Epicotyl

Saugy, M., Farkas, V., and Maclachlan, G. (1988) Phosphatases and phosphodiesterases interfere with 1,3-b-D-glucan synthase activity in pea epicotyl membrane preparations. EurJ.Biochem. 177 135-138. 

Melan, M. A. and Cosgrove, D. J. (1988) Evidence against the involvement of ionically bound cell wall proteins in pea epicotyl growth. Plant Physiol. 86, 469-474. 

Table I. Effects of auxin treatment on pea epicotyl apices. Apical 5 mm regions of etiolated epicotyls were delineated, seedlings sprayed once at zero time with or without 4.5 mM 2,4-D and marked regions examined after 48 h. Data compiled from refs. 28 and 32...

Table II. Effects of xyloglucan oligosaccharide subunits on auxin-stimulated growth of pea epicotyl segments in vivo and pea endo-1,4-/ -glucanase activity in vitro. Growth of segments in 1 //M 2,4-D was measured after 18 h. Endo-1,4-/J-gIucanase activity was determined viscometrically after 30 min using tamarind xyloglucan as substrate. Data calculated from refs. 50 and 51...

A reduction in cutinase production should result in the PNB-1 mutant being less virulent. The pathogenesis of the two strains were evaluated in a pea stem bioassay developed by Kolattukudy and coworkers in which infection by Fusarium solani results in wound formation within three days on the epicotyl of pea sedlings (15). The virulence of T-8 had previously been shown to be reduced in this assay by the addition of inhibitors of cutinase or by rabbit anticutinase antibodies (15-18), indicating that cutinase played an important role in pathogenesis. When the cutinase-defective mutant was evaluated in the bioassay, the mutant exhibited a 55% reduction (p < 0.05) in virulence compared with the T-8 parental strain and the addition of purified cutinase at 1 mg/ml to the mutant enhanced wound formation to 80% of that of the parent (p > 0.5). These data further support the notion that the mutant was defective in cutinase. 

Gibberellin A3 has been shown to shorten the rest period of certain trees, shrubs, and seeds (5,7,10), and is the only substance known to stimulate elongation of resting epicotyls of tree peony (Paeonia stiffruticosa Haw.) seedlings (I). In the tubers of the potato (Solatium tuberosum L.), the rest period lasts from the time of tuber enlargement to 5 to 17 weeks after harvest, depending upon age,... 

Esterification of the carboxyl group of GA3 resulted in compounds with no biological activity when applied to test systems in which hydrolysis to the free acid could not readily occur (1,2, 23). The butyl Cellosolve ester was as active as the free acid as assayed by the elongation of bean epicotyls or the parthenocarpic growth of tomato ovaries (2). 

The bioassay with dwarf peas is similar. Six to 7 days after the seed was planted the seedlings were about 4 cm. high. The first leaf infolded the growing point at the apex of the plant. The test solution was introduced onto the apical region with a 0.1-ml. pipet. Each treated plant received 0.05 fig. of gibberellic acid in a total volume of 0.01 ml. Five to 7 days after the time of treatment measurements were obtained for the shoot length from the point of seed attachment to the epicotyl. 

Enzyme Source and Hormonal Treatment. Crude buffer-soluble and -insoluble cellulases were extracted from the third intemode (1 cm long, 7-8 days) of etiolated pea epicotyls as described previously (3). Cellu-... 

For hormonal treatments, whole apices of intact epicotyls were sprayed with 0.1% 2,4-dichlorophenoxyacetic acid (2,4-D), or they were decapitated, i.e., the plumule and hook were detached (6), followed by application of 2.5 mg lanolin paste containing a suspension of indole-acetic acid (IAA, 0.5%, w/w) on each cut apex. Control tissue received lanolin paste alone. Both regulators caused massive swelling of the... 

Enzyme Fractionation. Buffer-soluble and -insoluble cellulases from auxin-treated apices of pea epicotyls were extracted in a crude form and purified to homogeneity as previously described (3). For fractionation, a Sephadex G-100 column (1.6 X 100 cm) was prepared and equilibrated with 20mM sodium phosphate, pH 6.2, containing 5% glycerol and 0.03% sodium azide at 2°C. Crude enzyme preparations (1.5 mL) containing... 

Growth inhibition activities Epicotyls of bean seedlings were treated and changes in the geotropic reaction were recorded. 

Table 1. IAA Content of Epicotyls from Control and Ethylene-Treated (24 hr) Etiolated Pea Seedlings...

Portulal (Figure 8) is a novel diterpene containing a perhydroazulene nucleus and was isolated from Portulaca grandi-flora Hook. It inhibits the elongation of Avena coleoptile sections induced by IAA. It also accelerates adventitious root formation of Azukia epicotyl cuttings. 

Control of the synthesis of amylase ntRNA s in barley aleurone cells and the synthesis of cellulase mRNAs in pea epicotyl cells are similar in some respects. The control of cellulase activity in pea epicotyl is the only known example of auxin-induced formation of specific mRNA molecules. The formation of cellulase mRNA was demonstrated by the isolation of poly A + RNA s and in vitro synthesis of cellulase (71) using the protein-synthesizing system of wheat germ (72). The formation of cellulase mRNA precedes the increase in cellulase levels by more than 12 hr. Thus, it appears that the increase in rate of synthesis of translatable cellulase mRNA s in the pea epicotyl (71) and that of -amylase mRNA s in barley aleurone cells (65,... 

From a critical study of the metabolism of poly (A) in auxin-treated pea epicotyl, Verma and Maclachlan (73) showed that discreet classes of poly (A) (presumably part of mRNA s) are differentially associated with free and membrane-bound polysomes. The induction of specific mRNA s, the decline in the rate of synthesis of mRNA s, the polysome content per cell, and the formation of cellulase were all related to the membrane-bound polysomes. Although the rate of in vivo enzyme synthesis is... 

Verma, D. P. S. MacLachlan, G. A. Byrne, H. Ewings, D. Regulation and in vitro translation of messenger ribonucleic acid for cellulase from auxintreated pea epicotyls. 

Fig. 5-17. A plot of specific activities of unsaturated compounds in pea epicotyl elongation against the formation constants (K) of their Cu(I) complexes.

---