Effects of Elevated Temperature and Reduced Water Uptake on Enzymes of Starch Synthesis in Developing Wheat Grains

Abstract

The mechanism of temperature regulation of endosperm development has been investigated by studying the effects of two temperature regimes on starch deposition and starch synthase activity during grain development in two cultivars of wheat. Most of the starch synthase activity was present throughout development as the granule-bound form using ADPglucose as the principal substrate. That starch synthase may be a rate-limiting enzyme for accumulation of starch, and hence dry weight, is suggested by: (1) rates are proportionately less in the cultivar with the lower final endosperm dry weight; (2) at elevated temperatures when starch content and dry weight are reduced, starch synthase activity falls; (3) the rate of starch deposition calculated to be possible from measured rates of starch synthase activity is close to the observed rate of starch deposition. On the other hand, it was concluded that it is not lack of starch synthase activity that causes termination of starch deposition, since activity is maintained well after starch deposition has ceased. Using the same two wheat cultivars, grown as detached ears in liquid culture, the effects of reduced endosperm water content, induced by the presence of polyethylene glycol in the culture medium, were investigated. Endosperm starch synthase activity was unaffected but ADPglucose pyrophosphorylase activity was greatly reduced, suggesting a possible role in the termination of starch synthesis.

The purification and characterisation of the two forms of soluble starch synthase from developing pea embryos

“…A reduction in the accumulation of starch at high temperatures appears to be a widespread phenomenon in starch-storing organs (cereals, Chowdhury and Wardlaw 1978;potato tubers, Krauss and Marschner 1984). It has been suggested that the decrease in the activity of soluble starch synthase in wheat endosperm at elevated temperatures may be responsible, at least in part, for reductions in the rate of starch synthesis which have been reported to occur over the same temperature range (Caley et al 1990).…”

“…Because of reports of the instability of soluble starch synthase at high temperatures, and the implication of this phenomenon in the sensitivity of starch synthesis as a whole to high temperature (Ozbun etal. 1971a;Rijven 1986;Caley et al 1990), we have examined the thermostability of purified isoforms of this enzyme from pea embryos.…”

The Effects of Environmental Conditions on the Structural Features and Physico-chemical Properties of Starches

“…This results in fewer and smaller granules per unit volume of tissue. In wheat, elevated growth temperature reduces grain filling by inactivating key enzymes and restricting metabolic interconversions [42][43][44][45]; soluble starch synthase is probably the most thermo-sensitive (regulated) enzyme [46][47][48]. In barley, growth temperature has also been studied with respect to the biochemical regulation of starch synthesis [49].…”

Desempenho de genitores e populações segregantes de trigo sob estresse de calor

“…Yang et al (2002) verificaram que o peso médio de grãos declinou de 55,6 para 27,9 mg quando a temperatura foi elevada de 20/15 °C (dia/noite) para 30/25°C(dia/noite), redução de 49,8% sobre a expressão deste caráter. De fato, a síntese de amido no endosperma é interrompida pela inibição de diversas enzimas sob temperaturas altas, resultando em grãos com pontos esbranquiçados e foscos (Caley et al, 1990) Para prela e ribeiro (2002), um dos métodos mais utilizados para relacionar a temperatura do ar com o desenvolvimento e/ou crescimento das plantas é o da soma térmica ou graus-dia acumulados, pois não depende da época e do local de plantio. Segundo hamada e pinto (2001), há poucos estudos utilizando método dos graus-dia a fim de estimar a duração das fases fenológicas de trigo no Brasil, sendo oportunos estes estudos como subsídios aos trabalhos de zoneamento agrícola.…”