Ba. Logan et al., SEASONAL DIFFERENCES IN XANTHOPHYLL CYCLE CHARACTERISTICS AND ANTIOXIDANTS IN MAHONIA REPENS GROWING IN DIFFERENT LIGHT ENVIRONMENTS, Oecologia, 116(1-2), 1998, pp. 9-17
We investigated differences between summer and winter in photosynthesi
s, xanthophyll cycle-dependent energy dissipation, and antioxidant sys
tems in populations of Mahonia repens (Lindley) Don growing in the eas
tern foothills of the Colorado Rocky Mountains in deep shade, full exp
osure, and under a single-layered canopy of Finns ponderosa (partially
shaded). In summer, increasing growth irradiance (from deep shade to
partial shade to full exposure) was associated with increased xanthoph
yll cycle-dependent energy dissipation in PSII and an increased capaci
ty to detoxify reactive reduced oxygen species, as measured by increas
es in the activities of ascorbate peroxidase, superoxide scavenging, g
lutathione reductase, and monodehydroascorbate reductase, as well as i
ncreases in leaf ascorbate and glutathione content. Leaves of exposed
and partially shaded plants exhibited decreased capacities for photosy
nthetic O-2 evolution in winter compared to summer, while in the deepl
y shaded plants this parameter did not differ seasonally. Seasonal dif
ferences in the levels of antioxidants generally exhibited an inverse
response to photosynthesis, being higher in winter compared to summer
in the exposed and partially shaded populations, but remaining unchang
ed in the deeply shaded population. In addition, total pool size and c
onversion state of the xanthophyll cycle were higher in winter than in
summer in all populations. These trends suggest that both xanthophyll
cycle-dependent energy dissipation in PSII and the capacity to detoxi
fy reactive reduced oxygen species responded to the level of excess li
ght absorption.