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Interaction of Growth-Retarding Compounds and Gibberellin on Indoleacetic Acid Oxidase and Peroxidase of Cucumber Seedlings" 2 Abraham H

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Interaction of Growth-Retarding Compounds and Gibberellin on Indoleacetic Acid Oxidase and Peroxidase of Cucumber Seedlings Interaction of Growth-retarding Compounds and Gibberellin on Indoleacetic Acid Oxidase and Peroxidase of Cucumber Seedlings" 2 Abraham H. Halevy The Hebrew University, Faculty of Agriculture, Rehovot, Israel Several groups of growth-retarding chemicals for each dish and 5 dishes for each treatment. have been reported in recent years. They belong to Dishes were covered immediately after sowing with quite distinct chemical classes, but their effect on several layers of black cloth, and placed at a constant plant growth is similar. These include nicotiniunm temperature of 250. After 94 hours, 10 seedlings compounds (31), quaternary ammonium carbamates were taken at random from each dish, measured, dis- (16), phosphonium compounds (37), choline ana- sected into cotyledons, radicles, and hypocotyl tips logues (42), and succinnamic acid derivatives (39). (upper 0.5 cm) and used for enzyme determinations. Unlike other types of growth inhibitors (e.g. maleic The chemicals used in these experiments were: hydrazide) these compounds retard stem elongation potassium gibberellate (GA), 2-isopropyl-4-dimethyl- without causing malformation of the plant. Their amino-5-methylphenyl-1-piperidinecarboxylate meth- effects on plants are in many aspects opposite to yl chloride (Amo-1618), an isomer of Amo-1618, 3- those of gibberellin (3,42). Most of these inverse isopropyl-4-dimethylamino-6-methylphenyl-1 -piperi- effects of the growth retardants and gibberellins are dine carboxylate methyl chloride (Carvadan) (pro- mutually antagonized when both chemicals are ap- vided by Dr. H. M. Cathey, Plant Industry Station, plied to the same plant (2, 3, 5, 7, 13, 14, 22, 27, 28, Beltsville), 2,4-dichlorobenzyl-tributylphosphonium 41). It was therefore suggested (27,42) that they chloride (Phosfon) (obtained from the Virginia an( be designated antigibberellins. This terminology Carolina Chemical Company), 2-chloroethyl trimeth- has caused controversy. While Lockhart (27) con- ylammonium chloride (CCC) (at gift of the Cyan- cluded that a functional interaction exists between amid International Company), N-dimethylamino suc- gibberellin and the growth retardants, Kuraishi and cinnamic acid (B-995) (obtained from Dr. J. A. Rid- Muir (25) came to the conclusion, that these com- dell, Naugatuck Chemical Div., U.S. Rubber Co.) pounds do not interact directly with gibberellin, but and maleic hydrazide (MH). rather with auxin. Stuart and Cathey (40) also felt Homogenates were made by blending 250 mg of that the growth-retarding chemicals should not be tissue from each organ in 10 ml of ice-chilled 0.1 M called antigibberellins. Our study presents data potassium phosphate, pH 6.1. The homogenates which are pertinent to this discussion. were filtered and immediately processed. Proper We have already shown that a growth-retarding dilutions were obtained using the buffer solution. substance (Amo-1618) increased peroxidase activity Results were calculated on a dry weight basis deter- in cucumber (13) and citrus (32) seedlings. Per- mined on parallel samples. oxidase is generally thought to participate in the Peroxidase determinations were made according IAA-oxidase system (38). We have suggested to McCune (29), using guaiacol as hydrogen donor. (13) that the growth retardants may affect the auxin The formation of tetraguaiacol was followed at 47C level of plant tissues by enhancing auxin destruc- mA in a spectrophotometer (Spectronic 20, Bausch tion. The present study gives support to this hypo- and Lomb). Activity was measured by increase in thesis. optical density (OD) from 60 to 90 seconds. The rate was found to be linear during this time period. Materials and Methods Activity is expressed as A OD in 60 to 90 second period per 1 mg of dry weight. Cucumber seeds (Cucumis sativus L. var Beit The oxidation of IAA was measured at 525 m,u Alpha, Hazera Seed Co., Tel Aviv) were sown in 9 using the Bausch and Lomb Spectronic 20 spectro- cm petri dishes on 2 layers of Whatman No. 2 filter photometer. The Salkowski reagent used was as paper, which had been saturated with water or the modified by Pilet (35). Reaction mixtures were indicated chemical solution. Fifteen seeds were used prepared according to the method of Goldacre et al. (12) and consisted of 10-4 M 2,4-dichlorophenol, 10-4 MnCl9, 2 x 10-4 M IAA and 1 ml of enzyme 3Received April 29, 1963. solution to 10 ml of 0.1 M potassium phosphate pH 2 Contribution from The National and University In- 6.1 added in stitute of Agriculture, Rehovot, Israel. 1963 Series, this order. Optical densities were con- 575-E. verted to ug of residual IAA using a curve prepared 731 732 PLANT PHYSIOLOGY J _ 0t 0 0 N 0 0 --e~ 'l ~- w _ _-- _-4. PEROXIDASE (COT) II 10-i 10 10 1O02 D-5 10-1104 10-3 GIBSERELLIN (M) AMO-1618 (M) FIG. 1. Effects of various concentrations of gibberellin on elongation of hypocotyl and relative peroxidase and IAA-oxidase activity in cotyledons and hypocotyl-tips of cucumber seedlings. Standard errors for each curve are drawn as vertical bars. Peroxidase values for water control of cotyledons and hypocotyl are respectively 102 and 141 A OD in 60 to 90 seconds period/i mg dry weight. IAA-oxidase values for water control of cotyledons and hy- pocotyl are respectively 165 and 189 gg IAA metabolized/mg dry weight hour. Length of hypocotyl in water was 40.5 mm. FIG. 2. Effects of various concentrations of Amo-1618 on elongation of hypocotyl and relative peroxidase and IAA-oxidase activity in cotyledons and hypocotyl-tips of cucumber seedlings. Standard errors for each curve are drawn as vertical bars. Values for water controls are as those stated in legend to figure 1. by plotting the optical densities of standards. Ac- Table I tivity is expressed as the disappearance of Ag IAA/ Effects of Variouis Concentrations of Gibberellic Acid nit mg dry weight hour. Activity of Peroxidase and IAA-Oxidase in Radicles of Cucumber Seedlings Figures in each column followed by the same letter Results are not significantly different. Figure 1 shows the effect of various concentra- Concentration of GA Peroxidase IAA-Oxidase tions of GA on elongation of the hypocotyl and en- (M) (A OD)* ** zymic activity in cotyledons and hypocotyl tips. It Olg) is obvious that an inverse relation exists between 0 92 a 123 a elongation and enzymic activity. The correlation 2.5 x 10-5 97 a 119 a between the effect of GA on hypocotyl growth and 10-4 87 a 90 b 2.5 x 10-4 84 a 75 b its effect on peroxidase and IAA oxidase in this or- 7.5 x 10-4 80 a 82 b = gan was found to be highly significant (r 10-3 83 a 68 b -0.620** and r = -0.735**, respectively). GA also 2.5 x 10-3 84 a 76 b inhibits enzyme activity in the cotyledons, but to a 5 x 10-3 79 a 80 b lesser extent. The reduction is proportional to the * A OD in 60 to 90 second/i mg dry weight. concentration of the reagent (fig 1). GA had no ** ,ug IAA/mg dry weight hour. HALEVY-GROWTH-RETARDING CHEMICALS AND GIBBERELLIN 733 Table II Effects of Gibberellic Acid and Amo-1618 on Growth and Peroxidase Activity in Various Organs of Cucumber Seedlings Figures in each column followed by the same letter are not significantly different. Treatment Average Length (mmn) Peroxidase Activity (A OD)* Hypocotyl Radicle Hypocotyl Radicle Cotyledons H20 39.2 b 50.8 a 130 b 81 b 90 b GA (7 x 10-4M) 62.7 a 48.3 a 71 c 66 b 68 c Amo-1618 (1.5 x 10-3M) 20.1 c 21.0 b 226 a 148 a 130 a GA (7 x 10-4 M) + Amo-1618 (1.5 x 10-8M) 40.3 b 19.9 b 146 b 143 a 85 b * A OD in 60 to 90 second/mg dry weight. significant effect on peroxidase activity of the radi- chemical but to its retardation effect on radicle cles, but inhibited IAA-oxidase activity (table I). growth (fig 3). It should be noted that GA did not stimulate radicle The interaction of GA and Amo-1618 on enzymic growth at this range of concentration (table II, see activity was studied at concentrations nullifying their also ref. 15, table II). inverse effect on hypocotyl length (14), and are The effect of various concentrations of Amo- summarized in tables II and III. 1618 on hypocotyl growth and enzymic activity in The inverse effects of GA and Amo-1618 on the cotyledons and hypocotyl tips is presented in figure activity of both enzymes in hypocotyl and cotyledons 2. Here again high correlation was found between were nullified by each other (tables II and III). the effect of the various concentrations of the chem- With respect to the radicle, a partial interaction be- ical on retardation of hypocatyl growth and its ef- tween GA and Amo-1618 was apparent in their ef- fect on stimulating activity of peroxidase and IAA- fects on IAA-oxidase activity (table III), but peroxi- oxidase in hypocotyl tips (r = -0.635** and r = dase was unaffected (table II). -0.689**, respectively). A similar but lesser effect To test whether the stimulating effect of Amo- was detected on enzymic activity in the cotyledons. 1618 on peroxidase and IAA-oxidase is common to The effect of Amo-1618 on radicle growth and other growth-retarding substances, the comparative enzymic activity is shown in figure 3. Retardation effect of 5 growth-retardants and one growth in- of radicle elongation began at a higher concentration hibitor (maleic hydrazide) on IAA oxidase and than that affecting hypocotyl growth (3 X 10-4 M peroxidase activity was studied (table IV).
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