JXB Advance Access originally published online on September 25, 2003
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Journal of Experimental Botany, Vol. 54, No. 392, pp. 2479-2488,
November 1, 2003
© 2003 Oxford University Press
Root pressurization affects growth-induced water potentials and growth in dehydrated maize leaves
Received 17 February 2003; Accepted 10 July 2003
College of Marine Studies and College of Agriculture and Natural Resources, University of Delaware, 700 Pilottown Road, Lewes, DE 19958, USA
* To whom correspondence should be addressed. Fax: +1 302 645 4007. E-mail: boyer{at}udel.edu
Abbreviations: P, pressure applied to soil/root system; dap, days after planting; X, water potential in the lumen of xylem in leaf elongating tissues; G, water potential outside the xylem in leaf elongating tissues; Ma, water potential of lower mature part of leaf; Mb, water potential of middle of mature part of leaf; Mc, water potential of tip of mature part of leaf; R, water potential of mature part of root; S, water potential of soil; 
w, water potential; s, osmotic potential; p, turgor pressure.
Profiles of water potential (w) were measured from the soil to the tips of growing leaves of maize (Zea mays L.) when pressure (P) was applied to the soil/root system. At moderately low soil w, leaf elongation was somewhat inhibited, large tensions existed in the xylem, and w were slightly lower in the elongating leaf tissues than in the xylem, i.e. a growth-induced w was present but small. With P, the tension was relieved, enlarging the difference in w between the xylem and the elongating tissues, i.e. enlarging the growth-induced w, which is critical for growth. Guttation occurred, confirming the high w of the xylem, and the mature leaf tissue rehydrated. Water uptake increased and met the requirements of transpiration. Leaf elongation recovered to control rates. Under more severe conditions at lower soil w, P induced only a brief elongation and the growth-induced w responded only slightly. Guttation did not occur, water flow did not meet the requirements of transpiration, and the mature leaf tissues did not rehydrate. A rewatering experiment indicated that a low conductance existed in the severely dehydrated soil, which limited water delivery to the root and shoot. Therefore, the initial growth inhibition appeared to be hydraulic because the enlargement of the growth-induced w by P together with rehydration of the mature leaf tissue were essential for growth recovery. In more severe conditions, P was ineffective because the soil could not supply water at the required rate, and metabolic factors began to contribute to the inhibition.
Key words: Gradients, leaf elongation, osmotic potential, turgor, Zea mays L.
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  A.-C. Tang and J. S. Boyer Xylem tension affects growth-induced water potential and daily elongation of maize leaves J. Exp. Bot., March 1, 2008; 59(4): 753 - 764. [Abstract] [Full Text] [PDF]
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