In this work, the effect of lead on sunflower seedlings with two root system types: primary - formed from embryonic tissues and adventitious - originating from hypocotyl after cutting off primary roots was investigated. The seedlings were subjected to Pb(NO₃)₂ in doses: 0, 0.5, 2.5, 5 and 20 mg(Pb) dm^-3 for a week. Lead accumulation, seedling length and mass as well as selected parameters representative of oxidative damage (malondialdehyde) and protection (superoxide dismutase and glutathione) were used to compare stress response of plants. The comparison showed significant differences between plants with different root systems in almost all the parameters and the plants with adventitious root were more tolerant to lead.

The role of glutathione (GSH) in the adaptation of wild type Arabidopsis thaliana plants to Cd stress was investigated. The nutrient solution (control or containing 50 or 100 μM Cd) was supplemented with buthionine sulfoximine (BSO; 50, 100, 500 μM, to decrease the GSH content in plants) or GSH (50, 100, 500 μM, to increase its content in plants) in order to find how GSH content could regulate Cd stress responses. BSO application did not influence plant biomass, while exogenous GSH (especially 500 μM) reduced root biomass. BSO (500μM) in combination with Cd (100 μM) increased Cd toxicity on root growth (by over 50 %), most probably due to reduced GSH content and phytochelatin (PC) accumulation (by over 96 %). On the other hand, combination of exogenous GSH (500 μM) with Cd (100 μM) was also more toxic to plants than Cd alone despite a significant increase in GSH and PC accumulation (up to 2.7 fold in the roots). This fact could indicate that the natural content of endogenous GSH in wild type A. thaliana plants is sufficient for Cd-tolerance. A decrease in this GSH content led to decreased Cd-tolerance of the plants but an increase in GSH content did not enhance Cd-tolerance, and it showed even toxic effect on the plants.

The effects of different growth conditions (ventilated and closed vessels, medium with 0, 15 and 30 g dm^-3 sucrose) during proliferation of donor quince (Cydonia oblonga Mill.) shoots (stage I) on net photosynthetic rate and soluble sugars content were evaluated. In order to assess the influence of these physiological parameters on morphogenesis, leaf explants harvested from donor shoots were induced to form somatic embryos and adventitious roots under ventilated and closed Petri dishes (stage II). Natural ventilation and low sucrose contents (0-15 g dm^-3) promoted the photosynthetic rate of quince shoots whereas biomass accumulation was the highest in those shoots cultured with 30 g dm^-3 sucrose in both vessel types and 15 g dm^-3 sucrose under natural ventilation. Increasing sucrose content in the medium induced greater accumulation of sucrose in leaf tissues of donor shoots. The content of reducing sugars was higher than that of sucrose, and it appeared to be higher in shoots cultured under natural ventilation compared to those in closed vessels. Somatic embryogenesis and root regeneration were influenced by stage I and II treatments. A significant correlation between sucrose content in the leaves of donor shoots and the number of somatic embryos regenerated was found, suggesting that identification of biochemical and physiological characteristics of donor shoots associated with increased regeneration ability might be helpful for improving morphogenesis in plant tissue culture.

The study was conducted to investigate the physiological effects of exogenous NO on potherb mustard (Brassica juncea Coss.) seedlings under salt stress. The plants were grown in Hogland nutrient solution for 15 d and treated with 150 mM NaCl, NO donor sodium nitropruside (SNP) and NO scavenger methylene blue (MB-1) for 4 d. The NaCl stress increased superoxide dismutase, peroxidase and ascorbate peroxidase activities and malondialdehyde (MDA) and free proline contents, and decreased soluble protein content. However, the application of exogenous NO limited the production of MDA and free proline, while markedly promoted SOD, POD and APX activity.

Embryogenic and non-embryogenic calli were induced from the Centella asiatica leaf explants on Murashige and Skoog medium supplemented with kinetin and 2,4-dichlorophenophenoxyacetic acid. The extracellular matrix (ECM) layer was seen on the surface of embryogenic cells but not on the non-embryogenic cells. The ECM formed bridges with net-like material between the embryogenic cells. This network like structure was believed to play an important role in plant morphogenesis and can serve as an early structural marker of embryogenic competence in Centella asiatica calli culture.

The effects of the ectopic expression of a barley transcription factor (HvCBF4) under the control of a constitutive (maize Ubi1) or a stress-inducible (Arabidopsis RD29A) promoter in the abiotic stress response in rice (Oryza sativa L.) was investigated. The transformed plants were analyzed both at molecular and physiological level and the AtRD29A::HvCBF4 plants were further analyzed using the GeneChip® rice genome array under control conditions. Only the plants constitutively expressing HvCBF4 have shown increased survival to drought stress, but not to cold or high-salinity. These plants have also shown better photosynthetic capacity, as determined by chlorophyll fluorescence. Plants expressing AtRD29A::HvCBF4 did not show increased survival to any of the stresses applied. However in the GeneChip® microarray, these plants have shown up-regulation of many stress-responsive genes (> 400) as compared to non-transformed plants. Interestingly, RT-PCR analysis revealed not only differential gene expression between roots and shoots, but also between transgenic lines with the different promoters. Our results indicate that different HvCBF4 expression levels resulted in different transcriptomes and drought tolerance. Given that AtRD29A::HvCBF4 plants did not show increased tolerance to any of the imposed stresses, we may conclude that this promoter may be inappropriate for rice transformation aiming for enhanced abiotic stress tolerance.

The effects of temperature (25-45 °C) and pH (7.5-5.5) on photosystem (PS) 2 was studied in spinach (Spinacia oleracea L.) thylakoid membranes using chlorophyll a fluorescence induction kinetics. In high temperature and low pH treated thylakoid membranes a decline in the variable to maximum fluorescence ratio (F_v/F_m) and PS 2 electron transport rate were observed. More stacking in thylakoid membranes, studied by digitonin fractionation method, was observed at low pH, while the degree of unstacking increased under high temperature conditions. We conclude that the change in pH does not significantly affect the donor/acceptor side of PS 2 while high temperature does. Fluorescence emission spectra at 77 K indicated that low pH is associated with energy redistribution between the two photosystems while high temperature induced changes do not involve energy re-distribution. We suggest that both, high temperature and low pH, show an inhibitory effect on PS 2 but their mechanisms of action are different.

Measurements of dependence of photosynthetic electron transport on irradiance and analyses of stable isotope ratios (δ¹⁸O, δ¹³C, δ¹⁵N) were performed on 4 to 6-year-old pine trees (Pinus sylvestris L.) in the primeval forest reserve of Białowieża and on 21-year-old pine trees of a plantation of different provenances at the Sękocin Forest Station near Warsaw, Poland. Small differences in maximum photosynthetic electron transport rates, ETR_max were related to growth. Stable isotope analyses suggest that water relations play an important role for the performance of P. sylvestris at the sites studied. The intraspecific comparisons showed a very high variability of photosynthetic capacity between needles of given trees and between individual trees under similar conditions. Differences between specific provenances were also observed. This is relevant for ecological niche occupation in a wide geographical growth range, where P. sylvestris is actually occurring. The high physiological plasticity demonstrated reveals a conspicuous trait of this tree species.

The effects of NaCl on the H₂O₂ content and the activities of catalase (CAT) and superoxide dismutase (SOD) were studied in diverse group of plants, such as a unicellular alga, Chlorella sp., an aquatic macrophyte, Najas graminea, and a mangrove plant, Suaeda maritima, all showing high tolerance to NaCl. Significant accumulation of H₂O₂ was observed in all the tested plants upon their exposure to 255 mM NaCl. The activity of both CAT and SOD increased significantly in response to the NaCl treatment. Growing the plants in presence of 255 mM NaCl also resulted in the synthesis of new isoforms of both CAT and SOD.

A combination of directed amplification of minisatellite DNA (DAMD) and random amplification of polymorphic DNA (RAPD) primes were used to assess the genetic variation within and between three isolated populations of Indian sandalwood (Santalum album). Eleven primers used in this study amplified 65.99 % polymorphic bands. Analysis of molecular variance revealed a high genetic variation among these populations (ϕ_ST = 0.549). There are indications of clonality within the existing Indian sandalwood populations which can be attributed to habitat fragmentation, isolation and vegetative reproduction.

We isolated and characterized eleven polymorphic microsatellite loci for Aegiphila sellowiana an outcrossing pioneer tree species that is frequently used in reforestation programs of tropical riparian forests in Brazil. A total of 38 alleles were detected across a sample of 45 individuals of A. sellowiana, with an average number of 3.45 alleles per locus. The average polymorphic information content (PIC) was 0.430 and the observed (H_O) and expected (H_E) heterozygosity values varied from 0.156 to 1.000 and 0.145 to 0.730, respectively. Eight loci exhibited significant deviation from Hardy-Weinberg equilibrium (P ≤ 0.001) and 32 pair combinations of loci showed significant linkage disequilibrium (P ≤ 0.001). All 11 primers were tested for cross amplification in 12 species belonging to the family Lamiaceae and 5 species belonging to the related family Verbenaceae. The sequence and diversity information obtained using these microsatellites and their cross-transferability to other species of Lamiaceae as well as Verbenaceae will increase our understanding of genetic structures and species relationships within Aegiphyla and other genera of these families.

Seeds of pearl millet [Pennisetum glaucum (L). R.Br.] susceptible cv. 7042S were treated with thiamine at 5, 10, 15, 20 and 25 mM concentrations and growth promotion and downy mildew resistance were tested. Seed treatment with 20 mM thiamine resulted in 72 and 70 % disease protection under greenhouse and field conditions, respectively, and enhanced vegetative and reproductive growth parameters. Analysis of lipoxygenase (LOX) activity in inoculated pearl millet seedlings at different time intervals indicated that increased LOX activity was initiated at 3 h after inoculation (hai) and maximum activity was observed at 24 hai. Northern analysis showed that LOX mRNA transcript accumulation was higher in the resistant seedlings (cv. IP18292) than in susceptible seedlings. Thiamine seed treatment induces rapid LOX gene expression and results in significant disease protection against downy mildew disease.

Plants are subjected to several abiotic stresses that adversely affect growth, metabolism and yield. The dynamic research in plant genetics complemented by genome sequencing has opened up avenues to address multiple problems caused by abiotic stresses. Though many drought-induced genes have been phytoengineered in a wide range of plants, the drought signal transduction pathways, and the alteration of plant sensing and signaling systems to adverse environments still remain an intriguing subject for comprehensive investigation. To impart enhanced drought tolerance in plants, a thorough perception of physiological, biochemical and gene regulatory networks is essential. Recent functional genomics tools have facilitated the progress in our understanding of stress signaling and of the linked molecular regulatory networks. This has revealed several stress-inducible genes and various transcription and signaling factors that regulate the drought stress-inducible systems. Translational genomics of these drought specific genes using model plants have provided encouraging outcomes, but the in-depth knowledge of the specific roles of various metabolites in plant stress tolerance will lead to evolvement of strategies for the phytoengineering of drought tolerance in plants in future.

Four mutants induced by ethylmethane sulphonate (N22-H-dgl56, N22-H-dgl101, N22-H-dgl162 and N22-H-dgl219) with conspicuous dark green leaves were identified in the drought and heat-tolerant rice cultivar Nagina22 (N22), when screened under prolonged drought and heat conditions in field. During dark-induced senescence, these mutants maintained higher chlorophyll and carotenoid contents, and photochemical efficiency of photosystem 2 in comparison with N22. Following heat treatment, these mutants accumulated less reactive oxygen species (assayed by histochemical staining for H₂O₂ and superoxide radicals) and maintained higher chlorophyll content than N22.

The paper reports the in vitro cultivation of two commercial lines and 23 wild populations (with 10, 20 and 30 chromosomes) of Brachypodium distachyon. Callus induction was assayed on Murashige and Skoog medium containing 1 mg dm^-3 2,4-dichlorophenoxyacetic acid (2,4-D) with 30 g dm^-3 of sucrose (MSs) or maltose (MSm). No significant differences were seen between the two media with respect to callus induction. Calli were transferred to MSm medium without 2,4-D but containing 0.1 mg dm^-3 of 6-benzylaminopurine for plant regeneration. The plant regeneration response was very variable depending on the original induction medium, although no overall preference for one or the other medium was seen. The three main culture stages (callus induction, plant regeneration, and green plantlets formation) are probably differently controlled in the plants with different chromosome numbers. This supports the idea that the three cytotypes of Brachypodium cultured actually belong to different species.

RFLP analysis of a cDNA probe SLG6, governing self incompatibility (SI) in Brassica oleracea, using a recombinant inbred population of Brassica campestris followed by genetic linkage analysis led to the detection of two marker loci, SLG6a and SLG6b controlling SI. SLG6a was mapped in linkage group (LG) 9 and was flanked by the RFLP markers ec4f10 (6.4 cM) and wg5b9 (4.2 cM). SLG6b positioned in LG 2 and was flanked by the RFLP markers wg2d11 (9.9 cM) and ec4e7 (26.9 cM). These results indicated the scope of marker-aided introgression of these genes into self-compatible genotypes for production of SI lines suitable for hybridization in B. campestris. Comparative mapping of LG 9 containing SLG6b with corresponding linkage groups of B. oleracea (BO 2) and B. napus (BN 16) led to the detection of small homologous regions with SLG6 locus linked with another RFLP locus. This evidenced for homology of the SLG genes across Brassica species and possibility of using any single cloned SLG gene for development of SI lines in any Brassica species.

A reproducible in vitro regeneration system for Nepalese kutki (Picrorhiza scrophulariiflora Pennell) was developed from in vitro leaf derived callus. Induction of more than seven shoot buds per explant was achieved on Woody plant medium (WPM) supplemented with 0.53 μM α-napthaleneacetic acid (NAA) and 0.23 μM kinetin (KIN). The shoots were elongated on WPM supplemented with 0.44 μM 6-benzylaminopurine (BAP) and rooted on WPM supplemented with 5.3 μM NAA within 2 weeks. The random amplified polymorphic DNA (RAPD) analysis indicated genetic uniformity of the micropropagated plants with its donor plants.

Cucumber plants were either self-grafted or grafted onto two salt-tolerant pumpkin rootstocks Chaojiquanwang (Cucurbita moschata Duch), and Figleaf Gourd (Cucurbita ficifolia Bouche). Plants were grown hydroponically in 0, 30, 60, or 90 mM NaCl for 16 d in greenhouse. Salinity induced a smaller decrease in plant shoot dry mass, leaf area, net photosynthetic rate, and stomatal conductance in the two rootstock-grafted plants compared to the self-grafted plants. In addition, a significant increase in intercellular CO₂ concentration, as well as a significant decrease in the initial and total ribulose-1,5-bisphosphate carboxylase/oxygenase activities were observed only in the self-grafted plants under 90 mM NaCl treatment. These results suggest that the use of salt tolerant rootstock can improve cucumber photosynthetic capacity under salt stress through both stomatal and non-stomatal pathways.

The primary objective of this work was to investigate the role of polyamines (PAs) on root formation and growth in two sweet orange (Citrus sinensis L. Osb.) cultivars Pineapple and Pêra. Adventitious shoots (30-d-old) derived from epicotyl explants were transferred to root induction medium containing Murashige and Skoog salts at different strengths and supplemented with different concentrations and combinations of auxins. Root formation and development decreased in both sweet orange cultivars concomitant with the reduction of medium strength. The α-naphtaleneacetic acid was important during the root differentiation phase, but its combination with indole-3-butyric acid was essential for root elongation. The addition of PAs significantly improved root formation and/or growth, depending on their concentration, whereas the presence of inhibitor of PAs biosynthesis α-difluoromethylornithine (DFMO) inhibited these processes. The rooting impairment caused by DFMO was partially reversed by the supplementation of putrescine. Aminoethoxyvinylglycine AVG and AgNO₃ also inhibited in vitro rooting in both sweet orange cultivars, indicating that ethylene was likewise important for rhizogenesis in sweet orange.

Lettuce plants were treated with gibberellic acid (GA₃) and uniconazole (UZ; a gibberellin synthesis inhibitor) to investigate the influence of GA₃ on cell division frequency in the shoot apical meristem (SAM) during stem elongation and flower initiation in lettuce (Lactuca sativa) grown in a greenhouse. GA₃ (0.1 mM) was sprayed on the surface of outer leaves and uniconazole solution (0.86 mM) was applied to the soil. GA₃ increased cell division frequency in the peripheral zone and the rib meristem of shoot apices, and this was associated with the stimulation of stem elongation. UZ treatment decreased cell division frequency in the peripheral zone, rib meristem and subapical pith, and this was associated with restricted stem elongation. Treatment with UZ and GA₃ together induced minor stem elongation. Flower induction occurred 3 d earlier in the GA₃ and UZ+GA₃ treatments than in the control, while the UZ treatment delayed flower initiation for more than 9 d relative to the control.

Thirteen genomic microsatellite (gSSR) and sixteen expressed sequence tag (EST)-SSR (eSSR) markers were compared to estimate genetic diversity among 29 cucumber (Cucumis sativus L.) accessions. gSSR markers detected mean 4.46 alleles with a mean polymorphic information content (PIC) of 0.664, against eSSR markers with mean 3.38 alleles and a mean PIC of 0.397. gSSRs amplified more null alleles than eSSRs. Genetic diversity within the accession set was estimated by construction of dendrograms using gSSR or eSSR data. There was a clear consistency between gSSR and eSSR trees in terms of positioning of most cucumber germplasms. gSSR markers could separate various types of cucumber germplasms on the whole, although clustering of some accessions was not based on their geographical origins in eSSR tree. eSSR markers identified an independent sub-cluster containing five accessions resistant to downy mildew, suggesting a probable relationship between eSSRs and disease-resistance trait in cucumber. The Mantel test between gSSR and eSSR matrices revealed a good fit correlation (r = 0.836). The general dendrogram constructed using the combined data of gSSRs and eSSRs was similar to those obtained separately with each marker.

A novel gene induced during hypersensitive reaction (HIR) in wheat was identified using in silico cloning and designated as TaHIR2. The TaHIR2 gene was deduced to encode a 284-amino acid protein, whose molecular mass and isoelectric point (pI) were 31.05 kD and 5.18, respectively. Amino acid sequence analysis demonstrated the presence of stomatins, prohibitin, flotillins, HflK/C (SPFH) domain and prohibitin homologue for the TaHIR2 protein. Phylogenetic analysis of 13 HIR genes from different monocots indicated that TaHIR2 was highly homologous to HvHIR2. Transient expression analysis using particle-mediated bombardment showed that the TaHIR2 fusion protein was located in the onion epidermal cells. Quantitative RT-PCR analyses revealed that TaHIR2 transcripts were significantly accumulated in adult wheat leaves with maximum induction at 18 h post inoculation with the stripe rust, whereas slightly up-regulation could also be observed in the compatible reaction at the seedling stage. These results suggest that TaHIR2 may play an active role in wheat defense against stripe rust.

Turnip (Brassica rapa L.) plants were grown in Perlite with low (< 2.5 μM) or adequate (25 μM) boron supply under well-watered and drought conditions for 12 weeks. Dry mass of leaves and roots was reduced under drought by about 61 and 56 % in plants supplied adequately with B, while up to 84 and 74 % under B starvation. Drought reduced B content by about 70 and 82 % for B-sufficient and B-deficient plants, respectively. According to the chlorophyll fluorescence parameters, the photosynthesis processes conserved their normal activities under low B supply in well-watered plants, while a serious damage to photosystem 2 occurred under drought stress. Stomatal limitation was the most important cause for a 17 % lower net photosynthetic rate (P_N) of drought stressed B-sufficient plants. In B-deficient plants, however, both stomatal and non-stomatal limitations were involved in 53 % reduction of P_N. Low B supply reduced strongly leaf water potential.

This work was performed to find out if metal resistant clones of Salix viminalis L. are capable to achieve high resistance to the metals by regulating their net accumulation. Salix clones with low or high resistance in combination with low or high accumulation capacity of either Zn or Cd were cultivated from cuttings in nutrient solution. The investigation included leakage and uptake experiments using ⁶⁵Zn or ¹⁰⁹Cd and analysis of root cation exchange capacity (CEC). Some plants were pre-treated with unlabeled 0.5 μM Cd or 2.5 μM Zn 24 h prior to the experiments to induce possible tolerance mechanisms. To find out if the regulation was a metabolic process, experiments were also performed with 2,4-dinitrophenol (DNP). Clones with high resistance and low Cd accumulation had higher efflux of Cd compared to the other clones, in both untreated and Cd pre-treated plants. This indicates a constitutive property to lower Cd accumulation by high Cd leakage. Pre-treatment with 0.5 μM Cd diminished the Cd net uptake to a level near zero in all clones, likely to be due to decreased the Cd uptake. In contrast, resistant clones with high Cd accumulation had the highest root CEC, which may be used to bind up Cd in the free space. No clear regulation of Zn net uptake was found in Zn-resistant clones. Pre-treatment with Zn decreased the uptake of Zn into the free space in Zn-resistant clones. The resistant high-accumulating clones, however, showed the highest leakage of Zn in both untreated and pre-treated plants, a constitutive process not related to high accumulation. Neither the influx nor the efflux of Cd or Zn was affected by DNP indicating passive transport across the plasma membrane.

Floral initiation in apple (Malus domestica Borkh) was studied by a novel morphogenetic approach. Developmental stages of apices were evaluated based on the morphology of shoot apical meristem (SAM) from various collection dates. Besides, the frequency of each stage was calculated within apices populations after full blooming (DAFB). Prior to doming of apex, three marked phases were found based on SAM morphology: 1) narrow appearance (vegetative phase), 2) broadened form (transition phase), and 3) prominent shape (commitment phase). A furrow region was formed at the base of leaf primordium during the bract initiation, while significant broadening of SAM was observed. Cell division patterns manifested in modification of anisotropic clusters from isotropic cellular packets, as a result of which profound morphological changes of apices occurred. Based on these findings, we propose that the structural alterations prior to doming may be taken into account for determination of the initial development and reproduction signs in apple trees.

Polygalacturonases are enzymes involved in plant cell wall growth and reorganization. Transgenic Arabidopsis thaliana plants with a Saccharomyces cerevisiae endopolygalacturonase gene (PGU1) were obtained. The yeast gene was properly expressed in the plants as it has been shown by RT-PCR as well as by the increase in the endopolygalacturonase activity. The transgenic plants showed conspicuous malformations in early stages of development probably due to a weak cell adhesion. On the other hand, adult plants exhibited almost no phenotypic differences as compared to the wild type plants, this suggesting the appearance of some mechanisms on the plant side to counteract the effect of the overexpressed polygalacturonase.

cDNA-AFLP fingerprinting was used to identify genes with modulated expression during germination in common bean (Phaseolus vulgaris L.). The analysis was performed on the embryo axes. Nine time points covering the whole germination were considered and 800 transcript-derived fragments (PvTDFs) were scored. Among them, 80 % showed no changes during germination. The 97 PvTDFs showing differential expressions during germination were sequenced along with 14 constant transcripts that were randomly chosen. The expression of seven variable PvTDFs was confirmed by real-time RT-PCR. We observed that 92 % of the transcript changes, including 35 % of appearing mRNAs, took place before radicule protrusion, 0-17 h after imbibition (HAI). A major shift in gene expression was observed between 9 and 14 HAI, suggesting a key moment of cell re-programming. Sequence homologies were found for 52 % of the sequenced PvTDFs. The identified transcripts encode proteins belonging to several functional groups including transcription factors, proteins involved in storage compound hydrolysis, cell elongation or oxidative stress protection.

A high frequency plant regeneration system was developed for the production of high yielding elite clones of Garcinia indica via direct organogenesis. A maximum number of 86.2 shoot buds per explant were induced from the mature seed segments cultured on Woody plant medium (WPM) supplemented with 2.0 mg dm^-3 N⁶-benzyladenine and 1 mg dm^-3 indole-3-acetic acid. Rooting was achieved on half-strength WPM medium supplemented with 3 mg dm^-3 indole-3-butyric acid. Rooted plantlets were acclimatized and transferred to greenhouse for further growth. The highest survival rate of 95 % was recorded using a mixture of garden soil and sand. Histological studies clearly revealed multiple shoot formation from mature seed segments.

We study apical dominance in Alstroemeria, a plant with an architecture very different from the model species used in research on apical dominance. The standard explant was a rhizome with a tip and two vertically growing shoots from which the larger part had been excised leaving ca. 1 cm stem. The axillary buds that resumed growth were located at this 1-cm stem just above the rhizome. They were released by removal of the rhizome tip and the shoot tips. Replacement of excised tips by lanolin with indole-3-butyric acid (IBA) restored apical dominance. The auxin transport inhibitors 2,3,5-triiodobenzoic acid (TIBA) and N-1-napthylphthalamic acid (NPA) reduced apical dominance. 6-Benzylaminopurine (BAP) enhanced axillary bud outgrowth but the highest concentrations (> 9 μM) caused fasciation. Thidiazuron (TDZ) did not show improvement relative to BAP. Even though the architecture of Alstroemeria and the model species are very different, their hormonal mechanisms in apical dominance are for the greater part very similar.

Microtubule cytoskeleton organization during microspore mother cell (MMC) meiosis in Allium cepa L. and microsporogenesis in Nicotiana tabacum L. was examined. The MMC microtubules (MTs) were short and well dispersed in the cytoplasm of both taxa. As the MMCs of both species entered metaphase of meiosis I, the MTs constructed a spindle that facilitated the chromosomes to orient in the meridian plane. At anaphase of meiosis I, the spindle MTs differentiated into two types: one MT type became short, pulled the chromosomes toward the two poles, and was designated as centromere MTs; the second type of MT connected the two poles, and was designated as pole MTs. In A. cepa, where successive cytokinesis was observed, pole MTs assumed a tubbish shape. Some new short MTs aggregated in the meridian plane and constricted to form a phragmoplast, which developed into a cell plate, divided the cytoplasm into two parts and produced a dyad. However, in tobacco, a phragmoplast was not generated in anaphase of meiosis I and II and cytokinesis did not occur. The spindle MTs depolymerized and reorganized the radial arrangement of MTs from the nucleate surface to the periplasm during anaphase. Following telophase of meiosis II, the cytoplasm produced centripetal furrows, which met in the center of the cell and divided it into four parts, serving as a form of cytokinesis. In this process, MTs appeared to bear no relationship to cytokinesis.