HYDRAULIC CONDUCTIVITY AND ANATOMY FOR LATERAL ROOTS OF AGAVE-DESERTI DURING ROOT-GROWTH AND DROUGHT-INDUCED ABSCISSION

Hydraulic conductivity (L(p)), radial conductivity (L(R)), axial conductance (K(h)), and related anatomical characteristics for lateral roots of Agave deserti were investigated during root growth and drought-induced abscission. The elongation rate of lateral roots averaged 5 mm d-1 under wet conditions and was reduced 95% by 17 d of drought (psi(soil) < -0.5 MPa); 46% of such roots abscised at 21 d of drought. Under wet conditions, L(p) decreased with age up to 30 d, mainly reflecting suberization of endodermal cells. L(p) and L(R) decreased basipetally along the roots under wet conditions and after 18 d of drought and were lower in the case of drought, both responses reflecting increases in the number of suberized endodermal cells. In contrast, L(p) and L(R) increased basipetally along abscised roots at 35 d of drought, presumably due to the collapse of cortical cells. K(h) increased with distance from the root tip; the greatest increase, which coincided with the loss of cross walls in late metaxylem vessels, occurred closer to the tip for roots from droughted plants compared with well-watered plants. K(h) was reduced during drought by embolism of the xylem vessels, similar to the results for other studies.