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PIF3 is a phytochrome-interacting basic helix-loop-helix transcription factor that negatively regulates light responses, including hypocotyl elongation, cotyledon opening, and hypocotyl negative gravitropism. However, the role of PIF3 in chlorophyll biosynthesis has not been clearly defined. Here, we show that PIF3 also negatively regulates chlorophyll biosynthesis by repressing biosynthetic genes in the dark. Consistent with the gene expression patterns, the etiolated pif3 mutant accumulated a higher amount of protochlorophyllide and was bleached severely when transferred into light. The photobleaching phenotype of pif3 could be suppressed by the gun5 mutation and mimicked by overexpression of GUN5. When 4 negative phytochrome-interacting protein genes (PIF1, PIF3, PIF4, and PIF5) were mutated, the resulting quadruple mutant seedlings displayed constitutive photomorphogenic phenotypes, including short hypocotyls, open cotyledons, and disrupted hypocotyl gravitropism in the dark. Microarray analysis further confirmed that the dark-grown quadruple mutant has a gene expression pattern similar to that of red light-grown WT. Together, our data indicate that 4 phytochrome-interacting proteins are required for skotomorphogenesis and phytochromes activate photomorphogenesis by inhibiting these factors.

Main conclusion The Arabidopsis transcription factor NAC103 is up-regulated and its encoding protein is stabilized by ABA treatment, which positively regulates several ABA-responsive downstream genes during seed germination and seedlings growth. The Arabidopsis transcription factor NAC103 was previously found to be involved in endoplasmic reticulum (ER) stress and DNA damage responses. In this study, we report the new biological function of NAC103 in abscisic acid (ABA) response during seed germination and seedling growth in Arabidopsis. The expression of NAC103 was up-regulated and the NAC103 protein was stabilized by ABA treatment. Both the loss-of-function mutants of NAC103 , created by targeted gene-editing, and the over-expression plants of NAC103 have no obvious germination-related phenotype under normal growth conditions. However, under exogenous ABA treatment conditions, the NAC103 mutants were less sensitive to ABA during seed germination; in contrast, the NAC103 over-expression plants were more sensitive to ABA during seed germination and young seedling growth. Further, NAC103 regulated several ABA-responsive downstream genes including MYB78 , MYB3 , PLP3 , AMY1 , and RGL2 . These results demonstrate that NAC103 positively regulates ABA response in Arabidopsis.

Many biochemical approaches show functions of calcium-dependent protein kinases (CDPKs) in abscisic acid (ABA) signal transduction, but molecular genetic evidence linking defined CDPK genes with ABA-regulated biological functions at the whole-plant level has been lacking. Here, we report that ABA stimulated two homologous CDPKs in Arabidopsis thaliana, CPK4 and CPK11. Loss-of-function mutations of CPK4 and CPK11 resulted in pleiotropic ABA-insensitive phenotypes in seed germination, seedling growth, and stomatal movement and led to salt insensitivity in seed germination and decreased tolerance of seedlings to salt stress. Double mutants of the two CDPK genes had stronger ABA- and salt-responsive phenotypes than the single mutants. CPK4- or CPK11-overexpressing plants generally showed inverse ABA-related phenotypes relative to those of the loss-of-function mutants. Expression levels of many ABA-responsive genes were altered in the loss-of-function mutants and overexpression lines. The CPK4 and CPK11 kinases both phosphorylated two ABA-responsive transcription factors, ABF1 and ABF4, in vitro, suggesting that the two kinases may regulate ABA signaling through these transcription factors. These data provide in planta genetic evidence for the involvement of CDPK/calcium in ABA signaling at the whole-plant level and show that CPK4 and CPK11 are two important positive regulators in CDPK/calcium-mediated ABA signaling pathways.

Allelopathic effects on the seed germination and seedling growth of the natives play a crucial role in the successful invasion of numerous invaders. Meanwhile, soil salinity is an emerging driver of the spread of many invaders, especially in the colonization of saline habitats. Thus, the allelopathic effects of the invaders on the seed germination and seedling growth of the natives may be altered or even reinforced under salt stress. This study aims to address the allelopathic effects of the notorious invader Canada goldenrod ( Solidago canadensis L.; goldenrod hereafter) on the seed germination and seedling growth of the native lettuce ( Lactuca sativa L.; lettuce hereafter) under a gradient of salt stress. Goldenrod leaf extracts with high concentration significantly decreased root length, leaf shape index, germination percentage, germination potential, germination index, germination vigor index, and germination rate index of lettuce. However, goldenrod leaf extracts with low concentration significantly increased root length and leaf width of lettuce. Goldenrod leaf extracts with high concentration display more serious allelopathic effects on the seed germination and seedling growth of lettuce than those with low concentration. Salt stress regardless of concentration significantly decreased seedling height, root length, leaf shape index, and seedling biomass (fresh weight) of lettuce. The combined goldenrod leaf extracts and salt stress have a synergistic effect on seedling height, root length, leaf shape index, germination percentage, germination potential, germination index, and germination rate index of lettuce. Thus, the allelopathic effects of the invaders on the seed germination and seedling growth of the natives may be reinforced under salt stress. Accordingly, salt stress may be beneficial to the further invasion of the invaders mainly via the reduced growth performance of the natives.

Common mycorrhizal networks (CMNs) influence competition between plants, but reports regarding their precise effect are conflicting. We studied CMN effects on phosphorus (P) uptake and growth of seedlings as influenced by various disruptions of network components. Tomato (Solanum lycopersicon) seedlings grew into established networks of Rhizophagus irregularis and cucumber (Cucumis sativus) in two experiments. One experiment studied seedling uptake of 32P in the network in response to cutting of cucumber shoots; the other analysed seedling uptake of P and nitrogen (N) in the presence of intact or severed arbuscular mycorrhizal fungus networks and at two soil P concentrations. Pre-established and intact networks suppressed growth of tomato seedlings. Cutting of cucumber shoots mitigated P deficiency symptoms of seedlings, which obtained access to P in the extraradical mycelium and thereby showed improved growth. Solitary seedlings growing in a network patch that had been severed from the CMN also grew much better than seedlings of the corresponding CMN. Interspecific and size-asymmetric competition between plants may be amplified rather than relaxed by CMNs that transfer P to large plants providing most carbon and render small plants P deficient. It is likely that grazing or senescence of the large plants will alleviate the networkinduced suppression of seedling growth.

The impacts of different concentrations of bulk and nanosized TiO2 on seed germination and seedling growth of wheat were studied in a randomized completely design with four replications in the College of Agriculture, Ferdowsi University of Mashhad, Iran, in 2011. The experimental treatments included five concentrations of bulk (1, 2, 10, 100, and 500 ppm), five concentrations of nanosized TiO2 (1, 2, 10, 100, and 500 ppm), and control (without any TiO2). Results indicated that among the wheat germination indices, only mean germination time was affected by treatments. The lowest and the highest mean germination time (0.89 vs. 1.35 days) were obtained in 10 ppm concentration of nanosized TiO2 and control treatments, respectively. In addition, shoot length, seedling length, and root dry matters were affected by bulk and nanosized TiO2 concentrations, significantly. Shoot and seedling lengths at 2 and 10 ppm concentrations of nanosized TiO2 were higher than those of the untreated control and bulk TiO2 at 2 and 10 ppm concentrations. Employing nanosized TiO2 in suitable concentration could promote the seed germination of wheat in comparison to bulk TiO2 but in high concentrations had inhibitory or any effect on wheat.

This review provides detailed insight on the effects of magnetic fields on germination, growth, development, and yield of plants focusing on ex vitro growth and development and discussing the possible physiological and biochemical responses. The MFs considered in this review range from the nanoTesla (nT) to geomagnetic levels, up to very strong MFs greater than 15 Tesla (T) and also super-weak MFs (near 0 T). The theoretical bases of the action of MFs on plant growth, which are complex, are not discussed here and thus far, there is limited mathematical background about the action of MFs on plant growth. MFs can positively influence the morphogenesis of several plants which allows them to be used in practical situations. MFs have thus far been shown to modify seed germination and affect seedling growth and development in a wide range of plants, including field, fodder, and industrial crops; cereals and pseudo-cereals; grasses; herbs and medicinal plants; horticultural crops (vegetables, fruits, ornamentals); trees; and model crops. This is important since MFs may constitute a non-residual and non-toxic stimulus. In addition to presenting and summarizing the effects of MFs on plant growth and development, we also provide possible physiological and biochemical explanations for these responses including stress-related responses of plants, explanations based on dia-, para-, and ferromagnetism, oriented movements of substances, and cellular and molecular changes.

This study evaluates induced allelopathy in a rye-pigweed model driven by rye's (Secale cereale L.) allelopathic potential as a cover crop and pigweed's (Amaranthus retroflexus L.) notoriety as a weed. The response of rye towards pigweed's presence in terms of benzoxazinoids (BXs) provides valuable insight into induced allelopathy for crop improvement. In the 2 week plant stage, pigweed experiences a significant reduction in growth in rye's presence, implying allelopathic effects. Rye exhibits increased seedling length and BXs upsurge in response to pigweed presence. These trends persist in the 4 week plant stage, emphasizing robust allelopathic effects and the importance of different co-culture arrangements. Germination experiments show rye's ability to germinate in the presence of pigweed, while pigweed exhibits reduced germination with rye. High-performance liquid chromatography with diode-array detection (HPLC-DAD) analysis identifies allelopathic compounds (BXs), 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) in rye. Rye significantly increases BX production in response to pigweed, age-dependently. Furthermore, pigweed plants are screened for possible BX uptake from the rhizosphere. Results suggest that allelopathy in rye-pigweed co-cultures is influenced by seed timing, and age-dependent dynamics of plants' allelopathic compounds, providing a foundation for further investigations into chemical and ecological processes in crop-weed interactions.

Plants use light as a source of energy for photosynthesis and as a source of environmental information perceived by photoreceptors. Testing whether plants can complete their cycle if light provides energy but no information about the environment requires a plant devoid of phytochromes because all photosynthetically active wavelengths activate phytochromes. Producing such a quintuple mutant of Arabidopsis thaliana has been challenging, but we were able to obtain it in the flowering locus T (ft) mutant background. The quintuple phytochrome mutant does not germinate in the FT background, but it germinates to some extent in the ft background. If germination problems are bypassed by the addition of gibberellins, the seedlings of the quintuple phytochrome mutant exposed to red light produce chlorophyll, indicating that phytochromes are not the sole red-light photoreceptors, but they become developmentally arrested shortly after the cotyledon stage. Blue light bypasses this blockage, rejecting the long-standing idea that the blue-light receptors cryptochromes cannot operate without phytochromes. After growth under white light, returning the quintuple phytochrome mutant to red light resulted in rapid senescence of already expanded leaves and severely impaired expansion of new leaves. We conclude that Arabidopsis development is stalled at several points in the presence of light suitable for photosynthesis but providing no photomorphogenic signal.

The ability to switch from skotomorphogenesis to photomorphogenesis is essential for seedling development and plant survival. Recent studies revealed that COP1 and phytochrome-interacting factors (PIFs) are key regulators of this transition by repressing the photomorphogenic responses and/or maintaining the skotomorphogenic state of etiolated seedlings. Here we report that the plant hormone ethylene plays a crucial role in the transition from skotomorphogenesis to photomorphogenesis by facilitating greening of etiolated seedlings upon light irradiation. Activation of EIN3/EIL1 is both necessary and sufficient for ethylene-induced enhancement of seedling greening, as well as repression of the accumulation of protochlorophyllide, a phototoxic intermediate of chlorophyll synthesis. EIN3/EIL1 were found to induce gene expression of two key enzymes in the chlorophyll synthesis pathway, protochlorophyllide oxidoreductase A and B (PORA/B). ChIP and EMSA assays demonstrated that EIN3 directly binds to the specific elements present in the PORA and PORB promoters. Genetic studies revealed that EIN3/EIL1 function in cooperation with PIF1 in preventing photo-oxidative damage and promoting cotyledon greening. Moreover, activation of EIN3 reverses the blockage of greening triggered by cop1 mutation or far-red light irradiation. Consistently, EIN3 acts downstream of COP1 and its protein accumulation is enhanced by COP1 but decreased by light. Taken together, EIN3/EIL1 represent a new class of transcriptional regulators along with PIF1 to optimize de-etiolation of Arabidopsis seedlings. Our study highlights the essential role of ethylene in enhancing seedling development and survival through protecting etiolated seedlings against photo-oxidative damage.