Inhibition of xylogenesis by morphactin in pith parenchyma explants of <italic>Lactuca</italic>

Abstract

Pith parenchyma explants of Romaine lettuce (Lactuca saliva Linn. var. Romanà) incubated in the dark for 7 days at 25°C on a nutrient medium containing sucrose, IAA. and kinetin exhibited extensive differentiation of tracheary elements. The addition of CFL to the medium strongly inhibited tracheary element formation. The lack of tracheary strand formation in the CFL-treated explants suggests the inhibition of auxin transport. Conclusive evidence that CFL influences the anatomy of differentiating xylem elements was lacking. The addition of CFL to various combinations of xylogenic media was not stimulatory to xylem element formation beyond the differentiation response observed in the absence of CFL. Unique patterns of tracheary element formation produced by cytokinin media containing IAA, 2,4-D, and NAA, respectively, were abolished by CFL. As indicated by counts of total tracheary elements formed per explant, the addition of cysteine to a CFL-containing medium reversed the inhibitory effect of CFL. Tracheary strand formation was not re-established in the explants cultured on the cysteine+CFL medium. Tracheary element formation was completely suppressed by TIBA. Cysteine had a slight effect on the inhibition of differentiation by TIBA. These observations suggest that CFL inhibits some sulfhydryl- containing system involved either in the process of xylem differentiation or in some prerequisite role necessary for the induction of tracheary element formation.