charge ( 12). This is contrasted with quiescence which is caused by external factors, e.g. anoxia, water drought. Without the onset and maintenance of dormancy there is the continued development of the embryo, otherwise referred to as 'vivipary' or 'preharvest sprouting.' Our current understanding of the onset of dormancy in maize seed is principally based on the characterization of several independent genes which control vivipary (7)(8)(9)(10)(11)13 possible temperature-dependent effects with material that was pollinated over a several-day period. At the appropriate DAP4, the husk leaves were cut and pulled back to expose the developing seeds. After the remaining silks were removed, solutions were sprayed or painted on the seeds. Fluridone (1-methyl-3-phenyl-5-[3-trifluoromethyl)phenyl]-4-( IH)-pyridinone) was applied in 1% (v,v) acetone-water. ABA was applied as a I mm aqueous solution. The husk leaves were gently refolded over the seeds, and the ear was rebagged, dated, and labeled. In all experiments reported here, the seeds were allowed to fully mature in the field until the stems and leaves had died, or at about 45 to 50 DAP.From five to ten ears were used for each treatment date. Ears which were damaged by insects or diseases were not used. After harvesting the ears, the seeds were removed from the ear and seeds separated from viviparous ones. Figure I shows the typical range of response seen with fluridone-treated seeds. RESULTSFluridone and other pyridinone, and pyridazinone, compounds, are known to inhibit the desaturation reactions converting phytoene to phytofluene in algae and in higher plants (1,6). Seeds treated with fluridone at 5 to 7 DAP appeared white at maturity whereas those seeds treated later in relation to the pollination date appeared increasingly yellow (Fig. 1)

No abstract

Membranes isolated from abscission zones of Phaseolus vulgaris L., cv. Red Kidney, contained cellulase activity. This particulate activity was enhanced 10-to 20-fold by treatment with Triton X-100. Sucrose density gradient analyses of cell fractions showed that the membranes with which celiulase was associated had a peak equilibrium density of 1.16 to 1.17 g/ cm3 which coincided with that of ion-activated ATPase, a marker for plasma membranes. The membrane fraction having the highest cellulase activity also contained a high proportion of plasma membranes as shown by electron microscopy of sucrose density gradient fractions after staining by periodic acid-chromic acid-phosphotungstic acid. It was concluded that the particulate celiulase was associated with the plasma membrane.Abscission zones from kidney bean seedlings contained cellulase which existed in two forms (9,14). An intracellular form with a p13 of 4.5 was present at all times, and an extracellular form with a pl of 9.5 increased during abscission or after treatment with ethylene (10). The 4.5-pI form was buffer-soluble whereas the 9.5-pI form was extracted from cell walls by high salt. The 9.5-pl form hydrolyzed cellulose (9) and appeared to cause breakdown of cell walls during abscission.The relationship between the forms of cellulase and their function during abscission is not known. One possibility is that the 4.5-pI form is transported out of the cell to give rise to the 9.5-pI form which functions in cell wall breakdown. As a first step to testing this hypothesis, we have determined that cellulase is associated with cell membranes and identified the membrane system with which it is associated. The results show that from 5 to 10% of the total cellulase activity in the tissue was associated with the plasma membrane whereas no significant activity was found in other membranes. MATERIALS AND METHODSPlant Material and Cell Fractionation. Seeds of Phaseolus vulgaris L., cv. Red Kidney, were germinated in a mixture of vermiculite and pea gravel (3:1) and grown for 10 to 12 days at 24 C and a light intensity of 2,000 ft-c. One-cm sections of petiole including the laminar abscission zone were excised into a chilled beaker and homogenized at a ratio of 3 ml buffer/I g fresh weight of tissue in a polytron (Brinkmann Instruments) at 2 C for 45 sec at a setting of 5. The homogenization buffer contained 20 mm tris-MES, pH 7.2, 0.3 M sucrose, 3 mM EDTA, and 0.1 % BSA. The homogenate was squeezed through a 50-,um mesh nylon cloth, and cell fractions were collected by centrifugation at 2,000g for 10 min and 13,000g for 15 min at 2 C. These pellets were washed by suspending in homogenization buffer and centrifuging at the original forces. An additional cell fraction was obtained by centrifuging the 13,000g supernatant at 80,000g for 45 min onto a cushion of 55% (w/w) sucrose.This fraction was washed by suspending in homogenization buffer without sucrose and pelleting again onto a sucrose cushion.Sucrose Density Gradients. Linear sucrose density gradients we...

Gibberellic acid added to isolated barley aleurone layers enhances orthophosphate incorporation into chloroform-methanol-soluble compounds. The effect is measurable at 4 to 6 hours after the addition of gibberellic acid and reaches a maximum after 8 to 12 hours. The increase in the rate of orthophosphate incorporation is 3-to 5-fold over the rate in control layers incubated without gibberellic acid.The gibberellic acid enhancement of the rate of phospholipid labeling is inhibited within 1 to 2 hours by cycloheximide, 6-methylpurine, and abscisic acid.The increase in labeling of phospholipids occurs throughout the subcellular fractions rather than being restricted to a specific fraction or organelle. The increase in radioactivity in phospholipids as shown by thin layer chromatography is due to a proportional increase in all phospholipids.The enhancement by gibberellic acid of the rate of phospholipid labeling may be required for the subsequent production of gibberellic acid-induced hydrolases.The seeds of the Gramineae consist of an embryo and an endosperm; the endosperm is composed of an inner starchy material surrounded by a layer of aleurone cells one to five cells thick. In barley, gibberellin-like substances secreted by the embryo during germination cause liquification of the endosperm (22, 30). Aleurone layers, whether as part of intact, embryoless half-seeds or isolated from the endosperm, will respond to added gibberellic acid by synthesizing and secreting several hydrolytic enzymes (3,5,22,29,30). Thus, the mobilization of reserves in the endosperm is under control of the germinating embryo via gibberellins (21,24,31).There is an 8-to 10-hr lag period (5) between the addition of GA to aleurone layers and the initiation of de novo synthesis of a-amylase (11) and protease (13) events occurring during this lag period will aid in the understanding of the effects of GA on the aleurone layer and the processes required for the ultimate synthesis of GA-induced hydrolases.During the lag period preceeding a-amylase synthesis there are several events controlled by GA which are directly related to protein synthesis. Jones (16) observed an increase in the amount of rough ER3 in electron micrographs of aleurone layers treated with GA for 10 hr. Evins and Varner (9) showed an increased incorporation of choline in vivo into a semipurified microsomal pellet starting after 4 hr of GA treatment.Two enzymes, phosphorylcholine-cytidyl transferase and phosphorylcholine-glyceride transferase, of the CDP-choline pathway for lecithin synthesis show increased activity within 2 hr of the addition of GA, reaching a maximum after 12 hr of GA treatment (14). Finally, enhanced polyribosome formation and an increase in the total number of ribosomes were observed after 4 to 5 hr and reached a maximum within 10 to 15 hr of GA treatment (8).Preliminary experiments showed that GA also enhanced the incorporation of 'Pi into chloroform-methanol-soluble components of aleurone layers. Phosphate is a general label for all phospholipids ...

Several parts of the 12-d-old seedling of Phaseolus vulgaris L. cv. Red Kidney were surveyed for cellulase activity. The laminar abscission zone and the cotyledon were highest in total cellulase while the petiole, stem, leaf and root had lesser activity. A portion of the cellulase from each tissue was associated with a membrane fraction which equilibrated on a sucrose density gradient at a density of 1.16 g/cm(3). Fortification of the buffer with 1 M NaCl was necessary for complete extraction of cellulase from all tissues. Ethylene treatment enhanced cellulase activity in the laminar abscission zone, the petiolar pulvinus, and somewhat in the stem, but not in the petiole nor the nodal region of the stem. Thus, those tissues which are target tissues for ethylene action also showed ethylene-enhanced cellulase activity.