Bingru Huang

Root carbon and protein metabolism associated with heat tolerance

Extensive past efforts have been taken toward understanding heat tolerance mechanisms of the aboveground organs. Root systems play critical roles in whole-plant adaptation to heat stress, but are less studied. This review discusses recent research results revealing some critical physiological and metabolic factors underlying root thermotolerance, with a focus on temperate perennial grass species. Comparative analysis of differential root responses to supraoptimal temperatures by a heat-adapted temperate C3 species, Agrostis scabra, which can survive high soil temperatures up to 45 °C in geothermal areas in Yellow Stone National Park, and a heat-sensitive cogeneric species, Agrostis stolonifera, suggested that efficient carbon and protein metabolism is critical for root thermotolerance. Superior root thermotolerance in a perennial grass was associated with a greater capacity to control respiratory costs through respiratory acclimation, lowering carbon investment in maintenance for protein turnover, and efficiently partitioning carbon into different metabolic pools and alternative respiration pathways. Proteomic analysis demonstrated that root thermotolerance was associated with an increased maintenance of stability and less degradation of proteins, particularly those important for metabolism and energy production. In addition, thermotolerant roots are better able to maintain growth and activity during heat stress by activating stress defence proteins such as those participating in antioxidant defence (i.e. superoxide dismutase, peroxidase, glutathione S-transferase) and chaperoning protection (i.e. heat shock protein).

Nutrient accumulation and distribution of wheat genotypes in response to waterlogging and nutrient supply

The effect of soil waterlogging and nutrient supply on plant nutrient accumulation and distribution was investigated for two genotypes of winter wheat (Triticum aestivum L.) differing in waterlogging resistance, ‘Bayles’ and ‘Savannah’. Plants were grown in waterlogged or drained sand and fertilized with half-strength or full-strength Hoaglands solution.Waterlogging reduced the concentrations of N, P, K, Mg, and Zn in leaves and stems and increased the concentrations of those elements in the root system. The effects were greater for waterlogging-sensitive Bayles than for waterlogging-resistant Savannah. Higher concentrations of Fe and Mn were found in waterlogged plants compared to the control plants for sensitive Bayles. Waterlogging increased the proportion of N and Zn in the root system and decreased that of K in stems for Bayles. The proportion of Fe increased in leaves and stems for Bayles and Savannah under waterlogged conditions, but to a greater extent for Bayles. Doubling the concentrations of all major and minor nutrient elements supplied to the waterlogged rooting medium improved plant nutrient status and enhanced plant dry matter production.

Soil Sheaths, Photosynthate Distribution to Roots, and Rhizosphere Water Relations for Opuntia ficus-indica

Soil sheaths incorporating aggregated soil particles surround young roots of many species, but the effects of such sheaths on water movement between roots and the soil are largely unknown. The quantity and location of root exudates associated with soil sheath formation and root water loss were therefore examined for Opuntia ficus-indica, which has prominent soil sheaths along the entire length of its young roots, except within 1.4 cm of the tip. The soil sheaths, which averaged 0.7 mm in thickness, were composed of soil particles and root hairs, both of which were covered with exuded mucilaginous material. As determined with a 14C pulse-labeling technique, 2% of newly fixed 14C-photosynthate was translocated into the roots at 3 d, 6% at 9 d, and 8% at 15 d after labeling. The fraction of insoluble 14C in the roots increased twofold from 3 d to 15 d. Over the same time period, 6%-9% of the 14C translocated to the roots was exuded into the soil. The soluble 14C compounds exuded into the soil were greater in the 3-cm segment at the root tip than elsewhere along the root, whereas mucilage was exuded relatively uniformly along roots 15 cm in length. The volumetric efflux of water increased for both sheathed and unsheathed roots as the soil water potential decreased from -0.1 MPa to -1.0 MPa. The efflux rate was greater for unsheathed roots than for sheathed roots, which were more turgid and had a higher water potential, especially at lower soil water potentials. During drying, soil particles in the sheaths aggregate more tightly, making the sheaths less permeable to water and possibly creating air gaps. The soil sheaths of O. ficus-indica thus reduce water loss from the roots to a drying soil.

Hydraulic and Structural Changes for Lateral Roots of Two Desert Succulents in Response to Soil Drying and Rewetting

To investigate whether lateral roots of Agave deserti and Ferocactus acanthodes exhibit rectifier-like behavior facilitating water uptake from wet soil but restricting water loss to dry soil, root hydraulic conductivity (Lp) was determined under wet conditions, at various times during drought, and after rewetting. Also, accompanying changes in root morphology and anatomy were examined. For A. deserti, Lp was lower for longer lateral roots and decreased about sixfold during 35 d of drought, whereas for F. acanthodes Lp was higher for longer roots and decreased twofold during drought. The drought-induced decreases in Lp were caused primarily by dehydration of cortical cells and increased suberization of the endodermis and the hypodermis for A. deserti and increased suberization of the periderm for F. acanthodes. After 18 d of drought, some of the decrease in La was reversible upon rewetting. Moreover, water loss during drought for A. deserti was reduced by abscission of most of the lateral roots, and water uptake after rewetting was enhanced by the induction of secondary lateral roots. Thus, just as for main roots of both species, the lateral roots also undergo structural changes that increase water uptake from wet soil and reduce water loss to dry soil, which is in addition to the rectification of water movement for the soil and root-soil air gaps accompanying changes in soil water status.

Responses of squash to salinity, waterlogging, and subsequent drainage: I. Gas exchange, water relations, and nitrogen status

Abstract To examine plant physiological responses to salinity, waterlogging, and subsequent drainage, summer squash (Cucurbita pepo) was grown in well watered or flooded sand with full‐strength Hoagland solution containing 100 mol/m3 sodium chloride (NaCl) or no NaCl for 14 d. Half of the waterlogged plants were transferred to drained conditions for 7 d of recovery, while half of salinized plants were continuously salinized until 21 d. Waterlogging or salinity alone reduced photosynthetic rate (Pn), stomatal conductance (gs), and leaf chlorophyll content to a greater extent with waterlogging. Waterlogging alone, however, did not affect leaf water potential (ψ leaf) Salinity alone did not affect leaf and root nitrogen content. A combination of waterlogging and salinity exacerbated the adverse effects of each factor alone for Pn, gs, leaf chlorophyll, and nitrogen content, but not for ψ leaf. Seven days after termination of waterlogging, a full recovery occurred for gs, ψ leaf, leaf chlorophyll content, and...

Responses of squash to salinity, waterlogging, and subsequent drainage: II. Root and shoot growth

Abstract The responses of root and shoot growth to concurrent salinity and waterlogging, and subsequent drainage of summer squash (Cucurbita pepo) were studied in a greenhouse experiment. Plants were well watered or flooded with full‐strength Hoagland solution containing 100 mol/m3 sodium chloride (NaCl) or no NaCl for 14 d. Waterlogged plants were then transferred to drained conditions for 7 d of recovery, while salinized plants were continuously salinized until 21 d. Waterlogging led to greater reductions in root and shoot growth, and fruit yield than did salinity. Waterlogging stimulated production of adventitious roots; however, salinity suppressed this enhancement effect. A combination of waterlogging and salinity exacerbated the adverse effects of each factor alone on root and shoot growth. Seven days after termination of waterlogging, a full recovery occurred for number and length of adventitious roots, number of lateral roots, and root dry weight for waterlogged plants under non‐saline conditions,...

Responses of triticale and wheat to hypoxia.

The responses of triticale (cv. Florico) and wheat (cvs. Bayles and Savannah) to hypoxia were evaluated by growing plants in nutrient solutions flushed with air (aerated control), or a mixture of 5% O2 and 95% N2 (hypoxia). Hypoxia for 21 d reduced the number of crown roots for Bayles and Florico, while the number of crown roots of Savannah was increased. Seminal and crown root lengths were reduced significantly for all genotypes. Hypoxia reduced lateral root length significantly for Bayles and Savannah, but not for Florico. Reduction in root dry weight after 21 d of hypoxia was less for Florico than Bayles and Savannah. Shoot growth was inhibited by hypoxia, to a less extent for Florico and Savannah than Bayles. Hypoxia stimulated formation of aerenchyma in crown roots, to a greater extent for Savannah and Florico than for Bayles. Stomatal conductance was reduced for Bayles, but not for Florico and Savannah.