Effect of the introduction of non‐ripening mutant genes on the composition and enzyme content of tomato fruit

Abstract

The genes Never ripe ( N r ) and ripening inhibitor ( r i l l ) were introduced by backcross programmes into the tomato variety Ailsa Craig to give nearly isogenic lines. The effect of each of these genes on the major constituents of fully-developed tomato fruit has been studied as part of a programme to select breeding lines bearing fruit having prolonged shelf-life. The N r gene produced high acid, low sugar, slow-ripening tomatoes that were very firm. Because of the adverse effect of this gene on tomato composition, even in heterozygous form, it has little or no commercial potential. The riri gene also led to the production of poor quality fruit. The heterozygote (Rill r i n ) gave fruit that were similar in compositon to that of the recurrent line, but despite possessing lower polygalacturonase activity were not significantly firmer. The distribution of isoenzymes in the normal and mutant tomato tissues was examined by gel electrophoresis. The majority of the enzymes investigated showed a diminished activity in N r and riri fruit compared with normal. The very low activities of polygalacturonase, phosphofructokinase and NADP'-malic enzyme in the fully-developed mutant lines offers an explanation for the weak climacteric respiration rise and slow ripening of N r fruit and the non-climacteric behaviour of riii fruit.

Molecular Cloning of Tomato Pectin Methylesterase Gene and its Expression in Rutgers, Ripening Inhibitor, Nonripening, and Never Ripe Tomato Fruits

“…Recently, Koch and Nevins (19) reported that the total uronic acid content oftomato fruit remains constant throughout ripening, whereas the degree of esterification decreases from 90% at mature green and breaker stages to 35% at the pink and ripe stages. Levels of PME activity in the ripeningimpaired mutant Nr have been reported to be similar to those observed in normally ripening cultivars (13), whereas lower levels of PME activity have been observed in rin fruit (6,14).…”

Ethylene-Independent and Ethylene-Dependent Biochemical Changes in Ripening Tomatoes

“…The 'malate effect' is well documented in Malus and Pyrus species (7) and there is one report of this in tomato fruit (14) where a single value for cv Ailsa Craig is quoted at the green and red stage. The loss of malate is consistently about onehalf of the amount found in fruit before the start of storage (9) and parallels the loss found during normal ripening.…”

Kinetic Comparison of Cytokinin Nucleosidase Activity Isolated from Normally Ripening and Mutant Tomato Varieties

“…An active cytokinin is one which can bind to a receptor and evoke a physiological response (8). The On the basis of the kinetic data presented in Table I, it is apparent that production of the active free base, I6Ade, takes place more rapidly in nucleosidase preparations from the Rutgers cultivar than in those from either the Nor or Rin varieties.…”