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

The unconjugated N-glycans Manalpha1-->6(Manalpha1-->3)Manalpha1-->6(Manalpha1-->3)-Manbeta1-->4GlcNac (Man5GlcNAc) and Manalpha1-->6(Manalpha1--> 3)(Xylbeta1-->2)-Manbeta1-->4GlcNAcbeta1-->4(Fucalpha1-->3)GlcNAc were shown to stimulate and delay ripening of mature green tomato fruit (Lycopersicon esculentum Mill. cv. Rutgers) at 1 and 10 ng (g fresh weight)-1, respectively (Priem and Gross 1992 Plant Physiol. 98: 399-401). Also, the occurrence and structure of 10 unconjugated N-glycans, including Man5GlcNAc. in tomato fruit were recently reported (Priem et al. 1993, Plant Physiol. 102: 445-458). In this work, we studied the potential interaction between Man5GlcNAc and several compounds by using a system that allowed pericarp discs to be kept up to 14 days after excision. Studies were performed to determine the effect of Man5GlcNAc, indole-3-acetic acid (IAA). concanavalin 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 showed delayed ripening with 10 ng (g fresh weight)-1, and the delay of coloration was galactose dependent. Man5GlcNAc at 10 na (g fresh weight)-1 inhibited the stimulation of coloration induced by 100 muM IAA in the presence of 40 mug (g fresh weight)-1 galactose. Man5GlcNAc lost biological activity in the presence of the two lectins. These results support the possible interaction of IAA and various oligosaccharides during plant growth and development, and for the first time suggest a physiological significance for tomato lectin.