approaches were applied. Genes such as Abnormal Root and Shoot (ARS), Lily
Protein Kinase 1(LPK1), p70 ribosomal S6 kinase (p70s6k) and 40S ribosomal
protein S6 which may be involved in meristematic activity were cloned.
Further functional analyses for these genes through transgenic plant approach
will reveal the mechanism controlling cell division and differentiation.
--------------------------------------------------------------------------------
植物葉片老化與程式性死亡
葉片老化是一個複雜的過程其中包含著細胞的大量死亡。這個機制必定是在基因的調控之
下，藉由內生性的因子諸如老化因素和植物荷爾蒙之間的平衡性，及受到外在環境訊息的
調節。由細胞的層次來看，老化過程總伴隨著葉片組織的脫水，核醣核酸分解酵素和蛋白
分解酵素活性的上升，和葉綠體的減少，結果造成葉片產生微黃的顏色。在植物界中，葉
片老化被認為是屬於程式性死亡(Programmed Cell Death或 Apoptosis)已有多年了，然
而卻沒有任何分子生物學上的研究報告去證實葉片老化確實為程式性死亡。我們藉由使用
不同種類的植物葉片，如鳳凰樹，膠蟲樹，羊蹄甲，蔓綠絨，黃金葛等，來觀察老化葉片
組織是否有程式性死亡現象的發生。DNA的階梯現象為證實細胞死亡是否為PCD的重要指標
，其結果是因Apoptotic cell核內DNA的斷裂會造成。藉由DNA電泳及南方墨漬法偵測到這
五種植物老化葉片中皆有DNA階梯之現象發生，但在非老化葉中則無此現象的發生。DNA的
斷裂及核的凝縮現象在進一步藉由螢光染色(TUNEL Assay)得到佐證。在老化葉片的葉肉
細胞上細胞核有明顯的TUNEL螢光反應，對照之下綠色健康葉片並無TUNEL螢光染色的反應
。這個結果提供了直接證據證實在植物發育過程中葉片的老化確實是PCD的現象。利用
cDNA subtraction的方法已由羊蹄甲及擬南芥中鑑識出許多可能是表現在PCD初期的cDNA
clones。將來的目標是更進一步的選殖和鑑定這些clones，如透過轉殖基因植物的穫得，
將使我們更深入的瞭解這個機制調控的過程。
Leaf Senescence And Programmed Cell Death (PCD)
Leaf senescence is a complex process which is involved in cell death in a
large-scale manner. At the cellular level, senescence is always accompanied
by dehydration of the leaf tissue, increased activity of RNases and
proteinases, and diminution of the chloroplasts, resulting in the yellowish
color of the leaves. In plants, senescence of the leaves has been thought to
be a type of programmed cell death (PCD or apoptosis) for many years,
however, no studies at the nuclear level associated with PCD have been
reported. By using leaf tissue from five different plant species,
Philodendron hastatum, Epipremnum aureum, Bauhinia purpurea, Delonix regia,
and Butea monosperma, the detection of PCD in senescent leaf tissue was
observed. DNA ladders, the hallmarks of apoptosis, resulting from the
cleavage of nuclear DNA into oligonucleosomal fragments in apoptotic cells,
were detected by gel electrophoresis and southern hybridization only in
senescent (but not in non-senescent) leaves in all five plant species. DNA
fragmentation and nuclear DNA condensation were further confirmed by using
the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end in
situ labeling (TUNEL) method. Fluorescence was clearly detected in the nuclei
of mesophyll cells in senescent leaves. By contrast, there was no TUNEL
staining in green healthy leaves. The results provide direct evidence to
support the notion that natural senescence of the leaves is indeed an
apoptotic process during plant development. A strategy by using cDNA
subtraction was used to identify several cDNA clones potentially involved in
the initial step of this process from B. purpurea and Arabidopsis. Further
cloning and characterization of these genes are in progress and should lead
to a deeper understanding of its mechanism.
--
The darkest hour is that before the dawn.
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 124.8.129.147