DELAY OF TOMATO FRUIT RIPENING BY AN OLIGOSACCHARIDE N-GLYCAN - INTERACTIONS WITH IAA, GALACTOSE AND LECTINS

The unconjugated N-glycans >3)Manalpha1-->6(Manalpha1-->3)-Manbeta1--> 4GlcNac (Man5GlcNAc) and Manalpha1-->6(Manalpha1--> )-Manbeta1-->4GlcN Acbeta1-->4(Fucalpha1-->3)GlcNAc were shown to stimulate and delay rip ening of mature green tomato fruit (Lycopersicon esculentum Mill. cv. Rutgers) at 1 and 10 ng (g fresh weight)-1, respectively (Priem and Gr oss 1992 Plant Physiol. 98: 399-401). Also, the occurrence and structu re of 10 unconjugated N-glycans, including Man5GlcNAc. in tomato fruit were recently reported (Priem et al. 1993, Plant Physiol. 102: 445-45 8). In this work, we studied the potential interaction between Man5Glc NAc and several compounds by using a system that allowed pericarp disc s to be kept up to 14 days after excision. Studies were performed to d etermine the effect of Man5GlcNAc, indole-3-acetic acid (IAA). concana valin A and tomato lectin on ripening as defined by red coloration of the skin. Ripening in pericarp discs. unlike that in intact fruit. was unaffected by 1 ng (g fresh weight)-1 Man5GlcNAc. However, discs show ed delayed ripening with 10 ng (g fresh weight)-1, and the delay of co loration was galactose dependent. Man5GlcNAc at 10 na (g fresh weight) -1 inhibited the stimulation of coloration induced by 100 muM IAA in t he presence of 40 mug (g fresh weight)-1 galactose. Man5GlcNAc lost bi ological activity in the presence of the two lectins. These results su pport the possible interaction of IAA and various oligosaccharides dur ing plant growth and development, and for the first time suggest a phy siological significance for tomato lectin.