Hyperspectral imaging sensors are promising tools for monitoring crop plants or vegetation in different environments. Information on physiology, architecture or biochemistry of plants can be assessed non-invasively and on different scales. For instance, hyperspectral sensors are implemented for stress detection in plant phenotyping processes or in precision agriculture. Up to date, a variety of non-imaging and imaging hyperspectral sensors is available. The measuring process and the handling of most of these sensors is rather complex. Thus, during the last years the demand for sensors with easy user operability arose. The present study introduces the novel hyperspectral camera Specim IQ from Specim (Oulu, Finland). The Specim IQ is a handheld push broom system with integrated operating system and controls. Basic data handling and data analysis processes, such as pre-processing and classification routines are implemented within the camera software. This study provides an introduction into the measurement pipeline of the Specim IQ as well as a radiometric performance comparison with a well-established hyperspectral imager. Case studies for the detection of powdery mildew on barley at the canopy scale and the spectral characterization of Arabidopsis thaliana mutants grown under stressed and non-stressed conditions are presented.

These authors contributed equally to this work. SUMMARYThe specification of vascular patterning in plants has interested plant biologists for many years. In the last decade a new context has emerged for this interest. Specifically, recent proposals to engineer C 4 traits into C 3 plants such as rice require an understanding of how the distinctive venation pattern in the leaves of C 4 plants is determined. High vein density with Kranz anatomy, whereby photosynthetic cells are arranged in encircling layers around vascular bundles, is one of the major traits that differentiate C 4 species from C 3 species. To identify genetic factors that specify C 4 leaf anatomy, we generated ethyl methanesulfonate-and cray-mutagenized populations of the C 4 species sorghum (Sorghum bicolor), and screened for lines with reduced vein density. Two mutations were identified that conferred low vein density. Both mutations segregated in backcrossed F 2 populations as homozygous recessive alleles. Bulk segregant analysis using nextgeneration sequencing revealed that, in both cases, the mutant phenotype was associated with mutations in the CYP90D2 gene, which encodes an enzyme in the brassinosteroid biosynthesis pathway. Lack of complementation in allelism tests confirmed this result. These data indicate that the brassinosteroid pathway promotes high vein density in the sorghum leaf, and suggest that differences between C 4 and C 3 leaf anatomy may arise in part through differential activity of this pathway in the two leaf types.

This article is protected by copyright. All rights reserved • Solar-induced fluorescence (SIF) is highly relevant in mapping photosynthesis from remotesensing platforms. This requires linking SIF to photosynthesis and understanding the role of non-photochemical quenching (NPQ) mechanisms under field conditions. Hence, active and passive fluorescence were measured in Arabidopsis thaliana with altered NPQ in outdoor conditions. • Plants had mutations in either violaxanthin de-epoxidase (npq1) or PsbS protein (npq4), resulting in reduced NPQ capacity. Parallel measurements of NPQ, photosystem II efficiency, SIF and spectral reflectance (ρ) were conducted diurnally on one sunny summer day and two consecutive days during a simulated cold spell. • Results showed that both npq mutants had higher levels of SIF compared to wild type. Changes in reflectance were related to changes in the violaxanthin-antheraxanthin-zeaxanthin cycle and not to PsbS-mediated conformational changes. When plants were exposed to cold temperatures, rapid onset of photoinhibition strongly quenched SIF in all lines. • Using well-characterized npq mutants of Arabidopsis, we could show for the first time the quantitative link between SIF, photosynthetic efficiency, NPQ components and leaf reflectance. We discuss the functional potential and limitations of SIF and reflectance measurements for estimating photosynthetic efficiency and NPQ in the field.

Sorghum [Sorghum bicolor (L.) Moench] is a model C4 cereal for both basic and applied research. It has most of the traits of a model plant species: large embryos that are easy to rescue, moderate genome size of about 760 Mb, several unique traits not found in other species, plenty of seeds, and many important agronomic as well as commercial uses. However, it takes a long time to complete its breeding cycle. Other problems encountered during the research on sorghum breeding were early desiccation of embryos from mutants and wide hybridization, and the high‐yielding cultivars and plants grown in controlled environments are usually uniculm, which limits their use in crossing to obtain both selfed and crossed seeds. The objective of this research was to find ways to obtain cross‐ and self‐pollinated seeds from the same plant, conserve the vital embryos, and most important, shorten the breeding cycle. Two methods are reported here. The first method was to produce crossed as well as selfed seeds on the same panicle of the usually uni‐culm plant. The second method was to carry out embryo rescue to save vital embryos as well as shorten the breeding cycle from the regular 17 to 11 wk. By these two methods, the breeding cycle of sorghum was made comparable or even shorter than that of other model crops, which would allow the development of breeding materials much faster.

C4 photosynthesis provides an effective solution for overcoming the catalytic inefficiency of Rubisco. The pathway is characterised by a biochemical CO2 concentrating mechanism that operates across mesophyll and bundle sheath (BS) cells and relies on a gas tight BS compartment. A screen of a mutant population of Setaria viridis, an NADP-malic enzyme type C4 monocot, generated using N-nitroso-N-methylurea identified a mutant with an amino acid change in the gene coding region of the ABCG transporter, a step in the suberin synthesis pathway. Here, Nile red staining, TEM, and GC/MS confirmed the alteration in suberin deposition in the BS cell wall of the mutant. We show that this has disrupted the suberin lamellae of BS cell wall and increased BS conductance to CO2 diffusion more than two-fold in the mutant. Consequently, BS CO2 partial pressure is reduced and CO2 assimilation was impaired in the mutant. Our findings provide experimental evidence that a functional suberin lamellae is an essential anatomical feature for efficient C4 photosynthesis in NADP-ME plants like S. viridis and have implications for engineering strategies to ensure future food security.