The development of glyoxysomes during germination has been studied in isolated peanut (Arachis hypogaea L.) cotyledons and in maize (Zea mays L.) scutella. In peanut cotyledons isocitratase, malate synthetase, and protein associated with the glyoxysomal fraction increase simultaneously from the 3rd to the 8th day of incubation. In scutella of germinating maize seeds the specific activities of isocitratase, malate synthetase, and catalase associated with the glyoxysomes rise until the 4th day of germination and then decline while the total amount of protein present in the fraction stays constant during the first 5 days. If the peanut cotyledons are cultured in 2% glucose, the development of isocitratase and malate synthetase is severely inhibited, but the level of the glyoxysomal protein is not measurably affected.Glyoxysomes are subcellular organelles, present in fat-storing tissues of higher plants, which contain the enzymes necessary for the operation of the glyoxylate cycle. They have been isolated by means of density gradient centrifugation from castor bean, watermelon, and peanut seeds (2, 4). The two key enzymes of the glyoxylate cycle, isocitratase and malate synthetase, which are localized chiefly in the glyoxysomes, undergo striking changes in activity during germination (5, 13). They are present at very low levels in the dry seeds, increase greatly during the first 4 to 5 days of germination, and then decline again. It has been shown that the increase of isocitratase and malate synthetase activity in peanut cotyledons is due to synthesis de novo of the two enzymes (8, 11), but comparatively little is known about the development of the particles themselves (7). It may be that the glyoxysomal particles are assembled at the same time that the glyoxylate cycle enzymes are synthesized. Alternatively, one could thing that newly synthesized enzymes are introduced into preexisting particles. This paper provides some information about the development of glyoxysomes in peanut cotyledons and maize scutella. MATERIALS AND METHODSPeanut seeds (Arachis hypogaea L.) were of the strain Virginia R-56, 1966 crop, maize seeds (Zea mays L.) of the strain

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Abstrae. Evidence for de

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.

Watermelon (Citrullus vulgaris Schrad.) cotyledons were excised from the seed after 24 h of imbibition and incubated for different times (ranging from 1 to 240 min) on filter paper saturated with 0.1 mM BA (benzyladenine) solution. After the incubation in BA the cotyledons were thoroughly rinsed in water and grown for 5 days in darkness on filter paper saturated with distilled water. Continuous presence of BA is not a prerequisite for optimal growth. Several effects of the hormone (stimulation of expansion growth, acceleration of lipid breakdown, enhancement of hydroxypyruvate reductase activity, increase in carotenoid content) are more intensive if the cotyledons are treated with BA for a relatively short time and then grown in water. Maximal effects are observed after a 4 h exposure to BA. A single 1 min exposure is sufficient to elicit measurable effects on growth, hydroxypyruvate reductase and carotenoid content. The sensitivity to very short exposures is considerably different for different hormone effects. Carotenoid content and hydroxypyruvate reductase activity are enhanced much more than expansion growth.