Source Of Indole-3-acetic Acid Research Articles

The Dependence of <i> N</i>-Malonyltryptophan Formation in Plants on Water Deficit (Review)

Drought stress in plants is accompanied by several metabolic changes. One of them is the appearance of N-malonyltryptophan (MT) during leaf wilting of many species, but there is a significant number of plant species in which the appearance of MT did not occur. Plants of some species were able to synthesize also N-acetyltryptophan (AT). Excised tomato leaves incubated with D-amino acids (including D-Trp) transform them into malonyl- and acetyl-derivatives even without water deficit. However, MT which appeared during water deficit has been shown to contain L-Trp. Amino acid—1-amino-cyclopropane-1-carboxylic acid (ACC) is also malonylated during water deficit, but other L-amino acids were not malonylated. N-malonyl transferases specific for Trp and ACC have been found in several plants. The existence of N-malonyltransferase specific to L-Trp and appeared during water deficit in plants forming MT is supposed, but clear experimental proof has not been obtained yet. Plants can transform MT applied exogenously into Trp and further to indole-3-acetic acid (IAA). But no evidence has been appeared up to now that endogenous MT may be a source of IAA. It is unknown till now why it is necessary for plants of many species to malonylate only Trp during water deficit. How MT metabolized in animals and if it affects them is also unknown. The necessity to use molecular-genetic approaches for the elucidation of the physiological significance of MT formation during water deficit is underlined.

English

Indole-3-acetic acid (IAA) is an important plant growth regulator. As the very first endeavor, the study is aimed at extracting and quantifying IAA from seedlings of Bambusa tulda and evaluating its bioactivity. The extraction of IAA was performed in organic solvent followed by sample evaporation and TLC with a mobile phase composed of chloroform, methanol and formic acid (77:22:1 v/v) in isocratic mode. The extract obtained from preparatory TLC was subjected to HPLC with acetic acid and methanol (75:25 v/v) as the mobile phase in isocratic mode at a flow rate of 0.8 ml/min and operation pressure of 54 MPa at 30°C, and detection was monitored at 280 nm. Bioassay of the extracted IAA was carried out in Abelmoschus esculentus seedlings. The similar Rf value (0.412) of the extract during TLC analysis and similar peak of HPLC chromatogram with retention time 28.71 min to that of standard IAA indicated the presence of IAA in B. tulda seedling extract. The extracted IAA was quantified to be 10.28 µg/ml. In bioassay experiment, the extracted IAA significantly enhanced root length, root fresh weight, root dry weight, shoot length, shoot fresh weight, shoot dry weight and significant increase of total chlorophyll and protein in A. esculentus leaves. Therefore, B. tulda seedlings could be a potential source of IAA, and it can be utilized for production of bio-fertilizer at a commercial scale. Key words: Abelmoschus esculentus, Bamboo, High performance liquid chromatography, indole-3 acetic acid.

Subcellular localization of endogenous IAA during poplar leaf rhizogenesis revealed by in situ immunocytochemistry

Poplar 741 [Populus alba × (P. davidiana + P. simonii) × P. tomentosa] leaves were rooted within 8 days when cultured on 1/2 MS medium. The subcellular localization of endogenous indole-3-acetic acid (IAA) in the rhizogenesis was investigated, using an immunocytochemical approach. The results of IAA subcellular localization revealed organelle-specific distribution. Three days after root induction, IAA in vascular cambium cells of the basal region of the petiole was distributed mainly in the plasma membrane, endoplasmic reticulum (ER), and nucleus, with a lesser amount in the cytoplasm. In phloem of the basal region of the petiole, IAA was detected in the plasma membrane and ER of the companion cell and in the plasma membrane of the sieve element. In xylem of the basal region of the petiole, no IAA gold particles were labeled. In mesophyll cells IAA was distributed in the chloroplast starch grains before root induction, and the amount in the chloroplast starch grains increased after 3 days after root induction. This suggests that the plasma membrane and nucleus of cambium cells may be the target sites where IAA performs its physiological activities during poplar leaf rhizogenesis. IAA polar transport from lamina mesophyll to the basal region of the petiole during rhizogenesis is mediated by phloem. The starch grains of mesophyll chloroplasts appeared to accumulate IAA and may be a source of IAA during poplar leaf rhizogenesis. Novel and direct evidence regarding the function of IAA during rhizogenesis is provided in this study.

Auxin from the developing inflorescence is required for the biosynthesis of active gibberellins in barley stems.

Multiple gibberellins (GAs) were quantified in the stems of intact, decapitated, and decapitated auxin-treated barley (Hordeum vulgare) plants. Removal of the developing inflorescence reduced the endogenous levels of indole-3-acetic acid (IAA), GA(1), and GA(3) and increased the level of GA(29) in internodal and nodal tissues below the site of excision. Application of IAA to the excised stump restored GA levels to normal in almost all cases. The conversion of [(14)C]GA(20) to bioactive [(14)C]GA(1) and of [(14)C]GA(5) to bioactive [(14)C]GA(3) was reduced by decapitation, and IAA application was able to restore conversion rates back to the levels found in intact plants. The amount of mRNA for the principal vegetative 3-oxidase (converting GA(20) to GA(1), and GA(5) to GA(3)) was decreased in decapitated plants and restored by IAA application. The results indicate that the inflorescence of barley is a source of IAA that is transported basipetally into the internodes and nodes where bioactive GA(1) and GA(3) are biosynthesized. Thus, IAA is required for normal GA biosynthesis in stems, acting at multiple steps in the latter part of the pathway.

The role of auxin in cell separation in the dehiscence zone of oilseed rape pods

Concentrations of both free and conjugated indole-3-acetic acid (IAA) were studied during development of pod wall, dehiscence zone and seeds of Brassica napus pods. A decrease in auxin content prior to moisture loss in the pods was observed specifically in the dehiscence zone, which was correlated with a tissue specific increase in β-1,4-glucanase activity. Furthermore, treatment of the pods with the auxin mimic 2-methyl-4-chlorophenoxyacetic acid resulted in a delay of 10 d of β-1,4-glucanase activity and concomitant cell separation in the dehiscence zone. This indicates that the activity of hydrolytic enzymes involved in cell separation in the dehiscence zone is regulated by auxin activity. Comparison of parthenocarpic pods with seeded pods pointed to the seeds as the source of IAA. Levels in the dehiscence zone of these pods were low over the entire sampling period, while cell separation in the dehiscence zone was delayed by about 4 d. These results indicate that a low level of auxins in the dehiscence zone is necessary for dehiscence to take place, but other factors may also be important.

Translocation of radiolabeled indole-3-acetic acid and indole-3-acetyl-myo-inositol from kernel to shoot of Zea mays L.

Either 5-[3H]indole-3-acetic acid (IAA) or 5-[3H]indole-3-acetyl-myo-inositol was applied to the endosperm of kernels of dark-grown Zea mays seedlings. The distribution of total radioactivity, radiolabeled indole-3-acetic acid, and radiolabeled ester conjugated indole-3-acetic acid, in the shoots was then determined. Differences were found in the distribution and chemical form of the radiolabeled indole-3-acetic acid in the shoot depending upon whether 5-[3H]indole-3-acetic acid or 5-[3H]indole-3-acetyl-myo-inositol was applied to the endosperm. We demonstrated that indole-3-acetyl-myo-inositol applied to the endosperm provides both free and ester conjugated indole-3-acetic acid to the mesocotyl and coleoptile. Free indole-3-acetic acid applied to the endosperm supplies some of the indole-3-acetic acid in the mesocotyl but essentially no indole-3-acetic acid to the coleoptile or primary leaves. It is concluded that free IAA from the endosperm is not a source of IAA for the coleoptile. Neither radioactive indole-3-acetyl-myo-inositol nor IAA accumulates in the tip of the coleoptile or the mesocotyl node and thus these studies do not explain how the coleoptile tip controls the amount of IAA in the shoot.

The role of free space calcium in the basipetal transport of indole‐3‐acetic acid in sunflower hypocotyls1

Abstract Calcium has been reported to be involved in the basipetal transport of indole‐3‐acetic acid (IAA). It has been suggested that basipetal transport of IAA requires the influx of Ca2+ into the cytoplasm from the cell wall free space and that Ca2+ acts as a second messenger. Experiments were conducted to determine the interaction of free space Ca2+ with the basipetal transport of IAA. Four day old sunflower (Helianthus annus L. cv ‘Russian Mammoth') seedlings grown in 0.20 strength Hoagland's solution were either left intact or excised below the cotyledonary node to remove the meristem, the source of IAA in the shoot. After removal of the node, the plants were treated with or without 500 μM IAA in lanolin paste. After 24 h, 3 mm segments were cut from the hypocotyls and incubated in KCl. Solution Ca2+ concentration, representing free space Ca2+, increased when the source of IAA was removed. Plants which were provided a source of IAA, either endogenously or exogenously, had low levels of free space Ca...

Effect of Deseeding on the Indole-3-acetic Acid Content of Shoots and Roots of Zea mays Seedlings

We wished to determine the effect of endosperm removal on the amounts of free and esterified indole-3-acetic acid (IAA) in young Zea mays seedlings. The increases of IAA derived from endosperm and from biosynthesis, but without correction for catabolic losses, were 0.9 picomole of free IAA per shoot per hour, and 1.1 picomoles per shoot per hour of ester IAA. After deseeding, free IAA in the shoot declines by 40% following kernel removal and total (free + ester) IAA declines at a rate of about 1 picomole per shoot per hour. A slight, but insignificant increase of ester IAA occurs following endosperm removal. In the primary roots, the decreases of free IAA and total (free + ester) IAA are accelerated by seed removal. Thus, the endosperm appears to be a major source of IAA for the shoot and root.

Sources of Free IAA in the Mesocotyl of Etiolated Maize Seedlings

Sources of free indole-3-acetic acid (IAA) for the mesocotyl of intact etiolized maize ((Zea mays L.) seedlings are evaluated. The coleoptile unit, which includes the primary leaves and the coleoptilar node, is the main source of free IAA for the mesocotyl. The seed and the roots are not immediate sources of IAA supply. Dependence of the apical growing region of the mesocotyl on the coleoptile unit as a source of free IAA is almost total. One-half or more of the supply of IAA comes from the coleoptile tip, the rest mainly from the primary leaves. Removal of the coleoptile tip results in inhibition of mesocotyl elongation. The hypothesis that growth of the mesocotyl is regulated by auxin supplied by the coleoptile is supported. Conjugated forms of IAA appear to play little part in regulating the levels of free IAA in the shoot.

Physiological significance of indoleacetic acid and factors determining its level in cotyledons of Lupinus albus during germination and growth

The results demonstrate the profile of the endogenous indole‐3‐acetic acid (IAA) in the cotyledons of Lupinus albus L. (L. termis Forssk.) during germination and seedling growth. The auxin level increases markedly after seed hydration, especially during the time of radicle emergence 24 h after the onset of imbibition. This rise is accompanied by a minimal IAA‐oxidase activity, formation of indoleacetylaspartic acid (IAAsp) and an increase in the endogenous tryptophan and tryptophan‐carboxyl‐14C degradation, though the latter cannot account for the high IAA level detected during early stages of germination. It is believed that cotyledons are a source of IAA to the developing embryonic axis. – The auxin level drops in the cotyledons during seedling growth, 2–18 days after sowing. This is true also for IAAsp and tryptophan‐degrading activity of enzyme extracts. Conversely, endogenous tryptophan is increasingly liberated up to day 14, and IAA‐oxidase activity climbs to a peak detected on day 12, prior to the appearance of senescence in the cotyledons. – The physiological significance of IAA and the factors regulating its level in the cotyledons during germination and growth are discussed.