Age‐related changes in stem cell dynamics,neurogenesis, apoptosis,and gliosis in the adult brain: A novel teleost fish model of negligible senescence

Adult neurogenesis, the generation of new neurons in the adult central nervous system, is a reported feature of all examined vertebrate species. However, a dramatic decline in the rates of cell proliferation and neuronal differentiation occurs in mammals, typically starting near the onset of sexual maturation. In the present study, we examined possible age‐related changes associated with adult neurogenesis in the brain of brown ghost knifefish (Apteronotus leptorhynchus), a teleost fish distinguished by its enormous neurogenic potential. Contrary to the well‐established alterations in the mammalian brain during aging, in the brain of this teleostean species we could not find evidence for any significant age‐related decline in the absolute levels of stem/progenitor cell proliferation, neuronal and glial differentiation, or long‐term survival of newly generated cells. Moreover, there was no indication that the amount of glial fibrillary acidic protein or the number of apoptotic cells in the brain was altered significantly over the course of adult life. We hypothesize that this first demonstration of negligible cellular senescence in the vertebrate brain is related to the continued growth of this species and to the lack of reproductive senescence during adulthood. The establishment of the adult brain of this species as a novel model of negligible senescence provides new opportunities for the advancement of our understanding of the biology of aging and the fundamental mechanisms that underlie senescence in the brain. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 74: 514–530, 2014     

Age‐dependent decline in fin regenerative capacity in the short‐lived fish Nothobranchius furzeri

The potential to regenerate declines with age in a wide range of organisms. A popular model system to study the mechanisms of regeneration is the fin of teleost fish, which has the ability to fully regrow upon amputation. Here, we used the short‐lived killifish Nothobranchius furzeri to analyse the impact of aging on fin regeneration in more detail. We observed that young fish were able to nearly completely (98%) regenerate their amputated caudal fins within 4 weeks, whereas middle‐aged fish reached 78%, old fish 57% and very old fish 46% of their original fin size. The difference in growth rate between young and old fish was already significant at 3 days post amputation (dpa) and increased with time. We therefore hypothesized that early events are crucial for the age‐related differences in regenerative capacity. Indeed, we could observe a higher percentage of proliferating cells in early regenerating fin tissue of young fish compared with aged fish and larger fractions of apoptotic cells in aged fish. Furthermore, young fish showed peak upregulation of several genes involved in fgf and wnt/β‐catenin signalling at an earlier time point than old fish. Our findings suggest that regenerative processes are initiated earlier and that regeneration overall is more efficient in younger fish.     

Adult neurogenesis in the short-lived teleost Nothobranchius furzeri: localization of neurogenic niches, molecular characterization and effects of aging

We studied adult neurogenesis in the short‐lived annual fish Nothobranchius furzeri and quantified the effects of aging on the mitotic activity of the neuronal progenitors and the expression of glial fibrillary acid protein (GFAP) in the radial glia. The distribution of neurogenic niches is substantially similar to that of zebrafish and adult stem cells generate neurons, which persist in the adult brain. As opposed to zebrafish, however, the N. furzeri genome contains a doublecortin (DCX) gene. Doublecortin is transiently expressed by newly generated neurons in the telencephalon and optic tectum (OT). We also analyzed the expression of the microRNA miR‐9 and miR‐124 and found that they have complementary expression domains: miR‐9 is expressed in the neurogenic niches of the telencephalon and the radial glia of the OT, while miR‐124 is expressed in differentiated neurons. The main finding of this paper is the demonstration of an age‐dependent decay in adult neurogenesis. Using unbiased stereological estimates of cell numbers, we detected an almost fivefold decrease in the number of mitotically active cells in the OT between young and old age. This reduced mitotic activity is paralleled by a reduction in DCX labeling. Finally, we detected a dramatic up‐regulation of GFAP in the radial glia of the aged brain. This up‐regulation is not paralleled by a similar up‐regulation of S100B and Musashi‐1, two other markers of the radial glia. In summary, the brain of N. furzeri replicates two typical hallmarks of mammalian aging: gliosis and reduced adult neurogenesis.     

Mosaic Heterochrony in Neural Progenitors Sustains Accelerated Brain Growth and Neurogenesis in the Juvenile Killifish N. furzeri

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Resilience to aging in the regeneration‐capable flatworm Macrostomum lignano

Animals show a large variability of lifespan, ranging from short‐lived as Caenorhabditis elegans to immortal as Hydra. A fascinating case is flatworms, in which reversal of aging by regeneration is proposed, yet conclusive evidence for this rejuvenation‐by‐regeneration hypothesis is lacking. We tested this hypothesis by inducing regeneration in the sexual free‐living flatworm Macrostomum lignano. We studied survival, fertility, morphology, and gene expression as a function of age. Here, we report that after regeneration, genes expressed in the germline are upregulated at all ages, but no signs of rejuvenation are observed. Instead, the animal appears to be substantially longer lived than previously appreciated, and genes expressed in stem cells are upregulated with age, while germline genes are downregulated. Remarkably, several genes with known beneficial effects on lifespan when overexpressed in mice and C. elegans are naturally upregulated with age in M. lignano, suggesting that molecular mechanism for offsetting negative consequences of aging has evolved in this animal. We therefore propose that M. lignano represents a novel powerful model for molecular studies of aging attenuation, and the identified aging gene expression patterns provide a valuable resource for further exploration of anti‐aging strategies.     

Quantification of noradrenergic‐, dopaminergic‐, and tectal‐neurons during aging in the short‐lived killifish Nothobranchius furzeri

Parkinson''s disease (PD) is characterized by phosphorylation and aggregation of the protein α‐Synuclein and ensuing neuronal death progressing from the noradrenergic locus coeruleus to midbrain dopaminergic neurons. In 2019, Matsui and colleagues reported a spontaneous age‐dependent degeneration of dopaminergic neurons and an even greater neurodegeneration of the noradrenergic neurons in the short‐lived killifish Nothobranchius furzeri. Given the great possible relevance of a spontaneous model for PD, we assessed neurodegeneration of noradrenergic and dopaminergic neurons in two further laboratory strains of N. furzeri. We implemented, for the first time in N. furzeri, a whole‐brain clarification technique and proceeded to entire 3D nuclei reconstruction to quantify total cell numbers in two different stains of N. furzeri. In both strains, we observed that age‐dependent neurodegeneration is limited to the locus coeruleus and does not involve the posterior tuberculum. We also applied 3D counting to the optic tectum, an area of active adult neurogenesis, and detected an increase of neurons with age. Our results confirm age‐dependent neurodegeneration of noradrenergic neurons, a condition reminiscent of the presymptomatic stage of PD indicating that N. furzeri could be used in the future to identify modifying factors for age‐dependent neurodegeneration and open the intriguing possibility that natural genetic variation may influence the susceptibility of dopaminergic neurons.     

Ventriculomegaly associated with ependymal gliosis and declines in barrier integrity in the aging human and mouse brain

Age‐associated ventriculomegaly is typically attributed to neurodegeneration; however, additional factors might initiate or contribute to progressive ventricular expansion. By directly linking postmortem human MRI sequences with histological features of periventricular tissue, we show that substantial lateral ventricle surface gliosis is associated with ventriculomegaly. To examine whether loss of ependymal cell coverage resulting in ventricle surface glial scarring can lead directly to ventricle enlargement independent of any other injury or degenerative loss, we modeled in mice the glial scarring found along the lateral ventricle surface in aged humans. Neuraminidase, which cleaves glycosidic linkages of apical adherens junction proteins, was administered intracerebroventricularly to denude areas of ependymal cells. Substantial ependymal cell loss resulted in reactive gliosis rather than stem cell‐mediated regenerative repair of the ventricle lining, and the gliotic regions showed morphologic and phenotypic characteristics similar to those found in aged humans. Increased levels of aquaporin‐4, indicative of edema, observed in regions of periventricular gliosis in human tissue were also replicated in our mouse model. 3D modeling together with volume measurements revealed that mice with ventricle surface scarring developed expanded ventricles, independent of neurodegeneration. Through a comprehensive, comparative analysis of the lateral ventricles and associated periventricular tissue in aged humans and mouse, followed by modeling of surface gliosis in mice, we have demonstrated a direct link between lateral ventricle surface gliosis and ventricle enlargement. These studies highlight the importance of maintaining an intact ependymal cell lining throughout aging.     

Mitochondrial mutations and aging: random drift is insufficient to explain the accumulation of mitochondrial deletion mutants in short‐lived animals

Mitochondrial DNA deletions accumulate over the life course in post‐mitotic cells of many species and may contribute to aging. Often a single mutant expands clonally and finally replaces the wild‐type population of a whole cell. One proposal to explain the driving force behind this accumulation states that random drift alone, without any selection advantage, is sufficient to explain the clonal accumulation of a single mutant. Existing mathematical models show that such a process might indeed work for humans. However, to be a general explanation for the clonal accumulation of mtDNA mutants, it is important to know whether random drift could also explain the accumulation process in short‐lived species like rodents. To clarify this issue, we modelled this process mathematically and performed extensive computer simulations to study how different mutation rates affect accumulation time and the resulting degree of heteroplasmy. We show that random drift works for lifespans of around 100 years, but for short‐lived animals, the resulting degree of heteroplasmy is incompatible with experimental observations.     

Longterm quiescent cells in the aged human subventricular neurogenic system specifically express GFAP‐δ

A main neurogenic niche in the adult human brain is the subventricular zone (SVZ). Recent data suggest that the progenitors that are born in the human SVZ migrate via the rostral migratory stream (RMS) towards the olfactory bulb (OB), similar to what has been observed in other mammals. A subpopulation of astrocytes in the SVZ specifically expresses an assembly‐compromised isoform of the intermediate filament protein glial fibrillary acidic protein (GFAP‐δ). To further define the phenotype of these GFAP‐δ expressing cells and to determine whether these cells are present throughout the human subventricular neurogenic system, we analysed SVZ, RMS and OB sections of 14 aged brain donors (ages 74‐93). GFAP‐δ was expressed in the SVZ along the ventricle, in the RMS and in the OB. The GFAP‐δ cells in the SVZ co‐expressed the neural stem cell (NSC) marker nestin and the cell proliferation markers proliferating cell nuclear antigen (PCNA) and Mcm2. Furthermore, BrdU retention was found in GFAP‐δ positive cells in the SVZ. In the RMS, GFAP‐δ was expressed in the glial net surrounding the neuroblasts. In the OB, GFAP‐δ positive cells co‐expressed PCNA. We also showed that GFAP‐δ cells are present in neurosphere cultures that were derived from SVZ precursors, isolated postmortem from four brain donors (ages 63‐91). Taken together, our findings show that GFAP‐δ is expressed in an astrocytic subpopulation in the SVZ, the RMS and the OB. Importantly, we provide the first evidence that GFAP‐δ is specifically expressed in longterm quiescent cells in the human SVZ, which are reminiscent of NSCs.     

Transcriptome analysis reveals the difference between “healthy” and “common” aging and their connection with age‐related diseases

A key goal of aging research was to understand mechanisms underlying healthy aging and develop methods to promote the human healthspan. One approach is to identify gene regulations unique to healthy aging compared with aging in the general population (i.e., “common” aging). Here, we leveraged Genotype‐Tissue Expression (GTEx) project data to investigate “healthy” and “common” aging gene expression regulations at a tissue level in humans and their interconnection with diseases. Using GTEx donors' disease annotations, we defined a “healthy” aging cohort for each tissue. We then compared the age‐associated genes derived from this cohort with age‐associated genes from the “common” aging cohort which included all GTEx donors; we also compared the “healthy” and “common” aging gene expressions with various disease‐associated gene expressions to elucidate the relationships among “healthy,” “common” aging and disease. Our analyses showed that 1. GTEx “healthy” and “common” aging shared a large number of gene regulations; 2. Despite the substantial commonality, “healthy” and “common” aging genes also showed distinct function enrichment, and “common” aging genes had a higher enrichment for disease genes; 3. Disease‐associated gene regulations were overall different from aging gene regulations. However, for genes regulated by both, their regulation directions were largely consistent, implying some aging processes could increase the susceptibility to disease development; and 4. Possible protective mechanisms were associated with some “healthy” aging gene regulations. In summary, our work highlights several unique features of GTEx “healthy” aging program. This new knowledge could potentially be used to develop interventions to promote the human healthspan.     

Differential expression of methyl CpG‐binding domain containing factor MBD3 in the developing and adult rat brain

Using subtractive hybridization screening, the methyl CpG‐binding domain containing protein MBD3 was identified as being more prevalently expressed in the embryonic brain than in the adult. In this report, we present the mRNA and protein expression patterns of MBD3 in the developing brain. MBD3 expression was detected in neuroepithelial cells of the developing forebrain, and in peripheral tissues such as liver and intestine during late embryogenesis. This is in contrast to its related family member MBD2, which displayed only minimal expression in the embryonic brain. Immunoblot analysis revealed that the levels of both MBD3 splice forms decrease in the maturing postnatal hippocampus and cortex, although the two forms do not decline at equivalent rates. Immunohistochemical analysis revealed strong MBD3 immunostaining in principal neurons of the hippocampus and cortex, but weak or nondetectable immunostaining in outer cortical layer cells. MBD3 was also selectively expressed in the adult retina, where strong immunoreactivity was detected in cells of the inner nuclear and ganglion cell layers, but no immunoreactivity was detected in cells of the outer nuclear layer. Taken together, these results illustrate that MBD3 displays a selective spatial and temporal pattern of expression in the embryonic and adult brain, thereby strengthening the possibility of MBD3 playing an important role in neuronal development. © 2003 Wiley Periodicals, Inc. J Neurobiol 55: 220–232, 2003     

Intraneuronal amyloid precursor protein (APP) and appearance of extracellular β‐amyloid peptide (aβ) in the brain of aging kokanee salmon

Antibodies to human amyloid precursor protein (APP₆₉₅) and beta‐amyloid peptide (Aβ_1‐42) were used to determine timing of amyloidosis in the brain of kokanee salmon (Oncorhynchus nerka kennerlyi) in one of four reproductive stages: immature (IM), maturing (MA), sexually mature (SM), and spawning (SP), representing a range of aging from somatically mature but sexually immature to spawning and somatic senescence. In IM fish, immunoreactive (ir) intracellular APP occurred in 18 of 23 brain regions. During sexual maturation and aging, the number of neurons expressing APP increased in 11 of these APP‐ir regions. Aβ‐ir was absent in IM fish, present in seven regions in MA fish, moderately abundant in 15 regions in SM fish, and was most abundant in all brain regions of SP fish exhibiting Aβ‐ir. Intracellular APP‐ir was observed in brain regions involved in sensory integration, olfaction, vision, stress responses, reproduction, and coordination. Intra‐ and extracellular Aβ_1‐42 immunoreactivity (Aβ‐ir) was present in all APP‐ir regions except the nucleus lateralis tuberis (hypothalamus) and Purkinje cells (cerebellum). APP‐ir and Aβ deposition increase during aging. APP‐ir is present in IM fish; Aβ‐ir usually appears first in MA or SM fish and increases in SM fish as does APP‐ir. Extracellular Aβ deposition dramatically increases between SM and SP stages (1–2 weeks) in all fish, indicating an extremely rapid and synchronized process. Rapid senescence observed in pacific salmon could make them a useful model to investigate timing of amyloidosis and neurodegeneration during brain aging. © 2002 Wiley Periodicals, Inc. J Neurobiol 53: 11–20, 2002     

Role of Adiponectin‐Notch pathway in cognitive dysfunction associated with depression and in the therapeutic effect of physical exercise

A substantial percentage of late‐life depression patients also have an cognitive impairment, which severely affects the life quality, while the co‐occurring mechanisms are still unclear. Physical exercise can ameliorate both depressive behaviors and cognitive dysfunction, but the molecular mechanisms underlying its beneficial effects remain elusive. In this study, we uncover a novel adipose tissue to hippocampus crosstalk mediated by Adiponectin‐Notch pathway, with an impact on hippocampal neurogenesis and cognitive function. Adiponectin, an adipocyte‐derived hormone, could activate Notch signaling in the hippocampus through upregulating ADAM10 and Notch1, two key molecules in the Notch signaling. Chronic stress inhibits the Adiponectin‐Notch pathway and induces impaired hippocampal neurogenesis and cognitive dysfunction, which can be rescued by AdipoRon and running. Inhibition Notch signaling by DAPT mimics the adverse effects of chronic stress on hippocampal neurogenesis and cognitive function. Adiponectin knockout mice display depressive‐like behaviors, associated with inhibited Notch signaling, impaired hippocampal neurogenesis and cognitive dysfunction. Physical exercise could activate Adiponectin‐Notch pathway, and improve hippocampal neurogenesis and cognitive function, while deleting adiponectin gene or inhibiting Notch signaling blocks its beneficial effects. Together, our data not only suggest that Adiponectin‐Notch pathway is involved in the pathogenesis of cognitive dysfunction associated with depression, but also contributes to the therapeutic effect of physical exercise. This work helps to decipher the etiology of cognitive impairment associated with depression and hence will provide a potential innovative therapeutic target for these patients.     

Association mapping in Salix viminalis L. (Salicaceae) – identification of candidate genes associated with growth and phenology

Willow species (Salix) are important as short‐rotation biomass crops for bioenergy, which creates a demand for faster genetic improvement and breeding through deployment of molecular marker‐assisted selection (MAS). To find markers associated with important adaptive traits, such as growth and phenology, for use in MAS, we genetically dissected the trait variation of a Salix viminalis (L.) population of 323 accessions. The accessions were sampled throughout northern Europe and were established at two field sites in Pustnäs, Sweden, and at Woburn, UK, offering the opportunity to assess the impact of genotype‐by‐environment interactions (G × E) on trait–marker associations. Field measurements were recorded for growth and phenology traits. The accessions were genotyped using 1536 SNP markers developed from phenology candidate genes and from genes previously observed to be differentially expressed in contrasting environments. Association mapping between 1233 of these SNPs and the measured traits was performed taking into account population structure and threshold selection bias. At a false discovery rate (FDR) of 0.2, 29 SNPs were associated with bud burst, leaf senescence, number of shoots or shoot diameter. The percentage of accession variation () explained by these associations ranged from 0.3% to 4.4%, suggesting that the studied traits are controlled by many loci of limited individual impact. Despite this, a SNP in the EARLY FLOWERING 3 gene was repeatedly associated (FDR < 0.2) with bud burst. The rare homozygous genotype exhibited 0.4–1.0 lower bud burst scores than the other genotype classes on a five‐grade scale. Consequently, this marker could be promising for use in MAS and the gene deserves further study. Otherwise, associations were less consistent across sites, likely due to their small estimates and to considerable G × E interactions indicated by multivariate association analyses and modest trait accession correlations across sites (0.32–0.61).     

Screening the expression characteristics of several miRNAs in G93A‐SOD1 transgenic mouse: altered expression of miRNA‐124 is associated with astrocyte differentiation by targeting Sox2 and Sox9

MicroRNA s (miRNA s) are suspected to be a contributing factor in amyotrophic lateral sclerosis (ALS ). Here, we assess the altered expression of miRNA s and the effects of miR‐124 in astrocytic differentiation in neural stem cells of ALS transgenic mice. Differentially expressed miRNA ‐positive cells (including miR‐124, miR‐181a, miR‐22, miR‐26b, miR‐34a, miR‐146a, miR‐219, miR‐21, miR‐200a, and miR‐320) were detected by in situ hybridization and qRT ‐PCR in the spinal cord and the brainstem. Our results demonstrated that miR‐124 was down‐regulated in the spinal cord and brainstem. In vitro , miR‐124 was down‐regulated in neural stem cells and up‐regulated in differentiated neural stem cells in G93A‐ superoxide dismutase 1 (SOD 1 ) mice compared with WT mice by qRT ‐PCR . Meanwhile, Sox2 and Sox9 protein levels showed converse change with miR‐124 in vivo and vitro . After over‐expression or knockdown of miR‐124 in motor neuron‐like hybrid (NSC 34) cells of mouse, Sox2 and Sox9 proteins were noticeably down‐regulated or up‐regulated, whereas Sox2 and Sox9 mRNA s remained virtually unchanged. Moreover, immunofluorescence results indicated that the number of double‐positive cells of Sox2/glial fibrillary acidic protein (GFAP) and Sox9/glial fibrillary acidic protein (GFAP) was higher in G93A‐SOD 1 mice compared with WT mice. We also found that many Sox2‐ and Sox9‐positive cells were nestin positive in G93A‐SOD 1 mice, but not in WT mice. Furthermore, differentiated neural stem cells from G93A‐SOD 1 mice generated a greater proportion of astrocytes and lower proportion of neurons than those from WT mice. MiR‐124 may play an important role in astrocytic differentiation by targeting Sox2 and Sox9 in ALS transgenic mice.

Cover Image for this issue: doi: 10.1111/jnc.14171 .

     

Aβ1–42 oligomer‐induced leakage in an in vitro blood–brain barrier model is associated with up‐regulation of RAGE and metalloproteinases,and down‐regulation of tight junction scaffold proteins

Accumulating evidence indicates that abnormal deposition of amyloid‐β (Aβ) peptide in the brain is responsible for endothelial cell damage and consequently leads to blood–brain barrier (BBB) leakage. However, the mechanisms underlying BBB disruption are not well described. We employed an monolayer BBB model comprising bEnd.3 cell and found that BBB leakage was induced by treatment with Aβ_1–42, and the levels of tight junction (TJ) scaffold proteins (ZO‐1, Claudin‐5, and Occludin) were decreased. Through comparisons of the effects of the different components of Aβ_1–42, including monomer (Aβ_1–42‐Mono), oligomer (Aβ_1–42‐Oligo), and fibril (Aβ_1–42‐Fibril), our data confirmed that Aβ_1–42‐Oligo is likely to be the most important damage factor that results in TJ damage and BBB leakage in Alzheimer's disease. We found that the incubation of bEnd.3 cells with Aβ_1–42 significantly up‐regulated the level of receptor for advanced glycation end‐products (RAGE). Co‐incubation of a polyclonal antibody to RAGE and Aβ_1–42‐Oligo in bEnd.3 cells blocked RAGE suppression of Aβ_1–42‐Oligo‐induced alterations in TJ scaffold proteins and reversed Aβ_1–42‐Oligo‐induced up‐regulation of RAGE, matrix metalloproteinase (MMP)‐2, and MMP‐9. Furthermore, we found that these effects induced by Aβ_1–42‐Oligo treatment were effectively suppressed by knockdown of RAGE using small interfering RNA (siRNA) transfection. We also found that GM 6001, a broad‐spectrum MMP inhibitor, partially reversed the Aβ_1–42‐Oligo‐induced inhibitor effects in bEnd.3 cells. Thus, these results suggested that RAGE played an important role in Aβ‐induced BBB leakage and alterations of TJ scaffold proteins, through a mechanism that involved up‐regulation of MMP‐2 and MMP‐9.

     

Wnt/β‐catenin signaling and adipogenic genes are associated with intramuscular fat content in the longissimus dorsi muscle of Korean cattle

Intramuscular fat (IMF) is an important trait that influences beef quality. In two studies, we examined the possible involvement of the Wnt/β‐catenin signaling pathway in IMF deposition in Korean cattle. In study 1, using a group of bulls and steers, we found that castration, a non‐genetic factor, decreased (P < 0.01) the expression of both the WNT10B and CTNNB1 genes, whereas it increased the expression of the Wnt antagonist secreted frizzled‐related proteins 4 (SFRP4, P < 0.001) and the adipogenic CCAAT/enhancer binding protein (C/EPB), alpha (CEBPA, P < 0.001) and peroxisome proliferator‐activated receptor gamma (PPARG, P < 0.05) genes in longissimus dorsi muscle (LM) tissue. The WNT10B and CTNNB1 mRNA levels showed strong (P < 0.001) negative correlations (r = ?0.68 and r = ?0.73 respectively) with the IMF content, whereas the SFRP4, CEBPA and PPARG mRNA levels showed strong (P < 0.01) positive correlations (r = 0.70, 0.70 and 0.64 respectively) with the IMF content. Large variation still exists in the IMF content of steers, implying that genetic factors affect IMF deposition. Using a different group of steers, a correlation analysis in study 2 also showed that the expression of the WNT10B and CTNNB1 genes, and SFRP4 and adipogenic genes was negatively and positively associated with the IMF content respectively. Our findings suggest that downregulation of the Wnt/β‐catenin signaling pathway genes, but upregulation of Wnt antagonist SFRP4 and adipogenic gene expression following castration, contributes to increased IMF deposition in the LM. Our results demonstrate that both non‐genetic factors (castration) and genetic variation within the steer group affect the gene expression pattern of the Wnt/β‐catenin signaling pathway.     

Physio‐biochemical assessment and expression analysis of genes associated with drought tolerance in sugarcane (Saccharum spp. hybrids) exposed to GA3 at grand growth stage

• Drought is one of the most serious environmental factors limiting production of sugarcane worldwide. In order to assess the influence of gibberellins (GA₃) on drought and plant growth, along with associated physio‐biochemical attributes, expression of eight drought‐responsive genes were quantified and analysed.
• At grand growth stage (120 DAP) two sugarcane varieties (CoLk94184, CoPK05191) were exposed to drought by withholding irrigation. GA₃ (35 ppm) was applied using battery‐operated uniform controlled dispensing sprayer twice at 1‐week intervals on 2‐week drought‐stressed plants. Physio‐biochemical attributes including antioxidant enzyme activities were estimated following standard protocols. RT‐PCR was performed to visualise the drought‐associated gene expression patterns.
• Drought triggered a reduction in RWC and chlorophyll content but these recovered when droughted plants were exposed to GA₃. Proline content increased many fold in both varieties under stress, but decreased under the influence of GA₃. There was a mixed response of antioxidant enzyme activity, which distinctly declined after GA₃ exposure, together with a lesser reduction in dry matter content over that of control plants. With increasing stress, expression of pyrroline‐5‐carboxylase synthetase (P5CS) and betaine‐aldehyde dehydrogenase genes was observed, selectively up‐regulated in CoPK05191. Expression of proline oxidase/transporter was high in CoPK05191 but diminished along with proline content after exposure to GA_3. CoLk94184 showed no significant difference in P5CS gene expression under stress condition, whereas expression of betaine‐aldehyde dehydrogenase gene was unchanged in response to stress.
• Results demonstrated that exposure of droughted plants to GA₃ not only led to recovery of activity of drought‐associated physio‐biochemical attributes, but also minimised impact on cane dry weight and quality. Further, GA₃ application caused differential gene expression that possibly triggers increased responsiveness towards drought tolerance in sugarcane.