Chlorophyll accumulation and protein synthesis in lettuce cotyledons treated with growth retardants, gibberellin, and benzylaminopurine

Abstract

Effect of four growth retardants: AMO-1618 1 ) (5 × 10 −4 M), B-Nine (5 × 10 −3 M), Phosfon D (5 × 10 −5 M) and CCC (5 × 10 −3 M), applied alone or in combination with GA 3 (10 −5 M) or BAP (5 × 10 −6 M), on growth, chlorophyll and protein synthesis in the cotyledons of 2- and 5-day old lettuce seedlings was studied. 1. Inhibitory effects of the growth retardants on radicle, hypocotyl and cotyledon growth were reduced by GA 3 which per se markedly stimulated cotyledon and hypocotyl growth. BAP severely inhibited radicle growth and did not potentiate the growth inhibitory effects of the retardants. 2. CCC decreased chlorophyll content in the cotyledons by about 75 %. Other growth retardants had no effect on greening, but they increased chlorophyll content per unit area or unit fr wt in consequence of inhibition of the cotyledon growth. GA 3 inhibited chlorophyll synthesis, especially in shorter 2 day lasting tests; the effect was not reduced by growth retardants. BAP slightly (25 %) inhibited chlorophyll synthesis only in prolonged tests, and reduced degree of the CCC dependent inhibition of greening. 3. AMO-1618 slightly reduced 14 C-leucine incorporation into total cotyledon proteins. Other growth retardants inhibited protein synthesis by about 50 %. Initial inhibitory effect of GA 3 on protein synthesis disappeared in longer, 5-day lasting tests. In spite of this fact, gibberellin markedly potentiated the inhibitory effect of AMO-1618, B-Nine and Phosfon D on protein synthesis as measured in 5th day. GA 3 reduced such the effect of CCC. Benzylaminopurine strikingly (2.5–3 fold) enhanced protein synthesis in the cotyledons of 2-day old lettuce seedlings. This effect was potentiated by AMO-1618 and Phosfon D. Cytokinin severely inhibited 14 C-leucine incorporation into polypeptides in 5-day old cotyledons, the effect being reduced by growth retardants. BAP alone and in combination with any of the growth retardant increased the protein content in the cotyledons. 4. All growth retardants inhibited 14 C-leucine uptake in prolonged tests. The effect was completely reversed by BAP and reduced by GA 3 . It is suggested that CCC inhibits synthesis of chloroplast proteins, the effect being responsible for selective arrest of chlorophyll accumulation. Other growth retardants possibly inhibit synthesis of proteins more important for growth processes than for chloroplast differentiation.