Differential expression of a chlorophyll a/b binding protein gene and a proline rich protein gene in juvenile and mature phase English ivy (Hedera helix)

Two cDNA clones representing mRNAs which are differentially expressed during in vitro culture of juvenile and mature leaf petioles of English ivy ( Hedera helix L.) were isolated by differential screening. The mRNA represented by clone HW101 is expressed at a higher level in untreated juvenile than in untreated mature in-vitro-cultured petioles. Treatment of petioles with α-naphthaleneacetic acid (NAA) at the initiation of culture decreases HW101 mRNA levels in juvenile but not mature, petioles. In intact plants. HW101 mRNA is expressed at a higher level in juvenile laminae, petioles and stems than in identical tissues of mature plants. DNA sequence analysis indicates that HW1O1 cDNA is significantly similar to a light harvesting chlorophyll a/b binding protein gene ( Lhcb ) of pea. The gene represented by the second clone. HW103, is expressed at a higher level in mature than in juvenile in-vitro-cultured petisoles. Treatment of petioles with NAA at the initiation of culture decreases HW103 mRNA levels in chronologically young mature but not older mature and juvenile petioles. However, expression of the HW103 gene is not detectable in petioles, or in any other vegetative organ tested, immediately after excision. It is, however, expressed in developing seeds. In otherwise intact plants, the HW103 gene is expressed in wounded petioles of mature plants 5 days after wounding but not in wounded petioles of juvenile plants. It is also expressed at a higher level in wounded stems of mature plants than in those of juvenile plants. However, it is not expressed in wounded lamina of either juvenile or mature plants. DNA sequence analysis indicates that HW103 cDNA is similar to a cell wall proline rich protein (PRP) gene of soybean. This is the first report of differential expression of a PRP gene in tissues from juvenile and mature plants. Southern blot analysis of nuclear DNA of H. helix shows that both HW101 and HW103 are members of small gene families.     

Latent root primordia in poplar stems

Root primordia initiate in poplar stems in the secondary growing parts, that is in the parts where the elongation growth is terminated and the leaves are mature. Their initiation is connected with the occurrence of unusual biseriate, rarely multiseriate rays. A small cell group in the secondary phloem is initiated by cell division of the ray. It gradually enlarges by continuing cell division, by the addition of cells adjacent to the cell group and by cambial activity. Thus, a hemispherical root primordium is formed, for which a permanent occurrence of reserve lipids is characteristic. In stems several years old the intraprimordial mitotic activity is rhythmically renewed together with the cambium function renewal. Latent root primordia slightly enlarge with the passing years, whereas mainly the cells localized in their centre divide. Further organization and root histogenesis was not observed either in older root primordia. Adjacent to root primordia, cambial initials produce the secondary xylem elements increasingly. Xylem protuberances are thus formed under root primordia. Primordia initiation is most frequent within the first year of stem development, though they can also initiate in later years.     

Anatomical and Biochemical Events duringin vitroRooting of Microcuttings from Juvenile and Mature Phases of Chestnut

A comparative study of thein vitrorooting process of chestnut(Castanea sativa)shoots of the same genotype exhibiting juvenile(easy-to-root) and mature (difficult-to-root) characteristicsis described. The two culture lines originated from shoots collectedfrom the base (juvenile) and crown (mature) of an 80-year-oldtree. Anatomically, juvenile and mature shoots had a similarstem structure at the time of excision, the main differencebeing that secondary phloem and xylem were more developed inmature than in juvenile shoots. A substantial reactivation ofcell division was observed in both shoot lines 48 h after theroot inductive treatment with indole-3-butyric acid. Meristemoidsand root primordia developed only in juvenile shoots, beginning3 d after the inductive treatment, and the first adventitiousroots emerged 10 d after treatment. However, in mature shootspericlinal divisions of cambial cells occurred, especially onthe phloem side, maintaining the normal orientation of the cambialderivatives. No meristemoids formed in this proliferating tissue.During the time course of the rooting process, more endogenousindole-3-acetic acid (IAA) was detected in mature than in juvenileshoots, indicating that the level of IAA is not the limitingfactor accounting for the lack of rooting capacity in matureshoots. The levels of polyamines (putrescine, spermine and spermidine)were also higher in mature than in juvenile shoots.Copyright1999 Annals of Botany Company Adventitious rooting, anatomy, auxins,Castanea sativaMill., chestnut, juvenile phase, mature phase, polyamines, tissue culture.     

Tissue-Specific Expression of Cell Wall Proteins in Developing Soybean Tissues

Cell wall hydroxyproline-rich glycoproteins (HRGPs) and glycine-rich proteins (GRPs) were examined at the protein and at the mRNA levels in developing soybean tissues by tissue print immunoblots and RNA blots. In young soybean stems, HRGPs are expressed most heavily in cambium cells, in a few layers of cortex cells surrounding primary phloem, and in some parenchyma cells around the primary xylem, whereas GRPs are highly expressed in the primary xylem and also in the primary phloem. In older soybean stems, HRGP genes are expressed exclusively in cambium cells and GRP genes are most heavily expressed in newly differentiated secondary xylem cells. Similar expression patterns of HRGPs and of GRPs were found in soybean petioles, seedcoats, and young hypocotyls, and also in bean petioles and stems. HRGPs and GRPs become insolubilized in soybean stem cell walls. Three major HRGP mRNAs and two major GRP mRNAs accumulate in soybean stems. Soluble HRGPs are abundant in young hypocotyl apical regions and young root apical regions, whereas in hypocotyl and root mature regions, soluble HRGPs are found only in a few layers of cortex cells surrounding the vascular bundles. GRPs are specifically localized in primary xylem cell walls of young root. These results show that the gene expression of HRGPs and GRPs is developmentally regulated in a tissue-specific manner. In soybean tissues, HRGPs are most heavily expressed in meristematic cells and in some of those cells that may be under stress, whereas GRPs are expressed in all cells that are or are going to be lignified.     

INITIATION AND DEVELOPMENT OF ROOTS IN JUVENILE AND MATURE LEAF BUD CUTTINGS OF FICUS PUMILA L.

Adventitious root formation (ARF) was studied in woody leaf bud cuttings of Ficus pumila L., creeping fig. Juvenile cuttings rooted easily, whereas only mature cuttings treated with indole-3-butyric acid (IBA) attained any rooting success. In the rooting process, both juvenile and mature material exhibited dedifferentiation of phloem ray parenchyma, root initial formation, primordia differentiation, and root elongation. The early stages of adventitious rooting were most critical since few primordia were observed in mature controls. The stages leading up to root primordia differentiation and elongation occurred more rapidly in IBA-treated juvenile vs. mature cuttings; however, time differences in both types between first observable roots and maximum rooting were comparable. Root primordia differentiated from basal callus of some cuttings, but neither these nor the few primordia in mature controls elongated into well-developed roots. Anatomical differences between the juvenile and mature material did not account for rooting disparity, nor did presence of perivascular fibers, sclereids, and laticifers retard rooting.     

白花泡桐不定根发生过程中内源激素和RNA的变化

白花泡桐（Ｐａｕｌｏｗｎｉａｆｏｒｔｕｎｅｉ（Ｓｅｅｍ．）Ｈｅｍｓｌ．）成年型和幼年型茎切段体外培养时不定根发生过程中内源ＩＡＡ、ＣＴＫ和ＡＢＡ含量测定表明：幼年型材料中内源ＩＡＡ和ＣＴＫ的含量在诱导的第２天同时达到高峰,而成年型材料中ＩＡＡ和ＣＴＫ含量的高峰则在第４天出现．两种类型切段根原基出现的时间都与其内源ＩＡＡ和ＣＴＫ的高峰一致．幼年型材料的内源ＡＢＡ含量在第４天达到高峰,随后迅速下降．成年型材料中内源ＡＢＡ则逐步下降．成年型和幼年型材料中ＲＮＡ的变化相同,在诱导的第２天稍有下降,随后显著增加．结果显示,不定根的发生与其内源激素和ＲＮＡ的变化密切相关．     

Mutations in the Diageotropica (Dgt) gene uncouple patterned cell division during lateral root initiation from proliferative cell division in the pericycle

In angiosperms, root branching requires a continuous re-initiation of new root meristems. Through some unknown mechanism, in most eudicots pericycle cells positioned against the protoxylem change identity and initiate patterned division, leading to formation of lateral root primordia that further develop into lateral roots. This process is auxin-regulated. We have observed that three mutations in the Diageotropica (Dgt) gene in tomato prevent primordium formation. Detailed analysis of one of these mutants, dgt1-1, demonstrated that the mutation does not abolish the proliferative capacity of the xylem-adjacent pericycle in the differentiated root portion. Files of shortened pericycle cells found in dgt1-1 roots were unrelated to primordium formation. Auxin application stimulated this unusual proliferation, leading to formation of a multi-layered xylem-adjacent pericycle, but did not rescue the primordium formation. In contrast to wild type, auxin could not induce any cell divisions in the pericycle of the most distal dgt1-1 root-tip portion. In wild-type roots, the Dgt gene promoter was expressed strongly in lateral root primordia starting from their initiation, and on auxin treatment was induced in the primary root meristem. Auxin level and distribution were altered in dgt1-1 root tissues, as judged by direct auxin measurements, and the tissue-specific expression of an auxin-response reporter was altered in transgenic plants. Together, our data demonstrate that the Dgt gene product, a type-A cyclophilin, is essential for morphogenesis of lateral root primordia, and that the dgt mutations uncouple patterned cell division in lateral root initiation from proliferative cell division in the pericycle.     

Differential Gene Expression in Response to Auxin Treatment in the Wild Type and rac,an Adventitious Rooting-Incompetent Mutant of Tobacco

Histological analyses of auxin-treated cuttings from the wild type and the rac mutant of tobacco (Nicotiana tabacum cv Xanthii) previously revealed that some rac phloem parenchyma or inner cortical parenchyma cells form callus in response to exogenous auxin treatment but these cells never undergo the organized divisions associated with adventitious root initiation in the wild type. Here we report the effect of the rac mutation on the temporal and spatial expression patterns of three genes previously shown to be associated with adventitious root meristems, HRGPnt3, iaa4/5, and gh3. Using histochemical staining analyses of HRGPnt3-GUS transformant cuttings, we determined that the rac mutation blocks auxin activation of the HRGPnt3 promoter. Thus, activation of the HRGPnt3 promoter occurs specifically during adventitious root initiation in tobacco cuttings. Histochemical staining analyses of iaa4/5-GUS and gh3-GUS transformant cuttings revealed that the rac mutation does not repress the auxin activation of the iaa4/5 and gh3 promoters. Based on our histochemical staining analyses, we conclude that differential gene expression occurs in response to auxin treatment during adventitious root initiation in the wild type compared with callus formation in rac cuttings. We also determined that HRGPnt3 mRNA accumulation occurs in response to components of our root-induction protocol other than auxin, indicating that HRGPnt3 expression is regulated both developmentally and environmentally.     

Developmental and environmental regulation of tissue- and cell-specific expression for a pea protein farnesyltransferase gene in transgenic plants

Farnesylation mediates membrane targeting and in vivo activities of several key regulatory proteins such as Ras and Ras-related GTPases and protein kinases in yeast and mammals, and is implicated in cell cycle control and abscisic acid (ABA) signaling in plants. In this study, the developmental expression of a pea protein farnesyl-transferase (FTase) gene was examined using transgenic expression of the β-glucuronidase (GUS) gene fused to a 3.2 kb 5′ upstream sequence of the gene encoding the pea FTase β subunit. Coordinate expression of the GUS transgene and endogenous tobacco FTase β subunit gene in tobacco cell lines suggests that the 3.2 kb region contains the key FTase promoter elements. In transgenic tobacco plants, GUS expression is most prominent in meristematic tissues such as root tips, lateral root primordia and the shoot apex, supporting a role for FTase in the control of the cell cycle in plants. GUS activity was also detected in mature embryos and imbibed embryos, in accordance with a role for FTase in ABA signaling that modulates seed dormancy and germination. In addition, GUS activity was detected in regions that border two organs, e.g. junctions between stems and leaf petioles, cotyledons and hypocotyls, roots and hypocotyls, and primary and secondary roots. GUS is expressed in phloem complexes that are adjacent to actively growing tissues such as young leaves, roots of light-grown seedlings, and hypocotyls of dark-grown seedlings. Both light and sugar (e.g. sucrose) treatments repressed GUS expression in dark-grown seedlings. These expression patterns suggest a potential involvement of FTase in the regulation of nutrient allocation into actively growing tissues.     

Developmental expression of tomato heat-shock cognate protein 80

Heat-shock protein 80 (HSP80) is a major heat-shock protein induced in yeast and animals both by heat shock and by specific developmental events. In plants, a heat-shock-induced HSP80 cDNA has been described, although no information concerning developmental regulation of HSP80 genes is available. We have characterized a tomato (Lycopersicon esculentum) gene encoding a typical HSP80 protein. This gene, called HSC80, is interrupted by two introns, 995 and 109 bp long. Northern blot analyses and in situ RNA hybridization show that HSC80 mRNA is abundant in shoot and root apices and in fertilized ovaries up to 6 d postanthesis but is rare in mature leaves. Heat shock increased mRNA levels in mature leaves but only 3-fold. Developmental regulation of the HSC80 gene was confirmed by fusing 2 kb of its 5′ region to the β-glucuronidase reporter gene and introducing the chimeric gene into tomatoes. The roots of transformants showed high β-glucuronidase expression in the apex and in lateral root primordia but not in mature tissue. Expression in the shoot was up to 10-fold higher in the apex than in mature leaves. Thus, HSC80 is preferentially expressed in shoot and root apices during normal development.     

Immunolocalization of mannitol dehydrogenase in celery plants and cells.

Immunolocalization of mannitol dehydrogenase (MTD) in celery (Apium graveolens L.) suspension cells and plants showed that MTD is a cytoplasmic enzyme. MTD was found in the meristems of celery root apices, in young expanding leaves, in the vascular cambium, and in the phloem, including sieve-element/companion cell complexes, parenchyma, and in the exuding phloem sap of cut petioles. Suspension cells that were grown in medium with mannitol as the sole carbon source showed a high anti-MTD cross-reaction in the cytoplasm, whereas cells that were grown in sucrose-containing medium showed little or no cross-reaction. Gel-blot analysis of proteins from vascular and nonvascular tissues of mature celery petioles showed a strong anti-MTD sera cross-reactive band, corresponding to the 40-kD molecular mass of MTD in vascular extracts, but no cross-reactive bands in nonvascular extracts. The distribution pattern of MTD within celery plants and in cell cultures that were grown on different carbon sources is consistent with the hypothesis that the Mtd gene may be regulated by sugar repression. Additionally, a developmental component may regulate the distribution of MTD within celery plants.     

ARL1, a LOB-domain protein required for adventitious root formation in rice

Adventitious roots constitute the bulk of the fibrous root system in cereals. Compared with the current understanding of shoot development, knowledge of the molecular mechanisms of development of the adventitious roots of cereals is limited. We have isolated and characterized a novel gene controlling the initiation of adventitious root primordia in rice (Oryza sativa L.). The gene, designated Adventitious rootless1 (ARL1), encodes a protein with a LATERAL ORGAN BOUNDARIES (LOB) domain. It is expressed in lateral and adventitious root primordia, tiller primordia, vascular tissues, scutellum, and young pedicels. ARL1 is a nuclear protein and can form homodimers. ARL1 is an auxin- and ethylene-responsive gene, and the expression pattern of ARL1 in roots parallels auxin distribution. Our findings suggest that ARL1 is an auxin-responsive factor involved in auxin-mediated cell dedifferentiation, and that it promotes the initial cell division in the pericycle cells adjacent to the peripheral vascular cylinder in the stem.     

The ubiquitin ligase XBAT32 regulates lateral root development in Arabidopsis

Ubiquitin-mediated protein modification plays a key role in many cellular signal transduction pathways. The Arabidopsis gene XBAT32 encodes a protein containing an ankyrin repeat domain at the N-terminal half and a RING finger motif. The XBAT32 protein is capable of ubiquitinating itself. Mutation in XBAT32 causes a number of phenotypes including severe defects in lateral root production and in the expression of the cell division marker CYCB1;1::GUS . The XBAT32 gene is expressed abundantly in the vascular system of the primary root, but not in newly formed lateral root primordia. Treatment with auxin increases the expression of XBAT32 in the primary root and partially rescues the lateral root defect in xbat32 - 1 mutant plants. Thus, XBAT32 is a novel ubiquitin ligase required for lateral root initiation.     

Life cycle stage and water depth affect flooding-induced adventitious root formation in the terrestrial species Solanum dulcamara

Background and Aims Flooding can occur at any stage of the life cycle of a plant, but often adaptive responses of plants are only studied at a single developmental stage. It may be anticipated that juvenile plants may respond differently from mature plants, as the amount of stored resources may differ and morphological changes can be constrained. Moreover, different water depths may require different strategies to cope with the flooding stress, the expression of which may also depend on developmental stage. This study investigated whether flooding-induced adventitious root formation and plant growth were affected by flooding depth in Solanum dulcamara plants at different developmental stages.Methods Juvenile plants without pre-formed adventitious root primordia and mature plants with primordia were subjected to shallow flooding or deep flooding for 5 weeks. Plant growth and the timing of adventitious root formation were monitored during the flooding treatments.Key Results Adventitious root formation in response to shallow flooding was significantly constrained in juvenile S. dulcamara plants compared with mature plants, and was delayed by deep flooding compared with shallow flooding. Complete submergence suppressed adventitious root formation until up to 2 weeks after shoots restored contact with the atmosphere. Independent of developmental stage, a strong positive correlation was found between adventitious root formation and total biomass accumulation during shallow flooding.Conclusions The potential to deploy an escape strategy (i.e. adventitious root formation) may change throughout a plant’s life cycle, and is largely dependent on flooding depth. Adaptive responses at a given stage of the life cycle thus do not necessarily predict how the plant responds to flooding in another growth stage. As variation in adventitious root formation also correlates with finally attained biomass, this variation may form the basis for variation in resistance to shallow flooding among plants.     

Adventitious Root Initiation In Reciprocally Grafted Leaf Cuttings from the Juvenile and Mature Phase of Hedera helix L

Reciprocal grafts involving leaf petioles and lamina of thejuvenile and mature phase of Hedera helix were prepared to determinethe relative importance of petiole and lamina on root initiationin leaf cuttings. The results indicated that root initiationwas mainly a function of the potential of cells in the petioleto respond in a specific morphogenetic pattern. Initially, rootinitiation was unaffected by the type of lamina. However, overtime, a factor translocated from the juvenile lamina promotedroot initiation in the mature petiole. This factor decreasedthe time taken for root initiation and increased the numberof roots per mature petiole. There was no evidence for an inhibitorfrom the mature lamina affecting root initiation in the juvenilepetiole. Key words: Rejuvenation, root initiation, rooting cofactors     

The SCARECROW gene's role in asymmetric cell divisions in rice plants

Asymmetric cell division is one of the most important mechanisms in the diversification of cell function and fate. In Arabidopsis, SCARECROW (SCR) is essential for the asymmetric division of the cortex/endodermis progenitor cell in the root. To learn more about how SCR is involved in asymmetric division, we analyzed the rice SCR (OsSCR) expression. In the root tip, OsSCR expression was observed in the endodermal cell layer and downregulated in the daughter cortex cell after asymmetric division, just as with Arabidopsis SCR. In leaf primordia, expression of OsSCR was observed in stomatal and ligule formation. In stomatal development, OsSCR was specifically expressed in the stomatal cell files before formation of guard mother cells (GMCs), and then, its expression was localized in GMCs, when the first asymmetric division occurred to generate the GMCs. Before the second asymmetric division of subsidiary mother cells (SMCs), localized OsSCR expression was observed in SMCs in the area close to the GMCs. Before these asymmetric divisions, the localization of OsSCR mRNA in GMC-forming cells and SMCs was observed in the area of the daughter GMC and subsidiary cells. OsSCR expression was also observed in the initiation area of ligule formation, and its downregulation occurred in the inner L2 cells generated by asymmetric division. Based on these observations, we proposed that OsSCR is involved not only in the asymmetric division of the cortex/endodermis progenitor cell but also during stomata and ligule formation by establishing the polarization of cytoplasm.     

The Medicago species A2-type cyclin is auxin regulated and involved in meristem formation but dispensable for endoreduplication-associated developmental programs

Phytohormones as well as temporal and spatial regulation of the cell cycle play a key role in plant development. Here, we investigated the function and regulation of an alfalfa (Medicago sativa) A2-type cyclin in three distinct root developmental programs: in primary and secondary root development, nodule development, and nematode-elicited gall formation. Using transgenic plants carrying the Medsa;cycA2;2 promoter-beta-glucuronidase gene fusion, in combination with other techniques, cycA2;2 expression was localized in meristems and proliferating cells in the lateral root and nodule primordia. Rapid induction of cycA2;2 by Nod factors demonstrated that this gene is implicated in cell cycle activation of differentiated cells developing to nodule primordia. Surprisingly, cycA2;2 was repressed in the endoreduplicating, division-arrested cells both during nodule development and formation of giant cells in nematode-induced galls, indicating that CycA2;2 was dispensable for S-phase in endoreduplication cycles. Overexpression of cycA2;2 in transgenic plants corresponded to wild type protein levels and had no apparent phenotype. In contrast, antisense expression of cycA2;2 halted regeneration of somatic embryos, suggesting a role for CycA2;2 in the formation or activity of apical meristems. Expression of cycA2;2 was up-regulated by auxins, as expected from the presence of auxin response elements in the promoter. Moreover, auxin also affected the spatial expression pattern of this cyclin by shifting the cycA2;2 expression from the phloem to the xylem poles.