PhD candidate University of California Davis Davis, California
Body of Abstract: Adaptation to abiotic stress is critical for the survival of perennial trees. Salinity affects plant growth and productivity by interfering with major biosynthetic processes, and the salinity detrimental effects may differ between different plant tissues. To understand how differences in protein and metabolite profiles among different plant tissues influence the survival adaptive strategy of trees to a changing environment, we compared the response(s) of leaf palisade (PAL) and midrib vascular (VAS) cells.
We used laser capture microdissection in clones of Populus tremula x alba (INRA 717 1-B4) to isolate PAL and VAS cells of plants that were exposed to salt 45 days after rooting. Plants were kept at 150 mM NaCl for 10 days (PSS, prolonged salt stress), followed by washing them and water with regular fertilization for 3 days (REC, recovery period). Both tissues from intermediate leaves were harvested for tissue-specific proteomics, primary metabolite profiling, and nitrogen assimilation enzymes. Stem tissue (ST) was also collected for total soluble protein analysis by SDS-PAGE.
Salinity treatments affected photosynthesis and stomata conductance, decreasing plant biomass at PSS. Tissue-specific proteomics indicated differential protein abundance changes in PAL and VAS tissues at both periods, suggesting tissue-specific functional specializations. It also indicated that salt treatments at PSS induced the accumulation of VAS-specific proteins associated with photorespiration. The decreased activities of NR and GDH suggested that the NH4+ accumulated in VAS tissue at PSS was photorespiration-dependent. Immunodetection and amino acid analyses demonstrated that NH4+ from photorespiration could be assimilated by chloroplastic GS2, yielding glutamine involved in N-reallocation in poplar trees. The total soluble proteins in ST showed the accumulation of bark storage proteins induced by the salinity treatments at PSS.
Collectively, our results suggest that salt-induced photorespiration in VAS tissue could mediate N-reallocation in poplar, an essential process for the adaptation of trees to adverse conditions.