Inhibition of tomato shoot growth by over-irrigation is linked to nitrogen deficiency and ethylene

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.

Interplay between ethylene and nitrogen nutrition: How ethylene orchestrates nitrogen responses in plants

The stress hormone ethylene plays a key role in plant adaptation to adverse environmental conditions. Nitrogen (N) is the most quantitatively required mineral nutrient for plants, and its availability is a major determinant for crop production. Changes in N availability or N forms can alter ethylene biosynthesis and/or signaling. Ethylene serves as an important cellular signal to mediate root system architecture adaptation, N uptake and translocation, ammonium toxicity, anthocyanin accumulation, and premature senescence, thereby adapting plant growth and development to external N status. Here, we review the ethylene-mediated morphological and physiological responses and highlight how ethylene transduces the N signals to the adaptive responses. We specifically discuss the N-ethylene relations in rice, an important cereal crop in which ethylene is essential for its hypoxia survival.

Ethylene Measurements from Sweet Fruits Flowers Using Photoacoustic Spectroscopy

Ethylene is a classical plant hormone and has appeared as a strong molecule managing many physiological and morphological reactions during the life of a plant. With laser-based photoacoustic spectroscopy, ethylene can be identified with high sensitivity, at a high rate and with very good selectivity. This research presents the dynamics of trace gases molecules for ethylene released by cherry flowers, apple flowers and strawberry flowers. The responses of distinctive organs to ethylene may fluctuate, depending on tissue sensitivity and the phase of plant development. From the determinations of this study, the ethylene molecules at the flowers in the nitrogen flow were established in lower concentrations when the value is correlated to the ethylene molecules at the flowers in synthetic air flow.

Assessing the performance of different irrigation systems on lettuce (Lactuca sativa L.) in the greenhouse

Lettuce (Lactuca sativa L.) is a very important leafy vegetable in China and is commonly grown using furrow irrigation. In order to improve production efficiency, greenhouse experiments were conducted at Experimental Station, China Agricultural University, Beijing, China using furrow irrigation (FI), micro-sprinkler irrigation (MS), plastic film mulching irrigation (PF) and a combined plastic film mulching-micro-sprinkler irrigation system (PF+MS) to study their effects on soil physical characteristics, water distribution, root morpho-physiological traits, nutrition absorption, lettuce yield and water use efficiency for a spring crop and autumn crop in 2015 (Fig 1). Root length, root surface area, and root density were significantly higher under PF and PF+MS than under FI. Moreover, these traits were higher under MS than under FI but these differences were not significant. The soluble protein, soluble sugar, and Vitamin C content of lettuce decreased in the order PF+MS > PF > MS > FI in both crops. In the spring crop, the biological yield of MS, PF, and PF+MS was 7.22%、36.77%、43.20% higher than FI, respectively. In the spring crop, biological water use efficiency (BWUE) of FI, MS, PF and PF+MS was 20.93, 25.24, 36.81 and 38.54 kg m-3, respectively. The BWUE of MS, PF, and PF+MS was 20.59%, 75.87% and 84.14% higher than FI. Economic water use efficiency (EWUE) of FI, MS, PF and PF+MS was 17.06, 21.31, 31.11 and 32.31 kg m-3, respectively. The EWUE of MS, PF, and PF+MS was 24.91%, 82.36% and 89.39% higher than FI, respectively. The autumn crop achieved a higher WUE than the spring crop. The results suggested that the combined plastic film mulching-micro-sprinkler irrigation was the most suitable irrigation approach for increasing lettuce yield.

Phospholipases AtPLDζ1 and AtPLDζ2 function differently in hypoxia

Besides hydrolyzing different membrane phospholipids, plant phospholipases D and molecular species of their byproducts phosphatidic acids (PLDs/PAs) are involved in diverse cellular events such as membrane-cytoskeleton dynamics, hormone regulation and biotic and/or abiotic stress responses at cellular or subcellular levels. Among the 12 Arabidopsis PLD genes, PLDζ1 and PLDζ2 uniquely possess Ca²⁺ -independent phox (PX) and pleckstrin (PH) homology domains. Here, we report that mutants deficient in these PLDs, pldζ1 and pldζ2, show differential sensitivities to hypoxia stimulus. In the present study, we used protoplasts of wild type and mutants and compared the hypoxia-induced changes in the levels of three major signaling mediators such as cytoplasmic free calcium [Ca²⁺_cyt. ], hydrogen peroxide (H₂ O₂ ) and PA. The concentrations of cytosolic Ca²⁺ and H₂ O₂ were determined by fluorescence microscopy and the fluorescent dyes Fura 2-AM and CM-H₂ DCFDA, specific for calcium and H₂ O₂ , respectively, while PA production was analyzed by an enzymatic method. The study reveals that AtPLDζ1 is involved in reactive oxygen species (ROS) signaling, whereas AtPLDζ2 is involved in cytosolic Ca²⁺ signaling pathways during hypoxic stress. Hypoxia induces an elevation of PA level both in Wt and pldζ1, while the PA level is unchanged in pldζ2. Thus, it is likely that AtPLDζ2 is involved in PA production by a calcium signaling pathway, while AtPLDζ1 is more important in ROS signaling.

Role of ethylene in responses of plants to nitrogen availability

Ethylene is a plant hormone involved in several physiological processes and regulates the plant development during the whole life. Stressful conditions usually activate ethylene biosynthesis and signaling in plants. The availability of nutrients, shortage or excess, influences plant metabolism and ethylene plays an important role in plant adaptation under suboptimal conditions. Among the plant nutrients, the nitrogen (N) is one the most important mineral element required for plant growth and development. The availability of N significantly influences plant metabolism, including ethylene biology. The interaction between ethylene and N affects several physiological processes such as leaf gas exchanges, roots architecture, leaf, fruits, and flowers development. Low plant N use efficiency (NUE) leads to N loss and N deprivation, which affect ethylene biosynthesis and tissues sensitivity, inducing cell damage and ultimately lysis. Plants may respond differently to N availability balancing ethylene production through its signaling network. This review discusses the recent advances in the interaction between N availability and ethylene at whole plant and different organ levels, and explores how N availability induces ethylene biology and plant responses. Exogenously applied ethylene seems to cope the stress conditions and improves plant physiological performance. This can be explained considering the expression of ethylene biosynthesis and signaling genes under different N availability. A greater understanding of the regulation of N by means of ethylene modulation may help to increase NUE and directly influence crop productivity under conditions of limited N availability, leading to positive effects on the environment. Moreover, efforts should be focused on the effect of N deficiency or excess in fruit trees, where ethylene can have detrimental effects especially during postharvest.