Ethylene auxin conjugation

It has been evidenced that auxin and ACC stimulate ethylene production in some lower plants, for example, in the moss Funaria hygrometrica and in the ferns Pteridium aquilinum and Matteuccia struthiopteris Moreover, ethylene synthesis via the ACC-dependent pathway and in the presence of endogenous ACC and its conjugate in marine unicellular Acetabularia algae was reported. Probably during the evolution of land plants, a relatively primitive pathway of ethylene production was replaced by the ACC-dependent synthesis pathway that now predominates. 

Another important factor of hormone-hormone interaction is the hormonal control of hormonal movement and polarity. Thus, various cytokinins have been reported to increase the polar movement of indole acetic acid and vice versa. Gibberellin treatment was shown also under cer- bain circumstances to increase the basipetal auxin movement. On the other hand, abscisic acid decreases the auxin movement and ethylene, according to some evidence, the gibberellin movement, perhaps through a promotion of conjugation of the auxins with aspartate and of the gibberellins with glucose (cf. Eef. 27). 

Useful progress has been made in the genetics of GAs, ABA and, more recently, ethylene [11]. However, relatively few mutations have been reported involving auxins or cytokinins. Both recessive and dominant mutants have been isolated with increased resistance to synthetic auxins [8, 14, 16], and two mutants have been described with significantly altered levels of lAA or lAA conjugates [20, 22]. Mutations have been reported that affect the cytokinin requirement of tobacco leaf cells in culture [15], and cytokinin resistance and production in the moss Phys-comitrella patens [23]. 

Furthermore, SAM not only plays a pivotal role in PA and ethylene biosynthesis, but also in the formation of putrescine-derived alkaloids. Thus, SAM acts as a methyl donor in the conversion of putrescine into A-methylputresdne, an intermediate in the biosynthesis of nicotine (Mizusaki et al., 197 lb). Therefore, it would be interesting to explore the auxin-ethylene-PAs interaction on PA conjugates and putrescine-derived alkaloids metabolism in the above-mentioned tobacco callus tissue system. Indeed, it has been reported that inhibition of SAM decarboxylase by MGBG resulted in an increase of nicotine production in tobacco root cell suspension cultures (Blume, 1985). Unfortunately, nothing about PA conjugates was indicated in this report. 

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