Analyses of OJIP transients in leaves of two epiphytic orchids under drought stress

Abstract The tolerance to low water availability is a decisive factor for growth and survival of orchids in their natural environment. objective this study was characterize the photochemical traits two epiphytic (Cattleya warneri Miltonia spectabilis) under deficit (WD). Chlorophyll fluorescence signals were recorded from young fully expanded leaves 5 plants/species after dark-adaption 60 minutes, between 6-9 a.m. 0, 30, 60, 90 days WD, using Handy-PEA fluorometer (Hansatech, UK). Increases O-J J-I phases L K-bands decreases I-P phase observed 30 especially C. warneri. Decreases capacity photochemically reduce quinone A (QA) kinetic properties required redox reactions plastoquinone pool, loss energetic connectivity units PSII, inactivation oxygen evolution complex, decrease overall rate reducing electron acceptor pool photosystem I M. spectabilis, more tolerant species. greater ability species maintain higher relative content (RWC) photosynthetic tissues allows activity.