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J. L. Zimmerman

Publications and source records attributed to J. L. Zimmerman.

4 recordsLinked to original sources
PubMed1994

Cell Differentiation and Morphogenesis Are Uncoupled in Arabidopsis raspberry Embryos.

We identified two Arabidopsis embryo mutants, designated as raspberry1 and raspberry2, by screening T-DNA-mutagenized Arabidopsis lines. Embryogenesis in these mutants is indistinguishable from that of wild-type plants until the late-globular stage, after which raspberry1 and raspberry2 embryos fail to undergo the transition to heart stage, remain globular shaped, and proliferate an enlarged suspensor region. raspberry1 and raspberry2 embryo-proper regions enlarge during embryogenesis, become highly vacuolate, and display prominent convex, or "raspberry-like" protuberances on their outer cell layers. In situ hybridization studies with several embryo cell-specific mRNA probes indicated that the raspberry1 and raspberry2 embryo-proper regions differentiate tissue layers in their correct spatial contexts and that the regulation of cell-specific genes within these layers is normal. Surprisingly, a similar spatial and temporal pattern of mRNA accumulation occurs within the enlarged suspensor region of raspberry1 and raspberry2 embryos, suggesting that a defect in embryo-proper morphogenesis can cause the suspensor to take on an embryo-proper-like state and differentiate a radial tissue-type axis. We conclude that cell differentiation can occur in the absence of both organ formation and morphogenesis during plant embryogenesis and that interactions occur between the embryo-proper and suspensor regions.

Journal Article↗
PubMed1994

LEAFY COTYLEDON1 Is an Essential Regulator of Late Embryogenesis and Cotyledon Identity in Arabidopsis.

LEAFY COTYLEDON1 (LEC1) is an embryo defective mutation that affects cotyledon identity in Arabidopsis. Mutant cotyledons possess trichomes that are normally a leaf trait in Arabidopsis, and the cellular organization of these organs is intermediate between that of cotyledons and leaves from wild-type plants. We present several lines of evidence that indicate that the control of late embryogenesis is compromised by the mutation. First, mutant embryos are desiccation intolerant, yet embryos can be rescued before they dry to yield homozygous recessive plants that produce defective embryos exclusively. Second, although many genes normally expressed during embryonic development are active in the mutant, at least one maturation phase-specific gene is not activated. Third, the shoot apical meristem is activated precociously in mutant embryos. Fourth, in mutant embryos, several genes characteristic of postgerminative development are expressed at levels typical of wild-type seedlings rather than embryos. We conclude that postgerminative development is initiated prematurely and that embryonic and postgerminative programs operate simultaneously in mutant embryos. The pleiotropic effects of the mutation indicate that the LEC1 gene plays a fundamental role in regulating late embryogenesis. The role of LEC1 and its relationship to other genes involved in controlling late embryonic development are discussed.

Journal Article↗
PubMed1992

Heat Shock Gene Expression Is Controlled Primarily at the Translational Level in Carrot Cells and Somatic Embryos.

We have determined that the synthesis of heat shock proteins is regulated ultimately at the translational level in heat-shocked carrot callus cells and somatic embryos. Polysome analysis revealed that heat-shocked callus cells do not translate most heat shock transcripts, which they abundantly synthesize and accumulate. By contrast, heat-shocked globular embryos accumulate low levels of heat shock mRNA but selectively translate more of the heat shock mRNA molecules compared to callus cells and embryos of later stages. The overall result of these different translational control schemes is that undifferentiated callus cells and globular embryos synthesize comparable levels of heat shock proteins even though they have large differences in heat shock transcript levels.

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