Massive Synthesis of Ribonucleic Acid and Cellulase in the Pea Epicotyl in Response to Indoleacetic Acid, With and Without Concurrent Cell Division

Abstract

Summiary. AMeasurements were made over a 4-day period of the effect of added indoleacetic acid (IAA), puromycin, actinomycin D and 5-fluorodeoxyuridine (1dt-(lR on growth and the levels of total DNA, RNA, protein and cellulase in seg-ments of tIisVue at the apex of decapitated etiolated epicotyls of Pis1luml satizvumnt, L. var. Alaska.The hormone induced swelling of parenchyma cells and cell division. By 3 days after IAA application, the amounts of DNA and protein w-ere approximately double, RN A\ triple and cellulase 12 to 16 times the levels in controls. All of these changes wvere prevented by both puromycin and actinomycin D. FUdR prevented DN'A svnthesi.s and cell division but not swelling or synthesis of RNA, protein and cellulase.It is concluded that IAA-induced RNA synthesis is requiired for cellulase s.ynthie& and lateral cell expansion, whether or not cell division takes place.'heA high concentratiolns of ilndoleacetic acid (IAA.) in lanolin paste are applied to the decapitated apex of etiolated pea epicotyls, in the first 10 mm of tissue beloxv the apex ther-e is a markedl increase in anmounlt anid specific activity of the enzyme cellulase (,f-1.4 glucan 4-glucainohldr-olase, EC 3.2.1.4.) (3).The increase can be inhibited by including in the lanolin any of a numiber of substances which interfere wvith protein sy-nthesis. Accordinlgly, it appears that IAA selectively bring-s into operatioln the coding systei ( s ) needed for exvenitual biosynthesis of cellulase.'T'lheoretically-, a hormonie could r-egulate the synthesis of a specific enzymlle by direct interaction with macronmolecuiles wvhich are important in the processes of iniformation transcription (2)

Indoleacetic Acid and the Synthesis of Glucanases and Pectic Enzymes

“…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.…”

“…There was no sig- Tajble IV gho-ws effects of 5-fluorodeoxyuridine (FUdR) on the increases due to IAA in total protein and pectinaise 'levels. T'his inhibitor completely prevents cell division in the segment (9) fig 1, taCble III); responses of the other enzymes studied here do not.…”

“…In the pea epicotyl segment, high levels of cellulase activity were located bound firmly to those subcelltular fractions containing polyribosomes plus membranes (20) and those containing wal(l material (10). Afte,r IAA treatment, lacunae can be seen to deveilop in the segment as a result of the disintegration and dissolution of primary wallis (9) and middle lamellae (27) This enzyme may 'have functioned in differentiation rather than growth of those cell wall's (e.g., sieve plates) w1hich were particularly rich in /3-1,3-glucan.…”

“…Pectinase synthesis conitintued in untreated segments for about 2 days and the effect of hormone was merely to maintain this rate ( (9,20) and these would be expected to increase the rate of synthesis of any protein for which the appropriate coding information was transcribed and available for translation.…”

“…The hormone causes lateral cell expansion, cell division, disintegration of the walll!s o)f swoLllen cells, lacunae formation, and root generation (9,27).…”