Changes in Antioxidant Enzyme Activities and Hydrogen Peroxide Concentration in Litchi chinensis during Floral Differentiation

摘要

Floral differentiation is induced by low temperatures and enhanced by autumn and winter drought. Antioxidant enzyme activities,hydrogen peroxide concentration,leaf water content,maximum photochemical efficiency of PS 2 (Fv/Fm) and SPAD value in Litchi chinensis Sonn.cvs.'Nuomici' and 'Feizixiao' during the chilled and drought-induced floral differentiation from Nov.to Feb.2006 were studied,with the aim to show the physiological changes during the stress-induced floral differentiation. The results showed that the SPAD value indicating chlorophyll concentration increased before and then decreased after the emergence of panicle primordia in 'Nuomici',while in 'feizixiao' SPAD values slowly rose during the period.Leaf water content in both cultivars decreased to the lowest level when panicle primordia emerged and increased thereafter.Fv/Fm decreased with the drop of temperature,and were higher in 'Feizixiao' than in 'Nuomici'. Activities of SOD and POD in the two cultivars increased at first and then decreased before panicle primordia emerged.But after that,the enzyme activities in 'Nuomiei' increased and remained at stable levels,while that in 'Feizixiao' increased to a high level but decreased thereafter. APX activity in 'Nnomici' increased during the whole stage while in 'Feizixiao' it increased then decreased but still remained at a higher level. On the whole,APX activities in the floral induction stage were lower than those in the panicle developmental stage.A sudden increase in H2O2 concentration in the two cultivars was found when panicle primordia emerged.H2O2 concentration before panicle emergence in both cultivars was lower than that after panicle emergence.