Kinetin and Carbohydrate Metabolism in Chinese Cabbage

Abstract

The effects of kinetin on starch and sugar levels and on 4CO2 and aP-orthophosphate labeling patterns of floated Chinese cabbage (Brassica pekinensis) leaf discs were investigated. Kinetin caused gross starch degradation. Neutral sugars were depressed by 30 to 40% in leaf tissue treated with kinetin for 24 hours. 14CO2 labeling of leaf discs pretreated with kinetin for 24 hours showed increased radioactivity in chloroform-soluble material and most sugar phosphates, and a 35 to 40% decrease in radioactivity in the neutral sugars, glucose, sucrose, and fructose. Incorporation into ATP was increased by 40 % by kinetin. "P-Orthophosphate uptake was inhibited 30 % by kinetin. When corrected for uptake, kinetin stimulated incorporation into chloroform-soluble material but had little effect on other cell fractions. These results indicate that kinetin mobilizes starch reserves and increases the flow of sugars required for the synthesis of lipids and structural materials in floated discs.We have previously shown (2) that cytokinins stimulate expansion of floated Chinese cabbage leaf discs while maintaining the levels of ribosomes and RNA in the discs. We report here effects of kinetin and sucrose on Chinese cabbage leaf disc expansion; on starch, sugar, and sugar phosphate levels; and on fixation and metabolism of "CO2 in floated leaf discs. MATERIALS AND METHODS PLANT GROVVTH AND SAMPLINGChinese cabbage (Brassica pekinensis, var. Wong Bok) plants were grown in a glasshouse at 25 C under natural light. Young rapidly expanding leaves 7 to 11 cm long from 4-to 6-weekold plants were routinely used. Discs (9-mm diameter) were removed from interveinal areas with a cork borer and floated on solutions made up in Vickery's solution (2). Equal numbers of discs from each half-leaf were randomly distributed between Petri dishes, and the dishes were incubated in a light room (600 lumens/sq ft) at 25 C under a 16-hr photoperiod. Following incubation the discs were washed with water, blotted dry, weighed and extracted.The mechanism of action of the plant hormones, cytokinins, is at present unknown. Cytokinins have been shown to modify the incorporation of radioactive precursors into nucleic acids and proteins in excised leaf tissue (11). However, recent more critical studies (8,14) (10,15). STARCH AND SUGAR DETERMINATIONStarch. Leaf discs were ground with 4 ml of TM buffer (0.01 M MgCl2, 0.01 M tris-HCl, pH 7.6). The homogenate was strained through fine cheesecloth. The mortar and cheesecloth were rinsed with 4 ml of TM buffer, and the total extract was centrifuged at 12,000g for 10 min. The pellet was extracted twice with TM buffer containing 2% Triton X-100 (to remove chlorophyll). After centrifugation the resulting pellet was suspended in 2 ml of TM buffer and incubated with pancreatic deoxyribonuclease I (10 ,tg) at 27 C for 25 min. The remaining insoluble material was washed twice with 95% ethanol. Starch in the residue was hydrolyzed with perchloric acid, and the resulting sugars were determined with anthrone (9).Sugars....

Combined Effect of Soil Water Availability and Growth Substances on Some Aspects of Chemical Composition of Cowpea Plants

“…8 b) kinetin treatments exhibited an analogous picture as those of the first stage. Such findings could agree with those of ERISMANN and FRANHAUSER (1967), BERRIDGE and RALPH (1971) and LUSTINEC et al (1974) who found excessive accumulation of starch in treated plants. Moreover, DEZSI and FRANKS (1968), 8S KHALIL and MANDURAH HEGAZV et al (1972) and ZERBE and WILD (1980) reported increase in reducing sugars and sucrose content of barley, beans and Sinapis alba.…”

Partial Restoration of the High Rate of Plastid Pigment Development and the Ultrastructure of Plastids in Detached Water-stressed Wheat Leaves

“…5). Berridge and Ralph (3) reported that kinetin induced starch degradation and increased the flow of sugars into lipids and structural materials in floating cabbage leaf discs. This result may mean that the nutrition of BA-treated detached wheat leaf tissue was directed towards the synthesis of cellular structural components.…”

Effect of Benzyladenine on Some Enzymes of Mitochondria and Microbodies in Excised Sunflower Cotyledons

“…The effect on growth is associated, at least in some cases, with an accelerated mobilization of starch reserves (1,9,10). We have recently observed that BA also accelerates the disappearance of reserve fat in excised sunflower cotyledons (O. Servettaz and C. P. Longo, unpublished data).…”