植物侧枝发育的调控研究进展

植物侧枝的发育在植物形态建成中具有十分重要的地位，侧枝的形态直接影响植物的产量。侧枝的发育由生长点干细胞持续分裂和分化形成，包括侧生分生组织特化，侧生分生组织起始和侧生分生组织外生。侧枝的发育受到内部生长因子和外部环境信号的共同调节。文中总结了侧枝发育过程中侧生生长点干细胞起源、形成和休眠等过程的基本问题，综述了转录因子、激素、表观遗传、外界环境共同决定侧生分生组织形成和发育中的作用机制，为探讨植物侧枝的形成机理提供参考。     

生长素调控植物株型形成的研究进展

高等植物通过调节顶端分生组织和侧生分生组织的活性建立地上株型系统,分生组织的活性受环境信号、发育阶段和遗传因素的综合调控,植物激素参与这些信号的整合。顶端优势是植物分枝调控的核心问题,而生长素对顶端优势的形成和维持发挥关键作用。本文综述了近几年与植物地上部分株型形成相关的生长素合成代谢、极性运输及信号转导领域的研究进展,并提出了展望。     

生长素调控植物株型形成的研究进展

高等植物通过调节顶端分生组织和侧生分生组织的活性建立地上株型系统, 分生组织的活性受环境信号、发育阶段和遗传因素的综合调控, 植物激素参与这些信号的整合。顶端优势是植物分枝调控的核心问题, 而生长素对顶端优势的形成和维持发挥关键作用。本文综述了近几年与植物地上部分株型形成相关的生长素合成代谢、极性运输及信号转导领域的研究进展, 并提出了展望。     

表观遗传修饰在作物重要性状形成中的作用

表观遗传修饰是指染色体DNA和组蛋白上的化学修饰,主要包括DNA甲基化、组蛋白修饰和非编码RNA。在不改变DNA序列的情况下,这些修饰可以通过改变染色质状态来影响遗传信息的表达,并具有可遗传性,对植物的生长发育具有重要的调控作用。当特定的表观遗传修饰发生改变时,农作物可以获得优异的表型、更强的环境适应性,因此人为改变表观遗传修饰有望获得更适于农业生产的优质种质资源。本文综述了植物表观遗传修饰的主要类型及其在作物重要性状的形成和环境胁迫响应中的相关研究进展,总结了表观遗传学应用于作物改良必须解决的主要问题,以期在表观遗传修饰层面为作物的育种改良提供新思路。     

植物茎分枝的分子调控

植物茎分枝结构决定了不同植物的不同形态结构.本文从腋生分生组织的发生、腋芽的生长两个方面综述了近年来植物分枝发生发育相关的分子机理研究及其进展.发现在不同植物中腋分生组织形成的基本机制是相似的,LS（lateral suppressor）及其同源基因在不同植物中都参与腋生分生组织的形成,而BL(blind)及其同源基因也参与调控腋生分生组织的形成.腋生分生组织的形成可能也是受激素调控的.目前,对腋芽生长的分子调控机制的认识主要集中于生长素通过二级信使的作用调控腋芽的生长.而生长素调控腋芽生长的机制已经较为清楚的有两条途径：一是生长素通过抑制细胞分裂素合成来调控腋芽的生长;另一途径是一种类胡萝卜素衍生的信号物质参与生长素的运输调控(MAX途径)来调控腋芽的生长.最新研究表明,TB1的拟南芥同源基因在MAX途径的下游负调控腋芽的生长.此外,增强表达OsNAC2也促进腋芽的生长.     

禾本科植物分蘖为茎的分枝研究提供新视角

分蘖(或分枝)是作物产量的一个主要决定因素,受植物激素、自身生长发育和环境等因素的调控。近年报道的单子叶植物新的分蘖(或分枝)基因和调控机制深化了对植物分蘖的认知。对以禾本科植物为代表的单子叶植物的分蘖(或分枝)相关基因和调控机制进行了综述,从激素、基因、转录等几方面比较了单子叶植物分蘖和双子叶植物分枝调控机制的异同,为植物产量形成、适应环境及提高生存竞争能力的研究提供理论依据。     

植物衰老过程中的表观遗传学调控

植物衰老是由内外环境因子共同调节的,发生在细胞、组织、器官和个体等多个层面上的衰退和死亡过程,涉及基因表达、蛋白翻译和修饰水平变化以及多种细胞结构和代谢途径的变化,并与激素和生物/非生物胁迫的应答等过程形成复杂的调控网络。近年的研究表明,表观遗传修饰参与了对植物衰老过程的调节,是除经典遗传学以研究基因序列影响生物学功能之外在非核酸序列改变的情况下导致可遗传的基因表达变化的机制。本文综述了植物衰老过程中表观遗传调控的机理,包括染色质构象变化、DNA甲基化、组蛋白修饰、ATP依赖的重构因子和非编码RNA介导的调控等,并对这一领域今后的发展方向进行了展望。     

表观遗传调控植物逆境胁迫的适应机制

植物表观遗传学不仅是基础科学研究的焦点,也是植物育种中获得新资源的一种方式。表观遗传机制可以通过非编码RNA,组蛋白修饰和DNA甲基化控制基因的表达,且越来越多的研究表明表观遗传机制对植物适应环境及胁迫记忆是必要的。本综述重点从DNA甲基化调控、组蛋白变异、组蛋白修饰调控、非编码RNA调控水平论述植物在各种逆境条件下如何通过表观遗传机制来适应环境。     

表观遗传调控植物响应非生物胁迫的研究进展

植物的生长发育容易受到外界环境变化的影响。非生物胁迫发生时, 表观遗传机制对胁迫应答基因的表达调控发挥了十分重要的作用。近年来, 调控植物非生物胁迫应答的表观遗传机制研究取得了一系列重要进展, 为进一步深入解析植物响应非生物胁迫的分子机制奠定了基础。该文对DNA甲基化修饰、组蛋白修饰、染色质重塑和非编码RNA等主要表观遗传调控方式在植物响应非生物胁迫中的作用进行了简要综述。     

表观遗传修饰介导的植物胁迫记忆

植物因其固着生长的方式, 已经进化出各类特殊的机制来适应多变的外界环境。为提高自身的存活率, 植物进化出一类胁迫记忆机制, 以适应环境和保护自己。表观遗传修饰不仅能调控植物的正常生长发育, 而且参与植物对各种非生物或生物胁迫的响应。近年的研究表明, 表观遗传修饰在植物胁迫记忆调控中也发挥重要作用。例如, DNA甲基化、组蛋白甲基化及乙酰化等表观遗传修饰参与并维持特定的胁迫记忆。该文主要对表观遗传修饰介导的植物胁迫记忆最新进展进行综述, 并展望未来的重点和热点研究方向。     

Overexpression of the maize Teosinte Branched1 gene in wheat suppresses tiller development

The number of viable shoots influences the overall architecture and productivity of wheat (Triticum aestivum L.). The development of lateral branches, or tillers, largely determines the resultant canopy. Tillers develop from the outgrowth of axillary buds, which form in leaf axils at the crown of the plant. Tiller number can be reduced if axillary buds are not formed or if the outgrowth of these buds is restricted. The teosinte branched1 (tb1) gene in maize, and homologs in rice and Arabidopsis, genetically regulate vegetative branching. In maize, increased expression of the tb1 gene restricts the outgrowth of axillary buds into lateral branches. In this study, the maize tb1 gene was introduced through transformation into the wheat cultivar "Bobwhite" to determine the effect of tb1 overexpression on wheat shoot architecture. Examination of multiple generations of plants reveals that tb1 overexpression in wheat results in reduced tiller and spike number. In addition, the number of spikelets on the spike and leaf number were significantly greater in tb1-expressing plants, and the height of these plants was also reduced. These data reveal that the function of the tb1 gene and genetic regulation of lateral branching via the tb1 mode of action is conserved between wheat, rice, maize and Arabidopsis. Thus, the tb1 gene can be used to alter plant architecture in agriculturally important crops like wheat.     

独脚金内酯调控植物侧枝发育的分子机制及其与生长素交互作用的研究进展

对独脚金内酯（strigolactones,SLs）调控植物侧枝发育的分子机制及其与生长素相互作用的相关研究结果进行了总结和归纳,在此基础上提出今后的重点研究方向。相关的研究结果显示：在拟南芥[Arabidops~thaliana（Linn．）Heynh．]、豌豆（Pisum sativum Linn．）和水稻（Oryza sativa Linn．）等植物多枝突变体中SLs作为可转导信号参与侧枝发育的分子调控,从这些植物中已克隆获得参与SLs生物合成及信号应答途径的一些基因。作为一种植物激素,SLs在侧枝发育调控网络中与生长素相互作用;腋芽发育与其中生长素的输出密切相关,SLs通过调控芽中生长素的输出间接抑制腋芽发育和侧枝生长,而生长素则在SLs生物合成中起调节作用。     

The role of hormones in apical dominance. New approaches to an old problem in plant development

The role of hormones in apical dominance has been under investigation with traditional 'spray and weigh' methods for nearly 5 decades. Even though the precision of hormone content analyses in tissue has greatly improved in recent years, there have been no significant breakthroughs in our understanding of the action mechanism of this classical developmental response. Auxin appears to inhibit axillary bud outgrowth whereas cytokinins will often promote it. Conclusive evidence for a direct role of these or other hormones in apical dominance has not been forthcoming. However, promising new tools and approaches recently have begun to be utilized. The manipulation of endogenous hormone levels via the use of transgenic plants transformed with bacterial genes ( iaaM and ipt from Agrobacterium tumefaciens and iaaL from Pseudomonas syringae pv. savastanoi ) has demonstrated powerful effects of auxin and cytokinin on axillary bud outgrowth. Also, possible auxin and cytokinin involvement of rolB and C genes from Agrobacterium rhizogenes whose activity is associated with reduced apical dominance in dicotyledons has received considerable attention. The characterization of unique mRNAs and proteins in non-growing and growing lateral buds before and after apical dominance release is helping to lay the groundwork for the elucidation of signal transduction and cell cycle regulation in this response. The use of auxin-deficient, and auxin/ethylene-resistant mutants has provided another approach for analyzing the role of these hormones. The presumed eventual employment of molecular assay systems (SAUR/GH3 promoters fused with GUS reporter gene) which are presently being developed for analyzing auxin localized in lateral buds will hopefully provide a critical test for the direct auxin inhibition hypothesis.     

Leaf size versus leaf numbertrade-offs in dioecious angiosperms

Aims We explore the possible role of leaf size/number trade-offs for the interpretation of leaf size dimorphism in dioecious plant species.Methods Total above-ground biomass (both male and female) for three herbaceous dioecious species and individual shoots (from both male and female plants) for three woody dioecious species were sampled to record individual leaf dry mass, number of leaves, dry mass of residual above-ground tissue (all remaining non-leaf biomass), number of flowers/inflorescences (for herbaceous species) and number of branches.Important findings For two out of three woody species and two out of three herbaceous species examined, male plants produced smaller leaves but with higher leafing intensity—i.e. more leaves per unit of supporting (residual) shoot tissue or plant body mass—compared with females. Male and female plants, however, did not differ in shoot or plant body mass or branching intensity. We interpret these results as possible evidence for a dimorphic leaf deployment strategy that promotes both male and female function, respectively. In male plants, capacity as a pollen donor may be favored by selection for a broadly spaced floral display, hence favoring relatively high leafing intensity because this provides more numerous axillary meristems that can be deployed for flowering, thus requiring a relatively small leaf as a trade-off. In one herbaceous species, higher leafing intensity in males was associated with greater flower production than in females. In contrast, in female plants, selection favors a relatively large leaf, we propose, because this promotes greater capacity for localized photosynthate production, thus supporting the locally high energetic cost of axillary fruit and seed development, which in turn requires a relatively low leafing intensity as a trade-off.     

Axillary bud banks of two semiarid perennial grasses: occurrence, longevity, and contribution to population persistence

The occurrence, longevity, and contribution of axillary bud banks to population maintenance were investigated in a late-seral perennial grass, Bouteloua curtipendula, and a mid-seral perennial grass, Hilaria belangeri, in a semiarid oak-juniper savanna. Axillary buds of both species were evaluated over a 2-year period in communities with contrasting histories of grazing by domestic herbivores. A double staining procedure utilizing triphenyl tetrazolium chloride and Evan's blue indicated that both viable and dormant axillary buds remained attached to the base of reproductive parental tillers for 18–24 months which exceeded parental tiller longevity by approximately 12 months. Bud longevity of the late-seral species, B. curtipendula, exceeded bud longevity of the mid-seral species, H. belangeri, by approximately 6 months. Younger buds located on the distal portion of the tiller base were 3.2 and 1.4 times more likely to grow out than older proximal buds of B. curtipendula and H. belangeri, respectively. The percentage of older proximal buds, which included comparable portions of viable and dormant buds, that grew out to produce tillers following mortality of parental tillers was 6.0% for B. curtipendula and 8.4% for H. belangeri. In spite of the occurrence of relative large axillary bud banks for both species, the magnitude of proximal bud growth did not appear sufficient to maintain viable tiller populations. We found no evidence to support the hypothesis of compensatory bud growth on an individual tiller basis for either species. Grazing history of the communities from which the buds were collected did not substantially affect the number, status, longevity, or outgrowth of axillary buds on an individual tiller basis for either species. However, long-term grazing by domestic herbivores influenced axillary bud availability by modifying population structure of these two species. Bud number per square meter for B. curtipendula was 25% lower in the long-term grazed compared to the long-term ungrazed community based on a reduction in both tiller number per plant and plant number per square meter. In contrast, bud number per square meter for H. belangeri was 190% greater in the long-term grazed than in the long-term ungrazed community based on a large increase in plant density per square meter. Minimal contributions of axillary bud banks to annual maintenance of tiller populations in this mid- and late-seral species underscores the ecological importance of consistent tiller recruitment from recently developed axillary buds. Consistent tiller recruitment in grasslands and savannas characterized by intensive grazing and periodic drought implies that (1) bud differentiation and maturation must be remarkably tolerant of adverse environmental conditions and/or (2) tiller recruitment may resume from buds that mature following the cessation of severe drought and/or grazing, rather than from mature buds that survive these disturbances. These scenarios warrant additional research emphasis given the critical importance of this demographic process to tiller replacement in species populations and the maintenance of relative species abundance in grasslands and savannas. Received: 12 August 1996 / Accepted: 30 December 1996     

The Effects of Temperature and Other Variables on the Contribution of Lateral Branches to Yield in Phaseolus vulgaris L.

At low temperatures (15/15 °C day/night) in controlled environmentsthe growth of lateral branches at the cotyledonary node ofPhaseolusvulgarts L is suppressed The suppression can be overcome byraising the temperature of the buds by approximately 6 °Cwith small electric heaters In order to test the practical significanceof the induction of branching for yields of the commercial crop,seedlings were raised in contrasted regimes and then transplantedto the field The effects of pretreatment regime on final yieldwere small, changes in the yield from axillary branches tendedto be balanced by compensatory changes in the yield from themain stem In another field experiment, synthetic growth substanceswere applied in order to suppress or enhance branching Changesin the amount of yield carned on branches were again offsetby compensatory changes in the yield from the main stem Compensatoryeffects between branches and main stem were also found in avariety trial However, in an experiment on a single cultivarand various levels of N fertilizer, compensatory effects werenot found, here, branch and main stem yields were positively,rather than negatively, correlated These results are discussedin relation to the intrinsic factors that govern yield in Pvulgaris Phaseolus vulgaris L, dwarf bean, axillary branches, correlative inhibition, temperature, growth substances, plant density, yield