For permanent secondary growth in plants, cell proliferation and differentiation should be strictly controlled in the vascular meristem consisting of (pro)cambial cells. A peptide hormone tracheary element differentiation inhibitory factor (TDIF) functions to inhibit xylem differentiation, while a plant hormone brassinosteroid (BR) promotes xylem differentiation in (pro)cambial cells. However, it remains unclear how TDIF and BR cooperate to regulate xylem differentiation for the proper maintenance of the vascular meristem. In this study, I developed an easy evaluation method for xylem differentiation frequency in a vascular induction system Vascular cell Induction culture System Using Arabidopsis Leaves (VISUAL) by utilizing a xylem-specific luciferase reporter line. In this quantitative system, TDIF suppressed and BR promoted xylem differentiation in a dose-dependent manner, respectively. Moreover, simultaneous treatment of TDIF and BR with (pro)cambial cells revealed that they can cancel their each other’s effect on xylem differentiation, suggesting a competitive relationship between TDIF and BR. Thus, mutual inhibition of “ON” and “OFF” signal enables the fine-tuned regulation of xylem differentiation in the vascular meristem.
Potato, Solanum tuberosum L. is an important crop. However, it is difficult to breed potato cultivars by applying conventional crossing methods because potato has a tetraploid genome and is vegetatively propagated. Flower formation and tuber development occur simultaneously. Many potato cultivars hardly produce any fruits after crossing and fail to produce seeds. We report an improved procedure for obtaining progeny seeds by grafting potatoes onto tomatoes. The rate of fruit formation was more than 19% when the grafted potatoes were used for the crossing experiments, whereas crossing using the ungrafted plants showed a rate of 1.1%. This result suggests that our procedure results in the easy acquisition of null-segregant progenies by crossing mutant lines. It is also expected to improve conventional potato breeding.
Pollen tube growth is essential for the fertilization process in angiosperms. When pollen grains arrive on the stigma, they germinate, and the pollen tubes elongate through the styles of the pistils to deliver sperm cells into the ovules to produce the seeds. The relationship between the growth rate and style length remains unclear. In previous studies, we developed a liquid pollen germination medium for observing pollen tube growth. In this study, using this medium, we examined the pollen tube growth ability in Petunia axillaris subsp. axillaris, P. axillaris subsp. parodii, P. integrifolia, and P. occidentalis, which have different style lengths. Petunia occidentalis had the longest pollen tubes after 6 h of culture but had a relatively shorter style. Conversely, the pollination experiments revealed that P. axillaris subsp. parodii, which had the longest style, produced the longest pollen tubes in vivo. The results revealed no clear relationship between the style lengths and the growth rate of pollen tubes in vitro. Interspecific pollinations indicated that the styles affected pollen tube growth. We concluded that, in vitro, the pollen tubes grow without being affected by the styles, whereas, in vivo, the styles significantly affected pollen tube growth. Furthermore, interspecific pollination experiments implied that the pollen tube growth tended to be suppressed in the styles of self-incompatibility species. Finally, we discussed the pollen tube growth ability in relation to style lengths.
L-3,4-dihydroxyphenylalanine (L-DOPA) is one of the important secondary metabolites of plants and has been used for various purposes, such as in clinical treatment for Parkinson’s disease and dopamine-responsive dystonia. In plants, L-DOPA is a precursor of many alkaloids, catecholamines, and melanin; the L-DOPA synthesis pathway is similar to that in mammals. L-DOPA acts as an allelochemical, has an important role in several biological processes, such as stress response and metabolism, in plants. L-DOPA is widely used in the clinical treatment as well as a dietary supplement or psychotropic drug, understanding of biosynthesis of L-DOPA in plant could lead to a stable supply of L-DOPA. This paper describes an improved method for simple and rapid quantification of L-DOPA content using liquid chromatography-tandem mass spectrometry. The standard quantitative methods for L-DOPA require multiple purification steps or relatively large amounts of plant material. In our improved method, quantification of L-DOPA was possible with extract of one–two pieces of cotyledon without any partitioning or column for purification. The endogenous L-DOPA (approximately 4,000 µg g−1 FW (fresh weight)) could be detected from the one pieces of cotyledon of the faba bean sprout using this method. This method was also effective for samples with low endogenous amounts of L-DOPA such as broccoli, Japanese white radish, pea, and red cabbage sprouts. Therefore, this improved method will allow to measurement of L-DOPA content easily and accurately from a small amount of plant tissue and contribute to understanding biosynthesis, catabolism, and transport of L-DOPA.
Compared with other organisms, plants have an extraordinary capacity for self-repair. Even if the entire tissues, including the stem cells, are resected, most plant species are able to completely regenerate whole tissues. However, the mechanism by which plants efficiently regenerate the stem cell niche during tissue reorganization is still largely unknown. Here, we found that the signaling mediated by plant steroid hormones brassinosteroids is activated during stem cell formation after root tip excision in Arabidopsis. Treatment with brassinazole, an inhibitor of brassinosteroid biosynthesis, delayed the recovery of stem cell niche after root tip excision. Regeneration of root tip after resection was also delayed in a brassinosteroid receptor mutant. Therefore, we propose that brassinosteroids participate in efficient root tip regeneration, thereby enabling efficient tissue regeneration to ensure continuous root growth after resection.
During embryogenesis of eudicots, the apical region of the embryo develops two cotyledon primordia and the shoot meristem. In Arabidopsis thaliana, this process is dependent on the functionally redundant activities of the CUP-SHAPED COTYLEDON (CUC) transcription factors, namely CUC1, CUC2, and CUC3, as well as the phytohormone auxin. However, the relationship between the CUC proteins and auxin has yet to be fully elucidated. In the present study, we examined whether the expression of auxin biosynthetic genes is dependent on CUC gene activities. Comprehensive quantitative RT-PCR analysis of the main auxin biosynthetic gene families of TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1/TRYPTOPHAN AMINOTRANSFERASE RELATED and YUCCA (YUC) showed that YUC1 and YUC4 expression levels were lower in cuc double mutant embryos than the expression levels of these genes in wild type embryos. Reporter analysis also revealed that the expression of YUC1 and YUC4 in the cotyledon boundary region was reduced in cuc double mutant embryos. In contrast, the loss of function mutation in the SHOOT MERISTEMLESS gene, a shoot stem cell regulator that acts downstream of the CUC genes, did not markedly affect YUC1 expression levels. These results demonstrate that CUC genes play an important role in the regulation of auxin biosynthetic gene expression during embryogenesis; furthermore, they raise the possibility that the auxin produced by this regulation contributes to cotyledon boundary development.