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Plants, being sessile, are subjected to multiple environmental stresses of varying intensity throughout their life cycle. Among the stresses, low fertility, drought, salinity, and nonoptimal temperatures limit crop productivity worldwide. Functional relationships between leaf N and crop growth are prerequisites to developing management tools that optimize productivity in the field. An outdoor pot‐culture experiment was conducted to determine the relationship between leaf N and sesame (Sesamum indicum L.) growth and development. Plants were grown in pots filled with fine sand and irrigated with full‐strength Hoagland's nutrient solution until 10 d after sowing (DAS). Five N treatments were then imposed: one treatment of full‐strength Hoagland's nutrient solution (control, 100% N), and four reformulations of Hoagland's nutrient solution containing reduced N at 60, 20, 10, and 0% of the control. Treatments were maintained until plants were harvested at 31 DAS. Growth, including several root traits, photosynthesis, and leaf N were measured at the end of the experiment. Maximum values were achieved at 5.3% leaf N in the leaves except for transpiration rate, stomatal conductance, and root/shoot ratio. Even though all growth rates declined with lower leaf N, the leaf area expansion among shoot and root volume among the root growth traits were most sensitive to leaf N. Among the root developmental traits, number of root tips was more sensitive to leaf N than other parameters. Among the plant dry components, leaf dry weight had the most considerable decrease. The root/shoot ratio increased under N deficiency. These N stress response indices and critical leaf N levels for various growth processes will help model and manage sesame crops in the field. Core Ideas: Sesame maximum growth rates were achieved at 5.3% leaf N.Sesame leaf area expansion and root volume were more sensitive to leaf N than other parameters.Nitrogen stress response indices will be useful to develop models and for sesame management. [ABSTRACT FROM AUTHOR]

Drought is a major environmental stress factor of plants influencing all growth stages. Drought occurring during germination affects both germination percentage and rate. An experiment was conducted to evaluate in vitro seed germination responses of nine corn (Zea mays L.) hybrids to declining osmotic potentials using polyethylene glycol. Time series data for seed germination were generated at different osmotic potentials from 0 to −1.2 MPa at −0.3‐MPa intervals at 25 °C. Maximum seed germination (MSG) and seed germination rate (SGR) were estimated by fitting the data to a three‐parameter sigmoid function. The minimum osmotic potentials at which MSG and SGR rate reached zero (MSGbase and SGRbase) were derived by first fitting linear and quadratic regression models as a function of osmotic potential and then calculating intercepts. Maximum seed germination and SGR decreased as osmotic potential decreased, and differences were identified among hybrids for MSG, SGR, MSGbase, and SGRbase. An osmotic stress response index was developed by summing individual response indices of each parameter for each hybrid and was used to classify the corn hybrids into tolerance groups. AgriGold A6659 and Terral REV 25BHR26 were identified as the most‐ and least‐tolerant corn hybrids during germination, with AgriGold A6659 performing 29% better than REV 25BHR26. Previous studies have used similar methods using polyethylene glycol to create osmotic stress but have not used the parameters used in this study. These parameters establish a new potential screening tool to identify osmotic stress tolerance in corn germplasm. [ABSTRACT FROM AUTHOR]

The objectives of this study were to determine the effects of UV-B radiation and atmospheric carbon dioxide concentrations ([CO2]) on leaf senescence of cotton by measuring leaf photosynthesis and chlorophyll content and to identify changes in leaf hyperspectral reflectance occurring due to senescence and UV-B radiation. Plants were grown in controlled-environment growth chambers at two [CO2] (360 and 720 µmol mol−1) and three levels of UV-B radiation (0, 7.7 and 15.1 kJ m−2 day−1). Photosynthesis, chlorophyll, carotenoids and phenolic compounds along with leaf hyperspectral reflectance were measured on three leaves aged 12, 21 and 30 days in each of the treatments. No interaction was detected between [CO2] and UV-B for any of the measured parameters. Significant interactions were observed between UV-B and leaf age for photosynthesis and stomatal conductance. Elevated [CO2] enhanced leaf photosynthesis by 32%. On exposure to 0, 7.7 and 15.1 kJ of UV-B, the photosynthetic rates of 30-day-old leaves compared with 12-day-old leaves were reduced by 52, 76 and 86%, respectively. Chlorophyll pigments were not affected by leaf age at UV-B radiation of 0 and 7.7 kJ, but UV-B of 15.1 kJ reduced the chlorophylls by 20, 60 and 80% in 12, 21 and 30-day-old leaves, respectively. The hyperspectral reflectance between 726 and 1142 nm showed interaction for UV-B radiation and leaf age. In cotton, leaf photosynthesis can be used as an indicator of leaf senescence, as it is more sensitive than photosynthetic pigments on exposure to UV-B radiation. This study revealed that, cotton leaves senesced early on exposure to UV-B radiation as indicated by leaf photosynthesis, and leaf hyperspectral reflectance can be used to detect changes caused by UV-B and leaf ageing. [ABSTRACT FROM AUTHOR]