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Vegetative storage protein accumulation and physiological changes occurring within interior spruce seedlings Binnie, Sheila Catherine


The appearance and accumulation of vegetative storage proteins in nursery-grown Interior spruce seedlings (Picea glauca and P.engelmanni complex) was evaluated along with changes in seedling physiology. The 30 kD and 27 kD vegetative storage proteins (VSP) appeared after vegetative maturity (budset) and accumulated during the development of rest and the acquisition of cold hardiness. This trend was observed in bud extracts of three seedlots QL, EK, and PG as well as in the ambient treatment (natural fluctuations in photoperiod and temperature) of seedlot FIN. Stem and root tissue had similar accumulation patterns. Cold hardiness levels were measured using the electrolyte leakage method. This test is used annually to predict lifting date for cold storage of seedlings. Both the LT₅₀ (temperature for 50% electrolyte leakage) and the index of injury at -18°C (I.I.@-18°C) were low during early fall when storage protein levels were negligible in seedlot QL extracts. Afterwards, hardiness (I.I.@-18°C) was acquired and VSP accumulated until late October. Scanning densitometry of SDS-PAGE gels indicated that 15% of total protein was VSP by early November. These changes were accompanied by a decline in photosystem II activity, mitotic index, and dormancy. In seedlot QL, vegetative storage protein patterns were correlated to LT₅₀ (r = -0.972), photosystem II activity (r = -0.971), index of injury at -18°C (r = -0.900) and days to budbreak (r = -0.893). Seedlings stored at 4°C showed a slight decline in VSP and a decrease in seedling quality after 6 months of storage. Fall acclimation treatments -- long day 16 hr, 10°C days/5°C night (LD/Cold), short day <12 hr, 22°C day/18°C night (SD/Warm), and Ambient treatment -- indicated that prolonged short days caused maximum VSP accumulation within 30 days whereas under ambient conditions it took between 80 to 100 days. Cold temperatures may help cause the normal gradual increase in VSP and cold hardiness within buds. The SD/warm root bark was not as strongly influenced by daylength as bud and stem tissue because VSP accumulation was gradual. Although SD/warm seedlings accumulated maximum VSP levels, these seedlings remained dormant and did not become cold hardy. The results indicate that VSP accumulation and cold hardiness usually develop in parallel but they are unrelated. Under normal fall acclimation conditions, VSP accumulation and cold hardiness acquisition patterns are very similar; therefore, both could be used to predict lifting date in the future, with VSP used to predict lifting date and hardiness testing used to ensure cold hardiness.

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