Leaf hyperspectral reflectance can be used by the wheat physiology and breeding communities to rapidly estimate Rubisco activity, electron transport rate, leaf nitrogen, leaf dry mass per area, and relative chlorophyll content.

Despite its relevance, protein regulation, metabolic adjustment, and the physiological status of plants under drought is not well understood in relation to the role of nitrogen fixation in nodules. In this study, nodulated alfalfa plants were exposed to drought conditions. The study determined the physiological, metabolic, and proteomic processes involved in photosynthetic inhibition in relation to the decrease in nitrogenase (Nase) activity. The deleterious effect of drought on alfalfa performance was targeted towards photosynthesis and Nase activity. At the leaf level, photosynthetic inhibition was mainly caused by the inhibition of Rubisco. The proteomic profile and physiological measurements revealed that the reduced carboxylation capacity of droughted plants was related to limitations in Rubisco protein content, activation state, and RuBP regeneration. Drought also decreased amino acid content such as asparagine, and glutamic acid, and Rubisco protein content indicating that N availability limitations were caused by Nase activity inhibition. In this context, drought induced the decrease in Rubisco binding protein content at the leaf level and proteases were up-regulated so as to degrade Rubisco protein. This degradation enabled the reallocation of the Rubisco-derived N to the synthesis of amino acids with osmoregulant capacity. Rubisco degradation under drought conditions was induced so as to remobilize Rubisco-derived N to compensate for the decrease in N associated with Nase inhibition. Metabolic analyses showed that droughted plants increased amino acid (proline, a major compound involved in osmotic regulation) and soluble sugar (D-pinitol) levels to contribute towards the decrease in osmotic potential (Ψs). At the nodule level, drought had an inhibitory effect on Nase activity. This decrease in Nase activity was not induced by substrate shortage, as reflected by an increase in total soluble sugars (TSS) in the nodules. Proline accumulation in the nodule could also be associated with an osmoregulatory response to drought and might function as a protective agent against ROS. In droughted nodules, the decrease in N2 fixation was caused by an increase in oxygen resistance that was induced in the nodule. This was a mechanism to avoid oxidative damage associated with reduced respiration activity and the consequent increase in oxygen content. This study highlighted that even though drought had a direct effect on leaves, the deleterious effects of drought on nodules also conditioned leaf responsiveness.

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The application of spectroradiometric index such as the normalized difference vegetation index (NDVI) to assess green biomass or nitrogen (N) content has focused on the plant canopy in precision agriculture or breeding programs. However, little is known about the usefulness of these techniques in isolated plants. The few reports available propose the use of a spectroradiometer in combination with special adaptors that improve signal acquisition from plants, but this makes measurements relatively slow and unsuitable. Here we studied the direct use (i.e. without adaptors) of a commercial cost-effective spectroradiometer, GreenSeeker™ (NTech Industries Ins., Ukiah, California, USA) provided with an active sensor (i.e. equipped with its own source of radiation) for measuring NDVI in four genotypes of durum wheat (Triticum turgidum L. var. durum) grown in pots under a range of water and N regimes. Strong correlations were observed between NDVI measurements and dry aboveground biomass (AB), total green area (TGA), green area without spikes (GA) and aboveground N content (AN). To prove the predictive ability of NDVI measured under potted conditions, linear regression models for each growth trait and for plant N content were built with the data of two genotypes. The models accurately predicted growth traits and N content, confirming the direct relationship between total plant biomass and spectroradiometric readings

SummaryWe present a non-intrusive method to quantify the relative contribution of different photosynthetic organs to grain filling in cereals based on their discrimination among isotopes of carbon fixed, highlighting the key role of the ear.

Summary One of the major challenges for plant scientists is increasing wheat ( Triticum aestivum ) yield potential ( YP ). A significant bottleneck for increasing YP is achieving increased biomass through optimization of radiation use efficiency ( RUE ) along the crop cycle. Exotic material such as landraces and synthetic wheat has been incorporated into breeding programmes in an attempt to alleviate this; however, their contribution to YP is still unclear. To understand the genetic basis of biomass accumulation and RUE , we applied genome‐wide association study ( GWAS ) to a panel of 150 elite spring wheat genotypes including many landrace and synthetically derived lines. The panel was evaluated for 31 traits over 2 years under optimal growing conditions and genotyped using the 35K wheat breeders array. Marker‐trait association identified 94 SNP s significantly associated with yield, agronomic and phenology‐related traits along with RUE and final biomass ( BM _ PM ) at various growth stages that explained 7%–17% of phenotypic variation. Common SNP markers were identified for grain yield, BM _ PM and RUE on chromosomes 5A and 7A. Additionally, landrace and synthetic derivative lines showed higher thousand grain weight ( TGW ), BM _ PM and RUE but lower grain number ( GM 2) and harvest index ( HI ). Our work demonstrates the use of exotic material as a valuable resource to increase YP . It also provides markers for use in marker‐assisted breeding to systematically increase BM _ PM , RUE and TGW and avoid the TGW / GM 2 and BM _ PM / HI trade‐off. Thus, achieving greater genetic gains in elite germplasm while also highlighting genomic regions and candidate genes for further study.

Water scarcity and nitrogen shortage are the main constraints on durum wheat productivity. This paper examines the combined effects of a constant water deficit and nitrogen supply (NS) on growth, photosynthesis, stomatal conductance (g s ) and transpiration, instantaneous and time-integrated water use efficiency (WUE) and nitrogen use efficiency (NUE) and carbon isotope discrimination (Á 13 C) in durum wheat genotypes grown in pots under greenhouse conditions. Three water levels (40%, 70% and 100% container capacity), two nitrogen doses (high and low N) and four genotypes were assayed in a total of 24 experimental treatments. Water and nitrogen treatments were imposed 2 weeks after plant emergence. The growth, nitrogen content and Á 13 C of the shoot and the gas exchange in the flag leaf were determined about 2 weeks after anthesis. As expected, both water and NS had a strong positive effect on growth. However, a reduction in water supply had low effect decreasing photosynthesis and transpiration, Á 13 C and NUE and increasing WUE. On the contrary, increasing the level of nitrogen supplied had a significant negative effect on g s , which decreased significantly the ratio of intercellular to ambient CO 2 concentrations and Á 13 C, and increased both instantaneous and time-integrated WUE. In addition, a higher N level also negatively affected the instantaneous and time-integrated NUE. The Á 13 C of shoots correlated significantly and negatively with either instantaneous or time-integrated measurements of WUE. Moreover, within each NS, Á 13 C also correlated negatively with the integrated NUE. We concluded that under our experimental conditions, Á 13 C gives information about the efficiency with which not just water but also nitrogen are used by the plant. In addition, this study illustrates that a steady water limitation may strongly affect biomass without consistent changes in WUE. The lack of effect of the different water regimes on gas exchange, WUE and Á 13 C illustrate the importance of how stress is imposed during growth.

HighlightThis study proves the key role of the ear as a source of assimilates for grain filling under good agronomical conditions and compares different methodologies of phenotyping.