Osmotic adjustment in indoor grown cassava in response to water stress

Abstract

The water content‐water potential relation in stressed and unstressed cassava (Man‐ihot species) was examined to ascertain (i) the magnitude of osmotic adjustment in response to water stress and (ii) the mechanisms of such adjustments.Water stress resulted in a displacement of the water content‐potential relation such that at any leaf water potential the water content was higher in the stressed plants. The osmotic potentials of turgid leaves (100% relative water content) were ‐0.97 and ‐1.00 MPa in the unstressed cultivars CMC 9 and MCOL 113 respectively. In the stressed plants, the values were‐1.13 MPa (CMC 9) and‐1.14 MPa (MCOL 113). The 0.14 to 0.16 MPa osmotic potential difference between the stressed and unstressed plants suggests that a stress‐induced osmotic adjustment occurred in both cultivars. The biiSk volumetric elastic moduli at turgor pressures above 0.10 MPa were 9.84 MPa (CMC 9) and 13.58 MPa (MCOL 113) in the unstressed plants. Tbe higher values found in the stressed plants, 14.56 MPa in CMC 9 and 16.91 MPa in MCOL 113, suggest a stress‐induced decrease in cell wall elasticity. Hence, the observed shift in the wafer content‐potential relations in the cassava involved both an osmotic adjustment and a decrease in cell wall elasticity. Increasing the number of stress cycles per plant did not cause a further displacement of the water content‐potential curves.