Abstract
When cucumber seeds germinate in a horizontal position, seedlings form a peg on the lower side of the transition zone. We have suggested that gravistimulation activates auxin efflux and suppresses peg formation on the upper side of the transition zone. To understand this mechanism, in this study we isolated 5 cucumber cDNAs of PIN auxin efflux carrier gene in addition to CsPIN1 cDNA previously isolated and investigated their mRNA accumulation by Northern hybridization and in situ hybridization. Our results showed that tissue specificities of CsPINs expression could be classified into three categories; CsPIN1-4 are expressed in vascular tissues, CsPIN5 is expressed in epidermis and cortex of roots, and CsPIN6 is expressed in root columella cells. Further investigations of CsPIN1 and CsPIN3-6 that are also expressed in the transition zone will reveal the mechanism of auxin transport to be involved in gravity-regulated peg formation.
