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Seed development in Pisum arvense L. cv. New Zealand Maple has been studied in relation to changes in level of total endogenous cytokinins. Growth of both the whole seed and the embryo is diauxic, having two phases of active growth separated by a lag period. The two maxima in the growth rates of the whole seed and the embryo occur about the 23rd and 31 st days after anthesis. The lag period occurs between days 26 and 28. Cell division is thought to have ceased prior to day 19 and the changes in total cytokinin content in lea seeds after this time are believed to be largely independent of cell division. The three maxima in the cytokinin content per gm. fresh weight of seed and per seed were found to be coincident with the maximum volume of endosperm per seed and the two maxima in the growth rates of the whole seed and the embryo. [ABSTRACT FROM AUTHOR]

The severe chlorosis observed in the lower most leaves of flooded sunflower plants (Helianthus annuus L. cv.Tall Single) may be initiated by a reduction in the import of cytokinins by the shoot from the flooded root system. Experiment indicates that during 12 hours following the release of flooding, plants previously flooded for 72 hours or less recover their ability to exude sap when the root systems are aerated, and the root systems synthesize and export amino-acids to the shoot. Plants flooded for longer periods lose these abilities. The metabolic activity of the root apices declines parallel with the decline in cytokinin concentration in the sap with increase in flooding time up to 72 hours. Flooding for 96 hours drastically reduces all four parameters of root activity. After flooding for this period there was a large increase in the number of blackened and tetrazolium-negative root apices which were in all probability dead. The correlation between the metabolic activity of the root apices and the total cytokinin content of the sap supports the view that root apices may be sites of cytokinin synthesis. [ABSTRACT FROM AUTHOR]