Soybean hypocotyl elongation

Meyer, R.F. Boyer, J.S. (1972). Sensitivity of cell division and cell elongation to low water potentials in soybean hypocotyls. Planta, 1 8,77-87. 

In auxin-depleted, excised stem sections (e.g., soybean hypocotyl) this initial burst of elongation is transient, lasting only some 30 to 90 min, depending upon the species and conditions. The rate of enlargement first increases, after a lag period of 15 min or less, then begins to decrease, with kinetics resembling (perhaps identical to) acid-induced growth. 

Walker, J.C., Key, J.L. 1982. Isolation of cloned cDNAs to auxin-responsive poly (A) +RNAs of elongating soybean hypocotyl. Proc. Natl. Acad. Sci. 

Both stem cell elongation and xylem differentiation are auxin-mediated processes. There has long been speculation that BRs act through alterations in the auxin response [109]. This is certainly not always the case, as BR induces elongation of soybean hypocotyls without activating any of the auxin-induced genes such as the SAUR genes [112]. On the other hand, one of the effects of BR in tomato hypocotyls appears to be to increase the sensitivity of the tissue to auxin [113]. Thus some BR effects may actually be mediated via auxin, while others are independent of auxin. 

SAURs are moderately abundant in freshly excised elongation zones of etiolated soybean hypocotyls, but rapidly disappear when excised sections are bathed in media lacking auxin. The soybean SAUR 10A5, 6B, and 15A genes show very rapid induction kinetics in response to auxin [58]. Increases in SAUR abundance can be detected within... 

In most cases, a detectable induction of mRNA levels is observed within 15-30 min following auxin exposure. The levels of three soybean mRNAs (detected by the cDNA clones 6, lOA and 15) are induced by 2.5 min of treatment of excised elongating soybean hypocotyl sections with the synthetic auxin 2,4-D [8]. These mRNAs and others identified in soybean [5, 16], pea [13] and tobacco [14] are specifically induced by auxins such as lAA and NAA, and not induced by nonauxin analogs. With some exceptions, these auxin-induced sequences do not accumulate in response to other plant growth regulators such as GA, ABA, cytokinins and ethylene, or to environmental stresses such as heat shock or cold... 

Stimulation of efflux is an important component of auxin action in many plant tissues [26]. A recent report indicates that active auxins directly stimulate a plasma membrane NADH oxidase from soybean hypocotyls. Enzyme from tissue which had completed elongation was no longer stimulable [27]. NADH oxidase is implicated in an electron transport-driven -efflux across the plasma membrane, a mechanism which co-exists with -pumping ATPases and, for cultured carrot cells, predominates specifically in young cells [28]. Because BA hyperpolarized the cell membrane and stimulated efflux in squash cotyledons, it was suggested that... 

Malik CP, Mehan M (1975 b) Interaction between cycocel and gibberellic-acid in pollen-tube elongation of Calotropis procera. Curr Sci 44 785-786 Manos GE (1961) The effects of growth substances on attached and detached root tips of Pisum sativum L. Physiol Plant 14 697-711 Manos PJ, Goldthwaite J (1976) An improved cytokinin bioassay using cultured soybean hypocotyl sections. Plant Physiol 57 894-897 Marinos NG (1960) Some responses of Avena coleoptiles to ethylene. J Exp Bot 11 227-235... 

Mertz D (1966) Hormonal control of root growth. Plant Cell Physiol 7 125-135 Metzger JD, Zeevaart JAD (1980) Comparison of the levels of six endogenous gibberellins in roots and shoots of spinach in relation to photoperiod. Plant Physiol 66 679-683 Meyer RF, Boyer JS (1972) Sensitivity of cell division and cell elongation to low water potentials in soybean hypocotyls. Planta 108 77-87 Milborrow BV (1966) The effects of synthetic DL-dormin (abscisin II) on the growth of the oat mesocotyl. Planta 70 155-171... 

In order to establish a molecular data base for BR and begin to address questions (a) and (b) above, we have examined whether BR affects the transcription of auxin-induced genes in elongating soybean epicotyl sections using available auxin-induced soybean sequences as probes. More generally, we have shown changes in protein synthesis caused by BR in soybean epicotyls and hypocotyls by in vitro translation of mRNA (+ or - BR) followed by 2-D gel electrophoresis. 

SAUR (Small Auxin Up RNA) cDNAs were first cloned from soybean elongating hypocotyl sections using a differential hybridization screen with hybrid selected RNA... 

Metabolic disruptions may result in inhibition of cell enlargement. Key (9) found that actinomycin D, an inhibitor of DNA directed RNA synthesis (10), and puromycin, an inhibitor of protein synthesis, will prevent cell enlargement in soybean Glycine max L. Merr.) hypocotyls. Key concluded RNA and protein synthesis are essential for the process of cell elongation to proceed at a normal rate. The following year, Cleland reported the inhibition of cell enlargement caused by actinomycin D was not caused by an inhibition of auxin-induced cell wall loosening... 

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