Annals of Botany 73: 65-73, 1994
© 1994 Annals of Botany Company
Stimulatory and Inhibitory Effects of Sucrose Concentration on Xylogenesis in Lettuce Pith Explants; Possible Mediation by Ethylene Biosynthesis
Division of Botany and Zoology, Faculty of Science, Australian National University, Canberra, ACT 0200, Australia, Department of Biological Science, University of Idaho, Moscow, Idaho 83843, USA, Plant Cell Biology Group, Research School of Biological Sciences, Australian National University, Canberra, ACT 0200, Australia and Plant Molecular Genetics, Institute of Agriculture, University of Tennessee, PO Box 1071, Knoxville, Tennessee 37901-1071, USA
Numbers of tracheary elements differentiating in lettuce pith explants rose with increase in concentration of sucrose in the medium up to an optimal concentration of 0·2%, and fell with further increase in concentration to about one-tenth maximal at 3% sucrose. Although a few tracheary elements formed without exogenous sucrose, a very low concentration of sucrose (0·001%) was sufficient to stimulate additional xylogenesis. Pretreatment of explants with 3% sucrose caused a persisting inhibition of xylogenesis, especially in tissue that had been near the site of sucrose application (sandwich technique). The requirement for adequate, but not inhibitory, concentrations of sucrose for xylogenesis may underlie the development of xylem alongside the sucrose-rich phloem in normal apical morphogenesis.
For callus growth the response to sucrose was different: the optimal concentration was 3%, with a broad plateau from 1 to 4% sucrose. Sucrose concentrations of 2 to 3%, used in many tissue culture media, are thus roughly optimal for callus growth, but ten times the optimum for xylogenesis in lettuce pith explants.
It is surprising that 0·001% (0·03 mM) sucrose, applied exogenously, can stimulate xylogenesis: endogenous sugar concentrations are normally higher. Perhaps the stimulation is mediated by ethylene biosynthesis, which is known to be xylogenic. Rates of ethylene production per explant rose with increasing sucrose concentration from about 0·1 nl h-1 at 0% sucrose to a slightly (significantly) higher level at 0·004% sucrose and to about 0·5 nl h-1 at 3% sucrose. D -glucose resembled sucrose in its effects on xylogenesis and ethylene production, but L-glucose yielded no xylogenesis and little stimulation of ethylene biosynthesis.Copyright 1994, 1999 Academic Press
Lactuca sativa, Coleus blumei, Nicotiana tabacum, lettuce pith explants, tracheary element differentiation, sucrose, glucose, ethylene
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