Pectic Enzymes

Indoleacetic acid (IAA) and/or inhibitors of DNA, RNA or protein synthesis were added to the apex of decapitated seedlings of Pisum sativum L. var. Alaska. At various times up to 4 days, enzymic protein was extraoted from a segment of epicotyl immediately below the apex and assayed for its ability to hydrolyse polysaccharides or their derivatives. With the exception of am;ylase, the total amounts per segment of all of the tested enzymes increased due to IAA treatment. The development of j3-1,4-glucanase (cellulase) activity per unit of protein or fresh weight proceeded according to a typical sigmoid induction curve. Pectinase was formed for about 2 days in control segments and IAA treatment resulted in continued synthesis for at least another 2 days provided cell division took place. 64,3-glucanase and pectinesterase activities were only enhanced by IAA to the extent that total protein levels increased. Reaction mechanisms for these effects and functions for the enzymes during growth are discussed. One aipproach to the problem of elucidating me,chanisms of hormone-regulated morphogenesis is to search for enzyme activities which increase after hormone treatment, choosing for investigation those enzymes which catalyse rea,dtions that could be essential for growth responises. Thi.s paper reports effects of indoleacetic acid ()IAA) on the activities of 4 pollysaccharidases and an esterase in the apical region o,f the epicotyl of decapitated pea seeddings. Enzymes which hydrolyze wall materials were selected becaulse several IAA-dependent changes in morphology oif the pea epicotyl appear to require a remodeling or loosening of primary wail structure. The hormone causes lateral cell expansion, cell division, disintegration of the walll!s o)f swoLllen cells, lacunae formation, and root generation (9, 27). Dtu,ring these events, there is a rapid and massive net synthesis of DNA, RNA and protein and a partitcularly marked increase in specific activity o-f the enzyme celilulase (8, 9). The responses are dramatic and undouibtedly magnified by the high level of IAA employed (albout 10 pg/seed'ling), but they are not qualitatively different from responses in this or other tissues to physiological levels of IAA. Segments which remained attached to the seedling were u,sed in preference to excised sections (cf. 10, 19) because their potential for continued growth anid synthesis was closer to that shown by undisturbed tissue. Changels in cellulase and f-1,3-glucan.ase levels were compa,red, in part because these enzymes occur widely in higher plants (5, 26) and, in part because either or both enzymes could be responsible for the loss or turnover of wall glucan which often accompanies cell enlargement. Glucan catabolism has been noted during incubation o,f sections excised from the pea epicotyl (19) aiid coleoptiles o,f wheat (21), oat (16,25) and maize (17). Paritially purified preparations of these enzymes effec.tively reduce the tenisile strength of dead primary walls (24), enhance the elongation of iliving oat coleop*tile sections (22) and bring about the swelling of root hairs (7). It is not difficult to visualize how celluilase activity in vivo coulld weaken the interwoven microfibrillar structure of primary walls in su'ch a way that wall expansion enisues (8). However, the di,sitri'bution and function,s of amorplhous P-1,3-glucan (e.g., calilose) within parenchyma cell walls i:s not yet understood (6). The development of pectinase and pectinesterase activities was examined because of periodic sulggestions (e.g., 3) that enzymic control over the solubility and rigidity of pedtcate gel's in the priimary wall determines wa-ll ex-tensibiiliity. Duiring growth, the amounts of polygailacturonic acild (19, 25) and the thickness of the middle ilamella (114) have been observed to decrease in some tissues. There are few reports, however, that higher plant tissues other than fruits synthesize pectinase and no evidence t.ha(t IAA affects its activity. On the other hand auxin doeis appear to influence the turnover of methoxyl gro-ups in the wall (15) anid it may affect the binding olf pectinesterafse to wall material (12, but see 3). Amylase activity was also examined in o(rder to contrast ilts responses to those of wall poilysaccharidases. Gibberellic acid controls the synthesis of this enzy-me in b-arley aleurone cell's (4). 735 www.plantphysiol.org on January 22, 2018 Published by Downloaded from Copyright © 1968 American Society of Plant Biologists. All rights reserved.