Recent Ecophysiological Findings for Opuntia ficus-indica


Recent research concerning Opuntia ficus-indica from our laboratory is reviewed. A root-soil air
gap that develops as the roots of O. ficus-indica shrink in response to drying conditions helps
retard water loss to the soil in the initial phases of drought, with cellular changes affecting the
root hydraulic conductivity playing a secondary role and decreases in soil hydraulic
conductivity becoming dominant after a few weeks of drought. The xylem is the vascular
system typically supplying water to plant parts, for which flow occurs toward regions of lower
water potential. However, both fruits and young daughter cladodes of O. ficus-indica have
higher water potentials than the supporting cladodes, which they depend on for organic
compounds. These compounds are transported in the phloem in a relatively dilute sap that
also supplies the water needed for growth of the new organs. Detached unrooted cladodes of
O. ficus-indica form a model system for studying environmental and solute responses of the
stem. Shading and injection of gibberellic acid can inhibit new organ initiation but injection of
indole-acetic-acid and kinetin accelerates it. New organ initiation is greatest when the cladodes
are detached in the winter. Low day/night air temperatures favor the initiation of flowers,
whereas high temperatures favor initiation of daughter cladodes.