As. Verhoeven et al., ENHANCED EMPLOYMENT OF THE XANTHOPHYLL CYCLE AND THERMAL-ENERGY DISSIPATION IN SPINACH EXPOSED TO HIGH LIGHT AND N STRESS, Plant physiology, 113(3), 1997, pp. 817-824
The involvement of the xanthophyll cycle in photoprotection of N-defic
ient spinach (Spinacia oleracea L. cv Nobel) was investigated. Spinach
plants were fertilized with 14 mM nitrate (control, high N) versus 0.
5 mM (low N) fertilizer, and grown under both high- and low-light cond
itions. Plants were characterized from measurements of photosynthetic
oxygen exchange and chlorophyll fluorescence, as well as carotenoid an
d chlorophyll analysis. Compared with the high-N plants, the low-N pla
nts showed a lower capacity for photosynthesis and a lower chlorophyll
content, as well as a lower rate of photosystem It photosynthetic ele
ctron transport and a corresponding increase in thermal energy dissipa
tion activity measured as nonphotochemical fluorescence quenching. The
low-N plants displayed a greater fraction of the total xanthophyll cy
cle pool as zeaxanthin and antheraxanthin at midday, and an increase i
n the ratio of xanthophyll cycle pigments to total chlorophyll. These
results indicate that under N limitation both the light-collecting sys
tem and the photosynthetic rate decrease. However, the increased dissi
pation of excess energy shows that there is excess light absorbed at m
idday. We conclude that spinach responds to N limitation by a combinat
ion of decreased light collection and increased thermal dissipation in
volving the xanthophyll cycle.