PHYSIOLOGICAL COMPARISON OF ABSCISING RUDIMENTARY LEAF AND VIGOROUSLY DEVELOPING PANICLE IN LITCHI: ANTIOXIDANT ENZYMES AND PHYTOHORMONES

Floral bud of litchi (Litchi chinensis Sonn.) is a mixed bud consisting of leaf primordia, rudimentary leaves and panicle primordia. According to field observation, vigorous development of panicle results in abscission of rudimentary leaves. In this study, abscising rudimentary leaves (AL) and their subtending developing panicle (DP) were sampled from the terminal shoots of cvs. ‘Nuomici’ and ‘Feizixiao’. In ‘Nuomici’, AL had a higher superoxide dismutase (SOD) activity compared to the DP. In ‘Feizixiao’, however, no significant difference was found between them, although AL had lower SOD activity. Peroxidase (POD) activity in AL was higher and ascorbate peroxidase (APX) was lower than that in DP, whereas H₂O₂ concentration was higher in AL than in DP in both cultivars. The DP had higher levels of zeatin plus zeatin riboside (ZRs) and auxin (IAA) and lower levels of abscisic acid (ABA) than AL. The results suggested that different developmental fates of AL and DP had different antioxidant activities and hormone balance. High levels of SOD and APX activities and low levels of POD activity and H₂O₂ concentration, together with high levels of ZRs, IAA and low level of ABA may be associated with the vigorous development of the panicle. Whereas low levels of SOD and APX activities, high levels of POD activity and H₂O₂ concentration, low levels of ZRs, IAA and high level of ABA may be associated with the senescence and abscission of rudimentary leaves caused by panicle development.