Indoleacetic Acid and the Synthesis of Glucanases and Pectic Enzymes

ABSTRACESuspension cultures of carrot (DaIcus carrota L.) which had an absolute requirement for exogenously supplied auxin were grown in medium containing indoleacetic acid (IAA) as the sole auxin source. Putative cell surface proteins were extracted from the intact cells. Resup-ply of IAA to cultures partially depleted of auxin resulted in rapidly increased activities of three enzyme activities subsequently extracted. Two of the enzyme activities which increased, peroxidase and pectinesterase, have been implicated in the literature as important to cell wail development, stucture, and growth. The other enzyme activity which was increased, IAA oxidase, may be involved in the degradation of IAA In rivo. Polypeptides in the extracts were found to increase equaly as rapidly as the enzymes in response to IAA as determined with sodium dodecyl sulfate-polyacrylamide electrophoretic gels stained with silver. It is not known whether the changes in enzyme and polypeptide levels in the protein extracts were due to auxin effects on protein synthesis, transport, or extractability.The effects of auxin on cell enlargement and tissue elongation have been the most extensively studied actions of this plant growth substance. It is clear that cell wall growth and extension are the events which limit and allow this enlargement and elongation. While cell wall acidification appears to be very important in the early stages of rapid auxin-induced growth (13), there is increasing evidence that DNA transcription and mRNA translation may play equally important roles in auxin induced growth (10,12,25,29

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confidence: 99%

Rapid Effects of IAA on Cell Surface Proteins from Intact Carrot Suspension Culture Cells

O'Neill¹,

Scott²

1987

“…But gation in decapitated, etiolated pea epicotyls when the apex was replaced with auxin in lanolin (5). They concluded that the enzymes needed for cell elongation were transcribed from a stable messenger present in the cells (4). Clearly this is not the case in excised or intact soybean tissues, and in most other tissues which have been studied (17,24).…”

Section: Discussionmentioning

confidence: 99%

Hormonal Regulation of Cell Elongation in the Hypocotyl of Rootless Soybean: An Evaluation of the Role of DNA Synthesis

Holm

Key

1969

Abstract. A method was developed where soybean seedlings were grown without roots to study the influence of hormones of root origin on shoot growth. Excision of the root resulted in inhibition of apical section growth and DNA synthesis and inhibited elongating section growth. A synthetic cytokinin restored DNA synthesis in the apical seotion, but did not influence growth in either the apical or elongating sections. Low concentrations of gibberellin with the cytokinin restored growth in the apical section. Gibberellin alone was sufficient to restore grow-th in the elongating section.An inhibitor of DNA synthesis, 5-fluorodeoxyuridine, inhibited the increase in apical section DNA without inhibiting control or gibberellin-induced growth in the elongating section. Experiments with 14C-thymidine resulted in no DNA labeling differences in the elongating section under conditions where gibberellin-induced elongation varied from 50 % to 73 % above controls. It was concluded that gibberellin-induced elongation in soybean hypocotyl occurred in the absence of DNA synthesis. Gibberellin does stimulate DNA synthesis in the apical tissue apart from its effect on cell elongation.Excised soybean hypocotyl elongated maximally at 10-8 M auxin. At higher auxin concentrations, fresh weight and ethylene production increased, but elongation was reduced. Addition of GA to the higher auxin concentations resulted in a 50 % inhibition in auxin-induced ethylene production and resumption in maximal elongation. Added ethylene inhibited elongation 30% at 2 A/l. Addition of up to 100 ll/ ethylene did not inhibit elongation with GA present in the incubation medium. Thus GA may counteract ethylene inhibition of cell elongation in addition to inhibiting othylene production in auxin-treated tissues.Thirty years ago Went (31) proposed the existence of-hormones produced by the roots that were necessary for stem growth. Chibnall (2), studying protein loss in detached leaves, suggested that the root system exerted an influence on leaf protein metabolism. He found that development of adventitious roots on the petioles of detached leaves caused a reduction in the rate of protein breakdown (3). Richmond and Lang (26) discovered a chemical basis -for senescence retardation when they showed that kinetin delayed yellowing of detached Xanthium

“…These findings suggest the possible role of pectolytic enzymes in the dissolution of the middle lamella during abscission. Studies on the role of pectinesterase (6,9,11,(18)(19)(20)(21) 25) and polygalacturonase (1,2,5,10,(17)(18)(19)22) The present paper reexamines the role of PG in the abscission of leaves of Phaseolus using recent techniques (16,22) for extracting the enzyme and measuring activity. The results show that PG is localized in the abscission zone, although changes in enzyme activity were not found to accompany abscission.…”

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confidence: 99%

Role of Polygalacturonase in Bean Leaf Abscission

Berger

Reid²

1979

The role of polygalacturonase in leaf abscission was studied in explants of Phaseols vudgaris L. cv. Red Kidley. Bean polygalacturonase was partiafly characterized and comparisons were made between the bean enzyme and previously reported higher plant polygalacturonases. Polygalacturonase isolated from bean leaf abscission zones has a pH optimum between 4.5 and 5.0 and hydrolyzed polygalacturonides in an exo-fashion.Activity was found to be higher with a deesterified substrate than with an esterifled pectin. No correlation between polygalacturonase activity and abscission was observed. Activity remained virtuafly constant over the course of abscission in explants aged either in air or in ethylene. The enzyme was primarily localized in the abscission zone, however, indicating a possible involvement in the abscission process. A theoretical model which could explain the relationship between polygalacturonase and bean leaf abscission is discussed.An increase in soluble pectins of the middle lamella in abscising tissue has been reported in several studies (3,10,(23)(24)(25). These findings suggest the possible role of pectolytic enzymes in the dissolution of the middle lamella during abscission. Studies on the role of pectinesterase (6,9,11,(18)(19)(20)(21) 25) and polygalacturonase (1,2,5,10,(17)(18)(19)22) The present paper reexamines the role of PG in the abscission of leaves of Phaseolus using recent techniques (16,22) for extracting the enzyme and measuring activity. The results show that PG is localized in the abscission zone, although changes in enzyme activity were not found to accompany abscission. MATERIALS AND METHODSPlant Material and Treatments. Seeds of Phaseolus vulgaris L. cv. Red Kidney were sown in flats of Vermiculite. The flats were kept in growth chambers programed for a 16-h photoperiod at 1,000 ft-c with a 28 C day temperature and a 26 C night temperature. The flats were watered every other day or when surface Vermiculite became dry. Seedlings were harvested when the primary leaves were fully expanded, usually 9 to 10 days after sowing. The cotyledons, leaf blades, and shoot apex were excised and the explants were placed in beakers filled with distilled H20. The beakers were left to sit either in air or in a desiccator injected with 50,u/ll ethylene.Extraction of Enzyme. Abscission zones were sliced from explants so that equal lengths of pulvinus and petiole surrounded the separation layer, making a total segment length of approximately 4 mm. In certain experiments which were conducted to determine enzyme localization, sections of petiole were used in place of abscission zones. For each replication of an experiment, 60 zones were weighed and ground in mortar and pestle with sea sand and 10 ml of 50 mm Na-phosphate buffer (pH 7.5) containing 6% (w/v) ammonium sulfate. Subsequent steps were carried out in an ice bath or under refrigeration using a modification of the method described by Riov (22).In the modified procedure, the ground homogenate was stirred for 30 min and filtered through f...