UDP-N-Acetylglucosamine Pyrophosphorylase 2 (UAP2) and 1 (UAP1) Perform Synergetic Functions for Leaf Survival in Rice

Functional inactivation of UDP-N-acetylglucosamine pyrophosphorylase 1 (UAP1) induces defense response-related lesion-mimic spots and subsequent early senescence in every newly grown leaf of the rice mutant uap1 after a short period's normal growth. However, the molecular mechanism of these leaves sustaining the short period's survival is still unknown. Phenotypic and molecular studies show that defense response-related lesion-mimic spots and early leaf senescence appear on the normally grown uap1 leaf and aggravate with the growth time. Bioinformatic analysis reveals that UAP proteins are evolutionarily conserved among eukaryotes, and there exists UAP2 protein except UAP1 protein in many higher organisms, including rice. Rice UAP2 and UAP1 proteins present high sequence identities and very similar predicted 3D structures. Transcriptional expression profile of the UAP2 gene decreases with the appearance and aggravating of leaf spots and early senescence of uap1, implying the role of the UAP2 gene in maintaining the initial normal growth of uap1 leaves. Enzymatic experiments verified that the UAP2 protein performs highly similar UAP enzymatic activity with the UAP1 protein, catalyzing the biosynthesis of UDP-GlcNAc. And these two UAP proteins are found to have the same subcellular localization in the cytoplasm, where they most presumably perform their functions. Overexpression of the UAP2 gene in uap1 plants succeeds to rescue their leaf mutant phenotype to normal, providing direct evidence for the similar function of the UAP2 gene as the UAP1 gene. The UAP2 gene is mainly expressed in the young leaf stage for functions, while the UAP1 gene is highly expressed during the whole leaf developmental stages. Based on these findings, it is suggested that UAP2 and UAP1 play key roles in rice leaf survival during its development in a synergetic manner, protecting the leaf from early senescence.

Características foliares y tasas vitales de árboles sucesionales tardíos de un bosque tropical perennifolio

Restoration of vegetation in perturbed areas (e.g., abandoned pastures) with late-successional tree species may help to bypass decades of low diversity by accelerating succession. To elucidate how leaf dynamics is related to high growth rates and survival in early successional environments, we evaluated the hypothesis that plasticity in foliar demography is positively related to establishment of seven late-successional tree species growing in sunny sites (pasture and edge) and dark sites (secondary forest) at Los Tuxtlas, Veracruz, Mexico. We monitored leaves from 517 individuals from all species at all habitats during one year. Individuals growing in secondary forest and edge showed higher leaf survival and lower leaf production than those growing in pasture. Individuals with higher growth rates and survival in pasture showed high plasticity in their leaf survival and low plasticity in their leaf production (stability) while individuals in edge and secondary forest with high survivorship were those with high stability in their leaf production. Our results indicate that <em>Nectandra ambigens, Licaria velutina</em> and <em>Pouteria rhynchocarpa</em> may be planted in pastures because they show high growth rates and survival there, besides, they have different maximal height as adults and therefore they will provide structural diversity to the restored forest. Species with low plant survivorship in pastures as <em>Calophyllum brasiliense, Pimenta dioica, Amphitecna tuxtlensis</em> and <em>Eugenia inirebensis</em> should be planted in great numbers or until a canopy of pioneers develop.

RESGATE DE MUDAS DE Lychnophora pohlii COMO ALTERNATIVA PARA RECUPERAÇÃO E CONSERVAÇÃO DE CAMPO RUPESTRE

O objetivo deste trabalho foi avaliar o efeito do tamanho da planta resgatada e dos níveis de redução foliar na sobrevivência, crescimento e emissão de folhas em mudas de arnica obtidas via resgate em um remanescente de campo rupestre. Foram resgatados 240 indivíduos, os quais foram divididos em duas classes de altura (Classe I – 2,5 a 20 cm e Classe II – 25 a 55 cm) e submetidos a três intensidades de redução foliar (0%, 50% e 100%). As medições de altura, diâmetro e emissão de novas folhas foram realizadas em nove tempos (0, 15, 30, 45, 60, 75, 90, 105 e 120 dias) e a avaliação da sobrevivência aos 120 dias. A taxa média de sobrevivência foi de 49,2%, sendo maior na Classe I e não apresentando diferença estatística quanto aos três tipos de redução foliar. A emissão de folhas foi maior nos indivíduos que sofreram redução foliar, observando-se uma diminuição ao longo do tempo, ao contrário das mudas com 0% de redução, que tiveram um crescimento linear. Portanto, é aconselhável que o resgate de mudas de arnica seja realizado para plantas com tamanho entre 2,5 e 20 cm, sem necessidade de redução foliar.AbstractEvaluation of the arnica plant rescue as an alternative to conservation and restoration of campo rupestre ecosystems. The objective of this research was to evaluate the effect of rescued plant size and levels of reduction in leaf survival, growth, and insertion of leaves in seedlings of Arnica obtained via salvage in a remnant of Campo Rupestre. We rescued 240 individuals and these were divided into two classes’ height (Class I - 2.5 to 20 cm and Class II - 25 - 55 cm) and subjected to three levels of reduction leaf (0%, 50% and 100%). The measurements of height and diameter and new leaves emission were collected at nine times (0, 15, 30, 45, 60, 75, 90, 105 and 120), and evaluation of survival at 120 days. The average survival rate was 49.2%, higher in Class I and had no significant difference regarding the three types of leaf reduction. The emission sheet was higher in subjects experiencing a leaf reduction observing a decrease over time, unlike the seedling with 0% reduction, which increased linearly. Therefore, it is advisable a size between 2.5 and 20 cm for the rescue of arnica seedling plant, without leaf reduction. Keywords: Lychnophora pohlii; seedlings production; leaf reduction; height class.

Xanthomonas albilineans OmpA1 Appears to be Functionally Modular and Both the OMC and C-like Domains Are Necessary for Leaf Scald Disease of Sugarcane

Several EZ-Tn5 insertions in gene locus XALc_0557 (OmpA1) of the sugarcane leaf scald pathogen Xanthomonas albilineans XaFL07-1 were previously found to strongly affect pathogenicity and endophytic stalk colonization. XALc_0557 has a predicted OmpA N-terminal outer membrane channel (OMC) domain and an OmpA C-like domain. Further analysis of mutant M468, with an EZ-Tn5 insertion in the upstream OMC domain coding region, revealed impaired epiphytic and endophytic leaf survival, impaired resistance to sodium dodecyl sulfate (SDS), structural defects in the outer membrane (OM), and hyperproduction of OM vesicles. Cloned full-length XALc_0557 complemented M468 for all phenotypes tested, including pathogenicity, resistance to SDS, and ability to survive both endophytically and epiphytically. Another construct, pCT47.3, which expressed only the C-like domain of XALc_0557, restored resistance to SDS in M468 but failed to complement any other mutant phenotype, indicating that the C-like domain functioned independently of the OMC domain to help maintain OM integrity. pCT47.3 also complemented pathogenicity, resistance to SDS, and stalk colonization in mutant M1152, which carries an EZ-Tn5 insert in the C-like coding region, indicating that both predicted domains are modular and necessary but neither is sufficient for X. albilineans pathogenicity, endophytic survival in, and epiphytic survival on sugarcane.

Leaf tissue water relations and hydraulic properties of sclerophyllous vegetation on white sands of the upper Rio Negro in the Amazon region

The objective of this study was to explore the leaf tissue water relations in terminal branches, as well as the relations between xylem structure and function of five sclerophyllous species coexisting on white sands within the Amazon region. In these species, which possess costly leaves and thrive in an extremely nutrient-poor habitat, the preservation of leaf survival would be of comparable importance to the preservation of xylem vessels. Three trees per species were tagged in the field for all measurements. Minimum leaf water potential (Ψ) was −1.53 ± 0.61 and −0.94 ± 0.10 MPa during rainless and rainy days, respectively. The Ψ for turgor loss averaged −1.92 ± 0.05 MPa. Therefore, minimum Ψ was maintained within a safety range above the critical value for turgor loss. Xylem (Kx) and leaf (Kl) specific conductivity averaged 1.4 ± 0.22 and 0.00033 ± 0.000045 kg m−1 s−1 MPa−1, respectively. Water supply was favoured in species with higher vessel density, and all species depended on relatively less abundant larger vessels for water transport. This would be advantageous because leaves were unable to develop very negative water potentials in order to maintain transpiration. High transpiration rates may be restricted to a few hours daily so as to prevent cavitation of widest vessels.

Basal medium improvement for routine micropropagation of Olea maderensis: physiological comparative studies

The routine micropropagation of Olea maderensis (Lowe) Rivas Mart. & Del Arco requires an adequate basal medium. To find the optimal basal medium, shoots were grown on four different media: olive medium (OM) and three modified OM media enriched with 2, 4, and 10 times the iron (Fe), magnesium (Mg), and manganese (Mn) concentrations of the OM medium, respectively (OMG, OMG4, and OMG10). For the elongation–proliferation stage, media were supplemented with 9.12 µmol·L–1 zeatin. Doubling the Fe, Mg, and Mn concentrations (OMG) provided green and healthy shoots, while in other media leaf chlorosis or necrosis and abscission occurred because of either deficiency (OM) or toxicity of the elements (OMG4 and OMG10). Shoots grown in the OMG medium also had the highest elongation–proliferation rates. Physiological studies were then performed only between OMG- and OM-grown shoots. Chlorophyll a and b contents and fluorescence (Fv, Fm) were higher in OMG-grown shoots. Doubling the concentration of Fe, Mg, and Mn (which are important in photosynthesis) stimulated leaf survival and photosynthesis. OMG-grown leaves had higher Mg, Fe, and Mn levels. Compared with field leaves, in vitro leaves had higher protein contents. Other physiological parameters (membrane integrity, water content, and osmolality) did not differ between the two media. The best rooting rates were obtained for shoots grown in OMG (>85%), and plants were successfully acclimatized. These studies improved the efficiency and quality of micropropagation of O. maderensis, thereby allowing germplasm preservation of this endangered species.

Response to terminal water deficit stress of cowpea, pigeonpea, and soybean in pure stand and in competition

The response to terminal water deficit stress of three grain legumes, soybean, cowpea and pigeonpea, was evaluated in plants grown in large tubes, in competition with either the same species or one of the other two species. The aim was to explore how species differences in drought response affected water use, growth and survival of plants in pure stand and in competition. Two plants, comprising the test species and its competitor, were grown in each tube. Water was withheld 26 days after sowing by which time each plant had at least three fully expanded trifoliolate leaves. Leaf water status and plant growth were measured through destructive samples when 80% and 90% of the estimated plant available water (PAW) was depleted and at plant death, while PAW depletion, node growth and leaf survival were monitored at 2–3 day intervals until the last plants died (61 days after water was withheld). In pure stand, the rate of PAW depletion was initially slowest in cowpea despite its much larger leaf area, and fastest in soybean. Node growth was most sensitive in cowpea, ceasing at 65% PAW depletion compared with 85% PAW depletion in pigeonpea and soybean, so that the latter two species produced relatively more nodes after water was withheld. However, senescence of the lower leaves was most rapid in soybean and slowest in cowpea. Cowpea and pigeonpea extracted almost all PAW and died an average 18 days and 14 days, respectively, after maximum PAW depletion. In contrast, soybean died before 90% of PAW was depleted and so in pure stand used less water. There were otherwise only minor differences between the species combinations in the timing and maximum level of PAW depletion. The ability of cowpea and pigeonpea to maintain leaf water status above lethal levels for longer was achieved through different means. Cowpea relied primarily on dehydration avoidance and maintained tissue water status higher for longer, whereas pigeonpea demonstrated greater dehydration tolerance. While significant levels of osmotic adjustment (OA) were identified in soybean and pigeonpea, OA appeared to be of limited benefit to leaf survival in soybean. Pigeonpea invested significantly more total dry matter (TDM) in roots than either cowpea or soybean. Cowpea survived longest in pure stand whereas pigeonpea and soybean survived shortest in pure stand, suggesting that the dehydration avoidance response of cowpea was more effective in competition with like plants whereas the dehydration tolerance strategies of pigeonpea and soybean were least effective when competing against like plants. On average, TDM per plant ranked in the order cowpea > soybean > pigeonpea, largely reflecting initial differences in plant size when water was withheld. However, there was an inverse relation between TDM of a species and that of its competitor, so that in effect, water not used by a given plant to produce TDM was used by its competitor and there were no differences in TDM production per tube.

Genotypic variation for drought stress response traits in soybean. III. Broad-sense heritability of epidermal conductance, osmotic potential, and relative water content

The broad-sense heritability of 3 traits related to leaf survival in severely stressed plants was studied in several hybrid soybean populations. The 3 traits were epidermal conductance (ge), osmotic potential (π), and relative water content (RWC). The populations were generated by hybridising unrelated parental genotypes previously shown to differ in the 3 traits. ge (mm/s) was measured on well watered plants from 10 populations involving all combinations of 5 parental lines, grown in soil-filled beds in the glasshouse. π (MPa) and RWC (%) were measured on severely stressed plants of 3 populations involving all combinations of 3 different parents, growing into a terminal water deficit under a rainout shelter in the field. Broad-sense heritability for ge was significantly different from zero (P < 0.05) in all 10 populations and ranged from 60% to 93%. Heritability estimates for π70 (the tissue osmotic potential at 70% RWC) ranged from 33% to 71%. Only two estimates were statistically significant (P < 0.05) because of large standard errors and the fact that parental differences were smaller than previously observed. Broad-sense heritability for RWC of severely stressed plants ranged from 40% to 74%, and was statistically significant (P < 0.05) for 2 of the 3 populations. For all 3 traits, F2 progeny distributions were consistent with quantitative inheritance with a high degree of additive gene action. It was concluded that capacity exists to breed varieties with low ge, low π70, and high RWC in stressed plants. However, in the case of osmotic potential, genotypes with lower π70 combined with greater precision of measurement would be needed than proved possible in these studies. Further, specific strategies would be needed to select for the critical RWC, the minimal RWC at which leaf tissues die and which provides a measure of tissue dehydration tolerance. More research is also needed to characterise the dynamic relations between ge, π, and RWC in influencing leaf survival in soybean, before they could be confidently used in a breeding program to improve drought tolerance.

Drought resistance of native and introduced perennial grasses of south-eastern Australia

Perennial grasses are the key to the economic and environmental sustainability of pastures for livestock grazing in south-eastern Australia. Mortality of perennial grasses can occur during drought periods and there is anecdotal evidence of differences in drought resistance among species, but information on the basic ecophysiological responses of these species to drought is lacking. An experiment was conducted to determine the responses of 7 native and 3 introduced perennial grass species to continuous drought. Leaf survival during severe drought varied among the species nearly 4-fold, from 11 to 40 days, and was considered a measure of their overall drought resistance. All of the species had good dehydration tolerance, so the differences in drought resistance were related more to their dehydration avoidance traits, specifically to the amount of water available to the plant at the point where plant transpiration became minimal. The native species had both the longest and shortest leaf survival periods, with the introduced species ranking intermediate. Species exhibited various morphological traits that contributed to dehydration avoidance during severe drought, including leaf folding or rolling, rapid leaf shedding, and large amounts of cuticular wax. The results are discussed in terms of their implications for perennial grass persistence in south-eastern and in south-western Australia.