MIZU-KUSSEI1 (MIZ1) and GNOM/MIZ2 control not only positive hydrotropism but also phototropism in Arabidopsis roots

In response to unilateral blue light illumination, roots of some plant species such as Arabidopsis thaliana exhibit negative phototropism (bending away from light), which is important for light avoidance in nature. MIZU-KUSSEI1 (MIZ1) and GNOM/MIZ2 are essential for positive hydrotropism (i.e. in the presence of a moisture gradient, root bending towards greater water availability). Intriguingly, mutations in these genes also cause a substantial reduction in phototropism. Here, we examined whether the same tissue-specific sites of expression required for MIZ1- and GNOM/MIZ2-regulated hydrotropism in Arabidopsis roots are also required for phototropism. The attenuated phototropic response of miz1 roots was completely restored when a functional MIZ1-green fluorescent protein (GFP) fusion was expressed in the cortex of the root elongation zone but not in other tissues such as root cap, meristem, epidermis, or endodermis. The hydrotropic defect and reduced phototropism of miz2 roots were restored by GNOM/MIZ2 expression in either the epidermis, cortex, or stele, but not in the root cap or endodermis. Thus, the sites in root tissues that are involved in the regulation of MIZ1- and GNOM/MIZ2-dependent hydrotropism also regulate phototropism. These results suggest that MIZ1- and GNOM/MIZ2-mediated pathways are, at least in part, shared by hydrotropic and phototropic responses in Arabidopsis roots.

Auxin biosynthesis, transport, and response directly attenuate hydrotropism in the latter stages to fine-tune root growth direction in Arabidopsis

Roots detect water potential gradients in the soil and orient toward moister areas, a response known as hydrotropism that aids drought avoidance. Although auxin is crucial in tropism, its polar transport is not essential for hydrotropism in Arabidopsis. Moreover, antiauxin treatments in Arabidopsis produced inconsistent outcomes: some studies indicated auxin action was necessary while others did not. In this study, we examined auxin's physiological role in hydrotropism. We found that inhibiting auxin biosynthesis or transport intensified hydrotropic bending not only in wild-type, but also in hydrotropism defective mutants, namely miz1-1 and miz2 plants. Given that miz1-1 and miz2 exhibited compromised hydrotropism even under clinorotated conditions, we infer that auxin biosynthesis and transport directly suppress hydrotropism. Additionally, tir1-10, afb1-3, and afb2-3 displayed augmented hydrotropism. We observed a significant delay in hydrotropic bending in arf7-1arf19-1, suggesting that ARF7 and ARF19 amplify hydrotropism in its early stages. To discern the functional ties of ARF7/19 with MIZ1 and MIZ2, we studied the hydrotropic phenotypes of arf7-1arf19-1miz1-1 and arf7-1arf19-1miz2. Both triple mutants had diminished early-stage hydrotropism yet showed partial but significant recovery in the later stages. Given MIZ1's role in reducing auxin levels and MIZ2's essentiality for MIZ1 functionality, we conclude that auxin inhibits hydrotropism downstream of MIZ1 in later stages to refine root bending. Furthermore, it is posited that gene expression driven by ARF7 and ARF19 is pivotal for early-stage root hydrotropism.

Rogue and solitary waves in coupled phononic crystals

In this work we present an analytical and numerical study of rogue and solitary waves in a coupled one-dimensional nonlinear lattice that involves both axial and rotational degrees of freedom. Using a multiple-scale analysis, we derive a system of coupled nonlinear Schrödinger-type equations in order to approximate solitary waves and rogue waves of the coupled lattice model. Numerical simulations are found to agree with the analytical approximations. We also consider generic initialization data in the form of a Gaussian profile and observe that they can result in the spontaneous formation of rogue-wave-like patterns in the lattice. The solitary and rogue waves in the lattice demonstrate both energy isolation and exchange between the axial and rotational degrees of freedom of the system. This suggests that the studied coupled lattice has the potential to be an efficient energy isolation, transfer, and focusing medium.

Correction to: Molecular mechanisms mediating root hydrotropism: what we have observed since the rediscovery of hydrotropism

The article Molecular mechanisms mediating root hydrotropism.

Molecular mechanisms mediating root hydrotropism: what we have observed since the rediscovery of hydrotropism

Roots display directional growth toward moisture in response to a water potential gradient. Root hydrotropism is thought to facilitate plant adaptation to continuously changing water availability. Hydrotropism has not been as extensively studied as gravitropism. However, comparisons of hydrotropic and gravitropic responses identified mechanisms that are unique to hydrotropism. Regulatory mechanisms underlying the hydrotropic response appear to differ among different species. We recently performed molecular and genetic analyses of root hydrotropism in Arabidopsis thaliana. In this review, we summarize the current knowledge of specific mechanisms mediating root hydrotropism in several plant species.

Circumnutational movement in rice coleoptiles involves the gravitropic response: analysis of an agravitropic mutant and space-grown seedlings

Plants exhibit helical growth movements known as circumnutation in growing organs. Some studies indicate that circumnutation involves the gravitropic response, but this notion is a matter of debate. Here, using the agravitropic rice mutant lazy1 and space-grown rice seedlings, we found that circumnutation was reduced or lost during agravitropic growth in coleoptiles. Coleoptiles of wild-type rice exhibited circumnutation in the dark, with vigorous oscillatory movements during their growth. The gravitropic responses in lazy1 coleoptiles differed depending on the growth stage, with gravitropic responses detected during early growth and agravitropism during later growth. The nutation-like movements observed in lazy1 coleoptiles at the early stage of growth were no longer detected with the disappearance of the gravitropic response. To verify the relationship between circumnutation and gravitropic responses in rice coleoptiles, we conducted spaceflight experiments in plants under microgravity conditions on the International Space Station. Wild-type rice seeds were germinated, and the resulting seedlings were grown under microgravity or a centrifuge-generated 1 g environment in space. We began filming the seedlings 2 days after seed imbibition and obtained images of seedling growth every 15 min. The seed germination rate in space was 92-100% under both microgravity and 1 g conditions. LED-synchronized flashlight photography induced an attenuation of coleoptile growth and circumnutational movement due to cumulative light exposure. Nevertheless, wild-type rice coleoptiles still showed circumnutational oscillations under 1 g but not microgravity conditions. These results support the idea that the gravitropic response is involved in plant circumnutation.

Gravitropism interferes with hydrotropism via counteracting auxin dynamics in cucumber roots: clinorotation and spaceflight experiments

Roots of land plants show gravitropism and hydrotropism in response to gravity and moisture gradients, respectively, for controlling their growth orientation. Gravitropism interferes with hydrotropism, although the mechanistic aspects are poorly understood. Here, we differentiated hydrotropism from gravitropism in cucumber roots by conducting clinorotation and spaceflight experiments. We also compared mechanisms regulating hydrotropism and auxin-regulated gravitropism. Clinorotated or microgravity (μG)-grown cucumber seedling roots hydrotropically bent toward wet substrate in the presence of moisture gradients, but they grew straight in the direction of normal gravitational force at the Earth's surface (1G) on the ground or centrifuge-generated 1G in space. The roots appeared to become hydrotropically more sensitive to moisture gradients under μG conditions in space. Auxin transport inhibitors significantly reduced the hydrotropic response of clinorotated seedling roots. The auxin efflux protein CsPIN5 was differentially expressed in roots of both clinorotated and μG-grown seedlings; with higher expression in the high-humidity (concave) side than the low-humidity (convex) side of hydrotropically responding roots. Our results suggest that roots become hydrotropically sensitive in μG, and CsPIN5-mediated auxin transport has an important role in inducing root hydrotropism. Thus, hydrotropic and gravitropic responses in cucumber roots may compete via differential auxin dynamics established in response to moisture gradients and gravity.

Auxin transport and response requirements for root hydrotropism differ between plant species

The direction of auxin transport changes in gravistimulated roots, causing auxin accumulation in the lower side of horizontally reoriented roots. This study found that auxin was similarly involved in hydrotropism and gravitropism in rice and pea roots, but hydrotropism in Lotus japonicus roots was independent of both auxin transport and response. Application of either auxin transport inhibitors or an auxin response inhibitor decreased both hydrotropism and gravitropism in rice roots, and reduced hydrotropism in pea roots. However, Lotus roots treated with these inhibitors showed reduced gravitropism but an unaltered or an enhanced hydrotropic response. Inhibiting auxin biosynthesis substantially reduced both tropisms in rice and Lotus roots. Removing the final 0.2 mm (including the root cap) from the root tip inhibited gravitropism but not hydrotropism in rice seedling roots. These results suggested that modes of auxin involvement in hydrotropism differed between plant species. In rice roots, although auxin transport and responses were required for both gravitropism and hydrotropism, the root cap was involved in the auxin regulation of gravitropism but not hydrotropism. Hydrotropism in Lotus roots, however, may be regulated by a novel mechanism that is independent of both auxin transport and the TIR1/AFBs auxin response pathway.

Root hydrotropism is controlled via a cortex-specific growth mechanism

Plants can acclimate by using tropisms to link the direction of growth to environmental conditions. Hydrotropism allows roots to forage for water, a process known to depend on abscisic acid (ABA) but whose molecular and cellular basis remains unclear. Here we show that hydrotropism still occurs in roots after laser ablation removed the meristem and root cap. Additionally, targeted expression studies reveal that hydrotropism depends on the ABA signalling kinase SnRK2.2 and the hydrotropism-specific MIZ1, both acting specifically in elongation zone cortical cells. Conversely, hydrotropism, but not gravitropism, is inhibited by preventing differential cell-length increases in the cortex, but not in other cell types. We conclude that root tropic responses to gravity and water are driven by distinct tissue-based mechanisms. In addition, unlike its role in root gravitropism, the elongation zone performs a dual function during a hydrotropic response, both sensing a water potential gradient and subsequently undergoing differential growth.

Root hydrotropism is controlled via a cortex-specific growth mechanism

Plants can acclimate by using tropisms to link the direction of growth to environmental conditions. Hydrotropism allows roots to forage for water, a process known to depend on abscisic acid (ABA) but whose molecular and cellular basis remains unclear. Here we show that hydrotropism still occurs in roots after laser ablation removed the meristem and root cap. Additionally, targeted expression studies reveal that hydrotropism depends on the ABA signalling kinase SnRK2.2 and the hydrotropism-specific MIZ1, both acting specifically in elongation zone cortical cells. Conversely, hydrotropism, but not gravitropism, is inhibited by preventing differential cell-length increases in the cortex, but not in other cell types. We conclude that root tropic responses to gravity and water are driven by distinct tissue-based mechanisms. In addition, unlike its role in root gravitropism, the elongation zone performs a dual function during a hydrotropic response, both sensing a water potential gradient and subsequently undergoing differential growth.

The gravity-induced re-localization of auxin efflux carrier CsPIN1 in cucumber seedlings: spaceflight experiments for immunohistochemical microscopy

Reorientation of cucumber seedlings induces re-localization of CsPIN1 auxin efflux carriers in endodermal cells of the transition zone between hypocotyl and roots. This study examined whether the re-localization of CsPIN1 was due to the graviresponse. Immunohistochemical analysis indicated that, when cucumber seedlings were grown entirely under microgravity conditions in space, CsPIN1 in endodermal cells was mainly localized to the cell side parallel to the minor axis of the elliptic cross-section of the transition zone. However, when cucumber seeds were germinated in microgravity for 24 h and then exposed to 1g centrifugation in a direction crosswise to the seedling axis for 2 h in space, CsPIN1 was re-localized to the bottom of endodermal cells of the transition zone. These results reveal that the localization of CsPIN1 in endodermal cells changes in response to gravity. Furthermore, our results suggest that the endodermal cell layer becomes a canal by which auxin is laterally transported from the upper to the lower flank in response to gravity. The graviresponse-regulated re-localization of CsPIN1 could be responsible for the decrease in auxin level, and thus for the suppression of peg formation, on the upper side of the transition zone in horizontally placed seedlings of cucumber.

Gravitropic response and circumnutation in pea (Pisum sativum) seedling roots

Plant circumnutation is a helical movement of growing organs such as shoots and roots. Gravitropic response is hypothesized to act as an external oscillator in shoot circumnutation, although this is subject to debate. The relationship between circumnutational movement and gravitropic response in roots remains unknown. In this study, we analyzed circumnutation of agravitropic roots using the ageotropum pea (Pisum sativum) mutant, and compared it with that of wild-type (cv. Alaska) pea roots. We further examined the relationship of gravitropic response to circumnutation of Alaska seedling roots by removing the gravisensing tissue (the root cap) and by treating the roots with auxin transport inhibitors. Alaska roots displayed circumnutational movements with a period of approximately 150 min, whereas ageotropum roots did not exhibit distinct circumnutational movement. Removal of the root cap in Alaska roots reduced gravitropic response and circumnutational movements. Treatment of Alaska roots with auxin transport inhibitors, 2,3,5-triiodobenzoic acid (TIBA) and N-(1-naphthyl)phthalamic acid (NPA), dramatically reduced gravitropic response and circumnutational movements. These results suggest that a gravity-regulated auxin transport is involved in circumnutation of pea seedling roots.

A Japanese single-hospital observational trial with a retrospective case-control analysis of varicella zoster virus reactivation after autologous peripheral blood stem cell transplantation

BACKGROUND

Varicella zoster virus (VZV) reactivation following hematopoietic stem cell transplantation (SCT) is common. To help reduce its incidence and to identify predictive factors for VZV reactivation after autologous SCT (auto-SCT), we conducted a retrospective analysis in patients with hematologic malignancy at our hospital.

METHODS

We conducted a single-hospital observational trial with a retrospective case-control analysis of post-auto-SCT VZV reactivation in patients with malignant lymphoma (ML) and multiple myeloma (MM) between January 2001 and December 2010, in the Department of Hematology at our hospital. First, we analyzed the cumulative incidence of VZV reactivation during the post-SCT period. Second, we conducted a case-control analysis to identify the risk factors for VZV reactivation within 1 year after SCT. Univariate analyses were performed using Fisher's exact test for categorical variables. A multivariable model and logistic regression were used to assess the risk factors for VZV reactivation.

RESULTS

We included 97 patients in this study. The median duration of follow-up was 1027 days. Forty-two patients experienced VZV reactivation after SCT, while 29 (69.0%) experienced reactivation within 1 year after SCT. The cumulative incidence was 30.7% at 1 year and 51.2% for the total observation period. Multivariate analysis showed that engraftment after day 10 was an independent risk factor for VZV reactivation (P = 0.03).

CONCLUSIONS

Our study showed a high incidence of VZV reactivation in the first year after auto-SCT in ML and MM patients. Patients with delayed engraftment are at high risk for VZV reactivation and should be considered for prolonged VZV prophylaxis.

GNOM regulates root hydrotropism and phototropism independently of PIN-mediated auxin transport

Plant roots exhibit tropisms in response to gravity, unilateral light and moisture gradients. During gravitropism, an auxin gradient is established by PIN auxin transporters, leading to asymmetric growth. GNOM, a guanine nucleotide exchange factor of ARF GTPase (ARF-GEF), regulates PIN localization by regulating subcellular trafficking of PINs. Therefore, GNOM is important for gravitropism. We previously isolated mizu-kussei2 (miz2), which lacks hydrotropic responses; MIZ2 is allelic to GNOM. Since PIN proteins are not required for root hydrotropism in Arabidopsis, the role of GNOM in root hydrotropism should differ from that in gravitropism. To examine this possibility, we conducted genetic analysis of gnom(miz2) and gnom trans-heterozygotes. The mutant gnom(miz2), which lacks hydrotropic responses, was partially recovered by gnom(emb30-1), which lacks GEF activity, but not by gnom(B4049), which lacks heterotypic domain interactions. Furthermore, the phototropic response of gnom trans-heterozygotes differed from that of the pin2 mutant allele eir1-1. Moreover, defects in the polarities of PIN2 and auxin distribution in a severe gnom mutant were recovered by gnom(miz2). Therefore, an unknown GNOM-mediated vesicle trafficking system may mediate root hydrotropism and phototropism independently of PIN trafficking.

MIZ1-regulated hydrotropism functions in the growth and survival of Arabidopsis thaliana under natural conditions

BACKGROUND AND AIMS

Root hydrotropism is a response to water-potential gradients that makes roots bend towards areas of higher water potential. The gene MIZU-KUSSEI1 (MIZ1) that is essential for hydrotropism in Arabidopsis roots has previously been identified. However, the role of root hydrotropism in plant growth and survival under natural conditions has not yet been proven. This study assessed how hydrotropic response contributes to drought avoidance in nature.

METHODS

An experimental system was established for the study of Arabidopsis hydrotropism in soil. Characteristics of hydrotropism were analysed by comparing the responses of the miz1 mutant, transgenic plants overexpressing MIZ1 (MIZ1OE) and wild-type plants.

KEY RESULTS

Wild-type plants developed root systems in regions with higher water potential, whereas the roots of miz1 mutant plants did not show a similar response. This pattern of root distribution induced by hydrotropism was more pronounced in MIZ1OE plants than in wild-type plants. In addition, shoot biomass and the number of plants that survived under drought conditions were much greater in MIZ1OE plants.

CONCLUSIONS

These results show that hydrotropism plays an important role in root system development in soil and contributes to drought avoidance, which results in a greater yield and plant survival under water-limited conditions. The results also show that MIZ1 overexpression can be used for improving plant productivity in arid areas.

Molecular mechanisms of hydrotropism in seedling roots of Arabidopsis thaliana (Brassicaceae)

Roots show positive hydrotropism in response to moisture gradients, which is believed to contribute to plant water acquisition. This article reviews the recent advances of the physiological and molecular genetic studies on hydrotropism in seedling roots of Arabidopsis thaliana. We identified MIZU-KUSSEI1 (MIZ1) and MIZ2, essential genes for hydrotropism in roots; the former encodes a protein of unknown function, and the latter encodes an ARF-GEF (GNOM) protein involved in vesicle trafficking. Because both mutants are defective in hydrotropism but not in gravitropism, these mutations might affect a molecular mechanism unique to hydrotropism. MIZ1 is expressed in the lateral root cap and cortex of the root proper. It is localized as a soluble protein in the cytoplasm and in association with the cytoplasmic face of endoplasmic reticulum (ER) membranes in root cells. Light and ABA independently regulate MIZ1 expression, which influences the ultimate hydrotropic response. In addition, MIZ1 overexpression results in an enhancement of hydrotropism and an inhibition of lateral root formation. This phenotype is likely related to the alteration of auxin content in roots. Specifically, the auxin level in the roots decreases in the MIZ1 overexpressor and increases in the miz1 mutant. Unlike most gnom mutants, miz2 displays normal morphology, growth, and gravitropism, with normal localization of PIN proteins. It is probable that MIZ1 plays a crucial role in hydrotropic response by regulating the endogenous level of auxin in Arabidopsis roots. Furthermore, the role of GNOM/MIZ2 in hydrotropism is distinct from that of gravitropism.

Overexpression of MIZU-KUSSEI1 enhances the root hydrotropic response by retaining cell viability under hydrostimulated conditions in Arabidopsis thaliana

Because of their sessile nature, plants evolved several mechanisms to tolerate or avoid conditions where water is scarce. The molecular mechanisms contributing to drought tolerance have been studied extensively, whereas the molecular mechanism underlying drought avoidance is less understood despite its importance. Several lines of evidence showed that the roots sense the moisture gradient and grow toward the wet area: so-called hydrotropism. We previously identified MIZU-KUSSEI (MIZ) 1 and MIZ2/GNOM as genes responsible for this process. To gain new insight into the molecular mechanism of root hydrotropism, we generated overexpressors of MIZ1 (MIZ1OEs) and analyzed their hydrotropic response. MIZ1OEs had a remarkable enhancement of root hydrotropism. Furthermore, a greater number of MIZ1OE root cells remained viable under hydrostimulated conditions than those of the wild type, which might contribute to retaining root growth under hydrostimulated conditions. Although overexpression of MIZ1 also caused a slight decrease in the root gravitropic response, it was not attributable to the enhanced hydrotropic response. In addition, miz2 mutation or the auxin response inhibitor nullified the enhanced hydrotropic response in MIZ1OEs. Furthermore, the expression of MIZ1 did not alter the expression of typical genes involved in drought tolerance. These results suggest that MIZ1 positively regulates hydrotropism at an early stage and its overexpression results in an enhancement of signal transduction unique to root hydrotropism to increase the degree of hydrotropic root bending.

A possible involvement of autophagy in amyloplast degradation in columella cells during hydrotropic response of Arabidopsis roots

Seedling roots display not only gravitropism but also hydrotropism, and the two tropisms interfere with one another. In Arabidopsis (Arabidopsis thaliana) roots, amyloplasts in columella cells are rapidly degraded during the hydrotropic response. Degradation of amyloplasts involved in gravisensing enhances the hydrotropic response by reducing the gravitropic response. However, the mechanism by which amyloplasts are degraded in hydrotropically responding roots remains unknown. In this study, the mechanistic aspects of the degradation of amyloplasts in columella cells during hydrotropic response were investigated by analyzing organellar morphology, cell polarity and changes in gene expression. The results showed that hydrotropic stimulation or systemic water stress caused dramatic changes in organellar form and positioning in columella cells. Specifically, the columella cells of hydrotropically responding or water-stressed roots lost polarity in the distribution of the endoplasmic reticulum (ER), and showed accelerated vacuolization and nuclear movement. Analysis of ER-localized GFP showed that ER redistributed around the developed vacuoles. Cells often showed decomposing amyloplasts in autophagosome-like structures. Both hydrotropic stimulation and water stress upregulated the expression of AtATG18a, which is required for autophagosome formation. Furthermore, analysis with GFP-AtATG8a revealed that both hydrotropic stimulation and water stress induced the formation of autophagosomes in the columella cells. In addition, expression of plastid marker, pt-GFP, in the columella cells dramatically decreased in response to both hydrotropic stimulation and water stress, but its decrease was much less in the autophagy mutant atg5. These results suggest that hydrotropic stimulation confers water stress in the roots, which triggers an autophagic response responsible for the degradation of amyloplasts in columella cells of Arabidopsis roots.

Light and abscisic acid signalling are integrated by MIZ1 gene expression and regulate hydrotropic response in roots of Arabidopsis thaliana

Plant roots undergo tropic growth in response to environmental cues, and each tropic response is affected by several environmental stimuli. Even its importance, molecular regulation of hydrotropism has not been largely uncovered. Tropic responses including hydrotropism were impacted by other environmental signal. We found that hydrotropism was reduced in dark-grown seedling. Moreover, we found that the expression of MIZ1, an essential gene for hydrotropism, was regulated by light signal. From our genetic analysis, phytochrome A (phyA)-, phyB- and HY5-mediated blue-light signalling play curial roles in light-mediated induction of MIZ1 and hydrotropism. In addition, we found that abscisic acid (ABA) also induced MIZ1 expression. ABA treatment could recover weak hydrotropism and MIZ1 expression level of hy5, and ABA synthesis inhibitor, abamineSG, further reduced hydrotropic curvature of hy5. In contrast, ABA treatment did not affect ahydrotropic phenotype of miz1. These results suggest that ABA signalling regulates MIZ1 expression independently from light signalling. Our results demonstrate that environmental signals, such as light and stresses mediated by ABA signalling, are integrated into MIZ1 expression and thus regulate hydrotropism. These machineries will allow plants to acquire sufficient amounts of water.

Accurate and rapid novel genetic diagnosis for detection of sentinel lymph node metastasis in breast cancer patients

Background:

The transcription-reverse transcription concerted reaction (TRC) test is a novel molecular-based procedure, which can assess nodal metastasis accurately and quickly. We examined the usefulness of the TRC test with a double marker, cytokeratin 19 (CK19) and carcinoembryonic antigen (CEA) mRNA, to detect sentinel lymph nodes (SLN) metastasis in breast cancer patients.

Methods:

A total of 264 SLNs from 131 breast cancer patients were assigned to a training set (109 SLNs from 50 patients) and validation set (155 SLNs from 81 patients). Cytokeratin 19 and CEA mRNA were detected by TRC tests, and the sensitivity and specificity of the SLN metastasis between the TRC and histology cohorts were compared.

Results:

Mean copy numbers of CK19 and CEA by TRC tests were increased according to the metastatic size. In the training set, TRC test showed 100% sensitivity, specificity and concordance rates against the permanent histopathology test. In the validation set, sensitivity was 97.1%, specificity was 99.2% and the concordance rate was 99.4%.

Conclusion:

Our results showed that the detection of CK19 and CEA mRNA using the TRC test is, an accurate and rapid method for detection of SLN metastasis and can be applied as an intraoperative molecular diagnosis in breast cancer patients.

Gravistimulation changes the accumulation pattern of the CsPIN1 auxin efflux facilitator in the endodermis of the transition zone in cucumber seedlings

Cucumber (Cucumis sativus) seedlings grown in a horizontal position develop a specialized protuberance (or peg) on the lower side of the transition zone between the hypocotyl and the root. This occurs by suppressing peg formation on the upper side via a decrease in auxin resulting from a gravitational response. However, the gravity-stimulated mechanism of inducing asymmetric auxin distribution in the transition zone is poorly understood. The gravity-sensing tissue responsible for regulating auxin distribution in the transition zone is thought to be the endodermal cell. To characterize the gravity-stimulated mechanism, the auxin efflux facilitator PIN-FORMED1 (CsPIN1) in the endodermis was identified and the localization of CsPIN1 proteins during the gravimorphogenesis of cucumber seedlings was examined. Immunohistochemical analysis revealed that the accumulation pattern of CsPIN1 protein in the endodermal cells of the transition zone of cucumber seedlings grown horizontally differed from that of plants grown vertically. Gravistimulation for 30 min prompted changes in the accumulation pattern of CsPIN1 protein in the endodermis as well as the asymmetric distribution of auxin in the transition zone. Furthermore, 2,3,5-triiodobenzoic acid inhibited the differential distribution of auxin as well as changes in the accumulation pattern of CsPIN1 in the endodermis of the transition zone during gravistimulation. These results suggest that the altered pattern of CsPIN1 accumulation in the endodermis in response to gravistimulation influences lateral auxin transport through the endodermis, resulting in asymmetric auxin distribution in the transition zone.

Hormonal regulation of lateral root development in Arabidopsis modulated by MIZ1 and requirement of GNOM activity for MIZ1 function

Plant organ development is important for adaptation to a changing environment. Genetic and physiological studies have revealed that plant hormones play key roles in lateral root formation. In this study, we show that MIZU-KUSSEI1 (MIZ1), which was identified originally as a regulator of hydrotropism, functions as a novel regulator of hormonally mediated lateral root development. Overexpression of MIZ1 (MIZ1OE) in roots resulted in a reduced number of lateral roots being formed; however, this defect could be recovered with the application of auxin. Indole-3-acetic acid quantification analyses showed that free indole-3-acetic acid levels decreased in MIZ1OE roots, which indicates that alteration of auxin level is critical for the inhibition of lateral root formation in MIZ1OE plants. In addition, MIZ1 negatively regulates cytokinin sensitivity on root development. Application of cytokinin strongly induced the localization of MIZ1-green fluorescent protein to lateral root primordia, which suggests that the inhibition of lateral root development by MIZ1 occurs downstream of cytokinin signaling. Surprisingly, miz2, a weak allele of gnom, suppressed developmental defects in MIZ1OE plants. Taken together, these results suggest that MIZ1 plays a role in lateral root development by maintaining auxin levels and that its function requires GNOM activity. These data provide a molecular framework for auxin-dependent organ development in Arabidopsis (Arabidopsis thaliana).

Factors responsible for deep-sowing tolerance in wheat seedlings: varietal differences in cell proliferation and the co-ordinated synchronization of epidermal cell expansion and cortical cell division for the gibberellin-mediated elongation of first internodes

BACKGROUND AND AIMS

A wheat cultivar, Triticum aestivum 'Hong Mang Mai', shows tolerance to deep-sowing conditions by extreme elongation of the first internode, likely mediated by the gibberellin (GA) response. To understand factors involved in the response of this deep-sowing-tolerant cultivar, cell expansion and division that confer elongation on the first internodes of wheat seedlings were investigated.

METHODS

The lengths and numbers of epidermal and cortical cells of the first internodes in three wheat cultivars were measured. These parameters were compared in wheat seedlings treated with gibberellin A(3) (GA(3)) or an inhibitor of GA biosynthesis, uniconazole.

KEY RESULTS

The varietal differences in the elongation of the first internodes were due to differences in cell numbers resulting from the different abilities of cell division, but not cell expansion. In seedlings treated with GA(3), the first internode of 'Hong Mang Mai' was 2-fold longer than the control. The GA-stimulated elongation of the first internodes was attributed to 2-fold increases in the number of cortical cells and length of epidermal cells. The different GA-responses observed in these two tissues were also detected in other cultivars, although the response was much lower than that noted in 'Hong Mang Mai'. The seedlings treated with uniconazole exhibited reduced numbers of cortical cells and reduced lengths of epidermal cells, with both of these effects being more pronounced in 'Hong Mang Mai'.

CONCLUSIONS

The deep-sowing-tolerant cultivar 'Hong Mang Mai' is able to elongate the first internode to a greater degree due to enhanced cell division and a heightened response to GA. In addition, cell expansion in the epidermis and cell division in the cortex are synchronized for the elongation of the first internodes. In response to GA, this well-co-ordinated synchronization yields the rapid elongation of the first internodes in wheat seedlings.

Hormonal interactions during root tropic growth: hydrotropism versus gravitropism

Terrestrial plants have evolved remarkable morphological plasticity that enables them to adapt to their surroundings. One of the most important traits that plants have acquired is the ability to sense environmental cues and use them as a basis for governing their growth orientation. The directional growth of plant organs relative to the direction of environmental stimuli is a tropism. The Cholodny-Went theory proposes that auxin plays a key role in several tropisms. Recent molecular genetic studies have strongly supported this hypothesis for gravitropism. However, the molecular mechanisms of other tropisms are far less clear. Hydrotropism is the response of roots to a moisture gradient. Since its re-discovery in 1985, root hydrotropism has been shown to be common among higher plant species. Additionally, in some species, gravitropism interferes with hydrotropism, suggesting that both shared and divergent mechanisms mediating the two tropisms exist. This hypothesis has been supported by recent studies, which provide an understanding of how roots sense multiple environmental cues and exhibit different tropic responses. In this review, we focus on the overlapping and unique mechanisms of the hormonal regulation underlying gravitropism and hydrotropism in roots.

GNOM-mediated vesicular trafficking plays an essential role in hydrotropism of Arabidopsis roots

Roots respond not only to gravity but also to moisture gradient by displaying gravitropism and hydrotropism, respectively, to control their growth orientation, which helps plants obtain water and become established in the terrestrial environment. As gravitropism often interferes with hydrotropism, however, the mechanisms of how roots display hydrotropism and differentiate it from gravitropism are not understood. We previously reported MIZU-KUSSEI1 (MIZ1) as a gene required for hydrotropism but not for gravitropism, although the function of its protein was not known. Here, we found that a mutation of GNOM encoding guanine-nucleotide exchange factor for ADP-ribosylation factor-type G proteins was responsible for the ahydrotropism of Arabidopsis (Arabidopsis thaliana), miz2. Unlike other gnom alleles, miz2 showed no apparent morphological defects or reduced gravitropism. Instead, brefeldin A (BFA) treatment inhibited both hydrotropism and gravitropism in Arabidopsis roots. In addition, a BFA-resistant GNOM variant, GNM696L, showed normal hydrotropic response in the presence of BFA. Furthermore, a weak gnom allele, gnomB/E, showed defect in hydrotropic response. These results indicate that GNOM-mediated vesicular trafficking plays an essential role in hydrotropism of seedling roots.

Effects of locally targeted heavy-ion and laser microbeam on root hydrotropism in Arabidopsis thaliana

Classical studies on root hydrotropism have hypothesized the importance of columella cells as well as the de novo gene expression, such as auxin-inducible gene, at the elongation zone in hydrotropism; however, there has been no confirmation that columella cells or auxin-mediated signaling in the elongation zone are necessary for hydrotropism. We examined the role of root cap and elongation zone cells in root hydrotropism using heavy-ion and laser microbeam. Heavy-ion microbeam irradiation of the elongation zone, but not that of the columella cells, significantly and temporarily suppressed the development of hydrotropic curvature. However, laser ablation confirmed that columella cells are indispensable for hydrotropism. Systemic heavy-ion broad-beam irradiation suppressed de novo expression of INDOLE ACETIC ACID 5 gene, but not MIZU-KUSSEI1 gene. Our results indicate that both the root cap and elongation zone have indispensable and functionally distinct roles in root hydrotropism, and that de novo gene expression might be required for hydrotropism in the elongation zone, but not in columella cells.

The gravity-regulated growth of axillary buds is mediated by a mechanism different from decapitation-induced release

When the upper part of the main shoot of the Japanese morning glory (Pharbitis nil or Ipomoea nil) is bent down, the axillary bud situated on the uppermost node of the bending region is released from apical dominance and elongates. Here, we demonstrate that this release of axillary buds from apical dominance is gravity regulated. We utilized two agravitropic mutants of morning glory defective in gravisensing cell differentiation, weeping (we) and weeping2 (we2). Bending the main shoots of either we or we2 plants resulted in minimal elongation of their axillary buds. This aberration was genetically linked to the agravitropism phenotype of the mutants, which implied that shoot bending-induced release from apical dominance required gravisensing cells. Previous studies have shown that basipetal translocation of auxin from the apical bud inhibits axillary bud growth, whereas cytokinin promotes axillary bud outgrowth. We therefore compared the roles of auxin and cytokinin in bending- or decapitation-induced axillary bud growth. In the wild-type and we plants, decapitation increased cytokinin levels and reduced auxin response. In contrast, shoot bending did not cause significant changes in either cytokinin level or auxin response, suggesting that the mechanisms underlying gravity- and decapitation-regulated release from apical dominance are distinct and unique.

P-chlorophenoxyisobutyric acid impairs auxin response for gravity-regulated peg formation in cucumber (Cucumis sativus) seedlings

Cucumber (Cucumis sativus L.) seedlings form a specialized protuberance, the peg, on the transition zone between the hypocotyl and the root. When cucumber seeds germinate in a horizontal position, the seedlings develop a peg on the lower side of the transition zone. To verify the role of auxin action in peg formation, we examined the effect of the anti-auxin, p-chlorophenoxyisobutyric acid (PCIB), on peg formation and mRNA accumulation of auxin-regulated genes. Application of PCIB to cucumber seedlings inhibited peg formation. The application of indole-3-acetic acid (IAA) competed with PCIB and induced peg formation. Furthermore, application of PCIB decreased auxin-inducible CsIAA1 mRNA and increased auxin-repressible CsGRP1 mRNA in the lower side of the transition zone. The differential accumulation of CsIAA1 and CsGRP1 mRNAs in the transition zone of cucumber seedlings grown in a horizontal position was smaller in the PCIB-treated seedlings. These results demonstrate that endogenous auxin redistributes and induces the differential expression of auxin-regulated genes, and ultimately results in the suppression or induction of peg formation in the gravistimulated transition zone of cucumber seedlings.

How do Arabidopsis roots differentiate hydrotropism from gravitropism?

Root hydrotropism is a response to moisture gradients, which is considered to be important for drought avoidance. Recent reevaluation of root hydrotropism has emphasised the dominating effect of root gravitropism on it. It has been suggested that amyloplast dynamics inside columella cells and auxin regulation play roles in this interacting mechanism, even though the existence of distinct pathways of two tropisms derived from different stimuli remained unclear. We have recently found two factors that separate the mechanism of hydrotropism from that of gravitropism in Arabidopsis seedling roots. One is the difference in the mode of auxin-mediated growth regulation between two tropisms, and the other is the identification of gene indispensable only for root hydrotropism. Here we summarize the recent progress on root hydrotropism research and discuss the remaining and emerging issues.

Biochemical and Molecular Biological Analyses of space-flown nematodes in Japan, the First International Caenorhabditis elegans Experiment (ICE-First)

The first International Caenorhabditis elegans Experiment (ICE-First) was carried out using a Russian Soyuz spacecraft from April 19-30, 2004. This experiment was a part of the program of the DELTA (Dutch Expedition for Life science Technology and Atmospheric research) mission, and the space agencies that participate in the International Space Station (ISS) program formed international research teams. A Japanese research team that conducted by Japan aerospace Exploration Agency (JAXA) investigated the following aspects of the organism: (1) whether meiotic chromosomal dynamics and apoptosis in the germ cells were normal under microgravity conditions, (2) the effect of the space flight on muscle cell development, and (3) the effect of the space flight on protein aggregation. In this article, we summarize the results of these biochemical and molecular biological analyses.

A gene essential for hydrotropism in roots

Roots display hydrotropism in response to moisture gradients, which is thought to be important for controlling their growth orientation, obtaining water, and establishing their stand in the terrestrial environment. However, the molecular mechanism underlying hydrotropism remains unknown. Here, we report that roots of the Arabidopsis mutant mizu-kussei1 (miz1), which are impaired in hydrotropism, show normal gravitropism and elongation growth. The roots of miz1 plants showed reduced phototropism and a modified wavy growth response. There were no distinct differences in morphological features and root structure between miz1 and wild-type plants. These results suggest that the pathway inducing hydrotropism is independent of the pathways used in other tropic responses. The phenotype results from a single recessive mutation in MIZ1, which encodes a protein containing a domain (the MIZ domain) that is highly conserved among terrestrial plants such as rice and moss. The MIZ domain was not found in known genomes of organisms such as green algae, red algae, cyanobacteria, or animals. We hypothesize that MIZ1 has evolved to play an important role in adaptation to terrestrial life because hydrotropism could contribute to drought avoidance in higher plants. In addition, a pMIZ1::GUS fusion gene was expressed strongly in columella cells of the root cap but not in the elongation zone, suggesting that MIZ1 functions in the early phase of the hydrotropic response.

Correlation between development of female flower buds and expression of the CS-ACS2 gene in cucumber plants

Ethylene plays a key role in sex determination of cucumber flowers. Gynoecious cucumber shoots produce more ethylene than monoecious shoots. Because monoecious cucumbers produce both male and female flower buds in the shoot apex and because the relative proportions of male and female flowers vary due to growing conditions, the question arises as to whether the regulation of ethylene biosynthesis in each flower bud determines the sex of the flower. Therefore, the expression of a 1-aminocyclopropane-1-carboxylic acid synthase gene, CS-ACS2, was examined in cucumber flower buds at different stages of development. The results revealed that CS-ACS2 mRNA began to accumulate just beneath the pistil primordia of flower buds at the bisexual stage, but was not detected prior to the formation of the pistil primordia. In buds determined to develop as female flowers, CS-ACS2 mRNA continued to accumulate in the central region of the developing ovary where ovules and placenta form. In gynoecious cucumber plants that produce only female flowers, accumulation of CS-ACS2 mRNA was detected in all flower buds at the bisexual stage and at later developmental stages. In monoecious cucumber, flower buds situated on some nodes accumulated CS-ACS2 mRNA, but others did not. The proportion of male and female flowers in monoecious cucumbers varied depending on the growth conditions, but was correlated with changes in accumulation of CS-ACS2 mRNA in flower buds. These results demonstrate that CS-ACS2-mediated biosynthesis of ethylene in individual flower buds is associated with the differentiation and development of female flowers.

Auxin response, but not its polar transport, plays a role in hydrotropism of Arabidopsis roots

Plants are sessile in nature, and need to detect and respond to many environmental cues in order to regulate their growth and orientation. Indeed, plants sense numerous environmental cues and respond via appropriate tropisms, and it is widely accepted that auxin plays an important role in these responses. Recent analyses using Arabidopsis have emphasized the importance of polar auxin transport and differential auxin responses to gravitropism. Even so, the involvement of auxin in hydrotropism remains unclear. To clarify whether or not auxin is involved in the hydrotropic response, Arabidopsis seedlings were treated with inhibitors of auxin influx (3-chloro-4-hydroxyphenylacetic acid), efflux (1-naphthylphthalemic acid and 2,3,5-triiodobenzoic acid), and response (p-chlorophenoxyisobutylacetic acid), and their effects were examined on both hydrotropic and gravitropic responses. In agreement with previous reports, gravitropism was inhibited by all the chemicals tested. By contrast, only an inhibitor of the auxin response (p-chlorophenoxyisobutylacetic acid) reduced hydrotropism, whereas inhibitors for influx or efflux of auxin had no effect. These results suggest that auxin response, apart from its polar transport, plays a definite role in hydrotropic response, and will evoke a new concept for the auxin-mediated regulation of tropisms.

Differential accumulation of the mRNA of the auxin-repressed gene CsGRP1 and the auxin-induced peg formation during gravimorphogenesis of cucumber seedlings

When cucumber seeds are germinated horizontally, an outgrowth (peg) develops on the lower side of the transition zone between the hypocotyl and the root for pulling the cotyledons and plumule out of the seed coat. We previously suggested that gravistimulation suppresses peg formation on the upper side of the transition zone when placed in a horizontal position. In the gravistimulated transition zone, auxin and the mRNAs of auxin-inducible genes are more abundant in the lower side than in the upper side. Here, using fluorescent differential display, we identified Cucumis sativus glycine-rich protein1(CsGRP1) as a gene whose mRNA accumulated more abundantly on the upper side than on the lower side of the transition zone in response to gravistimulation. Auxin starvation increased CsGRP1 mRNA in segments of the transition zone, and inhibition of polar auxin transport with 2,3,5-triiodobenzoic acid (TIBA) prevented the asymmetric accumulation of CsGRP1 mRNA. These results suggest that gravistimulation increases not only the expression of auxin-inducible genes on the lower side of the transition zone, but also the expression of auxin-repressed genes, such as CsGRP1, on the upper side of cucumber seedlings. In the hypocotyls of 3-day-old seedlings, neither gravistimulation nor changes in auxin level influenced the accumulation of CsGRP1 mRNA. These results suggest that the transition zone responds to gravistimulation in a specific manner by an asymmetric expression of CsGRP1 gene during regulation of peg formation.

Shoot circumnutation and winding movements require gravisensing cells

Circumnutation and winding in plants are universal growth movements that allow plants to survive despite their sessile nature. However, the detailed molecular mechanisms controlling these phenomena remain unclear. We previously found that a gravitropic mutant of Japanese morning glory (Pharbitis nil or Ipomoea nil), Shidare-asagao (weeping), is defective not only in circumnutation but also in the winding response. This phenotype is similar to that of the Arabidopsis SCARECROW (SCR) mutant. We therefore investigated whether morning glory SCR (PnSCR) is involved in the weeping phenotype. We found that one amino acid was inserted into the highly conserved VHIID motif in weeping-type PnSCR; this mutation caused abnormal endodermal differentiation. We introduced either the mutant or WT PnSCR into Arabidopsis scr mutants for complementation tests. PnSCR of the WT, but not of weeping, rescued the shoot gravitropism and circumnutation of scr. These results show that both the abnormal gravitropism and the circumnutation defect in weeping are attributable to a loss of PnSCR function. Thus, our data show that gravisensing endodermal cells are indispensable for shoot circumnutation and the winding response and that PnSCR is responsible for the abnormal phenotypes of weeping.

[A case of the multiple peripheral pulmonary artery branch stenosis]

A 31-year-old woman in whom primary pulmonary hypertension had been diagnosed at age 18, was admitted because of dyspnea on exertion and for evaluation of pregnancy risk. The perfusion scanning was not diagnostic, but chest CT suggested stenosis of pulmonary arteries instead of primary pulmonary hypertension. Echocardiograms and cardiac catheterization revealed pulmonary hypertension of pulmonary arterial pressure 71/13 (mean 39) mmHg with no cardiac defects. Selective pulmonary angiograms showed multiple stenosis of pulmonary arteries with poststenotic dilatations. We diagnosed multiple peripheral pulmonary artery branch stenosis with the pulmonary hypertension because systemic vasculitis was excluded because there were no signs of inflammation or any systemic arterial invlolvement This case was thought to be congenital, considering her history of over 30 years. In reports from western countries, maternal rubella and familial factors were important etiologic factors of this disease. Few cases have been reported in Japan and all cases, including the present case, were unrelated to the specific etiological factors. We recommended her to use birth control and have been observing her very carefully since the progression of the pulmonary hypertension is the major determinant of her prognosis.

Chemical regulation of abscisic acid catabolism in plants by cytochrome P450 inhibitors

Plant hormone abscisic acid (ABA) is an important factor for conferring drought stress resistance on plants. Therefore, small molecules that regulate ABA levels in plants can be useful both for investigating functions of ABA and for developing new plant growth regulators. Abscisic acid (ABA) catabolism in plants is primarily regulated by ABA 8'-hydroxylase, which is a cytochrome P450 (P450). We tested known P450 inhibitors containing a triazole group and found that uniconazole-P inhibited ABA catabolism in cultured tobacco Bright Yellow-2 cells. In a structure-activity study of uniconazole, we found a more effective ABA catabolic inhibitor (diniconazole) than uniconazole-P. Diniconazole, a fungicide, acted as a potent competitive inhibitor of recombinant Arabidopsis ABA 8'-hydroxylase, CYP707A3, in an in vitro assay. Diniconazole-treated plants retained a higher ABA content and higher transcription levels of ABA response genes during rehydration than did untreated plants and were more drought stress tolerant than untreated plants. These results strongly suggest that ABA catabolic inhibitors that target ABA 8'-hydroxylase can regulate the ABA content of plants and conferred drought stress resistance on plants. The optical resolution of diniconazole revealed that the S-form isomer, which is a weak fungicidal isomer, was more active as an ABA catabolic inhibitor than was the R-form isomer.

Checkpoint and physiological apoptosis in germ cells proceeds normally in spaceflown Caenorhabditis elegans

It is important for human life in space to study the effects of environmental factors during spaceflight on a number of physiological phenomena. Apoptosis plays important roles in development and tissue homeostasis in metazoans. In this study, we have analyzed apoptotic activity in germ cells of the nematode C. elegans, following spaceflight. Comparison of the number of cell corpses in wild type or ced-1 mutants, grown under either ground or spaceflight conditions, showed that both pachytene-checkpoint apoptosis and physiological apoptosis in germ cells occurred normally under spaceflight conditions. In addition, the expression levels of the checkpoint and apoptosis related genes are comparable between spaceflight and ground conditions. This is the first report documenting the occurrence of checkpoint apoptosis in the space environment and suggests that metazoans, including humans, would be able to eliminate cells that have failed to repair DNA lesions introduced by cosmic radiation during spaceflight.

CCLS96.1, a member of a multicopy gene family, may encode a non-coding RNA preferentially transcribed in reproductive organs of Silene latifolia

Dioecy in the model dioecious plant Silene latifolia is determined genetically by its heteromorphic sex chromosomes. A bacterial artificial chromosome (BAC) clone, #19B12, was isolated by screening a BAC library from S. latifolia using polymerase chain reaction (PCR) with a set of sequence tagged site (STS) primers, ScD05, which are specific to the Y chromosome. A portion of #19B12 was subcloned to construct plasmid #25-1, with an insert of 7.8 kb. This 7.8-kb fragment encodes ScD05 homolog and an anther-specific gene, CCLS96.1. Northern blot analysis of CCLS96.1 indicated a faint band of 1.8 kb in male and female flower buds. 5' and 3' rapid amplification of cDNA ends (RACE) indicated that transcripts of CCLS96.1 are very varied in size. Moreover, semi-quantitative reverse transcription-PCR (RT-PCR) showed that CCLS96.1 was also expressed in both male and female leaves. RACE produced at least ten species of transcripts, with 79-97% similarity among them. However, no significant ORFs could be predicted from their nucleotide sequences, since each has numerous stop codons throughout all three reading frames. Genomic Southern hybridization showed that the S. latifolia genome contains numerous CCLS96.1 homologs. These results suggest that the transcripts of CCLS96.1 play some role as multiple non-coding RNAs in S. latifolia.

Development of less invasive surgical procedures for thoracic esophageal cancer

In order to minimize the invasiveness of the operative procedure for thoracic esophageal cancer, several procedures have been introduced since January 1997. They included: (i) perioperative use of steroids; (ii) muscle-sparing thoracotomy without costectomy; (iii) preparation of the gastric tube with preservation of sufficient blood supply; (iv) reconstruction of the alimentary tract via posterior-mediastinal route; and (v) formation of anastomosis between the remaining esophagus and the gastric tube at a location between the gastroepiploic arteries of the gastric greater curvature. Twenty-one patients who did not receive preoperative chemoradiotherapy underwent the newly developed procedure, and were compared with those receiving the original procedure. Hospital mortality was zero, and postoperative systemic inflammatory response syndrome was suppressed. The mean postoperative hospital stay was 21.5 days, and the actuarial 3-year survival rate was 76.2%. From the comparison with those receiving the original procedure, it can be concluded that the newly developed procedures were effective in minimizing surgical invasiveness and were sufficiently curative in terms of cancer treatment.