Boric acid as a potential substitute for conventional ethylene antagonists in mitigating postharvest flower senescence of Digitalis purpurea

In the floriculture industry, postharvest senescence is one of the glaring challenges restricting the marketability of cut flowers. Hence, maintaining good quality of cut flowers and extending flower longevity are considered to be the most crucial factors in the cut flower trade. Therefore, to gain better understanding of the specific physiological and biochemical aspects of petal senescence we conducted an experiment to evaluate the efficacy of Boric acid (BA) on flower longevity in excised flowers of Digitalis purpurea L. Isolated buds were harvested at stage IV i.e, 1 day before anthesis and divided into 5 sets, with one set of buds held in distilled water (DW) designated as control. The other 4 sets were supplemented with 24h pulse treatment of different concentrations of BA viz., 50, 100, 150 and 200 µM. The application of BA at 150 µM concentration was found to be most effective in increasing flower longevity by about 4 days as compared to control. The enhanced longevity coincided with higher values of floral diameter, fresh mass, dry mass and solution uptake. Flowers with delayed senescence also retained higher soluble proteins, sugars and phenols in addition to lower bacterial density compared to control. Moreover, this ameliorated flower longevity has also been shown to be positively associated with increased activities of various antioxidant enzymes viz., superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) and reduced activity of lipoxygenase (LOX).

Nitrate fertilization may delay autumn leaf senescence, while amino acid treatments do not

Fertilization with nitrogen (N)-rich compounds leads to increased growth, but may compromise phenology and winter survival of trees in boreal regions. During autumn, N is remobilized from senescing leaves and stored in other parts of the tree to be used in the next growing season. However, the mechanism behind the N fertilization effect on winter survival is not well understood and it is unclear how N levels or forms modulate autumn senescence. We performed fertilization experiments and showed that treating Populus saplings with high or low levels of inorganic nitrogen resulted in a delay in senescence. In addition, by using precise delivery of solutes into the xylem stream of Populus trees in their natural environment, we found that delay of autumn senescence was dependent on the form of N administered: inorganic N (NO3-1) delayed senescence but amino acids (Arg, Glu, Gln, and Leu) did not. Metabolite profiling of leaves showed that the levels of tricarboxylic acids (TCA), arginine catabolites (ammonium, ornithine), glycine, glycine-serine ratio and overall carbon-to-nitrogen (C/N) ratio were affected differently by the way of applying NO3-1 and Arg treatments. In addition, the onset of senescence did not coincide with soluble sugar accumulation in any of the treatments. Taken together, metabolomic rearrangement under different N forms or experimental setups could modulate senescence process, but not initiation and progression in Populus. We propose that the different regulation of C and N status through direct molecular signaling of NO3-1 could account for the contrasting effects of NO3-1 and Arg on senescence.

The leaf senescence-promoting transcription factor AtNAP activates its direct target gene CYTOKININ OXIDASE 3 to facilitate senescence processes by degrading cytokinins

Cytokinins (CKs) are a class of adenine-derived plant hormones that plays pervasive roles in plant growth and development including cell division, morphogenesis, lateral bud outgrowth, leaf expansion and senescence. CKs as a “fountain of youth” prolongs leaf longevity by inhibiting leaf senescence, and therefore must be catabolized for senescence to occur. AtNAP, a senescence-specific transcription factor has a key role in promoting leaf senescence. The role of AtNAP in regulating CK catabolism is unknown. Here we report the identification and characterization of AtNAP-AtCKX3 (cytokinin oxidase 3) module by which CKs are catabolized during leaf senescence in Arabidopsis. Like AtNAP, AtCKX3 is highly upregulated during leaf senescence. When AtNAP is chemically induced AtCKX3 is co-induced; and when AtNAP is knocked out, the expression of AtCKX3 is abolished. AtNAP physically binds to the cis element of the AtCKX3 promoter to direct its expression as revealed by yeast one-hybrid assays and in planta experiments. Leaves of the atckx3 knockout lines have higher CK concentrations and a delayed senescence phenotype compared with those of WT. In contrast, leaves with inducible expression of AtCKX3 have lower CK concentrations and exhibit a precocious senescence phenotype compared with WT. This research reveals that AtNAP transcription factor˗AtCKX3 module regulates leaf senescence by connecting two antagonist plant hormones abscisic acid and CKs.

Dissecting Bread Wheat Heterosis through the Integration of Agronomic and Physiological Traits

To meet the challenge of feeding almost 10 billion people by 2050, wheat yield has to double by 2050. However, over the past 20 years, yield increase has slowed down and even stagnated in the main producing countries. Following the example of maize, hybrids have been suggested as a solution to overcome yield stagnation in wheat. However, wheat heterosis is still limited and poorly understood. Gaining a better understanding of hybrid vigor holds the key to breed for better varieties. To this aim, we have developed and phenotyped for physiological and agronomic traits an incomplete factorial design consisting of 91 hybrids and their nineteen female and sixteen male parents. Monitoring the plant development with normalized difference vegetation index revealed that 89% of the hybrids including the five higher yielding hybrids had a longer grain filling phase with a delayed senescence that results in larger grain size. This average increase of 7.7% in thousand kernel weight translated to a positive mid-parent heterosis for grain yield for 86% of hybrids. In addition, hybrids displayed a positive grain protein deviation leading to a +4.7% heterosis in protein yield. These results shed light on the physiological bases underlying yield heterosis in wheat, paving new ways to breed for better wheat hybrids.

Onset of autumn senescence in High Arctic plants shows similar patterns in natural and experimental snow depth gradients

Predicted changes in snow cover and temperature raise uncertainties about how the beginning and the end of the growing season will shift for Arctic plants. Snowmelt timing and temperature are known to affect the timing of bud burst, but their effects on autumn senescence are less clear. To address this, researchers have examined senescence under natural and experimental environmental gradients. However, these approaches address different aspects of plant responses and the extent to which they can be compared is poorly understood. In this study, we show that the effect of snowmelt timing on the timing of autumn senescence in High Arctic plants is the same between a natural and an experimental gradient in three out of four studied species. While the two approaches mostly produce comparable results, they give in combination greater insight into the phenological responses to predicted climate changes. We also showed that a short warming treatment in autumn delayed senescence by 3.5 days in D. octopetala, which is a 10 % extension of the growing season end for this species. Warming treatments have commonly been applied to the whole growing season, but here we show that even isolated autumn warming can be sufficient to affect plant senescence.

DNA Methylation Changes Were Involved in Inhibiting Ethylene Signaling and Delaying Senescence of Tomato Fruit Under Low Temperature

Objectives To comprehend the epigenetic mechanism of low temperature in delaying senescence of fruit, the changes of DNA methylation patterns of genes related to ethylene biosynthesis and signaling were analyzed in tomato fruit. Results In the present results, the expression level of LeEIN3, SlERF-A1 and LeERT10 decreased, and the expression level of LeCTR1 increased in tomato fruit stored at the low temperature of 11 oC. Meanwhile, the DNA methylation level of CpG island of LeEIN3, SlERF-A1 and LeERT10 increased, and the DNA methylation level of CpG island of LeCTR1 decreased in tomato fruit, respectively. The low temperature suppressed ethylene signaling via changing DNA methylation and gene expression, and delayed senescence of tomato fruit. Conclusions The present study offered valuable information for understanding the role of DNA methylation in senescence of fruit, and provided a foundation for genetic modifying the epigenetic target sites and controlling fruit senescence.

Enhancement of Nicotiana tabacum Resistance Against Dehydration-Induced Leaf Senescence via Metabolite/Phytohormone-Gene Regulatory Networks Modulated by Melatonin

Melatonin (MEL) is a pleiotropic agent with crucial functions reported in a variety of stress responses and developmental processes. Although MEL involvement in plant defense against natural leaf senescence has been widely reported, the precise regulatory mechanisms by which it delays stress-induced senescence remain unclear. In this study, we found that foliar spraying of melatonin markedly ameliorated dehydration-induced leaf senescence in Nicotiana tabacum, accompanied by attenuated oxidative damage, expression of senescence-related genes, and reduced endogenous ABA production. Metabolite profiling indicated that melatonin-treated plants accumulated higher concentrations of sugars, sugar alcohol, and organic acids, but fewer concentrations of amino acids in the leaves, than untreated plants after exposure to dehydration. Gene expression analysis revealed that the delayed senescence of stressed plants achieved by melatonin treatment might be partially ascribed to the upregulated expression of genes involved in ROS scavenging, chlorophyll biosynthesis, photosynthesis, and carbon/nitrogen balances, and downregulated expression of senescence-associated genes. Furthermore, hormone responses showed an extensively modulated expression, complemented by carotenoid biosynthesis regulation to achieve growth acceleration in melatonin-treated plants upon exposure to dehydration stress. These findings may provide more comprehensive insights into the role of melatonin in alleviating leaf senescence and enhancing dehydration resistance.

Regulation of brain aging by neutral sphingomyelinase 2

We have shown that deficiency of neutral sphingomyelinase 2 (nSMase2), an enzyme generating the sphingolipid ceramide, improves memory in adult mice. Here, we performed sphingolipid and RNA-seq analyses on the cortex from 10 months-old nSMase2-deficient (fro/fro) and heterozygous (+/fro) mice. fro/fro cortex showed reduced levels of ceramide, particularly in astrocytes. Differentially abundant transcripts included several functionally related groups, with decreases in mitochondrial oxidative phosphorylation and astrocyte activation transcripts, while axon guidance and synaptic transmission transcripts were increased, indicating a role of nSMase2 in oxidative stress, astrocyte activation, and cognition. Experimentally induced oxidative stress decreased the level of glutathione (GSH), an endogenous inhibitor of nSMase2, and increased immunolabeling for ceramide in primary +/fro astrocytes, but not in fro/fro astrocytes. β-galactosidase activity was lower in 5-weeks old fro/fro astrocytes, indicating delayed senescence due to nSMase2 deficiency. In fro/fro cortex, levels of the senescence markers C3b and p27, and the proinflammatory cytokines interleukin 1β, interleukin 6, and tumor necrosis factor α were reduced, concurrent with 2-fold decreased phosphorylation of their downstream target, protein kinase Stat3. RNA and protein levels of the ionotropic glutamate receptor subunit 2b (Grin2b or NR2B) were increased by 2-fold, an effect known to enhance cognition. This was consistent with 3.5-fold reduced levels of exosomes carrying miR-223-3p, a micro-RNA downregulating Grin2b. In summary, our data show that nSMase2 deficiency prevents oxidative stress-induced elevation of ceramide and secretion of exosomes by astrocytes that suppress neuronal function, indicating a role of nSMase2 in the regulation of neuroinflammation and cognition during brain aging.