Auxin-induced Conjugation Systems in Peas

Abstract

Pretreatment of pea (Pisum sativum var. Alaska) sections with any active auxin induces an enzyme which forms aspartate conjugates of exogenously supplied indoleacetic acid, naphthaleneacetic acid, or benzoic acid. Whereas induction of this system is ant absolutely auxin-specific process, another enzyme, which forms benzoyhnalic acid, is induced both by auxins and by physiologically inactive aromatic carboxylic acids. Induction of both enzymes is abolished by low levels of R1NA and protein synthesis inhibitors. The induction specificities and other characteristics of the two systems are compared.

The Effects of Exogenous Auxins on Endogenous Indole-3-Acetic Acid Metabolism (The Implications for Carrot Somatic Embryogenesis)

“…The concentration of the free, ester-bound, and amidebound ['H,]IAA were a11 much higher than the corresponding concentration of the endogenous forms of IAA in the 1-week cultures. The conjugated forms of ['H,]IAA were 250 times more abundant than free ['H,]IAA, suggesting that ['H,]IAA, and therefore IAA, induced its own conjugation, as was also observed by Venis (1972). This would explain the increase noted in the concentration of amide-conjugated, unlabeled IAA as well.…”

“…Nevertheless, the concentration of free NAA was significantly higher than the concentration of free IAA in untreated cultures, and, therefore, the free NAA seemed directly responsible for the observed auxin-like changes in the growth of these cultures. NAA, like IAA, has been shown to induce its own conjugation when applied to plants, thereby increasing the capacity for the formation of NAA-aspartate (Siidi, 1966;Johansson, 1971;Venis, 1972;Brenner and Tonkinson, 1974;Smulders et al, 1990). Cultured carrot hypocotyls conjugated NAA much more readily than they did 2,4-D, which in part accounted for the low free NAA content.…”

Mechanism of Naphthaleneacetic Acid Conjugation

“…However, a third radioactive product at RF 0.7 to 0.8 (Table I) (Table I) did not cochromatograph with NAAmd ( Fig. 1) but migrated similarly to NAGlu, as reported in other studies (8,32,34). Based on radioanalysis (scintillation counting of silica gel representing each RF zone) of developed chromatograms, separation of NAA, NAGlu, and NAAsp was excellent with more than 90% of applied radioactivity being associated with the specified RF zones.…”

“…Following an additional 16-hr incubation period in the presence or absence of cold NAA, the free NAA level dropped to less than 1%, and only traces of radioactivity were found in the ambient solution. Differences in total uptake (Table II) (31,34,39), it was still important to confirm this fact in our system. The formation of NAAsp was more than doubled when leaves were preincubated in nonlabeled NAA for 17 hr compared to buffer alone (Fig.…”

“…The conjugation enzyme, (L)-aspartic acid-N-acylase, which remains to be isolated, is probably formed during this initial lag period (39). Biologically active auxins can induce the formation of acyl-aspartate conjugate, while nonactive auxin analogues are ineffective (31,34). In contrast to the acyl-aspartate conjugate, glucosides are formed immediately following auxin uptake, thus serving as a mechanism for rapid detoxification of aromatic carboxylic acids while the acyl-aspartate conjugation system is formed in the plant (40).…”