A large portion of indoleacetic acid (IAA)-induced inhibition of excised root tips and virtually all such inhibition of intact roots are the result of IAA-dependent ethylene production. Under certain conditions an additional effect of IAA accounts for a small portion of the inhibition of excised root tips. Ethylene production in response to applied IAA is governed by the level of applied auxin found inside the root. Evidence is presented to confirm the participation of ethylene in the geotropic response of roots.Application of IAA to roots invariably causes an inhibition of elongation (3). We have presented evidence (18) that auxinmediated ethylene production accounts for the inhibition in pea roots, just as it does in pea buds (16) and etiolated pea stems (11). This paper presents additional data supporting the idea that ethylene is the normal intermediate in auxin-mediated root growth inhibition, both in intact plants and in excised root sections, and also that the gas plays a role in root geotropism.
MATERIALS AND METHODSSeeds of Pisum sativum (var. Alaska) were germinated as previously described (18), and all manipulations subsequent to planting were carried out in dim green light to avoid phototrophic and photomorphogenic involvement.Studies on Tissue Sections. When the roots were 2 to 3 cm long, usually 48 hr after planting, apical 5-mm segments were removed with a two-bladed cutter. Ten of these apices and 2, 5, or 10 ml of medium containing 2% sucrose (w/v), 5 J.M CoC12, 5 mM potassium phosphate buffer (pH 6.8), and an appropriate concentration of IAA were sealed in a 125-ml Erlenmeyer flask by means of a vaccine cap and gently shaken (68 cpm through a 4-cm stroke) in the dark for a predetermined number of hours. In a few cases when very small amounts of evolved ethylene had to be measured, 25-or 50-ml micro-Fernbach flasks were used. At the end of an incubation the ethylene production was determined by gas chromatography (11) immersed in a solution containing an appropriate concentration of IAA for 3 to 5 min, drained briefly, and placed in a 6-liter desiccator in the presence or absence of applied ethylene. The initial length and weight of the radicals were determined from a sample taken before immersion treatment, and final values after 9 or 18 hr. Ethylene production was measured under similar conditions using tissue grown in 300-ml glass bell jars filled with moist vermiculite and treated with IAA by the technique described above. Geotropic Studies. Presoaked seeds were planted in moist vermiculite in plastic bins (25 x 6 x 6 cm) and allowed to germinate. When the roots had attained a length of about 2.5 cm, the bins were covered with perforated plastic tops and sealed in 6-liter desiccators, the roots remaining vertical throughout. The pressure in each desiccator was reduced to about 380 mm Hg with a water aspirator, an appropriate amount of CO2 or C2H4 was injected, and then air was admitted until atmospheric pressure was again attained. After a 10-min equilibration period the desiccators ...
Diatomaceous deposits in the Miocene-Pliocene Pisco Formation contain abundant whales preserved in pristine condition (bones articulated or at least closely associated), in some cases including preserved baleen. The well-preserved whales indicate rapid burial. The 346 whales within ϳ1.5 km 2 of surveyed surface were not buried as an event, but were distributed uninterrupted through an 80-m-thick sedimentary section. The diatomaceous sediment lacks repeating primary laminations, but instead is mostly massive, with irregular laminations and speckles. There is no evidence for bioturbation by invertebrates in the whale-bearing sediment. Current depositional models do not account for the volume of diatomaceous sediments or the taphonomic features of the whales. These taphonomic and sedimentary features suggest that rapid burial due to high diatom accumulation, in part by lateral advection into protected, shallow embayments, is responsible for the superb preservation of these whales, leading to a higher upper limit on phytoplankton accumulation rates than previously documented.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.