The adaptive evolution of herbivory in freshwater systems

Herbivory is thought to be nutritionally inefficient relative to carnivory and omnivory, but herbivory evolved from carnivory in many terrestrial and aquatic lineages, suggesting that there are advantages of eating plants. Herbivory has been well-studied in both terrestrial and aquatic systems, and there is abundant information on feedbacks between herbivores and plants, coevolution of plant and herbivore defenses, mechanisms for mediating nutrient limitation, effects of nutrient limitation on herbivore life history, and, more recently, the origins of the herbivorous diet. Researchers have sufficiently defined the ecological context and evolutionary origins of the herbivorous diet, and these main areas of research have laid the groundwork for studying herbivory as an adaptation. However, we have yet to synthesize this information in a way that allows us to establish a framework of testable adaptive hypotheses. To understand the adaptive significance of this diet transition, we review the current literature and use evidence from these works as support for five hypotheses on the evolution of herbivory from carnivory: (1) intake efficiency—herbivores use part of their food source as habitat, thus minimizing the energy/time spent searching for food and avoiding predators; (2) suboptimal habitat—herbivory allows organisms to invade and establish populations in habitats that have high primary production but low abundance of animal prey; (3) heterotroph facilitation—herbivory is adaptive because herbivores consume microbes associated with producers; (4) lipid allocation—herbivory is adaptive because producers are rich in fatty acids, which fuel reproduction and storage; and (5) disease avoidance—herbivory minimizes animal-facilitated disease transmission. Due to the extensive literature, we have limited this review to discussing herbivory in freshwater systems. To our knowledge, no prior work has compiled a comprehensive list of conditions that favor an herbivorous diet in nature. With backgrounds in both theoretical and experimental ecology, the incorporation of these hypotheses to the current literature will provide information about diet evolution, where it is currently lacking

6-Shogaol Induces Apoptosis in Human Hepatocellular Carcinoma Cells and Exhibits Anti-Tumor Activity In Vivo through Endoplasmic Reticulum Stress

6-Shogaol is an active compound isolated from Ginger (Zingiber officinale Rosc). In this work, we demonstrated that 6-shogaol induces apoptosis in human hepatocellular carcinoma cells in relation to caspase activation and endoplasmic reticulum (ER) stress signaling. Proteomic analysis revealed that ER stress was accompanied by 6-shogaol-induced apoptosis in hepatocellular carcinoma cells. 6-shogaol affected the ER stress signaling by regulating unfolded protein response (UPR) sensor PERK and its downstream target eIF2α. However, the effect on the other two UPR sensors IRE1 and ATF6 was not obvious. In prolonged ER stress, 6-shogaol inhibited the phosphorylation of eIF2α and triggered apoptosis in SMMC-7721 cells. Salubrinal, an activator of the PERK/eIF2α pathway, strikingly enhanced the phosphorylation of eIF2α in SMMC-7721 cells with no toxicity. However, combined treatment with 6-shogaol and salubrinal resulted in significantly increase of apoptosis and dephosphorylation of eIF2α. Overexpression of eIF2α prevented 6-shogaol-mediated apoptosis in SMMC-7721 cells, whereas inhibition of eIF2α by small interfering RNA markedly enhanced 6-shogaol-mediated cell death. Furthermore, 6-shogaol-mediated inhibition of tumor growth of mouse SMMC-7721 xenograft was associated with induction of apoptosis, activation of caspase-3, and inactivation of eIF2α. Altogether our results indicate that the PERK/eIF2α pathway plays an important role in 6-shogaol-mediated ER stress and apoptosis in SMMC-7721 cells in vitro and in vivo

Resistance to downy mildew in pearl millet is associated with increased phenylalanine ammonia lyase activity

Phenylalanine ammonia lyase (PAL) activity was studied in pearl millet cultivars with different levels of resistance to the downy mildew disease caused by Sclerospora graminicola, an important oomycete pathogen. PAL activity was elevated in resistant host cultivar and decreased in susceptible cultivars following downy mildew pathogen infection. The enzyme activation varied between cultivars and was correlated with the degree of resistance to downy mildew disease. The induction of PAL as a response to pathogen inoculation was further corroborated by a time-course study in seedlings and cultured cells of pearl millet. The level of PAL activity was highest at 1.5 h in cultured cells and 4 h in seedlings of resistant host cultivar after inoculation with Sclerospora graminicola. Further studies on PAL activity in different tissues of seedlings showed highest enzyme activity in the young growing region of the root of the resistant host cultivars. The accumulation of wall-bound phenolics and lignin was higher in the resistant cultivar seedlings as evidenced by phloroglucinol–HCl staining and p-coumaric acid assay. The temporal changes in lignin concentration and the concentration of soluble phenolics were greater in root tissues of resistant cultivars than in those of susceptible cultivars. Treatment of resistant seedlings with a PAL inhibitor, α-aminooxy-β-phenylpropionic acid, resulted in the enhancement of the enzyme activity, whereas in the presence of 1 mm trans-cinnamic acid the pathogen-induced PAL was completely inhibited. Treatment of pearl millet seedlings with exogenously applied PAL inhibitors induced downy mildew disease susceptibility in the resistant pearl millet cultivar, consistent with direct involvement of PAL in downy mildew resistance. Results are discussed with respect to the presumed importance of host phenolic compounds and lignin accumulation and its relation to PAL activation as a response to the pathogen infection

A Chitosan formulation Elexa((TM)) induces downy mildew disease resistance and growth promotion in pearl millet

A commercially developed aqueous Chitosan formulation Elexa was used in different concentrations viz., 1:5, 1:10, 1:15, 1:19 and 1:25 as seed soaking treatment to pearl millet for 3, 6 and 9 h duration to test for its effect on germination and vigor index. Among the treatments used 1: 19 for 6 h soaking recorded maximum germination and seedling vigor. Seed treatment, foliar spray and combination of seed treatment and foliar spray were tested for control of downy mildew disease caused by Sclerospora graminicola in pearl millet under greenhouse and field conditions. Metalaxyl at the rate of 2.1 % a.i. in the form of Apron 35 SD seed treatment was used as check. Under greenhouse conditions seed treatment offered 48% protection. Foliar spray was carried out to two, seven and 14-day-old seedlings and there was marked reduction in downy mildew disease incidence. Maximum protection of 67% was recorded with foliar spray to 2-day-old seedlings. With the combination of seed treatment and foliar spray to 2-day-old seedlings offered 71 % protection. Under field conditions Elexa treatments were evaluated for their effect on incidence and severity of downy mildew disease. Seed treatment reduced downy mildew severity to 42.5% and recorded 38% protection, whereas foliar spray to 7-day-old seedlings gave 67% protection and reduced severity to 25%. Combination of seed treatment and foliar spray to 7-day-old seedlings recorded 69% protection and reduced severity by 23%. The nature of disease control mechanisms has been investigated and the results indicated that it is due to induction of systemic resistance. The induction of resistance was observed as early as 24 h time gap between the inducer treatment and pathogen inoculation and the maximum resistance developed at 24-48 h time gap and maintained thereafter. Elexa treated to pearl millet seeds offered growth promoting effect under greenhouse conditions and recorded increase in plant height, earhead length and seed weight. Hence, it is inferred that Elexa is a good downy mildew disease management commercial formulation and also exhibits growth-promoting effects in pearl millet. (C) 2004 Published by Elsevier Ltd

Osmopriming enhances pearl millet growth and induces downy mildew disease resistance

The osmoconditioning effect on pearl millet seeds was tested with different concentrations among which 1% showed an optimum effect. Seeds osmoprimed with mannitol for 3 h followed by overnight drying offered maximum germination of 99% and seedling vigour of 1465 followed by PEG and glycerol. All the three osmopriming agents recorded a significant increase on growth parameters like height of the plant, leaf area, number of tillers per plant. The results indicated that mannitol offered a maximum positive effect followed by PEG and glycerol. Notably, osmopriming has advanced five days of flowering and also has a positive effect on number and length of the earheads. The osmoconditioning agent increased the 1000 seed weight significantly over the untreated control. When the osmoprimed seeds were germinated and inoculated with downy mildew pathogen, the maximum protection of 61.76% was observed in mannitol treatment followed by PEG and glycerol under greenhouse conditions. Osmopriming has promoted seed germination percentage, seedling vigour index and growth parameters in pearl millet and also reduced downy mildew incidenc

Isolation and characterisation of a protein elicitor from Sclerospora graminicola and elicitor-mediated induction of defence responses in cultured cells of Pennisetum glaucum

Sclerospora graminicola (Sacc.) Schroet., an oomycete pathogen of Pennisetum glaucum (L.) R. Br. infects the meristematic tissues of young seedlings. The motile zoospores from the sporangia encyst, germinate and penetrate the plant tissue. Resistance to the invading pathogen is governed by the specific recognition of conserved pathogen-associated proteins or elicitors. In the present study, a zoospore protein was isolated and purified to homogeneity by a combination of size exclusion and high-performance liquid chromatography ( HPLC). The crude fractionated protein was able to elicit an array of defence responses in resistant and susceptible cells of pearl millet. Treatment of cultured cells of pearl millet with partially purified elicitor protein resulted in a rapid loss of cell viability in the resistant cells and the percentage of cell death was higher in the resistant than in the susceptible cells. Cultures of resistant cells showed a sharp increase in the extra cellular pH compared with susceptible cells when treated with the crude elicitor. Increased oxidative burst was also recorded in the cells treated with the crude elicitor. The purified elicitor showed unique properties. The purified protein was acidic with a pI of 5.6 as revealed by isoelectric focusing (IEF) and matrix-assisted laser desorption ionisation (MALDI) analysis showed that the elicitor had a molecular mass of 7040 daltons. The primary structure determined by N-terminal Edman degradation and searches with BLAST did not reveal similarities to any known plant pathogenic or oomycete elicitor. Higher activities of the important defence-related enzymes phenylalanine ammonia lyase ( PAL) and peroxidase in the resistant cell cultures than in the susceptible cell cultures treated with the purified elicitor were clearly evident. Studies of gene expression by northern blotting with heterologus peroxidase, PAL and oxalate oxidase probes showed that the mRNA transcripts were strongly up-regulated in resistant cell cultures within 30 min of elicitor treatment. The purified elicitor also demonstrated a very strong concentration-dependent sterol binding. The purified elicitor protein belongs to a class of low molecular weight oomycete elicitors with sterol carrier properties. The identified low molecular weight protein elicitor displays unique properties that can be exploited for synthesis of novel molecules for eco-friendly crop protection

Ability of vitamins to induce downy mildew disease resistance and growth promotion in pearl millet

The use of biotic and abiotic inducers for the development of host resistance is a sustainable approach for plant disease management. In the present study, vitamins, pyridoxine, folic acid, riboflavin, niacin, D-biotin and menadione sodium bisulphite (MSB) were used to treat pearl millet seeds to test their ability to induce resistance to downy mildew disease caused by Sclerospora graminicola. A 6h seed-soak treatment with vitamins at 20mM enhanced germination and seedling vigour significantly and also induced downy mildew disease resistance. Among them, MSB treatments offered 73 protection while niacin and riboflavin gave 63 and 62 protection, respectively. The vitamins offering promising protection were used in combination to treat the seeds, but no synergistic action was evident with either combination treatment. Vitamin seed treatment and foliar spray application showed similar results when applied individually. However, seed treatment followed by a foliar spray with a combination treatment of MSB and niacin at 7d after seedling emergence offered higher protection (74) against downy mildew disease. Seeds treated with vitamins induced maximum resistance in the seedlings by the fourth day after pathogen inoculation and the resistance persisted till the end of the growth period of the crop. The vitamin treatments had a growth promotional effect and significantly increased the yield compared with the untreated control. Possibilities for controlling downy mildew disease of pearl millet with vitamins are discussed