Touch induces ATP release in Arabidopsis roots that is modulated by the heterotrimeric G-protein complex

Amongst the many stimuli orienting the growth of plant roots, of critical importance are the touch signals generated as roots explore the mechanically complex soil environment. However, the molecular mechanisms behind these sensory events remain poorly defined. We report an impaired obstacle-avoiding response of roots in Arabidopsis lacking a heterotrimeric G-protein. Obstacle avoidance may utilize a touch-induced release of ATP to the extracellular space. While sequential touch stimulation revealed a strong refractory period for ATP release in response to mechano-stimulation in wild-type plants, the refractory period in mutants was attenuated, resulting in extracellular ATP accumulation. We propose that ATP acts as an extracellular signal released by mechano-stimulation and that the G-protein complex is needed for fine-tuning this response.     

A Golgi-localized hexose transporter is involved in heterotrimeric G protein-mediated early development in Arabidopsis

Signal transduction involving heterotrimeric G proteins is universal among fungi, animals, and plants. In plants and fungi, the best understood function for the G protein complex is its modulation of cell proliferation and one of several important signals that are known to modulate the rate at which these cells proliferate is D-glucose. Arabidopsis thaliana seedlings lacking the beta subunit (AGB1) of the G protein complex have altered cell division in the hypocotyl and are D-glucose hypersensitive. With the aim to discover new elements in G protein signaling, we screened for gain-of-function suppressors of altered cell proliferation during early development in the agb1-2 mutant background. One agb1-2-dependent suppressor, designated sgb1-1(D) for suppressor of G protein beta1 (agb1-2), restored to wild type the altered cell division in the hypocotyl and sugar hypersensitivity of the agb1-2 mutant. Consistent with AGB1 localization, SGB1 is found at the highest steady-state level in tissues with active cell division, and this level increases in hypocotyls when grown on D-glucose and sucrose. SGB1 is shown here to be a Golgi-localized hexose transporter and acts genetically with AGB1 in early seedling development.     

The distributional changes and role of microtubules in Nod factor-challenged<Emphasis Type="Italic"> Medicago sativa</Emphasis> root hairs

The normal tip-growing pattern exhibited by root hairs of legumes is disrupted when the hair is exposed to Nod factors generated by compatible bacteria capable of inducing nodule formation. Since microtubules (MTs) play an important role in regulating directionality and stability of apical growth in root hairs [T.N. Bibikova et al. (1999) Plant J 17:657–665], we examined the possibility that Nod factors might affect the MT distribution patterns in root hairs of Medicago sativa L. We observed that Nod factor application caused rapid changes in the pattern of MTs starting as early as 3 min after perfusion. Within 3 to 10 min after Nod factor application, first endoplasmic and then cortical MTs depolymerised, initially at the proximal ends of cells. Twenty minutes after exposure to Nod factors, a transverse band of microtubules was seen behind the tip, while almost all other MTs had depolymerised. By 30 min, very few MTs remained in the root hair and yet by 1 h the MT cytoskeleton re-formed. When Nod factors were applied in the presence of 10 M oryzalin or 5 M taxol, the MTs appeared disintegrated while the morphological effects, such as bulging and branching, became enhanced. Compared to the treatments with oryzalin or taxol alone, the combinatory treatments exhibited higher growth rates. Since microtubule reorganization is one of the earliest measurable events following Nod factor application we conclude that microtubules have an important role in the early phases of the signalling cascade. Microtubule involvement could be direct or a consequence of Nod factor-induced changes in ion levels.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00425-003-1097-1Abbreviations BNM buffered nodulation medium - CLSM confocal laser scanning microscopy - MT microtubule     

Association of Gestational Age at Birth with Reasons for Subsequent Hospitalisation: 18 Years of Follow-Up in a Western Australian Population Study

Background

Preterm infants are at a higher risk of hospitalisation following discharge from the hospital after birth. The reasons for rehospitalisation and the association with gestational age are not well understood.

Methods

This was a retrospective birth cohort study of all live, singleton infants born in Western Australia between 1^st January 1980 and 31^st December 2010, followed to 18 years of age. Risks of rehospitalisation following birth discharge by principal diagnoses were compared for gestational age categories (<32, 32–33, 34–36, 37–38 weeks) and term births (39–41weeks). Causes of hospitalisations at various gestational age categories were identified using ICD-based discharge diagnostic codes.

Results

Risk of rehospitalisation was inversely correlated with gestational age. Growth-related concerns were the main causes for rehospitalisation in the neonatal period (<1 month of age) for all gestational ages. Infection was the most common reason for hospitalisation from 29 days to 1 year of age, and up to 5 years of age. Injury-related hospitalisations increased in prevalence from 5 years to 18 years of age. Risk of rehospitalisation was higher for all preterm infants for most causes.

Conclusions

The highest risks of rehospitalisation were for infection related causes for most GA categories. Compared with full term born infants, those born at shorter GA remain vulnerable to subsequent hospitalisation for a variety of causes up until 18 years of age.