Young barley seedligs were stressed using nutrient solutions containing NaCI or polyethylene glycol and measurements were made of leaf growth, water potential, osmotic potential and turgor values ofboth growing (basal) Water stress is known to alter many plant functions, but cell growth is nearly universally reduced and is especially sensitive to water deficits (12). Hsiao et al. (1,13) demonstrated that very mild stress can reduce growth rates of corn and sorghum leaves, and Boyer (2) showed that stress levels required to reduce leaf elongation in sunflower, soybeans, and corn were substantially less than needed to affect photosynthesis. Acevedo et aL (1) also showed that growth rates of corn leaves could be changed within seconds following alterations of the water status of the root

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Root temperature strongly affects shoot growth, possibly via "nonhydraulic messengers" from root to shoot. In short-term studies with barley (Hordeum vulgare L.) and sorghum (Sorghum bicolor L.) seedlings, the optimum root temperatures for leaf expansion were 250 and 350C, respectively. Hydraulic conductance (Lp) of both intact plants and detached exuding roots of barley increased with increasing root temperature to a high value at 250C, remaining high with further warming. In sorghum, the Lp of intact plants and of detached roots peaked at 350C. In both species, root temperature did not affect water potentials of the expanded leaf blade or the growing region despite marked changes in Lp. Extreme temperatures greatly decreased ion flux, particularly K+ and N03-, to the xylem of detached roots of both species. Removing external K did not alter short-term K+ flux to the xylem in sorghum but strongly inhibited flux at high temperature in barley, indicating differences in the sites of temperature effects. Leaf growth responses to root temperature, although apparently "uncoupled" from water transport properties, were correlated with ion fluxes. Studies of putative root messengers must take into account the possible role of ions.Root zone temperature fluctuates both diurnally and seasonally, exerting diverse effects on plants. In many species, shoot growth responds strongly to changes in the temperature of the root environment (4-6, 18, 19, 27). In addition, root temperature significantly influences stomatal behavior (3,18,22), leaf water status (3,22), and the expression of symptoms due to nutrient deficiencies and other environmental stresses (4,22,26). Despite these important consequences, the mechanism(s) coupling root temperature to shoot responses are poorly characterized. Root temperature is reported to affect both water and ion transport (10,13) several reports have implicated nonhydraulic messengers (perhaps hormonal) from the root system in the control of shoot responses (18,22,27,30). The existence of such messengers is inferred, in part, from the failure to find changes in shoot water status associated with changes in shoot behavior. Although negative evidence may allow inferences about the existence of messengers, it does not per se establish their nature. Further deductions about the involvement of hormones require more detailed knowledge of the possible alternative messengers functioning within a system.Here we characterize the short-term responses of barley and sorghum to root temperatures from 15 to 40°C. These two species are acclimated to widely different temperature ranges during the growing season and were expected to be affected differently by root temperature. Root water transport properties (J2v and Lp) were studied using both intact plants and excised roots. Fluxes of K+, NO3-, and P043-were studied with detached roots. Because ion influx into the root and release to the xylem may be differentially regulated (12,21), an attempt was also made to separate these two processes and assess t...

Mason, H. S. and Matsuda, K. 1985. PoJyribosome metabolism,, growth and water status in the growing tissues of osmotically stressed plant seedlings. -Physiol. Relationships between growth of osmoticaliy stressed intact seedlings and polyribosome levels and water status of growing tissues were examined. Sudden exposure of barley (Hordeum vtilgare L. cv. Arivat) roots to a solution of -0.8 MPa polyethylene glycol caused ieaf growth to stop almost immedately, but growth resumed at a much iower rate after 0.5-1 h. In the growing region of leaves, the polyribosome: total ribosome ratio of free (non-membrane-bound) ribosomes was significantly reduced after 15 min stress, but a decrease in the large poiyribosome:toial poiyribosome ratio occurred only after 1-2 h. Membrane-bound and free polyribosome leveis both decreased to 70% of unstressed control values after 4 h stress. Recovery of total polyribosomes occurred within 1 h after relief of 4 h stress, but required 3 h after relief of 24 h stress. Stress detectably reduced the water potential and osmotic potential of growing tissue within 0.5-1.0 h, and osmotic adjustment continued for up to 10 h. Recovery of water status was incomplete after 1 h relief of a 4 h stress. In contrast, expanded blade tissues of stressed plants underwent minor changes in water status and slow decreases in polyribosomes levels. These results confirm that growing tissues of barley leaves are selectively responsive to stress, and suggest that changes in growth, water status and polyribosome leveis may be initiated by the same signal. Measurements of seedling growth, polyribosome levets and water status of growing tissues of bariey and wheat {Triticum aestivum L. cv. Zaragoza) leaves, etiolated pea {Pisum sativum L. cv. Alaska) epicotyl and etiolated squash (Cucurbita pepo L. cv. iilite) hypocotyl stressed with polyethylene glycol solutions of -0.3 to -0.8 MPa for 12 h or more showed that polyribosome leveis were highly correlated with seedling growlh rate as well as with tissue water and osmotic potentials, while turgor remained unchanged. These results suggest that long-term growth of osmotically stressed plants may be limited by a reduced capacity for protein synthesis in growing tissues and is not dictated by turgor loss.Additional key words -Cucurbita pepo, gel electrophoresis. Hordeum vulgare, osmotic adjustment, Pisum sativum, Triticum aestivum.H. 5. Mason and K. Matsuda (reprint requests),

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