INSTYTUT DENDROLOGII

The role of LEA proteins and sHSP in woody plant seeds

The experimental materials consisted of woody plant seeds that differ in tolerance to dehydration. Stress proteins like late embryogenesis abundant (LEA) and small heat shock proteins (sHSPs) were analyzed in 3 categories of seeds: orthodox (desiccation tolerant: Acer platanoides L.), recalcitrant (drought tolerant: Acer pseudoplatanus L., Acer saccharinum L., Castanea sativa Mill.) and intermediate (Fagus sylvatica L.). Beech seeds were analyzed at various developmental stages; during maturation, storage, germination and desiccation. Developing beech seeds became desiccation tolerant at 16 WAF. Decreasing electrolyte leakage and increasing germination capacity after previous drying indicated that desiccation tolerance was acquired. Apart from mass maturity, the presence of heat-stable proteins, 44 kDa dehydrin accumulation, and the peak of ABA content were measured according to desiccation tolerance acquisition. Decreased amounts of LEA (late embryogenesis abundant) proteins as well as reduced content of total soluble protein were detected during prolonged storage. The amounts of soluble proteins in embryonic axes and nearly all detected dehydrins and LEA-like proteins were correlated with germination capacity. Only one heat-stable dehydrin, with a molecular mass of approximately 44 kDa, maintained a relatively high amount. Moreover, a small heat shock protein with molecular mass of approximately 22 kDa was identified. Large amounts of this protein were observed in the oldest seeds, especially in embryonic axes. The identified proteins play a protective role during water deficit and storage participating in glassy state formation. Germinating beech seeds after drying presented 100% in cotyledons. The top of the root proved to be the most sensitive part of seed for desiccation. In cotyledons, LEA proteins and sHSP were detected only after drying. In watered radicles both 44 kDa dehydrin and 22 kDa sHSP were identified at first stages of germination, then they declined rapidly and disappeared. After drying these two proteins were present during all studied stages and their content decreased because of the lengthening of the radicles. The content of 44 kDa dehydrin was correlated with the resistance to drying the individual parts of root. In beech seeds dehydrins were detected in amyloplasts and could be connected with membranes. In recalcitrant seeds dehydrin appeared only in embryonic axes after drying (induced expression). However numerous LEA-like proteins were detected, which can protect seeds during drought stress. In orthodox seeds dehydrins weer present in e. axes and cotyledons of fresh and dried seeds (constitutive expression). 22 kDa sHSP was detected in all studied orthodox, intermediate and recalcitrant seeds on every stage of development and can be related to universal plant response to abiotic stress.