Location of deterioration within garden pea(Pisum sativum)cotyledons is associated with the timing of exposure to high temperature

Abstract

Plants of two garden pea (Pisum sativum) cultivars ('Alderman' and 'Early Onward') were exposed to high temperature (30/25°C; day/ night, 12h each) at five different stages (during seed development, S1-S2; at physiological maturity (PM), S3; and during seed maturation, S4-S5) to determine the effect of high temperature on seed quality parameters and the location of deteriorated tissues within the cotyledons at each stage. High temperature applied at the beginning of seed filling (S1) significantly decreased thousand seed weight in both cultivars, and germination in 'Alderman'. Hollow heart was significantly increased in both cultivars when high temperature was applied at the rapid seed fill stage (S2), but not when applied at other stages. There was a significant cultivar by treatment duration interaction at S2 for hollow heart incidence-'Alderman' was more susceptible to hollow heart than 'Early Onward'. Single seed conductivity was significantly increased by high temperature at S4 and S5 in both cultivars, and in 'Alderman' high temperature at S1-S3 also increased leachate from the seeds. cells within the cotyledons differed depending on the timing of the high temperature treatment. Treatment at S2 resulted in deterioration at the adaxial surface of the cotyledons; with treatments at S4-S5, deterioration occurred at the abaxial cotyledonary surface. The results suggest that the susceptible portion of pea cotyledons to high temperature during pre-PM stages is different from that during post-PM stages, and that the hollow heart test and the conductivity test detect deterioration located at different positions within the cotyledons. This may lead to the occasional inconsistency between the two tests.

Effects of elevated CO2and temperature on seed quality

“…To answer this question accurately will require substantially more research in order to determine the critical periods during seed development when seeds are sensitive to environmental stresses, and for temperature, how this interacts with the duration of exposure to elevated temperatures which are deleterious to seed quality. For example, Shinohara et al (2006b) found that during the rapid seed filling stage in pea, a temperature of 30/25°C for 2 days (120°Ch at Tb = 25°C) did not induce hollow heart, but 4 days induced hollow heart in one cultivar (see Table 2), and 6 days (360°Ch) induced the condition in both cultivars used (0•43 in cvar Alderman and 0•23 in cvar Early Onward). From the information that is available, it can be concluded that predicted environmental changes will lead to the increased occurrence of loss of seed quality, particularly seed vigour and possibly germination.…”

“…While there were cultivar differences, for one cultivar there was a linear increase in hollow heart incidence as the degree hours (°Ch) increased. In a follow-up controlled environment study, Shinohara et al (2006b) confirmed this result, by demonstrating that exposure to day/night temperatures of 30 and 25°C, respectively, for 4 days (240°Ch, Tb = 25°C) at the green-wrinkled pod stage induced hollow heart, but exposure to the same conditions at the beginning of seed fill (> 800 mg/g SMC), PM (550-650 mg/g SMC) or after PM did not (Table 2). Single-seed conductivity (which is an indicator of cell membrane integritysee Powell 2006) was increased only after exposure of the developing seeds to the high temperature at or after PM, and not before (Table 1).…”

“…Grass & Burris (1995) reported that high-temperature stress of the parent plant caused mitochondrial degeneration and reduced adenosine triphosphate (ATP) accumulation, energy levels and rates of oxygen uptake in imbibing wheat embryos (Table 3), providing clear evidence for metabolic changes at the mitochondrial level in early seed germination in response to heat stress during seed development and maturation. High temperatures during reproductive growth increase seed cell membrane damage (Nilsen & Orcutt 1996;Shinohara et al 2006b) so that electrolyte leakage from seeds is increased (Castillo et al 1994;Spears et al 1997;Shinohara et al 2006b). High leachate conductivity in pea has been associated with dead/deteriorating tissue on the abaxial surface of the cotyledons (Powell 1985;Shinohara et al 2006b), and on the adaxial cotyledonary surface for hollow heart (Don et al 1984;Shinohara et al 2006b).…”

“…High temperatures during reproductive growth increase seed cell membrane damage (Nilsen & Orcutt 1996;Shinohara et al 2006b) so that electrolyte leakage from seeds is increased (Castillo et al 1994;Spears et al 1997;Shinohara et al 2006b). High leachate conductivity in pea has been associated with dead/deteriorating tissue on the abaxial surface of the cotyledons (Powell 1985;Shinohara et al 2006b), and on the adaxial cotyledonary surface for hollow heart (Don et al 1984;Shinohara et al 2006b). However, temperature stress also results in damage to the shoot apical meristem of the embryonic axis (Fu et al 1988;Senaratna et al 1988).…”

“…Effect of high temperature (30/25°C) for 4 days at different stages of seed development and maturation in two cultivars of pea (Pisum sativum L.) on seed quality components (adapted fromShinohara et al 2006b) …”