A Kinetic Study of Growth Movements and Photomorphogenesis in Etiolated Pea Seedlings

Knowledge of the latency period between R4 irradiation of plants and expression of physiological or developmental changes is important in studying the mechanism of phytochrome action. Responses such as changes in membrane electrical potential may have latencies on the order of seconds (18), while several hours may be required for the appearance of certain inducible enzymes (17). Although growth is a complex process, possibly involving many limiting factors in different situations, there is much interest in understanding the mechanism by which phytochrome controls the growth of etiolated seedlings. There have been a few attempts to characterize the kinetics of such responses. The R-induced inhibition of intact pea stem elongation began about 6 h after irradiation (9), and a lag period of 4 h was reported for pea stem segments (3). The lag period for the R-induced growth promotion of apical oat coleoptile segments was less than 3 h (12). Recent work with optical and electronic transducers showed that auxin can promote the growth of pea stem and oat coleoptile segments within 15 min of application (7,24 mounted on a microscope mechanical stage, so that the transducer arm could be adjusted to the horizontal at the beginning of each experiment. The transducer was connected to an Omni-Scribe recorder (Houston Instruments). All manipulations were carried out under green safelights (18) in a room maintained at 23 ± 2 C. Irradiations were given from the side, with a mirror behind the plant, using a 300-w projector and the following filters: red, Rohm and Haas Plexiglas 2423 and Corning filter 3-66 (intensity 3.0 mw/cm2); far red, Corning filters 7-69 and 3-66 (1.4 mw/cm2) (18); blue, Wratten filters 2A and 47B (0.8 mw/cm2).Experiments with Oats. Seedlings ofAvena sativa L. cv. Victory were grown as described previously (19). Our initial experiments were conducted using segments in an Evans and Ray-type apparatus (7). Ten 1-cm apical segments were cut, the apical 1 mm was removed, and the segments strung on nylon line. A glass capillary tube was placed on top ofthe segment column, with the transducer arm resting on the flared-out top of the capillary. The growth chamber was filled with 1 mm K-phosphate (pH 6.2) containing 1.5% sucrose (12). The solution was circulated by air bubbled into the chamber.In most of the experiments, a single 2-cm apical segment (tip intact) was used. A snug fitting plastic sleeve was placed around the middle of the segment, and the sleeve and plant were inserted through a hole in the lid of a foil-wrapped 30-ml vial filled with the buffered sucrose solution. The sleeve and plant were firmly held by the lid, with about 0.8 cm of the coleoptile protruding above the lid. A small translucent conical cap was placed on the tip of the coleoptile, and the transducer arm rested on this cap. For application of test solutions to the plants, we used a slightly larger cap, containing a wad of cotton soaked in the solution.Experiments with Peas. Seedlings (Pisum sativum L. cv. Alaska) were grown as d...

Section: Discussioncontrasting

confidence: 60%

“…There have been a few attempts to characterize the kinetics of such responses. The R-induced inhibition of intact pea stem elongation began about 6 h after irradiation (9), and a lag period of 4 h was reported for pea stem segments (3). The lag period for the R-induced growth promotion of apical oat coleoptile segments was less than 3 h (12).…”

mentioning

confidence: 99%

Short Term Phytochrome Control of Oat Coleoptile and Pea Epicotyl Growth

Pike¹,

Richardson²,

Weiss³

et al. 1979

“…Gross hook angle was quantified from shadowgraphs with the aid of a protractor. As defined earlier (7), an open hook (i.e. straight stem) was defined to be 1800 while a closed hook (plumule parallel to the stem) would be 00.…”

Section: Methodsmentioning

confidence: 99%

“…Third, photomorphogenetically active light stimulates both hook opening and nutation (5,7). Finally, formation of the hook has an irregularly rhythmic component which indicates oscillations in growth ' Research supported by National Aeronautics and Space Administration Grant NSG-7290 to A. W. G. (7). This paper concentrates on the relation between the apical hook and nutation.…”

mentioning

confidence: 99%

Physiology of Movements in Stems of Seedling Pisum sativum L. cv Alaska

Britz

Galston²

1982

The relationship between the apical hook and stem nutation in The extension growth of cylindrical plant organs is often accompanied by oscillatory bending movements (nutations) with periods on the order of 1 to several h. A complete understanding of growth regulation in plants will require the elucidation of these rhythms. In an earlier study (5), we concluded that simple gravitropic overshoots (e.g. Ref. 10) were unlikely to cause nutation in the third internode of peas. However, the nutational patterns were consistent with internal events such as endogenous rhythms of growth as the cause of oscillatory bending. Further work on the physiology of nutation should attempt to identify and to localize the rhythmic process(es), if such exist, and to explain the coupling between the primary oscillator (or clock) and subsequent growth.Several observations seem to connect nutations in pea stems with the apical hook. In the first place, differential cell elongation on opposite sides of the stem is responsible not only for nutation, but also for the formation and maintenance of the hook. Both processes seem to be autonomous. Second, the patterns ofnutation and hook curvature have a common plane of symmetry (5). Third, photomorphogenetically active light stimulates both hook opening and nutation (5, 7). Finally, formation of the hook has an irregularly rhythmic component which indicates oscillations in growth

“…The chelator also increased the growth of segments in the dark. Using a one-way analysis of variance and the Dunn Test (7), all of the differences (2,5,20). The shorter, light-grown pea epicotyl contains considerably more wall-bound hydroxyproline than the dark-grown tissue (17).…”

Section: Resultsmentioning

confidence: 99%

Phytochrome Control of Cell Wall-bound Hydroxyproline Content in Etiolated Pea Epicotyls

Pike¹,

Un²,

Lystash³

et al. 1979

Te red light inhibition of growth of the intact pea (Pisum sdtvuwm L. cv. Alaska) third interode was correlated with an increase in the content of cell wail-bound hydroxyprolie. These changes were detected 3 hours after irradiation, and possibly at 1 hour. Far red light reversed the effects of red Nght. The iron chelator a,-dipyridyl reversed the red lht effects on both growth and hydroxyprolie content. Using sets incubated hi vnto, no phytochrome-medyated che in hydroxyproile content could be observed, perhaps because of an overwhelming wounding response. If plants were irradiated X situ and grown for 8 hours before excision and incubation of segments, some ement of hydroxylation by red ight was detectabl both corimetrkalBy and radolsotopicaly. The red fight inhibltio of segment growth was reversed by adipyridyL These results are examine in reference to the role of extensin in norm and induced growth cessatiozThe growth of a plant cell is significantly influenced by the properties of the cell wall. For elongation to proceed, the wall must be in a loose condition. Changes in growth rate are often caused by changes in certain crucial acid-labile, alkaline-stable bands (3). The initial stage of growth promotion by auxin may be the result of H+ secretion into the wall and consequent wall loosening (14). One type of acid-labile bond implicated in growth control is the hydroxyproline-O-arabinose bond, linking extensin, a hydroxyproline-rich glycoprotein, to the wall polysaccharides (8). There is considerable evidence that cells that have ceased elongating contain more wall-bound hydroxyproline (and thus have less plastic walls) than do elongating cells (4, 10, 17). Nonelongating pea epicotyl segments incorporated and hydroxylated more I'4Clproline than did elongating segments (17). The inhibition of growth by agents such as ethylene and benzimidazole was also accompanied by an increase in wall-bound hydroxyproline (15, 16) and in [14CJproline hydroxylation (16). The increase in hydroxyproline content was suggested to precede and to cause the growth inhibition, but the first assays were made 6 h (16) or 1 day (15) after hormone application.R5 strongly inhibits the growth of intact pea epicotyls (5) and epicotyl segments incubated in a buffered sucrose-cobalt medium (2), but little is known of the mechanism of action. R might accelerate the transition of cells from the elongation stage to the maturation stage (19). There is some evidence concerning a relationship of phytochrome control of growth and hydroxyproline. Pea seedlings grown in the light were much shorter and contained much more wall-bound hydroxyproline than etiolated seedlings (17). Although white light inhibited the growth of radish hypocotyls, light had no effect on wall hydroxyproline content (9). This study was undertaken to determine the influence of phytochrome on wall hydroxyproline level.The iron chelator a,a'-dipyridyl is widely used as an inhibitor of the hydroxylation of peptidyl proline (1,9,16). The reversal by this compound of the horm...