Water Relations in Pulvini from Samanea saman

Abstract

Biological Sciences Group U-42, University ofConnecticut, Storrs, Connecticut 06268 ABSTRACI The movement of Samwaea leaflets depends upon changes in the curvature of the pulvinus at the base of each leaflet. Pulvinar bending and straightening, in turn, are driven by the movement of water between opposing (extensor and flexor) sides of the pulvinus. Although water movement depends on water potential (1) and thus on osmotic potential (X) and hydrostatic pressure (P), none of these parameters have been measured in Samauea. In this investigation, il and X were measured and P was calculated for extensor Leaves and leaflets of the nyctinastic, leguminous tree Samanea saman (Jacq.) Merrill3 are usually spread horizontally during the day and folded tightly into a vertical orientation at night (2,20). These movements are brought about by the bending and straightening ofcylindrical motor organs, or pulvini, that subtend the leaf, the pinnae and the pinnules (see Fig. 2 (12,13,19). However, the magnitude and direction of the H+ fluxes varies with the 74 of the medium (16). These results are suggestive of a turgor-sensing mechanism, but they are difficult to interpret because we know very little about the I on the extensor and flexor sides of the pulvinus. If these in vitro experiments are to have maximum relevance to events occurring in whole pulvini, we must be able to design an appropriate bathing medium, with 7r balanced against the tissue , and we must understand the effects of excision.Pulvinar bending depends upon water movement, and thus on the I, wr, and P on the two sides of the pulvinus. regime at 27°C, as described in Gorton and Satter (10). Terminal secondary pulvini were used for all experiments. A protractor was used to measure leaflet angles (the angle between the rachis and the rachilla).Osmolality Measurements. Fluid from extensor and flexor tissues was obtained by two methods.1. Strips ofextensor and flexor tissue were excised as described in Iglesias and Satter (12). The tissue strips were squashed between a glass slide and a stainless steel spatula, and expressed fluid was collected with a glass microcapillary, all within a 4Abbreviations: ir = osmotic potential; PEG = polyethylene glycol (mol wt 3350); P = hydrostatic pressure; 1 = water potential (+ = r + P). 945www.plantphysiol.org on May 11, 2018 -Published by Downloaded from

H+ Uptake and Release during Circadian Rhythmic Movements of Excised Samanea Motor Organs

“…We conducted additional pH experiments at various times during 51 h of DD in the medium containing 0.4 M mannitol (osmotic potential = -1.2 MPa). This value is similar to the most negative water potential reported for Samanea motor tissue (7).…”

Light‐ and Clock‐Controlled Leaflet Movements in Samanea saman*: A Physiological, Biophysical and Biochemical Analysis**

“…Mannitol lowered the water potential of the solution, and this, in turn, would lower cell turgor. Gorton (1987a) reported that flexor cell turgor changes in vivo during leaflet movement, and we propose that these alterations in turgor may regulate H+ pump activity in vivo, as depicted in Fig. 1.…”

Water Relations in Pulvini from Samanea saman

“…The following discussion is based on (a) Figures 3 and 4; (b) I values measured by the droplet method (from Gorton [2]) as compared to the Chardakov method (Fig. 1); (c) measured ir values (from Gorton [2]); and (d) differences between the two derived P values, Pdr and PCh (Fig.…”

“…Merrill3 are often chosen for experimental work because they are large and easily dissected, so it is possible to do in vitro work on the antagonistic extensor and flexor sides ofthe pulvinus separately. Such experiments suggest that ion uptake in swelling pulvinar cells may be driven by an outwardly directed H+-pump (3,4) and that the magnitude and direction of H' fluxes depends on the I4 of the bathing medium (6 4Abbreviations: i = water potential (i = ir + P); wr = osmotic potential; P = hydrostatic pressure; *id, = water potential measured on extensor and flexor sides of intact pulvini using the droplet method (from Gorton [2]); ich, = water potential measured on excised strips ofextensor and flexor tissues using the Chardakov procedure; P& = pressure calculated using idr and r; Pch = pressure calculated using *Ch and r; PceII = pressure attributable to the water status and resistance to expansion of individual cells; Ptissue = pressure imposed on a given cell by other cells. When extensor or flexor tissues were excised from open or closed pulvini, they elongated immediately (Fig.…”