Plant hormones are small-molecule signaling compounds that are collectively involved in all aspects of plant growth and development. Unlike animals, plants actively regulate the spatial distribution of several of their hormones. For example, auxin transport results in the formation of auxin maxima that have a key role in developmental patterning. However, the spatial distribution of the other plant hormones, including gibberellic acid (GA), is largely unknown. To address this, we generated two bioactive fluorescent GA compounds and studied their distribution in Arabidopsis thaliana roots. The labeled GAs specifically accumulated in the endodermal cells of the root elongation zone. Pharmacological studies, along with examination of mutants affected in endodermal specification, indicate that GA accumulation is an active and highly regulated process. Our results strongly suggest the presence of an active GA transport mechanism that would represent an additional level of GA regulation.
"GAs), another class of plant hormones, may also have endodermis-specific roles in controlling root development and AM colonization. In Arabidopsis, fluorescently labeled GA derivatives predominantly accumulate in elongating endodermal cells in the root (Shani et al., 2013 "
[Show abstract][Hide abstract] ABSTRACT: The root endodermis is characterized by the Casparian strip and by the suberin lamellae, two hydrophobic barriers that restrict the free diffusion of molecules between the inner cell layers of the root and the outer environment. The presence of these barriers and the position of the endodermis between the inner and outer parts of the root require that communication between these two domains acts through the endodermis. Recent work on hormone signaling, propagation of calcium waves, and plant-fungal symbiosis has provided evidence in support of the hypothesis that the endodermis acts as a signaling center. The endodermis is also a unique mechanical barrier to organogenesis, which must be overcome through chemical and mechanical crosstalk between cell layers to allow for development of new lateral organs while maintaining its barrier functions. In this review, we discuss recent findings regarding these two important aspects of the endodermis.
"The contents of these hormones were dependent on low temperature, and exposure to variable low temperature treatments for 60 days could be used as the critical point for dormancy mediation in lily bulbs 'Siberia' and 'Tiber' (Hua et al., 2011). Chilling exposure of bulbs could lead to the production of growth promoting substances that were gibberellins-like (Shani et al., 2013) and auxin-like (Tsukamoto, 1971), and low temperature treatment promoted the translocation of gibberellins-like and auxin-like substances from the bulb scale to the shoot apex (Rodrigues-Pereira, 1964). Low temperature treatment promoted the breaking of bulb dormancy in L. hansoni, which was in accordance with the results of other studies that showed low temperature affects the carbohydrate contents and plant growth regulators that triggered shoot emergence. "
[Show abstract][Hide abstract] ABSTRACT: This study was conducted to determine the optimum low temperature treatment and the additive effect of soaking in hot water to overcome bulb dormancy of Hanson lily 'Lilium hansonii'. To accomplish this, bulbs were refrigerated at 1, 4, and 7A degrees C for 35, 50, and 65 days, respectively. As the control treatment, the bulbs were planted directly without any cold or hot water treatment. After the treatments, the bulbs were planted in pots filled with sterilized commercial soil mixture and vermiculite at a depth of about 5-10 cm in a greenhouse. The days to emergence, percentage of emergence, plant height (cm), number of leaves, number of flowers, and days to flowering were recorded. Bulbs soaked in hot water (45A degrees C) for 1 hour and stored at 4A degrees C for 65 days showed the earliest emergence and the maximum emergence percentage. Moreover, storage at 4A degrees C for 65 days (without hot water treatment) was found to promote stalk elongation and a higher number of leaves than the hot water treated bulbs. Results indicated that hot water treatment had a significant additive effect on breaking bulb dormancy in L. hansonii, particularly with respect to days to emergence. Hot water pre-treatment also equilibrated the internal conditions of the bulbs, which resulted in the uniformity of the physiological state of the bulb.
"After application, labeled GAs accumulate in the endodermis layer within the elongation zone of the root (Shani et al., 2013). Pharmacological studies combined with the analysis of mutants defective in endodermal cell layer identity revealed that the GA accumulation is regulated by an active mechanism (Shani et al., 2013). Furthermore, by using fluorescent GAs, it was confirmed that GA distribution is regulated by ethylene, adding another dimension to GA function in plant development (Shani et al., 2013). "
[Show abstract][Hide abstract] ABSTRACT: Plants have acquired the capacity to grow continuously and adjust their morphology in response to endogenous and external signals, leading to a high architectural plasticity. The dynamic and differential distribution of phytohormones is an essential factor in these developmental changes. Phytohormone perception is a fast but complex process modulating specific developmental reprogramming. In recent years, chemical genomics or the use of small molecules to modulate target protein function has emerged as a powerful strategy to study complex biological processes in plants such as hormone signaling. Small molecules can be applied in a conditional, dose-dependent and reversible manner, with the advantage of circumventing the limitations of lethality and functional redundancy inherent to traditional mutant screens. High-throughput screening of diverse chemical libraries has led to the identification of bioactive molecules able to induce plant hormone-related phenotypes. Characterization of the cognate targets and pathways of those molecules has allowed the identification of novel regulatory components, providing new insights into the molecular mechanisms of plant hormone signaling. An extensive structure-activity relationship (SAR) analysis of the natural phytohormones, their designed synthetic analogs and newly identified bioactive molecules has led to the determination of the structural requirements essential for their bioactivity. In this review, we will summarize the so far identified small molecules and their structural variants targeting specific phytohormone signaling pathways. We will highlight how the SAR analyses have enabled better interrogation of the molecular mechanisms of phytohormone responses. Finally, we will discuss how labeled/tagged hormone analogs can be exploited, as compelling tools to better understand hormone signaling and transport mechanisms.
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