Osmotic Adjustment and the Growth Response of Seven Vegetable Crops following Water-deficit Stress

Growth-chamber studies were conducted to examine the ability of seven vegetable crops-‘Blue Lake’ bean (Phaseolus vulgaris L.), ‘Detroit Dark Red’ beet (Beta vulgaris L.), ‘Burgundy’ okra (Abelmoschus esculentus (Moench), ‘Little Marvel’ pea (Pisum sativum L.), ‘California Wonder’ bell pepper (Capsicum annuum L.), ‘New Zealand’ spinach (Spinacia oleracea L.), and ‘Beefsteak’ tomato (Lycopersicon esculentum Mill.)–to adjust osmotically in response to water-deficit stress. Water stress was imposed by withholding water for 3 days, and the adjustment of leaf and root osmotic potentials upon relief of the stress and rehydration were monitored with thermocouple psychrometers. Despite similar reductions in leaf water potential and stomata1 conductance among the species studied, crop-specific differences were observed in leaf and root osmotic adjustment. Leaf osmotic adjustment was observed for bean, pepper, and tomato following water-deficit stress. Root osmotic adjustment was significant in bean, okra, pea, and tomato. Furthermore, differences in leaf and root osmotic adjustment were also observed among five tomato cultivars. Leaf osmotic adjustment was not associated with the maintenance of leaf growth following water-deficit stress, since leaf expansion of water-stressed bean and pepper, two species capable of osmotic adjustment, was similar to that of spinach, which exhibited no leaf osmotic adjustment. Osmotic adjustment has been suggested as a mechanism of drought tolerance whereby Received for publication 15 Nov. 1990. Research sponsored by the Arkansas Agricultural Experiment Station. The senior author was supported in part by the Alexander Hollaender Distinguished Postdoctoral Fellowship Program provided by the U.S. Dept. of Energy, Office of Health and Environmental Research, and administered by Oak Ridge Associated Universities. Publication no. 3738, Environmental Sciences Division, Oak Ridge National Laboratory. Oak Ridge National Laboratory is managed by Martin Marietta Energy Systems, Inc., under contract DE-AC05-84OR21400 with the U.S. Dept. of Energy. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1210 plants achieve either a survival or a productivity advantage under conditions of water shortage (Ludlow and Muchow, 1988; Turner, 1981; Wright et al., 1983). Lowered osmotic potential in response to water-deficit stress is proposed to play a significant role in turgor maintenance (Zimmermann, 1978), thereby regulating plant growth processes (Morgan, 1984; Turner, 1986). However, although osmotic adjustment has been implemented as a selection criterion for improved drought hardiness (Morgan, 1983), the importance of osmotic adjustment in maintaining leaf and root growth during waterdeficit stress remains controversial (Munns,