ABSTRACT
Arabidopsis thaliana has two isoforms of alpha-glycan phosphorylase (EC 2.4.1.1), one residing in the plastid and the other in the cytosol. The cytosolic phosphorylase, PHS2, acts on soluble heteroglycans that constitute a part of the carbohydrate pool in a plant. This study aimed to define a physiological role for PHS2. Under standard growth conditions phs2 knock-out mutants do not show any clear growth phenotype, and we hypothesised that during low-light conditions where carbohydrate imbalance is perturbed, this enzyme is important. Soil-grown phs2 mutant plants developed leaf lesions when placed in very low light. Analysis of soluble heteroglycan (SHG) levels showed that the amount of glucose residues in SHG was higher in the phs2 mutant compared to wild-type plants. Furthermore, a standard senescence assay from soil-grown phs2 mutant plants showed that leaves senesced significantly faster in darkness than the wild-type leaves. We also found decreased hypocotyl extension in in vitro-grown phs2 mutant seedlings when grown for long time in darkness at 6 °C. We conclude that PHS2 activity is important in the adult stage during low-light conditions and senescence, as well as during prolonged seedling development when carbohydrate levels are unbalanced.
Subject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/enzymology , Carbohydrate Metabolism , Gene Expression Regulation, Plant , Phosphorylases/metabolism , Arabidopsis/genetics , Arabidopsis/physiology , Arabidopsis/radiation effects , Arabidopsis Proteins/genetics , Cellular Senescence , Cytosol/enzymology , Darkness , Gene Knockout Techniques , Hypocotyl/genetics , Light , Mutation , Phenotype , Phosphorylases/genetics , Plant Leaves/metabolism , Plants, Genetically Modified , Polysaccharides/metabolism , Seedlings/growth & development , Stress, PhysiologicalABSTRACT
The majority of patients with a squamous cell carcinoma of the head and neck region (HNSCC) initially present in a locally advanced stage of the disease. Despite aggressive protocols in first-line treatment, some of these patients develop locoregional recurrences or metastases and are, in particular, extraordinarily challenging for the multidisciplinary treatment team. Therefore, among resectability and prior therapy, age, performance status and individual expectations of the patient have to be taken into account. Apart from surgical options like salvage surgery, chemotherapy and target therapy as well as reirradiation are possible treatment concepts. Unfortunately, most treatment options offer only little to no survival benefit.
