A New Method for Differential Quantitative Assay of Zeatin and Zeatin Riboside

A new method is proposed for differential quantitative assay of two major endogenous cytokinin forms. It is based on determination of two effective parameters—concentrations of zeatin and zeatin riboside—with the use of appropriate antigens as standards. The method can be used for determining cytokinins in small samples of plant tissues without extract fractionation. This study pioneers the quantitation of changes in the hormonal status of ovules and ovaries of Triticum aestivumL. at early stages of embryogeny. A gradual increase in the content of the active and storage forms of the hormones from the ovary to the ovule was revealed.     

The Metabolism of Zeatin and Zeatin Riboside by Soya Bean Callus

Five cell division inducing compounds were found in soya beancallus irrespective of whether it wes grown on a zeatin or zeatinriboside containing basal medium. In both cases the major metaboliteseems to be zeatin glucoside. The significance of this metabolicstep in plant tissue is discussed.     

Changes in Cytokinin Distribution in the Ovule and Ovary of Taraxacum officinale Web. in Early Stages of Embryogenesis

Quantitative changes in the hormonal status of the ovules and ovaries were first studied in Taraxacum officinale Web. at the early stages of embryogenesis. The plant material was analyzed by ELISA using labeled anti-rabbit antibodies. A new procedure for differential and quantitative determination of the main endogenous cytokinins based on the estimation of the effective zeatin and zeatin riboside concentrations from calibration curves constructed using zeatin and zeatin riboside as standard antigens was developed. It was shown that, at the three initial stages of embryogenesis examined, the concentration of zeatin uniformly increased in T. officinale ovules. The concentration of zeatin riboside, conversely, uniformly decreased. However, their total concentration changed insignificantly. A gradual increase in the concentration of the active and storage hormone forms from the ovary to the ovule was shown.     

The Putative Factors Involved in the Induction of Embryogenesis in Angiosperms

We quantified various endogenous cytokinins during wheat (Triticum aestivumL.) and dandelion (Taraxacum officinaleWeb.) ovary development. Wheat ovaries were studied at the following developmental stages: the mature embryo sac with eight nuclei (stage 1), the interphasic zygote 12 h and 24 h after fertilization (stage 2), and the onset of zygote division (stage 3). The dandelion ovaries were studied at the stage of the mature embryo sac (stage 1), in the interphase of the parthenogeneticaly developing ovule (stage 2), and during its first division (stage 3). The material was analyzed by the method of competitive solid-phase immunoenzyme assay (ELISA) using peroxidase-labeled anti-rabbit antibodies. The onset of embryogenesis in wheat and dandelion ovules was accompanied by the substantial rearrangement of their hormonal complexes, which preceded the morphogenetic processes leading to seed formation. This implies that the hormonal system of the whole maternal plant is involved in the induction of embryogenesis. The final stages of embryogenesis depend on the hormonal systems in the flower, ovary, and ovule.     

Cytokinins in photoperiodic induction of flowering in Chenopodium species

Changes in cytokinin (zeatin – Z, zeatin riboside – ZR, isopentenyladenine – iP, isopentenyladenosine – iPA) levels were determined under light regimes inductive and non-inductive for flowering in leaves, stems, roots and apical parts of short-day Chenopodium rubrum and long-day Chenopodium murale. In leaves. stems and roots of both plant species the level of cytokinins (in C. rubrum of Z and ZR, in C. murale of Z. ZR, iP and iPA) decreased by about 50% during the dark period and increased again during the subsequent light period, No significant changes in cytokinin levels were observed in continuous light. In apical parts of C. rubrum cytokinin level (Z, ZR, iP) was dramatically increased (by 400–500%) at the end of the dark period and decreased to about the original value during the following light period, while no changes were observed in continuous light. In apical parts of C. murale the level of cytokinins doubled during floral induction consisting of 10 days of continuous light. A red (R) break (15 min at the 6th h of darkness), which prevents flowering in C. rubrum , has no significant effect on cytokinin levels in leaves at the end of darkness. Cytokinin levels increased 1 h after R and decreased again rapidly. On the other hand, the increase of cytokinin level in the apical parts of C. rubrum was largely prevented by the R break. These effects of R on cytokinin levels were not reverted by far-red (FR), while the effect on flowering was reverted. It may be concluded that there is no correlation between changes in cytokinin levels in leaves. Stems and roots and photoperiodic flower induction, as both species, representing different photoperiodic types, showed similar changes under the same light regime. The increase of cytokinin levels in apical parts of both photoperiodic species during floral induction suggests a role (increased cell division and branching) for cytokinins in apex evocation.     

多花地宝兰胚囊和胚发育的细胞学研究

为探讨多花地宝兰(Geodorum recurvum)胚胎发育的系统分类学意义,采用石蜡制片法对多花地宝兰胚囊和胚的发育进行解剖学观察。结果表明,在开花前,多花地宝兰胚珠原基发育缓慢,开花授粉后胚珠原基快速发育成"树状二杈分枝结构",随后在"分枝结构"末端形成孢原细胞,开始胚囊发育。多花地宝兰的胚囊发育属于单孢蓼型胚囊,胚珠具有双层珠被。孢原细胞形成后,经过细胞膨大延长发育形成胚囊母细胞,胚囊母细胞经过减数分裂形成线性四分体,在珠孔端形成1个功能大孢子,功能大孢子经过3次有丝分裂形成8核胚囊。多花地宝兰的胚发育具有藜型和紫苑型两种方式。双受精完成后,多花地宝兰合子进行一次橫裂后形成基细胞和顶细胞;基细胞经过多次分裂形成细胞团,细胞团中的细胞向不同方向膨大延长形成多个胚柄细胞;顶细胞有两种分裂方式,一种是横裂形成藜型胚,一种是纵裂形成紫苑型胚。因此,推测多花地宝兰在兰科植物系统分类学上属于较为原始种。     

地钱颈卵器发育和卵发生的显微观察及细胞化学研究

对地钱（Marchantia polymorpha）颈卵器发育和卵发生过程进行了显微观察和细胞化学的研究,颈卵器起始于原始细胞,该细胞呈乳突状,经横分裂产生基细胞和顶细胞,顶细胞经3次纵斜向分裂和1次横分裂产生初生细胞,初生细胞是颈卵器内的第一个细胞,经横分裂产生中央细胞和颈沟母细胞,前者产生1个腹沟细胞和1个卵细胞,后者最终产生4个颈沟细胞。颈卵器的成熟表现为颈部显著伸长和腹部膨大,卵细胞成熟时具有不规则的核,细胞质内含有丰富的囊泡和颗粒物,卵细胞周围充满粘性物质,细胞化学研究表明,该粘性物质为多糖,卵细胞质中深染色的颗粒可能为脂类物质,腹沟细胞自产生后就逐渐退化,颈沟细胞的退化迟于腹沟细胞,其数量通常为4个,偶尔可见5个颈沟细胞或具有双核的现象。     

Hormones in the grains in relation to sink strength and postanthesis development of spikelets in rice

Inferior spikelets usually exhibit a slower grain filling rate and lower grain weight than superior spikelets in a rice (Oryza sativa L.) panicle. This study investigated whether the variations in grain filling between the two kinds of spikelets were attributed to their sink strength and whether the sink strength was regulated by the hormonal levels in the grains. Using two field-grown rice genotypes, the division rate of endosperm cells, hormonal levels in the grains, and grain weight of both superior and inferior spikelets were determined during the grain filling period. The results showed that superior spikelets had dominance over inferior spikelets in endosperm cell division rate and cell number, grain filling and grain weight. Changes in zeatin (Z) and zeatin riboside (ZR) contents paralleled and were very significantly correlated with the cell division rate and cell number. Cell division rate and the content of indole-3-acetic acid (IAA) in the grains were also significantly correlated. Gibberellin (GAs; GA₁+ GA₄) content of the grains was high but ABA levels were low at the early grain filling stage. ABA increased substantially during the linear phase of grain growth and was very significantly correlated with grain dry weight during this period. Application of kinetin at 2 through 6 days post anthesis (DPA) significantly increased cell number, while spraying ABA at 11 through 15 DPA significantly increased the grain filling rate. The results suggest that differences in sink strength are responsible for variations in grain filling between superior and inferior spikelets. Both cytokinins and IAA in the grains may mediate cell division in rice endosperm at early grain filling stages, and therefore regulate the sink size of the grain, whereas ABA content correlates with sink activity during the linear period of grain growth.     

Factors affecting in vitro shoot formation from vegetative shoot apices of apple and relationship between organogenic response and cytokinin localisation

ABSTRACT

The effects of macro- and micro-elements, benzyladenine (BA) concentration, and the period of auxin application on adventitious shoot formation from callus originating from vegetative shoot apices were tested on apple (Malus domestica Borkh) rootstock Jork 9. The putative relationship between organogenic response and cytokinin localisation was also studied by an immunolocalisation technique for in situ determination of free cytokinins. The use of MS (Murashige & Skoog, 1962) salts in the medium instead of those of LP (Quoirin & Lepoivre, 1977) had a strong positive effect both on shoot formation rate and on the number of shoots produced. The highest organogenic response from callus was induced using 17.8 μM BA in the presence of 2.7 μM NAA and by maintaining the explants for 20 days in darkness, then transferring them to fresh auxin-free medium and to the light. The in situ localisation studies, performed using antibodies with a marked specificity against zeatin and isopentenyladenine, revealed changes in the localisation of free zeatin in the tissues during the shoot-forming process, in particular during the active cell division phase leading to callus formation, and in the initial phase of bud formation. Changes in zeatin distribution in the tissues of the vegetative shoot apex during shoot formation may indicate a role for this cytokinin free base in cell differentiation and organogenesis.