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The vegetative cell nucleus proceeds ahead of a pair of sperm cells located beneath the pollen tube tip during germination. The tip-localized vegetative nucleus had been considered to play a pivotal role in the control of directional pollen tube growth and double fertilization. However, we recently reported the female-targeting behavior of pollen tubes from mutant plants, of which the vegetative nucleus and sperm nuclei were artificially immotile. We showed that the apical region of the mutant pollen tubes became physiologically enucleated after the first callose plug formation, indicating the autonomously growing nature of pollen tubes without the vegetative nucleus and sperm cells. Thus, in this study, we further analyzed another Arabidopsis thaliana mutant producing physiologically enucleated pollen tubes and discussed the mechanism by which a pollen tube can grow without de novo transcription from the vegetative nucleus. We propose several possible molecular mechanisms for persistent pollen tube growth, such as the contribution of transcripts before and immediately after germination and the use of persistent transcripts, which may be important for a competitive race among pollen tubes.

Heterosis contributes greatly to the worldwide agricultural yield. However, the molecular mechanism underlying heterosis remains unclear. This study took advantage of Arabidopsis intraspecific hybrids to identify heterosis-related metabolites. Forty-six intraspecific hybrids were used to examine parental effects on seed area and germination time. The degree of heterosis was evaluated based on biomass: combinations showing high heterosis of F 1 hybrids exhibited a biomass increase from 6.1 to 44% over the better parent value (BPV), whereas that of the low- and no-heterosis hybrids ranged from − 19.8 to 9.8% over the BPV. Metabolomics analyses of F 1 hybrids with high heterosis and those with low one suggested that changes in TCA cycle intermediates are key factors that control growth. Notably, higher fumarate/malate ratios were observed in the high heterosis F 1 hybrids, suggesting they provide metabolic support associated with the increased biomass. These hybrids may produce more energy-intensive biomass by speeding up the efficiency of TCA fluxes. However, the expression levels of TCA-process-related genes in F 1 hybrids were not associated with the intensity of heterosis, suggesting that the post-transcriptional or post-translational regulation of these genes may affect the productivity of the intermediates in the TCA cycle.

In pollen and pollen tubes, immotile sperm cells are enclosed by an inner vegetative plasma membrane (IVPM), a single endomembrane originating from the vegetative-cell plasma membrane. It is widely believed that sperm cells must be removed from the IVPM prior to gamete associations and fusions; however, details of the timing and morphological changes upon IVPM dissociation remain elusive. Here, we report a rapid IVPM breakdown immediately before double fertilization in Arabidopsis thaliana . The IVPM was stably observed in coiling pollen tubes when pollen tube discharge was prevented using lorelei mutant ovules. In contrast, a semi- in vivo fertilization assay in wild-type ovules demonstrated fragmented IVPM around sperm nuclei 1 min after pollen tube discharge. These observations revealed the dynamic alteration of released sperm cells and provided new insights into double fertilization in flowering plants. With a summary of recent findings on IVPM lipid composition, we discussed the possible physiological signals controlling IVPM breakdown.

Pollen tubes exhibit one of the fastest apical growth rates among plant cells. Maintaining the proper balance between turgor pressure and cell wall synthesis at the pollen tube tip is crucial for this rapid growth, and any disruption can result in pollen tube rupture. In our study, we reveal that exposure to short-wavelength visible light, specifically blue light, induces pollen tube rupture. The frequency of pollen tube rupture increases in an intensity-dependent manner. Additionally, we observed Ca2+ influx after blue light irradiation, accompanying with either pollen tube rupture or a temporary halt in elongation. These findings offer insights into the interplay between pollen tube integrity maintenance and Ca2+ influx at the pollen tube tip, presenting a novel and efficient method to control pollen tube burst. (1) growth and development (11) new methodology

The pollen tube plays a pivotal role in double fertilization by delivering sperm cells (SCs) to the ovule. In Arabidopsis thaliana, a pair of SCs tightly connects with the vegetative nucleus (VN) to form the male germ unit (MGU), which is located in the apical region during pollen-tube growth, keeping the VN ahead of the SCs. MGU transport relies on independent motility of VN and SC pairs. However, the complexity of this dual motive force has hindered our understanding of MGU behavior, including its positioning and nuclear order. We used Arabidopsis mutants or transgenic plants that produced semi-motile MGUs with aberrant VNs or SCs to analyze the positioning of VN or SCs after stochastically disconnecting the MGU. In pollen tubes with an immotile SC pair, the VN was ∼70 μm away from the tip, whereas in pollen tubes with an immotile VN, the SC pair was ∼100 μm away from the tip, implying that the VN and SCs have independent home positions. The position of MGU moved forward owing to the loss of the microtubule-destabilizing kinesin KINESIN-13A. Conversely, microtubule depolymerization by oryzalin treatment or introducing mutations in TUBULIN BETA 4 (TUB4) deregulated the position of the MGU and shifted its position backward. In addition, tub4 plants exhibited reduced fertility. These data indicate a significant role of microtubules in stable MGU positioning to ensure reproductive success.

Pollen tube attraction is a key event of sexual reproduction in flowering plants. In the ovule, two synergid cells neighboring the egg cell control pollen tube arrival via the active secretion of attractant peptides such as AtLURE1 and XIUQIU from the filiform apparatus facing toward the micropyle. Distinctive cell polarity together with longitudinal F-actin and microtubules are hallmarks of the synergid cell in various species, though functions of these cellular structures are still unclear. In this study we used genetic and pharmacological approaches to elucidate the roles of cytoskeletal components in filiform apparatus formation and pollen tube guidance in Arabidopsis thaliana. Inhibition of microtubule formation reduced invaginations of the plasma membrane but did not abolish micropylar AtLURE1.2 accumulation. In contrast, the expression of a dominant-negative form of ACTIN8 induced disorganization of the filiform apparatus and loss of polar AtLURE1.2 distribution toward the filiform apparatus. Interestingly, after pollen tube reception, F-actin became unclear for a few hours in the persistent synergid cell, which may be involved in pausing and resuming pollen tube attraction during early polytubey block. Our data propose the central role of F-actin in the maintenance of cell polarity and function of male-female communication in the synergid cell. Competing Interest Statement The authors have declared no competing interest.

Subtle deviations in biophysical parameters, particularly temperature, within deep-brain regions exert substantial effects on whole-body homeostasis and metabolism. However, the underlying mechanisms remain poorly understood because cellular-resolution measurements of these parameters in the deep brain have been technically inaccessible. Here, we present a lensless fiber-optic quantum-sensing endomicroscopy that enables cellular-resolution temperature mapping in the mouse deep brain. A microwire-coupled, lensless fiber bundle permits simultaneous temperature readout from optically detected magnetic resonance spectra of >50 fluorescent nanodiamonds, achieving cellular resolution (4.88 μm) with a precision of 0.49 ℃ (minimum precision, 0.18 ℃) within a 0.28 mm2 field of view. We demonstrated temperature mapping of multiple brain depths in head-fixed and vigorously behaving mice subjected to nociceptive stimulation, detecting lower temperatures during anesthesia compared to the awake state in ventromedial hypothalamic nucleus (VMH) at a 5 mm depth. These mappings reveal that spatio-temporal temperature distribution and its anesthesia-dependent reduction are heterogeneous rather than uniform in VMH. This endomicroscopy provides a promising platform to dissect how deviations in biophysical parameters modulate deep-brain function.