Reduced Shoot Growth Research Articles

Gas Chromatography Mass Spectrometry based metabolomic investigation on five different rice cutivars (Oryza sativa L.) under different induced Cadmium stress

Heavy Metals (HMs) are naturally occurring elements with high atomic weight and density. In this study, the metabolite profiling of five different indica rice varieties namely, IR-36, Triguna, IR-64, Muktasree and Ajit exposed to cadmium stress in concentrations from 0 µmolL−1, 25 µmolL−1, 50 µmolL−1 and 100 µmolL−1 has been performed using GC-MS. The score plots of PCA, PLS-DA and OPLS-DA analyses showed clear discrimination between control and Cd-treated seedlings of each variety. GC-MS based metabolomic study specified that HM like cadmium exposure could cause changes in metabolite levels mainly on amino acids, organic acids, sugars and their derivatives, phenolics, nitrogen bases and purine metabolites. These metabolomic responses are related with a reduction in shoot and root growth i.e, their photosynthetic capacity especially in IR-36, Triguna, IR-64 and Ajit variety. Only Muktasree showed a consistent increase in shoot and root length in the course of Cd exposure. Biochemical pathway analyses also demonstrated that exposure to cadmium affected the secondary metabolism pathways along with primary metabolism.

RESPONSE OF WHEAT TO DIFFERENT ABIOTIC STRESS CONDITIONS: A REVIEW

Wheat serves as the number one crop for ensuring food and nutritional security in the world. The production and productivity of wheat have been greatly influenced by global warming and climate change which have created environments such as drought, heat stress, and saline conditions. To address the advances in the study of the response of wheat against such climatic implications, this review was done. Abiotic stress mainly affects the morphology, phenology, and physiology of wheat. Abiotic stress induces reactive oxygen species (ROS) in wheat causing a reduction in root, shoot, and reproductive growth. Impact on important yield-related traits such as spike length, grains per spike, grain weight, thousand-grain weight, and reduces the yield of wheat. The plant has earliness as a phenological, rolling of leaves as morphological, waxiness as physiological, and production of heat shock proteins and proline content as a biochemical defense. A proper study of these effects and responses at the genetic and molecular level is necessary to cope with the existing yield gap in a farmer’s field as compared to normal conditions. The study of wheat against such circumstances would help plant breeders identify stress-tolerant genotypes that could significantly contribute to eradicating existing hunger and malnutrition in the world.

Managing Cone Formation and Leader Growth in Fraser Fir Christmas Tree Plantations with Plant Growth Regulators

Early cone formation is a consistent issue in Fraser fir Christmas tree plantations in the eastern United States. Growers must remove cones by hand, resulting in significant labor costs, as cones degrade the aesthetic value of Christmas trees. In this study, we conducted two series of experiments in collaboration with several Christmas tree farms to determine the effectiveness of applying plant growth regulators (PGRs), specifically GA-inhibitors, in reducing cone formation and shoot growth in Fraser fir. In the first experiments we investigated the effectiveness of paclobutrazol, applied as a soil injection or as a foliar spray in reducing cone formation. The highest rate of soil application (300 mL of paclobutrazol per tree) reduced cumulative coning by approximately 38%. Leader growth control of soil applied paclobutrazol increased with application rate. In the second set of experiments, we compared four GA-inhibitors (paclobutrazol, chlormequat chloride, uniconazole-p, daminozide) applied as foliar sprays on coning and leader growth. Overall, paclobutrazol was the most effective compound for reducing coning and shoot growth. The results confirm earlier findings that application of GA-inhibitors can reduce, but not eliminate, coning. Likewise, PGR application can reduce shoot growth and possibly increase tree density but will not eliminate the need for shearing.

The inhibition of putrescine synthesis affects the in vitro shoot development of Cedrela fissilis Vell. (Meliaceae) by altering endogenous polyamine metabolism and the proteomic profile

Polyamines —(PAs) and proteins have been demonstrated to be fundamental for in vitro shoot development of Cedrela fissilis. We evaluated the influence of 6-benzyladenine (BA) and putrescine (Put) on the growth of shoots, PA metabolism and proteomic profiles of C. fissilis. The longest shoots were obtained under 2.5 µM BA + 2.5 mM Put treatment. The inhibition of Put synthesis by d-arginine (d-arg) reduced the activities of the Put biosynthesis enzymes arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) and the endogenous contents of free Put, resulting in reduced shoot growth. The ODC activity was higher than that of ADC, being ODC the main enzyme in the synthesis of Put in C. fissilis. Inhibition of Put synthesis affected the proteomic profile, reducing the accumulation of the ubiquitin receptor RAD23c, peroxidase 15, ADP-ribosylation factor 1, ADP-ribosylation factor-like protein 8a, profilin-4, profilin-2, glucan endo-1,3-beta-glucosidase, and expansin-like B1 and increasing the accumulation of V-type proton ATPase catalytic subunit A and methionine gamma-lyase, highlighting the relevance of these proteins in promoting the length of shoots. Moreover, the transport protein SEC13 homolog B and the basic isoform glucan endo-1,3-beta-glucosidase, unique proteins in shoots treated with BA + Put, were related to the promotion of shoot growth. Our results show that the modulation of endogenous PAs and proteomic profiles is necessary to regulate in vitro morphogenesis in C. fissilis. Moreover, the ODC enzyme is highly involved in the synthesis of Put during in vitro shoot development and is described for the first time in this species.

Prevalence of fungi associated with seven wheat varieties and seed quality analysis

Seven varieties of wheat seeds, such as BARI Gom-25, BARI Gom-26, BARI Gom-27, BARI Gom-28, BARI Gom-29, BARI Gom-30 and Kanchan were studied to determine the prevalence of seedborne fungi and their effects on germinating seeds and seedlings. The seeds were categorized into apparently healthy seeds, black point seeds, and shriveled and undersized seeds. Variation in different parameters (viz.Grading, weight, purity percentage, germination and seedling growth) became evident among the varieties. Seed health test on blotters and agar plate method showed that the major fungi associated with healthy seeds and black point seeds were Alternaria alternata, A. triticina, Bipolaris sorokiniana, B. tetramera, Curvularia lunata, Fusarium spp., and species of Aspergillus. The incidence of B. sorokiniana increased with increasing severity of black point infection. Reduction in germination, seedling emergence, plant stand, root and shoot growth, and vigor index were directly related with the severity of black point. Aspergillus spp. were seen more frequently associated with non-germinated seeds. J. Biodivers. Conserv. Bioresour. Manag. 2022, 8(1): 33-48

Influences of Natural Antioxidants, Reactive Oxygen Species and Compatible Solutes of Panicum Miliaceum L. Towards Drought Stress.

In proso millet, in certain circumstances, drought stress greatly influences growth and metabolisms. Thus, the present study was aimed to examine morphological, biochemical and ROS mechanisms between plant and drought stress in Panicum miliaceum L. To create the drought condition, water irrigation was done at different time intervals including 4, 7, 10, 13 days and control. All the experiments were carried out at different maturity stages such as 30, 50, and 70 days (after sowing). The results demonstrated that the root length, proline, glycine betaine, amino acid and superoxide dismutase, catalase and peroxidase activities were boosted in all treatments as compared with control. As the proso millet matured, the length of shoots and the amount of chlorophyll pigment in the leaves reduced in all treatments as compared to control. Induced reduction of shoot growth, chlorophyll estimation and increases of root growth, osmolyte accumulations, antioxidant enzymes, were found to be drought-tolerant adaptative mechanisms in this study.

Evaluation of Phenotypic Responses of Selected Rice (Oryza sativa L.) Cultivars to Hexavalent Chromium Stress in Soil

The current work is designed to search for suitable rice (Oryza sativa L.) cultivars capable of growing on Cr(VI), hexavalent chromium contaminated soils. The study of tolerance and phenotypical changes of three selected rice cultivars like Bina Dhan 11, Kalachampa, and Pratikshya, at the seedling stages, was done under soil Cr(VI) concentrations up to 300 mg.kg-1 of soil. The 7-day seedlings of these rice cultivars growing on Cr(VI) treated soils were found to exhibit a significant reduction in shoot and root growth at p ≤ 0.05. The experimental results support that 7-day seedlings of Bina Dhan 11 were found to be the best among the three cultivars under soil Cr(VI) stress conditions. The present work may help in selecting suitable rice cultivar for paddy cultivation on Cr(VI) contaminated crop lands present in mining and industrial belts. Further work on this aspect may be useful in increasing rice productivity, catering to the increase in demand for food.

Genotypic-specific hormonal reprogramming and crosstalk are crucial for root growth and salt tolerance in bermudagrass (Cynodon dactylon).

Salt stress is one of the major abiotic factors limiting the productivity of bermudagrass (Cynodon dactylon). However, the role of hormonal reprogramming and crosstalk in regulating root growth and salt tolerance in bermudagrass was not reported. Here, we examined the physiological and hormonal responses of two contrasting bermudagrass genotypes; ‘C43,’ salt-tolerant ‘C198’ salt-sensitive. Under salt stress, ‘C43’ had better membrane stability and higher photosynthetic activity than the ‘C198.’ Salt stress promoted root growth and improved root/shoot ratio and root activity in ‘C43,’ but the root growth of ‘C198’ was inhibited by salt stress, leading to diminished root activity. The two bermudagrass genotypes also showed critical differences in hormonal responses, especially in the roots. The root contents of indole-3-acetic acid (IAA), cytokinin derivatives, such as trans-zeatin riboside (tZR) and dihydrozeatin riboside (DHZR) were increased in ‘C43,’ but decreased in ‘C198’ when exposed to salt stress. The root growth rate was positively correlated with the root IAA, tZR and DHZR, indicating their crucial role in root growth under salt stress. The expressions of TAA/YUCCA and CYP735A involved in IAA and tZR biosynthesis were induced by salt stress in ‘C43,’ but inhibited in ‘C198,’ leading to reduced hormone accumulations. Salt stress decreased the iP, tZ, and DHZ content in the roots of both genotypes, and no significant difference was observed between the two genotypes. Salt stress reduced the content of GA3 in both genotypes by inhibiting GA20ox and GA2ox genes, which could be attributed to the reduced shoot growth in both genotypes. The increased ABA level by salt stress was significantly higher in ‘C198’ than ‘C43.’ Furthermore, there were positive and negative correlations between different hormones and root growth, suggesting that root growth could be regulated by complex hormonal reprogramming and crosstalk. This study provides a foundation for understanding the underlying mechanisms of hormonal-mediated root growth and salt tolerance in bermudagrass.

Arabidopsis plants engineered for high root sugar secretion enhance the diversity of soil microorganisms.

Plants secrete sugars from their roots into the soil, presumably to support beneficial plant-microbe interactions. Accordingly, manipulation of sugar secretion might be a viable strategy to enhance plant health and productivity. To evaluate the effect of increased root sugar secretion on plant performance and the soil microbiome, we overexpressed glucose and sucrose-specific membrane transporters in root epidermal cells of the model plant Arabidopsis thaliana. These plants showed strongly increased rates of sugar secretion in a hydroponic culture system. When grown on soil, the transporter-overexpressor plants displayed a higher photosynthesis rate, but reduced shoot growth compared to the wild-type control. Amplicon sequencing and qPCR analysis of rhizosphere soil samples indicated a limited effect on the total abundance of bacteria and fungi, but a strong effect on community structure in soil samples associated with the overexpressors. Notable changes included the increased abundance of bacteria belonging to the genus Rhodanobacter and the fungi belonging to the genus Cutaneotrichosporon, while Candida species abundance was reduced. The potential influences of the altered soil microbiome on plant health and productivity are discussed. The results indicate that the engineering of sugar secretion can be a viable pathway to enhancing the carbon sequestration rate and optimizing the soil microbiome.

Effect of Self- and Inter-Cultivar Grafting on Growth and Nutrient Content in Sweet Basil (Ocimum basilicum L.).

Vegetable grafting has been applied to fruiting crops, yet only to a limited extent in leafy greens and herbs which may also benefit from grafting. In this study, we examined the effect of reciprocal grafting two sweet basil (Ocimum basilicum L.) cultivars of differing vigor on plant growth and leaf mineral nutrient concentration to test whether differences in growth exist due to grafting and whether such differences are due to altered plant nutrient status in two trials. Two cultivars ‘Nufar’ (NU), a high vigor cultivar, and ‘Dolce Fresca’ (DF), a cultivar developed for compact growth, were selected. Four grafted treatments (scion/rootstock) were created by self-grafting (NU/NU and DF/DF) and reciprocal inter-cultivar grafting (DF/NU and NU/DF). Un-grafted plants (ug-NU and ug-DF) served as controls. Following grafting, plants were grown for 26 or 21 days in a greenhouse. DF rootstocks decreased NU shoot dry mass (19–29%) and stem length (12%) compared to ug-NU in both trials, while dry root mass was reduced (28%) in the second trial. In contrast, NU rootstocks did not affect DF growth in the first trial but significantly decreased dry shoot (18%) and root (31%) mass, compared to ug-DF in the second. Concentration of most inorganic nutrients examined was affected by both rootstock and scion genotype. For NU scions, DF rootstocks resulted in significantly higher (5–29%) levels of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, copper, and zinc in leaf tissue than ug-NU. For DF scions, NU rootstocks resulted in significantly higher (7–9%) levels of potassium and phosphorus but significantly lower (11–23%) levels of magnesium, sulfur, boron, copper, and zinc when compared to ug-DF. Results of this study show that inter-cultivar grafting sweet basil using a more vigorous cultivar as a rootstock did not enhance the growth of a less vigorous scion and reduced concentrations of certain nutrients. However, grafting a vigorous scion to a less vigorous rootstock reduced shoot growth but generally increased nutrient concentrations. This suggests that changes in growth in grafted basil are not due to altered nutrient status. Further research is needed to determine specific physiological processes influencing grafted basil growth.

Response of African Basil (Ocimum gratissimum L.) to Salt Stress under Tropical Conditions in the Republic of Benin: Growth, Ions and Organic Solutes Accumulation

Aims: This research aims at evaluating the effect of salt stress on plant growth, Na+, K+, proline and soluble sugars contents in leaves and roots of local cultivar of African basil in Republic of Benin.
 Study Design: The experiment was laid out in a Completely Randomized Design (CRD) having five treatments and three replications.
 Place and duration of Study: The experiment was carried out in screening house under natural conditions at the Center of Agricultural Research of Agonkanmey, Commune of Abomey-Calavi, Republic of Benin from January to February, 2020.
 Methodology: Five salt concentrations (0, 30, 60, 90 and 120 mM) were used to irrigate three weeks old plants for two weeks. After two weeks, plant growth, sodium (Na) and potassium (K), proline, and soluble sugars contents of leaves and roots were determined.
 Results: Salt stress induced a significant reduction (p = .05) in shoot growth from 60 mM NaCl but had no impact on the number of leaves and shoot water content. Root growth was significantly reduced (p = .05) already at 30 mM NaCl. Leaf and roots Na+, proline and soluble sugars contents significantly increased (p = .05) under salt stress whereas K+ content decreased significantly (p = .05) only in root.
 Conclusion: Salt stress reduces the growth of African basil plants due mainly to Na+ ion toxicity. The ionic selectivity ratio (K+/Na+) rather than the K+ ion content plays an important role in the response of basil plants to salt stress, while both proline and soluble sugars accumulation may contribute to osmotic adjustment.

Ex situ conservation of the endangered “sempre-viva” species Comanthera mucugensis

The “sempre-viva” species Comanthera mucugensis is endemic to the municipality of Mucugê, Bahia, Brazil, where it was widely exploited through extractivism to be commercialized as an ornamental, causing a drastic reduction of its population, so that it is now classified as endangered. Although its main area of occurrence is now protected for being within Chapada Diamantina National Park, the continued risks of inclement conditions and anthropic actions make it necessary to develop alternative methods for ex situ conservation of the species, such as in vitro conservation. Therefore, the objective of this study was to test the effect of different concentrations of salts and sucrose on the in vitro conservation of Comanthera mucugensis. Two salts concentrations of the medium MS (½ and ¼) and two sucrose levels (7.5 and 15.0 g L-1) were tested, and the experimental design was completely randomized with four treatments. After 365 days, the survival, growth and regeneration of the conserved plants were analyzed, achieving up to 100% survival, reduced shoot growth and maintenance of regenerative capacity. Reduction of the concentration of salts and sucrose in the culture medium is indicated to conserve the plants in vitro for a period of one year.

Distinct salinity-induced changes in wheat metabolic machinery in different root tissue types

The impact of salinity on wheat plants is often studied by analysis of shoot responses, even though the main mechanism of tolerance is shoot Na+ exclusion. Wheat roots directly experience rising NaCl concentrations and show more physiological responses in root tips than in mature roots and altered responses with time; but the molecular reason for these differential responses is unclear. We have found that there is a distinct difference between the proteome responses of wheat root tip and mature root tissues to salinity. Translation and protein synthesis related proteins showed a significant decrease in abundance, most of the glycolytic enzymes and selected TCA cycle enzymes and ATP synthase subunits were significantly decreased in abundance under salt stress in root tips only. The root tip response in wheat indicates the protein synthesis capacity and energy production were impaired under salt stress which correlated with the anatomical response of root growth decrease and its respiratory rate. Wheat root responses are direct and rapid effects of the soil salinity in this species, therefore shoot responses such as reduction in shoot growth and photosynthetic capacity need to be considered in light of these effects on root metabolism. SignificanceSalinity is a critical environmental factor limiting crop production throughout the world. Wheat (Triticum aestivum) is the most significant cereal crop for human nutrition and both its growth and yield is negatively impacted by salinity. Salinity stress is known to impose osmotic stress in plants during the initial phase of exposure and ion toxicity in the later stages of development. Roots are the first plant organ to perceive the salt. However, intensive breading approaches to develop salt tolerant crops have mainly focussed on exclusion of salt from above ground tissues, and only achieved limited success to date. Wheat roots physiologically respond to salinity by overall reduction in the length of seminal roots. The stunting of the wheat root system is considered to be a result of higher sensitivity of root tips to salinity. However, the metabolic changes that underpin selective root tip sensitivity is largely unknown. Here, we carried out non-targeted profiling of mature root versus root tip proteomes under control and salt stress conditions. We found distinct changes in abundance of proteins involved in carbon and energy metabolism and protein metabolism in mature roots and root tips in response to salt stress. We further investigated the impact of these changes on metabolic machinery in the wheat root proteome using a targeted MS approach. We found evidence that protein synthesis and energy production machinery becomes limiting in root tips, while the same processes in mature root remains less affected by salt stress. Our proteomic data explain the impairment of root growth and physiological characteristics as well as improve the understanding of wheat root responses under salinity which is an essential first step for further investigation of molecular traits underpinning root characteristics to improve salt tolerance of wheat.

Modified protocol to overcome in vitro recalcitrance of premature micro-shoots abscission by silver supplementation in Kinnow mandarin (Citrus nobilis L. × Citrus deliciosa T.)

The present study focused on alleviating the issue of premature abscission of micro-shoots emerged from the cultured nodal segments in Kinnow mandarin. To resolve the problem, explants of different maturity stages, culture media, growth regulator combinations and ethylene inhibitors (silver compounds) were evaluated. Hardwood stage was observed to be the most efficient explant maturity stage to boost the vigorous early shoot emergence on MS (Murashige and Skoog) medium. Addition of GA3 (Gibberellic acid) 10 mg L−1 resulted in delayed abscission. Further reduction in abscission rate and healthy shoot growth were observed when subculturing of micro-shoots was done on MS medium supplemented with BAP 2.5 mg L−1, GA3 10 mg L−1 and silver thiosulfate 5 mg L−1. This modified procedure could be effectively utilized for mass multiplication as well as crop improvement in Kinnow mandarin.

Growth inhibition and microcystin accumulation in bush bean (Phaseolus vulgaris L.) plant irrigated with water containing toxic Chrooccocus minutus

Cyanobacterial blooms and microcystins (MCs) in irrigation waters have been recognized as an emergent environmental threat to many terrestrial plants. While several studies addressed the impacts of crude cyanobacterial extracts and dissolved MC-containing water on crop plants, less is known about the effects of irrigation water containing cyanobacterial blooms (i.e., intracellular plus extracellular toxins). In the present study, we investigated the effects of whole culture, cell-free culture filtrate and living cells of the toxic cyanobacterium Chroococcus minutus on growth, physiological parameters and MC accumulation in Phaseolus vulgaris (bush bean) plants. The plants were grown in pots containing agricultural soil, in order to mimic common agricultural practice. After 4 weeks of growth, treated plants exhibited substantial reduction in root and shoot growth, photosynthetic pigments, and protein contents compared to control plants. Treated plants also showed higher lipid peroxidation than control plants. The lowest inhibitory effects were observed in plants treated with culture filtrate containing extracellular MCs only (15.3 μg L−1). The highest inhibitory effects were recorded in plants treated with whole cyanobacterial culture containing both intra- and extracellular MCs (132 μg L−1), indicating the release of intracellular MCs from cells into the rizhosphere and their uptake by plant roots. MC concentrations in immature pods of P. vulgaris plants irrigated with whole culture and living cyanobacterial cells led to estimates of daily MCs intake (0.125–0.391 μg kg−1 body weight) that exceeded the total daily intake guidelines (0.04 μg kg−1 body weight) for human food consumption. This study suggests that irrigation water as well as plants used in human consumption should be regularly monitored for the presence of MCs and other cyanotoxins.

Endophytic Bacteria in Banana In Vitro Cultures: Molecular Identification, Antibiotic Susceptibility, and Plant Survival

Microbial contamination is a common problem that causes significant losses in plant micropropagation systems. The present study reports on the identification and control of bacterial contaminants in banana in vitro cultures. Twelve isolates belonging to Bacillus pumilus (S2), Bacillus subtilis (R2 and M4), Geobacillus stearothermophilus (S1, S3, S4, P2, M3 and R3) and Paenibacillus spp. (P1, R1 and M2) were identified by sequencing of 16S rRNA, gyrA or gyrB genes. Antibiotic susceptibility testing was performed with the disk diffusion method on bacterial isolates using 36 antimicrobial agents. Some antibiotics, notably Ticarcillin, Penicillin, Ampicillin, Cefazolin and Imipenem, had a broader range of bactericidal activity than others did. When contaminated axillary shoot cultures of banana were treated with 100 or 200 mg·L−1 of ticarcillin, ampicillin or penicillin the bacteria were eliminated, but a reduction in shoot multiplication and growth was observed. These findings contribute to minimizing the losses in the commercial micropropagation of banana.

Phenotypic plasticity versus ecotypic differentiation under recurrent summer drought in two drought‐tolerant pine species

Abstract Despite worldwide reports of high tree mortality, growing evidence indicates that many tree species are well adapted to survive repeated dry spells. The drought resilience of trees is related to their phenotypic plasticity and ecotypic differentiation. Whether these two mechanisms act at the same organisational level of a tree and involve similar plant traits is still unknown. We assessed phenotypic plasticity and ecotypic differentiation across four populations of Pinus sylvestris and Pinus nigra seedlings grown for 3 years under a recurrent summer drought treatment or well‐watered control conditions in a common garden. We measured the response to the summer drought treatment of a total of 26 traits including shoot and needle morphology, needle anatomy and foliar macronutrients, and related the traits to the growing season water deficit (GSWD) at the location of the seed origin. Foliar phenotypic plasticity in response to recurrent summer drought was surprisingly low, with the needle length and the fraction of mesophyll and phloem tissue adjusting to some extent. In comparison, shoot morphological traits were much more plastic in both species with predominant responses to the summer drought stress including shorter and less numerous apical and lateral shoots. These three traits were also correlated with GSWD at the seed origin, indicating local adaptation. In contrast, between‐population variation of foliar morphological and anatomical traits, and macronutrients were mostly unrelated to the GSWD at the seed origin. Consequently, phenotypic plasticity and ecotypic differentiation occurred at the same level of organisation and in the same plant traits, that is, shoot morphology. This combination of plasticity and ecotypic differentiation allowed P. sylvestris and P. nigra seedlings to rapidly acclimate to recurrent and long‐lasting dry spells. Synthesis. Pinus sylvestris and P. nigra seedlings showed considerable ecotypic differentiation and phenotypic plasticity of shoot morphological traits, and not foliar traits. Acclimation to recurrent severe summer drought was achieved by reducing shoot growth.

Siliceous and non‐nutritious: Nitrogen limitation increases anti‐herbivore silicon defences in a model grass

Abstract Silicon (Si) accumulation alleviates a diverse array of environmental stresses in many plants, including conferring physical resistance against insect herbivores. It has been hypothesised that grasses, in particular, utilise ‘low metabolic cost’ Si for structural and defensive roles under nutrient limitation. While carbon (C) concentrations often negatively correlate with Si concentrations, the relationship between nitrogen (N) status and Si is more variable. Moreover, the impacts of N limitation on constitutive physical Si defences (e.g. silica and prickle cells) against herbivores are unknown. We determined how N limitation affected Si deposition in the model grass Brachypodium distachyon and how changes in these constitutive defences impacted insect herbivore Helicoverpa armigera growth rates. We used scanning electron microscopy (SEM) and energy dispersive X‐ray spectrometry in conjunction with X‐ray mapping (XRM) to quantify physical structures on leaves and determine Si deposition patterns. We also determined how N limitation and Si supply impacted the jasmonic acid (JA) pathway, the master regulator of induced defences against arthropod herbivores. N limitation reduced shoot growth by over 40%, but increased root mass (+21%), leaf Si concentrations (+50%) and the density of silica (+28%) and flattened prickle (+76%) cells. Energy‐dispersive X‐ray spectroscopy and XRM established that Si was being deposited in these structures, together with hooked prickle cells and macro‐hairs. Herbivore relative growth rates (RGR) were more than 115% lower in Si‐supplied plants compared to plants without Si supply and negatively correlated with leaf Si concentration and silica cell density. RGR was further reduced by N limitation and positively correlated with leaf N concentrations. Increases in JA concentrations following induction of the JA pathway were at least doubled by N limitation. Synthesis. Si accumulation and deposition were highly regulated by N availability, with N limitation promoting both constitutive Si physical defences and induction of the JA defensive pathway, in line with the resource availability hypothesis. These results indicate that grasses use ‘low‐cost Si’ when resources are limited and suggest that plant productivity may benefit from optimising conventional fertilisers and Si fertilisation.

Assimilate highway to sink organs – Physiological consequences of SP6A overexpression in transgenic potato (Solanum tuberosum L.)

Leaf/stem-specific overexpression of SP6A, the FLOWERING LOCUS T homolog in potato (Solanum tuberosum), was previously shown to induce tuberization leading to higher tuber numbers and yield under ambient and abiotic stress conditions. In this study, we investigated the mechanism underlying SP6A action. Overexpression of SP6A reduced shoot growth, mainly by inhibition of stem elongation and secondary growth, and by repression of apical bud outgrowth. In contrast, root growth and lateral shoot emergence from basal nodes was promoted. Tracer experiments using the fluorescent sucrose analogue esculin revealed that stems of SP6A overexpressing plants transport assimilates more efficiently to belowground sinks, e.g. roots and tubers, compared to wild-type plants. This was accompanied by a lower level of sucrose leakage from the transport phloem into neighboring parenchyma cells and the inhibition of flower formation. We demonstrate the ability of SP6A to control assimilate allocation to belowground sinks and postulate that selection of beneficial SP6A alleles will enable potato breeding to alter plant architecture and to increase tuber yield under conditions of expected climate change.

Cytosolic phosphofructokinases are important for sugar homeostasis in leaves of Arabidopsis thaliana.

ATP-dependent phosphofructokinases (PFKs) catalyse phosphorylation of the carbon-1 position of fructose-6-phosphate, to form fructose-1,6-bisphosphate. In the cytosol, this is considered a key step in channelling carbon into glycolysis. Arabidopsis thaliana has seven genes encoding PFK isoforms, two chloroplastic and five cytosolic. This study focuses on the four major cytosolic isoforms of PFK in vegetative tissues of A. thaliana. We isolated homozygous knockout individual mutants (pfk1, pfk3, pfk6 and pfk7) and two double mutants (pfk1/7 and pfk3/6), and characterized their growth and metabolic phenotypes. In contrast to single mutants and the double mutant pfk3/6 for the hypoxia-responsive isoforms, the double mutant pfk1/7 had reduced PFK activity and showed a clear visual and metabolic phenotype with reduced shoot growth, early flowering and elevated hexose levels. This mutant also has an altered ratio of short/long aliphatic glucosinolates and an altered root-shoot distribution. Surprisingly, this mutant does not show any major changes in short-term carbon flux and in levels of hexose-phosphates. We conclude that the two isoforms PFK1 and PFK7 are important for sugar homeostasis in leaf metabolism and apparently in source-sink relationships in A. thaliana, while PFK3 and PFK6 only play a minor role under normal growth conditions.