Measurement of the in Vivo Rate of Indole-3-Acetic Acid Turnover

Nonhebel, Heather M.; Cooney, Terrence P.

doi:10.1007/978-3-642-74545-4_39

Cited by 8 publications

(10 citation statements)

References 19 publications

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“…5). The whole-plant turnover time calculated for the parent inbred line 3F7-11 was about 10 h (Table 1111, a value similar to that reported by Nonhebel and Cooney (1990) for IAA turnover in young leaves of tomato. The MTR lines, however, showed a much more rapid turnover rate than the parent lines.…”

Section: Iaa Turnover In Lemna Linessupporting

confidence: 80%

“…As previously discussed (Zilversmit et al, 1943;Epstein et al, 1980;Nonhebel and Cooney, 1990), use of this equation assumes that the change in isotope ratios obeys first-order kinetics and that the labeled material is metabolized at a rate similar to that of the unlabeled material.…”

Section: Iaa Turnovermentioning

confidence: 98%

“…One aspect of plant hormone metabolism that has attracted attention over the last 15 years is the rate of hormone turnover (Epstein et al, 1980;Nonhebel and Cooney, 1990). Hormonal homeostasis requires that increased rates of synthesis of IAA be offset by increasing rates of degradation, resulting in more rapid turnover.…”

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confidence: 99%

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Selection and Characterization of [alpha]-Methyltryptophan-Resistant Lines of Lemna gibba Showing a Rapid Rate of Indole-3-Acetic Acid Turnover

1995

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Turnover rate is an important aspect of the regulation of plant processes by plant growth substances. To study turnover of indole-3-acetic acid (IAA), two a-methyltryptophan-resistant lines (MTR1 and MTR2) of Lemna gibba were generated by nitrosomethyl urea treatment of an inbred line derived from L. gibba G-3. In this report we describe: (a) the development of a selection system using this near isogenic line of L. gibba; (b) techniques for chemical mutation of the lines and selection for a-methyltryptophan resistance; and (c) the partia1 characterization of the selected lines. MTR lines contained 3-fold higher levels of anthranilate synthase activity. The enzyme in the MTR lines required higher levels of tryptophan for feedback inhibition. MTR lines also contained 8-fold higher levels of tryptophan, 3-fold higher levels of free IAA, and similar levels of total IAA compared to the inbred line. Turnover rates in the inbred and selected lines were calculated, using the first-order rate equation, based on the decrease over time in isotopic enrichment of 13C,-IAA introduced into L. gibba during a 1-h pulse period. lsotope enrichment in IAA was determined by using gas chromatography-mass spectrometry. Both MTR lines had an approximately 10-fold higher rate of IAA turnover than the parent inbred lhe.IAA plays an important role in plant growth, development, and responses to the environment, yet after more than a century of study we still have large gaps in our knowledge of fundamental aspects of how the hormone acts and what controls its metabolism. One aspect of plant hormone metabolism that has attracted attention over the last 15 years is the rate of hormone turnover (Epstein et al., 1980;Nonhebel and Cooney, 1990). Hormonal homeostasis requires that increased rates of synthesis of IAA be offset by increasing rates of degradation, resulting in more rapid turnover. Studies of hormone turnover have been limited in number in part by lack of plant systems that overcome the difficulties of labeling interna1 pools. In many cases, IAA levels in plant tissues remain relatively constant, but changes in the rates of IAA biosynthesis and degradation are seen only as changes in turnover rate. To date we have information on turnover in only a few plants and no knowledge of how turnover might change relative to genetic, developmental, and environmental variation. Turnover can be expected to be an important metabolic parameter for hormone action, since rates of turnover must be rapid relative to the processes that are controlled by the particular hormone (see Cohen, 1983). A mechanism linking turnover and hormone action may involve the co-oxidation of plant fatty acids (Reineke, 1990).Studies of IAA biosynthesis have shown the utility of using mutants to study IAA and Trp metabolism (Wright et al., 1991;Normanly et al., 1993). Unlike mutants used for studies of metabolic pathways, those most useful for understanding the function of IAA turnover would not be auxotrophs, but rather would be modified in metabolism so as to result in...

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Section: Iaa Turnover In Lemna Linessupporting

confidence: 80%

Section: Iaa Turnovermentioning

confidence: 98%

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Selection and Characterization of [alpha]-Methyltryptophan-Resistant Lines of Lemna gibba Showing a Rapid Rate of Indole-3-Acetic Acid Turnover

1995

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“…At higher temperatures (30°C and 35°C), IAA turnover rates were also less than 1 h. At 25°C, the turnover time for IAA increased to almost 10 h, indicating enhanced IAA stability in vivo at this growth temperature. Although the t 1/2 at 25°C indicated a much slower rate of IAA turnover compared with that measured at all other temperatures, it is comparable with IAA turnover rates reported in other plants Temperature Regulation of Indole-3-Acetic Acid Metabolism (Epstein et al, 1980;Nonhebel and Cooney, 1990;Ljung et al, 2001). The reason for the slower turnover time at 25°C is not known.…”

Section: Measurement Of the Rate Of Iaa Turnoversupporting

confidence: 79%

“…Early studies that measured the rate of IAA turnover showed that IAA turnover has a turnover time (t 1/2 ) that falls within the range of 1 to 10 h in a variety of plants and tissues ranging from maize (Zea mays) endosperm (Epstein et al, 1980) and tomato (Lycopersicon esculentum) leaves (Nonhebel and Cooney, 1990) to intact Lemna gibba plants (Tam et al, 1995). Recent studies of developmental regulation of IAA turnover in Scots pine (Pinus sylvestris) revealed that there are more substantial differences in IAA t 1/2 during various stages of seedling growth (Ljung et al, 2001).…”

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confidence: 99%

Indole-3-Acetic Acid Metabolism in Lemna gibbaUndergoes Dynamic Changes in Response to Growth Temperature

et al. 2002

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Auxin is the mobile signal controlling the rate of growth and specific aspects of the development of plants. It has been known for over a century that auxins act as the messenger linking plant development to specific environmental changes. An often overlooked aspect of how this is accomplished is the effect of the environment on metabolism of the major plant auxin, indole-3-acetic acid (IAA). We have studied the metabolism of IAA in relation to one environmental variable, growth temperature. The model system used was an inbred line of the aquatic monocot Lemna gibba G-3, 3F7-11 grown at temperatures ranging from 5°C to 35°C. IAA levels, the rate of IAA turnover, and the patterns of label incorporation from IAA precursors were measured using stable isotope-mass spectrometric techniques and were evaluated relative to growth at the experimental temperatures. IAA levels exhibited unusually high variability in plants grown at 15°C and 20°C. Turnover rates were quite rapid throughout the range of experimental temperatures except at 25°C, where IAA turnover was notably slower. These results suggest that a transition occurred over these temperatures for some aspect of IAA metabolism. Analysis of [ 15 N]anthranilate and [ 2 H 5 ]tryptophan (Trp) incorporation into IAA showed that Trp-dependent biosynthesis predominated at 15°C; however, Trp-independent biosynthesis of IAA was the major route to IAA at 30°C. The effects of growth temperature on auxin levels have been reported previously, but no prior studies correlated these effects with which pathway becomes the primary one for IAA production.Plants, unlike most animals, cannot move to avoid environmental changes and thus, they must rely on other adaptive strategies to cope with a changing and often adverse habitat (Darwin, 1892; Basra, 1994). The perception of environmental signals triggers the specific modulation of metabolic and physical characteristics for optimal growth and survival. Plant hormone metabolism provides plants with a means by which they can transduce signals and adjust growth and development. The response of plants to drought stress mediated through changes in abscisic acid levels is one of the better documented cases of hormone metabolism regulated by environmental conditions (Cornish and Zeevaart, 1985). A long recognized but less well understood response of plants to environmental stress is the repression of growth rate (Berry and Raison, 1981). Temperature-dependent changes in growth can be mediated, in part, by the ability of the plant to respond to auxin (Rayle and Cleland, 1972). In addition, temperature modulation of the rate of plant growth has been correlated to changes in the level of auxin (Gray et al., 1998). Such changes in auxin level could result from a temperaturedependent effect on auxin transport or auxin metabolism.It is important to recognize that analysis of phytohormone levels only gives a measurement of the steady-state conditions prevailing at the time of analysis, and this measured level should not be viewed as static. Any ch...

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