788 



PLANT GROWTH 



lO 



TABLE 4 



EFFECTS OF VARIOUS INHIBITORS ON CELL ENLARGEMENT AND RESPIRATION 



IN THE SAME TISSUE 



Tissue 



Inhibitor Concn. needed for Inhibition of respiration Refer- 



50°/^ inhibition of caused by this concn. of inhibitor ence 

 cell enlargement 



References: a. Christiansen and Thimann (1950a) d. J. Bonner (1950) and Audus 



b. Commoner and Thimann (1941) 



c. W.D. Bonner and Thimann (1950) 



(1952) 



e. J. Bonner (1949) 



f. Hackett et al. (1953) and 

 Thimann et al. (1954) 



by cyanide, which inhibited growth and respiration of coleoptiles to the same 

 extent (Bonner, 1936). An extreme case is shown by potato tissue, in which con- 

 centrations of dinitrophenol or arsenite which inhibit water uptake about 50% 

 actually increase the respiration (Hackett and Thimann, 1953). This tissue also 

 shows a strong tendency for the inhibition of growth to disappear after 6 days, 

 while the inhibition of respiration remains. Such phenomena confirm the indica- 

 tion of Table 4 that the relationship between respiration and growth is an indirect 

 one. It is curious that mannitol, which inhibits elongation (see section below) 

 largely prevents the rise in respiration caused by auxin, both in tuber and coleop- 

 tile tissue (Bonner et at., 1953; Ordin et al., 1956). The explanation of this effect 

 is not yet clear [cf. Burstrom, 1953b). 



In root tissues the principal inhibitor studied has been auxin itself. The data 

 are less numerous but auxin appears to have a relatively small effect on respiration. 

 At growth inhibiting levels of lAA {ca. lO'^M) maize roots showed a small reduc- 

 tion in oxygen consumption, but after 4 days it approached the control and, if 

 calculated per mg of N, even exceeded it (Kandler and Vieregg, 1953). The RQ 

 went up to 1.3. Wheat roots in auxin behaved similarly when the respiration was 

 calculated per mg N, but the oxygen uptake j&^r root was markedly affected parallel 

 to the growth (Eliasson, 1955). Part of the explanation for the relative insensitivity 

 to auxins on a nitrogen basis lies in the great increase in dry weight of roots, per 

 unit length, when inhibited by lAA and the corresponding decrease when elonga- 

 tion is promoted by indoleisobutyric acid [of. the data on nitrogen, p. 792). Roots 



