Effects of potassium deficiency on cell water relations and elongation of tap and lateral roots of maritime pine seedlings

Abstract

SUMMARYThe effects of potassium deficiency (KD) and all-macronutrient deficiency (MD) on elongation of tap and lateral roots were studied on maritime pine seedlings (Pinus pinaster Ait.) in hydroponic culture.Tap root elongation was unaffected by either of the two deficiencies. By marked contrast, lateral root elongation was strongly reduced. The analyses of cell turgor pressure and relative elemental growth rate (REGR) profile in the growing zone allowed us to determine the effects of the nutrient stresses on celJ-wal] properties. For both deficiency treatments, elongation rate, REGR profile (measured only for control and KD) and turgor pressure in the fastest growing cells were unaffected in the tap root, suggesting that KD and MD did not modify cell-wall properties in the growing zone. In lateral roots, KD shortened the growing zone and significantly reduced REGR. However, turgor pressure remained unaffected in this region. The absence of turgor pressure change suggests that KD reduced elongation of lateral roots by tightening cell walls. In mature cells of the two types of roots, turgor and osmotic pressures tended to be reduced by the nutrient deficiencies, indicating that these parameters were better maintained in the growing cells.Cell turgor and osmotic pressures of control plants were 0-1 MPa lower at 30 mm (mature cells) than at 2-4 mm (expanding cells) from the meristem. Moreover, these parameters were 0-1 MPa lower in expanding cells of lateral roots than in those of tap the root. Turgor and osmotic pressures were not homogeneous throughout the root system and were affected differently by the nutrient deficiencies depending on the location in the root system.

Control of leaf cell elongation in barley. Generation rates of osmotic pressure and turgor, and growth-associated water potential gradients

“…However, most investigators concluded that the hydraulic conductance was suciently high and that, instead, control of wall properties was responsible for treatment-associated dierences in the expansion of leaf and root cells (e.g. Cosgrove et al 1984;Tomos and Pritchard 1994;Triboulot et al 1997). The latter conclusion has its origin in the work of Green et al (1971) on Nitella and Lockhart's (1965) empirical growth model, which relates RGR to the extensibility properties (m) and the yield threshold (Y) of the cell wall:…”

Measurement of a growth‐induced water potential gradient in tall fescue leaves

“…Such an increase in P is not the norm in plant tissues. In roots, P is usually 0.5 MPa in the growth zone, but it remains constant or decreases slightly as cells move away from the growth zone (Frensch & Hsiao, 1993 ;Pritchard, 1994 ;Triboulot et al, 1997). It would be interesting to assess whether this higher turgor in mature leaves compared with mature roots could depend on the structural requirements for self support in mature leaves.…”

The Role of Cytosolic Potassium and pH in the Growth of Barley Roots

“…Although the beneficial effect of increased K ϩ supply on wall extensibility has been demonstrated (Métraux and Taiz, 1977), the presence of K ϩ salts in the nutrient solution can inhibit root-cell elongation by reducing cell wall plasticity in the root-expansion zone (Pritchard et al, 1987). The effect of K ϩ on root elongation seems to be species specific (Pritchard, 1994), cultivar specific (Hackett, 1968), and root-type specific (Hackett, 1968;Triboulot et al, 1997).…”