Photoinhibition in differently coloured juvenile leaves of Syzygium species

Photoinhibition, as measured by the dark-adapted chlorophylla fluorescence ratioFv/Fm, was assessed inSyzygium moorei, a species with dark green juvenileleaves, Syzygium corynanthum, which has light greenjuvenile leaves, and two species with pink-red juvenile leaves(Syzygium wilsonii and Syzygiumluehmannii). All plants were glasshouse-grown (maximumPPFD 1500 molm^-2 s^-1) under optimumnutrition and water.When measured at midday, dark-adaptedFv/Fm ratios of juvenile leavesgradually increased in all species as percentage of full leaf expansion (%FLE) increased. Fluorescence measurement 3h aftersunset or pre-dawn also showed a developmental effect onFv/Fm, with juvenile leaves ofS. luehmannii and S. wilsoniishowing much lower Fv/Fm at allstages of development. Dark-adaptedFv/Fm, values in both juvenileand mature leaves generally never exceeded 0.8 at any stage in any of thespecies.Courses of Fv/Fm on sunnydays showed greater diurnal photoinhibition in green juvenile(c. 50% FLE) leaves ofS. moorei (24%) and S.corynanthum (36%) than in mature leaves of the previous flush inthese species (<10%). Diurnal photoinhibition was statisticallysimilar (18-24%) in pink-red juvenile and green mature leaves ofS. luehmannii and S. wilsonii.Re-positioning juvenile leaves of S. wilsoniihorizontally increased diurnal photoinhibition.Exposure of leaves to astandard mild photoinhibitory light treatment (30 min at 1000 molm^-2s^-1) showed that juvenileleaves of all species had a lower percentage of high energy state quenching(qE) and a higher percentage of photoinhibitoryquenching (qI) than matureleaves.