Activities of Key Enzymes in Sucrose-to-Starch Conversion in Wheat Grains Subjected to Water Deficit during Grain Filling

Abstract

This study tested the hypothesis that a controlled water deficit during grain filling of wheat (Triticum aestivum) could accelerate grain-filling rate through regulating the key enzymes involved in Suc-to-starch pathway in the grains. Two high lodgingresistant wheat cultivars were field grown. Well-watered and water-deficit (WD) treatments were imposed from 9 DPA until maturity. The WD promoted the reallocation of prefixed 14 C from the stems to grains, shortened the grain-filling period, and increased grain-filling rate or starch accumulation rate (SAR) in the grains. Activities of Suc synthase (SuSase), soluble starch synthase (SSS), and starch branching enzyme (SBE) in the grains were substantially enhanced by WD and positively correlated with the SAR. ADP Glc pyrophosphorylase activity was also enhanced in WD grains initially and correlated with SAR with a smaller coefficient. Activities of granule-bound starch synthase and soluble and insoluble acid invertase in the grains were less affected by WD. Abscisic acid (ABA) content in the grains was remarkably enhanced by WD and very significantly correlated with activities of SuSase, SSS, and SBE. Application of ABA on well-watered plants showed similar results as those by WD. Spraying with fluridone, an ABA synthesis inhibitor, had the opposite effect. The results suggest that increased grainfilling rate is mainly attributed to the enhanced sink activity by regulating key enzymes involved in Suc-to-starch conversion, especially SuSase, SSS, and SBE, in wheat grains when subjected to a mild water deficit during grain filling, and ABA plays a vital role in the regulation of this process.Starch in the endosperm of wheat (Triticum aestivum) is the major form of carbon reserves and comprises 65% to 75% of the final dry weight of the grain (Housley et al., 1981;Dale and Housley, 1986;Hurkman et al., 2003). Grain filling is therefore mainly a process of starch biosynthesis and accumulation. It is generally accepted that four enzymes may play a key role in this process: Suc synthase (SuSase; EC 2.4.1.13), ADP Glc pyrophosphorylase (AGPase; EC 2.7.7.27), starch synthase (StSase; EC 2.4.1.21), and starch branching enzyme (SBE; EC 2.4. 1.18;Hawker and Jenner, 1993; Ahmadi and Baker, 2001;Hurkman et al., 2003). SuSase catalyses the cleavage of Suc, the main transported form of assimilates in wheat plants (Fisher and Gifford, 1986), to form UDP-Glc and Fru, which is thought to be the first step in the Suc-to-starch conversion. Its activity is considered to be linked to sink strength in the developing rice (Oryza sativa) grain and tomato (Lycopersicon esculentum) fruit (Sun et al., 1992;Wang et al., 1993;Kato, 1995). AGPase produces ADP-Glc, the primer of the starch chain (Smith and Denyer, 1992), and is regarded as the rate-limiting enzyme in starch biosynthesis (Preiss, 1988). StSase, composed of both soluble and granule-bound isoforms, elongates the amylose and amylopectin chains (Déjardin et al., 1997). Soluble StSase (SSS) activity is reported to be positively correlate...

Photosynthetic carbon and nitrogen metabolism and the relationship between their metabolites and lipid peroxidation in dwarf bamboo (Fargesia rufa Yi) during drought and subsequent recovery

“…These results suggest that accumulated soluble sugar in dwarf bamboo under long-term severe drought is mainly due to the hydrolysis of previously stored starch rather than to de novo synthesis. Usually, drought can induce transformation of photosynthetic products by modulating the activities of key enzymes related to C metabolism (Yang et al 2004;Basu et al 2007). However, in our study, sucrose and soluble sugar in MD plants almost remained unchanged due to the relative changes in the activities of INV, SS, and SPS during the drought period (Figs.…”

“…Frozen leaves (0.2 g) were homogenized in pre-chilled water and extracted for 3 h in refrigerator. After centrifugation at 12,000g for 20 min, the supernatant was taken for determinations of INV and AMY by colorimetric method (Yang et al 2004;Zhang and Qu 2003).…”

Physiological Mechanisms of Poor Grain Growth in Abnormally Early Ripening Wheat Grown in West Japan

“…The remobilization and utilization of reserve materials for grain filling largely depends on the sink activity, i.e., starch biosynthesis in endosperm. Enhanced sink activity usually results in increased remobilization and grain filling rate (Yang et al, 2004). Therefore, the poor remobilization and poor utilization of culm reserves in AER plants at later phase of grain filling may be due to less sink demand, i.e., poor sink activity.…”

“…Therefore, the poor remobilization and poor utilization of culm reserves in AER plants at later phase of grain filling may be due to less sink demand, i.e., poor sink activity. Abnormally early ripening disorder is associated with high water status in the soil (Ikeda et al, 1994;Sano et al, 1994;Ishikawa et al, 1993) which may contribute to the poor sink activity by regulating the keys enzymes involved in sucrose-to starch conversion in endosperm (Yang et al, 2004).…”

Phenylalanine Ammonia-Lyase and Source-Flow-Sink Related Attributes in Rice Genotypes Subjected to High Night Temperatures

“…Besides, there is need to consider that SuSase is a main enzyme involved in the cleavage of sucrose in rice grains; because its importance in this event it have been considered as an important biochemical marker of sink activity (Kato, 1995;Liang et al, 2001;Zhang et al, 2014;You et al, 2016). In other way, AGPase has been also considered as a key enzyme participating in the starch synthesis, and its activity is associated with rate and quantity of starch synthesis (Ahmadi & Baker, 2001;Yang et al, 2004Yang et al, , 2017. AGPase at the early grain filling stage were decreased as result of supra-optimal temperatures (Ahmed et al, 2015); under other abiotic stress, as such water deficit, SuSase and AGPase had its activities levels influenced.…”