Effects of post–silking low temperature on the physicochemical properties of waxy maize starch

Highlights

• Starch physicochemical properties of waxy maize under two temperatures were investigated.

• Starch granule size and amylopectin chain length were reduced by post-silking low temperature.

• Relative crystallinity was decreased by post-silking low temperature.

• Reduced viscosity and increased retrogradation under LT were caused by changed starch structure.

Abstract

Low temperature (LT) at late growth stages is an important abiotic stress that affects the grain end–use quality of summer maize. In the present work, two experiments were conducted to study the effects of LT on the structural and functional properties of starches using two waxy maize hybrids (‘Suyunuo5’ and ‘Yunuo7’). In field trial, the plants were sown on July 1 (normal sowing date) and August 1 (late sowing date). In pot trial, the plants were sown on July 1, grown at natural environment till silking, and suffered two post–silking temperatures (normal temperature and LT were set as 28/20 and 23/15 °C, respectively). The result showed that the starch was composed of more small granules with oval polytope when sown late (August 1) or subjected to LT post–silking. The LT–stressed starch presented high proportion of short amylopectin chains and low relative crystallinity (RC). LT reduced the pasting viscosity, gelatinization enthalpy, and gelatinization temperatures but increased the retrogradation tendency. In conclusion, the low pasting viscosity and high retrogradation tendency under LT condition were caused by the decreased granule size, amylopectin chain length, and RC.

Introduction

Low temperature (LT) is an important abiotic stress that seriously affects plant growth and development and influences crop productivity and quality [1], [2], [3], [4]. LT considerably affects enzymatic activities related to starch biosynthesis and enhances granule bound starch synthase I [1]; therefore, it increases the amylose–amylopectin ratio [5]. Additionally, amylopectin chain–length is increased by the low activities of starch synthase and starch branching enzyme, which are responsible for amylopectin branching and elongation [5], [6], [7]. LT decreases the activities of starch synthase, sucrose synthase, and invertase, which results in a decrease in the contents of sucrose and many amino acids in chickpea [8]. LT also induces hormonal imbalance, reduces carbohydrate supply, increases grain abortion, and decreases grain filling rate [9]. Changes in starch metabolic enzymes and hormones affect grain quality [10]. LT during grain filling reduces peak, trough, and final viscosities [11], as well as the gelatinization temperatures, enthalpy, and deteriorate the grain quality of rice [12]. LT declines grain appearance and milling and cooking quality traits but enhances chalkiness, broken rice, and gelatinization temperature; the most responsive period of rice quality to extreme temperatures occurs during the second week of post–heading [13]. LT increases the number of mid–sized and large granules with irregular shape and reduces the relative crystallinity (RC) of rice grains [12]. Labuschagne et al. [14] suggested that LT at the grain–filling stage reduces the total starch content and increases the amylose content in different wheat cultivars. LT increases 2–AP biosynthesis, cooked rice elongation percentage, and amylose content [15]. Aoki et al. [16] reported that bread firming is slowed in rice flour filled at LT. In general, LT has a positive effect on the protein concentrations and processing quality of wheat but has a negative effect on starch concentration and appearance quality [17].

High temperature is a normal climatic condition during summer and affects maize plant growth, development, yield, and quality. Adjusting the sowing date can improve maize adaption to climate change; optimal sowing date can lead to high yield and good quality [18]. In China, the postponement of the sowing date for summer maize is a simple and efficient cultivation option to escape or avoid heat stress, but this method increases the probability of cold stress [19]. Study on maize in North China Plain reported that grain yield was affected by the sowing dates (mid–March to mid–July) and that plants suffered from high temperature (>30.2 °C) and LT (<20.7 °C) during grain filling under early and late sowing conditions, respectively, and ultimately decreased grain weight [20]. The sowing date of summer maize ranges from late May to early August in Southern China. Sowing early or late can induce heat or cold stress at later growth stages, respectively. Previous study focused on the effects of heat stress on the physicochemical properties of maize starch [21]. In comparison to normal temperature (AT, 25 °C), LT (16 °C) during grain filling disturbed hormone balance, decreased enzymatic activities related to starch biosynthesis during the mid–grain filling period, and limited starch accumulation [10]. However, the effect of LT stress on the physicochemical properties of maize remains unknown. The starch of waxy maize, a special maize type, is composed of nearly pure amylopectin, which endows high viscosity, high transmittance, high stability, and low retrogradation [22]. The starch physicochemical properties of waxy maize are affected by sowing dates [23], [24]. We hypothesized that post–silking LT affects the structural and functional properties of waxy maize starch. We verified this hypothesis by estimating the physicochemical properties of waxy maize starch in response to LT at the late growth stage. The results can provide a basis for the efficient utilization of waxy maize starch in areas that suffer LT at the late growth stage.