Interactive effects of water,light and heat stress on photosynthesis in Fremont cottonwood

Fremont cottonwood seedlings are vulnerable to water stress from rapid water‐table decline during river recession in spring. Water stress is usually cited as the reason for reduced establishment, but interactions of water stress with microclimate extremes are more likely the causes of mortality. We assessed photosynthetic responses of Fremont cottonwood seedlings to water, light and heat stresses, which commonly co‐occur in habitats where seedlings establish. Under moderate temperature and light conditions, water stress did not affect photosynthetic function. However, stomatal closure during water stress predisposed Fremont cottonwood leaves to light and heat stress, resulting in greatly reduced photosynthesis beginning at 31 °C versus at 41 °C for well‐watered plants. Ontogenetic shifts in leaf orientation from horizontal to vertical, which occur as seedlings mature, reduce heat and light stress, especially during water stress. When compared with naturally occurring microclimate extremes, seedling stress responses suggest that reduced assimilation and photoprotection are common for Fremont cottonwood seedlings on exposed point bars where they establish. These reductions in photosynthesis likely have negative impacts on growth and may predispose young (<90‐day‐old) seedlings to early mortality during rapid water‐table declines. Interactions with heat and light stress are more important in these effects than water stress alone.     

Impacts of dreissenid mussel invasions on chlorophyll and total phosphorus in 25 lakes in the USA

1. Invasions of zebra and quagga mussels have had long‐term, large‐scale impacts on lake ecosystems in the USA as characterised by high abundance, broad‐scale spread and effective adaption to new environmental conditions. Due to their high filtering capacity, decreases in chlorophyll a (Chl) and total phosphorus (TP) concentrations have been reported in many affected lakes. 2. In 25 US lakes, we analysed the effects of dreissenid invasions on changes in Chl and TP concentrations, measured as the probability of a concentration decrease in the post‐invasion period and changes in Chl–TP relationships using Bayesian hierarchical regressions. We also examined whether changes in Chl and TP concentrations and in the Chl–TP relationship differed according to lake hydromorphology, such as mean depth or mixing status (mixed versus stratified lakes). 3. Our results showed that dreissenid invasions were often, but not always, associated with subsequent TP and Chl declines. Dreissenid effects on Chl and TP may be influenced by lake thermal structure. Decreases in Chl and TP were consistently found in mixed lakes where benthic–pelagic coupling is tight, while the effects were less predictable in stratified lakes. Within stratified lakes, Chl and TP reductions were more clearly discernible in deeper lakes with long water residence times. 4. Regression results demonstrated that a joint increase in slope and decrease in intercept and a tighter correlation of the Chl–TP relationship were likely to occur in dreissenid‐invaded lakes; this does not support the idea of a shift from bottom‐up to top‐down control of primary production. These results have important implications for management, suggesting that a relaxation of TP standards would be unwarranted. 5. Across lakes, the slope of the Chl–TP relationship for mixed lakes was substantially higher than that for stratified lakes before mussel invasion, indicating an important role of light in limiting primary production. The slope differences between mixed and stratified lakes decreased in the post‐invasion period, possibly because mussel filtration results in a relaxation of light limitation that is more pronounced in deeper, stratified lakes.     

Production of phenolics and the emission of volatile organic compounds by perennial ryegrass (Lolium perenne L.)/Neotyphodium lolii association as a response to infection by Fusarium poae

Grasses very often form symbiotic associations with Neotyphodium/Epichloë endophytic fungi. These endophytes often allow the host grass to be protected from different pathogens. However, there is little known about the mechanisms of such endophyte influence on the host. Thus, the purpose of this research was to examine the effect of the N. lolii endophyte on the total production of phenolic compounds, VOCs emission and the resistance of three perennial ryegrass genotypes infected by pathogenic Fusarium poae. Analyses of total phenolics content were performed in control (not inoculated) and inoculated plants after 1, 2, 3, 4, 5, and 6 days (DAI) and for VOCs after 0, 3, 6 and 12 DAI. The presence of endophytes significantly reduced the disease index in two of the three genotypes relative to that in E−. Plants infected by N. lolii exhibited higher production of phenolics relative to the E− plants. The highest amounts of phenolics were observed on the second and sixth DAI. Genotype Nl22 showed the strongest effect of the endophyte on the production of phenolics, which increased by over 61%. Both the endophyte infected and non-infected plants emitted most abundantly two GLVs ((Z)-3-hexenal, (Z)-3-hexen-1-yl acetate), three terpenes (linalool, (Z)-ocimene, β-caryophyllene) and three shikimic acid pathway derivatives (benzyl acetate, indole, and methyl salicylate). The endophyte presence and the intervals of VOCs detection were a highly significant source of variation for all emitted volatiles (P < 0.001). The genotype of the perennial ryegrass significantly affected only the emission of methyl salicylate (P < 0.05) and β-caryophyllene (P < 0.05). Most of the VOCs ((Z)-3-hexen-1-yl acetate, (Z)-3-hexenal, linalool and methyl salicylate) reached their highest levels of emission on the sixth DAI, when averaged over genotypes and endophyte status. The results highlight the role of Neotyphodium spp. in the mediation of quadro-trophic interactions among plants, symbiotic endophytes, invertebrate herbivores and plant pathogenic fungi. Our results also confirm the fact that symbiotic plants can activate a defense reaction faster than non-symbiotic plants after a pathogen attack. Thus, N. lolii can be involved in the defense of perennial ryegrass against pathogens and potentially could be central to the host plants’ protection.     

Tiller number is altered in the ascorbic acid-deficient rice suppressed for l-galactono-1,4-lactone dehydrogenase

The tiller of rice (Oryza sativa L.), which determines the panicle number per plant, is an important agronomic trait for grain production. Ascorbic acid (Asc) is a major plant antioxidant that serves many functions in plants. l-Galactono-1,4-lactone dehydrogenase (GLDH, EC 1.3.2.3) is an enzyme that catalyzes the last step of Asc biosynthesis in plants. Here we show that the GLDH-suppressed transgenic rices, GI-1 and GI-2, which have constitutively low (between 30% and 50%) leaf Asc content compared with the wild-type plants, exhibit a significantly reduced tiller number. Moreover, lower growth rate and plant height were observed in the Asc-deficient plants relative to the trait values of the wild-type plants at different tillering stages. Further examination showed that the deficiency of Asc resulted in a higher lipid peroxidation, a loss of chlorophyll, a loss of carotenoids, and a lower rate of CO₂ assimilation. In addition, the level of abscisic acid was higher in GI-1 plants, while the level of jasmonic acid was higher in GI-1 and GI-2 plants at different tillering stages. The results we presented here indicated that Asc deficiency was likely responsible for the promotion of premature senescence, which was accompanied by a marked decrease in photosynthesis. These observations support the conclusion that the deficiency of Asc alters the tiller number in the GLDH-suppressed transgenics through promoting premature senescence and changing phytohormones related to senescence.     

Field trapping of male Phyllonorycter ringoniella using variable ratios of pheromone components

The sex pheromone of Phyllonorycter ringoniella (Matsumura) (Lepidoptera: Gracillariidae) has been identified to be a blend of (Z)‐10‐tetradecenyl acetate (Z10‐14:OAc) and E4,Z10‐tetradecadienyl acetate (E4,Z10‐14:OAc) in Japan, Korea, and China. However, the commercial product based on previous results is not attractive enough to be used for monitoring and controlling apple leafminer populations in the field. We re‐investigated the attractiveness of the two pheromone components, singly and in blends, in apple orchards in Shangdong and Shaanxi, the main apple‐growing provinces in China. Our results revealed that Z10‐14:OAc alone was not attractive to P. ringoniella male moths in the field, but E4,Z10‐14:OAc alone not only was strongly attractive but caught more males than any of the blends of Z10‐14:OAc and E4,Z10‐14:OAc tested. The most attractive blend ratios differed slightly for the two locations. No clear dose–response relationship was obtained for the 2:8 blend of Z10‐14:OAc and E4,Z10‐14:OAc. However, the dose–response field study of E4,Z10‐14:OAc alone showed that 1 mg per lure achieved the highest moth catch. These findings differ from the previous report of the best pheromone blend in China. Our data showed that E4,Z10‐14:OAc is the major component of the pheromone of P. ringoniella.     

Chlorophyll a phytylation is required for the stability of photosystems I and II in the cyanobacterium Synechocystis sp. PCC 6803

In oxygenic phototrophic organisms, the phytyl ‘tail’ of chlorophyll a is formed from a geranylgeranyl residue by the enzyme geranylgeranyl reductase. Additionally, in oxygenic phototrophs, phytyl residues are the tail moieties of tocopherols and phylloquinone. A mutant of the cyanobacterium Synechocystis sp. PCC 6803 lacking geranylgeranyl reductase, ΔchlP, was compared to strains with specific deficiencies in either tocopherols or phylloquinone to assess the role of chlorophyll a phytylatation (versus geranylgeranylation). The tocopherol‐less Δhpt strain grows indistinguishably from the wild‐type under ‘standard’ light photoautotrophic conditions, and exhibited only a slightly enhanced rate of photosystem I degradation under strong irradiation. The phylloquinone‐less ΔmenA mutant also grows photoautotrophically, albeit rather slowly and only at low light intensities. Under strong irradiation, ΔmenA retained its chlorophyll content, indicative of stable photosystems. ΔchlP may only be cultured photomixotrophically (due to the instability of both photosystems I and II). The increased accumulation of myxoxanthophyll in ΔchlP cells indicates photo‐oxidative stress even under moderate illumination. Under high‐light conditions, ΔchlP exhibited rapid degradation of photosystems I and II. In conclusion, the results demonstrate that chlorophyll a phytylation is important for the (photo)stability of photosystems I and II, which, in turn, is necessary for photoautotrophic growth and tolerance of high light in an oxygenic environment.     

He-Ne激光和增强UV-B辐射对小麦幼叶叶绿素荧光和Rubisco活化酶的影响

选用小麦‘ML7113’品种为材料,人工模拟He-Ne激光(5mJ·s-1·mm-2)、增强UV-B(10.8kJ·m-2·d-1)辐射及两者复合辐照进行处理,利用叶绿素荧光仪、考马斯亮蓝G-250染色法和PCR技术研究7d龄小麦幼苗叶绿素荧光特性、Rubisco活化酶含量、基因表达量及其基因序列的变化。结果表明:(1)与对照组相比,增强UV-B辐射后,小麦幼苗叶绿素荧光特性减弱,Rubisco活化酶含量及其基因表达量均下降;而低剂量的He-Ne激光辐照后能够在一定程度上修复经UV-B辐射后对小麦幼苗叶绿素荧光特性所造成的损伤,且使Rubisco活化酶含量及其基因表达量上升。(2)与对照组相比,经He-Ne激光和增强UV-B辐射以及两者复合辐照处理后基因序列均出现两个相同的点突变,但并未造成氨基酸序列的变化。研究认为,低剂量He-Ne激光辐照能够在一定程度上修复受UV-B辐射小麦幼苗叶绿素荧光活性、Rubisco活化酶含量及其基因表达量的降低;He-Ne激光和增强UV-B辐射对小麦幼苗Rubisco活化酶活性的影响可能发生在其转录水平,从而使小麦光合能力发生相应的变化。     

2-Ethyl-3-methylmaleimide in Tokyo Bay Sediments Providing the First Evidence for its Formation from Chlorophylls in the Present Photic and Oxygenic Zone

Tokyo Bay bottom sediments were analyzed for 2-ethyl-3-methylmaleimide, a degradation product of chlorophylls, which has been detected in ancient sediments. It was found in all sediments examined in concentrations of about 1 to 15 nmol/g- of dried sediment, and it was shown to be preserved for 100 years in the sediments. Its depth distribution agreed with that of the reported total organic carbon content of the sediments, reflecting a change in primary productivity. We concluded that this maleimide was produced under photic and oxygenic conditions in nature before the incorporation of photosynthesizing organisms into sediments.