Antarctic terrestrial ecosystems experience some of the most extreme growth conditions on Earth and are characterised by extreme aridity and sub-zero temperatures. Antarctic vegetation is therefore at the physiological limits of survival and, as a consequence, even slight changes to growth conditions are likely to have a large impact, rendering Antarctic terrestrial communities sensitive to climate change. Climate change is predicted to affect the high latitude regions first and most severely. In recent decades, the Antarctic has undergone significant environmental change, including the largest increases in ultraviolet B (UV-B; 290-320nm) radiation levels in the world and, in the maritime region at least, significant temperature increases. This review describes the current evidence for environmental change in Antarctica, and the impacts of this change on the terrestrial vegetation. This is largely restricted to cryptogams, such as bryophytes, lichens and algae; only two vascular plant species occur in the Antarctic, both restricted to the maritime region. We review the range of ecological and physiological consequences of increasing UV-B radiation levels, and of changes in temperature, water relations and nutrient availability. It is clear that climate change is already affecting Antarctic terrestrial vegetation, and significant impacts are likely to continue in the future. We conclude that, in order to gain a better understanding of the complex dynamics of this important system, there is a need for more manipulative, long-term field experiments designed to address the impacts of changes in multiple abiotic factors on the Antarctic flora.

In this study, we investigated whether changes in mitochondrial abundance, ultrastructure and activity are involved in the respiratory cold acclimation response in leaves of the cold-hardy plant Arabidopsis thaliana . Confocal microscopy [using plants with green fluorescence protein (GFP) targeted to the mitochondria] and transmission electron microscopy (TEM) were used to visualize changes in mitochondrial morphology, abundance and ultrastructure. Measurements of respiratory flux in isolated mitochondria and intact leaf tissue were also made. Warm-grown (WG, 25/ 20 ∞ C day/night), 3-week cold-treated (CT) and cold-developed (CD) leaves were sampled. Although CT leaves exhibited some evidence of acclimation (as evidenced by higher rates of respiration at moderate measurement temperatures), it was only the CD leaves that were able to reestablish respiratory flux within the cold. Associated with the recovery of respiratory flux in the CD leaves were: (1) an increase in the total volume of mitochondria per unit volume of tissue in epidermal cells; (2) an increase in the ratio of cristae to matrix within mesophyll cell mitochondria; and (3) an increase in the capacity of the energyproducing cytochrome pathway in mitochondria isolated from whole leaf homogenates. Regardless of growth temperature, we found that contrasting cell types exhibited distinct differences in mitochondrial ultrastructure, morphology and abundance. Collectively, our data demonstrated the diversity and tissue-specific nature of mitochondrial responses that underpin respiratory acclimation to the cold, and revealed the heterogeneity of mitochondrial structure and abundance that exists within leaves.

This review describes immunolocalization studies of the tissue and cellular location of glutamine synthetase (GS; EC 6.3.1.2) and glutamate synthase (Fd GOGAT; EC 1.4.7.1 and NADH-GOGAT; EC 1.4.1.14) proteins in roots and leaves of rice (Oryza sativa L.) and barley (Hordeum vulgare L.). In rice, cytosolic GS (GS1) protein was distributed homogeneously through all cells of the root. NADH GOGAT protein was strongly induced and its cellular location altered by ammonium treatment, becoming concentrated within the epidermal and exodermal cells. Fd GOGAT protein location changed with root development, from a widespread distribution in young cells to becoming concentrated within the central cylinder as cells matured. Plastid GS protein was barely detectable in rice roots, but was the major isoform in leaves, being present in the mesophyll and parenchyma sheath cells. GS1 was specific to the vascular bundle, as was NADH GOGAT, whereas Fd GOGAT was primarily found in mesophyll cells. In barley roots, GS1 protein was found in the cortical and vascular parenchyma and its concentration was highest in N-deficient seedlings. Plastid GS protein was detected in both cortical and vascular cells, where different plastid forms, containing different concentrations of GS protein, were identified. In barley leaves, GS2 protein was detected in the mesophyll chloroplasts and GS1 was found in the mesophyll and vascular cells. N nutrition strongly influenced this distribution, with a marked increase in GS1 concentration in the vascular cells in response to nitrate and ammonium, and an increase in mesophyll GS2 concentration in nitrate-grown seedlings. Fd GOGAT protein was found in both the mesophyll and vascular plastids. These localization studies show that the GS/GOGAT cycle is highly compartmentalized at both the subcellular and cellular levels. Reasons for this compartmentation, and the roles of each isoform, are discussed.

Potato tuber mitochondria oxidizing malate respond to NAD' addition with increased oxidation rates, whereas mung bean hypocotyl mitochondria do not. This is traced to a low endogenous content of NAD' in potato mitochondria, which prove to take up added NAD'. This Macrae and Moorhouse (15). The presence of these two enzymes in the matrix space (7) causes pyruvate and oxaloacetate to accumulate in the medium during malate oxidation. The rates and products of malate oxidation by plant mitochondria vary in response to changes in the pH of the incubation medium (16). In addition, the oxidation of malate which is coupled to three sites of ATP formation is stimulated under certain conditions by NAD+ (6,9,20).With the aim of further clarifying the mechanisms of malate oxidation in intact plant mitochondria this report details the effect of NAD+ on malate oxidation in potato tuber and mung bean hypocotyl mitochondria. Some of these results have been presented elsewhere (17).MATERIALS AND METHODS Preparation of Mitochondria. Mitochondria from potato (Solanum tuberosum L.) tubers and etiolated mung bean (Vigna radiata L.) hypocotyls cut from bean seedlings grown for 5 days in the dark at 26 C and 60%o RH were prepared and purified by methods previously described (10). All operations were carried out at 0-4 C. Following purification, the mitochondria appeared to be virtually free from extramitochondrial contamination and had a high degree of membrane intactness as judged by electron microscopy and by low activities of the inner membrane and ' Supported in part by a grant from the Centre National de la Recherche Scientifique (ERA 847: Interactions Plastes-cytoplasme-mitochondries).

SummaryLittle is known about the genetic control of mitochondrial morphology and dynamics in higher plants. We used a genetic screen involving¯uorescence microscopic analysis of ethyl methane sulphonate (EMS)-mutated Arabidopsis thaliana seedlings expressing GFP targeted to mitochondria to isolate eight mutants displaying distinct perturbations of the normal mitochondrial morphology or distribution. We describe ®ve mutants with distinct and unique mitochondrial phenotypes, which map to ®ve different loci, not previously implicated in mitochondrial behaviour in plants. We have used a combination of forward and reverse genetics to identify one of the genes, friendly mitochondria (FMT ), a homologue of the CluA gene of Dictyostelium discoideum, which is involved in the correct distribution of mitochondria in the cell. The ®ve mutants constitute a powerful resource to aid our understanding of mitochondrial dynamics in higher plants.