Fruit-specific lectins from banana and plantain

 One of the predominant proteins in the pulp of ripe bananas (Musa acuminata L.) and plantains (Musa spp.) has been identified as a lectin. The banana and plantain agglutinins (called BanLec and PlanLec, respectively) were purified in reasonable quantities using a novel isolation procedure, which prevented adsorption of the lectins onto insoluble endogenous polysaccharides. Both BanLec and PlanLec are dimeric proteins composed of two identical subunits of 15 kDa. They readily agglutinate rabbit erythrocytes and exhibit specificity towards mannose. Molecular cloning revealed that BanLec has sequence similarity to previously described lectins of the family of jacalin-related lectins, and according to molecular modelling studies has the same overall fold and three-dimensional structure. The identification of BanLec and PlanLec demonstrates the occurrence of jacalin-related lectins in monocot species, suggesting that these lectins are more widespread among higher plants than is actually believed. The banana and plantain lectins are also the first documented examples of jacalin-related lectins, which are abundantly present in the pulp of mature fruits but are apparently absent from other tissues. However, after treatment of intact plants with methyl jasmonate, BanLec is also clearly induced in leaves. The banana lectin is a powerful murine T-cell mitogen. The relevance of the mitogenicity of the banana lectin is discussed in terms of both the physiological role of the lectin and the impact on food safety. Received: 1 December 1999 / Accepted: 31 January 2000     

Light-harvesting complex II pigments and proteins in association with Cbr, a homolog of higher-plant early light-inducible proteins in the unicellular green alga Dunaliella

 Like higher plants, unicellular green algae of the genus Dunaliella respond to light stress by enhanced de-epoxidation of violaxanthin and accumulation of Cbr, a protein homologous to early light-inducible proteins (Elips) in plants. Earlier studies indicated that Cbr was associated with the light-harvesting complex of photosystem II (LHCII) and suggested it acted as a zeaxanthin-binding protein and fulfilled a photo-protective function (Levy et al. 1993, J. Biol. Chem. 268: 20892–20896). To characterize the protein-pigment subcomplexes containing Cbr in greater detail than attained so far, thylakoid membranes from Dunaliella salina grown in high light or normal light were solubilized with dodecyl maltoside and fractionated by isoelectric-focusing. Analysis of the resolved LHCII subcomplexes indicated preferred associations among the four LHCIIb polypeptides and between them and Cbr: subcomplexes including Cbr contained one or two of the more acidic of the four LHCIIb polypeptides as well as large amounts of lutein and zeaxanthin relative to chlorophyll a/b. After sucrose gradient centrifugation, Cbr free of LHCIIb polypeptides was detected together with released pigments; this Cbr possibly originated in subcomplexes dissociated in the course of the analysis. These results agree with the conclusion that Cbr is part of the network of LHCIIb protein-pigment complexes and suggest that the role played by Cbr involves the organization and/or stabilization of assemblies highly enriched in zeaxanthin and lutein. Such assemblies may function to protect PSII from photodamage due to overexcitation. Received: 6 August 1999 / Accepted: 23 November 1999     

Identification of a signal peptide for oryzacystatin-I

 A previously unidentified extension of an open reading frame from the genomic DNA of Japonica rice (Oryza sativa L.) encoding oryzacystatin-I (OC-I; access. M29259, protein ID AAA33912.1) has been identified as a 5′ gene segment coding for the OC-I signal peptide. The signal peptide appears to direct a pre-protein (SPOC-I; Accession No. AF164378) to the endoplasmic reticulum, where it is processed into the mature form of OC-I. The start codon of SPOC-I begins 114 bp upstream from that previously published for OC-I. A putative proteolytic site, which may yield a mature OC-I approximately 12 residues larger than previously described, has been identified within SPOC-I between Ala-26 and Glu-27. The signal peptide sequence was amplified by polymerase chain reaction using genomic DNA from O. sativa seedlings and ligated to the 5′ end of the truncated OC-I gene at the endogenous SalI site. Partially purified protein extracts from Escherichia coli expressing SPOC-I reacted with polyclonal antibodies raised against OC-I and revealed a protein of the expected molecular weight (15,355 Da). In-vitro translation of SPOC-I in the presence of microsomal membranes yielded a processed product approximately 2.7 kDa smaller than the pre-protein. Nicotiana tabacum L. cv. Xanthi plants independently transformed with the SPOC-I gene processed SPOC-I and accumulated the mature form of OC-I (approximately 12.6 kDa), which co-migrated with natural, mature OC-I extracted from rice seed when separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Received: 29 July 1999 / Accepted: 25 August 1999     

Conditional identification of phosphate-starvation-response mutants in Arabidopsis thaliana

Plants have evolved elaborate metabolic and developmental adaptations to low phosphorus availability. Biochemical responses to phosphate limitation include increased production and secretion of phosphate-acquisition proteins such as nucleases, acid phosphatases, and high-affinity phosphate transporters. However, the signal transduction pathways that sense phosphate availability and integrate the phosphate-starvation response in plants are unknown. We have devised a screen for conditional mutants in Arabidopsis thaliana (L.) Heynh. to dissect signaling of phosphate limitation. Our genetic screen is based on the facultative ability of wild-type Arabidopsis plants to metabolize exogenous DNA when inorganic phosphate is limiting. After screening 50,000 M2 seedlings, we isolated 22 confirmed mutant lines that showed severely impaired growth on medium containing DNA as the only source of phosphorus, but which recovered on medium containing soluble inorganic phosphate. Characterization of nine such mutant lines demonstrated an inability to utilize either DNA or RNA. One mutant line, psr1 (phosphate starvation response), had significantly reduced activities of phosphate-starvation-inducible isoforms of ribonuclease and acid phosphatase under phosphate-limiting conditions. The data suggest that a subset of the selected mutations impairs the expression of more than one phosphate-starvation-inducible enzyme required for utilization of exogenous nucleic acids, and may thus affect regulatory components of a Pi starvation response pathway in higher plants. Received: 23 September 1999 / Accepted: 10 November 1999     

The Lupinus albus class-III chitinase gene, IF3, is constitutively expressed in vegetative organs and developing seeds

 A cDNA fragment encoding a Lupinus albus. L. class-III chitinase, IF3, was isolated, using a cDNA probe from Cucumis sativus L., by in-situ plaque hybridization from a cDNA library constructed in the Uni-ZAP XR vector, with mRNAs isolated from mature lupin leaves. The cDNA had a coding sequence of 293 amino acids including a 27-residue N-terminal signal peptide. A class-III chitinase gene was detected by Southern analysis in the L. albus genome. Western blotting experiments showed that the IF3 protein was constitutively present during seed development and in all the studied vegetative lupin organs (i.e., roots, hypocotyls and leaves) at two growth stages (7- and 20-d-old plants). Accumulation of both the IF3 mRNA and IF3 protein was triggered by salicylic acid treatment as well as by abiotic (UV-C light and wounding) and biotic stress conditions (Colletotrichum gloeosporioides infection). In necrotic leaves, IF3 chitinase mRNA was present at a higher level than that of another mRNA encoding a pathogenesis-related (PR) protein from L. albus (a PR-10) and that of the rRNAs. We suggest that one role of the IF3 chitinase could be in the defense of the plant against fungal infection, though our results do not exclude other functions for this protein. Received: 15 March 1999 / Accepted: 12 July 1999     

Changes in carotenoids, tocopherols and diterpenes during drought and recovery, and the biological significance of chlorophyll loss in Rosmarinus officinalis plants

Two-year-old rosemary (Rosmarinus officinalis L.) plants were subjected to severe stress by exposure to prolonged drought during a Mediterranean summer. Severely stressed plants recovered completely after the autumn rainfalls although the relative water content remained below 35% for 3 months and the chlorophyll content of leaves was reduced by up to 85% during the drought. In severe stress: (i) α-tocopherol increased 9-fold per g dry weight and 20-fold per unit of chlorophyll; (ii) lutein and β-carotene contents decreased on a dry-weight basis, but an 80% increase in lutein and constant levels of β-carotene were observed on a chlorophyll basis; (iii) there were transient and sustained increases in the de-epoxidation state of the xanthophyll cycle; and (iv) the highly oxidised abietane diterpene isorosmanol increased 8-fold as a result of the oxidation of carnosic acid. With the autumn rainfalls, water status, α-tocopherol and violaxanthin recovered first and the levels of photosynthetic pigments and abietane diterpenes increased later. The photoprotection conferred by the xanthophyll cycle and the antioxidant function of tocopherols, lutein and diterpenes may help to avoid irreversible damage in severe drought, making possible the recovery of functional membranes after the autumn rainfalls. Besides, chlorophyll loss reduces the amount of photons absorbed by leaves, which enhances the photoprotective and antioxidant capacity of leaves per amount of photons absorbed, since the ratios of xanthophylls, α-tocopherol and abietane diterpenes to chlorophyll increase. Received: 12 July 1999 / Accepted: 25 November 1999     

Nitric oxide stimulates seed germination and de-etiolation, and inhibits hypocotyl elongation, three light-inducible responses in plants

Seed germination, greening of etiolated plants and inhibition of hypocotyl elongation are stimulated by light, which is sensed by various types of photoreceptor. Nitric oxide (NO) has proven to be a bioactive molecule, especially in mammalian cells and, most recently, in plants. Like some phytochrome-dependent processes, many NO-mediated ones are accomplished through increases in cGMP levels. Given these similarities, we proposed that NO could take part in light-mediated events in plants. Here we show that NO promotes seed germination and de-etiolation, and inhibits hypocotyl and internode elongation, processes mediated by light. Two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine induced germination of lettuce (Lactuca sativa L. cv. Grand Rapids) seeds in conditions in which this process is dependent on light (e.g. 26 °C). This was a dose-dependent response and was arrested by addition of an NO scavenger, carboxy-PTIO. In addition, nitrite and nitrate, two NO-decomposition products were ineffective in stimulating germination. Wheat seedlings sprayed with SNP and grown in darkness contained 30–40% more chlorophyll than control seedlings. Nitric-oxide-mediated partial greening was increased by light pulses, wounding and biotic stress. Arabidopsis thaliana (L.) Heynh. (ecotype Columbia) and lettuce seedlings grown in the dark had 20%-shorter hypocotyls in NO treatments than in control ones. On the other hand, internode lengths of potato plants growing under low light intensity and sprayed with 100 μM SNP were also 20% shorter than control ones. These results implicate NO as a stimulator molecule in plant photomorphogenesis, either dependent on or independent of plant photoreceptors. Received: 27 April 1999 / Accepted: 16 June 1999     

Chemical-induced apoptotic cell death in tomato cells: involvement of caspase-like proteases

 A new system to study programmed cell death in plants is described. Tomato (Lycopersicon esculentum Mill.) suspension cells were induced to undergo programmed cell death by treatment with known inducers of apoptosis in mammalian cells. This chemical-induced cell death was accompanied by the characteristic features of apoptosis in animal cells, such as typical changes in nuclear morphology, the fragmentation of the nucleus and DNA fragmentation. In search of processes involved in plant apoptotic cell death, specific enzyme inhibitors were tested for cell-death-inhibiting activity. Our results showed that proteolysis plays a crucial role in apoptosis in plants. Furthermore, caspase-specific peptide inhibitors were found to be potent inhibitors of the chemical-induced cell death in tomato cells, indicating that, as in animal systems, caspase-like proteases are involved in the apoptotic cell death pathway in plants. Received: 5 August 1999 / Accepted: 14 March 2000     

Drought induces fructan synthesis and 1-SST (sucrose: sucrose fructosyltransferase) in roots and leaves of chicory seedlings (Cichorium intybus L.)

 Seeds of Cichorium intybus L. var. foliosum cv. Flash were sown in acid-washed vermiculite and grown in a controlled-environment growth chamber. After 1 month of growth, plantlets did not contain sucrose:sucrose 1-fructosyltransferase (1-SST), the key enzyme in fructan biosynthesis. No fructan could be observed. Some of the plants were submitted to drought for 2 weeks. Glucose, fructose and sucrose concentrations increased in roots and leaves of stressed plants and the fructan concentration in roots and leaves was ten times higher than in control plants. The onset of fructan synthesis coincided with the increase in 1-SST activity in roots. Expression of the 1-SST gene could be observed in roots and leaves of stressed plants. Received: 12 July 1999 / Accepted: 16 October 1999     

Isolation and characterization of two acyl-CoA-binding proteins from proembryogenic masses of Digitalis lanata Ehrh.

 Two acyl-CoA-binding-protein (ACBP) isoforms were isolated from proembryogenic masses of Digitalis lanata Ehrh. by column chromatography and preparative HPLC. The ACBPs had molecular masses of 9926 and 9997 Da, respectively. Partial sequence data indicated high similarity to each other and to ACBPs of other plant species such as Ricinus communis, Brassica napus and Arabidopsis thaliana. The isolated ACBPs bound palmitoyl-CoA with high affinity as determined by isoelectric-point shift. Received: 29 May 1999 / Accepted: 28 August 1999     

Immunolocalization of LeAGP-1, a modular arabinogalactan-protein, reveals its developmentally regulated expression in tomato

 Arabinogalactan-proteins (AGPs) are highly glycosylated cell surface proteins that are thought to function in plant growth and development. The developmentally regulated expression of LeAGP-1, a novel and major AGP in tomato, was examined in different organs and tissues of tomato (Lycopersicon esculentum Mill. cv. UC82B) plants with an anti-peptide antibody (i.e. the PAP antibody) directed specifically against the lysine-rich subdomain of the LeAGP-1 core protein. During cell differentiation in tomato plants, LeAGP-1 was associated with cell wall thickening and lignification of particular cell types. Specifically, LeAGP-1 was detected in secondary wall thickenings of maturing metaxylem and secondary xylem tracheary elements in roots and stems, and in thickened cell walls of phloem sieve elements. However, LeAGP-1 was also present in thin-walled, cortical parenchyma cells of seedling roots as well as thick-walled collenchyma cells in young stems, both of which are not lignified. Based on these observed patterns, possible roles for LeAGP-1 in plant growth and development are discussed. Received: 17 August 1999 / Accepted: 7 October 1999     

Gravity independence of seed-to-seed cycling in Brassica rapa

 Growth of higher plants in the microgravity environment of orbital platforms has been problematic. Plants typically developed more slowly in space and often failed at the reproductive phase. Short-duration experiments on the Space Shuttle showed that early stages in the reproductive process could occur normally in microgravity, so we sought a long-duration opportunity to test gravity's role throughout the complete life cycle. During a 122-d opportunity on the Mir space station, full life cycles were completed in microgravity with Brassica rapa L. in a series of three experiments in the Svet greenhouse. Plant material was preserved in space by chemical fixation, freezing, and drying, and then compared to material preserved in the same way during a high-fidelity ground control. At sampling times 13 d after planting, plants on Mir were the same size and had the same number of flower buds as ground control plants. Following hand-pollination of the flowers by the astronaut, siliques formed. In microgravity, siliques ripened basipetally and contained smaller seeds with less than 20% of the cotyledon cells found in the seeds harvested from the ground control. Cytochemical localization of storage reserves in the mature embryos showed that starch was retained in the spaceflight material, whereas protein and lipid were the primary storage reserves in the ground control seeds. While these successful seed-to-seed cycles show that gravity is not absolutely required for any step in the plant life cycle, seed quality in Brassica is compromised by development in microgravity. Received: 3 August 1999 / Accepted: 27 August 1999     

Morphogenesis in cucumber seedlings is negatively controlled by gravity

 Seedlings of most cucurbitaceous plants develop a peg (protuberance caused by cell outgrowth) on the transition zone between the hypocotyl and root. The peg is necessary for removing the seed coat after germination. In our spaceflight experiments on the STS-95 space shuttle, Discovery, we found that cucumber (Cucumis sativus L.) seedlings grown under microgravity conditions developed two pegs symmetrically at the transition zone. Thus, cucumber seedlings potentially develop two pegs and do not require gravity for peg formation itself, but on the ground the development of one peg is suppressed in response to gravity. This may be considered as negative control of morphogenesis by gravity. Received: 17 August 1999 / Accepted: 4 October 1999     

Isoforms of chalcone synthase in Daucus carota L. and their differential expression in organs from the European wild carrot and in ultraviolet-A-irradiated cell cultures

 Two isoforms of chalcone synthase (CHS) were isolated from cDNA libraries derived from UV-A-irradiated anthocyanin-accumulating (DCb) and non-accumulating (DCs) cell cultures of carrot (Daucus carota L.). The clones designated as DcCHS1, which were present only in the DCb library, had a deduced primary sequence of 389 amino acids and an expected molecular mass of 42.7 kDa, and seem to be alleles of those cloned by Ozeki et al. (1993). The second isoform (DcCHS2) was present in both libraries. It had the highest degree of similarity (97.7%) to parsley CHS over all 397 amino acids. The expected molecular mass of the corresponding protein was 43.6 kDa. Results obtained from Southern blot analysis indicated the existence of at least two CHS genes in carrot. A transient enhancement of the DcCHS1 mRNA level after continuous irradiation with UV-A light could only be observed in anthocyanin-accumulating cultures, whereas an increase in DcCHS2 mRNA was seen in both cell lines. The maximum accumulation of CHS mRNA occurred 48 h after the onset of UV-A irradiation. In the European wild carrot the accumulation of DcCHS1 mRNA was restricted to the red central flowers, whereas the DcCHS2 mRNA was detectable in all red and white petals, as well as leaves, but was absent in stems and roots. The expression of DcCHS1 was restricted to anthocyanin-accumulating cells or organs. The heterologous expression of both cDNAs in Escherichia coli resulted in immunostainable bands of different sizes on the Western blot and high levels of catalytic CHS activity. Received: 2 September 1999 / Accepted: 30 November 1999     

Wood formation in poplar: identification, characterization, and seasonal variation of xylem proteins

Proteins that are preferentially produced in developing xylem may play a substantial role in xylogenesis. To reveal the identity of these proteins, comparative two-dimensional polyacrylamide gel electrophoresis was performed on young differentiating xylem, mature xylem, and bark of poplar (Populus trichocarpa Hook. cv. `Trichobel') harvested at different times of the year. The most-abundant xylem proteins were identified by microsequence analysis. For 17 of these proteins a putative function could be assigned based on similarity with previously characterized proteins, and for 15 out of these corresponding expressed sequence tags (ESTs) were found in the poplar EST database. The identified xylem–preferential proteins, defined by comparing the protein patterns from xylem and bark, were all involved in the phenylpropanoid pathway: two caffeoyl-coenzyme A O-methyltransferases (CCoAOMT), one phenylcoumaran benzylic ether reductase (PCBER), one bispecific caffeic acid/5-hydroxyferulic acid O-methyltransferase (COMT), five S-adenosyl-L-methionine synthetases, and one homologue of glycine hydroxymethyltransferase (GHMT). Remarkably, the biological function of the two most-abundant xylem-preferential proteins (PCBER and a GHMT homologue) remains unclear. In addition, several housekeeping enzymes were identified: two enolases, two glutamine synthetases, one 70-kDa heat-shock cognate, one calreticulin, and one α-tubulin. In comparison to the xylem-preferential proteins, the housekeeping proteins were expressed at significant levels in the bark as well. Also, several additional protein spots were detected for CCoAOMT, PCBER, and COMT by immunoblot. Our data show that for the study of xylogenesis, two-dimensional protein gel comparisons combined with systematic protein sequencing may yield information complementary to that from EST sequencing strategies. Received: 28 June 1999 / Accepted: 3 September 1999     

Phenylcoumaran benzylic ether reductase, a prominent poplar xylem protein, is strongly associated with phenylpropanoid biosynthesis in lignifying cells

 It has previously been shown (D.R. Gang et al., 1999, J Biol Chem 274: 7516–7527) that the most abundant protein in the secondary xylem of poplar (Populus trichocarpa cv. `Trichobel') is a phenylcoumaran benzylic ether reductase (PCBER), an enzyme involved in lignan synthesis. Here, the distribution and abundance of PCBER in poplar was studied at both the RNA and protein level. The cellular expression pattern was determined by immunolocalization of greenhouse-grown plants as well as of a field-grown poplar. Compared to other poplar tissues, PCBER is preferentially produced in the secondary xylem of stems and roots and is associated with the active growth period. The protein is present in all cells of the young differentiating xylem, corresponding to the zone of active phenylpropanoid metabolism and lignification. In addition, PCBER is located in young differentiating phloem fibers, in xylem ray parenchyma, and in xylem parenchyma cells at the growth-ring border. Essentially the same expression pattern was observed in poplars grown in greenhouses and in the field. The synthesis of PCBER in phenylpropanoid-synthesizing tissues was confirmed in a bending experiment. Induction of PCBER was observed in the pith of mechanically bent poplar stems, where phenylpropanoid metabolism is induced. These results indicate that the products of PCBER activity are synthesized mainly in lignifying tissues, suggesting a role in wood development. Received: 28 September 1999 / Accepted: 15 March 2000     

Expression analysis of the nucleocytoplasmic lectin 'Orysata' from rice in Pichia pastoris

The Oryza sativa lectin, abbreviated Orysata, is a mannose-specific, jacalin-related lectin expressed in rice plants after exposure to certain stress conditions. Expression of a fusion construct containing the rice lectin sequence linked to enhanced green fluorescent protein in Bright Yellow 2 tobacco cells revealed that Orysata is located in the nucleus and the cytoplasm of the plant cell, indicating that it belongs to the class of nucleocytoplasmic jacalin-related lectins. Since the expression level of Orysata in rice tissues is very low the lectin was expressed in the methylotrophic yeast Pichia pastoris with the Saccharomyces α-factor sequence to direct the recombinant protein into the secretory pathway and express the protein into the medium. Approximately 12 mg of recombinant lectin was purified per liter medium. SDS/PAGE and western blot analysis showed that the recombinant lectin exists in two molecular forms. Far western blot analysis revealed that the 23 kDa lectin polypeptide contains an N-glycan which is absent in the 18.5 kDa polypeptide. Characterization of the glycans present in the recombinant Orysata revealed high-mannose structures, Man9-11 glycans being the most abundant. Glycan array analysis showed that Orysata interacts with high-mannose as well as with more complex N-glycan structures. Orysata has potent anti-human immunodeficiency virus and anti-respiratory syncytial virus activity in cell culture compared with other jacalin-related lectins.     

Characterization of two cDNA clones encoding isozymes of the F1F0-ATPase inhibitor protein of rice mitochondria

Two cDNA clones encoding F₁F₀-ATPase inhibitor proteins, which are loosely associated with the F₁ part of the mitochondrial F₁F₀-ATPase, were characterized from rice (Oryza sativa L. cv. Nipponbare). A Northern hybridization showed that the two genes (designated as IF ₁ -1 and IF ₁ -2) are transcribed in all the organs examined. However, the steady-state mRNA levels varied among organs. A comparison of the deduced amino acid sequences of the two IF ₁ genes and the amino acid sequence of the mature IF₁ protein from potato revealed that IF₁-1 and IF₁-2 have N-terminal extensions with features that are characteristic of a mitochondrial targeting signal. To determine the subcellular localization of the gene products, the IF₁-1 or IF₁-2 proteins were fused in frame to the green fluorescent protein (GFP) or the fused GFP-β-glucuronidase, and expressed transiently in onion or dayflower epidermal cells. Localized fluorescence was detected in mitochondria, confirming that the two IF₁ proteins are targeted to mitochondria. Received: 9 July 1999 / Accepted: 17 August 1999     

Expression of cucumber lipid-body lipoxygenase in transgenic tobacco: lipid-body lipoxygenase is correctly targeted to seed lipid bodies

 A particular isoform of lipoxygenase (LOX, EC 1.13.11.12) localized on lipid bodies has been shown by earlier investigations to play a role during seed germination in initiating the mobilization of triacylglycerols. On lipid bodies of germinating cucumber (Cucumis sativus L.) seedlings, the modification of linoleoyl moieties by this LOX precedes the hydrolysis of the ester bonds. We analyzed the expression and intracellular location of this particular LOX form in leaves and seeds of tobacco (Nicotiana tabacum L.) transformed with one construct coding for cucumber lipid-body LOX and one construct coding for cucumber LOX fused with a hemagglutinin epitope. In both tissues, the amount of lipid-body LOX was clearly detectable. Biochemical analysis revealed that in mature seeds the foreign LOX was targeted to lipid bodies, and the preferred location of the LOX on lipid bodies was verified by immunofluorescence microscopy. Cells of the endosperm and of the embryo exhibited fluorescence based on the immunodecoration of LOX protein whereas very weak fluorescent label was visible in seeds of untransformed control plants. Further cytochemical analysis of transformed plants showed that the LOX protein accumulated in the cytoplasm when green leaves lacking lipid bodies were analyzed. Increased LOX activity was shown in young leaves of transformed plants by an increase in the amounts of endogenous (2E)-hexenal and jasmonic acid. Received: 9 August 1999 / Accepted: 28 September 1999     

The Rhodococcus fascians-plant interaction: morphological traits and biotechnological applications

Rhodococcus fascians is a Gram-positive bacterium that infects dicotyledonous and monocotyledonous plants, leading to an alteration in the normal growth process of the host. The disease results from the modulation of the plant hormone balances, and cytokinins are thought to play an important role in the induction of symptoms. Generally, on the aerial parts of the plants, existing meristems were found to be most sensitive to the action of R. fascians, but, depending on the infection procedure, differentiated tissues as well gave rise to shoots. Similarly, in roots not only actively dividing cells, but also cells with a high competence to divide were strongly affected by R. fascians. The observed symptoms, together with the determined hormone levels in infected plant tissue, suggest that auxins and molecules of bacterial origin are also involved in leafy gall formation. The complexity of symptom development is furthermore illustrated by the necessary and continuous presence of the bacteria for symptom persistence. Indeed, elimination of the bacteria from a leafy gall results in the further development of the multiple embryonic buds of which it consists. This interesting characteristic offers novel biotechnological applications: a leafy gall can be used for germplasm storage and for plant propagation. The presented procedure proves to be routinely applicable to a very wide range of plants, encompassing several recalcitrant species. Received: 14 January 1999 / Accepted: 19 June 1999