Upregulation of photosynthesis in mineral nutrition-deficient tomato plants by reduced source-to-sink ratio

Soil and Mineral Nutrients in Plant Health: A Prospective Study of Iron and Phosphorus in the Growth and Development of Plants

Plants being sessile are exposed to different environmental challenges and consequent stresses associated with them. With the prerequisite of minerals for growth and development, they coordinate their mobilization from the soil through their roots. Phosphorus (P) and iron (Fe) are macro- and micronutrient; P serves as an important component of biological macromolecules, besides driving major cellular processes, including photosynthesis and respiration, and Fe performs the function as a cofactor for enzymes of vital metabolic pathways. These minerals help in maintaining plant vigor via alterations in the pH, nutrient content, release of exudates at the root surface, changing dynamics of root microbial population, and modulation of the activity of redox enzymes. Despite this, their low solubility and relative immobilization in soil make them inaccessible for utilization by plants. Moreover, plants have evolved distinct mechanisms to cope with these stresses and coregulate the levels of minerals (Fe, P, etc.) toward the maintenance of homeostasis. The present study aims at examining the uptake mechanisms of Fe and P, and their translocation, storage, and role in executing different cellular processes in plants. It also summarizes the toxicological aspects of these minerals in terms of their effects on germination, nutrient uptake, plant-water relationship, and overall yield. Considered as an important and indispensable component of sustainable agriculture, a separate section covers the current knowledge on the cross-talk between Fe and P and integrates complete and balanced information of their effect on plant hormone levels.

Arabidopsis CDF3 transcription factor increases carbon and nitrogen assimilation and yield in trans-grafted tomato plants

Grafting in tomato (Solanum lycopersicum L.) has mainly been used to prevent damage by soil-borne pathogens and the negative effects of abiotic stresses, although productivity and fruit quality can also be enhanced using high vigor rootstocks. In the context of a low nutrients input agriculture, the grafting of elite cultivars onto rootstocks displaying higher Nitrogen Use Efficiency (NUE) supports a direct strategy for yield maximization. In this study we assessed the use of plants overexpressing the Arabidopsis (AtCDF3) or tomato (SlCDF3) CDF3 genes, previously reported to increase NUE in tomato, as rootstocks to improve yield in the grafted scion under low N inputs. We found that the AtCDF3 gene induced greater production of sugars and amino acids, which allowed for greater biomass and fruit yield under both sufficient and limiting N supplies. Conversely, no positive impact was found with the SlCDF3 gene. Hormone analyses suggest that gibberellins (GA4), auxin and cytokinins (tZ) might be involved in the AtCDF3 responses to N. The differential responses triggered by the two genes could be related, at least in part, to the mobility of the AtCDF3 transcript through the phloem to the shoot. Consistently, a higher expression of the target genes of the transcription factor, such as glutamine synthase 2 (SlGS2) and GA oxidase 3 (SlGA3ox), involved in amino acid and gibberellin biosynthesis, respectively, was observed in the leaves of this graft combination. Altogether, our results provided further insights into the mode of action of CDF3 genes and their biotechnology potential for transgrafting approaches.

Effects of Mars Global Simulant (MGS-1) on Growth and Physiology of Sweet Potato: A Space Model Plant

Growing food autonomously on Mars is challenging due to the Martian soil's low nutrient content and high salinity. Understanding how plants adapt and evaluating their nutritional attributes are pivotal for sustained Mars missions. This research delves into the regeneration, stress tolerance, and dietary metrics of sweet potato (Ipomoea batatas) across different Mars Global Simulant (MGS-1) concentrations (0, 25, 50, and 75%). In our greenhouse experiment, 75% MGS-1 concentration significantly inhibited sweet potato growth, storage root biomass, and chlorophyll content. This concentration also elevated the plant tissues' H2O2, proline, and ascorbic acid levels. Higher MGS-1 exposures (50 and 75%) notably boosted the vital amino acids and sugar groups in the plant's storage roots. However, increased MGS-1 concentrations notably diminished the total C:N ratio and elemental composition in both the vines and storage roots. In summary, sweet potato exhibited optimal growth, antioxidant properties, yield, and nutrient profiles at 25% MGS-1 exposure as compared to higher concentrations. This study underscores the need for future interventions, like nutrient enhancements and controlled metal accessibility, to render sweet potato a suitable plant for space-based studies.

Cucumber STACHYOSE SYNTHASE is regulated by its cis-antisense RNA asCsSTS to balance source-sink carbon partitioning

Photosynthate partitioning between source and sink is a key determinant of crop yield. In contrast to sucrose-transporting plants, cucumber (Cucumis sativus) plants mainly transport stachyose and stachyose synthase (CsSTS) synthesizes stachyose in the vasculature for loading. Therefore, CsSTS is considered a key regulator of carbon partitioning. We found that CsSTS expression and CsSTS enzyme activity were upregulated in the vasculature and downregulated in mesophyll tissues at fruiting. In situ hybridization and tissue enrichment experiments revealed that a cis-natural antisense noncoding transcript of CsSTS, named asCsSTS, is mainly expressed in mesophyll tissues. In vitro overexpression (OE), RNA interference (RNAi), and dual luciferase reporter experiments indicated that CsSTSs are negatively regulated by asCsSTS. Fluorescence in situ hybridization revealed that asCsSTS transcript localized in leaf cytoplasm, indicating that the regulation of CsSTS by asCsSTS is a posttranscriptional process. Further investigation revealed that this regulation occurred by reducing CsSTS transcript stability through a DICER-like protein-mediated pathway. Chemically induced OE and RNAi of asCsSTS led to promotion or inhibition, respectively, of assimilate export from leaves and altered fruit growth rates. Our results suggest that the regulation of CsSTSs between the mesophyll and vasculature reduces sugar storage in mesophyll tissue and promotes assimilate export from the leaf when the plant carries fruit.

Low sink demand caused net photosynthetic rate decrease is closely related to the irrecoverable damage of oxygen-releasing complex and electron receptor in peach trees

Source sink balance is one of the major determinants of carbon partitioning in plants. However, its effects on photosynthesis in fruit trees are largely unknown. In this work, the effects of low sink demand on net photosynthetic rate (P_n) and chlorophyll fluorescence after fruit removal (-fruit) in peach (Prunus persica (L.) Batsch cv. 'Zaojiubao') trees were investigated. The stepwise energy flow through photosystem II (PSII) at the reaction center (RC) was analyzed with quantitative analyses of fluorescence transient, also called JIP-test. We found that P_n was significantly lower and closely correlated to the leaf stomatal conductance (G_s) of -fruit trees than that of fruit retained (+fruit) trees. Leaf temperature (T_leaf) of -fruit trees was remarkably higher than that of +fruit trees. Day-time-period assays of chlorophyll (Chl) fluorescence revealed that, in the leaves of -fruit trees, the fluorescence parameters, such as NPQ (non-photochemical quenching coefficient) and ΦD₀ (maximum quantum yield of non-photochemical de-excitation), decreased in the morning and recovered to the normal level in the afternoon, whereas other parameters, such as ΦE₀ (quantum yield for electron transport at t = 0), Ψ₀ (probability that a trapped exciton moves an electron to Q_A pool), F₀ (minimum fluorescence, when all PSII RCs are open) and W_k (relative variable fluorescence at 300 μs of the chlorophyll fluorescence transient), did not. These results suggest that OEC complex and Q_A pool were irreversibly affected by low sink demand, whereas light harvest antenna and PSII potential efficiency retained a strong ability to recover.

Effects of Defoliation at Fruit Set on Vine Physiology and Berry Composition in Cabernet Sauvignon Grapevines

Grapevine canopy defoliation is a fundamentally important technique for the productivity and quality of grapes. Leaf removal is a pivotal operation on high-density vines which aims to improve air circulation, light exposure, and leaf gas exchange. The effects of leaf removal (LR) on vine physiology and berry composition in Cabernet Sauvignon grapevines were studied during the 2018–2019 growing season in the Bolgheri area, Tuscany, Italy. The basal leaves were removed at fruit set at two severity levels (removal of four basal leaves of each shoot (LR4) and removal of eight basal leaves (LR8)). The two treatments were compared with the not defoliated control (CTRL). The following physiological parameters of vines were measured: leaf gas exchange, leaf water potential, chlorophyll fluorescence and indirect chlorophyll content. The results showed that defoliation increased single leaf photosynthesis. In addition, qualitative grape parameters (phenolic and technological analyses) and daytime and night-time berry temperature were studied. The results showed that leaf removal had an impact on total soluble solids (°Brix), titratable acidity, and pH. The LR8-treated grapes had higher titratable acidity, while those in the LR4 treatment had higher °Brix and extractable anthocyanin and polyphenol content. Berry weight was not significantly influenced by the timing and severity of basal defoliation. Therefore, this research aims to investigate the effects of defoliation at the fruit set on vines performance.

Mutualism disruption by an invasive ant reduces carbon fixation for a foundational East African ant-plant

Invasive ants shape assemblages and interactions of native species, but their effect on fundamental ecological processes is poorly understood. In East Africa, Pheidole megacephala ants have invaded monodominant stands of the ant-tree Acacia drepanolobium, extirpating native ant defenders and rendering trees vulnerable to canopy damage by vertebrate herbivores. We used experiments and observations to quantify direct and interactive effects of invasive ants and large herbivores on A. drepanolobium photosynthesis over a 2-year period. Trees that had been invaded for ≥ 5 years exhibited 69% lower whole-tree photosynthesis during key growing seasons, resulting from interaction between invasive ants and vertebrate herbivores that caused leaf- and canopy-level photosynthesis declines. We also surveyed trees shortly before and after invasion, finding that recent invasion induced only minor changes in leaf physiology. Our results from individual trees likely scale up, highlighting the potential of invasive species to alter ecosystem-level carbon fixation and other biogeochemical cycles.