Musings about the effects of environment on photosynthesis.

Understanding of how plants respond to their environment, particularly to extreme conditions to which their metabolisms are not adapted, is advancing on many fronts. An enormous matrix of plant and environmental factors exists from which mechanisms and assessments of quantitative responses must be developed if further progress in understanding how to improve plant (and particularly crop) production is to be achieved. This Special Issue contains assessments of different areas of plant sciences, ranging from genome to field, but with a focus on photosynthesis. Photosynthesis is central to all aspects of plant biology as the provider of energy and assimilates for growth and reproduction, yet how it is regulated by abiotic stresses, such as salinity and water deficits, and by biotic stresses, such as insect herbivory, is still unclear. Differences in responses of C3, C4 and CAM plants are still uncertain and mechanisms unclarified. Gene distribution and transfer between chloroplasts and nucleus on an evolutionary time scale may reflect conditions in the cell and organelles relevant to the short-term effects of water deficits on photosynthetic rate and the function of ATP synthase. Regulation of conditions in tissues and cells depends not only on chloroplast functions but on mitochondrial activity, and their interaction and differences in responses have implications for understanding many aspects of cell metabolism. Adaptation of plant structure, such as stomatal frequency and composition of the photosynthetic machinery by changes to gene expression controlled by transcription factors, or arising from regulation of gene expression by redox state, is of major importance with implications for adaptation in the short- and long-term. The incisive and thought-provoking reviews in this Special Issue offer analyses of experimental information and develop concepts within the complex matrix, relating photosynthesis and associated metabolism to the environment and addressing mechanisms critically with a balanced assessment of the current state of the science.