Axillary Shoot Formation Research Articles

The wheat durable, multipathogen resistance gene Lr34 confers partial blast resistance in rice.

The wheat gene Lr34 confers durable and partial field resistance against the obligate biotrophic, pathogenic rust fungi and powdery mildew in adult wheat plants. The resistant Lr34 allele evolved after wheat domestication through two gain-of-function mutations in an ATP-binding cassette transporter gene. An Lr34-like fungal disease resistance with a similar broad-spectrum specificity and durability has not been described in other cereals. Here, we transformed the resistant Lr34 allele into the japonica rice cultivar Nipponbare. Transgenic rice plants expressing Lr34 showed increased resistance against multiple isolates of the hemibiotrophic pathogen Magnaportheoryzae, the causal agent of rice blast disease. Host cell invasion during the biotrophic growth phase of rice blast was delayed in Lr34-expressing rice plants, resulting in smaller necrotic lesions on leaves. Lines with Lr34 also developed a typical, senescence-based leaf tip necrosis (LTN) phenotype. Development of LTN during early seedling growth had a negative impact on formation of axillary shoots and spikelets in some transgenic lines. One transgenic line developed LTN only at adult plant stage which was correlated with lower Lr34 expression levels at seedling stage. This line showed normal tiller formation and more importantly, disease resistance in this particular line was not compromised. Interestingly, Lr34 in rice is effective against a hemibiotrophic pathogen with a lifestyle and infection strategy that is different from obligate biotrophic rusts and mildew fungi. Lr34 might therefore be used as a source in rice breeding to improve broad-spectrum disease resistance against the most devastating fungal disease of rice.

Axillary Meristem Formation in Rice Requires the WUSCHEL Ortholog TILLERS ABSENT1.

Axillary shoot formation is a key determinant of plant architecture. Formation of the axillary shoot is regulated by initiation of the axillary meristem or outgrowth of the axillary bud. Here, we show that rice (Oryza sativa) TILLERS ABSENT1 (TAB1; also known as Os WUS), an ortholog of Arabidopsis thaliana WUS, is required to initiate axillary meristem development. We found that formation of the axillary meristem in rice proceeds via a transient state, which we term the premeristem, characterized by the expression of OSH1, a marker of indeterminate cells in the shoot apical meristem. In the tab1-1 (wus-1) mutant, however, formation of the axillary meristem is arrested at various stages of the premeristem zone, and OSH1 expression is highly reduced. TAB1/WUS is expressed in the premeristem zone, where it shows a partially overlapping pattern with OSH1. It is likely, therefore, that TAB1 plays an important role in maintaining the premeristem zone and in promoting the formation of the axillary meristem by promoting OSH1 expression. Temporal expression patterns of WUSCHEL-RELATED HOMEOBOX4 (WOX4) indicate that WOX4 is likely to regulate meristem maintenance instead of TAB1 after establishment of the axillary meristem. Lastly, we show that the prophyll, the first leaf in the secondary axis, is formed from the premeristem zone and not from the axillary meristem.

Pogostemon cablin (Blanco) Benth. (Lamiaceae): It’s Ethnobotany & in vitro regeneration

Objectives: Since the beginning of human civilization various herbal medicines are employed for healing human and animal. Pogostemon cablin (Blanco) Benth., locally known as Patchouli (Assamese) is a very important medicinal plants belongs to mint family i.e. Lamiaceae. The main aim of this study was to collect ethnobotanical information’s and to study its in vitro regeneration results. All possible ethnobotanical literatures have been cited here. Methods: In vitro propagation was achieved from leaf and nodal explants of Pogostemon cablin on MS medium. Results: Callus development and in vitro axillary shoot formation was successfully made in MS basal medium containing BA (4.0 mg/L), NAA (2.0 mg/L)+ IAA (1.0 mg/L) and BA (3 mg/L)+IAA (1 mg/L). MS basal medium containing IBA (0.1/L) and Kn (2.5 mg/L) was best for induction of multiple shoots within 4 weeks of culture. Combination of NAA (0.1 mg/L). Kn (0.1 mg/L) and CH (100 mg/L) was best for callus induction which later on formed multiple shoots and caused elongation of roots. Micro shoots of varied length were produced on MS medium. Rooted plantlets were successfully acclimatized in green house for 1 month and then were transferred to the field. Conclusion: It can be concluded that pogostemon cablin has immense ethno botanical importance. For its rapid multiplication, in vitro technique was found very successful. In MS medium supplemented with Kn 2.5 mg/L and IBA 0.1mg/L found maximum multiplication rate. In this proportion rates of shoot generation, leaf, rooting, callus formation was maximum.

In vitro Axillary Shoot Regeneration and Direct Protocorm-like Body Induction from Axenic Shoot Tips of Doritis pulcherrima Lindl.

An efficient protocol for in vitro propagation of an important ornamental terrestrial orchid, Doritis pulcherima Lindl. through axillary shoot and direct protocorm-like body (PLB) formation from shoot tip explants derived from six- month-old axenic seedlings has been described. Shoot tips were cultured on modified nutrient medium of Knudson’s C supplemented with 0.1% peptone and combination of various concentrations of NAA and BAP. The effect of NAA and BAP on axillary shoot formation, protocorm-like body induction and root regeneration from the explants was significant. The highest frequency of axillary shoot formation was recorded in the medium containing 2 mg/l BAP and the PLB production was higher in the medium containing 2 mg/l NAA. A higher concentration of BAP showed inhibitory effects on the axillary shoot formation and PLB induction. Efficient root regeneration was observed in low concentration of NAA. However, the profuse root formation was common in the PGR free medium. Rooted plantlets were hardened successfully through the stepwise acclimation protocol and platelets were finally established in the potting mixture containing small pieces of dead tree bark of mango, charcoal pieces and broken bricks in 1 : 2 : 1 ratio. D. O. I. http://dx.doi.org/10.3329/ptcb.v23i2.17526 Plant Tissue Cult. & Biotech. 23(2): 251-261, 2013 (December)

Effect of plant growth regulators on growth patterns and enzymatic antioxidant activities in Hypericum calycinum shoot cultures

TRENEVA, G., Y. MARKOVSKA, E. WOLFRAM and K. DANOVA, 2014. Effect of plant growth regulators on growth patterns and enzymatic antioxidant activities in Hypericum calycinum shoot cultures. Bulg. J. Agric. Sci., Supplement 1: 46–50 Hypericum calycinum L. (section Ascyreia) is a species of the Hypericum genus, relative to the medicinal plant H. perforatum (St. Jonn’s worth). Unlike the widely studied H. perforatum, it is characterized by the lack of hypericins production. However, research has revealed its commensurable antidepressant activity, as compared with the latter species, and shown the presence of polyphenolics with marked radical scavenging activity. In order to develop an in vitro system with the potential of a novel source of bioactive constituent’s characteristic for the Hypericum genus, we initiated in vitro cultures of H. calycinum. In the present work we studiy the effect of exogenous BA and IBA treatments on the developmental patterns, enzymatic and non-enzymatic antioxidant defence of hypericin non-producing Hypericum calycinum shoot cultures. It was shown that supplementation of PGR led to stimulation of phenylalanine ammonia-lyase and superoxide dismuthase, as well as non-enzymatic antioxidant glutathione. However, they inhibited glutathione reductase, as well as lowered the levels of fl avonoids, ascorbate and dehydroascorbate in comparison with plant growth regulators-free control. Further on, it was established that elevation of IBA concentration slightly stimulated axillary shoot formation and shoot length, but inhibited polyphenolic levels in vitro. These results are in agreement with our previous results of interrelations between biomass formation and polyphenolics production in other Hypericum species in vitro. An in vitro culture system optimization is in progress in order to increase biomass production and retain biosynthetic capacity of the species. Abbreviations: BA – benzyl adenine, IBA – indole-3-butyric acid, PGR – plant growth regulators, DPPH 2,2-diphenyl-1-picrylhydrazyl, NO – nitric oxide, BAS – Bulgarian Academy of Sciences, PAL – Phenylalanine ammonia-lyase, SOD – superoxide dismuthase, GR – glutathione reductase, APX – ascorbate peroxidase, CAT – catalase, AsA – ascorbate, DHA – dehydrosacorbate, GSSG – oxidized glutathione, GSH – reduced glutathione, NADPH – Reduced nicotinamide adenine dinucleotide phosphate, KH 2 PO 4 – potassium phosphate monobasic, MgCl 2 – magnesium chloride, EDTA – Ethylenediaminetetraacetic acid, NaAA – sodium ascorbate, H 2 O 2 – hydrogen peroxide, DTNB – 5,50-dithiobis – (2-nitrobenzoic acid).

The impact of three bacteria isolated from contaminated plant cultures on in vitro multiplication and rooting of microshoots of four ornamental plants

ABSTRACT The strains of bacteria Paenibacillus glucanolyticus, Curtobacterium pusillum and Methylobacterium extorquens were isolated as non-deleterious contaminations from hosta or raspberry tissue cultures. Microshoots of chrysanthemum, gerbera, hosta and rose were inoculated with these bacteria and their influence on shoot multiplication and rooting was evaluated. None of the investigated bacteria caused symptoms of hypersensitivity or vitropathy on the shoot explants at rooting and shoots multiplication. C. pusillum stimulated axillary shoot formation in all studied plant genotypes. Length and number of rose roots and their length were higher but number of roots and their length in chrysanthemum were lower in inoculated than in controls. The number and the length of shoots and roots in gerbera and hosta and the number of shoots in chrysanthemum inoculated with M. extorquens were higher but shoot length of chrysanthemum and rose, and root length of rose were lower as compared with controls. P. glucanolyticus influenced higher number and length of chrysanthemum shoots and root length of chrysanthemum and gerbera than noninoculated control but the number of gerbera and hosta roots was lower and root length of rose was as low as 0.2 cm. All assessed bacteria were able to assimilate atmospheric nitrogen and M. extorquens and P. glucanolyticus were able to produce IAA.

Fundamentals and applications of light-emitting diodes (LEDs) in in vitro plant growth and morphogenesis

Advances in plant tissue culture methods with regard to lighting requirements are currently focused on the improved features of light-emitting diodes (LEDs). Over the years, the steady development of LED technology, with the emergence of new types of semi-conductor materials, has made it possible to apply it in an increasing number of new areas. As an alternative to conventional lighting systems, LED has been demonstrated to be an artificial flexible lighting source for plant tissue culture. Numerous studies have been conducted in order to investigate the effects of LED on plants, which have led to many satisfactory results. Various morphological, anatomical, and physiological attributes, such as shoot elongation, axillary shoot formation, somatic embryo induction, rhizogenesis, leaf anatomy, and photosynthetic abilities of plants grown in vitro have found to be regulated by spectral properties of LEDs. The present review gives an overview of the fundamentals of LEDs and describes their effects on in vitro plant growth and morphogenesis and their future potentials.

Conservation through in vitro propagation and restoration of Mahonia leschenaultii, an endemic tree of the Western Ghats

Conservation of Mahonia leschenaultii was achieved through multiple axillary shoot formation in single node cultures, in vitro and ex vitro rooting of the shoots, and successful reintroduction and establishment of the rooted plants in the forests of Palani hills in Southern India. A preliminary experiment on the culture of young nodal explants (1.0-1.5 cm) from field-grown plants in different basal nutrient media revealed high frequency bud beak in Schenk and Hildebrandt (SH) medium followed by Woody Plant medium and Murashige Skoog medium in 4 weeks. Subsequent culture of both shoot tips (0.5-0.8 cm) and nodes for 6 weeks in SH medium supplemented with various concentration of cytokinins resulted in optimal formation of 3.6 shoots in 80% of the nodes against 1.35 shoots in 75% of the shoot tips in the presence of 2.0 and 1.0 mg/l benzyl adenine (BA), respectively. Invariably, the resident apical and axillary meristems grew into a single shoot (1.0-1.8 cm) in 1-2 weeks followed by the characteristic differentiation of additional buds from its base. A synergistic combination of 1.0 mg/l BA and 0.02 mg/l indole-3-acetic acid (IAA) induced the maximum number (5.9) of axillary shoot formation which were relatively high (75%) when the explant was collected during May-June and the fifth nodes from the top of the growing shoots were used. Repeated subculture of the nodes from shoot cultures at 5-6 week intervals in medium supplemented with reduced concentrations of the growth regulators (0.5 mg/l BA, 0.01 mg/l IAA) through at least 10 passages enabled consistent production of 6-7 shoots per node at 92% success rate without loss of vigour, growth and morphological abnormalities. Shoots of 3-6 cm were rooted in vitro in the presence of 1.0 mg/l indole-3-butyric acid (IBA) and hardening in the mist house at 76-78% and these rooted plants established in a potting medium of river sand and top soil (1:1) under constant mist irrigation. The plants reared in the nursery for 5-8 weeks were successfully reintroduced into the natural forest segment of the Institute's campus (MSL 200 m) at Palode and Vattakanal shola forests of Palani hills (MSL 2500 m) with establishment frequencies of 78.8 and 90.6, respectively, after 18 months. Growth characteristics of the plants (height, number of leaves and branches) reintroduced into native habitat at Vattakanal were better than those at Palode. Genetic fidelity of the 12-month old plants established in the nursery/field was confirmed by analysis of amplified products of genomic DNA obtained with random primers.

Mutation of the cytosolic ribosomal protein-encoding RPS10Bgene affects shoot meristematic function in Arabidopsis

BackgroundPlant cytosolic ribosomal proteins are encoded by small gene families. Mutants affecting these genes are often viable, but show growth and developmental defects, suggesting incomplete functional redundancy within the families. Dormancy to growth transitions, such as the activation of axillary buds in the shoot, are characterised by co-ordinated upregulation of ribosomal protein genes.ResultsA recessive mutation in RPS10B, one of three Arabidopsis genes encoding the eukaryote-specific cytoplasmic ribosomal protein S10e, was found to suppress the excessive shoot branching mutant max2-1. rps10b-1 mildly affects the formation and separation of shoot lateral organs, including the shoot axillary meristems. Axillary meristem defects are enhanced when rps10b-1 is combined with mutations in REVOLUTA, AUXIN-RESISTANT1, PINOID or another suppressor of max2-1, FAR-RED ELONGATED HYPOCOTYL3. In some of these double mutants, the maintenance of the primary shoot meristem is also affected. In contrast, mutation of ALTERED MERISTEM PROGRAMME1 suppresses the rps10b-1axillary shoot defect. Defects in both axillary shoot formation and organ separation were enhanced by combining rps10b-1 with cuc3, a mutation affecting one of three Arabidopsis NAC transcription factor genes with partially redundant roles in these processes. To assess the effect of rps10b-1 on bud activation independently from bud formation, axillary bud outgrowth on excised cauline nodes was analysed. The outgrowth rate of untreated buds was reduced only slightly by rps10b-1 in both wild-type and max2-1 backgrounds. However, rps10b-1 strongly suppressed the auxin resistant outgrowth of max2-1 buds. A developmental phenotype of rps10b-1, reduced stamen number, was complemented by the cDNA of another family member, RPS10C, under the RPS10B promoter.ConclusionsRPS10B promotes shoot branching mainly by promoting axillary shoot development. It contributes to organ boundary formation and leaf polarity, and sustains max2-1 bud outgrowth in the presence of auxin. These processes require the auxin response machinery and precise spatial distribution of auxin. The correct dosage of protein(s) involved in auxin-mediated patterning may be RPS10B-dependent. Inability of other RPS10 gene family members to maintain fully S10e levels might cause the rps10b-1 phenotype, as we found no evidence for unique functional specialisation of either RPS10B promoter or RPS10B protein.

Synergistic effect of trimethoprim and bavistin for micropropagation of Bacopa monniera

A micropropagation protocol for Bacopa monniera (L.) Wettst., a medicinally important plant, has been developed. Direct organogenesis without callus formation was induced by culturing node, internode and leaf explants on growth regulator free Murashige and Skoog (MS) medium. MS medium supplemented with an antibiotic trimethoprim (TMP) and a fungicide bavistin (BVN) produced axillary shoots from node and adventitious shoot buds on the surface of all explants. The combination of 200 mg dm−3 TMP and 200 mg dm−3 BVN induced the optimum frequency of shoot formation as well as shoot number. Presence of both TMP and BVN induced multiple axillary shoot formation from the nodal segments and this ability was maintained for four subcultures.

Influence of Root Zone Calcium on Shoot Tip Necrosis and Apical Dominance of Potato Shoot: Simulation of This Disorder by Ethylene Glycol Tetra Acetic Acid and Prevention by Strontium

The important roles of calcium on plant growth and development including cell division and cell elongation is well documented. The purpose of the present study was to determine the impact of root zone calcium on the growth and health of potato apical meristem and on the maintenance of apical dominance. For this purpose, single-node potato cuttings (Solanum tuberosum L. cv. Dark Red Norland) were grown in sterilized modified Murashige and Skoog (MS) media containing varying concentrations of calcium (1 to 3000 μM). After 13 to 30 d of growth, plantlets were harvested and data for height of the main shoot and for the number of axillary shoots produced were recorded. Plantlets were ashed and tissue calcium concentration was determined. Shoot height was retarded with decreasing concentration of calcium in the media. Calcium deficiency induced shoot tip injury and loss of apical dominance. Tip injury was followed by the development of axillary shoots. The number of axillary shoots increased from one to 21 as calcium concentration in the media decreased from 3000 to 1 μM. At calcium concentration of 1500 μM or higher, there was a single main shoot with no axillary shoots. Addition of ethylene glycol tetra acetic acid (EGTA), a calcium chelator, to the media with 2720 μM calcium (sufficient calcium) resulted in the development of shoot injury and in the formation of axillary shoots. Calcium deficiency injury symptoms were prevented by the addition of a calcium analog, strontium, to MS media deficient in calcium. Strontium has been reported to strongly bind to plant cell walls and the inclusion of strontium prevented injury in shoots of plants grown on calcium-deficient media. These results suggest that strontium is able to mimic the role of calcium in the maintenance of cell wall integrity and supports previous studies that showed that calcium deficiency results from cell wall collapse of the subapical cells.

Topophysic effects differ between node and organogenic cultures of the eucalypt Corymbia torelliana × C. citriodora

The eucalypt Corymbia torelliana × C. citriodora is planted widely in India, Brazil and Australia although plantation establishment has been limited by inadequate seed supply and low amenability to propagation via cuttings. This study optimised node culture and organogenic culture methods for in vitro propagation of Corymbia hybrids by identifying explant position (topophysic) effects on rooting, shoot elongation and shoot proliferation. Strong, negative morphogenic gradients in shoot elongation and proliferation capacity were evident from the cotyledonary node to the fourth or fifth node of seedlings when their nodes were transferred to node culture (without benzyladenine). These topophysic effects were related to differences in rooting capacity of individual nodes. Root formation in node culture was associated with formation of long multi-nodal axillary shoots, and so higher rooting of shoots from the cotyledonary node or first true-leaf node was associated with higher shoot proliferation. However, all nodes were equally capable of shoot proliferation in organogenic culture (with 2.2 μM benzyladenine), where rooting and rapid stem elongation did not occur. Most shoots (61–100%) from both node culture and organogenic culture were converted to plantlets, with plantlet conversion and primary root number not differing significantly among explant node positions. The strong topophysic effect in node culture, combined with the lack of a topophysic effect in organogenic culture, provides for an optimised clonal propagation system based on segregation of nodes from the same seedling into separate node and organogenic culture pathways.

Low level expression of prokaryotic tzs gene enhances growth performance of transgenic poplars

We modulated the level of a hormone gene expression in poplars using either 35S promoter (p35S) of cauliflower mosaic virus (CaMV) or aux promoter (pAUX) of A. rhizogenes. The transgenic poplars (Populus alba × P.tremula var. glandulosa), in which the bacterial trans-zeatin secretion (tzs) gene was attached either to the 35S promoter or to the aux promoter, were compared for their performance in tissue culture as well as in nursery. Northern blot analysis of total RNA probed with tzs coding region showed that the total tzs mRNA expression by p35S was approximately 200–300-fold higher than that driven by pAUX. In contrast, the cellular zeatin content of p35S-tzs transgenic poplars was merely 13-fold of those found in pAUX-tzs plants. Due to different levels of cellular zeatin levels, the two types of transgenic poplars showed different morphogenetic as well as growth responses. The p35S-tzs transgenic plants showed morphological characteristics typical of those treated with cytokinin in culture. These include multiple axillary shoot formation, thick stems, narrow leaves and absence of roots. In contrast, the pAUX-tzs plants had slightly higher cellular cytokinin levels than did control plants and showed a lower degree of cytokinin-related phenotypes, including a few axillary shoots in root-inducing media. Since p35S-tzs did not develop roots, only pAUX-tzs transgenic poplars could be transplanted to the nursery where they resumed a close-to-normal growth. Nevertheless, pAUX-tzs plants transferred to the nursery developed cytokinin-related phenotypes, including greater number of shoots, smaller leaves and slightly retarded growth in height, but with a high total biomass.

Adventitious shoot formation is not inherent to micropropagation of banana as it is in maize

Despite their similar morphology, banana and maize shoot tips responded strikingly different with respect to the in vitro formation of homogeneous multiple shoot clusters. While up to 50 small shoots per maize explant could be induced within 1 month, zero to one additional shoot formed starting from a banana shoot tip. Subsequently, banana shoot tips were subjected to different combinations of five cytokinins (0–100 μM) and five auxins (0–5 μM). The cytokinins thidiazuron and benzylaminopurine stimulated multiplication to a higher extent compared to zeatin, kinetin and isopentenyl adenine. The addition of indoleacetic acid, naphthalene acetic acid or indolebutyric acid to cytokinin containing medium did not affect the in vitro response. In contrast, 2,4-dichlorophenoxyacetic acid (1 and 5 μM) and a higher concentration of picloram (5 μM) had a detrimental effect on shoot formation and resulted in explant death and globule development. When small (0.1 cm) shoot tips were grown on cytokinin medium without an auxin source, the average number of shoots was generally two to three times lower compared to bigger (0.5 cm) shoot tips. Based on our experience in maize and this large-scale study with banana shoot tips, we conclude that banana is extremely recalcitrant towards adventitious shoot formation. This recalcitrance could not be overcome by any of the 173 different plant growth regulator combinations tested. In vitro multiplication of banana thus appears solely restricted to axillary shoot formation.

Micropropagation of Adenia goetzei Harms, an attractive caudiciform from Central Africa

Adenia goetzei is a plant with a decorative prominent caudex. An efficient micropropagation system based on axillary shoot formation and subsequent rooting was developed. By alternating culture on a medium with 5µM BAP (a modified Murashige & Skoog (1962) medium) and a medium without BAP (Krogstrup et al., 1988), a multiplication factor of 3.93 /- 1.16 (mean /- SD) was achieved every 6 weeks. Approximately 61 % of the micro-cuttings rooted following a 24 day 5µM IBA treatment and 80–85% of the plants were successfully transplanted to soil. The juvenile twining growth- and leaf form reverted to a form with adult characteristics after 1–2 growth periods in soil. Using this micropropagation protocol for A. goetzei, it has been possible to produce several hundred vigorous and true-to-type plants, except for irregularly shaped caudices in contrast to the regular ones seen in seedlings.

Thidiazuron-induced high-frequency axillary and adventitious shoot regeneration in Vigna radiata (L.) Wilczek

Abstract Prolific shoot regeneration was achieved in mungbean Vigna radiata (L.) Wilczek from 3-d-old in vitro cotyledonary node and hypocotyl explants from seedlings derived from mature seeds on Murashige and Skoog (MS) medium supplemented with thidiazuron (TDZ) (0.9 μM). An initial exposure to TDZ for 20 d and three successive transfers to fresh medium with reduced thidiazuron levels (0.09 μM) resulted in the regeneration of 104 shoots/explant from the cotyledon and 30 shoots/explant from the hypocotyl. Thidiazuron-associated abnormalities such as short compact shoots, fasciation and leaf growth in the form of rosettes were observed in shoots regenerated from hypocotyl explants. Both axillary and adventitious shoot formation from the explants were confirmed by histology. Through repetitive cycles of regeneration in the presence of TDZ, the number of shoots that could be obtained from the two explant classes within 80 d was significantly higher than with previous reports in mungbean.

Light effects on the growth and morphogenesis of potato(Solanum tuberosum) in vitro: A review

Growth, morphogenesis, and tuberization of potato tissuesin vitro are affected by light. Measurements of the various aspects of light that control development and growth of potato are outlined. Physical parameters like light sources, delivery of the light source, and the degradation of culture media by light are discussed. Irradiance, photoautotrophic growthin vitro, spectral wavelength, and photoperiod modify the responses of potato tissues in culture. Acclimatization of tissue culture plantlets, vegetative growth, and the production, quality, and dormancy of microtubers are modified by light. New light sources such as light-emitting diode (LED) lamps are becoming available forin vitro research and for micropropagation of potato. Pulsed or chopper light has the potential to save energy costs. Light effects on potato protoplasts, anther culture, virus eradication, andin vitro conservation are discussed. Potential new research areas are the effect of the spectral quality of light on regeneration of shoots and somatic embryosin vitro, end-of-day red and far-red light treatments, axillary shoot formation in cultured plantlets, and the use of LEDs. The influence of monochromatic spectral filters on growth and development of potatoes in tissue culture could potentially lead to improvements in productivity. The relationship between daily quantum light integral and photoperiod and their effects on growth and morphogenesis of the potato will provide some useful areas of research.

Mitigation of Ethylene-promoted Leaf Senescence by a Natural Lipid, Lysophosphatidylethanolamine

Mitigation of ethylene promoted leaf senescence by lysophosphatidylethanolamine (LPE) was studied. Micropropagated `Russet Burbank' potato (Solanum tuberosum L.,) plantlets were grown on MS media in sterile culture tubes. After 2 weeks of growth, tubes were sealed and ethylene gas was applied to obtain 5 nL·L–1 final concentration in the culture tubes. Observations and measurements were taken two weeks after ethylene injection. Potato plantlets treated with ethylene showed severe leaf senescence symptoms such as epinasty, lack of growth, yellowing and axillary shoot formation. These observations indicate that apical dominance has been lost with ethylene treatment. The same experiment was repeated with different concentrations of LPE in the MS medium. Inclusion of 50 or 100 mg·L–1 of LPE in the medium mitigated the damage normally caused by applied ethylene. Leaves of plantlets exposed simultaneously to LPE and ethylene had significantly higher chlorophyll content and more healthy leaves compared to plantlets grown on medium lacking LPE. Results of this study suggest that LPE may have the potential to retard ethylene-promoted leaf senescence and may mitigate ethylene induced loss in apical dominance of micropropagated potato plantlets.

Micropropagation of socotran fig, Dorstenia gigas schweinf. Ex Balf. F. —A threatened species, endemic to the island of Socotra, Yemen

As an alternative to seed propagation, and efficient micropropagation system based on axillary shoot formation and subsequent rooting was developed for the threatened and medicinal plant species Dorstenia gigas (Moraceae). Three different basal media were tested. For the best basal medium, a modified WPM medium, different concentrations of the carbohydrates sucrose, glucose, fructose and maltose were tested. The total number of shoots was not markedly affected. For all carbohydrates but maltose, however, there was a reduction in the number of normal, healthy shoots for carbohydrate concentrations greater than 14.6 mM for the disaccharides and 27.8 mM for the monosaccharides (i.e., approximately 5 gl−1). Using 14.6 mM (5 gl−1) sucrose it has been possible to produce vigorous and true-to-type plants with a multiplication factor of approximately 2.6 per 6 wk.

Establishing Tissue-cultured Sweetgum Plants in Soil

Methods to enhance sweetgum (Liquidambar styraciflua L.) in vitro axillary shoot formation and shoot establishment into soil are presented. Sweetgum shoots grown in an automated plant culture system (APCS) produced 400 to 500 shoots via axillary branching compared to only 40 shoots produced within Magenta vessels containing agar medium after 8 weeks of incubation. Vitrification was observed in as many as 80% of the axillary shoots produced in the APCS. A continuous carbon dioxide (CO2)-flow-through system was tested on both vitrified and non-vitrified sweetgum shoots transferred from the APCS to soil. One- and two-cm-long vitrified shoots were grown within CO2-flow-through system chambers and subjected to 350, 1500, 3000, 10,000, or 30,000 μL·L–1 (ppm) CO2 for 4 weeks. Administering 10,000 μL·L–1 CO2 improved culture survival and enhanced overall shoot and root growth compared to shoots grown under ambient atmosphere (i.e., 350 μL·L–1 CO2).