Control of Protein and RNA Synthesis by AMO-1618 and other Growth Retardants in Cucumber Cotyledons

Abstract

Cotyledons dissected from 5 day old etiolated seedlings of cucumber were incubated with growth regulators for 21 or 45 hours in light and then fed with leucine- 14 C or uracil- 14 C; chlorophyll, protein and RNA were estimated. 1. AMO-1618 (0.001 M) inhibited growth and chlorophyll synthesis by about 50 %; the effects were completely reversed by KCl (0.025 M) and reduced by benzylaminopurine (BAP, 10 −5 M) or gibberellic acid (GA 3 , 10 −4 M). Other growth retardants, CCC (0.005 M), Phosfon D (10 −4 M) vnd B-Nine (0.01 M) decreased chlorophyll synthesis by about 50% with a little effect on growth 2. In the control cotyledons, incubated in light for 1 day, the level of protein was reduced and that of RNA increased from original 1.12 mg and 93 μg to 1.08 mg and 138 μg per cotyledon basis, respectively; incorporation of leucine- 14 C into protein and uracil- 14 C into RNA was increased, in comparison with the original cotyledons, by about 6 times. 3. KCl stimulated protein synthesis by about 250 per cent in comparison with the water treated control, and slightly reduced RNA sythesis. GA 3 and BAP transiently increased protein and RNA synthesis, respectively. Under the influence of BAP the content of RNA was increased to 206 μg/cotyledon. 4. AMO-1618 (0.001 M), B-Nine (0.01 M) and Phosfon D (10 −4 M) in 1 day tests inhibited leucine incorporation into protein by about 50 %. The retardants reduced a rise in RNA content. AMO-1618 had little effect on uraci- 14 C incorporation into RNA, the other 2 growth retardants inhibited this process. CCC at 0.005 M concentration inhibited RNA synthesis being without effect on protein synthesis; CCC at a higher concentration of 0.01 M or in 2 day lasting experiments also reduced protein synthesis. The effects of growth retardants on RNA synthesis were reduced by BAP and those on protein synthesis by KCl. CCC completely erased the stimulatory effect of GA 3 on protein synthesis. 5. B-Nine intensified leucine and uracil uptake from the incuhational media; the same was true for KCl. It is concluded that plant growth retarding chemicals inhibit chlorophyll synthesis in consequence of inhibition of protein (AMO-1618, B-Nine, Phosfon D) or RNA (CCC, Phosfon D) metabolism in detached cucumber cotyledons. K + -induced growth and chlorophyll synthesis follows the selective stimulation of protein synthesis.