Ontogenic Changes in the Rates of Amino Acid Transport from Seawater by Marine Invertebrate Larvae (\u3cem\u3eEchinodermata, Echiura, Mollusca\u3c/em\u3e)

Transport rates of amino acids were determined for larvae of different ages of the echiuran worm Urechis caupo, the gastropod Haliotis rufescens, the bivalve Crassostrea gigas, and the sea urchin Strongylocentrotus purpuratus. All larval forms showed an increase in the transport rate of amino acids during development. Trochophores of U. caupo increased their rate of net flux for each of 5 amino acids (100 nM each) by a factor of 1.6 and 2.2 during 1-3 days and 4-8 days, respectively, for two independent cultures. In H. rufescens, the maximum transport capacity (Jmax) for alanine increased 3-fold during the 24 h required for the trochophore to develop into a veliger. In C. gigas veligers, there was a 9-fold increase in the maximum transport capacity for alanine during larval development from an 80 μm to a 300 μm larva. In sea urchins, the prism-stage larvae (2-day-old) had an alanine transport system with a Kt of 1.9 μM and a Jmax of 8.1 pmol larvae -1h-1. The kinetics of alanine transport in the pluteus-stage (4-day-old) were best described by two systems (System I: Kt = 1.0 μM with a Jmax of 5.6 pmol larva -1h-1; System II: Kt = 132.0 μM with a Jmax of 8.4 pmol larva -1h-1). In larvae of C. gigas, the relationships between the rate of alanine transport and body size was described by the equation, log Jmax (pg larva-1h-1) = 1.6894(X) + (-0.5937), where X is the shell length in μm. It is illustrated that the allometric increased in respiration rates, during the growth of bivalve larvae, is matched by an ontogenic increase in amino acid transport capacity

ETHYLENE-INSENSITIVE5 Encodes a 5\u27→3\u27 Exoribonuclease Required for Regulation of the EIN3-Targeting F-Box Proteins EDF1⁄2

Ethylene is a gaseous plant growth regulator that controls a multitude of developmental and stress responses. Recently, the levels of Arabidopsis EIN3 protein, a key transcription factor mediating ethylene-regulated gene expression, have been demonstrated to increase in response to the presence of ethylene gas. Furthermore, in the absence of ethylene, EIN3 is quickly degraded through a ubiquitin/proteasome pathway mediated by two F-box proteins, EBF1 and EBF2. Here we report the identification of ETHYLENE-INSENSITIVE5 as the 5′→3′ exoribonuclease XRN4. Specifically, we demonstrate that EIN5 is a component of the ethylene signal transduction cascade acting downstream of CTR1 that is required for ethylene-mediated gene expression changes. Furthermore, we find that the ethylene insensitivity of ein5 mutant plants is a consequence of the over-accumulation of EBF1 and EBF2 mRNAs resulting in the under-accumulation of EIN3 even in the presence of ethylene gas. Together, our results suggest that the role of EIN5 in ethylene perception is to antagonize the negative feedback regulation on EIN3 by promoting EBF1 and EBF2 mRNA decay, which consequently allows the accumulation of EIN3 protein to trigger the ethylene response

Ontogenic Changes in the Rates of Amino Acid Transport from Seawater by Marine Invertebrate Larvae (Echinodermata, Echiura, Mollusca)

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