Aminoethoxyvinyl glycine (AVG) and silver thiosulfate, antagonists of ethylene biosynthesis and action in plants, both delayed onset of leaf epinasty in Xanthium strumarium L. (cocklebur) plants rotated on horizontal clinostats. Xanthium plants mechanically stressed by continuous horizontal or vertical shaking, or continuous twisting back and forth, did not develop any significant epinasty, while plants inverted every 20 minutes (upside down half the time) did develop epinasty. From this it appears that clinostat-induced epinasty is a result of gravity compensation rather than mechanical stress. Treatment of Xanthium, Lycopersicon esculentum Mill. (tomato), and Ricinus communis L. (castor bean) plants with inhibitors of ethylene biosynthesis, AVG and cobaltous ion, and inhibitors of ethylene action, silver ion and carbon dioxide, significantly delayed stem gravitropic response times. AVG and silver were dependably effective in delaying gravitropism, while carbon dioxide and cobalt were less effective. Unilateral application of ethephon solution (1%) to the upper 10 centimeters of tomato stems, caused stems to deflect up to 80° toward the side of application after 24 hours on a clinostat, while unilateral application of indole-3-acetic acid in lanolin paste (1%) to tomato and cocklebur stems caused up to 250° and 200° bending respectively, away from the side of application after 24 hours on a clinostat. Cocklebur stems that are restricted from bending after placing them horizontally store bending energy as seen from the springing upward that occurs when the stems are released (up to an average of 150° after 40 hours of restriction). Most of these stems also showed a stored stimulus of gravitropic bending, continuing to bend for several hours after release and being placed upright, before straightening.

Chez Arabidopsis, la protéine RISP est détournée par le virus CaMV pour assurer, ensemble avec la protéine virale TAV, la traduction de son ARN polycistronique. RISP a été identifiée comme une cible de la voie de signalisation de TOR et il a été montré que sa phosphorylation est requise pour promouvoir la réinitiation de la traduction activée par TAV. Les résultats que j’ai obtenus suggèrent que RISP, lorsqu’elle n’est pas phosphorylée, intervient ensemble avec eIF3, au niveau du complexe de pré-initiation 43S pour recruter le complexe ternaire grâce à l’interaction entre RISP et la sous-unité b du facteur eIF2. Il s’est avéré que RISP a la capacité, lorsqu’elle est phosphorylée, d’interagir non seulement avec la protéine ribosomique eL24 mais également avec eS6. Nos résultats indiquent que la liaison entre les sous-unités ribosomiques 60S et 40S sous l’effet de RISP, est régulée par la voie de TOR et qu’elle joue un rôle important dans le contrôle de la réinitiation de la traduction. / Many factors are required to recruit the tRNAi and a 60S ribosomal subunit to the 40S ribosomal subunit preinitiation complex. This recruitment is normally strictly limited during reinitiation of translation if factors recruited during the primary translation event are shed from 40S. However, factor retention can occur during long ORF translation if the CaMV viral factor TAV is present. RISP is a downstream target of TOR and found either within the 43S preinitiation complex, if bound to eIF3, and/or attached to 60S, if phosphorylated by TOR. We show here that RISP interacts with subunit b of eIF2 before phosphorylation. Critically, TOR activation up-regulates phosphorylation of both RISP and eS6 as well as the binding of both factors. Importantly, eS6-deficient plants are less active in TAV-mediated reinitiation and are thus less susceptible to CaMV infection. It is attractive to propose that eS6 phosphorylation contributes to retention and re-use of 60S during 40S scanning.