Responses of maize roots to drying – limits of viability

Abstract

Turgid pieces of mature maize roots were dried in air and progressive changes in their relative water content (RWC) determined. Viability was tested by reproducibility of the drying curves after dehydration to successively lower RWCs. After reaching a chosen RWC, the pieces were rehydrated (approximately 2 h), and a 2nd and 3rd dehydration curve measured. Each drying curve was characterized by two parameters (a scale parameter l l, and a shape parameter b b) of a survivorship function, which is a linear function of time. The parameter l l is more informative, and does not change in successive dehydrations for RWC > > 0·4, suggesting no irreversible damage to the roots. Damage and death were indicated by divergences of l l in successive dehydrations to RWC = = 0·35-0·15. Cryo-analytical microscopy confirmed these data while indicating specifically death of 50 and 100% of cortical cells at RWC 0·30 and 0·15, respectively, and survival of 50% or more of sieve tubes, pericycle and vascular parenchyma cells at root RWC as low as 0·15. This pattern of stelar cell survival may allow roots to preserve their capacity for renewal of axial conductivity and branch root development following periods of severe water stress.

Anatomical root variations in response to water deficit: wild and domesticated common bean (Phaseolus vulgaris L)

“…Modification of the isodiametric shape of parenchymatic cells was observed in dehydrated root seedlings growing under lower substrate ψ W (Figure 2 A and B, 3 A and B). Similar results for maize seedling roots were reported, including reduction of cortical cell size and modification of root shape when the relative water content reached a value of 0.5 (Facette et al, 1999).…”

“…The domesticated bean had significantly thicker xylem walls than the wild bean, independently of ψ W ; the highest difference (54 %) was reached at ψ W of -2.35 MPa ( Figure 5C). Recently, it was observed that dry weight increases in roots of wild and domesticated common bean seedlings by the effect of restrictive ψ W (Sanchez-Urdaneta et al, 2003), which can partially be explained by the growth of xylem cell walls (Facette et al, 1999).…”

Freeze avoidance: a dehydrating moss gathers no ice

“…Potassium concentration is a key indicator of cellular function with living cells having concentrations of approximately >50 mM (McCully, Canny & Vansteveninck 1987; Huang & Van Steveninck 1988; McCully 1994; Facette, McCully & Canny 1999). The IC cells had average potassium concentrations of 81 mM, consistent with normal cellular function (at the time of cryo‐fixing).…”

Seasonal water relations of Lyginia barbata (Southern rush) in relation to root xylem development and summer dormancy of root apices

“…There was no evidence of cell shrinkage in dormant roots whilst the plants were transpiring and xylem was not embolized (Fig. 5), in contrast to shrinkage recorded in cells of eucalypt leaves (Canny & Huang, 2006) and maize roots (Facette et al, 1999) during water stress. The thick lignified walls of all cells, except phloem, that developed relatively closer to tips of summer-dormant roots could have resulted, in part, from increased soil temperatures in the sandplain habitat, because lignification of xylem has been shown to occur closer to root tips in wheat with increasing root temperature (Huang et al, 1991).…”