The nonclimacteric guava cultivar ‘Jen-Ju Bar’ is defective in system 2 1-aminocyclopropane-1-carboxylate synthase activity

The ripening characteristics and physiology of two guava cultivars, ‘Jen-Ju Bar’ (‘JJB’) and ‘Li-Tzy Bar’ (‘LTB’), were investigated and compared because of their divergent storability. During storage at 20 °C, mature-green ‘LTB’ fruit exhibited ripening behavior typical for a climacteric fruit, including increases in respiration and ethylene production (3.75 mmol CO2 kg−1 h−1 and 1.37 × 103 nmol C2H4 kg−1 h−1 at peak levels, respectively), yellow color development, flesh softening, and volatile production. By contrast, ‘JJB’ is considered a nonclimacteric fruit because it features low and stable rates of respiration (0.61–0.73 mmol CO2 kg−1 h−1) and ethylene production (less than 4 nmol C2H4 kg−1 h−1) while retaining its pale-green color and firmness throughout a 20 d observation period. Furthermore, the nonclimacteric nature of ‘JJB’ fruit was revealed through its responses to various levels of applied ethylene, as its respiration rate increased in a concentration-dependent manner. This respiration enhancement occurred only when exogenous ethylene was present and could be evoked repeatedly in the same ‘JJB’ fruit. The ripening characteristics of ‘JJB’ do not result from a defect in ethylene signaling, but instead result from a lack of autocatalytic ethylene synthesis, as propylene ventilation stimulated normal fruit ripening and an upsurge of respiration without a massive endogenous ethylene release. However, a cutting treatment of ‘JJB’ was able to induce stress-responsive ethylene production expected from system 1 ethylene biosynthesis. The finding that 1-aminocyclopropane-1-carboxylic acid (ACC) content and ACC synthase (ACS) activity were significantly lower in ‘JJB’ than in ‘LTB’ fruit after harvest, together with the finding that treatment with ACC (rather than S-adenosyl-l-methionine) led to both fully ripened ‘JJB’ fruit and endogenous ethylene production, strongly suggest that insufficient ACC synthesis, i.e., the reaction catalyzed by ACS, prevents system 2 ethylene biosynthesis in ‘JJB’ guava fruit.

► Guava cultivar ‘Jen-Ju Bar’ (‘JJB’) had low production of CO2 and C2H4 during ripening.
► Application of propylene stimulated a rise in respiration without any C2H4 increase.
► Fruit respiration rate increased in an C2H4 concentration-dependent manner.
► The nonclimacteric nature of ‘JJB’ fruit is not a result of a defect in C2H4 signaling.
► The lack of autocatalytic C2H4 production appears to come from a shortage of 1-aminocyclopropane-1-carboxylic acid.