Transient Responses of Cell Turgor and Growth of Maize Roots as Affected by Changes in Water Potential

Abstract

Transient responses of cell turgor ( P ) and root elongation to changes in water potential were measured in maize (Zea mays 1.) to evaluate mechanisms of adaptation to water stress. Changes of water potential were induced by exposing roots to solutions of KCI and mannitol (osmotic pressure about 0.3 MPa). Prior to a treatment, root elongation was about 1.2 mm h-' and P was about 0. 67 MPa across the cortex of the expansion zone (3-10 mm behind the root tip). Upon addition of an osmoticum, P decreased rapidly and growth stopped completely at pressure below approximately 0.6 MPa, which indicated that the yield threshold (YtranS,') was just below the initial turgor. Turgor recovered partly within the next 30 min and reached a new steady value at about 0.53 MPa. lhe root continued to elongate as soon as P cose above a new threshold (Ytran,,J of about 0.45 MPa. The time between Yt,ans,l and Vtrans,, was about 10 min. During this transition turgor gradients of as much as 0.15 MPa were measured across the cortex. They resulted from a faster rate of turgor recovery of cells deeper inside the tissue compared with cells near the root periphery. Presumably, the phloem was the source of the compounds for the osmotic adjustment. Turgor recovery was restricted to the expansion zone, as was confirmed by measurements of pressure kinetics in mature root tissue. Withdrawal of the osmoticum caused an enormous transient increase of elongation, which was related to only a small initial increase of P. Throughout the experiment, the relationship between root elongation rate and turgor was nonlinear. Consequently, when Y were calculated from steady-state conditions of P and root elongation before and after the osmotic treatment, Y, was only 0.21 MPa and significantly smaller compared with the values obtained from direct measurements (0.42-0.64 MPa). Thus, we strongly emphasize the need for measurements of short-term responses of elongation and turgor to determine cell wall mechanics appropriately. Our results indicate that the rate of solute flow into the growth zone could become rate-limiting for cell expansion under conditions of mild water stress.In Lockhart's model of plant expansive growth (Lockhart, 1965;Boyer, 1985), P in excess of a Y is the driving force for irreversible cell expansion; the rate of how fast a cell expands per unit of pressure above Y is determined by the m ("cell wall extensibility"). Commonly, the effect of water stress (reduction in q ) on Y and m is evaluated from the analysis of steady turgor and growth rates before and after a perturbation of the environment. This approach has been chal- Sharp et al., 1988; Spollen and Sharp, 1991) and leaves (Saab et al., 1992) illustrate the complexity of modeling total plant growth based on single-cell models such as that of Lockhart.Under steady-state conditions of growth, P remains constant in growing roots of wheat (Pritchard et al., 1989(Pritchard et al., , 1991 Tomos et al., 1989) and maize (Pritchard et al., 1990a; Spollen and Sharp, 1991). The adaptati...

Effect of salt stress on antioxidant enzymes and lipid peroxidation in leaves in two contrasting corn, ‘Lluteño’ and ‘Jubilee

“…Root growth in 'Lluteño' appeared to be less affected by salinity than the aerial tissues (Carrasco-Ríos et al, 2013). In corn, for example, root cells are capable of recovering their turgor after an osmotic shock at a concentration of 150 mM NaCl, while leaves do not recover completely (Frensh and Hsiao, 1994). However, mechanisms involved in this response are still unknown (Munns and Tester, 2008).…”

A reduced xylem pressure altered the electric and growth responses in cucumber hypocotyls

“…We find contradictory results in the literature about the effect of F^ on plant growth. Some studies found no or only a small, transient, and hence inconsequential influence of P^ reduction (Termaat et al 1985;Stahlberg & Cosgrove 1992, 1995Frensch & Hsiao 1994), while other results indicate a lasting, regulatory growth adaptation (Okamoto etal. 1984(Okamoto etal.…”

Root Osmotic Adjustment under Osmotic Stress in Maize Seedlings 1. Transient Change of Growth and Water Relations in Roots in Response to Osmotic Stress

“…For the decrease of osmotic potential, the accumulation of compatible solute (Voetberg and Sharp, 1991) and the decrease in the rate of the water infl ux to the tissue and the tissue volume expansion (Sharp et al, 1990) were contributed in maize seminal root. Turgor was recovered by osmotic adjustment faster in the cells located deep inside the tissue compared with cells near the root surface, and this result showed that the phloem was the possible source of compounds for osmotic adjustment (Frensch and Hsiao, 1994).…”

“…Turner and Jones (1980) stated that osmotic adjustment in the root has a different role from that in the shoot, and Serraj and Sinclair (2002) stated that osmotic adjustment in root might be important in relation to crop production. As in leaf growth, root elongation is related with the turgor pressure in root elongation zone (Greacen and Oh, 1972;Sharp and Davies 1979;Westgate and Boyer, 1985;Frensch and Hsiao, 1994). The role of osmotic adjustment in root elongating zone is to maintain turgor pressure to continue root elongation and root growth in drying soils, which enable the plant to maintain its transpiration by exploiting a greater volume of soil or utilize available water in a given soil volume more effi ciently.…”