No abstract

Hydraulics of plants that have different strategies of stomatal regulation under water stress are relatively poorly understood. We explore how root and shoot hydraulics, stomatal conductance (g s), leaf and root aquaporin (AQP) expression, and abscisic acid (ABA) concentration in leaf xylem sap ([ABA] xylemsap) may be coordinated under mild water stress and exogenous ABA applications in two Vitis vinifera L. cultivars traditionally classified as near-isohydric (Grenache) and near-anisohydric (Syrah). Under water stress, Grenache exhibited stronger adjustments of plant and root hydraulic conductances and greater stomatal sensitivity to [ABA] xylemsap than Syrah resulting in greater conservation of soil moisture but not necessarily more isohydric behavior. Correlations between leaf (leaf) and predawn (PD) water potentials between cultivars suggested a "hydrodynamic" behavior rather than a particular iso-anisohydric classification. A significant decrease of leaf in well-watered ABA-fed vines supported a role of ABA in the soil-leaf hydraulic pathway to regulate g s. Correlations between leaf and root AQPs expression levels under water deficit could explain the response of leaf (K leaf) and root (Lp r) hydraulic conductances in both cultivars. Additional studies under a wider range of soil water deficits are required to explore the possible differential regulation of g s and plant hydraulics in different cultivars and experimental conditions.

The role of some aquaporins as CO permeable channels has been controversial. Low CO permeability of plant membranes has been criticized because of unstirred layers and other limitations. Here we measured both water and CO permeability (P , P ) using stopped flow on plasma membrane vesicles (pmv) isolated from Pisum sativum (pea) and Arabidopsis thaliana leaves. We excluded the chemical limitation of carbonic anhydrase (CA) in the vesicle acidification technique for P using different temperatures and CA concentrations. Unstirred layers were excluded based on small vesicle size and the positive correlation between vesicle diameter and P . We observed high aquaporin activity (P 0.06 to 0.22 cm s ) for pea pmv based on all the criteria for their function using inhibitors and temperature dependence. Inhibitors of P did not alter P . P ranged from 0.001 to 0.012 cm s (mean 0.0079 + 0.0007 cm s ) with activation energy of 30.2 kJ mol . Intrinsic variation between pmv batches from normally grown or stressed plants revealed a weak (R = 0.27) positive linear correlation between P and P . Despite the low P , aquaporins may facilitate CO transport across plasma membranes, but probably via a different pathway than for water.

The degree to which isohydric or anisohydric behaviour extends to the water balance of developing fruits has not previously been explored. Here, we examine the water relations and hydraulic behaviour of Vitis vinifera L. berries during development from two contrasting cultivars that display isohydric (cv. Grenache) or anisohydric (cv. Shiraz) behaviour. Hydraulic resistance normalised to the berry surface area of Grenache clusters was significantly lower and more constant during development, whereas that of Shiraz increased. Lower rachis hydraulic resistance in Grenache compared with Shiraz was inversely related to xylem vessel diameter. Berry transpiration and xylem water uptake measured on detached berries decreased alike during development. From veraison, detached berries of both cultivars showed a transition to a net imbalance between xylem water uptake and transpiration, with Shiraz showing a larger imbalance and berry dehydration towards the end of ripening. In planta, this imbalance must be counterbalanced by a larger phloem water influx in post-veraison berries. Concurrently, the calculated pressure gradients for xylem water uptake showed a decline, which broadly agreed with the measured values. Higher suction for xylem water uptake in pre-veraison berries was mainly generated by transpiration. We conclude that isohydric or anisohydric behaviour is reflected in the contrasting behaviour of fruit hydraulics and that a change from xylem water uptake to phloem import is correlated with the loss of the propensity to generate negative apoplastic pressure in the berry.

Russeting is an important surface disorder in fruit and mechanical growth stresses, among other factors, are considered causal in russet induction. To test this hypothesis, fruit development and russeting were monitored on a whole fruit level and also in the calyx, cheek, and neck region of developing 'Conference' and 'Condo' pear fruit (Pyrus communis L.). To quantify growth, the pear fruit was geometrically modeled as approximating to half of a prolate spheroid for the calyx region and two truncated cones for the cheek and neck regions, respectively. Mass and surface area of 'Conference' and 'Condo' fruit increased in a single sigmoidal pattern with time. Fruit volume, determined by buoyancy, using a hydrostatic balance, and the Archimedes' principle was closely related to that predicted by the model from fruit geometry. Growth rates of surface area in 'Conference' and 'Condo' peaked at ' '90 and 100 days after full bloom (DAFB), respectively, and were highest in the calyx followed by the cheek and neck regions. Relative growth rates, calculated by dividing growth rates by the absolute surface area present at that time, were at maximum during early development and thereafter continuously declined. In general, relative growth rates were highest for the cheek region, intermediate in the calyx, and lowest for the neck. 'Conference' fruit were always more russeted than 'Condo' with russeting generally decreasing from calyx to cheek and neck. Furthermore, russeting increased rapidly in 'Conference' during early development until ' '70 DAFB, particularly in the calyx and cheek regions and, to a lesser extent, in the neck region. There was little change in russeting after ' '70 DAFB. Plotting rates of russeting vs. relative growth rates in surface area indicate a positive and common relationship across regions where russeting increased when relative growth rates exceeded 0.03/day. Thus, differential growth rates between regions within 'Conference' or 'Condo', but not across the two cultivars, accounted for topical differences in russeting.

Well‐adapted root systems allow plants to grow under resource‐limiting environmental conditions and are important determinants of yield in agricultural systems. Important staple crops such as rice and maize belong to the family of grasses, which develop a complex root system that consists of an embryonic root system that emerges from the seed, and a postembryonic nodal root system that emerges from basal regions of the shoot after germination. While early seedling establishment is dependent on the embryonic root system, the nodal root system, and its associated branches, gains in importance as the plant matures and will ultimately constitute the bulk of below‐ground growth. In this review, we aim to give an overview of the different root types that develop in cereal grass root systems, explore the different physiological roles they play by defining their anatomical features, and outline the genetic networks that control their development. Through this deconstructed view of grass root system function, we provide a parts‐list of elements that function together in an integrated root system to promote survival and crop productivity.

No abstract

Information about the root system architecture of plants is of great value in modern crop science. However, there is a dearth of tools that can provide field-scale measurements of below-ground parameters in a non-destructive and non-invasive fashion. In this paper, we propose a multi-modal, non-contact thermoacoustic sensing system to address this measurement gap and discuss various system design aspects in the context of belowground sensing. We also demonstrate the first thermoacoustic images of plant material (potatoes) in a soil medium, with the use of highly sensitive capacitive micromachined ultrasound transducers enabling non-contact detection and cm-scale image resolution. Finally, we show high correlation (adj. R 2 = 0.95) between the measured biomass content and the reconstructed thermoacoustic images of the potato tubers.