Estimation of Osmotic Parameters Accompanying Zeatin-Induced Growth of Detached Cucumber Cotyledons

Abstract

Water potential (+), the osmotic potential (',,), and the pressure potential ('') of detached cotyledons isolated from Cucumis sativus L. cv Marketer seedlings after 0, 1.5, and 3 days growth with and without zeatin were determined. From zero time to 3 days, cotyledons incubated without exogenous zeatin exhibited a slight decrease in + (from -0.4 to -1.0 bars), while those grown with zeatin developed even more negative values (about -4 Cytokinins promote growth ofdetached cotyledons ofnumerous species in light or darkness. The most intensive investigations of this phenomenon have been performed with radish (1, 3, 6, 13, 18) and cucurbits (4,8,18). In these species, dry weight changes with or without cytokinin are negligible during growth periods of 3 d and, at least in radish (1, 3), cytokinesis is increased by cytokinins much less than is H20 uptake. In each species, cytokinins cause wall loosening that apparently contributes substantially to water uptake and thus growth promotion (16,18 were immediately utilized for measurements of ' and I,, (see below). Others were transferred to 9-cm Petri dishes and allowed to grow, adaxial surface down, under fluorescent laboratory light for 1.5 or 3 d at 25 to 30°C before ' and I,, measurements. Each Petri dish contained one disc of Whatman No. 1 filter paper and 3.5 ml of 20 mm KCl; dishes for zeatin-treated cotyledons also contained 56 /tM zeatin.Measurements of ' and I,. All *,, values were determined cryoscopically using an Osmette (Precision Systems, Framingham, MA). Techniques were as described previously (18), and results were corrected to 27°C by use of Van't Hoffs equation. All ' values were estimated by the gravimetric method of Ursprung (see Ref. 9). For zero-time measurements, two or three groups of20 cotyledons were blotted, weighed, and floated adaxial surface down on PEG 4,000 solutions contained in Petri dishes (9 cm diameter). After incubation for 1 to 5 h at 26 to 30°C under 20 ,uE m-2 s-' of laboratory light, they were removed from covered Petri dishes, blotted carefully, and weighed again. For cotyledons previously grown 1.5 or 3 d with or without zeatin, techniques were identical except that two or three groups of only 10 cotyledons were used to determine average weight changes in PEG solutions. In all cases, ' values were estimated by determining the ' of PEG solutions in which cotyledons neither gained nor lost weight. The ' values ofPEG solutions were, in turn, estimated from the closely agreeing standard curves of Nabors (12)

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Turgor and cell wall yielding in dicot leaf growth in response to changes in relative humidity

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Response of Growth of Tomato to Phosphorus and Nitrogen Nutrition

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