An Analysis of Auxin-gibberellin Interaction in Pea Stem Tissue.

Recent reports from several laboratories (1,6,8,12) on the effect of gibberellin treatment upon indole-3-acetic acid (IAA) In this paper we have investigated the growth stimulation and IAA oxidase activity in intact lupine plants which had been treated over an extended period with low doses of gibberellic acid (GA) and cultured under two different daylengths. A preliminary report of this work has been presented (12). The results support the views proposed by Vlitos and Meudt (15) and Galston and Warburg (3) that growth stimulation by GA is probably mediated through an auxin-sparing mechanism. Recently Philips and coworkers (7) have presented evidence that GA does not function by an auxin-sparing mechanism but forms a growth-stimulating complex which acts both as an auxin and gibberellin-like compound. It is suggested that had the other investigators (1, 6) assayed tissues which had been treated with GA over a longer period of time that they may have observed a reduction in IAA oxidase activity.

supporting

confidence: 82%

Section: Methodsmentioning

confidence: 99%

Effect of Gibberellic Acid and Photoperiod on Indoleacetic Acid Oxidase in Lupinus Albus L.

Watanabe

Stutz

1960

“…Like intact seedlings (6), the sections do not respond to added auxin, and the experiment with TIBA suggests that no interaction occurs between GA3 and endogenous auxin (Table II). In this respect the hypocotyl section of lettuce differs from many other dicotyledonous stem sections which show a marked interaction between IAA and GA3 (1,7,27).…”

Section: Discussionmentioning

confidence: 99%

Gibberellin Response in Lettuce Hypocotyl Sections

Silk¹,

Jones²

1975

Excised lettuce (Lactuca sativa L.) hypocotyl sections retain the ability to elongate in response to gibberellic acid (GA3) addition. In 48 hr at 30 C a GA3-treated segment more than doubles while a control segment elongates less than 50%70. Auxin has no detectable effect on this system. Sensitivity to GA3 is not decreased by apex or root removal. Of the experimental variables tested, temperature, sucrose, and preincubation in water affect growth both with and without GA3. Blue and far red light inhibit growth without GAs; this inhibition is reversed by GA3. Potassium chloride stimulates growth of illuminated sections treated with GA3 but has no effect on control growth. When sections are incubated in the dark, KCl has a promotive effect on elongation.There are numerous advantages to using excised plant segments to study the mechanism of hormone action. Interactions, such as transport of hormones and nutrients to the responding segment, are eliminated as variables. The recent advances which have been made in the characterization of the auxin response clearly demonstrate the utility of such isolated segments (4, 5).Research on the mechanism of gibberellin-induced elongation has been hampered by an apparent diminution in ability to respond to GA3 when stem segments are removed from meristematic regions (10). Recently, Kaufman and his colleagues (9,13,14,19) demonstrated a dramatic effect of GA3 on growth of excised stem segments of Avena, but sections from dicotyledonous plants have seemed less responsive. Brian and Hemming (1) showed that the growth of segments from dwarf pea stems was much less than that realized by similar regions of whole plants and was not elevated by GA3 application. Furthermore, the GA3 response of many isolated sections has been shown to be dependent on added auxin (1,27,30) or sucrose (24). This paper describes the GA3-induced growth of sections isolated from the hypocotyl of lettuce seedlings. MATERILS AND METHODSPlant Material. Seeds of lettuce (Lactuca sativa L. cv. Arctic) were obtained from Carter's Ltd., Raynes Park, London. Seeds were imbibed for 2 hr in an excess of distilled H20 and were sown in white light in 9-cm Petri dishes on a circle of Whatman No. 1 filter paper wetted with 5 ml of distilled H20. Germination proceeded in the dark at 25 C for 34 hr after which time the

“…This is particularly evident in studies with the gibberellins. The intact pea plants respond to gibberellin with large growth increments whereas sections cut fronm replicate plants are only slightly stimulated (6,11,22 …”

mentioning

confidence: 99%

Growth Promotion in Pea Stem Sections. I. Stimulation of Auxin and Gibberellin Action by Alkyl Lipids

Stowe

1960

A section of pea steimi after remloval from the plant elongates markedly less than the same zone when it is left on the intact plant. No growth factor or conmbination of known factors restores more than half of this missing growth. This is particularly evident in studies with the gibberellins. The intact pea plants respond to gibberellin with large growth increments whereas sections cut fronm replicate plants are only slightly stimulated (6,11,22