Rhizosheath drought responsiveness is variety-specific and a key component of belowground plant adaptation

Biophysicochemical rhizosheath properties play a vital role in plant drought adaptation. However, their integration into the framework of plant drought response is hampered by incomplete mechanistic understanding of their drought responsiveness and unknown linkage to intraspecific plant-soil drought reactions. Thirty-eight Zea mays varieties were grown under well-watered and drought conditions to assess the drought responsiveness of rhizosheath properties, such as soil aggregation, rhizosheath mass, net-rhizodeposition, and soil organic carbon distribution. Additionally, explanatory traits, including functional plant trait adaptations and changes in soil enzyme activities, were measured. Drought restricted soil structure formation in the rhizosheath and shifted plant-carbon from litter-derived organic matter in macroaggregates to microbially processed compounds in microaggregates. Variety-specific functional trait modifications determined variations in rhizosheath drought responsiveness. Drought responses of the plant-soil system ranged among varieties from maintaining plant-microbial interactions in the rhizosheath through accumulation of rhizodeposits, to preserving rhizosheath soil structure while increasing soil exploration through enhanced root elongation. Drought-induced alterations at the root-soil interface may hold crucial implications for ecosystem resilience in a changing climate. Our findings highlight that rhizosheath soil properties are an intrinsic component of plant drought response, emphasizing the need for a holistic concept of plant-soil systems in future research on plant drought adaptation.

Unraveling root and rhizosphere traits in temperate maize landraces and modern cultivars: Implications for soil resource acquisition and drought adaptation

A holistic understanding of plant strategies to acquire soil resources is pivotal in achieving sustainable food security. However, we lack knowledge about variety-specific root and rhizosphere traits for resource acquisition, their plasticity and adaptation to drought. We conducted a greenhouse experiment to phenotype root and rhizosphere traits (mean root diameter [Root D], specific root length [SRL], root tissue density, root nitrogen content, specific rhizosheath mass [SRM], arbuscular mycorrhizal fungi [AMF] colonization) of 16 landraces and 22 modern cultivars of temperate maize (Zea mays L.). Our results demonstrate that landraces and modern cultivars diverge in their root and rhizosphere traits. Although landraces follow a 'do-it-yourself' strategy with high SRLs, modern cultivars exhibit an 'outsourcing' strategy with increased mean Root Ds and a tendency towards increased root colonization by AMF. We further identified that SRM indicates an 'outsourcing' strategy. Additionally, landraces were more drought-responsive compared to modern cultivars based on multitrait response indices. We suggest that breeding leads to distinct resource acquisition strategies between temperate maize varieties. Future breeding efforts should increasingly target root and rhizosphere economics, with SRM serving as a valuable proxy for identifying varieties employing an outsourcing resource acquisition strategy.

Effects of hypothalamic releasing hormones and biogenic amines on identified neurones in the circumoesophageal ganglia of the water snail (Planorbis corneus)

1. The effect of locally applied releasing hormones, thyrotropin-releasing hormone (TRH) and luteinizing-hormone-releasing hormone (LHRH) and the putative neurotransmitters, acetylcholine (ACh) and dopamine (DA), on the neuronal excitability of identified invertebrate giant dopaminergic neurone (GDN) and serotoninergic neurone (5-HT) (Planorbis corneus) were investigated by intracellular recording in vitro. 2. The membrane potential of GDN was of the order of -60 to -70 mV. The microiontophoretically applied substances produced membrane depolarization as well as spike activation. Their order of efficacy was as follows: TRH greater than ACh greater than DA greater than LHRH. 3. The effects of the tested TRH, ACh, LHRH and DA on serotoninergic neurones were less pronounced. 4. During ACh depolarization the membrane resistance of GDN was found to be strongly reduced, whereas TRH produced only a small reduction in membrane resistance. 5. Dihydro-beta-erythroidin (DHE) added to the bath solution reversibly blocked ACh depolarization without influencing TRH depolarization. Concentrations of atropine sulfate required to block the ACh depolarization were higher by at least 100 order of magnitude. 6. These effects are discussed in relation to the immunoreactive TRH detected earlier in the central nervous system of invertebrates and vertebrates. The results are consistent with the postulate that TRH acts as a neuromodulator and/or neurotransmitter on invertebrate and vertebrate neurones.

Effects of releasing factors on hypothalamic neurones

Our previous reports on the effect of locally applied polyeptides such as ACTH, the releasing factors TRF and LRF on single unit activity of hypothalamic neurones have been confirmed and extended by several workers. These polypeptides also exhibit behavioural effects. The concept that such hormonal polypeptides may exert neurotransmitter as well as neuromodulator function has gradually become acceptable.

Steroid-sensitive single neurons in rat hypothalamus and midbrain: identification by microelectrophoresis

Minute amounts of Na-dexamethasone-21-phosphate administered by microelectrophoresis to the immediate extracellular environment promptly suppressed electrical activity of 15 out of 115 hypothalamic and mesencephalic neurons, the effect being readily reversible. Such neurons marked with fast green were found to lie in circumscribed areas of the periventricular gray of the third ventricle and aqueduct, and may represent a site of action of adrenocortical steroids in the regulation of corticotrophin releasing factor and/or adrenocortico-tropin secretion by negative feedback.