Different responses of photosystem I and photosystem II in three tropical oilseed crops exposed to chilling stress and subsequent recovery

Different responses of photosystem I and II to chilling. Tropical crops are sensitive to chilling stress, but the underlying physiological mechanisms are unclear. We investigated the maximum quantum yield of PSII (F (v)/F (m)), the maximum photo-oxidizable P700 (P (m)), the energy distribution in PSII, and the redox state of P700 in leaves of seedlings of three promising oilseed crops originating from tropical regions, Plukenetia volubilis, Jatropha curcas and Ricinus communis, during chilling treatment and subsequent recovery under a photon flux density of 450 mu mol m(-2) s(-1). Our results showed that F (v)/F (m) decreased progressively and significantly to about 44.7, 62.2 and 77.0 % of the control after chilling treatment for 3 days in P. volubilis, J. curcas and R. communis, respectively, mainly due to the decrease in F (m) (maximum fluorescence of PSII). After recovery under 18 A degrees C for 6 days, F (v)/F (m) recovered to 81.4 and 94.9 % of the control in J. curcas and R. communis, but only to 26.3 % in P. volubilis. Under chilling stress and subsequent recovery, P (m) remained stable in J. curcas and R. communis, whereas it decreased slightly in P. volubilis. These results indicated that PSII was more sensitive to chilling stress than PSI under moderate light for all three species, and that P. volubilis was the most susceptible. Cyclic electron flow around PSI and effective quantum yield of photosystem II [Y ((CEF))/Y ((II))] ratio were stimulated much more in J. curcas and R. communis compared with that in P. volubilis under chilling conditions, resulting in more severe injury as indicated by higher accumulation of hydrogen peroxide and malondialdehyde. There was a significantly negative relationship between F (v)/F (m) and Y ((CEF))/Y ((II)), suggesting that stimulation of Y ((CEF))/Y ((II)) plays a pivotal role in protecting PSI and PSII from photoinhibition caused by chilling stress.