木质部细胞分化的研究进展

本文主要从研究木质部细胞分化常用的实验系统,木质部分的诱导,木质部细胞的编程性死亡以及次生壁的构建4个方面阐述了木质细胞分的研究进展,并对目前研究的热点也是难点问题进行了展望,希望引起同行的兴趣。     

木质部细胞分化的程序

本文主要对近十几年来有关木质部细胞分化研究中使用的实验系统及用这些系统所取得的重要进展作了评述.并以作者实验室的研究成果为基础,结合国内外研究进展,提出木质部细胞分化程序由参与细胞编程死亡(PCD)和次生壁构建的全部基因综合编制而成.以PCD过程各阶段的划分标准来看,木质部细胞分化中从IAA诱导形成层细胞平周分裂到细胞扩大前为PCD的起始阶段,其间包括死亡信号的发生、接受和传导,以及启始caspase(半胱氨酰基天门冬氨酸蛋白酶)类似物(例如caspase-8类似物)的活化;木质部母细胞的径向扩大为PCD的效应阶段,而效应caspase类似物(例如caspase-3类似物)活化DNase、DNA的片段化及次生细胞壁的构建和各种细胞器的解体则为PCD的清除降解阶段.至今还无法将DNase活化及其引起的DNA断裂过程与次生细胞壁构建过程分开.     

杜仲次生木质部分化过程中的细胞编程死亡

通过电子显微镜观察、DNA断裂检测及类似半胱氨酸蛋白酶(caspase-like proteases,CLPs)降解检测等技术,对杜仲(Eucommia ulmoides Oliv.)次生木质部分化过程的细胞编程死亡进行了研究.分化中的次生木质部细胞总DNA凝胶电泳检测到DNA ladder,并通过TUNEL检测进一步确定了DNA被降解.Western blot结果表明;caspase-8和caspase-3状蛋白酶(caspase-8-和caspase-3-like proteases,CLPs)及多聚ADP-核糖聚合酶(poly(ADP-ribose)polymerase,PARP)在次生木质部分化过程中被降解.这些研究结果表明,杜仲次生木质部的细胞分化是一个典型的编程性死亡(Programmed cell death,PCD)过程,CLPs可能参与了此过程.     

杜仲次生木质部分化过程中的细胞编程死亡

通过电子显微镜观察、DNA断裂检测及类似半胱氨酸蛋白酶（caspase-like proteases,CLPs)降解检测等技术,对杜仲（Eucommia ulmoides Oliv.）次生木质部分化过程的细胞编程死亡进行了研究。分化中的次生木质部细胞总DNA凝胶电泳检测到DNA ladder,并通过TUNEL检测进一步确定了DNA被降解。Western blot结果表明：caspase-8和caspase-3状蛋白酶（caspase-8-和caspase-3-like proteases,CLPs)及多聚ADP-核糖聚合酶（poly(ADP-ribose) polymerase,PARP)在次生木质部分化过程中被降解。这些研究结果表明,杜仲次生木质部的细胞分化是一个典型的编程性死亡（Programmed cell death,PCD)过程,CLPs可能参与了此过程。     

星叶草下胚轴解剖

星叶草的茎部很短,下胚轴的长度几乎占有植株的整个高度。纤细的下胚轴主要依靠表皮层细胞外壁角质膜的增厚,以及中央初生木质部束的支持。初生木质部与初生韧皮部之间可见到2—3层排列规则或不规则的薄壁组织细胞,但是没有维管形成层的发生。这种植物的根茎维管组织的过渡区域,看不到一般双子叶植物中所见到的初生木质部束扭曲、分开或倒转的现象。伸向子叶的子叶迹,直接由原生木质部极外面的一群薄壁组织细胞分化形成。第一和第二片叶子的叶迹则在初生韧皮部中间发生。     

麻花秦艽根内中柱裂分的发育解剖研究

通过发育解剖学研究表明,麻花秦艽根的初生结构正常,初生木质部四原型。次生生长的早期阶段也是正常的。在以后的次生生长过程中,由于木质部柱局部区域外的维管形成层向内衍生的细胞分化成木薄壁组织细胞的数量多于导管,从而在木质部内形成薄壁组织细胞区域,并且由于此区域内细胞的增殖,将木质部分成两部分。以后韧皮部也随之分开,从而中柱被分成两个独立的裂分中柱。以后,每个裂分中柱又产生各自的周皮,进而使主根分裂成两个支根。每个支根也可以同样方式分裂产生许多支根。     

构树形成层活动周期中过氧化物酶和酯酶同工酶的变化

同工酶分析表明：在构树（Ｂｒｏｕｓｓｏｎｅｔｉａ ｐａｐｙｒｉｆｅｒａ （Ｌ．） Ｖｅｎｔ．）形成层活动周期中, 形成层区域和木质部中过氧化物酶酶带变化最大,参与ＩＡＡ 浓度调节的酶带在晚材形成前出现,当其它生长停止、韧皮部仍在分化时又消失,完全休眠后, 所有酶带又都出现。在周皮、形成层区域和木质部中,酯酶同工酶酶带变化明显与形成层活动有关,有些酶带只在木栓细胞和／或木质部细胞分化时出现     

水热耦合对沈阳地区油松木质部生长的影响

利用微树芯技术可以从细胞尺度研究树木形成层物候和径向生长的过程,揭示树木生长与气候的关系。油松是我国北方森林的建群树种之一,也是沈阳地区的优势树种。研究2020年整个生长季(4—11月)油松周尺度的形成层及木质部细胞变化,分析油松在沈阳地区的生长规律。结果表明: 油松形成层分裂活动开始于4月初,结束于9月末。木质部从扩大细胞出现(4月中旬)开始生长,到木质化细胞消失(10月下旬)结束,其生长符合“S”型曲线。2020年生长53个/列木质部细胞,最大生长速率(0.55个/列/d)出现在5月末,早晚材细胞于7月末发生转变。在沈阳地区最低温达到0 ℃以上时树木形成层开始活动,影响木质部生长开始和结束的最低临界温度为2～3 ℃。降水在油松整个生长过程中起到促进作用。沈阳地区7月末的高温和水分供给不足是木质部细胞分化形成早晚材的主要因子。     

植物木质部水力学研究进展

植物为适应陆地环境进化出木质部维管系统,通过水力学机制高效安全的向光合器官长距离运输水分,木质部水分运输对蒸腾、气孔运动、光合碳同化等生理过程有调控和协调作用,被称为植物生理学的支柱。植物水力学作为木质部水分运输的研究内容和手段,已成为整合植物与生态系统功能的中心枢纽。该文首先概述了植物水分运输的水力学机制、运输系统的局限性,以及木质部结构与功能之间的关系;其次,阐述了木质部栓塞的形成机制并详细介绍了栓塞的诱导方法和测试技术,分析了水分运输系统安全与效率之间的权衡关系,总结了植物对环境的响应和干旱致死的预测模型,讨论了测试技术问题及其引发的当前木质部逆压力修复和指数型木质部栓塞脆弱性曲线有效性的争议;最后,总结了目前植物木质部水力学研究的成果,提出了尚待解决的主要问题,探讨了研究机会与方向。     

第25届国际生物学奥林匹克竞赛试题 理论A-2

正植物解剖学与生理学11.下图显示植物细胞从一个分生细胞分化成代表性的最终产物。指出下列陈述正确与否。A.B、F、G是活细胞B.一个分生细胞分化成为A、B、C和D需要木质素生物合成C.细胞E可分化成细胞D D.细胞B在特定激素处理下可脱分化12.植物木质部运输仅可通过生物力学去理解。导管直径和长度对运输效率具有主要影响,这符合下面的Hagen-Poiseuille方程:     

The regulation of cambial division and secondary xylem differentiation in xanthium by auxins and gibberellin

Cambial division continued in decapitated Xanthium plants without concomitant xylem fiber differentiation. The application of indoleacetic acid to these plants did not affect the production of cambial derivatives or induce xylem fiber differentiation. When naphthaleneacetic acid was applied either to the second internode or to the stump of a lateral shoot, xylem fiber differentiation was induced in the newly formed cambial derivatives on the xylem side of the cambium in the stem. When naphthaleneacetic acid was applied unilaterally, xylem fiber differentiation was restricted to that side of the stem in the first internode and hypocotyl. Naphthaleneacetic acid also enhanced the production of cambial derivatives. Gibberellic acid enhanced cambial derivative production but did not affect the differentiation of xylem fibers. Similar numbers of cambial derivatives were produced in some naphthaleneacetic acid-treated plants in which xylem fiber differentiation was induced and in gibberellic acid-treated plants which did not differentiate xylem. When naphthaleneacetic acid was applied 72 hours after decapitation, the oldest of the cambial derivatives on the xylem side failed to develop into fibers although younger cells did. These results suggest that auxin has its direct effect on the induction of xylem differentiation rather than the induction of divisions prerequisite to differentiation.     

Thermospermine suppresses auxin-inducible xylem differentiation in Arabidopsis thaliana

Thermospermine, a structural isomer of spermine, is synthesized by a thermospermine synthase designated ACAULIS5 (ACL5). Thermospermine-deficient acl5 mutant of Arabidopsis thaliana shows severe dwarfism and excessive xylem differentiation. By screening for compounds that affect xylem differentiation in the acl5 mutant, we identified auxin analogs that remarkably enhanced xylem vessel differentiation in the acl5 mutant but not in the wild type. The xylem-inducing effect of auxin analogs was clearly suppressed by thermospermine, indicating that auxin-inducible xylem differentiation is normally limited by thermospermine. Here, we further characterized xylem-inducing effect of auxin analogs in various organs. Auxin analogs promoted protoxylem differentiation in roots and cotyledons in the acl5 mutant. Our results indicate that the opposite action between thermospermine and auxin in xylem differentiation is common in different organs and also suggest that thermospermine might be required for the suppression of protoxylem differentiation.     

Changes in the localization and levels of starch and lipids in cambium and phloem during cambial reactivation by artificial heating of main stems of Cryptomeria japonica trees

Background and Aims

Cambial reactivation in trees occurs from late winter to early spring when photosynthesis is minimal or almost non-existent. Reserve materials might be important for wood formation in trees. The localization and approximate levels of starch and lipids (as droplets) and number of starch granules in cambium and phloem were examined from cambial dormancy to the start of xylem differentiation in locally heated stems of Cryptomeria japonica trees in winter.

Methods

Electric heating tape was wrapped on one side of the stem of Cryptomeria japonica trees at breast height in winter. The localization and approximate levels of starch and lipids (as droplets) and number of starch granules were determined by image analysis of optical digital images obtained by confocal laser scanning microscopy.

Key Results

Localized heating induced earlier cambial reactivation and xylem differentiation in stems of Cryptomeria japonica, as compared with non-heated stems. There were clear changes in the respective localizations and levels of starch and lipids (as droplets) determined in terms of relative areas on images, from cambial dormancy to the start of xylem differentiation in heated stems. In heated stems, the levels and number of starch granules fell from cambial reactivation to the start of xylem differentiation. There was a significant decrease in the relative area occupied by lipid droplets in the cambium from cambial reactivation to the start of xylem differentiation in heated stems.

Conclusions

The results showed clearly that the levels and number of storage starch granules in cambium and phloem cells and levels of lipids (as droplets) in the cambium decreased from cambial reactivation to the start of xylem differentiation in heated stems during the winter. The observations suggest that starch and lipid droplets might be needed as sources of energy for the initiation of cambial cell division and the differentiation of xylem in Cryptomeria japonica.     

A chemical biology approach reveals an opposite action between thermospermine and auxin in xylem development in Arabidopsis thaliana

Thermospermine, a structural isomer of spermine, is produced through the action of ACAULIS5 (ACL5) and suppresses xylem differentiation in Arabidopsis thaliana. To elucidate the molecular basis of the function of thermospermine, we screened chemical libraries for compounds that can modulate xylem differentiation in the acl5 mutant, which is deficient in thermospermine and shows a severe dwarf phenotype associated with excessive proliferation of xylem vessels. We found that the isooctyl ester of a synthetic auxin, 2,4-D, remarkably enhanced xylem vessel differentiation in acl5 seedlings. 2,4-D, 2,4-D analogs and IAA analogs, including 4-chloro IAA (4-Cl-IAA) and IAA ethyl ester, also enhanced xylem vessel formation, while IAA alone had little or no obvious effect on xylem differentiation. These effects of auxin analogs were observed only in the acl5 mutant but not in the wild type, and were suppressed by the anti-auxin, p-chlorophenoxyisobutyric acid (PCIB) and α-(phenyl ethyl-2-one)-IAA (PEO-IAA), and also by thermospermine. Furthermore, the suppressor of acaulis51-d (sac51-d) mutation, which causes SAC51 overexpression in the absence of thermospermine and suppresses the dwarf phenotype of acl5, also suppressed the effect of auxin analogs in acl5. These results suggest that the auxin signaling that promotes xylem differentiation is normally limited by SAC51-mediated thermospermine signaling but can be continually stimulated by exogenous auxin analogs in the absence of thermospermine. The opposite action between thermospermine and auxin may fine-tune the timing and spatial pattern of xylem differentiation.     

Effect of the Gall-forming Aphid Slavum wertheimae on the Differentiation of Xylem in Branches of Pistacia atlantica

The gall-forming aphid Slavum wertheimae H.R.L., which formscoral-like galls on branches of Pistacia atlantica Desf. trees,induces both qualitative and quantiative changes in xylem differentiationin the branch below the gall. More xylem is formed than in ungalledbranches, and the aphid-induced xylem is characterized by numerouswide vessels in the latewood. In control branches that werenot carrying galls, only a few narrow vessels differentiatedin the latewood. The differentiation of numerous wide vesselsat the end of the growing season, when the population of aphidsin the gall reaches its maximum size, makes possible a substantialincrease of sap movement into the gall tissues Gall-forming aphids, Slavum wertheimae, Pistacia atlantica, vessel size, xylem differentiation (latewood)     

Chitosan and a fungal elicitor inhibit tracheary element differentiation and promote accumulation of stress lignin-like substance in Zinnia elegans xylogenic culture

We investigated the effect of elicitors on xylem differentiation and lignification using a Zinnia elegans xylogenic culture system. Water-soluble chitosan and a fungal elicitor derived from Botrytis cinerea were used as elicitors. Elicitor addition at the start of culturing inhibited tracheary element (TE) differentiation in a concentration-dependent manner, and 30 μg mL^?1 of chitosan or 16.7 μg mL^?1 of the fungal elicitor strikingly inhibited TE differentiation and lignification. Addition of chitosan (at 50 μg mL^?1) or the fungal elicitor (at 16.7 μg mL^?1) during the culturing period also inhibited TE differentiation without inhibiting cell division, except for immature TEs undergoing secondary wall thickening. Elicitor addition after immature TE appearance also caused the accumulation of an extracellular lignin-like substance. It appears that elicitor addition at the start of culturing inhibits the process by which dedifferentiated cells differentiate into xylem cell precursors. Elicitor addition during culturing also appears to inhibit the transition from xylem cell precursors to immature TEs, and induces xylem cell precursors or xylem parenchyma cells to produce an extracellular stress lignin-like substance.     

Cambial sensitivity to rising temperatures by natural condition and artificial heating from late winter to early spring in the evergreen conifer Cryptomeria japonica

Differences in the timing of cambial reactivation and the initiation of xylem differentiation in response to the sum of daily maximum temperatures were studied in two Cryptomeria japonica trees with cambium of different ages under natural and locally heated conditions. In addition, we observed the effects of low temperature on cambial activity. The timing of cambial reactivation and of the initiation of xylem differentiation differed between 55- and 80-year-old cambium under natural conditions. In the 55-year-old cambium, cambial reactivation occurred when the cambial reactivation index (CRI), calculated on the basis of daily maximum temperatures in excess of 10°C, was 94 and 97°C in 2007 and 2008, respectively. In 80-year-old cambium, cambial reactivation occurred when the CRI, calculated on the basis of daily maximum temperatures in excess of 11°C, was 69 and 71°C in 2007 and 2008, respectively. After cambial reactivation in 2007, normal cell division was evident in the cambium even though the minimum temperature had fallen between −2 and −3°C. Under natural conditions, xylem differentiation started 38–44 days after cambial reactivation. In heated stems, the time between cambial reactivation and the initiation of xylem differentiation ranged from 14 to 16 days, a much shorter time than under natural conditions, indicating that continuous exposure to an elevated temperature had induced earlier xylem differentiation. Our observations indicate that the sensitivity to reactivation inducing stimuli of the cambium depends on both the stage of dormancy and tree age of the cambium.