Precursor Of Indole-3-acetic Acid Research Articles

Role of Indole-3-Acetic Acid in Sprouting of Subterranean buds in Winter Initiated Sugarcane Ratoon

Sprouting of subterranean/stubble buds was studied in relation to indole-3-acetic acid (IAA) metabolism in two sugarcane varieties, CoLk 8102 (mid-late maturing) and CoS 88230 (early maturing) during different dates of harvesting in winter season (Nov. to Feb.) during the crop season 1997–98. Sprouting of stubble buds was significantly lesser in December and January than November and February initiated ratoon. Variety CoLk 8102 showed significantly higher bud sprouting per clump than CoS 88230. The sub-optimal temperature prevailing during the month of December and January seems to have more inhibitory effect on bud sprouting in variety CoS 88230. Tryptophan (a precursor of IAA) pool in the stubble buds was more in variety CoLk 8102 than CoS 88230. The tryptophan content in buds was positively correlated with concentration of zinc (essential for IAA synthesis). Specific activities of IAA oxidase and peroxidase were significantly higher in variety CoS 88230, which might have reduced IAA level as observed by relatively lower tryptophan and Zn contents in the stubble buds, thus indicating involvement of IAA in stubble bud sprouting of sugarcane at low temperature.

Indole-3-acetic acid metabolism in Lemna gibba undergoes dynamic changes in response to growth temperature.

Auxin is the mobile signal controlling the rate of growth and specific aspects of the development of plants. It has been known for over a century that auxins act as the messenger linking plant development to specific environmental changes. An often overlooked aspect of how this is accomplished is the effect of the environment on metabolism of the major plant auxin, indole-3-acetic acid (IAA). We have studied the metabolism of IAA in relation to one environmental variable, growth temperature. The model system used was an inbred line of the aquatic monocot Lemna gibba G-3, 3F7-11 grown at temperatures ranging from 5 degrees C to 35 degrees C. IAA levels, the rate of IAA turnover, and the patterns of label incorporation from IAA precursors were measured using stable isotope-mass spectrometric techniques and were evaluated relative to growth at the experimental temperatures. IAA levels exhibited unusually high variability in plants grown at 15 degrees C and 20 degrees C. Turnover rates were quite rapid throughout the range of experimental temperatures except at 25 degrees C, where IAA turnover was notably slower. These results suggest that a transition occurred over these temperatures for some aspect of IAA metabolism. Analysis of [(15)N]anthranilate and [(2)H(5)]tryptophan (Trp) incorporation into IAA showed that Trp-dependent biosynthesis predominated at 15 degrees C; however, Trp-independent biosynthesis of IAA was the major route to IAA at 30 degrees C. The effects of growth temperature on auxin levels have been reported previously, but no prior studies correlated these effects with which pathway becomes the primary one for IAA production.

Evidence for production of the phytohormone indole-3-acetic acid by cyanobacteria.

The ability of cyanobacteria to produce the phytohormone indole-3-acetic acid (IAA) was demonstrated. A colorimetric (Salkowski) screening of 34 free-living and symbiotically competent cyanobacteria, that represent all morphotypes from the unicellular to the highly differentiated, showed that auxin-like compounds were released by about 38% of the free-living as compared to 83% of the symbiotic isolates. The endogenous accumulation and release of IAA were confirmed immunologically (ELISA) using an anti-IAA antibody on 10 of the Salkowski-positive strains, and the chemical authenticity of IAA was further verified by chemical characterization using gas chromatography-mass spectrometry in Nostoc PCC 9229 (isolated from the angiosperm Gunnera) and in Nostoc 268 (free-living). Addition of the putative IAA precursor tryptophan enhanced IAA accumulation in cell extracts and supernatants. As the genome of the symbiotically competent Nostoc PCC 73102 contains homologues of key enzymes of the indole-3-pyruvic acid pathway, a transaminase and indolepyruvate decarboxylase (IpdC), the putative ipdC gene from this cyanobacterium was cloned and used in Southern blot analysis. Out of 11 cyanobacterial strains responding positively in the Salkowski/ELISA test, ipdC homologues were found in 4. A constitutive and possibly tryptophan-dependent production of IAA via the indole-3-pyruvic acid pathway is therefore suggested. The possible role of IAA in cyanobacteria in general and in their interactions with plants is discussed.

Continuous light alters indole-3-acetic acid metabolism in lemna gibba

Turnover is an important parameter of indole-3-acetic acid (IAA) metabolism, and IAA turnover may also be linked to the modulation of auxin-regulated responses. Previous studies have not, however, addressed whether environmental factors, including light, affect the turnover of IAA. We have used a model system consisting of normal Lemna gibba and a line of L. gibba that overproduces IAA precursors (MTR1) to measure IAA turnover in intact plants exposed to constant light, constant light followed by 24 h darkness, and a diurnal (12 h light) cycle. Turnover rates were determined by pulse labeling with [ 13C 6]IAA tracer followed by analysis by GC-MS. Free IAA levels and IAA uptake rates were also determined. These studies showed that IAA uptake in both lines was greater in the light in both light conditions (continuous and diurnal) than in the dark. In the dark, IAA turnover time in both lines was less than 1 h and IAA levels were 4–6 ng\\g fr. wt. Under constant light, IAA levels were higher in MTR1 and turnover time was much longer in the normal line. These studies suggest—based on the difference in response between the MTR1 and the normal line—that IAA turnover is regulated both by the rate of biosynthesis as well as the rate of catabolism.

Production of auxin and other indolic and phenolic compounds by Paenibacillus polymyxa strains isolated from different proximity to plant roots

We determined the actual (no tryptophan, Trp, addition) and potential (Trp 0.1 g l −1 added) production of indolic and phenolic compounds produced in different culture media by Paenibacillus polymyxa strains which had been isolated from different proximity to wheat roots. The production of indole-3-acetic acid (IAA) and related indolic metabolites by all strains tested was greatly enhanced upon Trp addition, suggesting that Trp is important as IAA precursor. A gradual decrease in potential IAA and an increase in potential indole-3-ethanol and indole-3-lactic acid production by strains isolated from non-rhizosphere soil (NRS) over rhizosphere soil (RS) to the rhizoplane (RP) were obtained. The NRS strain showed also a higher (potential) production of oxidized compounds such as indole-3-carboxylic and benzoic acid besides IAA. The determined metabolic differences indicate together with previous results on genetic and physiological parameters of P. polymyxa populations that plant roots select different P. polymyxa subpopulations. Our results suggest that the selected genotypes are differentially adapted to the decreasing oxygen pressure from NRS to RP. Possible effects of the probably microhabitat-specific metabolic profiles of the P. polymyxa isolates for plant growth are discussed.

In vitroでのブドウ'デラウェア'子房の生長におけるジベレリンとオーキシンの共働作用

The correlative effect of gibberellin A3 (GA3) and indole-3-acetic acid (IAA) on the development of 'Delaware' grape ovary was examined in vitro. GA3 induced a significant increase of the ovary fresh weight, proportionate to its concentration; IAA and tryptophan (Trp), a precursor of IAA, had little effect on increasing in fresh weight of the ovary. GA3 + IAA increased the ovary fresh weight more than GA3 or IAA alone. The fresh weights of the GA3 or IAA treated ovaries increased 1.08- to 1.56-fold over the control, whereas those treated with the combination of GA3 and IAA increased 1.85- to 2-fold over control after a 9-10 week-culture. The effect of GA3+ Trp on increasing in fresh weight of the ovary was about the same as that of GA3+IAA. These results indicate that GA3 promotes the ovary development more than IAA and that IAA and Trp enlarge the promotive effect of GA3.The ovary development in response to GA3 and GA3 + Trp was partly inhibited by anti-auxins such as N-(1-naphthyl) phthalamic acid (NPA), 2, 3, 5-triiodobenzoic acid (TIBA). Besides inducing an increase of the ovary fresh weight, GA3 increased the content of IAA-like substances in the ovary. From these results, it appears that the effect of GA3 on the ovary development is ascribed not only to its original action, but also to the synergistic action with IAA synthesized de novo.

Assimilation of exogenous 2′-14C-indole-3-acetic acid and 3′-14C-tryptophan exposed to the roots of three wheat varieties

This study was conducted to determine if plants can assimilate indole-3-acetic acid (IAA) from rooting media and if exogenous L-tryptophan (L-TRP) can be assimilated and converted by plants into auxins. The addition of 2′-14C-IAA (3.7 kBq plant-1) to wheat (Triticum aestivum L.) seedlings of three varieties grown in nutrient solution resulted in the uptake (avg.=7.6%) of labelled IAA. Most of the label IAA was recovered in the shoot (avg.=7.2%) with little accumulation in the root (avg.=0.43%). A portion of the assimilated IAA-label in the plant was identified by co-chromatography and UV spectral confirmation as IAA-glycine and IAA-aspartic acid conjugates. Little of the assimilated IAA label was found as free IAA in the wheat plants. These same assimilation patterns were observed when 2′-14C-IAA was added to wheat plants grown in sterile and nonsterile soil. In contrast, the wheat varieties assimilated considerably less (avg.=1.3%) of the added microbial IAA precursor, 3′-14C-L-TRP (3.7 kBq plant-1) and thus much lower amounts of IAA conjugates were detected. Glasshouse soil experiments revealed that 2 out of 3 wheat varieties had increased growth rates and increased yields when L-TRP (10-5 and 10-7M) was added to the root zone. It is surmised that this positive response is a result of microbial auxin production within the rhizosphere upon the addition of the precursor, L-TRP. The amino acid composition of the root exudates plays a critical role in microbial production of auxins in the rhizosphere. This study showed that wheat roots can assimilate IAA from their rooting media, which will supplement the endogenous IAA levels in the shoot tissue and may positively influence plant growth and subsequent yield.

Biosynthesis of indole-3-acetic acid in tomato shoots: Measurement, mass-spectral identification and incorporation of ?2H from ?2H2O into indole-3-acetic acid, d- and l-tryptophan, indole-3-pyruvate and tryptamine

Indole-3-acetic acid (IAA) and its putative precursors, L- and D-tryptophan, indole-3-pyruvate, and tryptamine were isolated from tomato (Lycopersicon esculentum (L.) Mill.) shoots, identified by mass spectrometry, and measured using capillary gas chromatography with an electron capture detector and radioactive internal standards. Average amounts present were 7.9ng · (g FW)(--1) IAA, 5.7ng · (g FW)(--1) indole-3-pyruvate, 132 ng · (g FW)(--1) tryptamine, 103 ng · (g FW)(--1) D-tryptophan, and 2250 ng · (g FW)(--1) L-tryptophan. Indole-3-acetaldoxime was not found; detection limits were less than 1ng · (g FW)(--1). When tomato shoots were incubated for 6, 10 and 21 h in 30% (-2)H2O, up to four positions in IAA, L- and D-tryptophan, tryptamine and indole-3-pyruvate became labelled with (-2)H. Compounds became labelled rapidly with 10% of IAA molecules containing (-2)H after 6 h. The percentage of labelled molecules of IAA and L-tryptophan increased up to 10 h but then decreased again, correlating with an increase in the total shoot tryptophan and presumably a result of protein hydrolysis in the excised, slowly senescing tissue. The amount of (-2)H in D-tryptophan also showed an increase followed by a decrease, but the proportion of labelled molecules was much less than in L-tryptophan and IAA. Tryptamine became labelled initially at a similar rate to IAA but continued to accumulate (-2)H up to 21 h. We conclude that tryptamine is synthesized from a different pool of tryptophan from that used in IAA synthesis, and is not a major endogenous precursor of IAA in tomato shoots. Indole-3-pyruvate was the most heavily labelled compound after 6 and 10 h incubation (21-h data not available). Furthermore, the proportion of (-2)H-labelled indole-3-pyruvate molecules was quantitatively consistent with the amount of label in IAA. On the other hand, a quantitative comparison of the IAA turnover rate and the rate of (-2)H incorporation into both L- and D-tryptophan indicates that IAA is not made from the total shoot pool of either L- or D-tryptophan. Instead IAA appears to be synthesized from a restricted pool which is turning over rapidly and which has access to both newly synthesized tryptophan and that from protein hydrolysis.

Effect of the ectomycorrhizal fungus Hebeloma hiemale on adventitious root formation in derooted Pinus halepensis shoot hypocotyls

The effect of the ectomycorrhizal fungus Hebeloma hiemale and of its culture filtrate on in vitro rooting of Pinus halepensis derooted shoot hypocotyls was studied in an attempt to determine if ectomycorrhizal fungi could enhance adventitious root formation in gymnosperms. Pinus halepensis hypocotyls did not root in the absence of hormonal treatment, whereas the rooting percentage was 87.3% in the presence of 5 μM indole-3-acetic acid (IAA). In the presence of tryptophan, which is a precursor of IAA, H. hiemale strongly enhanced rooting of hypocotyls cultivated in the absence of any hormonal treatment. In the presence of 0.1 mM tryptophan, the rooting percentage of the inoculated hypocotyls was 96.6%, whereas it was only 7.6% in the absence of the fungus. Hebeloma hiemale culture filtrate obtained in the absence of tryptophan did not contain IAA and did not stimulate rooting of the hypocotyls. In contrast, a culture filtrate obtained in the presence of tryptophan contained IAA; an ethyl acetate extract from this filtrate allowed 100% rooting. Different fractions were isolated by preparative thin-layer chromatography from the IAA-containing filtrate and studied for their effect on rooting. It was demonstrated that IAA was responsible for the rhizogenic activity of H. hiemale. These results suggest that ectomycorrhizal fungi which rapidly metabolize exogenously supplied tryptophan to IAA could be a suitable tool to enhance in vitro rooting of micropropagated gymnosperms. Key words: ectomycorrhizal fungus, indole-3-acetic acid, rooting, shoot hypocotyl, Hebeloma hiemale, Pinus halepensis.

Concentration and Metabolic Turnover of Indoles in Germinating Kernels of Zea mays L.

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.

La biosynthèse de l'acide indolyl‐3‐acétique en liaison avec le métabolisme du tryptophol et de l'indolyl‐3‐acétaldéhyde chez Rhizobium

AbstractSeveral indolic compounds are formed when tryptophan or tryptamine is metabolized by Rhizobium. Among these are indole‐3‐acetaldehyde (IAAld), tryptophol (Tr‐ol), and indole‐3‐acetic acid (IAA). The metabolic relationship among the three compounds was investigated. The experiments were carried out either in the culture medium of growing Rhizobium cultures or in suspensions of washed bacterial cells. In neither case Tr‐ol would function as a precursor of IAA, but tryptophan‐2‐14G gave rise to the formation of both IAA and Tr‐ol. The ratio of IAA to Tr‐ol depended on the experimental conditions, shaking favoring the formation of IAA. Also IAAld gave rise to the formation of IAA and Tr‐ol when incubated with suspensions of washed cells. The ratio of the two compounds depended on experimental conditions such as pH value and shaking, the latter reducing the formation of Tr‐ol. These results cannot be explained by the assumption of a dismutation mechanism catalyzed by a single enzymatic unit. The operation of two enzyme systems, responsible for the reduction and the oxidation, respectively, of IAAld is suggested and discussed.

The Influence of Plant-Growth Substances and Their Inhibitors On the Host-Parasite Relationships of Aphelenchoides Ritzemabosi in Culture

The multiplication of Aphelenchoides ritzemabosi on lucerne seedlings grown aseptically on nutrient agar medium without 2,4-dichlorophenoxyacetic acid was significantly increased by kinetin, gibberellic acid, indole-3-acetic acid (IAA) and by the IAA precursor tryptophane. The double treatments, gibberellic acid/IAA and gibberellic acid/tryptophane increased multiplication significantly more than gibberellic acid alone. (2-Chloroethyl) trimethylammonium chloride (a gibberellic acid antagonist), 7, azo-indole (IAA inhibitor) and 2-hydroxy-5-nitro-benzyl bromide (tryptophane inhibitor) decreased multiplication, significantly so in the presence of gibberellic acid. The nematodes multiplied fastest when plant growth or cell activity was greatest. It is suggested that the nematodes secrete proteolytic enzymes that release from the plant tissues amino acids such as tryptophane (precursor of IAA) and substances such as gibberellic acid, that stimulate cell activity and growth and provide a favourable nutritional environment for nematode multiplication.