Increasing attention is being given to improving agricultural productivity by genetically modifying the biochemical and physiological processes that contribute to plant growth. For this approach to be successful we require a thorough understanding of the impact of the environment on these processes. One of the most variable conditions under field conditions is temperature, with low temperatures being particularly important. Low temperatures have a major affect on the enzymatically catalyzed reactions and membrane processes necessary for plant growth, with the result that the growth and performance of many commercially important plant species is severely restricted by low temperatures. However, despite the importance of low temperatures in determining agricultural productivity, relatively little is known about many of the short- and long-term effects of cold on the underlying biochemical and physiological processes that contribute to plant growth. One of the most critical processes that contribute to plant growth is photosynthesis. Photosynthesis uses light energy to fix atmospheric carbon dioxide into sugars and other carbon-rich compounds. Cold-induced photoinhibition occurs when the ability to dissipate absorbed energy via carbon fixation and utilization is reduced by low temperatures. This inability to dissipate excess absorbed energy can lead to short and/or long term inhibition of photosynthesis and have a significant impact on plant growth and survival. Numerous studies have shown that photosynthesis decreases following short-term exposure to low temperature. Long-term exposure to low temperatures can result in acclimation to the cold, such that the rates at the low growth temperature are similar to those exhibited by plants grown under warmer conditions. The degree of acclimation varies greatly, with little or no acclimation occurring in some species.
Our work ranges from studies of thylakoid energy trapping efficiency and photosystem function, through altered activity of a range of Calvin cycle enzymes out to flux of fixed carbon though the cytosolic path for sucrose biosynthesis. Through these studies we have built a very detailed picture of both the structural and functional changes that occur to the photosynthetic apparatus and to carbon metabolism when plants are exposed to low growth temperatures. Our work has covered both monocots such as wheat and rye and dicots such as Brassica napus, Arabidopsis thaliana, and the tree species, Pinus sylvestris and now Populus tremuloides. Work with Arabidopsis has enabled us to test the significance of the changes in enzymatic activity we had observed at low temperature by producing specific sense and antisense transformants. From these studies we know that the increase in flux of fixed carbon into sucrose at low temperature is very important. With this in mind we have initiated studies into the effects of prolonged growth at low temperature on the expression and function of sugar transport proteins in both source and sink tissues. We have also initiated studies with transgenic poplar to determine whether similar changes in activity of enzymes for sucrose synthesis and transport will benefit sucrose production and phloem loading in this tree species.
Selected publications:
Hurry, V., Druart, N., Cavaco, A., Gardeström, P. & Strand, Å. () Photosynthesis at low temperatures: a case study with Arabidopsis. In Plant Cold Hardiness: gene regulation and genetic engineering. (P.H. Li & E.T. Palva, eds). Kluwer Academic Press, New York.
Hurry, V., Strand, Å., Furbank, R. & Stitt, M. () The role of inorganic phosphate in the development of freezing tolerance and the acclimation of photosynthesis to low temperature is revealed by the pho mutants of Arabidopsis thaliana L. The Plant Journal 24: 383-396.
Strand, Å., Hurry, V., Henkes, S., Huner, N., Gustafsson, P., Gardeström, P. & Stitt, M. () Acclimation of Arabidopsis leaves developing at low temperatures. Increasing cytoplasmic volume accompanies increased activities of enzymes in the Calvin cycle and in the sucrose biosynthesis pathway. Plant Physiology 119:.
Morcuende, R., Krapp, A., Hurry, V. & Stitt, M. () Sucrose feeding leads to increased rates of nitrogen assimilation, increased rates of a-oxoglutarate synthesis, and increased synthesis of a wide spectrum of amino acids in tobacco leaves. Planta, 206, 394-409.
Hurry, V. , Huner, N., Selstam, E., Gardeström, P. & Öquist, G. () Photosynthesis at low growth temperature. In Photosynthesis: A Comprehensive Treatise. (A. S. Raghavendra) pp. 238-249, Cambridge University Press, UK.
Strand, Å., Hurry, V., Gustafsson, P., Gardeström, P. () Development of Arabidopsis thaliana leaves at low temperature releases the suppression of photosynthesis and photosynthetic gene expression despite the accumulation of soluble carbohydrates. The Plant Journal, 12, 605-613.
Hurry, V., Anderson, J.M., Chow, W.S. & Osmond, C.B. () Accumulation of zeaxanthin in abscisic acid-deficient mutants of Arabidopsis does not affect chlorophyll fluorescence quenching or sensitivity to photoinhibition in vivo. Plant Physiology, 113, 639-648.
Hurry, V., Anderson, J.M., Badger, M.R. & Price, G.D. () Reduced levels of cytochrome b6/f in transgenic tobacco increases the excitation pressure on photosystem II without increasing sensitivity to photoinhibition in vivo. Photosynthesis Research, 50, 159-169.
