Nonmeristematic Tissues Research Articles

Rice KORPOKKUR gene is expressed in mitotic cells and regulates pleiotropic features during vegetative phase.

Cell division is important for organisms to grow and repair damaged tissues. A mutant screen in rice has identified dwarf korpokkur (kor) mutants that code for a novel protein potentially involved in mitosis including cytokinesis in rice. The KOR gene is expressed during the mitotic phase and a defect in the KOR gene induces cells with two nuclei. Analysis of kor mutants suggests that the KOR gene promotes cell division in the rice leaf primordia for a period after initiation, and maintains proper cell morphology especially in non-meristematic tissues. Additionally, kor mutants showed a delayed transition from juvenile phase to adult phase. Future research will shed light on the relationship between the mitotic defect and other features observed in the kor mutants.

Recalcitrance of Cannabis sativa to de novo regeneration; a multi-genotype replication study.

Cannabis sativa is relatively recalcitrant to de novo regeneration, but several studies have reported shoot organogenesis or somatic embryogenesis from non-meristematic tissues. Most report infrequent regeneration rates from these tissues, but a landmark publication from 2010 achieved regeneration from leaf explants with a 96% response rate, producing an average of 12.3 shoots per explant in a single drug-type accession. Despite the importance regeneration plays in plant biotechnology and the renewed interest in this crop the aforementioned protocol has not been used in subsequent papers in the decade since it was published, raising concerns over its reproducibility. Here we attempted to replicate this important Cannabis regeneration study and expand the original scope of the study by testing it across 10 drug-type C. sativa genotypes to assess genotypic variation. In our study, callus was induced in all 10 genotypes but callus growth and appearance substantially differed among cultivars, with the most responsive genotype producing 6-fold more callus than the least responsive. The shoot induction medium failed to induce shoot organogenesis in any of the 10 cultivars tested, instead resulting in necrosis of the calli. The findings of this replication study raise concerns about the replicability of existing methods. However, some details of the protocol could not be replicated due to missing details in the original paper and regulatory issues, which could have impacted the outcome. These results highlight the importance of using multiple genotypes in such studies and providing detailed methods to facilitate replication.

Cytokinin Signaling and De Novo Shoot Organogenesis.

The ability to restore or replace injured tissues can be undoubtedly named among the most spectacular achievements of plant organisms. One of such regeneration pathways is organogenesis, the formation of individual organs from nonmeristematic tissue sections. The process can be triggered in vitro by incubation on medium supplemented with phytohormones. Cytokinins are a class of phytohormones demonstrating pleiotropic effects and a powerful network of molecular interactions. The present study reviews existing knowledge on the possible sequence of molecular and genetic events behind de novo shoot organogenesis initiated by cytokinins. Overall, the review aims to collect reactions encompassed by cytokinin primary responses, starting from phytohormone perception by the dedicated receptors, to transcriptional reprogramming of cell fate by the last module of multistep-phosphorelays. It also includes a brief reminder of other control mechanisms, such as epigenetic reprogramming.

Inheritance and Expressivity of Neoplasm Trait in Crosses between the Domestic Pea (Pisum sativum subsp. sativum) and Tall Wild Pea (Pisum sativum subsp. elatius)

The Neoplasm trait in pea pods is reported to be due to the lack of ultraviolet (UV) light in glasshouse conditions or in response to pea weevil (Bruchus pisorum L.) damage. This pod deformation arises from the growth of non-meristematic tissue on pods of domesticated peas (Pisum sativum L. subsp. sativum). Neither expressivity, nor the effect of pea weevil on neoplasm in the tall wild pea (P. sativum L. subsp. elatius (M. Bieb.) Asch. & Graebn.), have been adequately studied. We aimed to study the expression and inheritance of neoplasm in the tall wild pea and crosses between domesticated and tall wild peas grown in the glasshouse (without pea weevils) and in the field (with pea weevils) under natural infestation conditions. Neoplasm was found in all pods in tall wild peas when grown in the glasshouse, while it was not detected on pods of field-grown plants despite heavy pea weevil damage. In inter-subspecific crosses between P. sativum subsp. sativum and P. sativum subsp. elatius, all F1 plants had neoplastic pods, and the F2 populations segregated in a good fit ratio of 3 (neoplasm): 1 (free from neoplasm) under glasshouse conditions, which suggests that neoplasm on pods of the tall wild pea was controlled by a single dominant gene. Expressivity of neoplasm in the progeny differed from parent to parent used in inter-subspecific crosses. There was no relationship between neoplasm and damage by pea weevil under heavy insect epidemics under field conditions. The neoplasm occurring under glasshouse conditions may be due to one or to a combination of environmental factors. Since wild peas are useful genetic resources for breeding programs aiming at fresh pea production that could be utilized under glasshouse conditions, negative selection could be considered in segregating populations.

Enhancing Neoplasm Expression in Field Pea (Pisum sativum) via Intercropping and Its Significance to Pea Weevil (Bruchus pisorum) Management.

Neoplasm formation, a non-meristematic tissue growth on young field pea (Pisum sativum L.) pods is triggered in the absence of UV light and/or in response to oviposition by pea weevil (Bruchus pisorum L.). This trait is expressed in some genotypes [neoplastic (Np) genotypes] of P. sativum and has the capacity to obstruct pea weevil larval entry into developing seeds. In the present study, 26% of the tested accessions depicted the trait when grown under greenhouse conditions. However, UV light inhibits full expression of this trait and subsequently it is inconspicuous at the field level. In order to investigate UV light impact on the expression of neoplasm, particular Np genotypes were subjected to UV lamp light exposure in the greenhouse and sunlight at the field level. Under these different growing conditions, the highest mean percentage of Np pods was in the control chamber in the greenhouse (36%) whereas in single and double UV lamp chambers, the percentage dropped to 10 and 15%, respectively. Furthermore, when the same Np genotypes were grown in the field, the percentage of Np pods dropped significantly (7%). In order to enhance Np expression at the field level, intercropping of Np genotypes with sorghum was investigated. As result, the percentage of Np pods was threefold in intercropped Np genotypes as compared to those without intercropping. Therefore, intercropping Np genotypes with other crops such as sorghum and maize can facilitate neoplasm formation, which in turn can minimize the success rate of pea weevil larvae entry into developing seeds. Greenhouse artificial infestation experiments showed that pea weevil damage in Np genotypes is lower in comparison to wild type genotypes. Therefore, promoting Np formation under field conditions via intercropping can serve as part of an integrated pea weevil management strategy especially for small scale farming systems.

Transcriptome profiling of soybean root tips.

Soybean (Glycine max L.), a major legume crop, is important to human nutrition and is a source of animal feed. Similar to many legumes, a key feature of the soybean is its symbiotic association with soil bacteria that fix atmospheric nitrogen. However, knowledge of the gene expression of its root system, particularly the root meristematic region, is limited. Here, we have addressed this by investigating the gene expression profile of the soybean root tip, using soybean Affymetrix chips containing 37500 probe sets (Affymetrix Inc.) and have compared this expression profile with that of the nonmeristematic tissue. We identified a total of 5012 upregulated and 4136 downregulated genes in the soybean root tip. Among the upregulated genes, 559 showed strong preferential expression in the root tip, indicating that they are likely to be associated with root apical meristem specificity and root tip function. Genes involved in membrane transport, defence signalling and metabolism were upregulated in the soybean root tip. Further, our data provide a resource of novel target genes for further studies involving root development and biology, and will possibly have a positive impact on future crop breeding.

Influence of a Heavy-Metal-Polluted Environment on Viola tricolor Genome Size and Chromosome Number

Intraspecific changes in genome size and chromosome number lead to divergence and species evolution. Heavy metals disturb the cell cycle and cause mutations. Areas contaminated by heavy metals (metalliferous sites) are places where microevolutionary processes accelerate; very often only a few generations are enough for a new genotype to arise. This study, which continues our long-term research on Viola tricolor (Violaceae), a species occurring on both metalliferous (Zn, Pb, Cd, Cu) and non-metalliferous soils in Western and Central Europe, is aimed at determining the influence of environments polluted with heavy metals on genome size and karyological variability. The genome size of V. tricolor ranged from 3.801 to 4.203 pg, but the differences between metallicolous and non-metallicolous populations were not statistically significant. Altered chromosome numbers were significantly more frequent in material from the polluted sites than from the non-polluted sites (43% versus 28%). Besides the standard chromosome number (2n = 26), aneuploid cells with lower (2n = 18–25) or higher (2n = 27, 28) chromosome numbers were found in plants from both types of site, but polyploid (2n = 42) cells were observed only in plants from the metalliferous locality. The lack of correlation between chromosome variability in root meristematic cells and genome size estimated from peduncle cells can be attributed to elimination of somatic mutations in generative meristem, producing chromosome-stable non-meristematic tissues in the peduncle.

Molecular dissection of the pea shoot apical meristem.

The shoot apical meristem (SAM) is responsible for the development of all the above-ground parts of a plant. Our understanding of the SAM at the molecular level is incomplete. This study investigates the gene expression repertoire of SAMs in the garden pea (Pisum sativum). To this end, 10 346 EST sequences representing 7610 unique genes were generated from SAM cDNA libraries. These sequences, together with previously reported pea ESTs, were used to construct a 12K oligonucleotide array to identify genes with differential SAM expression, as compared to axillary meristems, root apical meristems, or non-meristematic tissues. A number of genes were identified, predominantly expressed in specific cell layers or domains of the SAM and thus are likely components of the gene networks involved in stem cell maintenance or the initiation of lateral organs. Further in situ hybridization analysis confirmed the spatial localization of some of these genes within the SAM. Our data also indicate the diversification of some gene expression patterns and hence functions in legume crop plants. A number of transcripts highly expressed in all three meristems have also been uncovered and these candidates may provide valuable insight into molecular networks that underpin the maintenance of meristematic functionality.

Transcriptional profiling of the pea shoot apical meristem reveals processes underlying its function and maintenance.

BackgroundDespite the importance of the shoot apical meristem (SAM) in plant development and organ formation, our understanding of the molecular mechanisms controlling its function is limited. Genomic tools have the potential to unravel the molecular mysteries of the SAM, and legume systems are increasingly being used in plant-development studies owing to their unique characteristics such as nitrogen fixation, secondary metabolism, and pod development. Garden pea (Pisum sativum) is a well-established classic model species for genetics studies that has been used since the Mendel era. In addition, the availability of a plethora of developmental mutants makes pea an ideal crop legume for genomics studies. This study aims to utilise genomics tools in isolating genes that play potential roles in the regulation of SAM activity.ResultsIn order to identify genes that are differentially expressed in the SAM, we generated 2735 ESTs from three cDNA libraries derived from freshly micro-dissected SAMs from 10-day-old garden peas (Pisum sativum cv Torsdag). Custom-designed oligonucleotide arrays were used to compare the transcriptional profiles of pea SAMs and non-meristematic tissues. A total of 184 and 175 transcripts were significantly up- or down-regulated in the pea SAM, respectively. As expected, close to 61% of the transcripts down-regulated in the SAM were found in the public database, whereas sequences from the same source only comprised 12% of the genes that were expressed at higher levels in the SAM. This highlights the under-representation of transcripts from the meristematic tissues in the current public pea protein database, and demonstrates the utility of our SAM EST collection as an essential genetic resource for revealing further information on the regulation of this developmental process. In addition to unknowns, many of the up-regulated transcripts are known to encode products associated with cell division and proliferation, epigenetic regulation, auxin-mediated responses and microRNA regulation.ConclusionThe presented data provide a picture of the transcriptional profile of the pea SAM, and reveal possible roles of differentially expressed transcripts in meristem function and maintenance.

Expression and Nucleotide Diversity of the Maize RIK Gene

The K homology (KH) domain is a conserved sequence present in a wide variety of RNA-binding proteins. The rough sheath2-interacting KH domain (RIK) protein of maize has been implicated in the maintenance of the repressed chromatin state of knox genes during leaf primordia initiation. The amino acid sequences of the publicly available plant RIK proteins contain a splicing factor 1 (SF1)-like KH domain core sequence motif that distinguishes them from all other SF1-like KH domain-containing proteins. We demonstrate that the maize RIK gene exhibits surprisingly little nucleotide sequence diversity among Zea species and subspecies. Microarray hybridization experiments demonstrate that RIK has a higher level of expression in the shoot apical meristem as compared with 14-day seedling. Reverse transcriptase-polymerase chain reaction analysis of RIK indicates that the gene is expressed in many tissues, albeit at lower levels in older leaf samples. Taken together, these data suggest that the RIK protein may be involved in the maintenance of an inactive chromatin state of knox and possibly other genes in nonmeristematic tissues.

Proteomic Analysis of Root Meristems and the Effects of Acetohydroxyacid Synthase-Inhibiting Herbicides in the Root of Medicago Truncatula

Quantitative proteome analyses of meristematic and nonmeristematic tissues from Medicago truncatula primary and lateral roots and meristem tissues from plants treated with acetohydroxyacid synthase-inhibiting herbicides were made. The accumulation of 81 protein spots changed in meristematic and nonmeristematic tissues and 51 protein spots showed significant changes in accumulation in herbicide-treated meristems. Identified proteins indicate two trends, (i) increased accumulation of cell division and redox-mediating proteins in meristems compared to nonmeristematic tissues and (ii) increased accumulation of pathogenesis-related and decreased accumulation of metabolic proteins in herbicide-treated roots.

Putrescine Aminopropyltransferase Is Responsible for Biosynthesis of Spermidine, Spermine, and Multiple Uncommon Polyamines in Osmotic Stress-Tolerant Alfalfa.

The biosynthesis of polyamines from the diamine putrescine is not fully understood in higher plants. A putrescine aminopropyltransferase (PAPT) enzyme activity was characterized in alfalfa (Medicago sativa L.). This enzyme activity was highly specific for putrescine as the initial substrate and did not recognize another common diamine, 1,3-diaminopropane, or higher-molecular-weight polyamines such as spermidine and spermine as alternative initial substrates. The enzyme activity was inhibited by a general inhibitor of aminopropyltransferases, 5[prime]-methylthioadenosine, and by a specific inhibitor of PAPTs, cyclohexylammonium sulfate. The initial substrate specificity and inhibition characteristics of the enzyme activity suggested that it is a classical example of a PAPT. However, this enzyme activity yielded multiple polyamine products, which is uncharacteristic of PAPTs. The major reaction product of PAPT activity in alfalfa was spermidine. The next most abundant products of the enzyme reaction using putrescine as the initial substrate included the tetramines spermine and thermospermine. These two tetramines were distinguished by thin-layer chromatography to be distinct reaction products exhibiting differential rates of formation. In addition, the uncommon polyamines homocaldopentamine and homocaldohexamine were tentatively identified as minor enzymatic reaction products but only in extracts prepared from osmotic stresstolerant alfalfa cultivars. PAPT activity from alfalfa was highest in meristematic shoot tip and floral bud tissues and was not detected in older, nonmeristematic tissues. Product inhibition of the enzyme activity was observed after spermidine was added into the in vitro assay for alfalfa PAPT activity. A biosynthetic pathway is proposed that accounts for the characteristics of this PAPT activity and accommodates a novel scheme by which certain uncommon polyamines are produced in plants.

DNA content, interphase AgNOR-area, number of 3 HrDNA hybridization signals and the methylation level in coding rDNA sequence in different organs of Lupinus luteus L.

Nuclear DNA and AgNOR-area quantity have been measured cytophotometrically, the number of silver grains after in situ3 H rDNA/DNA hybridization has been counted, and the level of rDNA methylation has been estimated in root meristems, differentiated root zones, hypocotyls, cotyledons, and leaves of 7-day-old seedlings of Lupinus luteus. DNA content increases by endoreplication, reaching the average DNA C-value of 4.2, in the meristem, 6.6C in hypocotyl, 15.9C in cotyledon, and 3.3C in leaf. The quantity of AgNOR-area, the highest in root meristem, does not follow DNA C-value. Number of grains after in situ 3 H rDNA/DNA hybridization corresponds to DNA amount, but their distribution differs, showing in many cases perinucleolar localization in organs displaying low AgNOR-area quantity. Southern hybridization has not demonstrated detectable changes in level rDNA methylation. We suggest that the low level of rDNA expression in non-meristematic tissues coul d be related to rDNA inactivation caused by its translocation into nucleolus-associated heterochromatin.

Modular growth in verticillate podetia of Cladonia

Verticillate proliferations are characteristic of the podetia in certain species of Cladonia section Cladonia that have been informally classified in the Cladonia cervicornis group. The proliferations form at the center of the closed scyphus and they usually give rise to further tiers of central proliferations. They are initially formed from meristematic tissue that persists in the upper layer of the scyphus, which becomes surrounded by nonmeristematic tissue dur- ing widening of the scyphus. Once the supporting scyphus attains a certain width, this meristematic tis- sue becomes active, producing a vertical prolifera- tion. The proliferation, which starts as an indistinct mass of fungal tissue, later becomes lichenized and differentiates into a characteristic podetial morphol- ogy that includes a stipe and scyphus. The vertical proliferation represents a new module of the pode- tium.

EXTENT OF GENOTYPIC VARIATION AMONG SWEETPOTATOES PRODUCED THROUGH NODAL AND ADVENTITIOUS SPROUTS

Our research compared the extent of genomic variability between plants originating from adventitious sprouts and nodal cultures. Plant materials, derived from a single sprout and originating from a storage root each of `Jewel,' `Sumor,' and L87-95, were clonally propagated for seven generations nodally and through adventitious sprouts. PCR-based analysis using 15 random primers identified 58 scorable molecular markers, 37 (63.79%) of which were shared by all three genotypes represented by 60 samples (10 nodal and 10 adventitiously derived plants/genotype). Of 29 putatively polymorphic markers, 24 (82.75%) were putative polymorphisms across the entire data set. The remaining four (13.79%) represented putatively fixed genotypic differences that were monomorphic within genotypes. A multidimensional scaling analysis differentiated seven (23.33%) adventitiously derived phenotypic marker variants, compared to four (13.33%) among nodal materials. Our results support previous findings that, relative to nonmeristematic tissues, meristematic regions strictly control cell division and DNA synthesis that exclude DNA duplication and other irregularities.

Effect of cytokinins on plastid development and photosynthetic polypeptides during organogenesis ofPinus ponderosa Dougl. cotyledons culturedin vitro

InPinus ponderosa Dougl., application of the cytokinins, benzyladenine and 2-isopentenyl adenine, to excised cotyledons, promoted thein vitro formation of meristematic centers which led to bud and shoot production. Meristematic cells showed plastids with poorly developed thylakoid membranes and rudimentary grana, whereas cells in non-meristematic tissues and in growth regulator free medium, had chloroplasts with well developed inner membranes, and more thylakoid membranes and grana than plastids of meristematic cells. Chlorophyll and six polypeptides associated with photosynthesis were present in lower concentrations in cytokinin-treated cotyledons than in those cultured in growth regulator free medium. Both benzyladenine and 2-isopentenyl adenine are effective in inhibiting the accumulation of at least two photosynthetic polypeptides in the first 24 h in culture. The ability of cotyledons to respond in this way to cytokinins is lost after three days in culture in growth regulator free medium prior to treatment with cytokinin.

Identification of cyclic nucleotide constituents of meristematic and non-meristematic tissue of Pisum sativum roots

The extraction of endogenous 3′,5′-cyclic-AMP, 3′,5′-cyclie-GMP, 3′,5′-cyclic-CMP, 3′,5′-cyclic-UMP, 3′,5′-cyclic-IMP and 3′,5′-cyclic-deoxyTMP from meristematic and non-meristematic regions of Pisum roots is described. Extracts were subjected to a sequential purification procedure involving adsorption chromatography on alumina, ion-exchange chromatography, and preparative electrophoresis. Purified samples were compared with cyclic nucleotide standards by HPLC and UV absorbance spectrophotometry; further analysis was carried out by fast atom bombardment mass spectrometry and mass-analysed ion kinetic energy spectrometry. 3′,5′-Cyclic-AMP, -GMP, -CMP and -UMP were found to be present in Pisum meristematic tissue and 3′,5′-cyclic-AMP, -GMP, -CMP, -IMP and -DTMP are present in the non-meristematic regions. Data indicate that there is a significantly higher concentration of cyclic CMP in meristematic tissue relative to that in non-meristematic regions.

Photosynthetic performance of Laminaria solidungula measured in situ in the Alaskan High Arctic

Photosynthetic performance in the kelp Laminaria solidungula J. Agardh was examined from photosynthesis irradiance (P-I) parameters calculated from in situ 14C uptake experiments, using whole plants in the Stefansson Sound Boulder Patch, Alaskan Beaufort Sea, in August 1986. Rates of carbon fixation were determined from meristematic, basal blade, and second blade tissue in young and adult sporophytes. Differences in saturating irradiance (Ik, measured as photosynthetically active radiation, PAR), photosynthetic capacity (Pmax), and relative quantum efficiency (α) were observed both between young and adult plants and between different tissue types. Ik was lowest in meristematic tissue (20 to 30 μE m−2 s−1) for both young and adult plants, but consistently 8 to 10 μE m−2 s−1 higher in young plants compared to adults in all three tissues. Average Ik for non-meristematic tissue in adult plants was 38 μE m−2 s−1. Under saturating irradiances, young and adult plants exhibited similar rates of carbon fixation on an area basis, but under light limitation, fixation rates were highest in adult plants for all tissues. Pmax was generally highest in the basal blade and lowest in meristematic tissue. Photosynthetic efficiency (α) ranged between 0.016 and 0.027 μmol C cm−2 h−1/μE m−2 s−1, and was highest in meristematic tissue. The relatively lower Ik and higher α exhibited by L. solidungula in comparison to other kelp species are distinct adaptations to the near absence of light during the eight-month ice-covered period and in summer when water turbidity is high. Continuous measurement of in situ quantum irradiance made in summer showed that maximum PAR can be less than 12 μE m−2 s−1 for several days when high wind velocities increase water turbulence and decrease water transparency.

Les teneurs ioniques des plants d'Isoetes setacea au cours de la réactivation par réhydratation

Ionic amounts of S, P, K+, Ca2+, and Mg2+ have been determined by chemical measures in different parts of Isoetes setacea (shoot apical meristem, cortical zone, and central stele) for plants in normal growth, in drought resistance, and during rehydration. Study of modifications in the ionic amounts during experimental rehydration showed that the significant increase of K+, Ca2+, and Mg2+ by the 24th h of experimentation was one of the earliest signals observed for the cells of the apical meristem (which are at that time blocked in G1 presynthesis phase) as well as for the differentiated cells. By the 7th day of rehydration, just before their entrance into the synthesis phase, meristematic cells have recovered ionic rates equivalent to those measured for active plants. The same thing happens in the nonmeristematic tissues. This increase of ionic amounts in the whole plant can be explained by a differential entrance of ions with water. This new balance of the ionic amounts according to the pattern found in the active plants can be considered as a prerequisite event for the recovery of an active metabolism for a meristematic or differentiated cell in water stress.

Cadaverine formation by specific lysine decarboxylation in Pisum sativum seedlings

Cadaverine was found to be formed in Pisum sativum seedlings via a specific lysine decarboxylation pathway as revealed by specific inhibitor studies. Lysine decarboxylation activity was recorded in the meristems and non-meristematic tissue of the shoots and the roots. In the shoot elongation zone, the specific activity was double that in the other tissues and cadaverine level was 90-fold higher. The results presented in this study suggest possible regulatory control by polyamines of lysine decarboxylase activity in Pisum sativum seedlings.