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

Abstract

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.

Growth Patterns in Nutating and Nonnutating Sunflower (Helianthus annuus) Hypocotyls

“…In this context, Johnsson (1966) nature" recognizable from the strip chart growth records, that temperature shifts had profound effects on the frequency of fluctuations as well as on average growth rates, that manipulation generally reduced growth for a period, with response to and recovery from handling unpredictable, and that short period oscillations (SPO) of 5-25 min were found, sometimes superimposed on long period oscillations (LPO) of 45-120 min. Such oscillations often disappear after excision of the roots or of the upper part of the seedling (Kristie and Jolliffe, 1986) or disappear in excised sections (Cosgrove and Green, 1981), although others have found spontaneous changes or periodic fluctuations in growth ofplant sections (Evans and Schmitt, 1975;Prat, 1978). Kristie and Jolliffe (1986) considered that LPOs found in Helianthus, Raphanus, and Cucumis were probably due to nutational movements of the organ tip.…”

Role of the plasma membrane H + -ATPase in auxin-induced elongation growth: historical and new aspects

“…It has long been noticed that auxin-depleted segments from coleoptiles (Cline et al 1974) or hypocotyls (Prat 1978) that were submerged in water showed initially a very low growth rate. After a while the growth rate accelerated considerably, e.g., tenfold after 3.5 h (Vesper and Evans 1979).…”

Kinetics of indole acetic acid‐induced growth in hypocotyl sections of Vigna mdiata

“…Growth measurettients were made with Philips displacertjcnt transducers used as an auxanometer as previously reported (Prat 1978), but with the following modifications. Columns of 4 to 5 segments (20 mm total length) were tised for segments at b, c, and d levels, while single segments were tised for the a level.…”