Photochemical metabolism and fruit quality of Ubá mango tree exposed to combined light and heat stress in the field

Several experiments have highlighted the complexity of stress interactions, in field conditions, involved in plant response. However, these impacts on the mechanisms involved in plant photosynthetic response remains understudied. The aim of this work was to compare the photosynthetic efficiencies and fruit quality of mango tree (Mangifera indica L.) cv. Ubá harvested from plants cultivated on the east and west sides of a commercial orchard, according to the position of plants in relation to sunrise. Chlorophyll a fluorescence, was analyzed in leaves in four different periods: fruit growth phase, fruit ripening phase, post-harvest period and after plant pruning. Photoinhibitory damage was detected by the trapped energy flux and transported electron flux per reaction center during the fruit ripening phase, and by specific energy fluxes and yield quantum efficiency after plant pruning. Although high radiation caused photoinhibition on leaves from plants cultivated on the west side of the orchard, it provided sweeter fruits. In contrast to our initial hypothesis, it was verified that plants cultivated on the west side of the orchard presented better photochemical performance in periods with the greatest requirements of photoassimilates. In addition, plants demonstrated different abilities to deal with changes on photosynthetic active radiation and high temperature. This information suggests that the phenotypic plasticity of the Ubá mango cultivar is considerable, which can be exploited to be used in regions with great relief variations and the combination of increased irradiance and high temperature.     

Short Lag Times for Invasive Tropical Plants: Evidence from Experimental Plantings in Hawai'i

Background

The lag time of an invasion is the delay between arrival of an introduced species and its successful spread in a new area. To date, most estimates of lag times for plants have been indirect or anecdotal, and these estimates suggest that plant invasions are often characterized by lag times of 50 years or more. No general estimates are available of lag times for tropical plant invasions. Historical plantings and documentation were used to directly estimate lag times for tropical plant invasions in Hawai''i.

Methodology/Principal Findings

Historical planting records for the Lyon Arboretum dating back to 1920 were examined to identify plants that have since become invasive pests in the Hawaiian Islands. Annual reports describing escape from plantings were then used to determine the lag times between initial plantings and earliest recorded spread of the successful invaders. Among 23 species that eventually became invasive pests, the average lag time between introduction and first evidence of spread was 14 years for woody plants and 5 years for herbaceous plants.

Conclusions/Significance

These direct estimates of lag times are as much as an order of magnitude shorter than previous, indirect estimates, which were mainly based on temperate plants. Tropical invaders may have much shorter lag times than temperate species. A lack of direct and deliberate observations may have also inflated many previous lag time estimates. Although there have been documented cases of long lag times due to delayed arrival of a mutualist or environmental changes over time, this study suggests that most successful invasions are likely to begin shortly after arrival of the plant in a suitable habitat, at least in tropical environments. Short lag times suggest that controlled field trials may be a practical element of risk assessment for plant introductions.     

Evidence for the transmission of information through electric potentials in injured avocado trees

Electrical excitability and signaling, frequently associated with rapid responses to environmental stimuli, have been documented in both animals and higher plants. The presence of electrical potentials (EPs), such as action potentials (APs) and variation potentials (VPs), in plant cells suggests that plants make use of ion channels to transmit information over long distances. The reason why plants have developed pathways for electrical signal transmission is most probably the necessity to respond rapidly, for example, to environmental stress factors.We examined the nature and specific characteristics of the electrical response to wounding in the woody plant Persea americana (avocado). Under field conditions, wounds can be the result of insect activity, strong winds or handling injury during fruit harvest. Evidence for extracellular EP signaling in avocado trees after mechanical injury was expressed in the form of variation potentials. For tipping and pruning, signal velocities of 8.7 and 20.9 cm/s, respectively, were calculated, based on data measured with Ag/AgCl microelectrodes inserted at different positions of the trunk. EP signal intensity decreased with increasing distance between the tipping and pruning point and the electrode. Recovery time to pre-tipping or pre-pruning EP values was also affected by the distance and signal intensity from the tipping or pruning point to the specific electrode position. Real time detection of remote EP signaling can provide an efficient tool for the early detection of insect attacks, strong wind damage or handling injury during fruit harvest.Our results indicate that electrical signaling in avocado, resulting from microenvironment modifications, can be quantitatively related to the intensity and duration of the stimuli, as well as to the distance between the stimuli site and the location of EP detection. These results may be indicative of the existence of a specific kind of proto-nervous system in plants.     

热激转录因子在植物抗非生物胁迫中的功能研究进展

植物在遭受环境胁迫时会产生一系列应激反应,而热激转录因子可通过介导热激蛋白或其他热诱导基因的转录和表达,来参与调控植物抵抗逆境胁迫过程和其他生命活动。主要介绍了植物热激转录因子的基本蛋白结构域,阐述了3类热激转录因子在抗极端温度（高温、低温）胁迫、干旱胁迫、高盐胁迫、活性氧胁迫中的功能与作用机制,并探讨和展望了植物热激转录因子在植物育种和提高植物抗逆性的研究中的发展与应用前景,以期为深入研究热激转录因子在调控植物抵抗逆境胁迫中的生物学功能与机制提供理论参考。     

Influence of Pruning Measures on Recovery of Bois Noir‐infected Grapevines

In recent years, visual and analytical observations revealed a significant increase of ‘Bois noir’ (BN) in Austrian vineyards. Removing infected parts by pruning can prevent or reduce spread of the pathogen within the vines. Knowledge about the effect of pruning practices on recovery rates is essential for grapevine growers. Vines showing BN for the first time were visually categorized into classes of symptoms according to disease severity. In the ensuing winter, plants were pollarded 15 cm above the graft union (511 vines), cane pruned (529 vines) or spur pruned (heavy pruning of canes leaving spurs only; 31 vines). Pollarding resulted in significantly higher recovery rates (yearly average 62–84%) in the next growing season and significantly lower recurrence rates in the following years than cane pruning (yearly average 29–49% in the next growing season). Spur pruning was statistically indistinguishable from cane pruning. Our data allowed the conclusion that extensive removal of infected wood is crucial for immediate and persistent success of pruning measures. Recovery was significantly influenced by the severity of BN, by the cultivar and by the observation year. With pollarding treatments, a significant correlation between recovery and plant age was noticed.     

Effects of root pruning on the growth and water use efficiency of winter wheat

A pot experiment was conducted to study the effects of root pruning at the stem elongation stage on the growth and water use efficiency (WUE) of winter wheat (Triticum aestivum). The results showed that stomatal conductance (g) and transpiration (E) of wheat were very sensitive to root pruning. After root pruning, they declined rapidly and but returned to pre-pruning values 15 days after treatment. Under well-watered conditions, there was no significant difference in leaf water potential (ψ_leaf) between root pruned and control plants after root pruning. Under moderate drought stress, ψ_leaf of root pruned plants declined significantly compared to the control 3 days after root pruning. After 15 days, ψ_leaf of root pruned plants was similar to the controls. Under different soil moisture levels, net assimilation rate (A) of root pruned plants was lower than controls 3–7 days after root pruning, but was similar to the controls 15 days after pruning. At anthesis (50 days after root pruning), root pruned plants showed significantly higher A compared with the control. Leaf area per tiller and tiller number of root pruning plants was significant lower than the control at booting stage, which showed that root pruning restrained the growth of plants in the early growing stage, but leaf area per stem, of root pruned plants, was similar to the control at anthesis. Under both soil moisture levels, there was no significant difference in grain yield between root pruned and the control plants in the monoculture. In mixture with the control plants, the root pruned plants was less productive and had a lower relative yield (0.92 and 0.78, respectively) compared with the control (1.13 and 1.19, respectively), which suggested that the pruned plants lost some of its competing ability and showed a lower ability to acquire and use the same resources in the mixture compared with the control plant. Over the whole growing cycle, root pruning reduced water consumption (by 10% under well-watered conditions and 16% under moderate drought stress) of wheat significantly compared to the control (P < 0.05), and but there was no significant difference in grain yield between root pruned and control plants. Therefore root pruned wheat had a higher WUE with respect to grain yield compared with the controls. In conclusion, lowering water consumption by root pruning in the early growing stage is an effective way to improve water use efficiency in arid and semi arid areas.     

Field trials to optimise timing and frequency of pruning for cultivation of a New Zealand carrageenophyte, Gigartina atropurpurea

The endemic New Zealand red alga Gigartina atropurpurea has been identified as a candidate for aquaculture because of its high quality and value carrageenan and its broad-bladed morphology. As G. atropurpurea has not so far been exploited commercially, trials were conducted to investigate the effect of timing and frequency of pruning on the growth of plants in the wild and explants on ropes, in spring, and autumn. Plants were monitored monthly by measuring the length of the two longest blades (a proxy for biomass) and wet weights of all plant material retrieved. The results suggested five broad conclusions: (1) spring growth was much greater than autumn growth; (2) regardless of season, maximal growth rates were achieved 4–6 weeks post pruning; (3) pruning accelerated growth; (4) pruning plants twice during spring generated up to four times more biomass than when plants were pruned only once, and (5) there was no difference in the response of farmed and wild plants to pruning treatments. Based upon these preliminary trials, plant material from wild tetrasporic and female G. atropurpurea could be harvested up to three times during the growth period (August–December). However, further research on the feasibility of G. atropurpurea aquaculture is justified.     

Quantitative analysis of transpiration stream dynamics in an intact cucumber stem by a heat flux control method

Water flux of transpiration stream in an intact stem of the 10 leaf stage cucumber plant (Cucumis sativus L. cv. Chojitsu-Ochiai) was measured by a novel system of heat flux control method with a resolution of 1 × 10⁻³ grams per second and a time constant of 1 minute; two heat flux control sensors were attached to the seventh internode and the stem base. The transpiration stream responded clearly to leaf transpiration and root water absorption when the plant was exposed to light, and the water flux at the stem base corresponded to the transpiration rate per plant in steady state. Root water absorption lagged about 10 minutes behind leaf transpiration. Dynamics of water fluxes were affected by the lag of water absorption in roots, and temporary water loss caused by rapid increase in leaf transpiration was buffered by about 5% of the water content in the stem.     

Xylem exudate yield from detopped maize plants as an estimator of root pruning

Current methods of studying roots are either labour intensive or require expensive equipment. In 1986 and 1987 root pruning treatments were given to maize plants grown indoors. In both years the amount of xylem exudate collected from plant stumps shortly after root pruning increased with the dry weight of roots attached to the plant. The measurement of xylem exudation is presented as an alternative for conventional laborious root-study methods.     

Comparison of lag times in plant physiology

Abstract Comparison of lag (or latent) times is a useful tool in plant physiology for investigating potential mechanisms involved in a response. There are two main ways of deriving the lag time, but only one of these can be properly used for comparative purposes. The other method is biased by the faster responding plants and may not give a representative estimate for the lag time in the population. The fact that the two methods give different, non-comparable results has been widely overlooked. We suggest more care should be taken for their correct use, and propose two terms which can be used to describe the different estimates of the lag time to avoid confusion.     

Influence of pruning management on P and N distribution and use efficiency by N2 fixing and non-N2 fixing trees used in alley cropping systems

Pruning of hedgerow trees is an important management practice for the successful establishment of an alley cropping system. Although pruning affects biomass production, only meager evidence of this management on distribution of nutrients among the different plant organs after tree regrowth is available. This study examined the effect of pruning on the distribution and use efficiency of N and P in a N₂ fixing leguminous tree species, Gliricidia sepium, and two non-N₂ fixing leguminous tree species, Senna siamea and S. spectabilis, grown in a field on an Alfisol (low in P) at Fashola (Guinea Savanna Zone), Southwestern Nigeria. Four P rates, 0, 20, 40 and 80 kg P ha^–1 as single superphosphate were used and management treatments included pruned versus unpruned plants. The ¹⁵N isotope dilution technique was used to measure N₂ fixation in G. sepium. Partitioning of total P among different plant organs was influenced by plant species and pruning management, but was not affected by P application rates. The distribution of total P in the various plant organs followed that of dry matter yield while N partitioning had a different pattern. Pruned plants distributed about 118% more total P to branches and had a higher physiological P use efficiency (PPUE) than unpruned plants. Leaves were the biggest sink for total N and N allocation in the other plant organs was influenced by plant species and pruning management, G. sepium had relatively more of its total N and P partitioned into roots (about double that of the non-N₂ fixing trees) but had a lower PPUE. Unpruned and pruned G. sepium derived 35 and 54% respectively of their total N from atmospheric N2, with about 54% of the fixed N2 being allocated to leaves and roots. Results showed that N and P pools turned over in the branches during plant regrowth after pruning but the causative factors associated with this phenomenon were not clear.     

Ozone induced emissions of biogenic VOC from tobacco: relationships between ozone uptake and emission of LOX products

Volatile organic compound (VOC) emissions from tobacco ( Nicotiana tabacum L. var. Bel W3) plants exposed to ozone (O₃) were investigated using proton-transfer-reaction mass-spectrometry (PTR-MS) and gas chromatography mass-spectrometry (GC-MS) to find a quantitative reference for plants' responses to O₃ stress. O₃ exposures to illuminated plants induced post-exposure VOC emission bursts. The lag time for the onset of volatile C₆ emissions produced within the octadecanoid pathway was found to be inversely proportional to O₃ uptake, or more precisely, to the O₃ flux density into the plants. In cases of short O₃ pulses of identical duration the total amount of these emitted C₆ VOC was related to the O₃ flux density into the plants, and not to ozone concentrations or dose–response relationships such as AOT 40 values. Approximately one C₆ product was emitted per five O₃ molecules taken up by the plant. A threshold flux density of O₃ inducing emissions of C₆ products was found to be (1.6 ± 0.7) × 10⁻⁸ mol m⁻² s⁻¹.     

黄土丘陵区辽东栎和刺槐树干液流时滞效应与蒸腾特征的关联性

运用Granier热扩散探针法,于2016年7-9月对半干旱黄土丘陵区天然次生林树种辽东栎和人工林树种刺槐的树干液流进行连续测定,并同步监测气象因子和土壤含水量,用错位相关法分析液流通量密度与空气水汽压亏缺日变化的时滞长度,研究2个树种不同径级个体在不同土壤水分条件下液流通量密度与蒸腾驱动因子之间的时滞效应.结果表明:辽东栎和刺槐液流通量密度的日变化节律与气象因子显著相关,空气水汽压亏缺峰值的出现较辽东栎树干液流通量密度滞后118.2 min,较刺槐树干液流通量密度滞后39.5 min;而光合有效辐射的峰值通常滞后于辽东栎12.4 min,提前于刺槐68.5 min.液流通量密度和空气水汽压亏缺的时滞长度与树种和土壤含水量显著相关,辽东栎、刺槐在土壤含水量较高时段的时滞长度分别大于土壤含水量较低时段32.2和68.2 min.时滞长度与径级的相关性整体上未达到显著水平,但在土壤含水量较低时段小径级刺槐的时滞长度大于大径级21.4 min,差异达到了显著水平.两树种液流通量密度与空气水汽压亏缺之间的时滞效应反映了对蒸腾驱动因子的敏感性,较好的土壤水分条件有利于液流通量密度提早达到峰值,较低土壤水分会导致树干液流对气象环境因子响应的敏感性降低;刺槐树干液流受土壤水分的影响更显著.     

Effects of Intermittent and Continuous Light on the Chlorophyll Formation in Etiolated Plants at Various Ages

The effect of the tissue age of dark-grown bean plants on the chlorphyll formation under continuous illumination or short impulses of white light has been studied. It was found that the protochlorophyllide present in the tissue is age-dependent and reaches a plateau at about 10 days of age, as judged by the chlorophyll formed in etiolated plants of various ages after 5 min illumination. The amount of chlorophyll a and chlorophyll b formed under short impulses of while light increases up to about 9 days of age and thereafter decreases. However, the decrease in chlorophyll a is sharper than that of chlorophyll b, the amount of which remains almost constant. The ratio of chlorophyll a lo chlorophyll b under the short impulses of white light is higher in the younger plant. Similar results are obtained after transfer of the plants from the flashing light to continuous illumination In the young plant there is no lag phase in the chlorophyll biosynthesis while as the age is increased the lag phase is evident and its duration increases as the plant ages. After protochlorophyllide phototransformation under continuous illumination the lag phase in chlorophyll biosynthesis is also age-dependent. Leaves up to 5 days old show no lag phase in chlorophyll synthesis; after this point, however, the lag phase's duration increases continuously with age.     

The effects of (2RS, 3RS)-1-(4-chlorophenyl)-4, 4-dimethyl-2-(1H-1,2,4 triazol-1-yl) pentan-3-ol (Paclobutrazol:PP333) and root pruning on the growth,water use and response to drought of Colt Cherry rootstocks

The effect of (2RS, 3RS)-1-(4-Chlorophenyl)-4, 4-dimethyl-2-(1H-1,2,4 triazol-1-yl) pentan-3-ol (PP333) on the growth and transpiration of normal and root pruned colt rootstocks was measured. PP333 reduced plant height, stem diameter increment, leaf number, area and weight and stem weight. Root pruning reduced root, leaf and stem weight, and plant height in control plants. PP333 reduced both total water use and transpiration per unit leaf area and increased stomatal resistance. In control plants root pruning also reduced total water use and increased stomatal resistance. 15 days after the beginning of the experiment half the plants in all treatments were allowed to dry out. The effects of drought, i.e. reduced transpiration, growth and leaf water potentials, were smaller in PP333 treated than in control plants.     

Accumulation of free proline and glycine betaine in Aster tripolium subjected to a saline shock: A kinetic study related to light period

On transferring three-week-old plants of Aster tripolium L. growing in a half strength Hoagland's medium to the same medium containing 333 m M NaCl a very quick uptake of salt and, after a lag phase of 3 to 5 h, an increase in free proline level was observed. During the time course of imino acid storage, the accumulation rates were higher in the light than in the dark, thereby suggesting some kind of photocontrol on solute metabolism. At zero time, high levels of glycine betaine were present in young plants grown without salt. However, after the application of saline shock, the betaine level also increased significantly. The highest rate of betaine accumulation was detected during the third day of treatment when the rate of proline storage decreased. Glycine betaine storage could also be linked to light dependent processes; whatever its importance in response to salt shock was, the levels observed were lower than those of plants directly grown on 333 m M NaCl for three weeks. When saline stressed plants were transferred to a medium without NaCl, the proline level quickly decreaed while that of glycine betaine remained stable.     

Effects of Root Pruning on Translocation of Photosynthates in Phaseolus vulgaris L

Root pruning increased the level of ethanol soluble sugars inred kidney bean plants (Phaseolus vulgaris L. ) grown in aeratednutrient solution. However, the concentration gradient of thesesugars down the stem and its translocation velocity remainedunchanged. Removal of 50% of the roots had no effect on thetotal photosynthates exported from source leaves but the finaldistribution pattern of photosynthates was altered; less movingtoward the upper plant parts, and accumulation occurring inthe lower stems. Translocation velocity of photosynthates towardthe upper plant parts was drastically reduced by root pruning. Key words: Phaseolus vulgaris, Photosynthate translocation, Root pruning     

Explicit solution of fractional order atmosphere-soil-land plant carbon cycle system

In this paper, the dynamical behaviours and mathematics of the fractional order atmosphere-soil-land plant carbon cycle system involving the time dependent variable of carbon flux in atmosphere, the carbon flux of soil, and the carbon flux of animals and plants are qualitatively and numerically investigated. Explicit solutions in terms of the Mittag-Leffler functions to the terrestrial carbon cycle system around the equilibrium point are first time reported by applying Laplace transform of Caputo fractional derivative. The graphs of obtained solutions the time dependent variable of carbon flux in atmosphere, the carbon flux of soil and the carbon flux of animals and plants are plotted against each other. Explicit solutions to original system and stability of the fractional order linearized system around the equilibrium point are graphically compared as well.     

EFFECTS OF ROOT PRUNING AT THE REGREENING STAGE ON DROUGHT TOLERANCE AND WATER USE EFFICIENCY OF WINTER WHEAT IN LATE GROWING STAGE

 通过盆栽试验研究了返青期根修剪对冬小麦(Triticum aestivum)后期耐旱性及水分利用效率的影响。在返青期设置了两个根修剪处理: 1)小剪根, 在植株一侧切去部分侧生根; 2)大剪根, 在主茎四周切去部分侧生根。不剪根者设为对照(CK)。研究结果显示, 两个根修剪处理均显著减少了小麦的根系, 但对根冠比没有显著影响。在花期, 两个根修剪处理的小麦旗叶的叶绿素荧光参数最大光化学效率(The maximum photochemical efficiency of PSⅡ, F_v/F_m)、 PSⅡ潜在活性 (PSⅡ potential activity, F_v/F_o)、实际光化学量子产量(Effective PSⅡ quantum yield, Φ_PSⅡ)、表观光合电子传递速率(Apparent rate of photosynthetic electron transport, ETR)、光化学淬灭系数( Coefficient of photochemical quenching, q_P)和非光化学淬灭系数(Coefficient of non-photochemical quenching, NPQ)值, 在停止供水7 d后, 均显著高于对照, 这表明根修剪小麦的耐旱性强于对照, 因此在干旱胁迫下有较高的光化学活性。小剪根处理在高水条件下对小麦产量无显著影响, 而在中度干旱条件下显著提高了小麦的产量, 因此, 小剪根处理显著提高了小麦的抗旱系数; 小剪根处理在高水分处理(土壤水分含量为田间持水量的85%)和中度干旱胁迫处理(土壤水分含量为田间持水量的55%)条件下, 均显著提高了小麦的水分利用效率。但大剪根处理由于严重影响了群体数量和产量, 水分利用效率和抗旱系数均没有提高。可见, 适当地减少根系有助于小麦的耐旱性和水分利用效率的提高。     

Expression of animal CED-9 anti-apoptotic gene in tobacco modifies plasma membrane ion fluxes in response to salinity and oxidative stress

Apoptosis, one form of programmed cell death (PCD), plays an important role in mediating plant adaptive responses to the environment. Recent studies suggest that expression of animal anti-apoptotic genes in transgenic plants may significantly improve a plant’s ability to tolerate a variety of biotic and abiotic stresses. The underlying cellular mechanisms of this process remain unexplored. In this study, we investigated specific ion flux “signatures” in Nicotiana benthamiana plants transiently expressing CED-9 anti-apoptotic gene and undergoing salt- and oxidative stresses. Using a range of electrophysiological techniques, we show that expression of CED-9 increased plant salt and oxidative stress tolerance by altering K⁺ and H⁺ flux patterns across the plasma membrane. Our data shows that PVX/CED-9 plants are capable of preventing stress-induced K⁺ efflux from mesophyll cells, so maintaining intracellular K⁺ homeostasis. We attribute these effects to the ability of CED-9 to control at least two types of K⁺-permeable channels; outward-rectifying depolarization-activating K⁺ channels (KOR) and non-selective cation channels (NSCC). A possible scenario linking CED-9 expression and ionic relations in plant cell is suggested. To the best of our knowledge, this study is the first to link “ion flux signatures” and mechanisms involved in regulation of PCD in plants.