Spatial O2 Profile in Coix lacryma-jobi and Sorghum bicolor along the Gas Diffusion Pathway under Waterlogging Conditions

While internal aeration in plants is critical for adaptation to waterlogging, there is a gap in understanding the differences in oxygen diffusion gradients from shoots to roots between hypoxia-tolerant and -sensitive species. This study aims to elucidate the differences in tissue oxygen concentration at various locations on the shoot and root between a hypoxia-tolerant species and a -sensitive species using a microneedle sensor that allows for spatial oxygen profiling. Job's tears, a hypoxia-tolerant species, and sorghum, a hypoxia-susceptible species, were tested. Plants aged 10 days were acclimated to a hypoxic agar solution for 12 days. Oxygen was profiled near the root tip, root base, root shoot junction, stem, and leaf. An anatomical analysis was also performed on the roots used for the O2 profile. The oxygen partial pressure (pO2) values at the root base and tip of sorghum were significantly lower than that of the root of Job's tears. At the base of the root of Job's tears, pO2 rapidly decreased from the root cortex to the surface, indicating a function to inhibit oxygen leakage. No significant differences in pO2 between the species were identified in the shoot part. The root cortex to stele ratio was significantly higher from the root tip to the base in Job's tears compared to sorghum. The pO2 gradient began to differ greatly at the root shoot junction and root base longitudinally, and between the cortex and stele radially, between Job's tears and sorghum. Differences in the root oxygen retention capacity and the cortex to stele ratio are considered to be related to differences in pO2.

The original polyethylene microplastics inhibit the growth of sweet potatoes and increase the safety risk of cadmium

Microplastics (MPs) and heavy metals (HMs) co-exist in sweet potato fields of China. As the main component of agricultural field mulch and one of the most polluting and harmful HMs, the effects of polyethylene microplastics (PE MPs) and cadmium (Cd) on sweet potato and soil environment are remains unclear. Here, pot and hydroponic experiments are used to explore the effects of original and weathered PE MPs on growth and Cd uptake of sweet potatoes. The results of pot experiments reveal that compared with the control (0%), 5% of weathered PE MPs can significantly increase soil electrical conductivity (EC); both 5% of the original PE MPs and weathered PE MPs can significantly reduce the concentration of Olsen phosphorus (P) and Olsen potassium (K) in soil, inhibit plant growth, but significantly increase Cd accumulation and glutathione (GSH) level in tissues of sweet potatoes, and also induce membrane lipid peroxidation. In addition, compared to 5% weathered PE MPs, 5% original PE MPs significantly reduce soil EC, growth and peroxidase level of sweet potatoes, but significantly increase Cd concentration in leaves and stems. The results of hydroponic experiment show that original PE MPs significantly increase the P, K, and Cd adsorption compared with weathered PE MPs, and Cd increases the original PE MPs accumulation in the root cortex but decrease PE MPs accumulation in shoots. To sum up, our study investigates the differences and reasons of the effects of original and weathered PE MPs on growth and Cd absorption of sweet potatoes.

Nodulating Legumes Are Distinguished by a Sensitivity to Cytokinin in the Root Cortex Leading to Pseudonodule Development

Root nodule symbiosis (RNS) is a feature confined to a single clade of plants, the Fabids. Among Fabids capable of RNS, legumes form root cortex-based nodules in symbioses with rhizobia, while actinorhizal species form lateral root-based nodules with actinomycetes. Cytokinin has previously been shown to be sufficient for "pseudonodule" initiation in model legumes. Here, we tested whether this response correlates with the ability to nodulate across a range of plant species. We analyzed the formation of pseudonodules in 17 nodulating and non-nodulating legume species, and 11 non-legumes, including nodulating actinorhizal species, using light and fluorescence microscopy. Cytokinin-induced pseudonodules arising from cortical cell divisions occurred in all nodulating legume species, but not in any of the other species, including non-nodulating legumes. Pseudonodule formation was dependent on the CRE1 cytokinin receptor in Medicago truncatula. Inhibition of root growth by cytokinin occurred across plant groups, indicating that pseudonodule development is the result of a specific cortical cytokinin response unique to nodulating legumes. Lack of a cortical cytokinin response from the Arabidopsis thaliana cytokinin reporter TCSn::GFP supported this hypothesis. Our results suggest that the ability to form cortical cell-derived nodules was gained in nodulating legumes, and likely lost in non-nodulating legumes, due to a specific root cortical response to cytokinin.

A new three-locus model for rootstock-induced dwarfing in apple revealed by genetic mapping of root bark percentage

Rootstock-induced dwarfing of apple scions revolutionized global apple production during the twentieth century, leading to the development of modern intensive orchards. A high root bark percentage (the percentage of the whole root area constituted by root cortex) has previously been associated with rootstock-induced dwarfing in apple. In this study, the root bark percentage was measured in a full-sib family of ungrafted apple rootstocks and found to be under the control of three loci. Two quantitative trait loci (QTLs) for root bark percentage were found to co-localize to the same genomic regions on chromosome 5 and chromosome 11 previously identified as controlling dwarfing, Dw1 and Dw2, respectively. A third QTL was identified on chromosome 13 in a region that has not been previously associated with dwarfing. The development of closely linked sequence-tagged site markers improved the resolution of allelic classes, thereby allowing the detection of dominance and epistatic interactions between loci, with high root bark percentage only occurring in specific allelic combinations. In addition, we report a significant negative correlation between root bark percentage and stem diameter (an indicator of tree vigour), measured on a clonally propagated grafted subset of the mapping population. The demonstrated link between root bark percentage and rootstock-induced dwarfing of the scion leads us to propose a three-locus model that is able to explain levels of dwarfing from the dwarf 'M.27' to the semi-invigorating rootstock 'M.116'. Moreover, we suggest that the QTL on chromosome 13 (Rb3) might be analogous to a third dwarfing QTL, Dw3, which has not previously been identified.

Rhizobial infection does not require cortical expression of upstream common symbiosis genes responsible for the induction of Ca(2+) spiking

For the establishment of an effective root nodule symbiosis, a coordinated regulation of the infection processes between the epidermis and cortex is required. However, it remains unclear whether the symbiotic genes identified so far are involved in epidermal and/or cortical infection, e.g. epidermal and cortical infection thread formation or cortical cell division. To analyze the symbiotic gene requirements of the infection process, we have developed an epidermis-specific expression system (pEpi expression system) and examined the symbiotic genes NFR1, NFR5, NUP85, NUP133, CASTOR, POLLUX, CCaMK, CYCLOPS, NSP1 and NSP2 for involvement in the infection process in the epidermis and cortex. Our study shows that expression of the upstream common symbiosis genes CASTOR, POLLUX, NUP85 and NUP133 in the epidermis is sufficient to induce formation of infection threads and cortical cell division, leading to the development of fully effective nodules. Our system also shows a requirement of CCaMK, CYCLOPS, NSP1 and NSP2 for the entire nodulation process, and the different contributions of NFR1 and NFR5 to cortical infection thread formation. Based on these analyses using the pEpi expression system, we propose a functional model of symbiotic genes for epidermal and cortical infection.

QUNTITATIVE ION DISTRIBUTION WITHIN ROOT CELLS OF SALT-SENSITIVE AND SALT-TOLERANT MAIZE VARIETIES

Significant varietal differences were apparent in the survival of seedlings of maize in saline conditions but only at relatively high external concentrations (200 mol m^-3 NaCl), where there was a range from 0 to 66% survival, 25 d after salinization. For the varieties examined there was a strong negative correlation between Na concentrations in the third leaf and survival. Two resistant varieties (Across 8024 and Protador) and one salt-sensitive variety (LG₁₁ ) were identified. The characteristics of ion accumulation were clearly different in salt-tolerant and salt-sensitive types, the difference becoming more pronounced with plant age. The distribution of ions, particular those of Na, K and Cl, was determined within subcellular compartments of roots cells using X-ray microanalysis of freeze-substituted tissue. Salinity induced a greater increase (about 1.7 times) in cytoplasmic Na concentration in the salt-sensitive variety (LG₁₁ ) than in resistant varieties (Across 8024 or Protador). The mean K:Na ratio in the cytoplasm of the root cortical cells in the salt-resistant varieties grown for 15 d in saline conditions (100 mol m^-3 NaCl) was twice that found for LG₁₁ . Sodium and Cl concentrations in the vacuoles decreased radially inwards from the epidermal cells in salt-treated roots of LG₁₁ .

MORPHOLOGICAL AND ANATOMICAL EFFECTS OF SEVERE DROUGHT ON THE ROOTS OF LOLIUM PERENNE L

Three experiments using soil-grown Lolium perenne plants were performed in order to investigate the effects of a gradually increasing drought stress on the death of root cells and the growth of lateral roots. Water potentials of -2 to -10 MPa caused death of the root cortex, but death of root tips occurred only at soil water potentials below -10 MPa. Low soil water potentials promoted lateral root initiation and elongation, the total length of lateral roots being between three and five times that of control plants. On rewetting severely droughted plants, root growth continued by elongation of existing, previously initiated, lateral roots.