Effect of benzyladenine on the development of plastids and microbodies in excised watermelon cotyledons

Abstract

Excised watermelon (Citrullus vulgaris Schrad.) cotyledons were grown in the dark in the presence of 0.1 mM benzyladenine (BA). Under these conditions reserve breakdown and organelle differentiation progress very slowly. Treatment with BA accelerates, breakdown of reserves and stimulates development of organelles. Electron micrographs of cells from treated cotyledons show a larger number of plastids with a more developed inner membrane system. The levels of plastid pigments and enzymes are increased while starch content is reduced. Glyoxysomal enzyme levels are increased by BA during the first three days of development and their decline is accelerated thereafter. Also the activity of hydroxypyruvate reductase (EC 1.1.1.81.), a peroxisomal enzyme, is increased, but this increase is not followed by a decay phase. In water controls, hydroxypyruvate reductase bands together with glyoxysomal enzymes after equilibrium centrifugation in a sucrose gradient. In treated cotyledons the equilibrium position of glyoxysomal enzymes is uchanged while that of hydroxypyruvate reductase is shifted to a lower density.

Uptake of Benzyladenine by Excised Watermelon Cotyledons

“…Of course the nature of this particulate material is not determined but it is reasonably sure that protein bodies must be its main component. This is clear from electron micrographs of cotyledons at day zero (9). Other indirect evidence suggesting that exogenous BA may become adsorbed to protein bodies is that BA loss at low temperature is considerably increased when measured in cotyledons grown in water for 48 h after excision.…”

“…of BA + derivatives) present in the cotyledons and the magnitude of hormonal responses that are observed four days after uptake. This relationship holds regardless of whether a given level of radioactivity has been reached after a short period of uptake or after a long period of uptake followed by washing.Although the action of exogenous cytokinins on excised plant organs is well documented (6,8,9) much less is known about their absorption. Studies on cytokinin uptake have been done with cultured cells (3) and with moss protonemata (5), but comparatively little work has been done with whole organs from higher plants (2, 10).…”

“…Although the action of exogenous cytokinins on excised plant organs is well documented (6,8,9) much less is known about their absorption. Studies on cytokinin uptake have been done with cultured cells (3) and with moss protonemata (5), but comparatively little work has been done with whole organs from higher plants (2,10).…”

Uptake and Effects of N6-Benzyladenine in Excised Watermelon Cotyledons

“…Sensitivity to the growth regulator is acquired around 2 d after excision. This is a highly critical time in development: the cotyledons begin to turn yellow, owing to carotenoid synthesis, and the development of cell organelles takes off suddenly (7,8). Treatment with BA enhances all developmental phenomena that start at this particular time, but does not anticipate the time of their onset.…”

“…Exogenous cytokinins accelerate development of excised cotyledons (2,4,7,15). We have shown (6) that continuous exposure to BA is not required for maximal effect.…”