Embryo physiological responses to cold by two cultivars of oat during germination

Physiological responses and mechanisms triggered by cold are known for seed lings and mature plants, but are poorly understood for early developmental stages. Previous research on seedlings of two oat (Avena sativa L.) cultiva rs, 'Ot220xOmihi' (Ot220) and 'America', characterized them as cold toleran t and cold sensitive, respectively. This study investigates if cold respons es during seed germination, at the phases of coleorhiza (1-2 mm elongation) and radicle (10 mm elongation) emergence, are similar to those described f or these same cultivars at later developmental stages. Accumulation of cryo protective solutes, degree of fatty acid unsaturation, oxygen consumption, and oxidative damage were evaluated. From imbibition until coleorhiza or ra dicle protrusion, seeds were maintained in darkness at constant temperature s of 17 degreesC (control) or 3 degreesC (low temperature treatment). Numbe r of days to initiate germination (Di), days to reach 50% germination (D-50 ), and lethal temperature for 50% of the population (LT50) were determined. At 3 degreesC, Di and D-50 occurred significantly earlier in Ot220. LT50 v alues, however, did not differ significantly. At the coleorhiza stage, embr yos of both cultivars at 3 degreesC accumulated soluble sugars; fructans ac cumulated only in Ot220. At the radicle stage, proline and fructans accumul ated in both cultivars. No clear differences between cultivars were detecte d with regard to the relative composition or degree of unsaturation of fatt y acids at tow temperatures. However, at 3 degreesC, Ot220 exhibited greate r oxygen consumption and catalase activity than did America. Significant li poperoxidative damage occurred only in America. As for the seedling stage, Ot220 can be characterized as cold tolerant and America as cold sensitive d uring germination. Responses to low temperature at this early development s tage, however, were indicative of higher metabolic-rates and less oxidative damage, rather than an accumulation of cryoprotective solutes.