Early Responses of Excised Stem Segments to Auxins

Penny, Pauline; Penny, David; Marshall, David; Heyes, J. K.

doi:10.1093/jxb/23.1.23

Cited by 49 publications

(20 citation statements)

References 24 publications

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“…Nevertheless, significant variations in the rate of growth (arrow 3', Fig. 4) (23,25). Mean values obtained from several experiments correspond well with the parameters defined by Vanderhoef (lag time, maximum of the two phases, minimum).…”

Section: Discussionsupporting

confidence: 79%

Gradient of Growth, Spontaneous Changes in Growth Rate and Response to Auxin of Excised Hypocotyl Segments of Phaseolus aureus

Prat

1978

Plant Physiol.

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Spontaneous growth was studied in excised mung bean ( Phaseolus aureus Roxb.) hypocotyl segments. Measurements were made with a growth-recording apparatus using displacement transducers on single 5-to 6-millimeter samples excised from the growth zone immediately below the hook.Even for a given zone and under controlled experimental conditions, there are differences in the spontaneous growth of individual explants. Nevertheless, in every case, two phases of endogenous acceleration are found at 15 to 20 minutes, and 120 to 150 minutes after excision. Accelerations were separated by steady growth phases. Knowledge of the spontaneous growth curve appears important for the choice of the time of application of experimental stimuli. Auxin was added at various times after excision (0 to 6 hours). The (4, 5,16,20). Numerous studies of cell growth have been made, but there are conflicting results between studies concerned with short term effects (7, 9, and references therein), and those looking only at long term over-all growth. It is only since 1974 that the precise characteristics of endogenous growth have begun to be understood (6,10,17 The potential for cell growth can now be studied as a function both of time and of degree of differentiation. In actively growing organs, important differences in the rate of growth are often observed, according to the particular region studied. The results presented here are of two types: in our experimental plan we wanted to define exactly the characteristics of endogenous growth so as to be able to choose the best defined experimental conditions. We then proceeded to a study of the development of the potentialities for endogenous and auxin-induced growth. The existence of a well defined gradient of growth may permit a clearer understanding of growth regulation. MATERIALS AND METHODSSeedlings of mung bean (P. aureus Roxb.) were grown on moist Vermiculite at 26 C in the dark for 3 days. The hypocotyls were 40 ± 10 mm in length. Segments were excised from different levels of the straight part of the plumular hook. In experiments to measure long term over-all growth, 20 segments of 20-mm length were marked at 2-mm intervals with India ink and incubated with 20 ml of medium in Petri dishes for 24 hr in the dark with constant agitation. The incubation medium was 2 mm Na/K phosphate buffer (pH 6.5) plus or minus auxin (IAA, 10 fLM). For long term growth experiments, 1% sucrose was added to the medium. The growth of individual 5-to 6-mm segments in incubation chambers with a continuous flow of test medium was measured using Philips displacement transducers. Growth curves were registered for four segments simultaneously with a 2-min interval between each measured point and the next. A detailed description of the apparatus has been previously given (26). The rate of growth was calculated directly from the chart recordings in ,um/2 min with an accuracy of ± 0.2 ,um.

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Section: Discussionsupporting

confidence: 79%

Gradient of Growth, Spontaneous Changes in Growth Rate and Response to Auxin of Excised Hypocotyl Segments of Phaseolus aureus

Prat

1978

Plant Physiol.

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“…9 pea, possessing a low content of endogenous IAA compared with tal1 cv Alaska (Law and Davies, 1990;R.H. Hamilton, perjonal communication), are remarkably similar to isolated stem segments in their response to exogenous IAA, with respect to both dose-response (Brian and Hemming, 1955;Galston and Kaur, 1961) antd short-term kinetics (Barkley and Leopold, 1972;Penny et al, 1972). This may suggest that elongation induced by exogenous IAA in intact stems involves the same mechanism of mxin action as in isolated stem segments.…”

Section: Characteristics Of Iaa Action In Lntact Stemsmentioning

confidence: 98%

“…Auxin-depleted, isolated pea stem segments are capable of large growth responses to added exogenous IAA (Penny et al, 1972;Pamsh and Davies, 1975). Interestingly, we found that intact stems of dwarf cv Progress No.…”

Section: Characteristics Of Iaa Action In Lntact Stemsmentioning

confidence: 99%

Magnitude and Kinetics of Stem Elongation Induced by Exogenous Indole-3-Acetic Acid in Intact Light-Grown Pea Seedlings

1993

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Exogenously applied indole-3-acetic acid (IAA) strongly promoted stem elongation over the long term in intact light-grown seedlings of both dwarf (cv Progress No. 9) and tal1 (cv Alaska) peas (Pisum safivum l.), with the relative promotion being far greater in dwarf plants. In dwarf seedlings, solutions of IAA (between 10-4 and 10-3 M), when continuously applied to the uppermost two internodes via a cotton wick, increased whole-stem growth by at least 6-fold over the first 24 h. The magnitude of growth promotion correlated with the applied IAA concentration from 10-6 to 10-3 M, particularly over the first 6 h of application. IAA applied only to the apical bud or the uppermost internode of the seedling stimulated a biphasic growth response in the uppermost internode and the immediately lower internode, with the response in the latter being greatly delayed. This demonstrates that exogenous IAA effedively promotes growth as it is transported through intact stems. IAA withdrawal and reapplication at various times enabled the separation of the initial growth response (ICR) and prolonged growth response (PCR) induced by auxin. The ICR was inducible by at least 1 order of magnitude lower IAA concentrations than the PCR, suggesting that the process underlying the ICR is more sensitive to auxin indudion. In contrast to the magnitude of the IAA effect in dwarf seedlings, applied IAA only doubled the growth in tal1 seedlings. These results suggest that endogenous IAA is more growth limiting in dwarf plants than in tal1 plants, and that auxin promotes stem elongation in the intact plant probably by the same mechanism of adion as in isolated stem segments. However, since dwarf plants to which IAA was applied failed to reach the growth rate of tal1 plants, auxin cannot be the only limiting factor for stem growth in peas.

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“…In creep relaxation tests, such an effect could not be detected with the ends of the collocyte samples being inserted between the pincers of a creep apparatus. However, most extensibility results of short-time experiments done with auxin have shown that extensibility changed after growth stimulation (14,17); also, during the beginning of the response, the growth observed may have occurred in the ends of the segments as reported for the effect of low pH on extension (6).…”

mentioning

confidence: 97%

“…In order to test only the interactions between growth and the rheology of the collocyte walls, we decided to use FC. This substance can stimulate growth, while biphasic auxin responses suggest that the auxin action may consist of at least two stages (16,17,28). It has also been shown that the FC effect is not reduced by some inhibitors, e.g., abscisic acid (19,21).…”

mentioning

confidence: 99%

Growth and rheological changes of collenchyma cells: The fusicoccin effect

1979

Plant and Cell Physiology

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Fusicoccin enhanced the growth of collocytes from Apium Gravtolens petioles and modified the rheological parameters tested. But these changes do not sufficiently explain the variations of the cell wall extension. Such effects are discussed. Key words: Cell wall -Fusicoccin -Growth -pH Effect -Rheology -Wall extension.Fusicoccin (FC), a diterpene glucoside, promoted the elongation of various organs within minutes of application (12,13,26). Such action was similar to the effect of low pH and auxin on cell growth. FC has been reported to increase the proton concentration in the cell wall. The similar action of FC, low pH, and auxin on growth (3,4,24) may explain the primary action of auxin; the hypothesis presented (7, 23) is discussed in references {16, 27,29).Collenchyma is a choice material for testing cell wall extension and rheology during growth processes (8, 9). The rheology (including rheological parameters and the effect low pH on extension rate) of isolated collocyte bundles has been shown to change during growth and differentiation of the tissues. In order to test only the interactions between growth and the rheology of the collocyte walls, we decided to use FC. This substance can stimulate growth, while biphasic auxin responses suggest that the auxin action may consist of at least two stages (16,17,28). It has also been shown that the FC effect is not reduced by some inhibitors, e.g., abscisic acid (19,21). Changes of extensibility and induced growth have been also reported for isolated collocyte bundles incubated 4 hr in a solution containing auxin (20). But collenchyma can undergo passive growth, like the epidermis (25), being extended by the other tissues of the organs. Thus, the growth behavior of collocytes isolated from the petiole or naturally associated with it could be different. Collocyte walls prepared from intact collenchyma bundles, inside the petiole itself, were used in this study. Materials and methodsPlants of Apium Graveolens were cultivated in a greenhouse (under controlled temperature and humidity). High-and low-growing petioles (see 9) were detached from the shoot and washed in a beaker with distilled water. After alcohol sterilization, the basal part of the petiole (9) was cut, the initial length of the collocyte

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Early Responses of Excised Stem Segments to Auxins

Cited by 49 publications

References 24 publications

Gradient of Growth, Spontaneous Changes in Growth Rate and Response to Auxin of Excised Hypocotyl Segments of Phaseolus aureus

Gradient of Growth, Spontaneous Changes in Growth Rate and Response to Auxin of Excised Hypocotyl Segments of Phaseolus aureus

Magnitude and Kinetics of Stem Elongation Induced by Exogenous Indole-3-Acetic Acid in Intact Light-Grown Pea Seedlings

Growth and rheological changes of collenchyma cells: The fusicoccin effect

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