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Biomass partitioning is one of the pivotal determinants of crop growth management, which is influenced by environmental cues. Light and CO2 are the main drivers of photosynthesis and biomass production in plants. In this study, the effects of CO2 levels: ambient 400 ppm (a[CO2]) and elevated to 1,000 ppm (e[CO2]) and different light intensities (75, 150, 300, 600 μmol·m−2·s−1 photosynthetic photon flux density – PPFD) were studied on the growth, yield, and biomass partitioning in chrysanthemum plants. The plants grown at higher light intensity had a higher dry weight (DW) of both the vegetative and floral organs. e[CO2] diminished the stimulating effect of more intensive light on the DW of vegetative organs, although it positively influenced inflorescence DW. The flowering time in plants grown at e[CO2] and light intensity of 600 μmol·m−2·s−1 occurred earlier than that of plants grown at a[CO2]. An increase in light intensity induced the allocation of biomass to inflorescence and e[CO2] enhanced the increasing effect of light on the partitioning of biomass toward the inflorescence. In both CO2 concentrations, the highest specific leaf area (SLA) was detected under the lowest light intensity, especially in plants grown at e[CO2]. In conclusion, elevated light intensity and CO2 direct the biomass toward inflorescence in chrysanthemum plants.

Low temperatures are an important limitation for geographic distributions of warm-season crops like cucumber (Cucumis sativus L.). Tolerance to low temperatures varies among different plant species and genotypes when changes in normal environmental cues occur. To cope with low temperature, biochemical and biophysical events should be coordinated to form a physiological response. We examined how light intensity influences the effects of low temperature on photosynthesis machinery and some biochemical traits. We used chlorophyll fluorescence imaging and polyphasic fluorescence transient (OJIP) to analyze cold stress (4 ºC) damage to photosynthetic electron transport chain (ETC) under different Photosynthetic Photon Flux Densities (PPFDs; 0, 300 and 600 μmol m-2 s-1), in four accessions of cucumber. The results showed that, the negative effects of cold stress are PPFD-dependent. The adverse effect of cold stress on ETC was more pronounced in plants exposed to 600 μmol m-2 s-1 compared to the control and dark-exposed plants; indicated by disturbance in ETC and higher energy dissipation. Moreover, biochemical traits including H2O2 content, ascorbate peroxidase activity and electrolyte leakage, and water-soluble carbohydrate was increased under low temperature by increase in PPFD, while chlorophyll and carotenoid contents decreased under low temperature by PPFD elevation. Low temperature induced H2O2 accumulation via suppressing APX activity in a PPFD-dependent manner. In conclusion, high PPFDs exacerbate the adverse effects of low temperature on the cucumber seedlings.

GABA (gamma-aminobutyric acid) and melatonin are endogenous compounds that enhance plant responses to abiotic stresses. The response of Vicia faba to different stressors (salinity (NaCl), poly ethylene glycol (PEG), and sulfur dioxide (SO2)) was studied after priming with sole application of GABA and melatonin or their co-application (GABA + melatonin). Both melatonin and GABA and their co-application increased leaf area, number of flowers, shoot dry and fresh weight, and total biomass. Plants treated with GABA, melatonin, and GABA + melatonin developed larger stomata with wider aperture compared to the stomata of control plants. The functionality of the photosynthetic system was improved in primed plants. To investigate the photosynthetic functionality in details, the leaf samples of primed plants were exposed to different stressors, including SO2, PEG, and NaCl. The maximum quantum yield of photosystem II (PS II) was higher in the leaf samples of primed plants, while the non-photochemical quenching (NPQ) of primed plants was decreased when leaf samples were exposed to the stressors. Correlation analysis showed the association of initial PIabs with post-stress FV/FM and NPQ. Stressors attenuated the association of initial PIabs with both FV/FM and NPQ, while priming plants with GABA, melatonin, or GABA + melatonin minimized the effect of stressors by attenuating these correlations. In conclusion, priming plants with both GABA and melatonin improved growth and photosynthetic performance of Vicia faba and mitigated the effects of abiotic stressors on the photosynthetic performance.

Light emitting diodes (LEDs) now enable precise light quality control. Prior to commercialisation however, the plant response to the resultant light quality regime ought to be addressed. The response was examined here in chrysanthemum by evaluating growth, chlorophyll fluorescence (before and following water deficit), as well as stomatal anatomy (density, size, pore dimensions and aperture heterogeneity) and closing ability. Plants were grown under blue (B), red (R), a mixture of R (70%) and B (RB), or white (W; 41% B, 39% intermediate spectrum, 20% R) light LEDs. Although R light promoted growth, it also caused leaf deformation (epinasty) and disturbed the photosynthetic electron transport system. The largest stomatal size was noted following growth under B light, whereas the smallest under R light. The largest stomatal density was observed under W light. Monochromatic R light stimulated both the rate and the degree of stomatal closure in response to desiccation compared with the other light regimes. We conclude that stomatal size is mainly controlled by the B spectrum, whereas a broader spectral range is important for determining stomatal density. Monochromatic R light enhanced stomatal ability to regulate water loss upon desiccation.

Environmental stresses are among the most important threats for food security since it adversely affects agricultural productivity. Among them, drought stress and water scarcity stand as major problems, especially in developing countries. Thus, understanding molecular mechanisms involving drought stress response is of essential importance for coping with its detrimental effects. Calcium is an essential macro-element, taking part in the regulation of many aspects of plant growth and development along with playing the role of ubiquitous secondary messenger, thus taking part in the generation of adaptive responses toward various developmental and environmental stimuli. Therefore, understanding the calcium signaling and calcium-dependent processes is crucial for improving plant productivity under environmental stresses. Formation of calcium signature through subsequent oscillations is at the onset of calcium signaling which further activates calcium-binding proteins which are acting as signal decoders, makes it possible to perceive the nature of stimuli. Further, protein kinases and transcription factors are activated in a stimuli-specific manner to create a stress-specific response. Understanding of calcium signaling processes and modulations is a promising step for unraveling the molecular mechanism of drought stress tolerance and engineering stress-tolerant crops. In this chapter, calcium-signaling components involving in drought stress signal perception and transition through calcium-signaling pathway and final formation of stress response have been discussed in detail.

Drought and salt stresses are among abiotic stresses that hinder plants from reaching their maximum productivity and thus menacing food security by reducing crop yield worldwide. The mechanisms that stressors affect the plants are very complicated. To cope with environmental stresses, evolutionary processes have been developed through natural selection, which enables plants to integrate molecular and cellular mechanisms to develop adaptive responses. Mechanism by which plant perceive stress signals and further transmission of perceived signals to cell machinery has long been of concern and is still an ongoing point of discussion. In the last decade, introduction of molecular techniques has been used to unravel the mechanism of perception and transmission of stress signals along with plant’s adaptive responses. Understanding the physiological and molecular mechanisms of abiotic stress response and tolerance mechanisms may advance our knowledge about candidate genes involving in genetic or epigenetic aspects of stress response, which are essential for improving stress tolerance in plants. In this chapter, the most recent literature on the mechanisms involving in salt and drought stress signal transduction including their signaling pathways and signaling components are used to best elaborate underlying stress response mechanisms involved in salt and drought stresses.

In plants dehydration imposed by salinity can invoke physical changes at the interface of the plasma membrane and cell wall. Changes in hydrostatic pressure activate ion channels and cause depolarization of the plasma membrane due to disturbance in ion transport. During the initial phases of salinity stress, the relatively high osmotic potential of the rhizosphere enforces the plant to use a diverse spectrum of strategies to optimize water and nutrient uptake. Signals of salt stress are recognized by specific root receptors that activate an osmosensing network. Plant response to hyperosmotic tension is closely linked to the calcium (Ca(2+)) channels and interacting proteins such as calmodulin. A rapid rise in cytosolic Ca(2+) levels occurs within seconds of exposure to salt stress. Plants employ multiple sensors and signaling components to sense and respond to salinity stress, of which most are closely related to Ca(2+) sensing and signaling. Several tolerance strategies such as osmoprotectant accumulation, antioxidant boosting, polyaminses and nitric oxide (NO) machineries are also coordinated by Ca(2+) signaling. Substantial research has been done to discover the salt stress pathway and tolerance mechanism in plants, resulting in new insights into the perception of salt stress and the downstream signaling that happens in response. Nevertheless, the role of multifunctional components such as Ca(2+) has not been sufficiently addressed in the context of salt stress. In this review, we elaborate that the salt tolerance signaling pathway converges with Ca(2+) signaling in diverse pathways. We summarize knowledge related to different dimensions of salt stress signaling pathways in the cell by emphasizing the administrative role of Ca(2+) signaling on salt perception, signaling, gene expression, ion homeostasis and adaptive responses.