The Dependence of Auxin-induced Growth on Auxin-independent Metabolic Changes in Slices of Storage Tissue.

Water absorption by slices of storage organ tissue is markedly enhancedl in the presence of auxin (1,3,4,5). A lag period that varies from hours to days, depending on the type of tissue and its storage history, precedes auxin-indlucedl enlargement (1, 2, 3). When bulky storage organs are sliced, there is a general quickening of metabolic activity which increases with time (1, 6, 7, 10). In potato, for example, the respiration rises approximately fourfold within a day, andl starch degradation, protein synthesis and salt absorbing capacity increase sharply (10, 15, 18). In slices of both potato (16) an(d red beet (15) the onset of vigorous salt absorption is precedecl by a period roughly equal in (luration to the growth lag phase, although the enhancement of salt absorbing capacity is independent of auxinl. There is considerable evidence that the induce(d respiration in storage organ slices is largely different in kind from the initial, or basal, respiration (6, 7, 9,13). In particular, slicing is followed by a dramatic enhancement of oxidative phosphorylation which far exceeds expectations basedl simply on the gross increase of respiratory activity (11). It is well established that auxin-induced water uptake is respiration dependent (3). The question wvhiclh is raisecl herein is whetlher auxin-induce(l growth of storage organ slices is (lependent upon the respiratory changes which follow slicing. The hypothesis which underlies this investigation is that the onset of active phosphorylation associatedl with the inducecl respiration is causative to the nmany physiological changes noted in aging tissue slices-inclu(inlg the development of auxin responsiveness. In most of the experimlents which have dlealt with auxin induced enlargement in storage tissue, slices were routinely brought to a fully turgid condition in a preliminary 24-hour incubation period in Nwater in an air atmiiosphere (2, 3. 4). The rej)orted respiration rates at the beginning of the experimlental periocl for both potato an(l artichoke slices indicate that the respiratory rise has largely taken place by that time. As will be more fully discussed below, Adanmson has recently recognized that the preliminary periodI is in fact of special importance. and his observations have ledl him to conclusions similar to