Transcriptomic and physiological approaches to decipher cold stress mitigation exerted by brown-seaweed extract application in tomato.

Chilling temperatures represent a challenge for crop species originating from warm geographical areas. In this situation, biostimulants serve as an eco-friendly resource to mitigate cold stress in crops. Tomato (Solanum lycopersicum L.) is an economically important vegetable crop, but quite sensitive to cold stress, which it encounters in both open field and greenhouse settings. In this study, the biostimulant effect of a brown-seaweed extract (BSE) has been evaluated in tomato exposed to low temperature. To assess the product effects, physiological and molecular characterizations were conducted. Under cold stress conditions, stomatal conductance, net photosynthesis, and yield were significantly (p ≤ 0.05) higher in BSE-treated plants compared to the untreated ones. A global transcriptomic survey after BSE application revealed the impact of the BSE treatment on genes leading to key responses to cold stress. This was highlighted by the significantly enriched GO categories relative to proline (GO:0006560), flavonoids (GO:0009812, GO:0009813), and chlorophyll (GO:0015994). Molecular data were integrated by biochemical analysis showing that the BSE treatment causes greater proline, polyphenols, flavonoids, tannins, and carotenoids contents.The study highlighted the role of antioxidant molecules to enhance tomato tolerance to low temperature mediated by BSE-based biostimulant.

A dual-omics approach for profiling plant responses to biostimulant applications under controlled and field conditions.

A comprehensive approach using phenomics and global transcriptomics for dissecting plant response to biostimulants is illustrated with tomato (Solanum lycopersicum cv. Micro-Tom and Rio Grande) plants cultivated in the laboratory, greenhouse, and open field conditions. Biostimulant treatment based on an Ascophyllum nodosum extract (ANE) was applied as a foliar spray with two doses (1 or 2 l ha-1) at three different phenological stages (BBCH51, BBCH61, and BBCH65) during the flowering phase. Both ANE doses resulted in greater net photosynthesis rate, stomatal conductance, and fruit yield across all culture conditions. A global transcriptomic analysis of leaves from plants grown in the climate chamber, revealed a greater number of differentially expressed genes (DEGs) with the low ANE dose compared to the greater one. The second and third applications induced broader transcriptome changes compared to the first one, indicating a cumulative treatment effect. The functional enrichment analysis of DEGs highlighted pathways related to stimulus-response and photosynthesis, consistent with the morpho-physiological observations. This study is the first comprehensive dual-omics approach for profiling plant responses to biostimulants across three different culture conditions.

Transcriptional and Physiological Analyses to Assess the Effects of a Novel Biostimulant in Tomato.

This work aimed to study the effects in tomato (Solanum lycopersicum L.) of foliar applications of a novel calcium-based biostimulant (SOB01) using an omics approach involving transcriptomics and physiological profiling. A calcium-chloride fertilizer (SOB02) was used as a product reference standard. Plants were grown under well-watered (WW) and water stress (WS) conditions in a growth chamber. We firstly compared the transcriptome profile of treated and untreated tomato plants using the software RStudio. Totally, 968 and 1,657 differentially expressed genes (DEGs) (adj-p-value < 0.1 and |log2(fold change)| ≥ 1) were identified after SOB01 and SOB02 leaf treatments, respectively. Expression patterns of 9 DEGs involved in nutrient metabolism and osmotic stress tolerance were validated by real-time quantitative reverse transcription PCR (RT-qPCR) analysis. Principal component analysis (PCA) on RT-qPCR results highlighted that the gene expression profiles after SOB01 treatment in different water regimes were clustering together, suggesting that the expression pattern of the analyzed genes in well water and water stress plants was similar in the presence of SOB01 treatment. Physiological analyses demonstrated that the biostimulant application increased the photosynthetic rate and the chlorophyll content under water deficiency compared to the standard fertilizer and led to a higher yield in terms of fruit dry matter and a reduction in the number of cracked fruits. In conclusion, transcriptome and physiological profiling provided comprehensive information on the biostimulant effects highlighting that SOB01 applications improved the ability of the tomato plants to mitigate the negative effects of water stress.

Deep root growth, ABA adjustments and root water uptake response to soil water deficit in giant reed.

BACKGROUND AND AIMS: Giant reed (Arundo donax L.) is a deep-rooted crop that can survive prolonged dry periods probably as a result of its capacity to uptake water from below ground, but specific information on the functioning of deep/shallow roots is missing. The objective of this study was to understand the dynamic interrelationships of root water acquisition, canopy water conservation and abscisic acid (ABA) signals from both shallow and deep roots. METHODS: In transparent split top-bottom rhizotron systems (1-m-high columns), where hydraulically isolated and independently watered layers were created with the aid of calibrated soil moisture sensors, water uptake trends were monitored. Rooting patterns were traced on the walls of the rhizotrons. Leaf gas exchange was determined using a portable infrared gas analyser. Leaf and root ABA concentrations were monitored. KEY RESULTS: Under well-watered conditions, water uptake from both upper and deeper soil layers was similar. Water uptake from deeper soil layers increased gradually by up to 2.2-fold when drought stress was imposed to upper layers compared to the control conditions. Despite the significant increase in water uptake from deeper layers, surface root length density of drought-treated plants remained unchanged, suggesting increased root water uptake efficiency by these roots. However, these adjustments were not sufficient to sustain photosynthesis and therefore biomass accumulation, which was reduced by 42 %. The ABA content in shallower drought-treated roots increased 2.6-fold. This increase closely and positively correlated with foliar ABA concentration, increased intrinsic water use efficiency and leaf water potential (LWP). CONCLUSIONS: Giant reed is able to change its water sources depending on water availability and to maximize water uptake efficiency to satisfy canopy evapotranspirative demands. The regulation of deep root functioning and distribution, adjustment of canopy size, and root/foliar synthesized ABA play a central role in controlling LWP and leaf transpiration efficiency.

Giant reed genotypes from temperate and arid environments show different response mechanisms to drought.

Studies at the root level and how the root-shoot interactions may influence the whole crop performance of giant reed (Arundo donax L.) under limited water conditions are largely missing. In the present study, we illustrate the effects of water stress on some phenotypic traits at the root-shoot levels of two giant reed genotypes (from Morocco and Northern Italy) that were reported to have different adaptive hydraulic stem conductivities despite the limited genetic variability of the species. The trial was carried out in 1 m3 rhizotrons (1 × 1 × 1 m) for two consecutive growing seasons. As expected, both genotypes showed an effective behavior to contrast water shortage; however, the Moroccan genotype showed a higher leaf water potential, a lower root length density (RLD) and thinner roots in the upper soil layer (0-20 cm), and similar to control RLD values at deep soil layers (40-60 cm). On the other hand the Italian genotype showed the opposite pattern; that is no drought (DR) effects in RLD and root diameter at upper soil layers and reduced RLD in deep layers, thus revealing different DR adaptation characteristics between two genotypes. This DR adaptation variability might bring new insights on DR tolerance of giant reed identifying potential traits aimed to improve the integral plant functioning, to a more efficient use of water resources, and to a more effective crop allocation to targeted stressful conditions under a climate change scenario that foresees the increase of DR periods.

Differential characteristics of photochemical acclimation to cold in two contrasting sweet sorghum hybrids.

Sweet sorghum has a photosynthetic system which is highly sensitive to cold stress and hence strongly limits its development in temperate environments; therefore, the identification of key exploitable cold tolerance traits is imperative. From a preliminary field trial, two dissimilar sweet sorghum hybrids (ICSSH31 and Bulldozer), in terms of early vigor and productivity, were selected for a controlled-environment trial aiming at identifying useful traits related to acclimation mechanisms to cold stress. The higher cold tolerance of Bulldozer was partially related to a more efficient photochemical regulation mechanism of the incoming light energy: the higher tolerance of photosystem II (PSII) to photo-inactivation was because of a more effective dissipation capacity of the excess of energy and to a more balanced diversion of the absorbed energy into alternative energy sinks. ICSSH31 increased the dissipation and accumulation of a large amount of xanthophylls, as in Bulldozer, but, at the same time, inactivated the oxygen evolving complex and the re-synthesis of chlorophyll (Chl) a and b, thus, leading to an overproduction of CO2 fixation enzymes after re-warming. In summary, in Bulldozer, the acclimation adjustments of the photosynthetic apparatus occurred through an efficient control of energy transfer toward the reaction centers, and this likely allowed a more successful seedling establishment; ICSSH31, conversely, exhibited a fast re-synthesis of Chl pigments, which appears to divert photosynthates from dry matter accumulation. Such broad acclimation traits may constitute a source for selecting higher genetic gain traits relevant for enlarging the growing season of promising biomass sorghum ideotypes in temperate climates.

Photosynthetic response of sweet sorghum to drought and re-watering at different growth stages.

Sweet sorghum (Sorghum bicolor) is a C4 drought resistant species with a huge potential for bioenergy. Accentuated reductions in water availability for crop production and altered rainfall distribution patterns, however, will have direct impact on its physiological attributes, metabolic functions and plant growth. The objective of this study was to evaluate the effects of drought and re-watering on the photosynthetic efficiency of sweet sorghum. Durable or short transient drought stress periods were imposed at early and late growth stages and compared with well-watered plants. In spite of very similar drought levels at early and late growth stages (Ψsoil = -1.6 and -1.7 MPa), the decrements in maximum quantum yield (ϕPo ) and performance index (PI) were about twice at late than at early growth stages. All the PI components, that is, density of active reaction centers (RCs), excitation energy trapping and conversion of excitation energy into electron flow followed a similar decreasing pattern. Upon re-watering and regardless the duration and growth stage of the drought period, all the photosynthetic functions, and particularly those of photosystem II (PSII), fully recovered. Such effective self-regulating functional activity by PSII photochemistry likely contributes to both high drought resistance and photosynthetic recovery capacity of sweet sorghum. At vegetative growth stages, the down regulation of the photochemistry seems to be the main photoprotective/regulative mechanisms, while at late growth stages, the accumulation of compatible solutes likely has a more preponderant role. The observed sugar concentration increments likely contributed to prevent permanent photo-oxidative destruction of the PSII RCs of mature droughted sweet sorghum plants.