蚕豆叶片细胞中IAA的胶体金免疫电镜定位

利用胶体金免疫电镜技术对蚕豆(Vicia faba L.)叶片细胞中的IAA定位进行了研究。幼嫩叶片的叶肉细胞中金颗粒主要分布在细胞核和叶绿体中,细胞质及细胞壁也有金颗粒标记。成熟叶片的叶肉细胞中金颗粒主要分布在叶绿体和细胞质,细胞壁也有少量金颗粒标记,液泡中没有发现金颗粒标记。成熟叶片小叶脉的韧皮细胞发现有大量的金颗粒标记,金颗粒主要标记在传递细胞的细胞壁中。小叶脉的维管束鞘细胞中也有很多的金颗粒标记,金颗粒主要分布在叶绿体、细胞质及细胞壁中。幼嫩叶片组织不进行IAA的固定或用正常兔IgG代替IAA抗体染色的对照,很难发现金颗粒标记。对IAA在组织及亚细胞中的定位及其生理意义进行了讨论。     

应用免疫胶体金技术定位感病大麦细胞中的大麦和性花叶病毒

本文报道免疫胶体金标记技术的建立,并用此技术定位大麦叶和根组织超薄切片中大麦和性花叶病毒(BaMMV)。在感染病毒的大麦叶和根细胞中,病毒束、游离病毒颗粒和病毒外壳蛋白多分布于细胞质丰富的细胞中,且以液泡和叶绿体(仅叶组织)周围较多。在细胞器已解体的病根表皮细胞中,有时也可检测到大量游离病毒粒子。少数风轮体或板状集结体上也存在病毒或病毒外壳蛋白。细胞核、叶绿体、线粒体、细胞膜以及其他细胞器上都未见有特异性金颗粒标记。     

茄子幼苗初生维管系统的解剖学研究

对茄子幼苗的初生维管系统以子叶节区理论为指导,进行解剖学研究。经研究表明,其初生维管组织的器官间过渡形式,属顶枝伸长型的子叶节区。子叶节区下部较短,中部较长,故只有一个极短的子叶节区－根过渡区和上胚轴苗区,与子叶节区之间的维管组织连接区,其维管组织的转化,主要存在于子叶节区中部与子叶之间。     

独叶草的根和节部及叶的解剖学研究

报道了独叶草根、节部和叶的剖解学特征。这些器官在解剖学上表现出的突出点是：根具２个以上的根毛区（与星叶草机相同）,中有少量的次生生长,皮层细胞中具内生真菌;变态叶的叶迹或为单迹单维管组织束,或为单迹２维管组织束,或２迹在向皮层外部延伸过程中合并为具２条维管组织束的单迹;叶柄维管束不存在厚壁的维管束鞘,且在由基部向顶部延伸的过程中常发生复杂的分枝及汇合;叶片具有同形的叶肉植物,叶脉维管束鞘具２层细胞     

PLDα1介导ABA调控的拟南芥主根伸长并参与根毛生长

探讨了磷脂酶Dα1（PLDα1）在ABA抑制拟南芥主根伸长过程中的作用。PLOα1基因突变体pldα1主根伸长受ABA抑制小于野生型（WT）;根系PLDα1活性在ABA处理下升高;拟南芥根细胞原生质体中活性氧（ROS）含量在ABA处理下升高,但是pldα1升高小于WT;根系NADPH氧化酶活性在ABA处理下升高,pldα1升高小于WT,外源加入10μmol/L^-1 PA（磷脂酸,PLD水解产物）后,前者活性显著升高;外源加入H2O2可诱导WT和pldα1主根伸长都受到抑制,且二者差异不明显。结果表明,PLDα1产生的PA通过激活NADPH氧化酶产生ROS介导ABA调控的拟南芥主根伸长过程。此外,初步探讨了PLDα1在拟南芥根毛尖端生长中的作用：pldα1突变体根毛长度小于WT,根毛尖端ROS和Ca^2＋浓度低于WT。     

蚕豆（Vicia faba L．）叶肉细胞中ABA的胶体金免疫电镜定位

利用胶体金免疫电镜定位技术对蚕豆叶肉细胞中ＡＢＡ定位的研究表明,在以ＡＢＡ抗体处理的切片中,叶绿体有大量的金颗粒标记,细胞质和细胞核也有金颗粒标记,但液泡和细胞壁中没有金颗粒标记。免疫染色前用胰蛋白酶处理可显著增强金颗粒标记密度,而不用ＥＤＣ固定或以免疫前兔血清处理的切片中几乎没有金颗粒标记。本实验为蚕豆叶肉细胞中ＡＢＡ的分布提供了直接的证据并说明了该技术是研究ＡＢＡ定位的一种可靠的方法。     

蚕豆叶肉细胞中ABA的胶体金免疫电镜定位

利用胶体金免疫电镜定位技术对蚕豆叶肉细胞中ＡＢＡ定位的研究表明,在以ＡＢＡ抗体处理的切片中,叶绿在有大量的金颗粒标记,细胞质和细胞核也有金颗粒标记,但液泡和细胞壁中没有金颗粒标记,免疫染色前用胰蛋白酶处理可显著增强金颗粒标记密度,而不用ＥＤＣ固定或以免疫前兔血清处理的切片中几乎没有金颗粒标记。本实验为蚕豆叶肉细胞中ＡＢＡ的分布提供了直接的证据并说明了该技术是研究ＡＢＡ定位的一种可靠的方法。     

冬小麦生育中后期次生根特殊根毛的发生与形态结构

大田试验条件下,研究了冬小麦次生根特殊根毛的发生规律和形态结构特征.结果表明,拔节后次生根近植株基部根体上特殊根毛普遍发生,其在次生根根体上的分布可区分为集中区、适中区和稀少区.特殊根毛集中区根毛的长度、直径、密度分别均大于适中区和稀少区,其中,长度和密度的差异达极显著水平(P<0.01).随着生育期推进, 特殊根毛长度、直径和密度均呈下降趋势.大多数特殊根毛呈现出不同程度的扭曲、变形, 根毛细胞突起和分枝现象较为普遍,特殊根毛细胞次生壁出现加厚现象.     

甘蓝型油菜根系突变体lrn1、prl1和野生型根系显微结构的差异

油菜外源细胞分裂素不敏感突变体lrn1和prl1表现为磷高效。营养液培养0.2μmol/L细胞分裂素(6-BA)处理,与甘蓝型油菜野生型‘宁油7号’(WT)相比,突变体lrn1侧根较多,prl1主根较长。本研究利用体式显微技术、非切片压片法以及石蜡切片等技术,对3个基因型在ddH2O和0.2μmol/L 6-BA处理下的根毛、根表皮细胞分化及根尖解剖结构的差异进行了观察,结果表明:ddH2O处理,种子发芽后第1、3、6、9 d,lrn1、prl1和WT根尖成熟区根毛较少。0.2μmol/L 6-BA处理,种子发芽后第3 d,lrn1、prl1和WT根尖形成大量根毛,其中WT根毛最多、密度最大;prl1根毛最少,密度也最小;lrn1处于两者之间。种子发芽后第6 d,lrn1、prl1和WT分生区和伸长区明显缩短,lrn1和prl1分生区面积无显著差异,但两者均显著大于WT;lrn1和prl1根冠细胞结构较正常,而WT根冠细胞结构畸形;lrn1皮层原细胞之间排列较WT和prl1紧密。种子发芽后第9 d,lrn1已有4条侧根,但prl1与WT无侧根形成。6-BA处理,prl1主根较长,与其根尖分生区面积较大密切相关;lrn1侧根较多,可能与中柱原细胞排列密度较高密切相关。     

绿豆上胚轴细胞中BR的胶体金免疫电镜定位

利用葡萄球菌A蛋白与胶体金连接的复合物为探针的免疫电镜定位技术对绿豆上胚轴细胞中BR定位的结果表明,在用抗BR抗体处理的超薄切片中,叶绿体、核仁和液泡内有大量的金颗粒标记,细胞膜和淀粉粒也有金颗粒标记,但细胞壁中没有观察到金颗粒。在不用EDC固定的切片中,金颗粒标记密度非常低,而在用正常兔血清处理的切片中,所有细胞器内几乎没有金颗粒.该实验为绿豆上胚轴细胞中BR的分布提供了直接的证据。     

An Immunogold Microscopic Study on the Effects of Water Stress on ABA Localization and Contents in Roots of Vicia faba

ABA localization in roots of Vicia faba L. was studied using immunogold microscopy. In cells of promeristem gold particles were mainly localized in the nuclei. In cells of ground meristem and cortex of the front part of elongation zone, some gold particles were found in cytoplasm near. the plasmalemma. Substantial amounts of gold particles were observed in cells of vascular cylinder especially in apoplast of vascular tissue. Cells of middle elongation zone and root hair zone were also labelled by many gold particles. In cells of the primary meristem and the front part of elongation zone, water stress could lead to acute increase of the gold particle density, and also in the cells of the elongation and root hair zone. The distribution of ABA in subcellular level and its relationship with transportation were discussed in the text. and the results provided evidence for ABA as a root-to-shoot transporting stress signal.     

Constitutive autophagy in plant root cells

In previous studies, using a membrane-permeable protease inhibitor, E-64d, we showed that autophagy occurs constitutively in the root cells of barley and Arabidopsis. In the present study, a fusion protein composed of the autophagy-related protein AtAtg8 and green fluorescent protein (GFP) was expressed in Arabidopsis to visualize autophagosomes. We first confirmed the presence of autophagosomes with GFP fluorescence in the root cells of seedlings grown on a nutrient-sufficient medium. The number of autophagosomes changed as the root cells grew and differentiated. In cells near the apical meristem, autophagosomes were scarcely found. However, a small but significant number of autophagosomes existed in the elongation zone. More autophagosomes were found in the differentiation zone where cell growth ceases but the cells start to form root hair. In addition, we confirmed that autophagy is activated under starvation conditions in Arabidopsis root cells. When the root tips were cultured in a sucrose-free medium, the number of autophagosomes increased in the elongation and differentiation zones, and a significant number of autophagosomes appeared in cells near the apical meristem. The results suggest that autophagy in plant root cells is involved not only in nutrient recycling under nutrient-limiting conditions but also in cell growth and root hair formation.     

Cellular analysis of UV-B-induced barley root subapical swelling

UV-B irradiation of barley (Hordeum vulgare L.) roots (1 W/m², 15 min) or leaves (3 W/m², 3.3 h) and also one-day-long root incubation in the Knop solution supplemented with 1–4 μM ABA, 1 mM salicylic acid, 16 μM ionomycin, or 0.1 mM colchicine induced growth retardation and subapical root swelling. All factors, except for colchicine, initiated growth of root hairs on the surface of swellings and suppressed their initiation and growth in more basal root region. During the first hour after unilateral root UV-B irradiation, their growth sharply retarded and hydraulic conductivity of membranes in the rhizodermis of growth zone rose 1.5-fold. In 2.5 h, root tips bent toward the source of irradiation. In 4.5 h, the ratio of longitudinal to transverse root extensibility in the root growth zone reduced twofold. In 8 h, root diameter in the subapical zone increased and root hairs appeared in this zone and attained 300 μm in length. In a day after irradiation, on unirradiated root side, meristematic cells continued to divide and grow, although at a much lower rate. On the irradiated root side, the cells of the rhizodermis and outer cortex ceased to divide and produced vacuoles. Vacuolation did not occur in the cells of the quiescent center and a distal part of the meristem. The lower part of the elongation zone swelled due to cortical cell expansion (except for the endodermis) in both irradiated and unirradiated root sides. It is supposed that cortical microtubule randomization plays an important role in the changed anisotropy of cell wall extensibility and cytosolic calcium is involved in this process. The role of oxidative stress and hormonal shifts in the development of subapical root swelling and root hair formation caused by UV-B radiation is discussed.     

A late embryogenesis abundant protein HVA1 regulated by an inducible promoter enhances root growth and abiotic stress tolerance in rice without yield penalty

Regulation of root architecture is essential for maintaining plant growth under adverse environment. A synthetic abscisic acid (ABA)/stress‐inducible promoter was designed to control the expression of a late embryogenesis abundant protein (HVA1) in transgenic rice. The background of HVA1 is low but highly inducible by ABA, salt, dehydration and cold. HVA1 was highly accumulated in root apical meristem (RAM) and lateral root primordia (LRP) after ABA/stress treatments, leading to enhanced root system expansion. Water‐use efficiency (WUE) and biomass also increased in transgenic rice, likely due to the maintenance of normal cell functions and metabolic activities conferred by HVA1 which is capable of stabilizing proteins, under osmotic stress. HVA1 promotes lateral root (LR) initiation, elongation and emergence and primary root (PR) elongation via an auxin‐dependent process, particularly by intensifying asymmetrical accumulation of auxin in LRP founder cells and RAM, even under ABA/stress‐suppressive conditions. We demonstrate a successful application of an inducible promoter in regulating the spatial and temporal expression of HVA1 for improving root architecture and multiple stress tolerance without yield penalty.     

A mechanism coordinating root elongation,endodermal differentiation,redox homeostasis and stress response

Root growth relies on both cell division and cell elongation, which occur in the meristem and elongation zones, respectively. SCARECROW (SCR) and SHORT-ROOT (SHR) are GRAS family genes essential for root growth and radial patterning in the Arabidopsis root. Previous studies showed that SCR and SHR promote root growth by suppressing cytokinin response in the meristem, but there is evidence that SCR expressed beyond the meristem is also required for root growth. Here we report a previously unknown role for SCR in promoting cell elongation. Consistent with this, we found that the scr mutant accumulated a higher level of reactive oxygen species (ROS) in the elongation zone, which is probably due to decreased expression of peroxidase gene 3, which consumes hydrogen peroxide in a reaction leading to Casparian strip formation. When the oxidative stress response was blocked in the scr mutant by mutation in ABSCISIC ACID 2 (ABA2) or when the redox status was ameliorated by the upbeat 1 (upb1) mutant, the root became significantly longer, with longer cells and a larger and more mitotically active meristem. Remarkably, however, the stem cell and radial patterning defects in the double mutants still persisted. Since ROS and peroxidases are essential for endodermal differentiation, these results suggest that SCR plays a role in coordinating cell elongation, endodermal differentiation, redox homeostasis and oxidative stress response in the root. We also provide evidence that this role of SCR is independent of SHR, even though they function similarly in other aspects of root growth and development.     

Constitutive Autophagy in Plant Root Cells

In previous studies, using a membrane-permeable protease inhibitor, E-64d, we showed that autophagy occurs constitutively in the root cells of barley and Arabidopsis. In the present study, a fusion protein composed of the autophagy-related protein AtAtg8 and green fluorescent protein (GFP) was expressed in Arabidopsis to visualize autophagosomes. We first confirmed the presence of autophagosomes with GFP fluorescence in the root cells of seedlings grown on a nutrient-sufficient medium. The number of autophagosomes changed as the root cells grew and differentiated. In cells near the apical meristem, autophagosomes were scarcely found. However, a small but significant number of autophagosomes existed in the elongation zone. More autophagosomes were found in the differentiation zone where cell growth ceases but the cells start to form root hair. In addition, we confirmed that autophagy is activated under starvation conditions in Arabidopsis root cells. When the root tips were cultured in a sucrose-free medium, the number of autophagosomes increased in the elongation and differentiation zones, and a significant number of autophagosomes appeared in cells near the apical meristem. The results suggest that autophagy in plant root cells is involved not only in nutrient recycling under nutrient-limiting conditions but also in cell growth and root hair formation.

Addendum to:

AtATG Genes, Homologs of Yeast Autophagy Genes, are Involved in Constitutive Autophagy in Arabidopsis Root Tip Cells

Y. Inoue, T. Suzuki, M. Hattori, K. Yoshimoto, Y. Ohsumi and Y. Moriyasu

Plant Cell Physiol 2006; 47:1641-52     

Which cells respond to gravitropic stimulus in the lentil root?

When roots of lentil ( Lens culinaris L., cv. Large blonde) were placed in horizontal position for 2 h, their upper side elongated faster than their lower side, and also faster than vertical controls. The length of the cortical cells was greater in the upper half than in the lower half of roots which had been horizontally stimulated for 2 h. The zone of curvature extended from the distal part of the meristem to the proximal part of the cell elongation zone. The curvature in the meristem was due to early differentiation of the cells of its upper part. In the proximal part of the cell elongation zone, bending took place due to inhibition of cell growth in the lower half of the root. The results obtained are in agreement with the hypothesis of lateral transport of an inhibitor in gravistimulated roots. This inhibitor should be present in greater amounts in the lower side of the stimulated root and in lower amounts in its upper side than in the vertical controls.     

Reactive oxygen species localization in roots of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> seedlings grown under phosphate deficiency

Arabidopsis plants responding to phosphorus (P) deficiency increase lateral root formation and reduce primary root elongation. In addition the number and length of root hairs increases in response to P deficiency. Here we studied the patterns of radical oxygen species (ROS) in the roots of Arabidopsis seedlings cultured on media supplemented with high or low P concentration. We found that P availability affected ROS distribution in the apical part of roots. If plants were grown on high P medium, ROS were located in the root elongation zone and quiescent centre. At low P ROS were absent in the elongation zone, however, their synthesis was detected in the primary root meristem. The proximal part of roots was characterized by ROS production in the lateral root primordia and in elongation zones of young lateral roots irrespective of P concentration in the medium. On the other hand, plants grown at high or low P differed in the pattern of ROS distribution in older lateral roots. At high P, the elongation zone was the primary site of ROS production. At low P, ROS were not detected in the elongation zone. However, they were present in the proximal part of the lateral root meristem. These results suggest that P deficiency affects ROS distribution in distal parts of Arabidopsis roots. Under P-sufficiency ROS maximum was observed in the elongation zone, under low P, ROS were not synthesized in this segment of the root, however, they were detected in the apical root meristem.     

Regulation of Intercellular Water Exchange in Various Zones of Maize Root under Stresses

Apical root meristems and segments of root elongation zone were sampled from 4- to 5-day-old Zea mays L. seedlings. The vacuolar ATPase and pyrophosphatase, the tonoplast marker enzymes, and the tonoplast -, -, and -aquaporins were visualized by means of indirect immunofluorescent microscopy with the use of the respective antibodies. Following cell plasmolysis (700 mM mannitol, 2.5 h), the vacuolar ATPase and pyrophosphatase were detected in cell wall pores where plasmodesmata remained detached from the plasmolyzed protoplasts. This finding provides further evidence for existence of the vacuolar symplast in the elongation zone of maize root, which may ensure intercellular continuity of plant tissues. The pulsed NMR method was used to study the self-diffusion of water molecules. The diffusive decay in the root elongation zone was nonexponential, and it was transformed to three exponential terms with characteristic coefficients of self-diffusion; two of these coefficients (D ₂ and D ₃) characterize the water self-diffusion in the cytoplasmic and vacuolar symplasts of root, respectively. The root apical meristem was also investigated with NMR technique by virtue of paramagnetic doping of the apoplast. This approach allowed selective studying of water diffusion within the symplast compartments. Partial dehydration with PEG-6000, 12 and 20%, for 2.5 h and chemical stressors (ABA and salicylic acid, 0.1 mM, 24 h) were applied to modify water permeability of plasmodesmata and tonoplast aquaporins. The transcellular water permeability increased in the root meristem under the action of all stress factors. In the root elongation zone exposed to partial dehydration, the water exchange in the apoplast became the dominant component. Other stress factors affected water relations in different manners. ABA elevated the water permeability of the vacuolar symplast, in contrast to salicylic acid that decreased water conductance of both the cytoplasmic and vacuolar symplasts.     

Ultrastructural Localization of ATPase Activity in the Cells of the Apical Meristem Zone,Elongation Zone and Root Hair Zone of Tomato Roots

A comparative study on the cytochemical localization of adenosine triphosphatase (ATPase) activity reaction in the cells of the apical meristem zone, elongation zone and root hair zone of tomato roots was carried out by electron microscopic observations of lead phosphate precipitation. The following experimental results have been obtained: In the meristematic cells of tomato roots, the heavy lead phosphate deposits indicating a very high activity of ATPase were localized at plasmalemma, plasmodesmata, endoplasmic reticulum, Golgi bodies, nucleoli and chromatin (Figs. 1—2). The reaction products of ATPase activity were also observed at some sites of ground cytoplasm and cell wall, but they were not found in little vacuoles and on tonoplast. In the cells of elongation zone, the ATPase activity at plasmalemma and plasmodesmata was as high as that in the meristematic cells of root tip, while the ATPase activity at nucleoli, chromatin, endoplasmic reticulum and Golgi bodies was markedly lowered. On the other hand, the high ATPase activity was produced on the tonoplast of the developing and enlarging vacuoles (Fig. 3). In the cells of root hair zone, the high ATPase activity was shown at plasmalemma, tonoplast and intercellular spaces, but the ATPase activity at nucleoli, chromatin and endoplasmic reticulum was wholly inactivated. (Figs. 4—7). The above results indicate that the ATPase activity with membranes and organelles is altered when the functions of cells and organelles change. Therefore, it is evident that the ATPase activity may be closely related to many physiological functions.