Sucrose phosphate synthase and acid invertase activities in the mature leaves of roses (Rosa hybrida cv Golden Times) were greater in plants grown under a higher night temperature than under a lower temperature regime. In young shoots, the activity of acid invertase was promoted by the lower temperature while that of sucrose synthase was increased at the higher temperature. At both temperatures benzyladenine when applied to the axillary bud stimulated sucrose phosphate synthase activity and advancement of its peak of activity in the leaf subtending to the bud, and also stimulated sucrose synthase activity in the young shoot. At the lower temperature, application of benzyladenine to the axillary bud stimulated acid invertase activity in the young shoot but not in the leaves.Flower bud atrophy in rose plants is promoted by a decline in solar radiation and a drop in temperature (21, 22). The effects of these two environmental factors are more pronounced in the lower shoots on the stem than in the upper ones (23). Atrophy of the flower buds has been attributed to a reduced transport of assimilates to the apices at the early stages of shoot development (10, 14) and to alterations in the distribution of assimilates among the various parts of the plant (10). The application of cytokinins to axillary buds or sprouting shoots resulted in increased mobilization of carbohydrates at the treated apex (15) and reduced flower bud abortion (24, 25).Sucrose is the main carbohydrate transported in plants. SPS' plays a key role in the conversion oftriose-P to sucrose in source leaves and may be subject to coarse control by the demand of the sink tissues for assimilates (18). SS and acid invertase are present in source and sink tissues (7). Both sucrose synthase and acid invertase activities in the sink tissue can be taken as a reflection of the mobilization strength of the sink (3, 4).The purpose of the present study was to investigate the effect of night temperature and cytokinin application on the activities of SPS, SS, and acid invertase in source and sink tissues extracts of rose plants. MATERIALS (HTR). During the day, temperatures were maintained in both treatments at a minimum of 18°C and a maximum of 30°C (21). In plants grow at both night temperature regimes branches bearing flower buds with unopened sepals were decapitated above the third 5-leaflet leaf from the top. The activity of SS (UDPglucose:i-fructose 2-glucosyl transferase, EC 2.4.2.13) was measured in the newly growing, second shoot from the top of the branch. The activity of SPS (UDP-glucose:-fructose-6-P 2 glucosyl transferase, EC 2.4.1.14) was determined in the leaf adjacent to this shoot at 5-or 10-d intervals following decapitation.Acid invertase (f3-D-fructofuranoside fructohydrolase, EC 3.2.1.26) activity was measured in both tissues. All samples were harvested and extracted at 0800 (about 2 h after the transition of dark to light periods).Enzyme Extraction. Young shoots, 10 to 15 mm long, or their subtending leaves, were ground by hand in liqu...
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