Quantifying cutin and wax deposition in developing apple fruit

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Appearance determines the fresh market value in most fleshy fruit. Even cosmetic damage severely reduces the market value. Economically important examples include russeting and skin spot of apple. Both disorders are preceded by microscopic failure of the cuticular membrane (CM) resulting in impaired barrier function. Maintaining an intact CM requires a better understanding of cuticle formation in developing fruit. Recent studies suggest that continuous deposition of cutin and wax plays an important role in minimizing stress and strain in the CM of developing apple thereby minimizing the risk of CM failure. The objectives of our study are to (1) establish a system for quantifying rates of cutin and wax deposition in developing apple fruit using labeled precursors, (2) compare rates of deposition established using 13C-labeled precursors (stable isotopes) with those determined gravimetrically and (3) quantify any spatial radial heterogeneity in the deposition within the cuticle. In the first and second year, we will utilize 14C (in the lab) and 13C -labeled (in the field) C16 and C18 fatty acid precursors to quantify rates of cutin and wax deposition. In laboratory experiments the amount of radioactivity associated with the cutin and wax fraction is determined and treatment conditions leading to maximum incorporation are identified. In the field 13C incorporation will be quantified by mass spectrometry and compared with deposition rates determined gravimetrically. The third year will focus on potential spatial heterogeneity of cutin and wax deposition in developing fruit supplied with 13C fatty acid. The methods developed will be useful in studying the role of cutin and wax deposition in russet susceptibility of apple as affected by genotype and environmental factors.