Jay D. Mann, Henry Hield, Kung-Hing Yung, and Douglas Johnson. Department of Horticultural .... ellinantavonist. Z. Pflanzenphysiol 54: 118-24. (Gihberellin.
Planit Phvsiol. (1966) 41, 1751-1752
Short Communication
Independence of Morphactin and Gibberellin Effects Upon Higher Plants Jay D. Mann, Henry Hield, Kung-Hing Yung, and Douglas Johnson Department of Horticultural Science, University of California, Riverside, California 92502 Received September 26, 1966.
Two fltnorene-9-carboxylic acid derivatives (fig 1, I and II) have recently been shown to be potent growth regulators in higher plants (1), and have been givein the trivial name, morphactins. The structtural similarity between the morphactins and gibberellic acid (fig 1, III) immediately suggested a common site of action. In fact, Ziegler, et al. (4) have claimed that methyl-morphactin (I) is a
competitive inhibitor of the action of gibberellin; they also showed that methyl morphactin did not inhibit biosynthesis of gibberellin by Fusarium oxyformtis. Their data with regard to a competitive relationship between gibberellin and morphactin was obtained only from measturements of pea seedling height. This data can be interpreted in other ways than by asstuming a common receptor site for the 2 compoutnds. 0
X
o °I
I R:Me, X=CI
OH
HO
34CH
COH
CH2
test. Nor did morphactin replace gibberellin in stimulating amvlase biosynthesis. The foregoing data stuggested that the morphactin esters do not directly antagonize gibberellin, at least in the assay used. Ziegler et al. (2) had demonstrated that morphactins do not inhibit gibberellin synthesis by Fusariumiii, bult it was possible that gibberellin synthesis by higher plants may be inhibited by morphactins. If so, then replacem-Int of missing endogenously-made gibberellin with exogenous gibberellin, should completely overcome all morphactin ef fects. Citrus seedlings respond to morphactin sprays in 2 ways. Internode shortening becomes apparent, as well as a loss of dormancy of lateral huds (fig 2). When gibberellin is also sprayed on these seedlings, the internode shortening is completely overcome, but not the loss of lateral btud dormancy (table I). The positive effect of gibberellin in promoting internode elongation suggests that penetration and translocation of gibberellin occtIrred, yet morphactin-induiced loss of buid dormancy was not prevented. Branching, in fact, seemed to be an additive response to both compouinds. Mor-
0
Di
II R: Bu, X H FIG. 1. Structures of 2 morphactinis (I and II) and of gibberellic acid.
WN-hen embryo-free half-seeds of barley are treated with gibberellin, alpha-amylase synthesis and release follows after 15 hours (3). This system thtus provides a simplified bio-assay for measurement of a gibberellin-induced response under conditions where gibberellin synthesis is tunimportant. This assay was performed with 1 ,UM gibberellin, a concentration causing maximal response, since ptublished data (4) indicated that high gibberellin levels did not overcome inhibition by morphactin. Both morphactins (I and II) were tested at concentrations ranging from 0.01 to 100 mM. No antagonism between either morphactin I or II, oIn the one hand, and gibberellic acid, on the other, could be detected in the barley half-seed 175'
FIG. 2. Effect of morphactin (I) upon sweet orange seedlings. Left, check; center, sprayed with 500 ppm of morphactin; right, sprayed with 1000 ppm morphactin. Sprayed on May 29, 1966, photographed on July 14, 1966.
1752
PLANT PHYSIOLOGY
T'able 1. In/croction of MIcthy/ .llorplhactin (I) and Giblbcerchic rcid, With/ K csPc to JcH'it/i/, In/ren,od' Len/th, (an,d Branching, in Sccd/ins0V/J S..('/t Oa'(717i(( Tlhree miionitlh-old sxx-eet orange seedlinigs were sprayed with the id(licated concentrations of morp)haclti:1 al a i:l l)er cllini. MIeasnrcments xvere maIle 16 davs later. All treatmenits xere in triplicate. (Gihberell in rm)
MIorpliactin
0
0
1.7
0 3.7 3.7 0 3.7
0
1.7 3.3
3.3
Av-g Height (cmil) 14.2 15.2
phactin may have interfered with aulx.in-regullated apical dlomilnanice (2). Thuls the actioln of morphactins appeari to be at least partially incdepenidenit of both gibberellin synthesis anid actioni. M\lorphactiln-iniduice(d shorteniing of initerinodes is readily overcome by added gibberellin, buit not the morphactin-iinduiice(d loss of apical (lon iiniance. Combiinations of morphacti n with gibberellini, uised as general foliar sprays, may be tuseful in chemical shapinig of plalnts when increased buishiniess is dlesire(l.
[M orphactins have become popullar research in the short time sinice samples have been ma(le available. Dulring the preparationi of the above manuscript, similar resuilts were reporte(d by Tognonii, et al. (2), an(l vwe were informed that Dr. V. F. \ arner (personal commuinicationi ) also foLunid( nio effect of morplhactinis u1poIn amylase initems
duictionl.]
initernode lenigtlh
Branll'llc-. ;
