Alterations in stem sugar content and metabolism in sorghum genotypes subjected to drought stress

Abstract

Changes in stem sugar concentrations due to drought stress at the early reproductive stage were studied in seven sorghum (Sorghum bicolor (L.) Moench) genotypes that differ in their stem sugar storage ability. Total sap sugar concentration increased in most genotypes. ANOVA showed a significant contribution of genotype and treatment to the variation in sugar levels. Two genotypes showed little variation in total sugar levels at the fifth internode from the peduncle and five genotypes showed significant increases in total sugar levels under drought; these groups were used to compare sugar metabolism. Drought led to a decrease in catabolic sucrose synthase activity in both groups. Invertase activities increased significantly in two genotypes and correlated with the increase in reducing sugar concentrations under drought. Stem sugar hydrolysis probably had a role in osmotic adjustment under drought and correlated with retention of sap volume. However, the activities of sugar-metabolising enzymes did not correlate with their gene expression levels. After resuming irrigation, grain yields, stalk yields and juice volume at physiological maturity were lower in plants recovering from drought stress compared with the controls. In some genotypes, there were similar losses in grain yields and stem sugars due to drought, indicating photoassimilate source limitation; in other genotypes, grain yield losses were less than stem sugar losses in drought-exposed plants compared with the controls, suggesting mobilisation of sugars from the storage internodes to the developing panicle. Accumulation of stem sugars appears to be an adaptive strategy against drought stress in some sorghum genotypes.

Identification of Putative RuBisCo Activase (TaRca1)—The Catalytic Chaperone Regulating Carbon Assimilatory Pathway in Wheat (Triticum aestivum) under the Heat Stress

“…Stem-reserves have been recognized as an important source of carbon for grain-filling, when photosynthesis is inhibited by the abiotic stresses such as heat and drought (Blum, 1998 ). Accumulation of sugars in stem has been predicted to be an adaptive strategy against different stresses, as found in different genotypes of sorghum under the drought stress (Quazi et al, 2014 ). Asthir and Bhatia ( 2014 ) have reported that HS causes built-up of total free sugars and decreases the starch content of grains in wheat.…”

Accumulation of stem sugar and its remobilisation in response to drought stress in a sweet sorghum genotype and its near‐isogenic lines carrying different stay‐green loci

“…; Qazi et al . ). Hence the adaptation of sorghum to drought through mobilisation of soluble sugars appears to be genotype‐dependent.…”

“…There are reports that stem reserves in sorghum contribute to grain filling under drought stress conditions, during which photosynthesis is inhibited (Blum et al 1997). However in some sorghum genotypes, the losses in grain yields and stem sugars due to drought stress were similar, indicating that the panicle and stems serve as independent sinks, both being affected by source limitation (Gutjahr et al 2013b;Qazi et al 2014). Hence the adaptation of sorghum to drought through mobilisation of soluble sugars appears to be genotype-dependent.…”

Sorghum bicolorcultivars have divergent and dynamic gene regulatory networks that control the temporal expression of genes in stem tissue

“…Since C4 grasses can be grown on marginal lands not suitable for most food crops, the high biomass producing vegetative tissues of sorghum, miscanthus, and sugarcane are desirable targets for engineering efforts aimed at producing and/or storing lipids (Carlsson et al , 2011; Sanjaya et al , 2011; Weselake, 2016a; Lima et al , 2017). For example, stem tissues engineered to divert energy from nonstructural carbohydrates into the lipid biosynthesis pathway through strategies such as increasing the supply of FAs, increasing TAG assembly activities, and blocking TAG breakdown pathways have resulted in higher amounts of TAGs accumulating in vegetative tissues (Papini-Terzi et al , 2009; Waclawovsky et al , 2010b; Sanjaya et al , 2011; Qazi et al , 2014; Sekhon et al , 2016). Other proof-of-concept studies for increasing TAGs in vegetative tissues have been performed in Arabidopsis thaliana, Brachypodium distachyon, Nicotiana benthamiana, Nicotiana tabacum , sugarcane ( Saccharum spp.…”