298 Auxins in Agriculture 



availability of phosphate acceptors in the metabolic milieu. The 

 climacteric rise in respiration rate is thought to be due to progressively 

 increasing availability ot phosphate acceptors in the fruit. Agents 

 such as 2,4-dinitrophenol which uncouple oxidation from phosphoryl- 

 ation processes can stimulate respiration (and hence presumably the 

 ripening process) only in the preclimacteric period, because only in 

 that period do phosphate acceptors limit respiration. The relation of 

 auxin effects upon respiration to phosphorylation phenomena were 

 discussed in chapter V, where it was indicated that auxin effects in- 

 volve the utilization of high-energy phosphate bonds — a process which 

 would make phosphate acceptors available for further respiratory 

 functions. In the light of these observations, it is not surprising that 

 auxin effects upon ripening are smaller and smaller as the time of 

 application approaches the time of ripening, for according to the evi- 

 dence of Millerd et al phosphate acceptors limit respiration less and 

 less as the climacteric approaches. Evidence for the same type of un- 

 coupling action in the ripening of apples has been obtained by Pear- 

 son and Robertson (1952). 



It has been reported that 2,4-D can induce ripening of stored 

 bananas (Marth and Mitchell, 1949). This is probably not an effect 

 of the auxin, but rather of the common impurity in 2,4-D prepara- 

 tions: 2,4-dichlorophenol. That the effects of this compound may be 

 easily confused with effects of 2,4-D has been pointed out by Gold- 

 acre et al, 1953. This impurity is a strong uncoupling agent like 

 2,4-dinitrophenol, and would consequently be expected to increase 

 the rate of ripening of green fruits. 



It is interesting to note that ethylene can induce early ripening in 

 harvested bananas but is ineffective on post-climacteric fruits (Hansen 

 and Hartman, 1937). 



STRENGTHENING FLOWERING STALKS 



Auxins have been observed to strengthen pedicels or peduncles 

 luider the fruits of grape (Weaver and Williams, 1950) and lime 

 (Erickson and Brannaman, 1950). It has been commonly observed that 

 tomatoes show a thickening of the pedicel and enlargement of the 

 sepals upon auxin application for parthenocarpic set. 



As remarked in chapter XIV, tlie use of auxins to induce flower- 

 ing in pineapple results in an unfavorable side effect in which the 

 peduncle which supports the fruit l:)ecomes abnormally long and 

 spindly. As a consequence the fruits often tip sideways from their own 

 weight and much loss is incurred from sunburn to the sides of the 

 fruits. A second application of auxin spray shortly after the naph- 



