使陆地植物远离其水生亲本植物的是它们在空气中向上发芽、以及依靠木质组织支撑自身的能力。木质结构由纤维素组成,其中填充木质素分子。大约4亿7500万年前含木质素细胞壁的出现被认为是陆地植物由水生祖先进化过程中的一个重要变革。生物燃料研究人员对木质素尤为感兴趣,因为它将细胞壁联在一起,阻止了纤维素的提取,而后者是生物燃料产品的一个重要成分。
二次生长和木质化细胞是维管植物独有的特征,起码科学家是这样认为。美国哥伦比亚大学和斯坦福大学的一组研究人员最近鉴定出一种具有木质细胞的海藻。这些科学家在发表于Current Biology上的文章中指出,“考虑到红藻和维管植物在10亿年前便已经分化,这一发现使人们开始考虑这些性状是趋同进化还是深度保守进化的问题”。(生物谷Bioon.com)
生物谷推荐原始出处:
Current Biology, 22 January 2009 doi:10.1016/j.cub.2008.12.031
Discovery of Lignin in Seaweed Reveals Convergent Evolution of Cell-Wall Architecture
Patrick T. Martone1,2,7,8,,,José M. Estevez3,7,9,Fachuang Lu4,5,7,Katia Ruel6,Mark W. Denny1,2,Chris Somerville2,3,10andJohn Ralph4,5
1 Hopkins Marine Station of Stanford University, 120 Ocean View Boulevard, Pacific Grove, CA 93950, USA
2 Department of Biological Sciences, Stanford University, Stanford, CA 94305, USA
3 Carnegie Institution, Stanford University, Stanford, CA 94305, USA
4 Department of Biochemistry, University of WisconsinMadison, Madison, WI 53706, USA
5 U.S. Dairy Forage Research Center, USDA Agricultural Research Service, Madison, WI 53706, USA
6 Centre de Recherches sur les Macromolécules Végétales (CERMAV)-CNRS, 38041 Grenoble cedex 9, France
7 These authors contributed equally to this work
8 Present address: Department of Botany, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
9 Present address: Laboratorio de Fisiología y Biología Molecular, IFIByNE (CONICET), FCEyN-UBA, Pab.2, Ciudad Universitaria, Buenos Aires C1428EGA, Argentina
10 Present address: Energy Biosciences Institute, University of CaliforniaBerkeley, Berkely, CA 94720, USA
Summary
Lignified cell walls are widely considered to be key innovations in the evolution of terrestrial plants from aquatic ancestors some 475 million years ago [1,2,3]. Lignins, complex aromatic heteropolymers, stiffen and fortify secondary cell walls within xylem tissues, creating a dense matrix that binds cellulose microfibrils [4] and crosslinks other wall components [5], thereby preventing the collapse of conductive vessels, lending biomechanical support to stems, and allowing plants to adopt an erect-growth habit in air. Although lignin-like compounds have been identified in primitive green algae [6,7], the presence of true lignins in nonvascular organisms, such as aquatic algae, has not been confirmed [2,3,8,9]. Here, we report the discovery of secondary walls and lignin within cells of the intertidal red alga Calliarthron cheilosporioides. Until now, such developmentally specialized cell walls have been described only in vascular plants. The finding of secondary walls and lignin in red algae raises many questions about the convergent or deeply conserved evolutionary history of these traits, given that red algae and vascular plants probably diverged more than 1 billion years ago.