Park YI, Chow WS, Anderson JM, Hurry VM
Differential susceptibility of Photosystem II to light stress in light-acclimated pea leaves depends on the capacity for photochemical and non-radiative dissipation of light
Plant Science: 1996 115:137-149
The importance of photoprotective strategies for Photosystem (PS) II function under all light regimes was determined from the content of functional PS II, measured by repetitive flash yield of oxygen evolution, in leaves of pea (Pisum sativum L.) grown under 50 (low light), 250 (medium light), and 650 (high light) mu mol photons m(-2) s(-1). The modulation of PS II functionality in vivo was induced in 1.1% CO2 after infiltration of leaves with water (control), nigericin (a lipophilic uncoupler) or dithiothreitol (DTT, inhibitor of violaxanthin to zeaxanthin conversion) through the cut petioles of leaves of 22-24 day-old plants. In all nigericin-treated pea leaves, photoinactivation of PS II was greatly increased with increasing photon exposure (mel photons m(-2)). This nigericin-induced increase of photoinactivation of PS II was greater than that induced by DTT in medium- and high-light pea leaves, but comparable in low-light peas. In low-light peas during steady-state photosynthesis, the development of non-photochemical quenching of chlorophyll fluorescence (NPQ, measured as F-m/F'(m)-1) was lowest, accompanying the highest reduction state of PS II (measured by photochemical quenching, qp) Further, the susceptibility of PS II to light stress, estimated as (1-qp)/NPQ [Park et al., Plant Cell Physiol., 36 (1995) 1163-1167], was highest in low-light peas. The decline of chlorophyll fluorescence from maximum (F-m) to steady-state level during induction phase of chlorophyll fluorescence was retarded by nigericin treatment, with a greater inhibitory effect in high- and medium- than low-light pea leaves. From these results, we suggest that the greater susceptibility of low-light peas to light stress than medium- and high-light peas is ascribed to lower capacities for both the utilization of absorbed light by photosynthesis and for non-radiative dissipation of absorbed light as heat.
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