Light-induced root hair formation in lettuce (Lactuca sativa L. cv. Grand Rapids) roots at low pH is brought by chlorogenic acid synthesis and sugar

An improved and convenient petri plate-based method for studying the root growth of plants

Plant scientists across the globe are interested in studying the root growth architecture of plants to understand different processes determining growth and development in plants. In the majority of cases, root growth-related experiments are carried out on petri plates filled with solid nutrient media. However, plants growing in these plates are often exposed to conditions that are not close to the natural conditions. Also, it is difficult to pour two different media on the same plate which is quite a useful feature to study the effect of specific treatment on plant growth. In the present work, we describe an improved and easy-to-use petri plate system useful for studying root growth characteristics of young plants grown over solid nutrient media. In comparison to the conventional methods, the present plate system offers an advantage in terms of facilitating the pouring of two different media in the same plate, avoiding contact of the aerial part of the plant with nutrient media, and ensuring the growth of roots under dark conditions. The described plate, therefore, provides a convenient system to study root growth under conditions close to natural conditions and hence minimizing experimental artifacts. •The plate system facilitates the pouring of two different nutrient media into the same plate.•The aerial part of the seedling does not come in contact with the media.•Ensures growth of roots under dark conditions.

Comparative Transcriptomic Analysis of the Metabolism of Betalains and Flavonoids in Red Amaranth Hypocotyl under Blue Light and Dark Conditions

Amaranth plants contain abundant betalains and flavonoids. Anthocyanins are important flavonoids; however, they cannot coexist in the same plant with betalains. Blue light influences metabolite synthesis and hypocotyl elongation; accordingly, analyses of its effects on betalain and flavonoid biosynthesis in Amaranthus tricolor may provide insight into the distribution of these plant pigments. We analyzed the betalain and flavonoid content and transcriptome profiles in amaranth hypocotyls under blue light and dark conditions. Furthermore, we analyzed the expression patterns of key genes related to betalains and flavonoids. Amaranth hypocotyls were shorter and redder and showed higher betalain and flavonoid content under blue light than in dark conditions. Key genes involved in the synthesis of betalains and flavonoids were upregulated under blue light. The gene encoding DELLA was also upregulated. These results suggest that blue light favors the synthesis of both betalains and flavonoids via the suppression of bioactive gibberellin and the promotion of DELLA protein accumulation, which also suppresses hypocotyl elongation. The metabolite profiles differed between plants under blue light and dark conditions. These findings improve our understanding of the environmental cues and molecular mechanisms underlying pigment variation in Amaranthus.

Phytotoxic Potential of Zanthoxylum affine and Its Major Compound Linarin as a Possible Natural Herbicide

Four compounds, the flavone linarin (1), the triterpene lupenone (2), the tocopherol (vitamin E, 3), and the new natural alkaloid 1,2,3,4-tetrahydro-1,1-dimethyl-6,7-isoquinolindiol (affineine, 4), were the major natural products isolated from Zanthoxylum affine (syn. Zanthoxylum fagara, Rutaceae). Compound 1 is highly abundant in this plant and was isolated as a white precipitate obtained from the acetone and methanol extracts. The structure of these four compounds was established by 1D and 2D NMR spectroscopy including 1H, 13C, DEPT, COSY, HSQC, and HMBC experiments. The hexane, acetone, and methanol extracts, as well as 1, were evaluated for their potential phytotoxic effects in pre- and post-emergent assays, as well as to identify their mechanisms of action. As pre-emergent phytotoxic agents, the hexane, acetone, and methanol extracts inhibited germination and residual growth (root and stem elongation) of Lactuca sativa (lettuce) and Lolium perenne (perennial ryegrass). As post-emergent agents, they inhibited dry biomass. Compound 1 acts as a pre-emergent herbicide, by inhibiting germination, seed respiration, residual seedling growth and, notably, root hair development. Furthermore, 1 inhibited the synthesis of ATP and the electron transport chain of isolated spinach chloroplasts; in this way, it behaves as a Hill reaction inhibitor. The site of inhibition was located at the donor site of PSII from the oxygen evolving complex to QA, thus acting as a multisite compound. These results suggest that compound 1 can be used as a lead for a potential green herbicide with different targets.

Effects of glucose and ethylene on root hair initiation and elongation in lettuce (Lactuca sativa L.) seedlings

Root hair formation occurs in lettuce seedlings after transfer to an acidic medium (pH 4.0). This process requires cortical microtubule (CMT) randomization in root epidermal cells and the plant hormone ethylene. We investigated the interaction between ethylene and glucose, a new signaling molecule in plants, in lettuce root development, with an emphasis on root hair formation. Dark-grown seedlings were used to exclude the effect of photosynthetically produced glucose. In the dark, neither root hair formation nor the CMT randomization preceding it occurred, even after transfer to the acidic medium (pH 4.0). Adding 1-aminocyclopropane-1-carboxylic-acid (ACC) to the medium rescued the induction, while adding glucose did not. Although CMT randomization occurred when glucose was applied together with ACC, it was somewhat suppressed compared to that in ACC-treated seedlings. This was not due to a decrease in the speed of randomization, but due to lowering of the maximum degree of randomization. Despite the negative effect of glucose on ACC-induced CMT randomization, the density and length of ACC-induced root hairs increased when glucose was also added. The hair-cell length of the ACC-treated seedlings was comparable to that in the combined-treatment seedlings, indicating that the increase in hair density caused by glucose results from an increase in the root hair number. Furthermore, quantitative RT-PCR revealed that glucose suppressed ethylene signaling. These results suggest that glucose has a negative and positive effect on the earlier and later stages of root hair formation, respectively, and that the promotion of the initiation and elongation of root hairs by glucose may be mediated in an ethylene-independent manner.

Formin homology 1 (OsFH1) regulates root-hair elongation in rice (Oryza sativa)

The outgrowth of root hairs from the epidermal cell layer is regulated by a strict genetic regulatory system and external growth conditions. Rice plants cultivated in water-logged paddy land are exposed to a soil ecology that differs from the environment surrounding upland plants, such as Arabidopsis and maize. To identify genes that play important roles in root-hair growth, a forward genetics approach was used to screen for short-root-hair mutants. A short-root-hair mutant was identified, and the gene was isolated using map-based cloning and sequencing. The mutant harbored a point mutation at a splicing acceptor site, which led to truncation of OsFH1 (rice formin homology 1). Subsequent analysis of two additional T-DNA mutants verified that OsFH1 is important for root-hair elongation. Further studies revealed that the action of OsFH1 on root-hair growth is dependent on growth conditions. The mutant Osfh1 exhibited root-hair defects when roots were grown submerged in solution, and mutant roots produced normal root hairs in the air. However, root-hair phenotypes of mutants were not influenced by the external supply of hormones or carbohydrates, a deficiency of nutrients, such as Fe or P i , or aeration. This study shows that OsFH1 plays a significant role in root-hair elongation in a growth condition-dependent manner.

An improved agar-plate method for studying root growth and response of Arabidopsis thaliana

Arabidopsis thaliana is a widely used model plant for plant biology research. Under traditional agar-plate culture system (TPG, traditional plant-growing), both plant shoots and roots are exposed to illumination, and roots are grown in sucrose-added medium. This is not a natural environment for the roots and may cause artifact responses. We have developed an improved agar-plate culture system (IPG, improved plant-growing) where shoots are illuminated but roots are grown in darkness without sucrose addition. Compared to TPG, IPG produced plants with significantly less total root length, lateral root length and root hair density, although their primary roots were longer. Root gravitropism, PIN2 (an auxin efflux carrier) abundance, H⁺ efflux or Ca²⁺ influx in root apexes, were weaker in IPG-grown roots than those in TPG-grown roots. We conclude that IPG offers a more natural way to study the root growth and response of Arabidopsis thaliana.