The pedicel of tomato fruit (Lycopersicon esculentum Mill., cv 'Rutgers') of different developmental stages from immaturegreen (IG) to red was injected on the vine with 7 microcuries [14C(U)]sucrose and harvested after 18 hours. Cell walls were isolated from outer pericarp and further fractionated yielding ionically associated pectin, covalently bound pectin, hemicellulosic fraction 1, hemicellulosic fraction 11, and cellulosic fraction I. The dry weight of the total cell wall and of each cell wall fraction per gram fresh weight of pericarp tissue decreased after the mature-green (MG) stage of development. Incorporation of radiolabeled sugars into each fraction decreased from the IG to MG3 (locules jellied but still green) stage. Incorporation in all fractions increased from MG3 to breaker and tuming (T) and then decreased from T to red. Data indicate that cell wall synthesis continues throughout ripening and increases transiently from MG4 (locules jellied and yellow to pink in color) to T, corresponding to the peak in respiration and ethylene synthesis during the climacteric. Synthesis continued at a time when total cell wall fraction dry weight decreased indicating the occurrence of cell wall tumover. Synthesis and insertion of a modified polymer with removal of other polymers may produce a less rigid cell wall and allow softening of the tissue integrity during ripening. no detectable PG activity, soften extensively (11) and apples, which contain no endo-PG, soften and show increases in soluble polyuronide during ripening (1) suggesting that softening involves other mechanisms. Using tomato fruit, Gross and Wallner (5) and Gross (6) showed that a net loss of galactosyl residues from the pectic portion of tomato fruit cell wall occurs during ripening. This loss does not result from PG activity (5-7) and strongly suggests that other enzymes or mechanisms, in addition to PG, are involved in cell wall modifications that occur during ripening of tomato fruit.Little research has addressed the synthesis and turnover of cell wall polysaccharides during fruit development and ripening and their potential role in cell wall modifications that lead to softening (14). Cell expansion ceases at the MG stage oftomato fruit development (9). It has generally been assumed that cell wall synthesis also ceases at this time. However, the radiolabeling studies necessary to measure cell wall synthesis have not been conducted. The objective of this study was to measure synthesis of tomato fruit cell wall components at various stages of development from IG to R using a [14C] sucrose pedicel injection technique developed to radiolabel fruit cell walls in vivo.The fruit cell wall has generally been viewed as a static structure which is enzymically degraded during ripening leading to fruit softening. Much emphasis in studies of softening has been placed on the activity of endo-D-galacturonase (EC 3.2.1.15, PG2), an enzyme which cleaves a 1 ,4-galacturonosyl linkages in pectin (2)(3)(4)16). Expression of the PG gene increases at t...
Tomato (Lycopersicon esculentum Mill.) genotypes evaluated for early blight [Alternaria solani (Ellis & Martin) Jones and Grout] resistance included five tolerant breeding lines, a susceptible cultivar, and seven hybrids among them. Three of the genotypes (`Castlejay', NC EBR-2, and 87B187) were crossed in a diallel mating design to estimate general combining ability and specific combining ability for the resistance trait. Parental, F1, F2, and backcross generations of the family Cl943 x `Castlejay' were evaluated for resistance and included in generation mean analysis. Hybrid means for area under the disease progress curve were not significantly different from respective midparent values, indicating additive genetic control. Diallel and generation mean analyses also detected significant additive genetic effects. Epistasis was present in the Cl943 × `Castlejay' family.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.