Decarboxylative metabolism of [1′-14C]indole-3-acetic acid by tomato pericarp discs during ripening

Abstract

Abstract. The rate of decarboxylation of [1'-14C]indole-3-acetic acid (IAA) infiltrated into tomato (Lycopersicon esculentum Mill.) pericarp discs was much more rapid in green than in breaker and pink tissues. Studies were carried out in order to determine whether the decarboxylative catabolism occurring in the green pericarp discs was associated with ripening or was a consequence of woundinduced peroxidase activity and/or ethylene production. After a 2-h lag, the decarboxylative capacity of the green pericarp discs increased exponentially during a 24-h incubation period. This increase was accompanied by increases in IAA-oxidase activity in cell-free preparations from the intercellular space and cut surface of the discs. Although higher IAA-oxidase activity was detected in extracts from the tissue residue, which comprises mainly intracellular peroxidases, this activity did not increase during the 24-h incubation period. Analysis of the cellfree preparations by isoelectric focusing revealed the major component in all samples was a highly anionic peroxidase (pI = 3.5) the levels of which did not increase during incubation. However, the intercellular and cut-surface preparations contained additional anionic and cationic peroxidases which increased in parallel with the increases in both the IAA-oxidase activity of the preparations and the decarboxylative capacity of the green pericarp discs from which they were derived. Treatment of green discs with the ethylene-biosynthesis inhibitors aminooxyacetic acid and COC12, inhibited the development of an enhanced capacity to decarboxylate [l'-14C]IAA but the inhibition was not counteracted by exogenous ethylene. Another ethylene-biosynthesis inhibitor, aminoethoxyvinyl glycine, also reduced ethylene levels but did not affect IAA decarboxylation, indicating that the decarboxylation was not a consequence of wound-induced ethylene production. The data obtained thus demonstrate that the enhanced capacity to decarAbbreviations: AOA = aminooxyacetic acid; ACC = 1-aminocyclopropane-l-carboxylic acid; AVG = aminoethoxyvinyl glycine; IAA = indole-3-acetic acid Correspondence to: J. Chamarro; FAX: 34 (6) 3 93 00 01 boxylate [l'-14C]IAA that develops in green tomato pericarp discs following excision is not associated with ripening but instead is attributable to a wound-induced increase in anionic and cationic peroxidase activity in the intercellular fluid and at the cut surface of the excised tissues.

Developmental Regulation of Indole-3-Acetic Acid Turnover in Scots Pine Seedlings

“…This also supports our view that the two new conjugates are irreversible inactivation forms of IAA in this system. Precautions have been taken during these experiments to avoid formation of metabolites caused by feeding with unphysiologically high hormone levels, microbiological activity, or the preparation itself (Ö stin et al, 1998;Catalá et al, 1994). Thus, we are confident that the metabolic profile presented in Figure 4 is representative of the physiological metabolic pathways of IAA in Scots pine seedlings.…”

Identification of glucopyranosyl‐β‐1,4‐glucopyranosyl‐β‐1‐N‐oxindole‐3‐acetyl‐N‐aspartic acid, a new IAA catabolite, by liquid chromatography/tandem mass spectrometry

“…This metabolism is attributable to wound-induced increases in anionic and cationic peroxidase activity in the intercellular fluid and at the cut surface of the excised tissues. 13 according to the methods of Lyon and Pratt.14 They were picked as green fruits at approximately 80% maturity, 100% being the average time after anthesis for the appearance of red colour in representative fruit still attached to the plant.…”

In vitro Tomato Fruit Cultures Demonstrate a Role for Indole-3-acetic Acid in Regulating Fruit Ripening

“…In addition to changes in the levels of IAA, tomato fruit also changes in its capacity to metabolize IAA during growth and ripening (Catalá et al, 1992(Catalá et al, , 1994Riov and Bangerth, 1992;Slovin and Cohen, 1993). Thus, the fruit is undergoing significant changes in both steady-state levels of IAA and in the metabolic processes that regulate the conjugation and degradation of IAA.…”

“…Unfortunately, the dangers of extrapolating from results obtained with wounded and rapidly repairing tissue to what is occurring in a bulky fruit in a maintenance phase as it moves toward ripening and senescence, have been only occasionally noted (Brady, 1987;Gouble and Soudain, 1993). The use of tissue discs have some advantages over whole fruit in terms of reduction of entry problems and tissue volume, but problems result from IAA oxidation at the cut surface (Castillo, 1986;Catalá et al, 1994) and a variety of wound effects including wound ethylene formation (Campbell et al, 1990;Catalá et al, 1992;Gouble and Soudain, 1993). In addition, tissue discs only undergo a limited program similar to the early events of the ripening period, show inconsistent effects upon treatment with physiological levels of IAA (Yunovitz and Gross, 1994), and show an altered pattern of ethylene evolution (Campbell et al, 1990;Gouble and Soudain, 1993).…”

“…Extension of such labeling techniques to fruit tissue presented significant problems. For example, wounded tissue has high peroxidative activity, which is known to degrade IAA (Kokkinakis and Brooks, 1979;Catalá et al, 1994). Thus, when using tissue sections, Yunovitz and Gross (1994) found no consistent effects of IAA until applications reached a level estimated to be 5000 fold the endogenous level (Buta and Spaulding, 1994).…”