Brian Loveys

Thermal infrared imaging of crop canopies for the remote diagnosis and quantification of plant responses to water stress in the field.

Thermal imaging using infrared (IR) is now an established technology for the study of stomatal responses and for phenotyping plants for differences in stomatal behaviour. This paper outlines the potential applications of IR sensing in drought phenotyping, with particular emphasis on a description of the problems with extrapolation of the technique from the study of single leaves in controlled environments to the study of plant canopies is field plots, with examples taken from studies on grapevine (Vitis vinifera L.) and rice (Oryza sativa L.). Particular problems include the sensitivity of leaf temperature (and potentially the temperature of reference surfaces) to both temporal and spatial variation in absorbed radiation, with leaf temperature varying by as much as 15°C between full sun and deep shade. Examples of application of the approach to phenotyping in the field and the steps in data analysis are outlined, demonstrating that clear genotypic variation may be detected despite substantial variation in soil moisture status or incident radiation by the use of appropriate normalisation techniques.

Gradients in stomatal conductance, xylem sap ABA and bulk leaf ABA along canes of Vitis vinifera cv. Shiraz: molecular and physiological studies investigating their source

Gradients were observed in xylem sap ABA and in stomatal conductance along canes of Vitis vinifera L. cv. Shiraz. To investigate the source of the ABA responsible for these gradients a series of girdling and decapitation experiments were carried out. Leaf stomatal conductance and bulk ABA of leaves and apices were measured in control plants and in response to apex removal or girdling. Gradients in leaf ABA were observed over the first eight expanded leaves of field-grown Shiraz, with higher concentrations of ABA observed towards the apex. Gradients in stomatal conductance that correlated negatively with the concentration of ABA in the leaf ([ABA]leaf) were also observed over the first eight leaves. No significant effect of decapitation was observed on either leaf ABA or stomatal conductance except for the leaf immediately below the apex where a transient increase in [ABA]leaf was observed after 24 h with no corresponding decrease in conductance. Girdling resulted in an increase in [ABA]leaf in leaves distal to the girdle without the corresponding effect on conductance. These effects were further studied at the level of gene activity. To facilitate this, gene sequences encoding two key enzymes involved in the biosynthetic pathway of ABA in grape, zeaxanthin epoxidase (Zep) and 9-cis-epoxycarotenoid dioxygenase (NCED), were isolated and characterised. The cDNA sequences were used as probes to measure the abundances of their respective mRNAs in the leaf and apical material. Levels of expression of one of the two genes encoding NCED, VvNCED1, reflected the gradients in [ABA]leaf in control vines, however treatment-induced changes in ABA were not always associated with corresponding changes in VvNCED1 expression. The abundances of both the VvNCED2 mRNA and Zep mRNA increased with increasing leaf age and did not appear to be associated with either the [ABA]leaf or the expression of VvNCED1.

Expression of ABA synthesis and metabolism genes under different irrigation strategies and atmospheric VPDs is associated with stomatal conductance in grapevine (Vitis vinifera L. cv Cabernet Sauvignon)

The influence of different levels of irrigation and of variation in atmospheric vapour pressure deficit (VPD) on the synthesis, metabolism, and transport of abscisic acid (ABA) and the effects on stomatal conductance were examined in field-grown Cabernet Sauvignon grapevines. Xylem sap, leaf tissue, and root tissue were collected at regular intervals during two seasons in conjunction with measurements of leaf water potential (Ψleaf) and stomatal conductance (gs). The different irrigation levels significantly altered the Ψleaf and gs of the vines across both seasons. ABA abundance in the xylem sap was correlated with gs. The expression of genes associated with ABA synthesis, NCED1 and NCED2, was higher in the roots than in the leaves throughout and highest in the roots in mid January, a time when soil moisture declined and VPD was at its highest. Their expression in roots was also inversely related to the levels of irrigation and correlated with ABA abundance in the roots, xylem sap, and leaves. Three genes encoding ABA 8’-hydroxylases were isolated and their identities confirmed by expression in yeast cells. The expression of one of these, Hyd1, was elevated in leaves when VPD was below 2.0–2.5 kPa and minimal at higher VPD levels. The results provide evidence that ABA plays an important role in linking stomatal response to soil moisture status and that changes in ABA catabolism at or near its site of action allows optimization of gas exchange to current environmental conditions.

Influence of low oxygen storage on aroma compounds of whole pears and crushed pear flesh.

Controlled atmosphere storage is known to decrease pome fruit aroma. Here results are presented showing that low O2 storage (3 kPa) for 2 months reduced character impact compounds of ‘Packham’s Triumph’ pears, namely methyl and ethyl decadienoates, during subsequent ripening. This reduction was detected in both whole pears and crushed pear flesh, used here to approximately reproduce mastication. The relative abundance of more than 20 volatile compounds is presented. Analyses after grouping the results by alcohol or acyl moiety suggest that the synthesis of the decadienoate moiety was more depressed than the methyl or ethyl moieties. Other esters were less abundant after low O2 storage, particularly various acetates (butyl, hexyl, heptyl). Their reduction was particularly revealed in crushed flesh which had been incubated at 40°C. Phenyl ethanol and phenylethyl acetate levels were also reduced after low O2 storage.

Abscisic acid synthesis and metabolism in barley leaves and protoplasts

Abstract Protoplasts isolated from barley ( Hordeum vulgare L. cv. Clipper) leaves contained abscisic acid (ABA). The ABA content of these protoplasts did not change when they were incubated for up to 6 h in media of decreasing osmotic potential. There was a substantial, but transient, increase in ABA in barley leaf segments during protoplast isolation. The magnitude of this increase was inversely dependent on the osmotic potential of the isolation medium. Maximum ABA content was recorded after 2 h of exposure to the sorbitol-containing medium. The subsequent decline was due to conversion of ABA to phaseic acid (PA) and to other metabolites. Barley mesophyll protoplasts were not able to metabolise ABA, PA or any of the other metabolites formed from ABA by intact leaf tissue.

Water relations and gas exchange of the root hemiparasite Santalum acuminatum (quandong)

The water relations and leaf gas-exchange characteristics of the root hemiparasite quandong (Santalum acuminatum (R.Br.) A.DC) and its neighbouring plants were examined at three field sites in central Southern Australia. This paper examines the role of water potential and osmotic gradients in facilitating the movement of water from host plants to quandong. Quandong exhibited a significantly more negative water potential than the neighbouring plant species at both field sites during summer and winter. A significant proportion of the osmotic potential was accounted for by mannitol, Na + , K + and Cl - . A water potential difference of 1.7 MPa was maintained between quandong and its putative host over a measurement period of 24 h. Xylem sap and leaves of quandong contained considerable concentration (0.1–0.4 mol (kg tissue water) –1 ) of mannitol. Stomatal conductance and assimilation of quandong were lower than those of the neighbouring plants at both Middleback and Aldinga during both summer and winter measurements. Measurements of transpiration for quandong differed between the two sites. The lower transpirational water loss resulted in quandong at Middleback having an instantaneous water-use efficiency higher (0.13–2.2 µmol (CO 2 ) mmol –1 (H 2 O)) than the neighbouring plants. Daily sap flow and calculated hydraulic conductivity were not significantly different between quandong and putative host plant.

Effect of different host plants on the growth of the root hemiparasite Santalum acuminatum (quandong)

In recent years, the root hemiparasite Santalum acuminatum (quandong) has become an increasingly important commercial crop within the indigenous foods market. Relatively little is known of the significance of the host species on quandong growth and development. This paper presents data from a glasshouse pot experiment showing the effect of 4 different host species on the growth of quandong. Quandong growth, as measured by height and dry-mass accumulation, was significantly improved when grown in the presence of a host plant compared with being grown alone. Quandong grown with a host achieved an average height of 45 cm, while those grown alone grew up to only 37 cm. The host species also had an impact on the growth of quandong. Quandong had no detrimental effect on the growth of its host plant. Quandong grown with Myoporum parvifolium and Atriplex nummularia accumulated a significantly greater amount of dry biomass than quandong grown alone.

Manipulation of flowering and vegetative growth of Brown Boronia (Boronia megastigma Nees.) and White Myrtle (Hypocalymma angustifolium Endl.) using plant growth regulators

Abstract Plant growth regulators had a variety of effects on growth and flowering of Brown Boronia and White Myrtle. Morphactin, TIBA and benzyladenine stimulated lateral vegetative growth in warm conditions. Benzyladenine treatment of plants decreased the number of weeks of cool conditions (17°C day/9°C night) required to reach anthesis in both species, in Brown Boronia reducing the number of weeks required from 22 to 14. Paclobutrazol also decreased the number of weeks to anthesis in Brown Boronia and increased the percentage of axils with flowers. Paclobutrazol enabled White Myrtle plants to flower in an environment considered non-inductive for flowering. Many treatments that encouraged vigorous vegetative growth inhibited flowering in both species. The timing of growth regulator treatment in relation to flower evocation, and the environment in which the plants are growing can greatly influence the response of these species to plant growth regulator treatment.

Effects of CO2 enrichment on the physiology and propagation of two Australian ornamental plants, Chamelaucium uncinatum (Schauer) × Chamelaucium floriferum (MS) and Correa schlechtendalii (Behr)

Abstract Root formation on both Chamelaucium and Correa cuttings maintained at high humidity in an enclosed fog tunnel was significantly enhanced when ambient CO2 was increased from 350 to 800 μbar. CO2 enrichment resulted in decreased transpiration and increased water potential of cuttings implying an effect of CO2 on stomatal conductance. CO2 enrichment led to increased starch levels in cuttings of both species probably by raising the intercellular partial pressure of CO2. Increased starch content with CO2 enrichment was able to account for 70–90% of the dry weight increase in Correa, but only for 10–30% of the dry weight increase in Chamelaucium. It is suggested that the stimulation of rooting associated with CO2 enrichment probably derives from the improved water relations of the cuttings rather than from increased carbohydrate levels.

Uptake and retention of external solutes from the digest medium during preparation of protoplasts

Abstract The extent to which solutes present in the digest medium enter cells and are retained during preparation of protoplasts was investigated. When barley (Hordeum vulgare, L. cv. Clipper) leaf slices were incubated in sorbitol there was considerable uptake of sorbitol into the tissue, which continued for up to 6 h and was dependent on the sorbitol concentration in the external medium. Protoplasts prepared by digesting leaf slices in a medium containing [14C]sorbitol but isolated and purified in media with unlabelled sorbitol contained significant amounts of [14C]sorbitol. From measurements of the protoplast volume, the internal sorbitol concentration was calculated to be 100 mM, assuming uniform distribution of the sorbitol throughout the protoplasm. The uptake of sorbitol during digestion and its retention by protoplasts was confirmed by measuring sugars in protoplast extracts by gas sucrose or inositol. Vacuoles prepared from the protoplasts contained 83% of the sorbitol present in protoplasts. It is concluded that considerable uptake of solutes from the external medium occurs during digestion of leaf tissue and that these solutes are retained within the protoplasts during isolation and purification. The solutes appear to be uniformly distributed throughout the subcellular compartments of the protoplast.