玉米叶片细脉原生韧皮部筛分子的分化和超微结构 : 原生质体的变化

玉米（ＺｅａｍａｙｓＬ．）叶片细脉原生韧皮部筛分子开始分化时,首先出现长的粗面内质网潴泡和增厚的细胞壁,随后在质体中出现其特征性的拟晶体内含物。随着分化的进行,长的粗面内质网潴泡转化为较短的形态,最后聚集成一些小的堆叠并失去其核糖体。细胞核发生退化,但常保持到成熟期的后期,此时的细胞核由双层核膜或某些部位仅由内核膜包被,内含电子致密的不定形染色质团块。随后双层核膜破裂而变得不连续。在细胞核开始退化时,核周腔局部膨大。有的膨大核周腔的外核膜破裂,并伴随邻近的部分细胞质解体。在核退化过程中,除内质网外,质体和线粒体的结构也发生变化,而核糖体、细胞质基质、液泡和高尔基体则解体消失。成熟原生韧皮部筛分子的原生质组分分布在细胞边缘,由质膜、线粒体、小的滑面内质网堆叠及具拟晶体的Ｐ型质体组成。随着邻近后生韧皮部筛分子分化的进行,成熟原生韧皮部筛分子的原生质组分逐渐退化,最后消失。     

Early Development and Ultrastructure of the Major Veins and Their Sheath Tissues in the Maize Leaves

The report described the ultrastructural changes that occurred in the major veins and their associated bundle sheaths (BS) of the maize ( Zea mays L. ) leaf blade in the process of their differentiation from three adjacent cells in the middle layer of the ground meristem, the minimal number of cells involved with the initiation of a procambial strand and the associated BS. The inner cell underwent two successive unequal periclinal divisions: a smaller cell that later differentiated into the adaxial BS cell precursor, and a larger one that divided once again periclinally yielding an abaxial BS cell precursor and a centrally located procambial initial cell. One of the two lateral cells immediately adjacent to either side of the inner cell also divided periclinally; these derivatives, along with another lateral cell of the original three-celled unit formed the precursor cells of the lateral BS. Prior to the initiation of protophlcem differentiation, all of the procambial cells showed ultrastructural characteristics basically similar to the procambial initial. They possessed a prominent nucleus with electron-dense aggregates of heterochromatin, a dense cytoplasm rich in ribosomes, proplastids and mitochondria; also a thin wall containing numerous plasmodesmata. In many cases, only short pieces of rough endoplasmic reticulum cistemae and a few small sized vacuoles were present. In adclifton, evidence of cytoplasmic disintegration leading to new vacuole formation was noted in the process of proeambium development. It was observed that certain endoplasmic reticulum was engaged in the sequestration and lysis of cytoplasm. No apparent uhrastmctuml difference was found between the BS cell precursors and the procambial initials, that was, the distinction between the procambium and the surrounding BS cells occurred gradually after vein initiation, The major ultrastmctural changes which occurred during the differentiation of the meristematic BS cells into the vacuolated cells were (1) a proplastid to chloroplast transformation going through a prolamellar body stage, and (2) the appearance of the multi-concentric membrane complex which might play a role in the degradation of some ribosomes and other cytoplasmic components during the differentiation of BS cells.     

The Ultrastructure of Protophloem Sieve Elements in Leaves of Aegilops comosa var. thessalica

The differentiation and obliteration of protophloem sieve elementsin leaves of the grass Aegilops comosa var. thessalica havebeen studied by electron microscopy. These elements differentiatesimilarly to metaphloem sieve elements of the same plant andother monocotyledons. Plasmalemma, smooth endoplasmic reticulum(ER), mitochondria, P-type plastids and sometimes nuclear remnantsconstitute the protoplasmic components at maturity, all areperipherally distributed. The differentiation of end walls intosieve plates and the presence of sieve areas on the lateralwalls indicate that protophloem sieve elements are componentsof sieve-tube. They may be functional for a brief period butsoon after their maturation they are compressed and finallyobliterated by the stretching of actively-growing surroundingcells. The protoplasmic components of mature elements degenerateand are destroyed during obliteration of the sieve elements. Aegilops comosa var. thessalica, protophloem, sieve elements, differentiation, ultrastructure     

Sieve Elements of Minor Veins in the Leaves of Beta vulgaris L.

End walls of sieve elements of minor veins of the leaves ofBeta vulgaris L. do not contain the multi-perforate sieve plateswhich typically occur on the end walls of sieve-tube membersof major veins. Instead, both end and side walls of the sieveelements of minor veins contain scattered pores which may occursingly or in small numbers. These pores are similar to thosewhich are grouped in sieve plates of major veins in size, possessionof callose and plugs of filaments. In addition to these pores,there are tubular connections 0.1 µ in diameter throughcharacteristically thickened parts of the cell wall betweensieve cells and companion cells. Sieve elements of minor veinsdiffer from those of major veins in structure as well as infunction.     

桑叶细脉中伴胞的超微结构研究

为了解桑叶细脉中伴胞的超微结构,采用透射电子显微技术对桑叶细脉中伴胞进行观察,着重伴胞与相邻细胞界面上胞间连丝发生频率.结果表明,(1)伴胞含丰富细胞器,细胞壁光滑,无壁内突;(2)伴胞细胞壁上具有大量胞间连丝,胞间连丝通常聚集,并常发生分枝;(3)伴胞与不同类型细胞界面上的胞间连丝发生频率有差异,伴胞-维管束鞘细胞界面上发生频率为25.12±1.83个/μm²,伴胞-伴胞界面上20.18±1.7个2/μm²,伴胞-维管薄壁细胞界面上5.42±0.6个/μm².基于上述观察,认为桑叶细脉中的伴胞属于1-2a型,韧皮部装载途径属于共质体类型.     

Modified Clearing Method to Show Sieve Tubes in Minor Veins of Leaves

Leaf samples of Glycine max and numerous other dicotyledonous species were cleared by a common, well established procedure modified by using more concentrated (10% w/v) aqueous NaOH, and by leaving samples in NaOH for 2-4 weeks and in chloral hydrate for 3 days, all at mom temperature. A single dye, chlorazol black E (1g/100 ml absolute ethanol), is used to stain for 3-6 min. Samples are mounted with the lower epidermis upward. Sieve tubes in favorable material can be seen in minor veins and vein endings.     

玉米雌、雄穗与叶片内几种激素含量的比较

以甜玉米为材料,采用扫描电镜观察雌、雄花序发育过程,并用ＥＬＩＳＡ 和ＨＰＬＣ 检测雌、雄花序发育过程中内源激素（ｉＰＡｓ 、ＺＲｓ、ＤＨＺＲｓ、ＺＴ、ＩＡＡ、ＧＡ３） 和内源玉米赤霉烯酮（ｚｅａｒａｌｅｎｏｎｅ, ＺＥＮ） 含量,分析激素含量变化与玉米性别决定的关系。结果表明：玉米花序经过了无性、双性到单性的发育过程,在茎尖伸长和小穗原基突起时期,雄花序中内源ｉＰＡｓ、ＺＲｓ、ＧＡ３ 和ＺＥＮ 含量最高并高于雌花序;在玉米性别决定的关键时期,即花器官原基突起到雌、雄性器官选择退化阶段,雄花序中ｉＰＡｓ、ＺＲｓ、ＺＴ 和ＺＥＮ 含量明显增加并高于雌花序,此时在两种花序中的ＧＡ３ 含量差异不明显。正常果穗上、中、下不同部位果穗内源ｉＰＡｓ、ＺＲｓ、ＺＴ、ＧＡ３ 和ＺＥＮ 含量无明显差异,顶端小穗雄性化的果穗顶部内源ｉＰＡｓ、ＺＲｓ、ＺＴ、ＧＡ３ 和ＺＥＮ 含量急剧增加。这些结果说明高水平的细胞分裂素、ＧＡ３ 和ＺＥＮ 可能有利于玉米雄性器官的发育。     

玉米杂种与亲本穗分化期功能叶基因差异表达与杂种优势

为探讨玉米杂种优势的分子机理,以10个玉米自交系及其组配的38个杂交种为材料,利用cDNA-AFLP技术,分析杂种与亲本在玉米雌穗小穗分化期功能叶片的基因差异表达类型与主要农艺性状的杂种表现及杂种优势的关系。研究表明：（1）杂种的基因相对于其双亲,存在质和量的表达差异,其中质的差异表达类型包括：单亲沉默表达,双亲沉默表达,亲本显性表达和杂种特异表达等类型。（2）在雌穗小穗分化期,同一差异表达类型中不同杂交组合间差异很大;从总体平均看,杂种特异表达类型占25.22%,亲本显性表达类型占21.46%,双亲沉默表达类型占8.27%,单亲沉默表达类型占33.49%。（3）单亲沉默表达与株高的杂种表现呈显著正相关;双亲沉默表达与穗粗的杂种优势呈显著负相关,显性表达与行粒数和单株粒重的杂种优势呈显著负相关,其余表达类型与所有农艺性状杂种表现及杂种优势均不相关,并对结果进行了讨论。     

Changes in Growth and Nitrogen Assimilation in Maize Plants Induced by NaCl and Growth Regulators

Experiments were conducted to determine the interactive effects of salinity and certain growth regulators on growth and nitrogen assimilation in maize (Zea mays L. cv. GS-2). 100 mM NaCl inhibited the biomass accumulation, chlorophyll and carotenoid contents in leaves, nitrate content and uptake and nitrate reductase activity. The application of kinetin, ascorbic acid and 10 and 50 μM abscisic acid in the first experiment and 50 and 100 μM abscisic acid in the second experiment induced a substantial increase in the above parameters, the effect was highest with abscisic acid in salinized as well as non-salinized plants. This revised version was published online in July 2006 with corrections to the Cover Date.     

萌发玉米种子脱水耐性与胚根细胞超微结构的变化

玉米种子脱水试验表明,25℃下萌发24h种子脱水耐性开始丧失,丧失50％和100％的时间分别为33h、58h。萌发过程中随着吸胀时间增加,玉米种子脱水耐性逐步丧失。显微观察显示,种子吸胀过程中,胚根细胞的贮藏物质逐步减少,线粒体等细胞器的分化程度则不断提高,尤其是脂类物质的分解程度与脱水耐性变化的关系似乎更明显。     

Photosynthesis and Dark Respiration in Leaves of Different Ages of Partly Flooded Maize Seedlings

Maize seedlings were flooded for periods from 1 to 15 days, and the leaves of different ages were then taken to examine photosynthesis, dark respiration, transpiration, chlorophyll content, and some morphometric parameters. The responses of leaves to root submergence essentially depended on the leaf layer and the treatment duration. A short-term flooding (1–24 h) induced primary stress responses in the first leaf. Photosynthesis and respiration in this leaf oscillated around the control levels with amplitudes of ±15–25% and ±40–60%, respectively. After a longer flooding, the CO₂ exchange in the second leaf was suppressed, while oxygen uptake was stimulated. In the third leaf, which was formed during submergence, the photosynthetic rate increased and the respiratory activity decreased. The transpiration rate did not change in these leaves for 15 days of flooding. The hypoxic treatment, at its early stages, retarded growth and disturbed the source–sink relations. At later stages the plants adapted to hypoxic environment: the seedling growth was restored, which elevated the demand for assimilates and stimulated photosynthesis. It is concluded that plants overcome negative impact of the root hypoxia at the systemic level.     

拟南芥根原生韧皮部筛管分子的超微结构

运用高压冷冻替代方法固定处理材料,在透射电镜下观察了拟南芥(Arabidopsis thaliana L.)根原生韧皮部筛管分子在发育过程中的超微结构变化.结果表明:在筛管分子发育过程中,细胞核具有细胞程序化死亡的典型特征,出现核膜内陷、核质聚集并边缘化、核膜破毁以及最后核消失.核膜在破毁前一直呈饱满状态,未出现核膜皱缩、核裂瓣和核周腔明显膨大等现象.在成熟筛管分子的细胞质内,具单层膜的淀粉状颗粒.这些淀粉状颗粒常与线粒体在一起,可能为线粒体的产能活动提供基质.小液泡发生于内质网,未见大液泡的形成.     

拟南芥根原生韧皮部筛管分子的超微结构

运用高压冷冻替代方法固定处理材料,在透射电镜下观察了拟南芥（Arabidopsis thaliana L.)根原生韧皮部筛管分子在发育过程中的超微结构变化。结果表明：在筛管分子发育过程中,细胞核具有细胞程序死亡的典型特征,出现核膜内陷、核质聚集并边缘化,核膜破毁以及最后核消失,核膜在破毁前一直呈饱满状态,未出现核膜皱缩,核裂瓣和核周腔明显膨大等现象。在成熟筛管分子的细胞质内,具单层膜的淀粉状颗粒,这些淀粉状态颗粒常与线粒体在一起,可能为线粒体的产能活动提供基质,小液泡发生于内质网,未见大液泡的形成。     

Involvement of Polyamine Oxidase in Abscisic Acidinduced Cytosolic Antioxidant Defense in Leaves of Maize

Using pharmacological and biochemical approaches, the role of maize polyamine oxidase （MPAO） in abscisic acid （ABA）- induced antioxidant defense in leaves of maize （Zea mays L.） plants was investigated. Exogenous ABA treatment enhanced the expression of the MPAO gene and the activities of apoplastic MPAO. Pretreatment with two different inhibitors for apoplastic MPAO partly reduced hydrogen peroxide （H202） accumulation induced by ABA and blocked the ABA-induced expression of the antioxidant genes superoxide dismutase 4 and cytosolic ascorbate peroxidase and the activities of the cytosolic antioxidant enzymes. Treatment with spermidine, the optimum substrate of MPAO, also induced the expression and the activities of the antioxidant enzymes, and the upregulation of the antioxidant enzymes was prevented by two inhibitors of MPAO and two scavengers of H202. These results suggest that MPAO contributes to ABA-induced cytosolic antioxidant defense through H202, a Spd catabolic product.     

Hardly Increased Oxidative Stress After Exposure to Low Temperature in Chilling-Acclimated and Non-Acclimated Maize Leaves

Abstract: Seedlings of Zea mays L. were grown at optimal (25 °C) and suboptimal (15 °C) temperature and then exposed to severe chilling temperature (6 °C) at their growth light intensity (450 ìmol quanta m⁻² s⁻¹) for 4 d. Photosynthetic parameters, hydrogen peroxide, antioxidant contents, and activity of scavenging enzymes were investigated before, during, and after chilling stress. This stress caused a stronger reduction in photosynthetic activity, maximum quantum efficiency of photosystem II primary photochemistry ( F _v/ F _m), and catalase activity in plants which had been grown at 25 °C rather than at 15 °C. Maize plants grown at suboptimal temperature de-epoxidized their xanthophyll cycle pool to a greater extent and exhibited a faster recovery from chilling stress than plants which had not been acclimated to chilling. Antioxidant content, activity of scavenging enzymes, with the exception of catalase, hydrogen peroxide formation, and the size of the xanthophyll cycle pool were hardly affected by chilling stress. However, chilling induced a temporary increase in the glutathione content and triggered the synthesis of á-tocopherol during the phase of recovery at 25 °C. The results indicate that leaves respond to chilling stress by down-regulation of photosystem II accompanied by de-epoxidation of the xanthophyll cycle pool, probably to prevent enhanced formation of superoxide radicals at photosystem I and, consequently, other reactive oxygen species.     

Involvement of Polyamine Oxidase in Abscisic Acid induced Cytosolic Antioxidant Defense in Leaves of Maize

Using pharmacological and biochemical approaches, the role of maize polyamine oxidase (MPAO) in abscisic acid (ABA)induced antioxidant defense in leaves of maize (Zea mays L.) plants was investigated. Exogenous ABA treatment enhanced the expression of the MPAO gene and the activities of apoplastic MPAO. Pretreatment with two different inhibitors for apoplastic MPAO partly reduced hydrogen peroxide (H2O2) accumulation induced by ABA and blocked the ABA-induced expression of the antioxidant genes superoxide dismutase 4 and cytosolic ascorbate peroxidase and the activities of the cytosolic antioxidant enzymes. Treatment with spermidine, the optimum substrate of MPAO, also induced the expression and the activities of the antioxidant enzymes, and the upregulation of the antioxidant enzymes was prevented by two inhibitors of MPAO and two scavengers of H2O2. These results suggest that MPAO contributes to ABA-induced cytosolic antioxidant defense through H2O2, a Spd catabolic product.     

Ultrastructure of Mesophyll Cells and Pigment Content in Senescing Leaves of Maize and Barley

Leaf senescence is a genetically regulated stage in the plant life cycle leading to death. Ultrastructural analysis of a particular region of the leaf and even of a particular mesophyll cell can give a clear picture of the time development of the process. In this study we found relations between changes in mesophyll cell ultrastructure and pigment concentration in every region of the leaf during leaf senescence in maize and barley. Our observations demonstrated that each mesophyll cell undergoes a similar senescence sequence of events: a) chromatin condensation, b) degradation of thylakoid membranes and an increase in the number of plastoglobules, c) damage to internal mitochondrial membrane and chloroplast destruction. Degradation of chloroplast structure is not fully correlated with changes in photosynthetic pigment content; chlorophyll and carotenoid content remained at a rather high level in the final stage of chloroplast destruction. We also compared the dynamics of leaf senescence between maize and barley. We showed that changes to the mesophyll cells do not occur at the same time in different parts of the leaf. The senescence damage begins at the base and moves to the top of the leaf. The dynamics of mesophyll cell senescence is different in leaves of both analyzed plant species; in the initial stages, the process was faster in barley whereas in the later stages the process occurred more quickly in maize. At the final stage, the oldest barley mesophyll cells were more damaged than maize cells of the same age.     

发育中玉米胚结合蛋白(BiP)的动态变化及定位

Western blot检测表明,在玉米胚发育过程中结合蛋白(BiP)含量与胚可溶性蛋白含量变化一致,在授粉16d后BiP含量随发育而增加;对热激不敏感.组织化学免疫定位表明,在玉米胚发育的不同时期,BiP主要定位在胚芽端、初生维管组织和糊粉层中,提示胚在构建器官的同时,也为其功能执行准备了条件;热激不影响其定位.     

Effect of Elevated Temperatures on the Activity of Alternative Pathways of Photosynthetic Electron Transport in Intact Barley and Maize Leaves

The light-induced rise in chlorophyll fluorescence and the subsequent decay of fluorescence in darkness were measured in barley and maize leaves exposed to heat treatment. The redox conversions of the photosystem I primary donor P700, induced by far-red light, were also monitored from the absorbance changes at 830 nm. After heating of leaves at temperatures above 40°C, the ratio of variable and maximum fluorescence decreased for leaves of both plant species, indicating the inhibition of photosystem II (PSII) activity. A twofold reduction of this ratio in barley and maize leaves was observed after heating at 45.3 and 48.1°C, respectively, which suggests the higher functional resistance of PSII in maize. The amplitude of the slow phase in the dark relaxation of variable fluorescence did not change after the treatment of barley and maize leaves at temperatures up to 48°C. In leaves treated at 42 and 46°C, the slow phase of dark relaxation deviated from an exponential curve. The relaxation kinetics included a temporary increase in fluorescence to a peak about 1 s after turning off the actinic light. Unlike the slow component, the fast and intermediate phases in the dark relaxation of variable fluorescence disappeared fully or partly after the treatment of leaves at 46°C. The photooxidation of P700 in heat-treated leaves was saturated at much higher irradiances of far-red light than in untreated leaves. At the same time, the dark reduction of P700⁺ was substantially accelerated after heat treatment. The data provide evidence that the heating of leaves stimulated the alternative pathways of electron transport, i.e., cyclic transport around photosystem I and/or the donation of electrons to the plastoquinone pool from the reduced compounds located in the chloroplast stroma. The rate of alternative electron transport after the heat treatment was higher in maize leaves than in barley leaves. It is supposed that the stimulation of alternative electron transport, associated with proton pumping into the thylakoid, represents a protective mechanism that prevents the photoinhibition of PSII in leaves upon a strong suppression of linear electron transport in chloroplasts exposed to heat treatment.