Three grass species, switchgrass ( Panicum virgatum ), foxtail millet ( Setaria italica ), and Old World bluestem ( Bothriochloa ischaemum ), referred to as introduced, traditional, and indigenous species, respectively, in the Loess hilly gully region on Loess Plateau in China, were grown in a growth chamber. Water was withheld to let the soil gravimetric moisture content (SGMC) decline gradually from 14.92% for 15 days. The gas exchange characteristics, leaf water conditions, root and shoot growth, and water use efficiency (WUE) of the three grasses were compared. The SGMC of foxtail millet declined faster than that of switchgrass and Old World bluestem, and it maintained higher leaf water potential at a lower soil water content, indicating that it might have greater drought tolerance. During the process of soil drying, the stomatal conductance (Gs), photosynthesis rate, and transpiration rate (Tr) of foxtail millet and Old World bluestem declined linearly, whereas those of switchgrass declined parabolically. The Gs of each grass was significantly different between the stressed and well-watered (WW) conditions. When the SGMC declined to ≈ 11.0%, 9.5%, and 8.6%, respectively, the leaf water potential was significantly different between the two growing conditions, showing the appearance of non-hydraulic and hydraulic signals. As a result of greater stomatal adjustment ability and a smaller Gs, foxtail millet had a high WUE. Among the three grasses, switchgrass had a high Tr and root/shoot (R/S) ratio under both WW and stressed conditions, and water stress significantly improved its R/S ratio. The results showed that foxtail millet seedlings have the best drought adaptability in the flexible soil-water environment, whereas switchgrass seedlings have the worst, but a high R/S ratio might be advantageous under drought conditions once the seedlings are established.

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RESEARCH R oot parasitic plants belonging to the genus Orobanche (broomrapes) lack chlorophyll and depend totally on their host plants to provide water, assimilates, and inorganic nutrients. Orobanche spp. cause dramatic damage to vegetable and field crops

Strigolactones (SLs) are plant hormones that play various roles in plant physiology, including provoking the germination of parasitic weeds Orobanche and Striga. A family of α/β-hydrolases have been proposed to be the SL receptor proteins. Effective assays for measuring the activity of SL receptors could promote the development of SL-related biology and chemistry. In this study, we developed a new approach called pharmacophore-linked probe virtual screening (PPVS). Its application yielded an effective "off−on" probe named Xilatone Red (XLR). This probe showed a broad spectrum and excellent sensitivity toward SL receptors, including ShD14 (Striga D14), for which the detection limit was determined to be in the micromolar range, outperforming that of the commercial fluorogenic agonist Yoshimulactone Green (YLG). Upon hydrolysis by SL receptors, XLR provided fluorogenic and colorimetric signaling responses. Furthermore, XLR could induce germination of Phelipanche aegyptiaca seeds and prevent Arabidopsis max4-1 branching defects at micromolar concentrations. Our molecular simulations revealed the essential factors in the molecular perception of XLR. We anticipate that this study can prompt the discovery of high-performance SL agonists/antagonists to combat parasitic weeds.

Wheat (Triticum aestivum L.) is a common name for cereal grasses of a genus of the grass family, cultivated for food since prehistoric times by the people of the temperate zones and now the most important grain crop of those regions. It has allelopathic potential if used as a cover crop for weed control in various cropping systems. Research results indicate that, among modern varieties, there is a variable resistance potential against weeds. Numerous allelochemicals have been identified in wheat, mainly belonging to the categories of phenolic acids, hydroxamic acids and short-chain fatty acids. Some researchers conceived that wheat allelopathy is genetically controlled, but systematic research on gene behaviors is lacking. The negative effects of wheat on other crops under different agricultural production systems have been reported. Research is needed to determine the genetic control of wheat allelopathy prior to the development of allelopathic wheat varieties. Further research is needed to conduct in vitro studies to isolate, identify and quantify allelochemicals from living wheat plants at different growth stages. Also, the relationship between heritages of modern varieties and the allelopathic characteristics of wheat during their evolution and selection by humans is still unclear. There is also a lack of research on the modern varieties as to whether the allelopathic potential can be genetically transferred to the next generation. In the future, more models and assessment systems must be developed to illuminate the essence of allelopathy and the genomes of wheat with allelopathic traits should be constructed to make available allelopathic bioinformation on wheat.

Germination of witchweed (Striga hermonthica [Del.] Benth), an important root parasite on poaceous crops, requires pretreatment ‘conditioning’ in a warm moist environment and a subsequent exposure to a stimulant. The roles of conditioning period, CO2 and a strigol analogue (GR24) in ethylene biosynthesis and germination of the parasite were investigated. Conditioning increased the seeds’ capacity to oxidize exogenous 1‐aminocyclopropane‐1‐carboxylic acid (ACC). Exogenous CO2 increased the seeds capacity to oxidize ACC by 3‐ to 9‐fold. A combination of GR24 and ACC increased ethylene production by more than 3‐fold in comparison with the rates obtained using these compounds separately. Aminoethoxyvinylglycine (AVG) completely inhibited ethylene induction by GR24, but not by ACC. A GR24 treatment, made subsequent to conditioning in GR24, did not induce ethylene. However, seeds conditioned in GR24 and then given 1 mM ACC produced 293 nl l−1 ethylene. ACC oxidase (ACCO) activity in crude extracts was increased by conditioning and CO2. The enzyme displayed an absolute requirement for ascorbate. Absence of exogenous Fe2+ reduced enzyme activity only by 14%. GR24 applied during conditioning reduced germination in response to a subsequent GR24 treatment. ACC was, invariably, less effective in inducing S. hermonthica germination than GR24 even at concentrations which induce more ethylene than concurrent GR24 treatments. The results are consistent with a model in which conditioning removes a restriction on the ethylene biosynthetic pathway in S. hermonthica seeds. GR24 modulates the key enzymes in ethylene biosynthesis. The stimulant suppresses ethylene biosynthesis in unconditioned seeds and promotes it in conditioned ones. Germination of S. hermonthica results from the joint action of GR24 and the ethylene it induces.