Abscisic acid metabolism and episodic growth in cocoa

Abscisic acid (ABA) levels and metabolism were investigated in relation to shoot growth in cocoa (Theobroma cacao L.). ABA levels were high (14 nmoles/g fwt) in young flush leaves during shoot growth but gradually declined during the subsequent dormant period. ABA levels were low (1-2 nmoles/g fwt) in mature leaves when the terminal bud re-initiated growth. ABA-glucose ester (ABA-glu) levels were low (3-4 nmoles/g fwt) in the flush leaves during shoot growth and dormancy, however, ABA-glu levels increased more than 7-fold in these same leaves during the next flush cycle. ABA-glu levels then dropped significantly during the dormant period. Radiolabeled-ABA was metabolized to three products in cocoa leaves: ABA-glu, phaseic acid and dihydrophaseic acid. Catabolism of radiolabeled ABA was significantly greater in mature leaves during the dormant period when endogenous levels of ABA were high as compared to the period of active shoot growth when endogenous levels of ABA in mature leaves were low.