A pivotal role for starch in the reconfiguration of 14C-partitioning and allocation in Arabidopsis thaliana under short-term abiotic stress.

Plant carbon status is optimized for normal growth but is affected by abiotic stress. Here, we used 14C-labeling to provide the first holistic picture of carbon use changes during short-term osmotic, salinity, and cold stress in Arabidopsis thaliana. This could inform on the early mechanisms plants use to survive adverse environment, which is important for efficient agricultural production. We found that carbon allocation from source to sinks, and partitioning into major metabolite pools in the source leaf, sink leaves and roots showed both conserved and divergent responses to the stresses examined. Carbohydrates changed under all abiotic stresses applied; plants re-partitioned 14C to maintain sugar levels under stress, primarily by reducing 14C into the storage compounds in the source leaf, and decreasing 14C into the pools used for growth processes in the roots. Salinity and cold increased 14C-flux into protein, but as the stress progressed, protein degradation increased to produce amino acids, presumably for osmoprotection. Our work also emphasized that stress regulated the carbon channeled into starch, and its metabolic turnover. These stress-induced changes in starch metabolism and sugar export in the source were partly accompanied by transcriptional alteration in the T6P/SnRK1 regulatory pathway that are normally activated by carbon starvation

How environmental stress affects starch composition and functionality in cereal endosperm

Stressful environments can alter starch biosynthesis in cereal endosperm. The aim of this review is to carefully examine how starch functional properties are altered when plants encounter environmental parameters outside of the normal range. This is important because while growers and processors require grain yield stability and product uniformity this will be challenging in an era of variable weather patterns. Being able to predict the general physico-chemical nature of the starch as a result of growth status is a step towards the precise agriculture required for the 21st century. Variations in soil moisture and nutrient availability, ambient temperature, and atmospheric composition were all shown to affect starch functionality. Elevated temperature led to the most significant changes in both tropical and temperate cereals and amylose content was the most sensitive parameter under various environmental conditions. Genotypic variation appears to be a primary contributor for the response of cereal starches to environmental stress. Nonetheless, while a large amount of data from single controlled environmental stress experiment is currently available, comparably little is known about whether similar results would be achieved in multifactorial and large-scale settings. The challenges in terms of the need for more detailed experimental descriptions to lessen the study-to-study discrepancies of data and to enhance their interpretability were also discussed. © 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

Effect of salinity stress on growth and carbohydrate metabolism in three rice (<i>Oryza sativa </i>L.) cultivars differing in salinity tolerance

736-742 Rice seedlings cv. Khao Dawk Mali 105 (salt-sensitive), Luang Anan (moderately salt-tolerant) and Pokkali (salt-tolerant) were exposed to 0, 50, 100 and 150 mM NaCl for 9 d. Salinity stress caused reduction in leaf relative water contents in all cultivars. Shoot length of cv. Pokkali was least affected by salinity stress whereas increased root length in response to salinity stress was apparent in cvs. Khao Dawk Mali 105 and Luang Anan. Increased salinity level also caused reduction in fresh and dry weights in cvs. Khao Dawk Mali 105 and Luang Anan, but had no effect in cv. Pokkali except at 150 mM. Accumulation of total soluble sugars and sucrose in mature leaves were observed in cv. Khao Dawk Mali 105 exposed to high level of salinity whereas their concentrations in cvs. Luang Anan and Pokkali remained the same as control plants. Accumulation of sucrose in cv. Khao Dawk Mali 105 was suggested to be resulted from the alteration of photosynthate partitioning since the activities of sucrose phosphate synthase were not affected by salinity in this cultivar. On the contrary, salinity stress induced an accumulation of starch in cv. Pokkali. It is suggested that partitioning sugars into starch may involve in salinity tolerance by avoiding metabolic alterations. </smarttagtype

How rice Glycogen Synthase Kinase-like 5 (OsGSK5) integrates salinity stress response to source-sink adaptation: A proposed model.

We have previously shown that overexpression of GSK3-like kinase 5 in rice (OsGSK5) was associated with higher starch accumulation and better growth under severe salinity stress. Short-term 14CO2 feeding experiments suggested that OsGSK5 promoted higher flux to starch accumulation in the roots under this condition and that this mechanism may help to underscore the better growth characteristics observed. Here, we expand upon this hypothesis and consider (1) how OsGSK5 action could fit into a signaling model that integrates salinity stress to changes in starch metabolism, and (2) how this would facilitate whole plant physiological adaptations in source-to-sink partitioning. We also discuss additional functions of OsGSK5, necessary to support this adaptive mechanism

Yield, Grain Quality, and Starch Physicochemical Properties of 2 Elite Thai Rice Cultivars Grown under Varying Production Systems and Soil Characteristics

Rice production systems and soil characteristics play a crucial role in determining its yield and grain quality. Two elite Thai rice cultivars, namely, KDML105 and RD6, were cultivated in two production systems with distinct soil characteristics, including net-house pot production and open-field production. Under open-field system, KDML105 and RD6 had greater panicle number, total grain weight, 100-grain weight, grain size, and dimension than those grown in the net-house. The amounts of reducing sugar and long amylopectin branch chains (DP 25&ndash;36) of the RD6 grains along with the amounts of long branch chains (DP 25&ndash;36 and DP &ge; 37), C-type starch granules, and average chain length of the KDML105 were substantially enhanced by the open-field cultivation. Contrastingly, the relative crystallinity of RD6 starch and the amounts of short branch chains (DP 6&ndash;12 and DP 13&ndash;24), B- and A-type granules, and median granule size of KDML105 starch were significantly suppressed. Consequently, the open-field-grown RD6 starch displayed significant changes in its gelatinization and retrogradation properties, whereas, certain retrogradation parameters and peak viscosity (PV) of KDML105 starches were differentially affected by the distinct cultivating conditions. This study demonstrated the influences of production systems and soil characteristics on the physicochemical properties of rice starches

Overexpression of GSK3-like Kinase 5 (OsGSK5) in rice (Oryza sativa) enhances salinity tolerance in part via preferential carbon allocation to root starch

Rice (Oryza sativa L.) is very sensitive to soil salinity. To identify endogenous mechanisms that may help rice to better survive salt stress, we studied a rice GSK3-like isoform (OsGSK5), an orthologue of a Medicago GSK3 previously shown to enhance salinity tolerance in Arabidopsis by altering carbohydrate metabolism. We wanted to determine whether OsGSK5 functions similarly in rice. OsGSK5 was cloned and sequence, expression, evolutionary and functional analyses were conducted. OsGSK5 was expressed highest in rice seedling roots and was both salt and sugar starvation inducible in this tissue. A short-term salt-shock (150mM) activated OsGSK5, whereas moderate (50mM) salinity over the same period repressed the transcript. OsGSK5 response to salinity was due to an ionic effect since it was unaffected by polyethylene glycol. We engineered a rice line with 3.5-fold higher OsGSK5 transcript, which better tolerated cultivation on saline soils (EC=8 and 10dSm-2). This line produced more panicles and leaves, and a higher shoot biomass under high salt stress than the control genotypes. Whole-plant 14C-tracing and correlative analysis of OsGSK5 transcript with eco-physiological assessments pointed to the accelerated allocation of carbon to the root and its deposition as starch, as part of the tolerance mechanism