Cell wall changes involved in the automorphic curvature of rice coleoptiles under microgravity conditions in space

Seedlings of rice (Oryza sativa L. cv. Koshihikari and cv. Tan-ginbozu) were cultivated on board the Space Shuttle STS-95 mission and changes in the morphology and the cell wall properties of coleoptiles were analyzed. In space, rice coleoptiles showed a spontaneous (automorphic) curvature toward the caryopsis in the elongating region. The angle of automorphic curvature was larger in Koshihikari than in a gibberellin-deficient dwarf cultivar, Tan-ginbozu, and the angle gradually decreased during the growth of coleoptiles in both cultivars. The more quickly expanding convex side of the bending region of the rice coleoptiles showed a greater extensibility of the cell wall than the opposite side. There was a significant correlation between the angle of curvature and the difference in the cell wall extensibility between the convex and the concave sides. Both the levels of the cell wall polysaccharides per unit length of coleoptile and the ratio of high-molecular-mass polysaccharides in the hemicellulose fraction were lower in the convex side than the concave one. Also, the activity of (13),(14)--glucanases in the cell wall was higher in the convex side than the concave one. These results suggest that the uneven modifications of cell wall metabolism bring about the difference in the levels and the molecular size of the cell wall polysaccharides, thereby causing the difference in capacity of the cell wall to expand between the dorsal and the ventral sides, leading to the automorphic curvature of rice coleoptiles in space. The data also suggest the involvement of gibberellins in inducing the automorphic curvature under microgravity conditions.     

Acrylamide inhibits gravitropism and affects microtubules in rice coleoptiles

Summary. To find components which participate in gravitropic signal transmission, we screened different cell biological inhibitors for their effect on gravitropic bending of rice coleoptiles. Acrylamide, which is known to affect intermediate filaments in mammalian cells, strongly inhibited gravitropic bending at concentrations that did not inhibit growth of coleoptile segments. This inhibition was reversible. Investigating the acrylamide effect further, we found that it interferes with an event that occurs around 15 min after the onset of stimulation. We also observed that acrylamide inhibits polar indolyl-3-acetic acid transport. Furthermore, acrylamide efficiently eliminated microtubules, whereas actin filaments remained intact. To our knowledge this is the first report of effects of monoacrylamide in plant cells. Correspondence and reprints (present address): Laboratoire de Génétique Végétale, Sciences III, Université de Genève, 30 Quai Ernest-Ansermet, 1211 Genève, Switzerland.     

Phototropic fluence-response relations for Avena coleoptiles on a clinostat

Phototropism of Avena sativa L. has been characterized using a clinostat to negate the gravitropic response. The kinetics for development of curvature was measured following induction by a single pulse of blue light (BL), five pulses of BL at 20-min intervals, and this same pulsed-light regime following a 2-h red light (RL) pre-irradiation. A final curvature of about 14° is expressed within 180 min following the single pulse; a final curvature of about 62° in about 240 min following five pulses without pre-irradiation; and a curvature of over 125° in 360 min following five pulses after the RL pre-irradiation. For seedlings not pre-irradiated, the final curvature to five pulses of BL at a total fluence of 9.4 pmol·cm^-2 increases with time of darkness between pulses up to 15 min; with seedlings pre-irradiated with RL, curvature increased more slowly with time of darkness between pulses to a maximum at 35 min. The final curvature induced by a constant fluence of 9.4 pmol·cm^-2 increases linearly with time between the first pulse and last pulse of a five-pulse sequence. The curvature induced by a single BL pulse with a 5-min RL co-irradiation increases with fluence to a maximum of about 60° at about 10 pmol·cm^-2, and then decreases to 0° at about 200 pmol·cm^-2. Curvature induced by five BL pulses following a 2-h RL pre-irradiation increased with fluence from a threshold of about 0.05 pmol·cm^-2 to a maximum of 90° at about 10 pmol·cm^-2, and then gradually decreased with fluence to 50° at 1 000 pmol·cm^-2. Based on these data, it is concluded that the initial photoproduct formed by a BL pulse has a limited lifetime, that there is a kinetic limitation downstream of the photoreceptor pigment for phototropism, and that the additivive effect of pulsed BL is distinct from the potentiating effect of RL on phototropism. Thus, any degree of curvature from 0° to over 90° may be induced by a fluence in the ascending arm of what is traditionally called the first positive phototropic response.Abbreviations BL blue light - RL red light     

Crystal structure of nucleoside diphosphate kinase required for coleoptile elongation in rice (Oryza sativa L.)

Nucleoside diphosphate kinase (NDK) is a ubiquitous enzyme found in all organisms and cell types, and catalyzes the transfer of the phosphoryl group from a nucleoside triphosphate to a nucleoside diphosphate. The enzyme is involved in and required for coleoptile elongation in rice as the level of the rice NDK (rNDK) changes during seed germination and the early stages of seedling growth. The expression of rice NDK gene is up-regulated in the growing coleoptiles when the anaerobic stress persists. The rNDK structure determined at 2.5 A resolution consists of a four-stranded anti-parallel beta-sheet, of which the surfaces are partially covered with six alpha-helices; its overall and active site structures are similar to those of homologous enzymes except the major conformation variations of residue 132-138 regions, involving significant structural contacts. The model contains 148 residues of 149 residues in total and averaged 19 water molecules per monomer for 12 molecules in an asymmetric unit. A mold of 12 superimposed molecules shows that the alphaA-alpha2 area has greater variations and higher temperature factors, indicating the flexibility for a substrate entrance. Hexameric molecular packing in both crystal and solution implies that rNDK functions as hexamers. This rNDK structure, which is the first NDK structure from a higher plant system, provides the structural information essential to understand the functional significance of this enzyme during growth and development in both rice and other plants.     

Distribution of pectins in cell walls of maize coleoptiles and evidence against their involvement in auxin-induced extension growth

Summary Aiming to elucidate the possible involvement of pectins in auxin-mediated elongation growth the distribution of pectins in cell walls of maize coleoptiles was investigated. Antibodies against defined epitopes of pectin were used: JIM 5 recognizing pectin with a low degree of esterification, JIM 7 recognizing highly esterified pectin and 2F4 recognizing a pectin epitope induced by Ca²⁺. JIM 5 weakly labeled the outer third of the outer epidermal wall and the center of filled cell corners in the parenchyma. A similar labeling pattern was obtained with 2F4. In contrast, JIM 7 densely labeled the whole outer epidermal wall except the innermost layer, the middle lamellae, and the inner edges of open cell corners in the parenchyma. Enzymatic de-esterification with pectin methylesterase increased the labeling by JIM 5 and 2F4 substantially. A further increase of the labeling density by JIM 5 and 2F4 and an extension of the labeling over the whole outer epidermal wall could be observed after chemical de-esterification with alkali. This indicates that both methyl- and other esters exist in maize outer epidermal walls. Thus, in the growth-controlling outer epidermal wall a clear zonation of pectin fractions was observed: the outermost layer (about one third to one half of wall thickness) contains unesterified pectin epitopes, presumably cross-linked by Ca²⁺ extract. Tracer experiments with³H-myo-inositol showed rapid accumulation of tracer in all extractable pectin fractions and in a fraction tightly bound to the cell wall. A stimulatory effect of IAA on tracer incorporation could not be detected in any fraction. Summarizing the data a model of the pectin distribution in the cell walls of maize coleoptiles was developed and its implications for the mechanism of auxin-induced wall loosening are discussed.Abbreviations CDTA trans-1,2-diaminocyclohexane-N,N,N,N-tetraacetic acid - CWP cell-wall pellet - IAA indole-3-acetic acid - LSE low-salt extract - TCA trichloroacetic acid; Tris tris-(hydroxy-methyl)aminoethane     

Protective effect of exogenous nitrate on the mitochondrial ultrastructure ofOryza sativa coleoptiles under strict anoxia

Summary The effect of exogenous KNO₃, the terminal acceptor of electrons in oxygen-free medium, on mitochondrial ultrastructure and on the growth rate of 4-day-old rice coleoptiles under strictly anoxic conditions was studied. Exogenous nitrate (10 mM) did not exert any significant effect on the growth rate of coleoptiles of intact seedlings compared to their growth in KNO₃-free medium. Anaerobic incubation of detached coleoptiles in KNO₃-free medium for 48 h resulted in the complete destruction of mitochondrial and other cell membranes. In the presence of KNO₃, no mitochondrial-membrane destruction was observed even after 48 h anoxia although the mitochondrial ultrastructure was modifed. Cristae were arranged in parallel rows and elongated dumbbell-shaped mitochondria appeared in some cells. The data obtained indicate a protective role of exogenous nitrate as electron acceptors in oxygen-free medium. The results of the present investigation are discussed and compared with reports of either markedly damaging or favorable effects of exogenous nitrate on the growth, metabolism, and energetics of rice and other plants under hypoxic and anoxic conditions.     

Detection of a highly heterozygous locus in recombinant inbred lines of rice and its possible involvement in heterosis

Forty-seven recombinant inbred (RI) lines derived from a cross between two indica rices, cv Phalguna and the Assam land race ARC 6650, were subjected to restriction fragment length polymorphism (RFLP) analysis using cloned probes defining 150 single-copy loci uniformly dispersed on the 12 chromosomes of rice. Of the probes tested, 47 detected polymorphism between the parents. Heterozygosity was calculated for each line and for each of the polymorphic loci. Average heterozygosity per line was 9.6% but was excessive (>20%) in the 5 lines that seemed to have undergone outcrossing immediately prior to harvest. Average heterozygosity detected by each probe across the 47 RI lines was 9.7%. The majority of probes revealed the low level of heterozygosity (<8%) expected for F₅-F₆ lines in a species showing about 5% outbreeding. On the other hand, 7 probes exhibited heterozygosity in excess of 15%, while with a eighth probe (RG2 from chromosome 11) heterozygosity varied according to the restriction enzyme employed, ranging from 2% with SaII to 72% with EcoRV. The presence of 34 recombination sites in a segment of the genome as short as 24 kb indicates a strong selection for recombination between two neighbouring loci, one required as homozygous for the Phalguna allele, and the other heterozygous. Since selection was principally for yield advantage over that of the high-yielding parent, Phalguna, one or both of these loci may be important for heterosis in this cross. The results also indicate that heterozygosity as measured by RFLP can depend on the particular restriction endonuclease employed.     

RFLP tagging of a gene for aroma in rice

Summary We report here the identification of a DNA marker closely linked to a gene for aroma in rice. The DNA marker was identified by testing 126 mapped rice genomic, cDNA, and oat cDNA, clones as hybridization probes against Southern blots, consisting of DNA from a pair of nearly isogenic lines (NILs) with or without the aroma gene. Chromosomal segments introgressed from the donor genome were distinguished by RFLPs between the NILs. Linkage association of the clone with the gene was verified using an F₃ segregating for aroma. Cosegregation of the scented phenotype and donor-derived allele indicated the presence of linkage between the DNA marker and the gene. RFLP analysis showed that the gene is linked to a single-copy DNA clone, RG28, on chromosome 8, at a distance of 4.5 cM. The availability of a linked DNA marker may facilitate early selection for the aroma gene in rice breeding programs.     

Interaction of auxin, light, and mechanical stress in orienting microtubules in relation to tropic curvature in the epidermis of maize coleoptiles

Summary Changes in the orientation of cortical microtubules (longitudinal vs. transverse with respect to the long cell axis) at the outer epidermal wall of maize coleoptile segments were induced by auxin, red or blue light, and mechanical stresses (cell extension or compression produced by bending). Immunofluorescent techniques were used for the quantitative determination of frequency distributions of microtubule orientation. Detailed kinetic studies showed that microtubule reorientations are temporally correlated with the simultaneously measured changes in growth rate elicited by auxin, red light, or blue light. Growth inhibition induced by depletion of endogenous auxin produces a longitudinal microtubule pattern that can be changed into a transverse pattern in a dose-dependent manner by applying exogenous auxin. A mid-point pattern with equal frequencies of longitudinal and transverse microtubules was adjusted at 2 mol/1 auxin. Bending stress applied under these conditions adjusts permanent, maximally longitudinal and transverse microtubule orientations at the compressed and extended segment sides, respectively, quantitatively mimicking the responses to differential flank growth during phototropic and gravitropic curvature. During tropic curvature the changes in microtubule pattern reflect the distribution of growth rather than the distribution of auxin. The microtubule pattern responds to auxin-dependent growth changes and mechanical stress in a synergistic manner, confirming the functional equivalence of these factors in affecting microtubule orientation. Similar results were obtained when segment growth was altered by blue or red light instead of auxin in the presence or absence of mechanical stress. It is concluded from these results that growth changes, elicited by auxin, light, etc., and mechanical stress affect microtubule orientation through a common signal perception and transduction chain.Abbreviations IAA indole-3-acetic acid (auxin) - MT cortical microtubule     

Senescence in the nongreening region of the rice (Oryza sativa) coleoptile

Summary The coleoptile of rice (Oryza sativa L. cv. Nippon-bare) emerges from the imbibed seed on day 2 after sowing and ceases its growth on day 3. In cross section, the cells near the outer epidermis turn into green between days 2 and 3, while those near the inner epidermis remain colorless. In this study, the complete process of the development in the nongreening cells in the coleoptile was examined by fluorescence and electron microscopy. Embryonic morphology on day 0 was rapidly converted into the differentiated greening or nongreening cells between days 1 and 2. Senescence in the inner, nongreening region first appeared on day 4 in the third or fourth cell layer from the inner epidermis and then spread towards both the inner and the outer epidermis, and the inner cells collapsed completely before the outer cells senesced. Cells adjacent to the inner epidermis, which senesced slowly, followed a sequence of events during development: (1) degradation of plastid DNA; (2) dispersal of nuclear chromatin, differentiation of plastids into amyloplasts, degradation of mitochondrial DNA; (3) degradation of the starch in amyloplasts; (4) disorganization of plastids; (5) condensation of the nucleus, shrinkage of mitochondria; (6) complete loss of cellular components, distortion of cell walls. In the interior cells, the early events including degeneration of plastid DNA and mitochondrial DNA occurred in parallel with those in the cells adjacent to the inner epidermis, yet rapid collapse of all the cellular components proceeded between days 3 and 5, and nuclear condensation could not be detected.Abbreviations cpDNA chloroplast DNA - DAPI 4,6-diamidino-2-phenylindole - DiOC₇ 3,3-dihexyloxacarbocyanine - IE inner epidermis - mtDNA mitochondrial DNA - mt-nucleoid mitochondrial nucleoid - OE outer epidermis - ptDNA plastid DNA - pt-nucleoid plastid nucleoid     

<Emphasis Type="Italic">Gypsy embryo</Emphasis> specifies ovule curvature by regulating ovule/integument development in rice

The embryo position in a seed is stable in most plant species, indicating the existence of a strict regulatory mechanism that specifies the embryo position in the seed. To elucidate this mechanism, we analyzed the gypsy embryo (gym) mutant of rice, in which the position of the mature embryo in the seed is altered at a low frequency. Analyses of early embryogenesis and ovule development showed that the ectopic embryo was derived from an ill-positioned egg cell, which resulted from the incomplete curvature of the ovule. Although the development of both the inner and outer integuments was impaired, the ovule curvature was associated closely with the extent of inner integument growth. Therefore, inner integument development controls ovule curvature in rice. The expression patterns of OSH1 and OsMADS13 indicated that, in gym, a small number of indeterminate cells are maintained on the style side of the ovule and then in the integument primordium at a low frequency. The prolonged survival of these indeterminate cells disturbs normal integument development. The gym fon2 double mutant suggests that GYM and FON2 are involved redundantly in floral meristem determinacy. Possible functions of the GYM gene and the ovule developmental mechanism are discussed.     

Identification of microsatellite markers for fragrance in rice by analysis of the rice genome sequence

Several chemical constituents are important to the fragrance of cooked rice. However, the chemical compound 2-acetyl-1-pyrroline (AP) is regarded as the most important component of fragrance in the basmati- and jasmine-style fragrant rices. AP is found in all parts of the plant except the roots. It is believed that a single recessive gene is responsible for the production of fragrance in most rice plants. The detection of fragrance can be carried out via sensory or chemical methods, although each has their disadvantages. To overcome these difficulties, we have identified an (AT)₄₀ repeat microsatellite or simple sequence repeat (SSR) marker for fragrant and non-fragrant alleles of the fgr gene. Identification of this marker was facilitated through use of both the publicly available and restricted access sequence information of the Monsanto rice sequence databases. Fifty F₂ individuals from a mapping population were genotyped for the polymorphic marker. This marker has a high polymorphism information content (PIC = 0.9). Other SSR markers linked to fragrance could be identified in the same way of use in other populations. This study demonstrates that analysis of the rice genome sequence is an effective option for identification of markers for use in rice improvement.     

A cytoskeletal basis for wood formation in angiosperm trees: the involvement of cortical microtubules

Rearrangements of cortical microtubules (CMTs) during the differentiation of axial secondary xylem elements within taproots and shoots of Aesculus hippocastanum L. (horse-chestnut) are described. A correlative approach was employed using indirect immunofluorescence microscopy of α-tubulin in 6- to 10-μm sections and transmission electron microscopy of ultrathin sections. All cell types – fibres, vessel elements and axial parenchyma – derive from fusiform cambial cells which contain randomly oriented CMTs. At the early stages of development, fibres and axial parenchyma cells possess helically arranged CMTs, which increase in number as secondary wall thickening proceeds and simple pits develop. In contrast, incipient vessel elements are distinguished by the marking out of sites of bordered pits; these sites first appear as microtubule-free regions within the reticulum of randomly oriented CMTs that characterises their precursor fusiform cambial cells. Subsequently, the ring of CMTs which develops at the periphery of the microtubule-free region decreases in diameter as the over-arching pit border is formed. Like bordered pits, large-diameter, non-bordered pits (contact pits) which develop between vessel elements and adjacent contact ray cells originate as microtubule-free regions and are also associated with development of a ring of CMTs at the periphery. In the case of contact pits, however, there is no reduction in the diameter of the CMT ring during pit development. Tertiary cell wall thickenings are also a feature of vessel elements and appear to form at sites where bands of laterally associated, transversely oriented CMTs, separated from each other by microtubule-free zones, are found. Later, these bands of CMTs become narrower, and separate into pairs of microtubule bundles located on each side of the developing wall thickening. Development of perforations between vessel elements is also associated with the presence of a ring of CMTs at their periphery. Received: 13 July 1998 / Accepted: 30 November 1998     

Identification of a high-affinity binding protein for N-acetylchitooligosaccharide elicitor in theplasma membrane from rice leaf and root cells

Presence of a high-affinity binding protein for N-acetylchitooligosaccharide (fragments of chitin) elicitor in the plasma membrane from rice leaf and root cells was shown by affinity labeling experiments with an ¹²⁵I-labeled N-acetylchitooligosaccharide derivative. Binding studies also showed that binding site in the leaf cells has a high affinity to highly elicitor-active, larger chitin fragments but much lower or no affinity to less elicitor-active or elicitor-inactive oligosaccharides. The amount of the binding protein in the leaf cells was slightly smaller than that in the suspension-cultured cells but much larger compared to that in the root cells. These results indicate the possible- involvement of the elicitor binding protein in the perception of the elicitor signal in intact rice plant.     

Concentration and release level of momilactone B in the seedlings of eight rice cultivars

The release levels of a growth inhibitor, momilactone B, from rice (Oryza sativa L.) seedlings of eight cultivars were compared with the endogenous concentrations of momilactone B in their seedlings. All rice cultivars contained momilactone B in the seedlings, and their concentrations differed between the cultivars. Momilactone B was also found in all culture solutions in which these rice seedlings were grown, and the concentrations differed between the cultivars. The momilactone B concentrations in the culture solutions were reflected in the momilactone B concentrations in the seedlings. These results suggest that all rice cultivars may produce momilactone B and release momilactone B into the culture solutions. In addition, the release level of momilactone B may depend on the production level of momilactone B in the seedlings, which may affect allelopathic potential of these rice cultivars because as a growth inhibitor, momilactone B is able to act as an allelochemical.     

Proteomics of the rice cell: systematic identification of the protein populations in subcellular compartments

Despite recent progress in sequencing the complete genome of rice (Oryza sativa), the proteome of this species remains poorly understood. To extend our knowledge of the rice proteome, the subcellular compartments, which include plasma membranes (PM), vacuolar membranes (VM), Golgi membranes (GM), mitochondria (MT), and chloroplasts (CP), were purified from rice seedlings and cultured suspension cells. The proteins of each of these compartments were then systematically analyzed using two-dimensional (2D) electrophoresis, mass spectrometry, and Edman sequencing, followed by database searching. In all, 58 of the 464 spots detected by 2D electrophoresis in PM, 43 of the 141 spots in VM, 46 of the 361 spots in GM, 146 in the 672 spots in MT, and 89 of the 252 spots in CP could be identified by this procedure. The characterized proteins were found to be involved in various processes, such as respiration and the citric acid cycle in MT; photosynthesis and ATP synthesis in CP; and antifungal defense and signal systems in the membranes. Edman degradation revealed that 60–98% of N-terminal sequences were blocked, and the ratios of blocked to unblocked proteins in the proteomes of the various subcellular compartments differed. The data on the proteomes of subcellular compartments in rice will be valuable for resolving questions in functional genomics as well as for genome-wide exploration of plant function.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by G. Jürgens     

Development of a simple functional marker for fragrance in rice and its validation in Indian Basmati and non-Basmati fragrant rice varieties

Fragrance development in rice has been reported due to a 8-bp deletion in the exon 7 of badh2 gene located on Chromosome 8S. Multiplex markers targeting the functional InDel polymorphism was earlier reported for genotyping fragrance trait, but the marker was observed to be inconsistent and difficult to use. We have developed a simple, co-dominant, functional marker for fragrance trait, which can be resolved in an agarose gel and validated in Basmati and non-Basmati aromatic rice varieties and in a mapping population segregated for fragrance trait. The marker targets the InDel polymorphism in badh2 gene and amplifies 95 and 103 bp fragments in fragrant and non-fragrant genotypes, respectively. The newly developed marker was highly efficient in discriminating all fragrant and non-fragrant genotypes and showed perfect co-segregation with the trait of fragrance in the mapping population. We recommend the use of this simple, low-cost marker in routine genotyping for fragrance trait in large scale breeding materials and germplasm.     

Regulation of the spatial order of cortical microtubules in developing guard cells ofAllium

The organization of microtubules (MTs) in the cortex of cells at interphase is an important element in morphogenesis. Mechanisms controlling the initiation of MTs and their spatial ordering, however, are largely unknown. Our recent study concerning the generation of a radial array of MTs in stomatal guard cells inAllium showed that the MTs initiate in a cortical MT-organizing zone adjacent to the ventral wall separating the two young guard cells (Marc, Mineyuki and Palevitz, 1989, Planta179, 516, 530). In an attempt to detect MT-ordering mechanisms separate from the sites of MT initiation, we now employ various drugs to manipulate the geometry and integrity of the ventral wall and thereby also the associated MT-organizing zone. In the presence of cytochalasin D the ventral wall is tilted away from its normal mid-longitudinal anticlinal alignment, while treatments with the herbicide chloroisopropyl-N-phenylcarbamate (CIPC) induce the formation of a branched ventral wall. Nonetheless, in either case the MTs still form a radial array, although this is asymmetric as it is centered in accordance with the misaligned or branched ventral wall. Since the MTs maintain their original course undisturbed as they extend beyond the abnormal ventral wall, there is no evidence for the presence of an inherent MT-ordering mechanism at locations remote from MT-initiation sites. Following treatments with caffeine, which abolishes the formation of the ventral wall, the MTs revert to a transversely oriented cylindrical array as in normal epidermal cells. Thus the presence of the ventral wall, and presumably also the associated MT-organizing zone, is essential for the establishment of the radial array. The MT-organizing zone is therefore involved not only in the initiation of MTs, but also in determining their spatial order throughout the cell cortex. We thank Drs. Richard J. Cyr and Yoshi Mineyuki for providing valueable suggestions during the course of this work, and Ms. Elizabeth Bruce printing some of the figures. This research was supported by Funds from the National Science Foundation grants DCB-8703292 to B.A.P. and DCB-8803286 to B.A.P. and J.M.     

Phosphate solubilization potential and stress tolerance of rhizobacteria from rice soil in Northern Thailand

Plant growth-promoting rhizobacteria (PGPR) are known to influence plant growth by various direct or indirect mechanisms. A total of 216 phosphate-solubilizing bacterial isolates were isolated from different rice rhizospheric soil in Northern Thailand. These isolate were screened in vitro for their plant growth-promoting activities such as solubilization of inorganic phosphate, ammonia (NH₃), catalase and cell wall-degrading enzyme activity. It was found that 100% solubilized inorganic phosphate, 77.77% produced NH₃ and most of the isolates were positive for catalase. In addition, some strains also produced cell wall-degrading enzymes such as protease (7%), chitinase (1%), cellulase (3%) and β-glucanase (3%), as evidenced by phenotypic biochemical test and quantitative assay using spectrophotometry. The isolates could exhibit more than two or three plant growth-promoting (PGP) traits, which may promote plant growth directly or indirectly or synergistically. Part of this study focused on the effect of NaCl, temperature, and pH on a specific the bacterial isolate Acinetobacter CR 1.8. Strain CR 1.8 was able to grow on up to 25% NaCl, between 25 and 55°C, and at pH 5–9. Maximum solubilization of tricalcium phosphate and aluminium phosphate was obtained at neutral pH, and 37°C. Strain CR 1.8 had protease activity but no cellulase, β-glucanase and cellulase activities.     

Influence of boric acid on somatic embryogenesis of a cytosterile line of indica rice

The effect of boric acid on somatic embryo induction in rice was investigated using mature seeds of a widely used cytoplasmic male sterile line of indica rice IR-58025. Boric acid was added at a concentration of 100.00, 161.29, 241.93, 322.58 and 403.22 μM to the embryo induction medium containing basal salts, with 9.84 μM 2,4-dichlorophenoxyacetic acid. Boric acid was found to exert different effects on scutellum, coleoptile and root tissues. Increased growth of embryogenic masses with increasing boric acid concentrations was observed on coleoptile tissues of mature seed. Embryogenic response was observed at 161.29 μM boric acid on coleoptile and 241.93 μM boric acid on root tissue. Scutellum tissue showed embryonic response in 161.29 and 241.93 μM boric acid. The results indicate that the boric acid used in standard Murashige and Skoog medium is not sufficient to support induction of somatic embryogenesis in IR-58025 A. This revised version was published online in June 2006 with corrections to the Cover Date.