In vitro clonal propagation of Nyctanthes arbor-tristis

Rapid shoot multiplication of Nyctanthes arbor-tristis L. was achieved from axillary meristems on Murashige and Skoog (MS) basal medium supplemented with 1.0–1.5 mg dm⁻³ 6-benzylaminopurine (BA), 50 mg dm⁻³ adenine sulfate (Ads) and 3 % (m/v) sucrose. Inclusion of indole-3-acetic acid (IAA) in the culture medium along with BA + Ads promoted a higher rate of shoot multiplication. Maximum mean number of microshoots per explant (6.65) was achieved on the MS medium supplemented with 1.5 mg dm⁻³ BA, 50 mg dm⁻³ Ads and 0.1 mg dm⁻³ IAA after 4 weeks of culture. The elongated shoots rooted within 13 to 14 d on half-strength MS medium supplemented with either indole-3-butyric acid (IBA), IAA or 1-naphthaleneacetic acid (NAA) with 2 % sucrose. Maximum percentage of rooting was obtained on medium having 0.25 mg dm⁻³ IBA and 0.1 mg dm⁻³ IAA. About 70 % of the rooted plantlets survived in the greenhouse. The in vitro raised plants were grown normally in the field.     

In vitro plant regeneration from leaf explants of Ophiorrhiza japonica

An efficient in vitro plant regeneration system from leaves of Ophiorrhiza japonica Blume was established for the first time. Callus formation rate was more than 90.4 % from leaf segments on Murashige and Skoog (MS) supplemented with either α-naphthaleneacetic acid (NAA) alone or in combination with 6-benzyladenine (BA). The highest shoot regeneration (78.9 %) was achieved on MS medium containing 2.0 mg dm⁻³ BA and 0.2 mg dm⁻³ NAA, with an average of 9.4 shoots developed per leaf segment. Shoot regeneration was also improved when the leaf explants were cultured in MS basal medium supplemented with 0.5 % (m/v) polyvinylpyrrolidone (PVP). The leaf explants from seedlings with age of about 18–27 d showed the highest shoot regeneration. The regenerated shoots were rooted on half-strength basal MS medium supplemented with 0.5 mg dm⁻³ indole-3-butyric acid (IBA), which averagely produced 24.8 roots per shoot. The plantlets were transferred to soil, where 100 % survived after 1 month of acclimatization.     

Micropropagation of Sesbania rostrata from the Cotyledonary Node

Multiple shoots were induced from the cotyledonary nodes derived from seedling of Sesbania rostrata on Nitsch (1969; N) medium supplemented with various concentrations of benzyladenine (BA). 1 mg dm⁻³ BA proved to be the best, eliciting 5.8 ± 1.0 shoots per explant in 100 % cultures. The elongation of shoots was best at 2.0 mg dm⁻³ BA. The shoot proliferation capacity increased to 7.5 shoots per explant following transfer of explants to the fresh shoot multiplication medium (MS + 1.0 mg dm⁻³ BA), after an initial incubation of 30 d. To further enhance number of shoots per explant an alternative strategy of cultivation of mother explant on fresh shoot multiplication medium after excision of shoots was adopted. Following the repeated harvesting of shoots an average of 33 shoots per explant could be obtained. The in vitro regenerated shoots produced roots when transferred to half-strength MS medium supplemented with 3 % sucrose and 1 mg dm⁻³ IBA. The developed plantlets were planted in the soil and transferred to the field after an acclimatization period of 3 – 4 months. These plants produced flowers and fruits in the field and exhibited the development of prominent and more organized stem nodules as compared to the in vivo raised plants of the same age. This revised version was published online in July 2006 with corrections to the Cover Date.     

茎顶端分生组织在植物发育过程中的保持、转变和逆转

顶端分生组织(shoot apical meristems,SAM)为产生新的器官和组织而不断提供新的细胞,它的活性依赖于平衡分生组织细胞的增殖和器官发生之间关系的调控基因.来自不具备光合能力的顶端分生组织的细胞可形成具有光合能力的营养器官.在从营养生长到生殖发育的转变过程中,茎顶端分生组织,转变为花序分生组织,最终形成花分生组织.在进入开花决定状态以前,SAM的状态很大程度上受到环境信号和转录调控因子的影响.以模式植物拟南芥为主,对在顶端分生组织的保持和转变中复杂同时又有差异的基因调控网络进行讨论.在花和花序分生组织逆转过程中,SAM中的细胞也受到相关基因的调控,且表达方式存在明显的时空差异.因此,具有决定性的和未决定性双重特性的分生组织之间的转变和相互协调,对于器官发生和形态建成起到至关重要的作用.     

Flooding tolerance in halophytes

Flooding is a common environmental variable with salinity. Submerged organs can suffer from O₂ deprivation and the resulting energy deficits can compromise ion transport processes essential for salinity tolerance. Tolerance of soil waterlogging in halophytes, as in glycophytes, is often associated with the production of adventitious roots containing aerenchyma, and the resultant internal O₂ supply. For some species, shallow rooting in aerobic upper soil layers appears to be the key to survival on frequently flooded soils, although little is known of the anoxia tolerance in halophytes. Halophytic species that inhabit waterlogged substrates are able to regulate their shoot ion concentrations in spite of the hypoxic (or anoxic) medium in which they are rooted, this being in stark contrast with most other plants which suffer when salinity and waterlogging occur in combination. Very few studies have addressed the consequences of submergence of the shoots by saline water; these have, however, demonstrated tolerance of temporary submergence in some halophytes.     

Oligogalacturonides enhance cytokinin-induced vegetative shoot formation in tobacco explants, inhibit polyamine biosynthetic gene expression, and promote long-term remobilisation of cell calcium

Long-sized oligogalacturonides (OGs) are cell wall fragments that induce defence and developmental responses. The Ca²⁺-dependent “egg-box” conformation is required for their activity, and polyamines may prevent them from adopting this conformation. Although OGs are known to inhibit auxin-induced growth processes, their effect on cytokinin-induced ones requires investigation. In the present work OGs were shown to promote cytokinin (benzyladenine, BA)-induced vegetative shoot formation from tobacco leaf explants, independent of the presence of CaCl₂ in the medium and of auxin (indoleacetic acid, IAA) supply. The effect of polyamines, putrescine (PU) and spermidine (SD) supplied with/without their biosynthetic inhibitors (DFMO, CHA) was also investigated, and showed that spermidine enhanced adventitious vegetative shoot formation, but only on medium containing Ca²⁺ and IAA. Treatments with inhibitors blocked this promotive effect. OGs did not alter free polyamine concentrations, but caused a moderate increase of conjugated ones, and exhibited an early inhibitory effect on polyamine biosynthetic gene expression. OGs, but not SD, caused long-term changes in calcium-associated epifluorescent signals in the cell walls, and, later, inside the cells of specific tissues. Electron microscopy analysis (ESI system) demonstrated that calcium accumulated in the cell walls and vacuoles of OG-cultured explants. The relationship between OGs, cytokinin, calcium, and polyamines in adventitious vegetative shoot formation is discussed.     

The rice flattened shoot meristem, encoding CAF-1 p150 subunit, is required for meristem maintenance by regulating the cell-cycle period

We isolated flattened shoot meristem (fsm) mutants in rice that showed defective seedling growth and died in the vegetative phase. Since most fsm plants had flat and small shoot apical meristems (SAMs), we suggest that FSM is required for proper SAM maintenance. FSM encodes a putative ortholog of Arabidopsis FASCIATA1 (FAS1) that corresponds to the p150 subunit of chromatin assembly factor-1 (CAF-1). FSM is expressed patchily in tissues with actively dividing cells, suggesting a tight association of FSM with specific cell-cycle phases. Double-target in situ hybridization counterstained with cell-cycle marker genes revealed that FSM is expressed mainly in the G₁ phase. In fsm, expressions of the two marker genes representing S- and G₂- to M-phases were enhanced in SAM, despite a reduced number of cells in SAM, suggesting that S- and G₂-phases are prolonged in fsm. In addition, developmental events in fsm leaves took place at the proper time, indicating that the temporal regulation of development occurs independently of the cell-cycle period. In contrast to the fasciated phenotype of Arabidopsis fas1, fsm showed size reduction of SAM. The opposite phenotypes between fsm and fas1 indicate that the SAM maintenance is regulated differently between rice and Arabidopsis.     

Hormonal control of shoot branching

Shoot branching is the process by which axillary buds, located on the axil of a leaf, develop and form new flowers or branches. The process by which a dormant bud activates and becomes an actively growing branch is complex and very finely tuned. Bud outgrowth is regulated by the interaction of environmental signals and endogenous ones, such as plant hormones. Thus these interacting factors have a major effect on shoot system architecture. Hormones known to have a major influence are auxin, cytokinin, and a novel, as yet chemically undefined, hormone. Auxin is actively transported basipetally in the shoot and inhibits bud outgrowth. By contrast, cytokinins travel acropetally and promote bud outgrowth. The novel hormone also moves acropetally but it inhibits bud outgrowth. The aim of this review is to integrate what is known about the hormonal control of shoot branching in Arabidopsis, focusing on these three hormones and their interactions.     

Polymorphism of the Stamina pistilloida Gene in Pea Plants

Using the direct amplification of genomic DNA from two pea (Pisum sativum) cultivars, we obtained four new homologs of the Stamina pistilloida (Stp) gene, an ortholog of the UNUSUAL FLORAL ORGANS (UFO) and Fimbriata (Fim) of arabidopsis and snapdragon. The UFO/Fim gene is involved in cell determination in the shoot apical meristem and the floral meristem and controls the expression of B- and C-class genes of flower organ differentiation; in addition, in pea plants, the Stp gene controls leaf shape, plant height, and the number of internodes to the first inflorescence. The nucleotide and deduced amino acid sequences of the Stp homologs characterized in this study were very similar to the prototype gene from pea cv. Torsdag (98%) and significantly differed between cvs. Filby and Sebeco 59-61-65-6 contrasting in the compound-leaf architecture.     

Micropropagation of fig (Ficus carica L.) ‘Roxo de Valinhos’ plants

Summary An in vitro protocol for Ficus carica cv. ‘Roxo de Valinhos’ was optimized. Nodal explants containing two buds were excised from field-grown mature plants, and transferred to different proliferation media consisting of combinations of distinct concentrations of activated charcoal with benzyladenine (BA), kinetin with gibberellic acid (GA₃), and WPM (woody plant medium) with kinetin. The regular strength of WPM in combination with 0.5 mgl⁻¹ kinetin was the best condition for shoot proliferation of Ficus carica ‘Roxo de Valinhos’ plants. The addition of activated charcoal in the medium completely inhibited shoot proliferation. The inclusion of BA in the medium induced excessive callus formation as well as small and vitrified shoots, while GA₃ induced excessive elongation associated with vitrification, chlorosis, and tip-burned shoots.