Real-Time Determination of Photosynthesis, Transpiration, Water-Use Efficiency and Gene Expression of Two Sorghum bicolor (Moench) Genotypes Subjected to Dry-Down.

Alessandra Fracasso,Adriano Marocco,Stefano Amaducci,Eugenio Magnanini

doi:10.3389/fpls.2017.00932

Alessandra Fracasso, Adriano Marocco + Show 2 more

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https://doi.org/10.3389/fpls.2017.00932

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Abstract

Plant growth and productivity are strongly affected by limited water availability in drought prone environments. The current climate change scenario, characterized by long periods without precipitations followed by short but intense rainfall, forces plants to implement different strategies to cope with drought stress. Understanding how plants use water during periods of limited water availability is of primary importance to identify and select the best adapted genotypes to a certain environment. Two sorghum genotypes IS22330 and IS20351, previously characterized as drought tolerant and drought sensitive genotypes, were subjected to progressive drought stress through a dry-down experiment. A whole-canopy multi-chamber system was used to determine the in vivo water use efficiency (WUE). This system records whole-canopy net photosynthetic and transpiration rate of 12 chambers five times per hour allowing the calculation of whole-canopy instantaneous WUE daily trends. Daily net photosynthesis and transpiration rates were coupled with gene expression dynamics of five drought related genes. Under drought stress, the tolerant genotype increased expression level for all the genes analyzed, whilst the opposite trend was highlighted by the drought sensitive genotype. Correlation between gene expression dynamics and gas exchange measurements allowed to identify three genes as valuable candidate to assess drought tolerance in sorghum.

Highlights

Drought and problems related to water supply will be exacerbated under the current climate change scenario (ICPP, 2014)
Lack of significant correlation between water use efficiency (WUE) measured at leaf level and WUE measured at whole canopy level has been reported (Tomás et al, 2012) and it was attributed to the inadequacy of single-leaf measurements to represent the spatial variability occurred at the whole-canopy level, or to the inadequacy of single-leaf measurements to take into account nocturnal water loss and respiration (Escalona et al, 2012), and changes in dry matter partitioning among different sinks (e.i. shoot or root) (Tomás et al, 2014)
The objective of the present study was: (a) assess the diurnal gas exchange dynamics of two sorghum genotypes, explore the variation in Pn, E, and wcWUEi under increasing drought stress and confirm the strategies adopted by the sorghum genotypes to cope with drought stress; (b) establish which gene could better explain the variation in Pn, E, and wcWUEi encountered during the day and which gene could be used as a proxy for drought tolerance and a potential candidate for genetic improvement in sorghum

Summary

Introduction

Drought and problems related to water supply will be exacerbated under the current climate change scenario (ICPP, 2014). At canopy or field level, it is calculated as the yield of harvested product achieved from the water available to the crop through precipitation and/or irrigation (Condon et al, 2002). Punctual singleleaf measurements are inadequate to represent the temporal variability that occurs along the day and during the entire crop growing period. For these reasons, we choose to investigate the instantaneous WUE at canopy level using an automated multi-chamber whole-canopy system that allows for continuous monitoring of net photosynthetic (Pn) and transpiration (E) rate. Numerous researches have been carried out on trees using wholecanopy gas exchange systems (Dragoni et al, 2005; Intrigliolo et al, 2009; Rodrigues et al, 2016), but very few are reported on field crops (Timlin et al, 2006; Cantore et al, 2009; CabreraBosquet et al, 2011) and none on sorghum

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