Embryo Physiological Responses to Cold by Two Cultivars of Oat during Germination

Physiological responses and mechanisms triggered by cold are known for seedlings and mature plants, but are poorly understood for early developmental stages. Previous research on seedlings of two oat (Avena sativa L.) cultivars, `Ot220×Omihi' (Ot220) and `America', characterized them as cold tolerant and cold sensitive, respectively. This study investigates if cold responses during seed germination, at the phases of coleorhiza (1–2 mm elongation) and radicle (10 mm elongation) emergence, are similar to those described for these same cultivars at later developmental stages. Accumulation of cryoprotective solutes, degree of fatty acid unsaturation, oxygen consumption, and oxidative damage were evaluated. From imbibition until coleorhiza or radicle protrusion, seeds were maintained in darkness at constant temperatures of 17°C (control) or 3°C (low temperature treatment). Number of days to initiate germination (Di), days to reach 50% germination (D50), and lethal temperature for 50% of the population (LT50) were determined. At 3°C, Di and D50 occurred significantly earlier in Ot220. LT50 values, however, did not differ significantly. At the coleorhiza stage, embryos of both cultivars at 3°C accumulated soluble sugars; fructans accumulated only in Ot220. At the radicle stage, proline and fructans accumulated in both cultivars. No clear differences between cultivars were detected with regard to the relative composition or degree of unsaturation of fatty acids at low temperatures. However, at 3°C, Ot220 exhibited greater oxygen consumption and catalase activity than did America. Significant lipoperoxidative damage occurred only in America. As for the seedling stage, Ot220 can be characterized as cold tolerant and America as cold sensitive during germination. Responses to low temperature at this early development stage, however, were indicative of higher metabolic rates and less oxidative damage, rather than an accumulation of cryoprotective solutes.