The amounts and rates of metabolic turnover of the indolylic compounds in germinating kernels of sweet corn were determined. Knowledge of pool size and rate of pool turnover has permitted: (a) identification of indole-3-acetyl-myo-inositol as the major chemical form for transport of indole-3-acetic acid (IAA) from endosperm to shoot; (b) demonstration that the free IAA of the endosperm is turning over rapidly with a half-life of 3.2 hours; (c) identification of esters of IAA as the immediate precursors of IAA in the endosperm and shoot-, (d) demonstration that neither tryptophan nor tryptamine is a major precursor of IAA for the seed or shoot-, (e) identification of IAA-myo-inositol glycosides as precursors of IAA-myo-inositol.It is concluded that seedlings of Zea mays utilize esters of IAA, and not tryptophan or its derivatives, for the IAA requirements of the germinating seedling.The endosperm of kernels of Zea mays contains small amounts of indole-3-acetic acid and large amounts of esterified IAA (5,15,26,27,35,38). The esterified IAA has been chemically characterized (1,21,26,36) and assayed quantitatively in the dry seed (35) and during ripening (9 and unpublished data) and during germination of the kernels (ref. 35 and unpublished data). It remained necessary to measure the rate ofmetabolic turnover ofthe indolylic compounds to permit determining which are being exported from the kernel to the shoot and to search for metabolic functions.We previously demonstrated that: (a) the esters play a role in hormonal homeostasis in the seedling vegetative shoot (4); and (b) that esterification plays a protective role in preventing peroxidative attack upon IAA (8). Now, with knowledge of turnover in the endosperm, we can add additional functions for the esters; they are: (c) transport of IAA-myo-inositol from the kernel to the shoot in amounts sufficient to provide the seedlings needs (24); and (d) providing the kernel with a large and renewable amount of free IAA during germination. The resultant free IAA is, in small part, transported to the shoot, with the bulk decarboxylated or otherwise metabolized in the endosperm. The rates of destruction and formation of IAA are equal so that the amount of free IAA in the endosperm remains steady-state. Neither tryptophan nor tryptamine serves as a major source of IAA in Zea kernels.We also demonstrate that the IAA-myo-inositol esters turnover Stowell's Evergreen Sweet Corn) were surface-sterilized in 1% NaOCl for 10-20 min, soaked in running water at 25 C for 16 h, then placed in rows across paper towels. The towels were rolled, secured with tape, placed in a beaker containing water and incubated in the dark for an additional 80 h. About 30%o of the endosperm was cut from the end of the kernels leaving the embryo and scutellum intact, so that an endosperm surface was exposed for isotope application. All manipulations were at 25 C, 90%o RH, and with use of a phototropically inactive green safelight.Application of Labeled Compounds-Recovery Corrections.Ten ,ul of th...

Amide-linked indole-3-acetic acid (IAA) conjugates constitute approximately 90% of the IAA pool in the dicot Arabidopsis, whereas ester-linked conjugates and free IAA account for approximately 10% and 1%, respectively when whole seedlings are measured. We show here that IAA-aspartate Asp, IAA-glutamate (Glu), and IAA-glucose (Glc) are present at low levels in Arabidopsis. Nine-day-old wild-type Arabidopsis seedlings yielded 17.4 Ϯ 4.6 ng g Ϫ1 fresh weight IAA-Asp and 3.5 Ϯ 1.6 ng g Ϫ1 fresh weight IAA-Glu, and IAA-Glc was present at 7 to 17 ng g Ϫ1 fresh weight in 12-d-old wild-type seedlings. Total IAA content in 9-d-old Arabidopsis seedlings was 1,200 Ϯ 178 ng g Ϫ1 fresh weight, so these three IAA conjugates together made up only 3% of the conjugate pool throughout the whole plant. We detected less than wild-type levels of IAA-Asp and IAA-Glu (7.8 Ϯ 0.4 ng g Ϫ1 fresh weight and 1.8 Ϯ 0.3 ng g Ϫ1 fresh weight, respectively) in an Arabidopsis mutant that accumulates conjugated IAA. Our results are consistent with IAA-Asp, IAA-Glu, and IAA-Glc being either minor, transient, or specifically localized IAA metabolites under normal growth conditions and bring into question the physiological relevance of IAA-Asp accumulation in response to high concentrations of exogenous IAA.

Mutants and wild type plants of Arabidopsis thaliana were analysed for differences in glucosinolate accumulation patterns, indole-3-acetic acid (IAA) biosynthesis and phenotype. A previously identified series of mutants, termed TU, with altered glucosinolate patterns was used in this study. Only the line TU8 was affected in shoot phenotype (shorter stems, altered branching pattern). Synthesis of IAA and metabolism were not much affected in the TU8 mutant during seedling development, although the content of free IAA peaked earlier in TU8 during plant development than in the wild type. Indole glucosinolates and IAA may, however, be involved in the development of clubroot disease caused by the obligate biotrophic fungus Plasmodiophora brassicae since the TU3 line had a lower infection rate than the wild type, and lines TU3 and TU8 showed decreased symptom development. The decline in clubroot formation was accompanied by a reduced number of fungal structures within the root cortex and slower development of the fungus. Indole glucosinolates were lower in infected roots of TU3 and TU8 than in control roots of these lines, whereas in wild-type plants the differences were not as prominent. Free IAA and indole-3-acetonitrile (IAN) were increased in infected roots of the wild type and mutants with normal clubroot symptoms, whereas they were reduced in infected roots of mutants TU3 and TU8. These results indicate a role for indole glucosinolates and IAN/IAA in relation to symptom development in clubroot disease.