Delay Of Senescence Research Articles

Exogenous nitric oxide delays salt-induced leaf senescence in cotton (Gossypium hirsutum L.)

Nitric oxide (NO) is a signaling molecule which plays an important role in delaying leaf senescence and increasing abiotic stress tolerance, but it is not clear if and how exogenous NO delays salt-induced leaf senescence in cotton. In this study, uniform cotton seedlings with five true main-stem leaves were cultured in hydroponics for 20 days and subjected to 150 mM NaCl. Seedlings were then treated with foliar spray of 300 μM sodium nitroprusside (SNP), a nitric oxide donor, and those with water spray were used as control. The effects of SNP on leaf senescence and expression of senescence-related genes were examined. Foliar spray with SNP significantly delayed leaf senescence in terms of the increased chlorophyll (Chl) content, photosynthetic (Pn) rate and expression of LHCB gene at 22 days after salt stress (DAS). The SNP significantly (p < 0.05) increased the expression of SOS1 and NHX1 genes and K+ content in leaves, but decreased leaf Na+ content. It also reduced (p < 0.05) the expression of ABA biosynthesis genes, NCED2, NCED9, and ABA content but increased the expression of cytokinin biosynthesis gene, IPT1 and ZR and iPA contents at 22 DAS. The overall results suggest that the delay in salt-induced leaf senescence by SNP was due to marked decrease in Na+ and ABA contents and increase in K+ and cytokinin through regulation of the expression of SOS1, NHX1, NCED2, NCED9 and IPT1 genes under salt stress. Foliar spray with SNP can be potentially useful in delaying leaf senescence, thereby increasing the economic yield of cotton under salt stress.

Seasonal life history trade-offs in two leafwing butterflies: Delaying reproductive development increases life expectancy

Surviving inhospitable periods or seasons may greatly affect fitness. Evidence of this exists in the prevalence of dormant stages in the life cycles of most insects. Here I focused on butterflies with distinct seasonal morphological types (not a genetic polymorphism) in which one morphological type, or form, delays reproduction until favorable conditions return, while the other form develops in an environment that favors direct reproduction. For two butterflies, Anaea aidea and A. andria, I tested the hypothesis that the development of each seasonal form involves a differential allocation of resources to survival at eclosion. I assayed differences in adult longevity among summer and winter forms in either a warm, active environment or a cool, calm environment. Winter form adults lived 40 times longer than summer form but only in calm, cool conditions. The magnitude of this difference provided compelling evidence that the winter form body plan and metabolic strategy (i.e. resource conservatism) favor long term survival. This research suggests that winter form adults maintain lowered metabolic rate, a common feature of diapause, to conserve resources and delay senescence while overwintering.

Cytokinin delays dark-induced senescence in rice by maintaining the chlorophyll cycle and photosynthetic complexes.

The phytohormone cytokinin (CK) is known to delay senescence in plants. We studied the effect of a CK analog, 6-benzyl adenine (BA), on rice leaves to understand the possible mechanism by which CK delays senescence in a drought- and heat-tolerant rice cultivar Nagina22 (N22) using dark-induced senescence (DIS) as a surrogate for natural senescence of leaves. Leaves of N22-H-dgl162, a stay-green mutant of N22, and BA-treated N22 showed retention of chlorophyll (Chl) pigments, maintenance of the Chl a/b ratio, and delay in reduction of both photochemical efficiency and rate of oxygen evolution during DIS. HPLC analysis showed accumulation of 7-hydroxymethyl chlorophyll (HmChl) during DIS, and the kinetics of its accumulation correlated with progression of senescence. Transcriptome analysis revealed that several plastid-localized genes, specifically those associated with photosystem II (PSII), showed higher transcript levels in BA-treated N22 and the stay-green mutant leaves compared with naturally senescing N22 leaves. Real-time PCR analyses showed that genes coding for enzymes associated with Chl a/b interconversion and proteins associated with light-harvesting complexes maintained higher transcript levels up to 72h of DIS following BA treatment. The pigment-protein complexes analyzed by green gel remained intact in both N22-H-dgl162 and BA-treated N22 leaves even after 96h of DIS. Thus, CK delays senescence by accumulation of HmChl and up-regulating genes in the Chl cycle, thereby maintaining the Chl a/b ratio. Also, CK treatment retains higher transcript levels of PSII-related genes, resulting in the stability of photosynthetic pigment complexes and functional stay-greenness in rice.

Evidence for a rhizobia-induced drought stress response strategy in Medicago truncatula

Drought stress hampers plant energy and biomass production; however it is still unknown how internal C:N balance and rhizobial symbiosis impact on plant response to water limitation. Here, the effect of differential optimal nitrogen nutrition and root nodule symbiosis on drought stress and rehydration responses of Medicago truncatula was assessed.Two groups of plants were nodulated with Sinorhizobium medicae or Sinorhizobium meliloti — differing in the performance of N fixation; the third group grew in a rhizobia-free medium and received mineral nitrogen fertilizer. In addition to growth analyses, physiological and molecular responses of the two systems were studied using ionomic, metabolomic and proteomic techniques.We found a significant delay in drought-induced leaf senescence in nodulated relative to non-nodulated plants, independent of rhizobial strain and uncoupled from initial leaf N content. The major mechanisms involved are increased concentrations of potassium and shifts in the carbon partitioning between starch and sugars under well-watered conditions, as well as the enhanced allocation of reserves to osmolytes during drought. Consequently, nodulated plants recovered more effectively from drought, relative to non-nodulated M. truncatula. Proteomic data suggest that phytohormone interactions and enhanced translational regulation play a role in increased leaf maintenance in nodulated plants during drought.

Seasonal photosynthetic response of European beech to severe summer drought: Limitation, recovery and post-drought stimulation

Trees experience frequent periods of severe drought during their long lives and must therefore be able to recover and compensate for the limitations of previous stresses. In this study, the response of photosynthesis to a severe, long-lasting summer drought and drought release was followed in saplings of a mesic and xeric provenance of European beech transplanted to mesocosms with experimentally controlled water supply. Photosynthesis was assessed in stressed and non-stressed saplings over the course of an entire vegetation season. The drought response was divided into three phases: (1) limitation, (2) recovery and (3) post-drought stimulation. Limitation of photosynthesis developed gradually and caused, in both provenances, a major loss of cumulated photosynthetic activity. It was accompanied by impaired PSII photochemistry indicating severe stress. Recovery started rapidly after re-watering and was fully accomplished within 20 and 10 days in the mesic and xeric provenances, respectively. After recovery, photosynthesis remained at high levels while decreasing in control trees. This post-drought stimulation was sustained until the end of the vegetation period, partly counterbalancing the previous loss of photosynthetic activity. It was attributable to an altered leaf ontogeny as indicated by a delay of autumnal leaf senescence. These observed responses might be important factors when modelling seasonal carbon uptake and phenology of forest ecosystem under future climate change.

Effects of chlorine dioxide on mitochondrial energy levels and redox status of ‘Daw’ longan pericarp during storage

Mitochondrial redox status and adenosine triphosphate (ATP) production play a central role in responding to physiological and environmental changes and metabolic control. Changes in mitochondrial redox potential are intimately associated with oxidative stress which could lead to plant senescence. This study aimed to demonstrate the involvement of an alteration of the redox status in energy production and fruit senescence of longan (Dimocarpus longan Lour. cv. Daw) during storage and to investigate the effects of gaseous chlorine dioxide (ClO2) both on the redox and the energy status and on delaying senescence. Fresh longan fruit were fumigated with 5, 10 and 25mg/L ClO2 for 10min and then stored in a cardboard box at 25°C with 82% relative humidity for 7 days. ATP content and energy charge (EC), and activities of respiratory enzymes such as succinate dehydrogenase (SDH) and cytochrome c oxidase (CCO) were found to be steadily decreased in the untreated group during storage. These reductions coincided with a decrease in the redox status as determined by pyridine nucleotide (NAD/NADH) and ubiquinone (Q/QH2) ratios and with fruit senescence including browning and the onset of disease symptoms. However, in the ClO2 fumigated fruit, ATP content, EC, SDH and CCO activities as well as NAD/NADH ratio were immediately and markedly increased after treatment. The effects can be seen through the fourth day of storage. The Q/QH2 ratio remained unchanged before rising after Day 4. Higher concentrations of ClO2 (10 and 25mg/L) were more effective than the lower one (5mg/L) in altering the redox balance and increasing energy production. The altered redox state and increased energy by ClO2 were found to be closely associated with a delay in fruit senescence during storage. These findings support the notion that energy production and redox balance involve directly in longan senescence and demonstrated that ClO2 could restore ATP and the redox balance, leading to reduction and delay in fruit senescence.

Slight shading after anthesis increases photosynthetic productivity and grain yield of winter wheat (Triticum aestivum L.) due to the delaying of leaf senescence

The solar radiation intensity and duration are continuously decreasing in the major wheat planting area of China. As a con-sequence, leaf senescence, photosynthesis, grain filling and thus wheat yield shall be affected by light deficiency. Therefore, two winter wheat (Triticum aestivum L.) cultivars, Tainong 18 (a large-spike cultivar) and Ji'nan 17 (a multiple-spike cultivar), were subjected to shading during anthesis and maturity under field condition in 2010–2011 and 2011–2012. Under the slight shading treatment (S1, 88% of full sunshine), leaf senescence was delayed, net photosynthesis rate (Pn) and canopy apparent photosynthesis rate (CAP) were improved, and thus thousand-kernel weight (TKW) and grain yield were higher as compared with the control. However, mid and severe shading (S2 and S3, 67 and 35% of full sunshine, respectively) led to negative effects on these traits substantially. Moreover, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities in flag leaf were significantly greater under slight shading than those in other treatments, while the malondialdehyde (MDA) content was less than that under other treatments. In addition, the multiple-spike cultivar is more tolerant to shading than large-spike cultivar. In conclusion, slight shading after anthesis delayed leaf senescence, enhanced photosynthesis and grain filling, and thus resulted in higher grain yield.

Bioactive Peptides from Angelica sinensis Protein Hydrolyzate Delay Senescence in Caenorhabditis elegans through Antioxidant Activities.

Since excessive reactive oxygen species (ROS) is known to be associated with aging and age-related diseases, strategies modulating ROS level and antioxidant defense systems may contribute to the delay of senescence. Here we show that the protein hydrolyzate from Angelica sinensis was capable of increasing oxidative survival of the model animal Caenorhabditis elegans intoxicated by paraquat. The hydrolyzate was then fractionated by ultrafiltration, and the antioxidant fraction (<3 kDa) was purified by gel filtration to obtain the antioxidant A. sinensis peptides (AsiPeps), which were mostly composed of peptides with <20 amino acid residues. Further studies demonstrate that AsiPeps were able to reduce the endogenous ROS level, increase the activities of the antioxidant enzymes superoxide dismutase and catalase, and decrease the content of the lipid peroxidation product malondialdehyde in nematodes treated with paraquat or undergoing senescence. AsiPeps were also shown to reduce age pigments accumulation and extend lifespan but did not affect the food-intake behavior of the nematodes. Taken together, our results demonstrate that A. sinensis peptides (AsiPeps) are able to delay aging process in C. elegans through antioxidant activities independent of dietary restriction.

Exogenous Hsp70 delays senescence and improves cognitive function in aging mice

Molecular chaperone Heat Shock Protein 70 (Hsp70) plays an important protective role in various neurodegenerative disorders often associated with aging, but its activity and availability in neuronal tissue decrease with age. Here we explored the effects of intranasal administration of exogenous recombinant human Hsp70 (eHsp70) on lifespan and neurological parameters in middle-aged and old mice. Long-term administration of eHsp70 significantly enhanced the lifespan of animals of different age groups. Behavioral assessment after 5 and 9 mo of chronic eHsp70 administration demonstrated improved learning and memory in old mice. Likewise, the investigation of locomotor and exploratory activities after eHsp70 treatment demonstrated a significant therapeutic effect of this chaperone. Measurements of synaptophysin show that eHsp70 treatment in old mice resulted in larger synaptophysin-immunopositive areas and higher neuron density compared with control animals. Furthermore, eHsp70 treatment decreased accumulation of lipofuscin, an aging-related marker, in the brain and enhanced proteasome activity. The potential of eHsp70 intranasal treatment to protect synaptic machinery in old animals offers a unique pharmacological approach for various neurodegenerative disorders associated with human aging.

HDAC4 stabilizes SIRT1 via sumoylation SIRT1 to delay cellular senescence.

The nicotinamide adenine dinucleotide-dependent protein deacetylase silent information regulator 2 (Sir2) regulates cellular lifespan in several organisms. Histone deacetylase 4 (HDAC4) belongs to the class IIa group of HDACs; this class of HDACs is composed of proteins that are important regulators of gene expression that control pleiotropic cellular functions. However, the role of HDAC4 in cellular senescence is still unknown. This study shows that the expression patterns of HDAC4 and Sirtuin 1 (SIRT1; the mammalian homolog of Sir2) are positively correlated during cellular senescence. Moreover, the overexpression of HDAC4 delays senescence, whereas the knockdown of HDAC4 leads to premature senescence in human fibroblasts. Furthermore, it is demonstrated that HDAC4 increases endogenous SIRT1 expression by enhancing its sumoylation modification levels, thereby stabilizing its protein levels. This study, therefore, provides a new molecular mechanism for the regulation of cellular senescence.

Identification of SNPs in candidate genes potentially involved in bud burst in European beech (Fagus sylvatica L.)

AbstractEuropean beech (Fagus sylvatica L.) is one of the most important deciduous tree species in Central Europe. Higher annual mean temperatures caused by climate change lead to earlier bud burst in spring and/or a delay of leaf senescence in autumn. Since earlier bud burst might increase the late frost risk, adaptive traits like bud burst may gain more importance in the future. Nevertheless, knowledge of the genetic background of leaf unfolding is still scarce for European beech. In the present study, we analyzed parts of ten different candidate genes for bud burst with a total length of 12,290 bp. Comparative sequencing with plant material of 12 different beech populations distributed over Germany revealed 116 SNPs (single nucleotide polymorphisms) and 20 indels. A subset of 46 SNPs was successfully used for genotyping of 100 offspring of a beech population in Germany confirming the suitability of the newly developed SNP set for population genetic studies. The provided data may be useful for further investigations of adaptation in F. sylvatica.

PHENOTYPIC AND GENOTYPIC VARIANCE AND HERITABILITY OF STAY GREEN CHARACTER AMONG 22 ELITE SORGHUM (Sorghum bicolor (L.) Moench) GENOTYPES

&lt;p&gt;Delaying of leaf senescence (stay green) is an effective strategy for increasing of crop yield, particularly under water-limited conditions. Study of genotypic variance of stay green is very useful for breeding program of stay green character. Replicated field experiment was carried out in Farm Experimental Station, Faculty of Agriculture Padjadjaran University during dry season. The objectives of this study were: i) to estimate genotypic and phenotypic variances of stay green character; ii) to evaluate and investigate stay green performance of the 22 elite sorghum genotypes. High genotypic and phenotypic variances were observed for plant morphology (plant height, stem diameter), leaf morphology (leaf number, leaf width, leaf length and total leaf area) and yield component (panicle length) and were supported by high estimation of heritability value. Corresponding heritability ranged between 0.77 and 0.94. Genotypic variance of stay green characters was narrow and estimation of broad sense heritability was low. Stay green characters in sorghum might be a quantitative character that was controlled by many genes. Unpad 1.3, Unpad 1.1 and 1090 genotype showed good performance for stay green character. These genotypes can be recommended as stay green parental in breeding program.&lt;/p&gt;&lt;p&gt;&lt;br /&gt;&lt;strong&gt;Keywords&lt;/strong&gt;: Genotypic variance, Heritability, Phenotypic variance, Sorghum, Stay green&lt;/p&gt;

Limits to Future Adaptation in the Invasive Plant Polygonum cespitosum: Expression of Functional and Fitness Traits at Elevated CO2.

For organisms to adapt to future environments, they must both evolve appropriate functional responses and phenotypically express those responses under future climatic and CO2 conditions. We examined these 2 components of future adaptation in an invasive annual plant (Polygonum cespitosum) by performing a "resurrection" experiment under field conditions simulating a future environment. Resurrection experiments reveal recent evolution by comparing genotypes from natural populations sampled across a multigeneration interval. We collected genotypes from the same 3 North American populations in 1994 and 2005 and raised inbred lines from these collections under free air CO2 enrichment to examine functional and fitness traits expressed in hot, dry conditions at both ambient and elevated CO2 (N = 295 plants). The species has rapidly evolved in its introduced range to increase photosynthetic rate (collection year effect P ≤ 0.011) and delay senescence (P = 0.017) under full-sun, dry field conditions, but these adaptive changes were not expressed when the field environment included elevated CO2 (within-treatment year effect P ≥ 0.20 for both traits). Populations showed different levels of reproductive output and its genetic variance in these novel, stressful conditions. These findings illustrate constraints on evolutionary adaptation to predicted future conditions at both the species and population levels.

The Japanese diet from 1975 delays senescence and prolongs life span in SAMP8 mice

ObjectiveLife expectancy in Japan is high, suggesting that the Japanese diet, Nihon shoku (Japanese food), has significant health benefits. However, these benefits have been called into question over the past 50 y, during which time the Japanese diet has become increasingly Westernized. The aim of the present study was to focus on senescence delay and to examine the effects of Japanese diets from different years to identify which Japanese diet is most effective in enhancing life expectancy and delaying senescence. MethodsWeekly menus from the years 1960, 1975, 1990, and 2005 were reproduced based on the National Health and Nutrition Survey in Japan and prepared as powdered foods. The senescence-accelerated mouse prone 8 (SAMP8) mice were fed standard laboratory chow supplemented with a 30% mix of Japanese meals from various years ad libitum throughout their lifetime. Additionally, the control group was given standard laboratory chow only, to examine the development of mice reared under standard conditions. ResultsIn the group that ingested the traditional 1975 Japanese diet, life span was prolonged, senescence was delayed, and learning and memory capacities were maintained compared with the group fed the 2005 Japanese diet. The life span of the group that ingested the 1990 Japanese diet showed a tendency to be longer than SAMP8 mice fed the 2005 diet. ConclusionThe results of the present study suggested that the traditional Japanese diet is more effective in enhancing life expectancy and delaying senescence than the current Japanese diet.

Nitric oxide prevents wound-induced browning and delays senescence through inhibition of hydrogen peroxide accumulation in fresh-cut lettuce

As a source of bioactive ingredients, lettuce is a preferable component of a healthy diet. In recent years the production of fresh-cut produce has become a fast growing business. However, the shreds are highly sensitive to wound-induced browning and premature senescence that substantially reduces the visual and sensory qualities and shortens the shelf life. To improve the fresh-cut quality, in this work, short pre-storage exposure of shreds from butterhead and iceberg lettuce to nitric oxide (NO) gas was applied. It was found that fumigation with 100 and 200 ppm NO for 1 or 2 h remarkably inhibited the browning of the cut surface and of other injured leaf areas; NO treatment delayed the senescence and substantially prolonged the shelf life upon storage at 4 °C and 12 °C. To obtain information on the physiological processes involved in the wound response, the generation of hydrogen peroxide (H2O2) and the occurrence of cell death were analyzed. The results revealed that the wounding stimulated the accumulation of H2O2 thus generating oxidative stress leading to cell death. A correlation between elevated H2O2 levels, cut surface browning, senescence and storability of the fresh-cuts was established. In comparison to mature leaves, younger leaves expressed a lesser susceptibility to wound-induced browning and the associated oxidative stress. Applied NO strongly inhibited the H2O2 accumulation which may explain its beneficial effects.

Changes in autumn senescence in northern hemisphere deciduous trees: a meta-analysis of autumn phenology studies.

Many individual studies have shown that the timing of leaf senescence in boreal and temperate deciduous forests in the northern hemisphere is influenced by rising temperatures, but there is limited consensus on the magnitude, direction and spatial extent of this relationship. A meta-analysis was conducted of published studies from the peer-reviewed literature that reported autumn senescence dates for deciduous trees in the northern hemisphere, encompassing 64 publications with observations ranging from 1931 to 2010. Among the meteorological measurements examined, October temperatures were the strongest predictors of date of senescence, followed by cooling degree-days, latitude, photoperiod and, lastly, total monthly precipitation, although the strength of the relationships differed between high- and low-latitude sites. Autumn leaf senescence has been significantly more delayed at low (25° to 49°N) than high (50° to 70°N) latitudes across the northern hemisphere, with senescence across high-latitude sites more sensitive to the effects of photoperiod and low-latitude sites more sensitive to the effects of temperature. Delays in leaf senescence over time were stronger in North America compared with Europe and Asia. The results indicate that leaf senescence has been delayed over time and in response to temperature, although low-latitude sites show significantly stronger delays in senescence over time than high-latitude sites. While temperature alone may be a reasonable predictor of the date of leaf senescence when examining a broad suite of sites, it is important to consider that temperature-induced changes in senescence at high-latitude sites are likely to be constrained by the influence of photoperiod. Ecosystem-level differences in the mechanisms that control the timing of leaf senescence may affect both plant community interactions and ecosystem carbon storage as global temperatures increase over the next century.

Physiological responses of grapevine leaves to Bordeaux mixture under light stress conditions

The effect of Bordeaux mixture on the physiology of leaves of Vitis vinifera L., cv. Touriga Nacional, growing under field conditions in the Douro Wine Region, was evaluated. Especially in late summer, this fungicide modifies the light microclimate and leaf physiological characteristics, namely stomatal aperture and photosynthesis. Leaves treated with Bordeaux mixture showed higher reflectance, whereas transmitted photon flux density and temperature were lower compared to control leaves. Photosynthetic rates of treated leaves increased due to a lowering of both, stomatal and non-stomatal limitation. In addition, transpiration rates were higher, but neither the intrinsic efficiency of water use nor leaf water potentials were affected. Delay of leaf senescence of grapevines sprayed with Bordeaux mixture inhibited scorching of clusters and, consequently, led to higher yields per plant.

Y-27632, a ROCK inhibitor, delays senescence of putative murine salivary gland stem cells in culture

ObjectiveA loss of functional salivary glands often occurs after radiotherapy for head and neck tumour, and causes many problems in oral health. Recently, the use of salispheres, which consist of salivary gland stem cells (SGSCs), has been suggested as therapy for these problems. However, an insufficient number of cells can be obtained and cultured for cell transplantation. In the present study, salispheres were propagated and passaged by suspension culture to acquire a sufficient number of SGSCs for cell therapy. DesignThe relationship between sphere formation and the degree of cellular senescence was investigated by analysing senescence-associated β-galactosidase activity and the expression of senescence-related markers such as CDKN2A (p16) and p21. Because the sphere formation potential of SGSCs was decreased and the senescence of the cells was increased after passaging subculture, Y-27632, a Rho-associated kinase inhibitor, was used to treat the passaging subculture to aid the proliferation of the cells in culture. ResultsThe number of spheres was higher in the Y-27632 treatment group than in the control group, and the expression of c-Kit, a proliferation marker, was also increased. In addition, the expression of p16 and p21 proteins tended to be lower in the Y-27632 group. ConclusionY-27632 suppresses the expression of senescence-related proteins and enhances cellular proliferation. This study points to the possibility of scaling-up the therapeutic use of SGSCs, which requires a large amount of cells.

Moderately enhancing cytokinin level by down-regulation of GhCKX expression in cotton concurrently increases fiber and seed yield.

Cotton is the leading natural fiber crop in the world. Cotton seeds are also an important oil and protein source. However, enhancement of fiber abundance usually leads to a smaller seed. Thus, it has become a challenge for cotton breeding to concurrently increase fiber yield and seed yield. To improve cotton yield, we elevated the endogenous cytokinin level in transgenic cotton by constitutive suppression of cytokinin dehydrogenase (CKX), a key negative regulator controlling endogenous cytokinin in plants. The slightly and moderately suppressed transgenic cotton plants showed normal growth and development, while the severely suppressed plants exhibited a typical cytokinin-overproduction alteration. The suppression of CKX led to an enhancement of endogenous cytokinins in transgenic cotton plants. Total cytokinins in moderately suppressed lines, CR-3 and CR-6, increased by 20.4 and 55.5 % respectively, and that in the severely suppressed line (CR-13) increased by 134.2 % compared to the wild type. The moderately suppressed lines showed a delay in leaf senescence, higher photosynthesis, more fruiting branches and bolls, and bigger seed size. Field trials showed that seed yield and lint yield of the moderately suppressed CR-6 line increased by 15.4 and 20.0 %, respectively. Meanwhile, the enhanced cytokinin level in transgenic cottons did not show significant influence on fiber qualities. Our data demonstrated that CKX is a promising gene for crop yield improvement.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-015-0232-6) contains supplementary material, which is available to authorized users.

Regulated expression of a cytokinin biosynthesis gene IPT delays leaf senescence and improves yield under rainfed and irrigated conditions in canola (Brassica napus L.).

Delay of leaf senescence through genetic modification can potentially improve crop yield, through maintenance of photosynthetically active leaves for a longer period. Plant growth hormones such as cytokinin regulate and delay leaf senescence. Here, the structural gene (IPT) encoding the cytokinin biosynthetic enzyme isopentenyltransferase was fused to a functionally active fragment of the AtMYB32 promoter and was transformed into canola plants. Expression of the AtMYB32xs::IPT gene cassette delayed the leaf senescence in transgenic plants grown under controlled environment conditions and field experiments conducted for a single season at two geographic locations. The transgenic canola plants retained higher chlorophyll levels for an extended period and produced significantly higher seed yield with similar growth and phenology compared to wild type and null control plants under rainfed and irrigated treatments. The yield increase in transgenic plants was in the range of 16% to 23% and 7% to 16% under rainfed and irrigated conditions, respectively, compared to control plants. Most of the seed quality parameters in transgenic plants were similar, and with elevated oleic acid content in all transgenic lines and higher oil content and lower glucosinolate content in one specific transgenic line as compared to control plants. The results suggest that by delaying leaf senescence using the AtMYB32xs::IPT technology, productivity in crop plants can be improved under water stress and well-watered conditions.