caa a22 4500 60548094X CHVBK 20210128100418.0 cr unu---uuuuu 210128e20151201xx s 000 0 eng 10.1007/s11099-015-0136-z doi (NATIONALLICENCE)springer-10.1007/s11099-015-0136-z In vivo evaluation of the high-irradiance effects on PSII activity in photosynthetic stems of Hexinia polydichotoma [Elektronische Daten] [L. Li, Z. Zhou, J. Liang, R. Lv] Green photosynthetic stems are often responsible for photosynthesis due to the reduction of leaves in arid and hot climates. We studied the response of PSII activity to high irradiance in the photosynthetic stems of Hexinia polydichotoma in the Taklimakan Desert by analysis of the fast fluorescence transients (OJIP). Leaf clips of a chlorophyll fluorometer were used in conjunction with a sponge with a 4-mm-width groove to prevent light leakage for precise in vivo measurements. High irradiance reduced performance indices, illustrating the photoinhibition of PSII to some extent. However, the decrease in active reaction centers (RC) per PSII absorption area and maximum quantum yield indicated a partial inactivation of RCs and an increase in excitation energy dissipation, resulting in downregulation of photosynthetic excitation pressure. In addition, the increased efficiency of electron transport to PSI acceptors alleviated overexcitation energy pressure on PSII. These mechanisms protected the PSII apparatus as well as PSI against damages from excessive excitation energy. We suggested that H. polydichotoma exhibited rather photoadaptation than photodamage when exposed to high irradiance during the summer in the Taklimakan Desert. The experiment also demonstrated that the modified leaf clip can be used for studying dark adaptation in a photosynthetic stem. The Institute of Experimental Botany, 2015 cylindrical photosynthetic stems nationallicence dark adaptation nationallicence thermal dissipation nationallicence ABS/RC : average absorbed photon flux per PSII reaction center nationallicence Chl : chlorophyll nationallicence DIo/RC : dissipated energy flux per PSII nationallicence ETo/RC : electron transport flux from QA to QB nationallicence HI : high irradiance nationallicence LI : low irradiance nationallicence PIabs : performance index for energy conservation from photons absorbed by PSII antenna to the reduction of QB nationallicence PItotal : performance index for energy conservation from photons absorbed by PSII antenna to the reduction of PSI acceptors nationallicence RC : reaction center nationallicence REo/RC : electron transport flux until PSI acceptors per PSII nationallicence TRo/RC : maximum trapped excitation flux per PSII nationallicence φDo : dissipated energy flux nationallicence φEo : quantum yield of the electron transport flux from QA to QB nationallicence φPo : maximum quantum yield of primary PSII photochemistry nationallicence φRo : quantum yield of the electron transport flux until the PSI electron acceptors nationallicence δRo : efficiency with which an electron from QB is transferred until PSI acceptors nationallicence Li L. State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, 830011, Urumqi, China aut Zhou Z. College of Plant Science, Tarim University, 843300, Alar, China aut Liang J. College of Plant Science, Tarim University, 843300, Alar, China aut Lv R. College of Plant Science, Tarim University, 843300, Alar, China aut Photosynthetica The Institute of Experimental Biology of the Czech Academy of Sciences 53/4(2015-12-01), 621-624 0300-3604 53:4<621 2015 53 11099 https://doi.org/10.1007/s11099-015-0136-z text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 brief-communication jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s11099-015-0136-z text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Li L. State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, 830011, Urumqi, China aut NATIONALLICENCE 700 1- Zhou Z. College of Plant Science, Tarim University, 843300, Alar, China aut NATIONALLICENCE 700 1- Liang J. College of Plant Science, Tarim University, 843300, Alar, China aut NATIONALLICENCE 700 1- Lv R. College of Plant Science, Tarim University, 843300, Alar, China aut NATIONALLICENCE 773 0- Photosynthetica The Institute of Experimental Biology of the Czech Academy of Sciences 53/4(2015-12-01), 621-624 0300-3604 53:4<621 2015 53 11099