Under strong light, photosystem II (PSII) of oxygenic photosynthetic organisms is inactivated, and this phenomenon is called photoinhibition. In a widely accepted model, photoinhibition is induced by excess light energy, which is absorbed by chlorophyll but not utilized in photosynthesis. Using monochromatic light from the Okazaki Large Spectrograph and thylakoid membranes from Thermosynechococcus elongatus, we observed that UV and blue light inactivated the oxygen-evolving complex much faster than the photochemical reaction center of PSII. These observations suggested that the light-induced damage was associated with a UV- and blue light-absorbing center in the oxygen-evolving complex of PSII. The action spectrum of the primary event in photodamage to PSII revealed the strong effects of UV and blue light and differed considerably from the absorption spectra of chlorophyll and thylakoid membranes. By contrast to the photoinduced inactivation of the oxygen-evolving complex in untreated thylakoid membranes, red light efficiently induced inactivation of the PSII reaction center in Tris-treated thylakoid membranes, and the action spectrum resembled the absorption spectrum of chlorophyll. Our observations suggest that photodamage to PSII occurs in two steps. Step 1 is the light-induced inactivation of the oxygen-evolving complex. Step 2, occurring after step 1 is complete, is the inactivation of the PSII reaction center by light absorbed by chlorophyll. We confirmed our model by illumination of untreated thylakoid membranes with blue and UV light, which inactivated the oxygen-evolving complex, and then with red light, which inactivated the photochemical reaction center.

The influence of regular post-exercise cold application to exercised muscles trained by ergometer cycling (leg muscles) or handgrip exercise using a weight-loaded handgrip ergometer (forearm flexor muscles) was studied in human volunteers. Muscle loads were applied during exercise programs three to four times a week for 4-6 weeks. Besides measuring parameters characterizing muscle performance, femoral and brachial artery diameters were determined ultrasonographically. Training effects were identified by comparing pre- and post-training parameters in matched groups separately for the trained limbs cooled after exercise by cold-water immersion and the corresponding trained limbs kept at room temperature. Significant training effects were three times more frequent in the control than in the cold group, including increases in artery diameters in the control but not in the cold group. It is concluded that training-induced molecular and humoral adjustments, including muscle hyperthermia, are physiological, transient and essential for training effects (myofiber regeneration, muscle hypertrophy and improved blood supply). Cooling generally attenuates these temperature-dependent processes and, in particular, hyperthermia-induced HSP formation. This seems disadvantageous for training, in contrast to the beneficial combination of rest, ice, compression and elevation in the treatment of macroscopic musculo-tendinous damage.

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This study examined the effects of regular post-exercise cold application on muscular and vascular adaptations induced by moderate-intensity resistance training. 14 male subjects participated in resistance training: 5 sets of 8 wrist-flexion exercises at workload of 70?80% of the single repetition maximum, 3 times a week for 6 weeks. 7 subjects immersed their experimental forearms in cold water (10?1?C) for 20?min after wrist-flexion exercises (cooled group), and the other 7 served as control subjects (noncooled group). Measurements were taken before and after the training period; wrist-flexor thickness, brachial-artery diameter, maximal muscle strength, and local muscle endurance were measured in upper extremities. Wrist-flexor thicknesses of the experimental arms increased after training in both groups, but the extent of each increase was significantly less in the cooled group compared with the noncooled group. Maximal muscle strength and brachial-artery diameter did not increase in the cooled group, while they increased in the noncooled group. Local muscle endurance increased in both groups, but the increase in the cooled group tended to be lower compared to the noncooled group. Regular post-exercise cold application to muscles might attenuate muscular and vascular adaptations to resistance training.