A protocol for efficient transformation and regeneration of Carica papaya L.

Summary A reproducible and effective biolistic method for transforming papaya (Carica papaya L.) was developed with a transformation-regeneration system that targeted a thin layer of embryogenic tissue. The key factors in this protocol included: 1) spreading of young somatic embryo tissue that arose directly from excised immature zygotic embryos, followed by another spreading of the actively growing embryogenic tissue 3 d before biolistic transformation; 2) removal of kanamycin selection from all subsequent steps after kanamycin-resistant clusters were first isolated from induction media containing kanamycin; 3) transfer of embryos with finger-like extensions to maturation medium; and 4) transferring explants from germination to the root development medium only after the explants had elongating root initials, had at least two green true leaves, and were about 0.5 to 1.0 cm tall. A total of 83 transgenic papaya lines expressing the nontranslatable coat protein gene of papaya ringspot virus (PRSV) were obtained from somatic embryo clusters that originated from 63 immature zygotic embryos. The transformation efficiency was very high: 100% of the bombarded plates produced transgenic plants. This also represents an average of 55 transgenic lines per gram fresh weight, or 1.3 transgenic lines per embryo cluster that was spread. We validated this procedure in our laboratory by visiting researchers who did four independent projects to transform seven papaya cultivars with coat protein gene constructs of PRSV strains from four different countries. The method is described in detail and should be useful for the routine transformation and regeneration of papaya. Based in part on a presentation at the 1997 SIVB Congress on In Vitro Biology held in Washington, DC, June 14–18, 1997.     

The role of thrombin in the regulation of the endothelial prostaglandin production

Prostaglandin synthesis in endothelial cells may be initiated by the addition of exogenous substrate (arachidonic acid) or by addition of thrombin or the CA2+-ionophore A23187, which leads to prostacyclin formation from endogenous substrates. We noticed that endothelial cells produce more than twice the amount of prostacyclin when incubated with thrombin and arachidonic acid together than with arachidonic acid alone. In addition, it was found that the thrombin-induced conversion of endogenous substrates was inhibited by exogenous arachidonic acid. This means that the conversion of exogenous added arachidonic acid to prostacyclin was stimulated by thrombin. This activation of the enzymes involved in prostacyclin synthesis lasted about 5 min and could be inhibited by phospholipase inhibitors such as mepacrine and p-bromophenyl-acylbromide but not by the cAMP analogue dibutyryl cAMP, an inhibitor of arachidonic acid release from cellular phospholipids. These data demonstrate that, in addition to causing release of endogenous substrate, thrombin and the Ca2+-ionophore also activate the enzyme system involved in the further transformation of arachidonic acid.     

Comparison of secretion and subcellular localization of von Willebrand protein with that of thrombospondin and fibronectin in cultured human vascular endothelial cells

Cultured human vascular endothelial cells synthesize von Willebrand protein, thrombospondin and fibronectin. These proteins are secreted in the culture medium and incorporated into the extracellular matrix. We have compared the subcellular localization and the secretion of these proteins in response to stimulants in cultured human umbilical vein endothelial cells. Density gradient centrifugation using colloidal silica showed that the storage and secretion organelle with von Willebrand protein did not contain thrombospondin or fibronectin. Indirect immunofluorescence microscopy indicated that thrombospondin and fibronectin are not located in the rod-shaped organelles containing von Willebrand protein. Thrombin, ionophore A23187 and phorbol myristate acetate did not affect secretion of thrombospondin and fibronectin, while von Willebrand protein secretion was stimulated upon incubation of cells with these agents for 30 min. Prolonged incubation of cultured endothelial cells after a 1-h treatment with phorbol myristate acetate resulted in an increased secretion of von Willebrand protein into the conditioned medium; in contrast, accumulation of thrombospondin and fibronectin in endothelial cell-conditioned medium was decreased. These findings indicate that, unlike in platelets, these major endothelial proteins are not located in the same subcellular compartments. Von Willebrand protein is distinguished from thrombospondin and fibronectin both by its unique subcellular localization and its secretion rate in response to stimuli.     

Studies on an anophthalmic strain of mice. VI. Lens and cup interaction

In the embryology of the eye region in the anophthalmic strain of mice ($\text{ZRDCT}\text{Ch}$), development proceeds normally until Day 10 (26 somites). At this time a lens is induced, but it is smaller in size and may be improperly centered in the optic cup. Where the lens is centered in relation to the optic cup determines whether microphthalmia or anophthalmia will occur. Also, we observed that optic cup formation is different in normal control strains.     

Transgenic peanut plants containing a nucleocapsid protein gene of tomato spotted wilt virus show divergent levels of gene expression

The nucleocapsid protein (N) gene of the lettuce isolate of tomato spotted wilt virus (TSWV) was inserted into peanut (Arachis hypogaea L.) via microprojectile bombardment. Constructs containing the hph gene for resistance to the antibiotic hygromycin and the TSWV N gene were used for bombardment of peanut somatic embryos. High frequencies of transformation and regeneration of plants containing the N gene were obtained. Southern blot analysis of independent transgenic lines revealed that one to several copies of the N gene were integrated into the peanut genome. Northern blot, RT-PCR and ELISA analyses indicated that a gene silencing mechanism may be operating in primary transgenic lines containing multiple copy insertions of the N transgene. One transgenic plant which contained a single copy of the transgene expressed the N protein in the primary transformant, and the progeny segregated in a 3 :1 ratio based upon ELISA determination. Received: 24 October 1997 / Revision received: 9 February 1998 / Accepted: 21 February 1998     

Transgenic papaya plants from Agrobacterium-mediated transformation of somatic embryos

Summary Transgenic papaya (Carica papaya L.) plants were regenerated from embryogenic cultures that were cocultivated with a disarmed C58 strain of Agrobacterium tumefaciens containing one of the following binary cosmid vectors: pGA482GG or pGA482GG/cpPRV-4. The T-DNA region of both binary vectors includes the chimeric genes for neomycin phosphotransferase II (NPTII) and ß-glucuronidase (GUS). In addition, the plant expressible coat protein (cp) gene of papaya ringspot virus (PRV) is flanked by the NPTII and GUS genes in pGA482GG/cpPRV-4. Putative transformed embryogenic papaya tissues were obtained by selection on 150 g·ml^–1 kanamycin. Four putative transgenic plant lines were obtained from the cp gene^– vector and two from the cp gene⁺ vector. GUS and NPTII expression were detected in leaves of all putative transformed plants tested, while PRV coat protein expression was detected in leaves of the PRV cp gene⁺ plant. The transformed status of these papaya plants was analyzed using both polymerase chain reaction amplification and genomic blot hybridization of the NPTII and PRV cp genes. Integration of these genes into the papaya genome was demonstrated by genomic blot hybridizations. Thus, like numerous other dicotyledonous plant species, papayas can be transformed with A. tumefaciens and regenerated into phenotypically normal-appearing plants that express foreign genes.Journal Series no. 3757 of the Hawaii Institute of Tropical Agriculture and Human Resources     

The action of divalen Zn,Cd, Hg,Cu and Pb ions on the ATPase activity of a plasma membrane fraction isolated from roots ofZea mays

The effects of the divalent metal ions Zn, Cd, Hg, Cu and Pb on the ATPase activity of a plasma membrane fraction isolated from roots ofZea mays have been investigated. When Mg-ions (3 mM), with or without K-ions (50mM) are included in the reaction medium, inhibition of ATPase activity was found in all cases, the relative order of the inhibitors over the concentration range 10 to 100M, being Hg>>CuCd>ZnPb. Below 1.0M only Hg caused substantial inhibition. In the absence of Mg ions, Zn and to a lesser extent Cd, activated the enzyme up to a concentration of 1 mM, activity being further stimulated in the presence of K-ions (50mM). No activation of ATPase activity was found for Hg, Cu or Pb. It was concluded that Zn-ATP and Cd-ATP are both alternative substrates for the enzyme. Further experiments showed that both K_m and V_max for the substrates Zn-ATP and Cd-ATP are very much lower than for the usual substrate Mg-ATP.These present results are discussed in relation to the known actions of these divalent cations on the trans-root potential and H-ion efflux in excised maize roots (Kennedy and Gonsalves, 1987).     

Characterization of Insertion Sites in Rainbow Papaya, the First Commercialized Transgenic Fruit Crop

Inserts and insert sites in transgenic, papaya ringspot virus (PRSV)-resistant commercial papaya Rainbow and SunUp, were characterized as part of a petition to Japan to allow import of fresh fruit of these cultivars from the U.S. and to provide data for a larger study aimed at understanding the global impact of DNA transformation on whole genome structure. The number and types of inserts were determined by Southern analysis using probes spanning the entire transformation plasmid and their sequences determined from corresponding clones or sequence reads from the whole-genome shotgun (WGS) sequence of SunUp papaya. All the functional transgenes, coding for the PRSV coat protein (CP), neophosphotransferase (nptII) and β-glucuronidase (uidA) were found in a single 9,789 basepair (bp) insert. Only two other inserts, one consisting of a 290 bp nonfunctional fragment of the nptII gene and a 1,533 bp plasmid-derived fragment containing a nonfunctional 222 bp segment of the tetA gene were detected in Rainbow and SunUp. Detection of the same three inserts in samples representing transgenic generations five to eight (R5 to R8) suggests that the three inserts are stably inherited. Five out of the six genomic DNA segments flanking the three inserts were nuclear plastid sequences (nupts). From the biosafety standpoint, no changes to endogenous gene function based on sequence structure of the transformation plasmid DNA insertion sites could be determined and no allergenic or toxic proteins were predicted from analysis of the insertion site and flanking genomic DNA.     

Development and evaluation of an enzyme-linked immunosorbent assay to detect Pieris rapae remains in guts of arthropod predators

An enzyme-linked immunosorbent assay (ELISA) was developed to detect remains of Pieris rapae L. (Lepidoptera: Pieridae) immature stages in the guts of field collected arthropod predators. The assay can be used to help ascertain the relative importance of arthropod predator species in suppressing P. rapae in cabbage, Brassica oleracea var. capitata L. The ELISA is sensitive to all immature stages of P. rapae, although first and fifth instars can be detected more readily than eggs or pupae and third instars showed intermediate detectability. Assays on whole body homogenates of predators readily detected predation on P. rapae first instars by all seven of the predator species tested, although response generally declined with increasing predator size. Together the results show that the P. rapae ELISA possesses a sufficiently high level of sensitivity and specificity to be a useful tool in helping to elucidate the roles of arthropod predator species in reducing populations of P. rapae in cabbage.