High light stress in the kelp Ecklonia cava

Acclimation to high light stress was studied in different developmental and life-history stages of Ecklonia cava (gametophytes and young sporophytes cultivated in the laboratory and old sporophytes collected in situ). Changes in optimal quantum yield (F-v/F-m), photosynthetic efficiency (a) and capacity (ETRmax), measured by pulse amplitude modulation (PAM) fluorometry of chlorophyll a of PSII, were studied in order to investigate the inhibition and recovery kinetics of each stage. After 2 h in high irradiance (500 mumol m(-2) s(-1) PAR), hemiglobular tufts of gametophytes were not stressed, whereas sporophytes underwent severe photoinhibition (65%), with differences depending on the developmental stage. In old sporophytes, inhibition and recovery (dim light conditions, 10 mumol m(-2) s(-1) PAR) kinetics were faster than in young sporophytes, as denoted the values of the parameter m estimated from the logarithmic fittings of both periods. Furthermore, alpha and ETRmax of old sporophytes hardly changed compared to those of young sporophytes. Therefore, dynamic photoinhibition may occur in old sporophytes, but chronic photoinhibition with photodamage in young ones. Morphological features and physiological light acclimation differences among these stages may explain the differences in sensitivity to high irradiance. Dense tuft-like morphology may self-shade and protect inner cells of gametophytes against high light stress. The parenchymatous structure of old sporophytes with higher pigment contents may offer more protection against high irradiance than the less complex structure of young sporophytes. However, differences in the pre-treatment conditions may also explain this difference. (C) 2004 Elsevier B.V. All rights reserved.