Abraham H. Halevy

Bio: Abraham H. Halevy is an academic researcher from Hebrew University of Jerusalem. The author has contributed to research in topics: Shoot & Petal. The author has an hindex of 42, co-authored 169 publications receiving 5734 citations. Previous affiliations of Abraham H. Halevy include University of California, Davis.

Interorgan regulation of ethylene biosynthetic genes by pollination.

Abstract: Pollination initiates a syndrome of developmental events that contribute to successful reproduction, including perianth senescence, changes in pigmentation, and ovule differentiation in preparation for impending fertilization. In orchid flowers, initiation of each of these processes in distinct floral organs is strictly and coordinately controlled by pollination, thus providing a unique opportunity to study the signals that coordinate interorgan postpollination development. Because ethylene has been implicated in contributing to regulation of severa1 aspects of postpollination development, we focused on determining the expression of its biosynthetic genes and their possible role in regulation. The abundance of mRNA encoding both 1-aminocyclopropane-l-carboxylic acid (ACC) synthase and ACC oxidase in the stigma, ovary, and labellum was found to be coordinately regulated by emasculation, auxin, and ethylene. Although petals contribute up to 26% of total flower ethylene and accumulate high levels of ACC oxidase mRNA and activity following pollination, no ACC synthase mRNA or activity was detected in this tissue. Together, these results support a model of interorgan regulation of postpollination development that depends on pollination-stimulated accumulation of mRNA encoding ethylene biosynthetic enzymes in a developmentally regulated and tissue-specific manner. This model relies on the translocation of a soluble hormone precursor, ACC, rather than on the translocation of the hormone itself. In this way, ACC serves to actuate the response already initiated by ethylene perceived by other parts of the flower. Thus, ACC may function as a secondary transmissible signal that coordinates postpollination development in diverse floral organs.

Factors influencing the production of hardened glaucous carnation plantlets in vitro

Abstract: Medium type, its water status and the relative humidity in the culture vessel modified carnation leaf development in vitro. Carnation shoot apices cultured on liquid or on 0.8% agar solidified media developed into plantlets having succulent and translucent leaves which are not transplantable to non-aseptic conditions. Increasing the agar and/or sucrose concentration in the medium as well as decreasing the relative humidity in the culture vessel by a desiccant promoted glaucous leaf production. Increased water status (ψH2O and relative humidity) increased shoot proliferation and translucency of leaves. Decreased water status reduced shoot proliferation but induced the formation of glaucous leaves. The culture of apices for 5–6 days on liquid medium prior to their sub-culture to 1.5% agar medium improved shoot proliferation and normal leaf development. An agar slant prevented the submergence of apices in water accumulating on the medium and thus reduced leaf translucency. Survival was further increased by the transfer of plantlets in uncapped culture vessels to a desiccator for 1–2 weeks prior to transplanting to soil.

Acceleration of membrane senescence in cut carnation flowers by treatment with ethylene.

Abstract: The lipid microviscosity of microsomal membranes from senescing cut carnation (Dianthus caryophyllus L. cv. White Sim) flowers rises with advancing senescence. The increase in membrane microviscosity is initiated within 3 to 4 days of cutting the flowers and coincides temporally with petal-inrolling denoting the climacteric-like rise in ethylene production. Treatment of young cut flowers with aminoethoxyvinylglycine prevented the appearance of petal-inrolling and delayed the rise in membrane microviscosity until day 9 after cutting. When freshly cut flowers or aminoethoxyvinylglycine-treated flowers were exposed to exogenous ethylene (1 microliter per liter), the microviscosity of microsomal membranes rose sharply within 24 hours, and inrolling of petals was clearly evident. Thus, treatment with ethylene accelerates membrane rigidification. Silver thiosulphate, a potent anti-ethylene agent, delayed the rise in microsomal membrane microviscosity even when the flowers were exposed to exogenous ethylene. Membrane rigidification in both naturally senescing and ethylene-treated flowers was accompanied by an increased sterol:phospholipid ratio reflecting the selective loss of membrane phospholipid that accompanies senescence. The results collectively indicate that the climacteric-like surge in ethylene production during senescence of carnation flowers facilitates physical changes in membrane lipids that presumably lead to loss of membrane function.

Stamens and gibberellin in the regulation of corolla pigmentation and growth in Petunia hybrida.

Abstract: Removal of stamens, or even of only the anthers, at an early stage of corolla development, before the start of main anthocyanin production, inhibited both growth and pigmentation of attached corollas of Petunia. When only one or two stamens were removed from one side, the inhibition was restricted to the corolla side adjacent to the detached stamens. Application of gibberellic acid (GA3) substituted for the stamens in its effect on both growth and pigmentation. In detached corollas, isolated at the early-green stage and grown in vitro in sucrose medium, GA3 promoted growth and was essential for anthocyanin synthesis. A marked enhancement of anthocyanin production was observed 48 h before the increase in corolla growth rate. Corollas detached at later stages were able to continue their growth and pigmentation in sucrose without GA3. When Paclobutrazol (β-[(4-chlorophenyl)-ethyl]-α(1,1-dimethylethyl)-H-1,2,4-triazol-1-ethanol), an inhibitor of gibberellin biosynthesis, was added to the growth medium of in-vitro-grown corollas, pigmentation was inhibited but there was no effect on corolla growth. Low levels of GA3 counteracted the Paclobutrazol effect on pigmentation but did not affect growth. The above results indicate that the effect of GA3 (and probably that of the stamens) on corolla growth is independent of its effect on pigmentation. Gibberellic acid and paclobutrazol had no effect on [(14)C]sucrose uptake by in-vitro-grown corollas. The activity of phenylalanine ammonialyase was correlated with the effect of stamens and GA3 on pigmentation in corollas grown in vivo and in vitro.

Analysis of the genome sequence of the flowering plant Arabidopsis thaliana.

Abstract: The flowering plant Arabidopsis thaliana is an important model system for identifying genes and determining their functions. Here we report the analysis of the genomic sequence of Arabidopsis. The sequenced regions cover 115.4 megabases of the 125-megabase genome and extend into centromeric regions. The evolution of Arabidopsis involved a whole-genome duplication, followed by subsequent gene loss and extensive local gene duplications, giving rise to a dynamic genome enriched by lateral gene transfer from a cyanobacterial-like ancestor of the plastid. The genome contains 25,498 genes encoding proteins from 11,000 families, similar to the functional diversity of Drosophila and Caenorhabditis elegans--the other sequenced multicellular eukaryotes. Arabidopsis has many families of new proteins but also lacks several common protein families, indicating that the sets of common proteins have undergone differential expansion and contraction in the three multicellular eukaryotes. This is the first complete genome sequence of a plant and provides the foundations for more comprehensive comparison of conserved processes in all eukaryotes, identifying a wide range of plant-specific gene functions and establishing rapid systematic ways to identify genes for crop improvement.

Ethylene biosynthesis and its regulation in higher plants

Abstract: PATHWAY OF ETHYLENE BIOSyNTHESIS 156 Methionine as an Intermediate ....... 157 S-Adenosylmethionine as an Intermediate 158 I-Aminocyclopropanecarboxylic Acid as an Intermediate . ......... 158 Methionine Cycle ........ 161 Conversion of l-Aminocyclopropanecarboxylic Acid to Ethylene 164 REGULATION OF ETHYLENE BIOSYNTHESIS 167 Regulation in Ripening Fruits and Senescing Flowers ...... 167 Auxin-Induced Ethylene Production 169 Regulation of Ethylene Biosynthesis by Ethylene 169 Stress-Induced Ethylene Production . . . . . . . . 171 Regulation by Light and Carbon Dioxide 173 Inhibitors of Ethylene Biosynthesis : 174 Conjugation of l-Aminocyclopropanecarboxylic Acid to l-(Malonylamino) cyclopropanecarboxylic Acid 178 CONCLUDING REMARKS 180

The genome of the cucumber, Cucumis sativus L.

Abstract: Cucumber is an economically important crop as well as a model system for sex determination studies and plant vascular biology. Here we report the draft genome sequence of Cucumis sativus var. sativus L., assembled using a novel combination of traditional Sanger and next-generation Illumina GA sequencing technologies to obtain 72.2-fold genome coverage. The absence of recent whole-genome duplication, along with the presence of few tandem duplications, explains the small number of genes in the cucumber. Our study establishes that five of the cucumber's seven chromosomes arose from fusions of ten ancestral chromosomes after divergence from Cucumis melo. The sequenced cucumber genome affords insight into traits such as its sex expression, disease resistance, biosynthesis of cucurbitacin and 'fresh green' odor. We also identify 686 gene clusters related to phloem function. The cucumber genome provides a valuable resource for developing elite cultivars and for studying the evolution and function of the plant vascular system.