Changes in the ascorbate-glutathione system during storage of recalcitrant seeds of Acer saccharinum L.

Two seed lots of Acer saccharinum (recalcitrant), with an initial moisture content of 50% and 55%, were stored at +3oC for 6 months. After this time, their viability (measured as germinability) reached 100% and 30%, respectively. In embryo axes and cotyledons extracted from seeds, two major low molecular antioxidants were assayed: ascorbate (ASA and DHA) and glutathione (GSH and GSSG); and activities of enzymes of the ascorbate-glutathione cycle were measured: ascorbate peroxidase (APO) (E.C. 1.11.1.11), monodehydroascorbate reductase (MR) (E.C. 1.6.5.4), dehydroascorbate reductase (DHAR) (E.C. 1.8.5.1), and glutathione reductase (GR) (E.C. 1.6.4.2.). GSH and GSSG contents of embryo axes of stored seeds decreased, as compared to the control (fresh, non-stored seeds), but a larger decrease was observed in seeds with 30% viability. In cotyledons, a particularly high increase in the GSH content in relation to the control was observed in seeds with 100% viability, while the GSSG content was significantly lower in both stored seed lots than in the control. The ASA level was twice as high in seeds with 30% viability as in the control, both in embryo axes and in cotyledons. The activity of enzymes of the ascorbate-glutathione cycle was higher in embryo axes than in cotyledons. In embryo axes of seeds with 100% viability, enzyme activities were slightly lower than in the control, while in those of seeds with 30% viability, their activities were higher than in the control. The observed changes in activities of enzymes of the ascorbate-glutathione cycle and in ascorbate and glutathione levels suggest that the stored seeds of A. saccharinum have an active antioxidant system, which plays an important role in maintaining their viability during storage

Dehydration Sensitivity at the Early Seedling Establishment Stages of the European Beech (Fagus sylvatica L.)

Shortage of water is a limiting factor for the growth and development of plants, particularly at early developmental stages. We focused on the European beech (Fagus sylvatica L.), which produces seeds and further seedlings in large intervals of up to ten years. To explore the beech seedling establishment process, six stages referring to embryo expansion were studied to determine sensitivity to dehydration. The characterization of the response of elongating embryonic axes and cotyledons included a viability test before and after dehydration and measurement of the amounts of electrolyte leakage, concentration, and arrangement of storage materials, changes in chaperone proteins related to water deficit, and accumulation of hydrogen peroxide and superoxide anion radicals. Elongating embryonic axes and cotyledons differed in water content, dehydration rates, membrane permeability before and after dehydration, protein, and lipid decomposition pattern, and amount of 44-kDa dehydrin and 22-kDa small heat shock protein (sHSP). Protruding embryonic axes were more sensitive to dehydration than cotyledons, although dehydration caused transient reinduction of three dehydrin-like proteins and sHSP synthesis, which accompany desiccation tolerance. Extended deterioration, including overproduction of hydrogen peroxide and depletion of superoxide anion radicals, was reported in dehydrated embryonic axes longer than 10 mm characterized by highly elevated cellular leakage. The apical part elongating embryonic axes consisting of the radicles was the most sensitive part of the seed to dehydration, and the root apical meristem area was the first to become inviable. The effects of severe dehydration involving ROS imbalance and reduced viability in beech seedlings with embryonic axes longer than 10 mm might help to explain the difficulties in beech seedling establishment observed in drought-affected environments. The conversion of environmental drought into climate-originated oxidative stress affecting beech seedling performance is discussed in this report

The involvement of the mitochondrial peroxiredoxin PRXIIF in defining physiological differences between orthodox and recalcitrant seeds of two Acer species

Ratajczak E, Stroeher E, Oelze M-L, Kalemba EM, Pukacka S, Dietz K-J. The involvement of the mitochondrial peroxiredoxin PRXIIF in defining physiological differences between orthodox and recalcitrant seeds of two Acer species. Functional Plant Biology. 2013;40(10):1005-1017.Norway maple (Acer platanoides L., orthodox) and sycamore (Acer pseudoplatanus L., recalcitrant) belong to the same genus and grow under similar climatic conditions, but their seeds differ in their tolerance to desiccation. The initial water content (WC) of the seeds used in this study was 50%, and they were dried to 40, 20 and 7%. The mitochondrial peroxiredoxin IIF (PRXIIF) was identified in seeds of both species by immunoblotting. Semiquantitative RT-PCR analyses indicated that the transcript level of PRXIIF in both types of seeds increased during different stages of desiccation and was higher in seeds of Norway maple than in sycamore. General proteome analyses showed important differences between orthodox and recalcitrant seeds. In sycamore seeds that had been desiccated to a 7% WC, the number of protein spots and the levels of those spots were lower than in desiccation-tolerant Norway maple seeds. Post-translational modifications of PRXIIF in seeds at a 50% WC were detected via 2D electrophoresis and subsequent western blot analysis. The detected shift in the pI values (+/- 0.3) in A. pseudoplatanus was possibly caused by phosphorylation because several potential phosphorylation sites were predicted in silico for that protein. The gene and amino acid sequences were obtained and aligned with known sequences of other plant PRXIIF genes and proteins. High values of sequence identity were noted between the PRXIIF protein sequences of Acer species, Populus trichocarpa Torr. & A. Gray and Arabidopsis thaliana (L.) Heynh. The involvement of PRXIIF in defining the physiological differences between desiccation-tolerant and desiccation-sensitive Acer seeds is discussed in the context of its role in mitochondrial redox homeostasis