Photosynthesis Research 46: 129-139, 1995. (~) 1995 KluwerAcademic Publishers. Printedin the Netherlands. Minireview The grand design of photosynthesis: Acclimation of the photosynthetic apparatus to environmental cues Jan M. Anderson, Wah Soon Chow & Youn-I1 Park Cooperative Research Centre for Plant Science and CSIRO, Division of Plant Industry, GPO Box 1600, Canberra ACT2601, Australia Received23 February 1995;accepted in revisedform 14April 1995 Key words: light quantity, light quality, temperature, photoreceptors, photosystem stoichiometry, redox sensing Abstract Dynamic acclimation of the photosynthetic apparatus in response to environmental cues, particularly light quantity and quality, is a widely-observed and important phenomenon which contributes to the tolerance of plants against stress and helps to maintain, as far as possible, optimal photosynthetic efficiency and resource utilization. This mini-review represents a scrutiny of a number of possible photoreceptors (including the two photosystems acting as light sensors) and signal transducers that may be involved in producing acclimation responses. We suggest that regulation by signal transduction may be effected at each of several possible points, and that there are multiple regulatory mechanisms for photosynthetic acclimation. Abbreviations: FR- far-red light; LHC I, LHC II - light-harvesting chlorophyll a/b-protein complex of PSI and PS II, respectively; P700 - primary electron donor of PS I; Pmax - maximum photosynthetic capacity; QA - primary quinone electron acceptor of PS II; qN, qP -- non-photochemical and photochemical quenching, respectively; R - red light Introduction Daniel Arnon never ceased to wonder at and delight in the 'grand design of photosynthesis' (Arnon 1982), be it in others' achievements in photosynthesis or his own heroic discoveries of photophosphorylation. Part of the grand design of photosynthesis involves the exquisite acclimation of the photosynthetic apparatus to ever- changing environmental stimuli. It is well established that marked modulations of the composition, function and structure of the photosynthetic apparatus occur in response particularly to light, but also to temperature and the availability of water, nutrients and CO2. Due to the extremely limited abilities of plants to change their surroundings, these highly regulated, dynamic responses occur to make the best of whatever situa- tion the plant is faced with. Above all, it is imperative that plants maintain an effective balance between ener- gy supply through light-harvesting and electron trans- port on the one hand, and energy consumption, mainly by carbon fixation on the other, since photosynthesis drives life on earth. Coordinated interactions between light-harvesting, energy conversion, electron trans- port, proton translocation and carbon fixation are inex- tricably linked in photosynthesis in response to sudden and sustained environmental fluctuations. Short-term responses such as state transitions, protective ener- gy dissipation and the down-regulation of PS II in response to fluctuations in irradiance, serve to min- imise change due to excess light by rendering some PS IIs non-functional, while simultaneously allowing efficient use of incident irradiance (cf. Horton and Ruban 1992; Chow 1994). On the other hand long- term acclimation, mediated by multitudes of signal cascades and networks, involves the coordinated real- location of resources to achieve and maintain, not only optimal rates of photosynthesis, but also high quan- tum yields under limiting light and protective strate-