An integrated proteomic and metabolomic study to evaluate the effect of nucleus-cytoplasm interaction in a diploid citrus cybrid between sweet orange and lemon.

KEY MESSAGE: Our results provide a comprehensive overview how the alloplasmic condition might lead to a significant improvement in citrus plant breeding, developing varieties more adaptable to a wide range of conditions. Citrus cybrids resulting from somatic hybridization hold great potential in plant improvement. They represent effective products resulting from the transfer of organelle-encoded traits into cultivated varieties. In these cases, the plant coordinated array of physiological, biochemical, and molecular functions remains the result of integration among different signals, which derive from the compartmentalized genomes of nucleus, plastids and mitochondria. To dissect the effects of genome rearrangement into cybrids, a multidisciplinary study was conducted on a diploid cybrid (C2N), resulting from a breeding program aimed to improve interesting agronomical traits for lemon, the parental cultivars 'Valencia' sweet orange (V) and 'femminello' lemon (F), and the corresponding somatic allotetraploid hybrid (V + F). In particular, a differential proteomic analysis, based on 2D-DIGE and MS procedures, was carried out on leaf proteomes of C2N, V, F and V + F, using the C2N proteome as pivotal condition. This investigation revealed differentially represented protein patterns that can be associated with genome rearrangement and cell compartment interplay. Interestingly, most of the up-regulated proteins in the cybrid are involved in crucial biological processes such as photosynthesis, energy production and stress tolerance response. The cybrid differential proteome pattern was concomitant with a general increase of leaf gas exchange and content of volatile organic compounds, highlighting a stimulation of specific pathways that can be related to observed plant performances. Our results contribute to a better understanding how the alloplasmic condition might lead to a substantial improvement in plant breeding, opening new opportunities to develop varieties more adaptable to a wide range of conditions.

Tamarix arborea var. arborea and Tamarix parviflora: Two species valued for their adaptability to stress conditions.

The choice of stress resistant and highly adaptable species is a fundamental step for landscaping and ornamental purposes in arid and coastal environments such as those in the Mediterranean basin. The genus Tamarix L. includes about 90 species with a high endurance of adversity. We investigated the water relations and photosynthetic response of Tamarix arborea (Sieb. ex Ehrenb.) Bge. var. arborea and T. parviflora DC. growing in an urban environment. Both species showed no evidence of drought or salt stress in summer, and appeared to follow two strategies with T. arborea var. arborea investing in high carbon gain at the beginning of the summer, and then reducing photosynthetic activity at the end of the season, and T. parviflora showing lower but constant levels of photosynthetic activity throughout the vegetative season. For landscaping and ornamental purposes, we suggest T. arborea var. arborea when a fast-growing, high-cover species is necessary, and T. parviflora when less-invasive species are required.

Carbon and nitrogen isotopic values in Lithops aucampiae during leaf development.

Lithops (Aizoaceae) are succulent plants consisting of a pair of opposite succulent leaves inserted on an extremely short stem. The apical meristem produces a new leaf pair that develops between the older pair, recycling water and metabolites. This peculiar anatomy and growth form make ecophysiological studies quite challenging. Lithops are considered to have CAM metabolism, though experimental evidence is scarce. We followed the changes in carbon and nitrogen isotopic values in mature leaves, young leaves and roots, with the aim of investigating how the use of resources is optimized to achieve survival in extremely arid environments. Two-year-old plants of Lithops aucampiae were grown in pots with no irrigation for six months. Plants were sampled periodically, and isotopic values were recorded in relation to the developmental pattern of the leaves. δ13C ranged from -16.4 to -13.1‰ with leaves showing less negative values than roots. δ15N ranged between -0.8 and 3.9‰ with leaves showing higher values than roots. To the best of our knowledge, this is the first experimental evidence of carbon and nitrogen isotope values in Lithops, the former providing evidence for CAM metabolism.

Water relations of two Sicilian grapevine cultivars in response to potassium availability and drought stress.

We investigated the response of two Sicilian grapevine cultivars, Catarratto and Nero d'Avola, to potassium deficiency and drought stress. Two-year-old plants grafted on 1103 Paulsen were grown in agriperlite, with or without potassium in the fertigation solution for six weeks, and subjected to moderate drought stress by suspending irrigation for one week. Potassium content of leaves, roots and xylem sap were measured with an ion-selective electrode. Changes in stomatal conductance, stem and leaf water potential and hydraulic conductance were compared between genotypes and treatments. Potassium deficiency led to significant decreases in leaf potassium content in both cultivars and under both well-watered and drought stress conditions. Potassium content in xylem sap showed no significant differences between cultivars and was correlated with stem hydraulic conductance, particularly in the drought stress treatments. Under drought stress conditions, potassium availability led to an increase in stomatal conductance, particularly in Nero d'Avola. Both cultivars showed a rather isohydric behavior under these experimental conditions, and the level of isohydry varied with potassium availability. These results can be useful for the development of optimal fertigation practices and the selection of drought tolerant varieties.

Effects of foliar application of glycine betaine and chitosan on Puccinellia distans (Jacq.) Pari, subjected to salt stress.

INTRODUCTION: Using brackish water for irrigation may expose turfgrasses to salinity stress. Employing the best treatments to maintain high-quality turfs under saline conditions is an important requirement for turfgrass management. METHODS: We tested the response of a halophyte grass, Puccinellia distans, to irrigation with saline solutions and to foliar application of two osmoprotectants, such as glycine betaine (GB) or chitosan (CH). Plants were grown in pots under controlled conditions and irrigated with 200 mM or 600 mM of NaCl solutions. The response to salinity treatments and osmoprotectant application was evaluated after 90 days by measuring leaf firing, leaf density, shoot length and biomass, root length, and shoot water potential. RESULTS: Increasing salinity reduced shoot density, shoot and root length, shoot water potential, and increased leaf firing and shoot solute potential at 200 mM of NaCl. These effects were more pronounced at 600 mM of NaCl. Application of GB greatly increased shoot growth traits at 200 mM of NaCl and also showed beneficial effects on most traits at 600 mM. Application of CH showed positive effects only on leaf firing and leaf water potential at 600 mM. CONCLUSIONS: Our results show that P. distans can tolerate high levels of salt stress, which can be best alleviated by GB treatment.

Is in vitro micrografting a possible valid alternative to traditional micropropagation in Cactaceae? Pelecyphora aselliformis as a case study.

Several taxa of Cactaceae are endangered by overcollection for commercial purposes, and most of the family is included in the Convention on International Trade in Endangered Species of Fauna and Flora (CITES). Micropropagation may play a key role to keep the pressure off wild populations and contribute to ex situ conservation of endangered taxa. One of the limits of micropropagation is the species-specific requirement of plant regulators for each taxon and sometimes even for different genotypes. With the micrografting technique the rootstock directly provides the scion with the necessary hormonal requirements. In this paper we present data on in vitro grafting of Pelecyphora aselliformis Ehrenberg, an Appendix I CITES listed species critically endangered and sought after by the horticultural trade, on micropropagated Opuntia ficus-indica Miller. Apical and sub-apical scions of P. aselliformis were used to perform micrografting with a successful rate of 97 and 81 % respectively. Survival rate after ex vivo transfer was 85 %. We hypothesize that this method could be applied to other endangered, slow growing taxa of Cactaceae thus contributing to the conservation of this endangered family.

Does short-term potassium fertilization improve recovery from drought stress in laurel?

Xylem hydraulic conductance varies in response to changes in sap solute content, and in particular of potassium (K(+)) ion concentration. This phenomenon, known as the 'ionic effect', is enhanced in embolized stems, where it can compensate for cavitation-induced loss of hydraulic conductance. Previous studies have shown that in well-watered laurel plants (Laurus nobilis L.), potassium concentration of the xylem sap and plant hydraulic conductance increased 24 h after fertilization with KCl. The aim of this work was to test whether water-stressed laurel plants, grown under low potassium availability, could recover earlier from stress when irrigated with a KCl solution instead of potassium-free water. Two-year-old potted laurel seedlings were subjected to water stress by suspending irrigation until leaf conductance to water vapour (g(L)) dropped to ∼30% of its initial value and leaf water potential (ψ(L)) reached the turgor loss point (ψ(TLP)). Plants were then irrigated either with water or with 25 mM KCl and monitored for water status, gas exchange and plant hydraulics recovery at 3, 6 and 24 h after irrigation. No significant differences were found between the two experimental groups in terms of ψ(L), g(L), plant transpiration, plant hydraulic conductance or leaf-specific shoot hydraulic conductivity. Analysis of xylem sap potassium concentration showed that there were no significant differences between treatments, and potassium levels were similar to those of potassium-starved but well-watered plants. In conclusion, potassium uptake from the soil solution and/or potassium release to the xylem appeared to be impaired in water-stressed plants, at least up to 24 h after relief from water stress, so that fertilization after the onset of stress did not result in any short-term advantage for recovery from drought.

Short-term effects of potassium fertilization on the hydraulic conductance of Laurus nobilis L.

This study reports experimental evidence on the effect of short-term potassium fertilization on potassium uptake, tissue concentration and hydraulic conductance of pot-grown laurel plants. Potassium uptake and loading into the xylem of laurel seedlings increased within 24 h after fertilization. Potassium was not accumulated in roots and leaves, but the [K(+)] of xylem sap was 80% higher in fertilized plants (+K) than in potassium-starved plants (-K), as a likely result of recirculation between xylem and phloem. Increased xylem sap [K(+)] resulted in a 45% increase in transpiration rate, a 30% increase in plant hydraulic conductance (K(plant)) and a 120% increase in leaf-specific conductivity of the shoot (k(shoot)). We suggest that this increase was due to ion-mediated up-regulation of xylem hydraulics, possibly caused by the interaction of potassium ions with the pectic matrix of intervessel pits. The enhancement of hydraulic conductance following short-term potassium fertilization is a phenomenon that can be of advantage to plants for maintaining cell turgor, stomatal aperture and gas exchange rates under moderate drought stress. Our data provide additional support for the important role of potassium nutrition in agriculture and forestry.

An investigation of the seasonal pattern of mannitol content in deciduous and evergreen species of the oleaceae growing in northern Sicily.

In several species of the Oleaceae, mannitol, already present at considerable levels, accumulates in response to stress. This family comprises both deciduous and evergreen species, and we investigated the role of mannitol in deciduous malacophyll and evergreen sclerophyll species growing under the same conditions in the field. The relationship between mannitol content and changes in rainfall or temperature was also studied. The mannitol content of leaves of Fraxinus ornus L., F. angustifolia Vahl., Olea europaea L. and Phillyrea media L. was determined by gas chromatography. Leaf samples were collected once a month for 1 year. In the two ash species, the seasonal pattern of mannitol content appeared the same: a gradual increase in spring, peaking in summer, followed by a gradual decrease. The mannitol content was similar in both species, ranging between 260 and 720 micromol g(-1) d. wt. The seasonal pattern of mannitol content in Olea and Phillyrea was similar for both species, but unlike that of Fraxinus did not show a summer peak. Rainfall was negatively correlated with the seasonal increase of mannitol content in ash. Mannitol content increased gradually during drought, reaching a maximum value at the end of the dry season. Temperature did not have a direct influence on mannitol content. In Olea and Phillyrea, variations in mannitol content were poorly correlated with rainfall or temperature, indicating that mannitol does not have a primary role in the response of these species to the hot, dry summer conditions.