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The initiation of starch granule formation is still poorly understood. However, the soluble starch synthase 4 (SS4) appears to be a major component of this process since it is required to synthesize the correct number of starch granules in the chloroplasts of Arabidopsis thaliana plants. A yeast two-hybrid screen allowed the identification of several putative SS4 interacting partners. We identified the product of At4g32190 locus as a chloroplast-targeted PROTEIN INVOLVED IN STARCH INITIATION (named PII1). Arabidopsis mutants devoid of PII1 display an alteration of the starch initiation process and accumulate, on average, one starch granule per plastid instead of the five to seven granules found in plastids of wild-type plants. These granules are larger than in wild-type, and they remain flat and lenticular. pii1 mutants display wild-type growth rates and accumulate standard starch amounts. Moreover, starch characteristics, such as amylopectin chain length distribution, remain unchanged. Our results reveal the involvement of PII1 in the starch priming process in Arabidopsis leaves through interaction with SS4.

Transitory starch plays a central role in the life cycle of plants. Many aspects of this important metabolism remain unknown; however, starch granules provide insight into this persistent metabolic process. Therefore, monitoring alterations in starch granules with high temporal resolution provides one significant avenue to improve understanding. Here, a previously established method that combines LCSM and safranin-O staining for in vivo imaging of transitory starch granules in leaves of Arabidopsis thaliana was employed to demonstrate, for the first time, the alterations in starch granule size and morphology that occur both throughout the day and during leaf aging. Several starch-related mutants were included, which revealed differences among the generated granules. In ptst2 and sex1-8, the starch granules in old leaves were much larger than those in young leaves; however, the typical flattened discoid morphology was maintained. In ss4 and dpe2/phs1/ss4, the morphology of starch granules in young leaves was altered, with a more rounded shape observed. With leaf development, the starch granules became spherical exclusively in dpe2/phs1/ss4. Thus, the presented data provide new insights to contribute to the understanding of starch granule morphogenesis.

In human diet, the products of starch digestion are a major energy source. Starch is stored as water insoluble granules composed of amylose and amylopectin. The susceptibility of starch granule to digestive enzymes is affected by starch granule size, shape, and composition. In this study, starch characteristics and in vitro enzymatic hydrolysis in three rice (Oryza sativa L.) mutants (RSML 184, RSML 278 and RSML 352) with similar amylose concentration (24.3–25.8%) was compared to parent ADT 43 (21.4%). The three mutants had reduced thousand grain weight and starch concentration but higher protein and dietary fiber concentrations. The mutant RSML 352 had small starch granules and reduced short glucan chains [Degree of polymerization (DP) 6–12] compared to the other two mutants (RSML 184 and RSML 278). The mutant RSML 352 had the highest hydrolytic index (HI) and least concentration of resistant starch (RS) compared to the other two mutants and parent rice ADT 43. The two rice mutants (RSML 184 and RSML 278) had reduced HI and increased RS concentration than the parent ADT 43. The results showed that starch granule size and amylopectin structure influence starch enzymatic digestibility and RS concentration.

The aim of this study was to determine the effects of different varieties, year and location of growing, and their interactions, on wheat starch and flour properties, and to analyze the relationship between these attributes. The set of 92 wheat samples chosen to cover wide ranges in the parameters commonly used for the assessment of wheat flour and starch properties was reduced to a representative set of 27 samples. The obtained results showed that wheat variety and year significantly affected maximum viscosity (MV), alpha–amylase activity (AA), amylose content (AM), volume proportion of A-, B- and C-starch granules, as well as gelatinization temperatures, while the year and location by year interaction had a significant effect on the falling number (FN). In this work, a number of significant correlations were observed among analyzed starch and flour properties. AA was mostly influenced by the changes in packing of starch granules and granule size distribution, while gelatinization temperatures were affected by particle size distribution. Additionally, when testing the suitability of the parameters for the estimation of alpha–amylase activity, it was determined that Amylograph was more reliable in predicting alpha–amylase than FN because it provided a better description of the state of flour starch complex.

Traditional rice varieties have been neglected for human consumption and genetic improvement research. In the previous two decades, rice breeding initiatives have mostly concentrated on yield and yield contributing traits. In this study, 21 rice landraces were collected from various locations in Tamil Nadu, India, and their grain composition and enzymatic digestibility were evaluated. The rice landraces investigated showed significant differences in in vitro starch digestibility in meal and pure starch. Significant differences were also found in total dietary fiber (2.8–8.7), protein (6.2–12.3), fat (0.6–3.2%), and total phenol (1.3–6.9 mg GAE g-1). Katta Samba had the lowest hydrolysis index (HI) in both pure starch and meal samples. Except for Katta samba and Pavizham, B1 chains contributed more than 50% of total amylopectin in all landraces. The proportion of small (5 μm) starch granules ranged from 19.6 to 42.0%, while the proportion of medium (5–15 microns) size granules was between 52.6 and 79.8%. The percentage of large granules above 15 microns varied substantially from 0 to 21.0%. The principal component analysis showed that the first seven principal components explained 86.3% of the total variation. This splits the landraces into three subgroups with three outliers. The rice landraces that were found to have good grain qualities could be directly used for consumption or used in pre-breeding to develop rice varieties suitable for different end users.

Maize starch is an important source of industrial starch in the world, and its production is seriously affected by water deficit. Waxy maize starch is composed of nearly pure amylopectin, which endows with its high economic value. The effects of mild, moderate, and severe drought stresses during grain filling on the structural and functional properties of waxy maize starch were evaluated using two hybrids as materials. In general, the starch granule size enlarged, the branching degree decreased, and amylopectin chain length and relative crystallinity increased when both hybrids suffered post‐silking water deficit in 2 years. Meanwhile, the influence of drought degree on these starch structures depended on the hybrid and year. Peak, breakdown, and setback viscosities gradually decreased with the severity of water shortage, and trough and final viscosities were the lowest under severe drought conditions. Gelatinization enthalpy gradually decreased with the water supply decrease, and gelatinization temperatures showed an opposite trend and were the highest during severe drought. Correlation analysis indicated that the decrease in pasting viscosities and gelatinization enthalpy and the increase in gelatinization peak temperature may be due to the high proportion of low‐molecular‐weight amylopectin, low proportion of DP 25–36 chains and large granule size of starch. Furthermore, drought stress was easily destroyed the starch structure of JKN2000 and the pasting viscosities and gelatinization enthalpy of SYN5. In conclusion, water deficit during grain filling affected the structural and physicochemical properties of waxy maize starch. The lowest pasting viscosities and gelatinization enthalpy and the highest gelatinization temperatures were observed when these plants suffered severe water shortage during grain filling.

Starch granules in potato tubers exist with varying sizes and size distribution in nature. In this study, both the tubers of seed potato (‘Lady Rosetta’) and true potato seed (TPS) (‘BARI TPS-1’) varieties were stored at 5°C for 0 to 4 months, and the changes in the starch break down were analyzed physiologically and histologically to investigate how cold storage affects the starch break down. Although the starch content of both varieties reduced during cold storage, the reduction of starch content in ‘BARI TPS-1’ was higher than that of ‘Lady Rosetta’. However, both volume and ovality (length:width) of starch granule did not change significantly throughout the storage period irrespective of variety, suggesting a non-uniform breakdown of starch granules. Scanning Electron Microscope (SEM) images of starch granule showed non-uniformed deformation and enlarged cavity or hole along the storage period, which indicated that starch breakdown occurred at a specific part of starch granule rather than peripherally and penetration would be deeper in ‘BARI TPS-1’ than that of ‘Lady Rosetta’. However, there was no significant change in granule size distribution in spite of rapid degradation of amylopectin percentage in ‘BARI TPS-1’ than that of ‘Lady Rosetta’, suggesting more susceptibility of ‘BARI TPS-1’ to starch degrading enzyme and higher enzymatic action would cause deeper penetration in ‘BARI TPS-1’ than that of ‘Lady Rosetta’.

The application of exogenous plant growth regulator can improve plant resistance to drought stress. The effects of application of exogenous cytokinin (CTK), brassinolide (BR), or gibberellic acid (GA) at the silking time on the grain quality of two waxy maize hybrids under drought stress at grain formation stage were studied. Grain weight of both hybrids was unaffected by exogenous phytohormones under control conditions but increased under drought conditions with the application of BR. The grain starch content in response to drought varied with hybrid and phytohormone. Starch granule size and protein content in grains were increased by drought under all conditions, but various phytohormones exerted different forms of influence. The starch λmax in Yunuo7 was unaffected by single or interaction of phytohormones and water deficit, λmax in Jingkenuo2000 with BR was unaffected but with CTK or GA increased by drought. Relative crystallinity was reduced by drought without the application of phytohormone, but with phytohormones in response to drought it was different. Flour peak viscosity was reduced by drought. The value was increased with BR spraying under control and drought conditions. Retrogradation percentage under drought conditions was unaffected by exogenous phytohormones in Jingkenuo2000. In Yunuo7, retrogradation percentage was unaffected by BR but reduced by CTK and GA. In conclusion, spraying phytohormones at the silking stage can affect grain weight and starch quality, grains with a sticky taste can be improved by applying BR, and grains with low retrograde tendency can be produced by applying CTK.

The combined stress of waterlogging and shading (WS) caused by continuous rain threatens the production of high-quality weak gluten wheat in China (Triticum aestivum L.). To evaluate its influences on wheat quality formation, Yangmai 158 was chosen to be subjected to WS at 0–7 days after anthesis (DAA, WS0–7), 8–15 DAA (WS8–15), 16–23 DAA (WS16–23), and 24–31 DAA (WS24–31), respectively, with non-stressed plants as control (Non-WS). Compared with Non-WS, WS reduced the amylopectin content and enhanced amylose content in the mature grains. WS enhanced the number and surface but reduced the size of the starch granules. The number, volume, and surface area percentages of B-type starch granules were enhanced, and the number and volume percentages of A-type starch granules were reduced by WS. The peak viscosity and gelatinization temperature were enhanced and the low viscosity and final viscosity were decreased by WS. WS applied at the mid-grain-filling stage (WS8–15 and WS16–23) had greater modification on the starch content, granule size distribution and pasting characteristics than that applied at early (WS0–7) or late (WS24–31). The changes of starch pasting characteristics under WS had a significant correlation with the amylase and amylopectin content, amylase/amylopectin, and the ratio of the volume percent of B-type and A-type starch granules.

This study investigated the effect of high temperature and drought (during grain-filling) on the quality and components yield of five winter wheat varieties. Drought and drought + heat were found to have a much greater influence on the yield and quality than heat stress alone. Averaged over the varieties, the yield losses were 57% after drought, 76% after drought + heat, and only 31% after heat stresses. The reductions in the unextractable polymeric protein fraction and glutenin-to-gliadin ratio indicated a poorer grain yield quality, despite the higher protein content. Quality deterioration was observed after drought or drought + heat, while high temperatures alone resulted in no change or in a better ratio of protein components. A significant negative correlation was observed between starch granule size and relative protein content after drought.