Increase In Indole-3-acetic Acid Content Research Articles

Auxin and Cell Wall Invertase Related Signaling during Rice Grain Development

Indole-3-acetic acid (IAA) synthesis is required for grain-fill in maize and appears to be regulated by cell-wall invertase (CWIN) activity. OsYUC12 is one of three IAA biosynthesis genes we previously reported as expressed during early rice grain development, correlating with a large increase in IAA content of the grain. This work aimed to investigate further the role of OsYUC12 and its relationship to CWIN activity and invertase inhibitors (INVINH). The analysis shows a brief peak of OsYUC12 expression early in endosperm development. Meta-analysis of microarray data, confirmed by quantitative expression analysis, revealed that OsYUC12 is coexpressed with OsIAA29, which encodes an unusual AUX/IAA transcription factor previously reported as poorly expressed. Maximum expression of OsYUC12 and OsIAA29 coincided with maximum CWIN activity, but also with a peak in INVINH expression. Unlike ZmYUC1, OsYUC12 expression is not reduced in the rice CWIN mutant, gif1. Several reports have investigated CWIN expression in rice grains but none has reported on expression of INVINH in this species. We show that rice has 54 genes encoding putative invertase/pectin methylesterase inhibitors, seven of which are expressed exclusively during grain development. Our results suggest a more complex relationship between IAA, CWIN, and INVINH than previously proposed.

A large increase in IAA during development of rice grains correlates with the expression of tryptophan aminotransferase OsTAR1 and a grain‐specific YUCCA

The indole-3-acetic acid (IAA) content of developing grains of Oryza sativa subsp. japonica was measured by combined liquid chromatography, tandem mass spectrometry in multiple-reaction-monitoring mode. The increase from 50 ng g(-1) fresh weight to 2.9 µg g(-1) fresh weight from 1 to 14 days after pollination was much larger than that previously reported by enzyme-linked immunoassay methods. The largest increase in IAA content coincided with the start of the major starch deposition phase of grain-fill. The increase in IAA content was strongly correlated with the expression of putative IAA biosynthesis genes, OsYUC9, OsYUC11 and OsTAR1, measured by quantitative reverse transcriptase polymerase chain reaction. These results confirm the importance of the tryptophan aminotransferase/YUCCA pathway in this system. All three genes were expressed in endosperm; expression of OsYUC11 appeared to be confined to endosperm tissue. Phylogenetic analysis indicated that OsYUC11 and AtYUC10 belong to a separate clade of YUCCAs, which do not have orthologues outside the Angiosperms. This clade may have evolved with a specific role in endosperm. Expression of tryptophan decarboxylase in developing rice grains did not correlate with IAA levels, indicating that tryptamine is unlikely to be important for IAA synthesis in this system. In light of these observations, we hypothesize that IAA production in developing rice grains is controlled via expression of OsTAR1, OsYUC9, OsYUC11 and that IAA may be important during starch deposition in addition to its previously suggested role early in grain development.

Auxin polar transport is essential for the development of zygote and embryo in Nicotiana tabacum L. and correlated with ABP1 and PM H+-ATPase activities.

Auxin is an important plant growth regulator, and plays a key role in apical–basal axis formation and embryo differentiation, but the mechanism remains unclear. The level of indole-3-acetic acid (IAA) during zygote and embryo development of Nicotiana tabacum L. is investigated here using the techniques of GC-SIM-MS analysis, immunolocalization, and the GUS activity assay of DR5::GUS transgenic plants. The distribution of ABP1 and PM H+-ATPase was also detected by immunolocalization, and this is the first time that integral information has been obtained about their distribution in the zygote and in embryo development. The results showed an increase in IAA content in ovules and the polar distribution of IAA, ABP1, and PM H+-ATPase in the zygote and embryo, specifically in the top and basal parts of the embryo proper (EP) during proembryo development. For information about the regulation mechanism of auxin, an auxin transport inhibitor TIBA (2,3,5-triiodobenzoic acid) and exogenous IAA were, respectively, added to the medium for the culture of ovules at the zygote and early proembryo stages. Treatment with a suitable IAA concentration promoted zygote division and embryo differentiation, while TIBA treatment obviously suppressed these processes and caused the formation of abnormal embryos. The distribution patterns of IAA, ABP1, and PM H+-ATPase were also disturbed in the abnormal embryos. These results indicate that the polar distribution and transport of IAA begins at the zygote stage, and affects zygote division and embryo differentiation in tobacco. Moreover, ABP1 and PM H+-ATPase may play roles in zygote and embryo development and may also be involved in IAA signalling transduction.

Influence of elevated CO<sub>2</sub> and O<sub>3</sub> on IAA, IAA oxidase and peroxidase in the leaves of ginkgo trees

This study examined the impacts of elevated CO2 or O3 on indole-3-acetic acid (IAA) content, activities of IAA oxidase (IAAO) and peroxidase (POD) in Ginkgo biloba leaves. Plants grown in open-top chambers were exposed to ambient atmosphere (control; C), elevated CO2 and elevated O3 from 1 June to 30 September. An increase in IAA content and decrease in IAAO and POD activities were observed in plants exposed to elevated CO2 compared with C. Elevated O3 had no significant effect on IAA content and IAAO activity, but increased POD activity during the early days. When trees pre-exposed to elevated CO2 were transferred to elevated O3 or C, the increase in IAAO activity resulted in the decrease in IAA content. When trees pre-exposed to elevated O3 were transferred to elevated CO2 or C, IAA content, IAAO and POD activities showed no significant changes. The influence of POD activity on the IAA activity was low.

Effects of elevated CO2 and/or O3 on hormone IAA in needles of Chinese pine

This study examined the effects of season-long exposure of Chinese pine (Pinus tabulaeformis) to elevated carbon dioxide (CO2) and/or ozone (O3) on indole-3-acetic acid (IAA) content, activities of IAA oxidase (IAAO) and peroxidase (POD) in needles. Trees grown in open-top chambers (OTC) were exposed to control (ambient O3, 55 nmol mol−1 + ambient CO2, 350 μmol mol−1, CK), elevated CO2 (ambient O3 + high CO2, 700 μmol mol−1, EC) and elevated O3 (high O3, 80 ± 8 nmol mol−1 + ambient CO2, EO) OTCs from 1 June to 30 September. Plants grown in elevated CO2 OTC had a growth increase of axial shoot and needle length, compared to control, by 20% and 10% respectively, while the growth in elevated O3 OTC was 43% and 7% less respectively, than control. An increase in IAA content and POD activity and decrease in IAAO activity were observed in trees exposed to elevated CO2 concentration compared with control. Elevated O3 decreased IAA content and had no significant effect on IAAO activity, but significantly increased POD activity. When trees pre-exposed to elevated CO2 were transferred to elevated O3 (EC–EO) or trees pre-exposed to elevated O3 were transferred to elevated CO2 (EO–EC), IAA content was lower while IAAO activity was higher than that transferred to CK (EC–CK or EO–CK), the change in IAA content was also related to IAAO activity. The results indicated that IAAO and POD activities in Chinese pine needles may be affected by the changes in the atmospheric environment, resulting in the change of IAA metabolism which in turn may cause changes in Chinese pine’s growth.

Endogenous indole-3-acetic acid and ethylene evolution in tilted Metasequoia glyptostroboides stems in relation to compression-wood formation.

Eight-year-old Metasequoia glyptostroboides seedlings were tilted at a 45 degrees angle to induce compression-wood formation on the lower side of the stems. After 2 weeks of treatment, half of the seedlings were sampled and the remaining half were tilted to the opposite orientation to exchange the upper and lower sides and were kept for 2 more weeks until sampled. Cambium-emitted ethylene was analyzed by gas chromatography with flame-ionization detection. Endogenous indole-3-acetic acid (IAA) was measured by gas chromatography-mass spectrometry. Tracheid production and compression-wood formation were determined by light microscopy. Anatomical studies showed that tracheid production was promoted and compression-wood tracheids always developed on the gravitationally lower side of tilted stems in both the original tilting and the subsequent reverse-tilting periods. These were accompanied by an increase in IAA content in and an accelerated ethylene-evolution rate from the cambial region of the same side.

Changes in the Content of Indole-3-Acetic Acid and Cytokinins in Spruce, Fir and Oak Trees after Herbicide Treatment

Treatment of spruce, fir and oak trees with herbicides, which may be one of the forest damage inducing agents, caused pronounced changes in the contents and distribution of indole-3-acetic acid (IAA) and cytokinins (CKs) one year after treatment, i.e. at the time of the first microscopically visible damage in treated trees. In Picea pungens IAA content increased in the terminal buds by about 105 % and in the apical buds of the first order branches by 220 %. The same was true for young sprouts of Abies nordmanniana, while in leaves of oak trees IAA content was decreased by 15 % after glyphosate treatment and by 30 % after 2,4-dichlorophenoxyacetic acid (2,4-D) treatment. Another striking feature was a significantly decreased content of IAA in the lower parts of roots in Picea pungens (50 % of the control), which is accompanied by an increase in IAA content in the middle part of the roots (130 %). On the other hand, the IAA content of both sprouts and roots of A. nordmanniana was significantly increased after herbicide treatment.In P. pungens, the content of free cytokinins (sum of zeatin, zeatin riboside, isopentenyladenine and isopentenyladenosine) decreased due to herbicide treatment. The strongest decrease was seen in roots, especially in their upper and middle parts (the average reduction of cytokinin content in roots was 63 %). In the above-ground organs the reduction was seen namely for isopentenyladenine and isopentenyladenosine, while the abundance of zeatin riboside was, on the other hand, higher in treated plants. In Quercus robur leaves, the total content of cytokinins also decreased, namely after glyphosate treatment. In consequence of these changes, CK/IAA ratio decreased pronouncedly in all organs of herbicide-treated trees, with the exception of oak leaves treated by 2,4-D.

Physiological analysis of transgenic Arabidopsis thaliana plants expressing one nitrilase isoform in sense or antisense direction

The biosynthesis of IAA in Arabidopsis thaliana can proceed via different pathways, which involve indole-3-acetonitrile (IAN) as an intermediate. The enzyme nitrilase, which converts IAN to the auxin indole-3-acetic acid (IAA), might be a key enzyme in this biosynthetic pathway. To elucidate the role of nitrilase during the development of the plant, we have investigated transgenic Arabidopsis plants, carrying one of the four nitrilase isoforms so far identified in Arabidopsis in either sense or antisense direction. The plants have been analyzed for their phenotype, auxin content, nitrilase transcript and protein amounts, and nitrilase activity. Analysis of free IAA content in seedlings did not reveal any prominent differences between the different lines, whereas the total IAA content was slightly increased in the line overexpressing NIT2 (sNIT2). In two of the antisense lines (aNIT1 and aNIT2) the total auxin content was about 75% lower than in the wild type, while IAN was increased in these two antisense lines by about 2-fold. In sNIT2 plants the IAN content was slightly decreased compared with the wild type. When IAN was added to the medium, a strong increase in IAA content was found in sNIT2 seedlings (ca. 22-fold), which was much lower in wild type and antisense plants. In mature plants levels of free IAA were decreased by about 25% and 50% in the antisense lines aNIT2 and aNIT1, respectively, whereas the IAA content in the other lines did not differ much. sNIT2/aNIT2 plants were further characterized because it was shown by Northern and Western analysis as well as enzyme activity measurements that sNIT2 plants overexpress nitrilase constitutively. The results with these plants have shown that i) both nitrilase 1 and nitrilase 2 accept the same substrates, and ii) overexpression of nitrilase does not lead to a visible phenotype because in vivo IAN might be the limiting factor in these plants. Application of IAN leads to an increase in total nitrilase protein as shown by Western blotting. Using transgenic lines with promoter-GUS fusions for each NIT gene, it was shown that i) NIT1 is highly expressed in seedlings and ii) NIT2 is strongly induced (21-fold) after IAN application.

Glyphosate‐increased levels of indole‐3‐acetic acid in yellow nutsedge leaves correlate with gentisic acid levels

The effects of glyphosate [N‐(phosphonomethyl)glycine] on endogenous in‐dole‐3‐acetic acid (IAA) level, IAA oxidase activity, and possible interactions with alterations in phenolic metabolism have been examined in yellow nutsedge (Cyperus esculentus L.) plants. IAA was quantified by flame ionization detector gas‐chroma‐tography, phenols were quantified by high‐performance liquid chromatography and the auxin protection and the IAA oxidase activities were determined spectrophoto‐metrically and/or polarographically. A significant increase in IAA content was recorded after glyphosate treatment. No IAA oxidase activity was detected in control and treated tissues. Auxin protection activity and gentisic acid were present in all extracts assayed, and their concentrations increased as the rate of glyphosate application increased. Addition of gentisic acid to an extract of control plants increased the auxin protection detected. These findings indicate that the high levels of free IAA in yellow nutsedge leaves after glyphosate application are due to the inhibition of the IAA oxidase activity by increased levels of the IAA‐protecting phenol gentisic acid.