Chloroplast replication and growth in tobacco

SUMMARY AND CONCLUSIONS 1. The greening and the growth of chloroplasts as induced by light has been investigated in leaf discs from etiolated tobacco leaves in sterile culture. 2.On a medium containing salts after Murashige and Skoog plus sucrose, chlorophyll synthesis proceeds very slowly during the first day after the transfer from darkness to light. Thereafter the rate of chlorophyll synthesis increases considerably. The chlorophyll content reaches its maximum after 4-6 days in the light. 3.In whole leaves in sterile culture chlorophyll synthesis progresses in about the same pattern and at the same rate as in leaf discs. 4.When etiolated intact plants were illuminated, chlorophyll synthesis started immediately at a high rate, and continued at a much higher rate than in the isolated leaves and discs. Moreover, in whole plants the chlorophyll content reached a much higher final value. Glucose, fructose, various vitamins, inositol, auxin, kinetin and gibberellin failed to bring the rate of chlorophyll synthesis in leaf discs on the level of that in the whole plant. 5.During the light-induced development of the etiolated tissue on standard medium the number of plastids per cell increases considerably. 6.The number of chloroplasts per cell has also been determined in barley and oats. In these species light-induced greening is not accompanied by plastid replication..