Leaf Lateral Asymmetry in Morphological and Physiological Traits of Rice Plant

Leaf lateral asymmetry in width and thickness has been reported previously in rice. However, the differences between the wide and narrow sides of leaf blade in other leaf morphological and physiological traits were not known. This study was conducted to quantify leaf lateral asymmetry in leaf width, leaf thickness, specific leaf weight (SLW), leaf nitrogen (N) concentration based on dry weight (Nw) and leaf area (Na), and chlorophyll meter reading (SPAD). Leaf morphological and physiological traits of the two lateral halves of the top three leaves at heading stage were measured on 23 rice varieties grown in three growing seasons in two locations. Leaf lateral asymmetry was observed in leaf width, leaf thickness, Nw, Na, and SPAD, but not in SLW. On average, the leaf width of the wide side was about 17% higher than that of the narrow side. The wide side had higher leaf thickness than the narrow side whereas the narrow side had higher Nw, Na, and SPAD than the wide side. We conclude that the narrow side of leaf blade maintained higher leaf N status than the wide side based on all N-related parameters, which implies a possibility of leaf lateral asymmetry in photosynthetic rate in rice plant.     

Differences in Leaf Flammability,Leaf Traits and Flammability-Trait Relationships between Native and Exotic Plant Species of Dry Sclerophyll Forest

The flammability of plant leaves influences the spread of fire through vegetation. Exotic plants invading native vegetation may increase the spread of bushfires if their leaves are more flammable than native leaves. We compared fresh-leaf and dry-leaf flammability (time to ignition) between 52 native and 27 exotic plant species inhabiting dry sclerophyll forest. We found that mean time to ignition was significantly faster in dry exotic leaves than in dry native leaves. There was no significant native-exotic difference in mean time to ignition for fresh leaves. The significantly higher fresh-leaf water content that was found in exotics, lost in the conversion from a fresh to dry state, suggests that leaf water provides an important buffering effect that leads to equivalent mean time to ignition in fresh exotic and native leaves. Exotic leaves were also significantly wider, longer and broader in area with significantly higher specific leaf area–but not thicker–than native leaves. We examined scaling relationships between leaf flammability and leaf size (leaf width, length, area, specific leaf area and thickness). While exotics occupied the comparatively larger and more flammable end of the leaf size-flammability spectrum in general, leaf flammability was significantly correlated with all measures of leaf size except leaf thickness in both native and exotic species such that larger leaves were faster to ignite. Our findings for increased flammability linked with larger leaf size in exotics demonstrate that exotic plant species have the potential to increase the spread of bushfires in dry sclerophyll forest.     

植物叶片衰老的分子机制

文章就叶片衰老过程中基因表达调控机制的研究进展作了介绍     

Cultural Differences and Urban Spatial Forms: Elements of Boundedness in an Accra Community

In this article, I expand on Coquery-Vidrovitch's observation (1991) that to understand each African urban milieu, we must view it as more than a fusion of European, American, or traditional culture. Rather, we must see each African city as unique, that is, in fact, internally differentiated, containing a multitude of enclaves that vary one from another in their respective social, physical, and architectural spatial forms. I focus on one community in Accra known as Sabon Zongo. Founded by migrant Hausa from northern Nigeria almost a century ago, it is neither typically southern Ghanaian nor Hausa, having adapted to a mixed cultural milieu. Laid out by the British as part of their town plan, its manner of growth has blurred the original scheme. I examine a number of components that define the uniqueness of this particular urban community, including physical delineations (within Sabon Zongo and between it and the city at large), local knowledge, the landscape, the infrastructure, market and street trade, and centripetal socio-spatial structures such as the family compound. [Ghana, zongo, social-spatial linkage]     

The Relationship Between Leaf Thickness and Plant Water Potential

Leaf thickness was continuously measured in a wide range ofenvironments using a new type of displacement transducer whichis easy to set-up and automatically compensates for the effectsof temperature. Simultaneous measurements were made of waterpotential using either a psychrometer attached to the leaf petioleor a leaf pressure chamber. Thickness of leaves was a sensitiveindicator of plant water status but calibrations against anindependent method were necessary in every plant for accurateestimates of water potential. The relationship between leafthickness changes and water potential, measured in detachedleaves, was usually curvilinear and was strongly influencedby leaf age, stress history and, in young leaves, by the effectsof leaf growth. Leaf thickness growth was absent in mature cabbageleaves. Key words: Leaf thickness, plant water potential, psychrometer     

植物叶片衰老与氧化胁迫

叶片衰老是叶片生长发育进程中的最后阶段,与活性氧伤害有着密切的关系。介绍了植物叶片衰老过程中活性氧产生及清除系统的变化,讨论了对水分胁迫与氧化胁迫的交叉抗性,并对下一步的研究作出了展望     

互花米草与芦苇耐盐生理特征的比较分析

以天津滨海滩涂外来植物互花米草和本地种芦苇为研究对象,对两种植物根、茎、叶3个器官保护酶(超氧化物歧化酶(SOD)、过氧化物酶（POD）、过氧化氢酶(CAT))和膜脂过氧化产物丙二醛(MDA)、游离脯氨酸、可溶性糖以及质膜相对透性及其季节动态变化进行了测定。结果表明：（1）互花米草体内SOD、POD、CAT酶活性、游离脯氨酸、可溶性糖含量在整个生长季节较芦苇偏低;（2）游离脯氨酸和可溶性糖是互花米草和芦苇体内重要的有机渗透调节物质;(3)两种植物根、茎、叶的质膜相对透性在整个生长季节基本保持稳定,但互花米草质膜相对透过性高于芦苇。该研究有利于解释互花米草适应潮间带生存环境的部分机制,并且从生理生态学特性角度说明其竞争力高于芦苇的原因。     

The Leaf Movements of Soybean, a Short-day Plant

If Bünning is correct in supposing that illumination ofa short-day plant during its skotophases prevents its generalmetabolism from reaching the normal ‘skotophile maximum’,leaf movements, too, should be diminished in non-inductive daylengths.‘Biloxi’ soybean is a well-known short-day plantand its leaflets show pronounced movement between day and night.However, measurement of the angle between the day and nightpositions of the leaves did not reveal any difference in longand short days.     

Comparison of Chlorophyll Meter Readings with Leaf Chlorophyll Concentration in Amaranthus vlitus: Correlation with Physiological Processes1

The portable chlorophyll meter (SPAD-502) has been successfully used for a rapid and direct estimation of total chlorophyll content (TCHL) in the leaves of some crops. In this work, SPAD-502 meter readings and TCHL concentration were compared for the leaves of Amaranthus vlitus L., a common weed. SPAD readings were linearly and positively correlated to TCHL concentration in the leaves. A linear correlation was also shown between SPAD-502 readings and some physiological parameters of the leaves, such as photosynthesis, transpiration, and stomatal conductance.     

Physiological Characterization of Dicarboxylate-Induced Pleomorphic Forms of Bradyrhizobium japonicum

When Bradyrhizobium japonicum I-110 was transferred into medium containing 40 mM succinate or 40 mM fumarate, over 90% of the bacteria acquired a swollen, pleomorphic form similar to that of bacteroids. The induction of pleomorphism was dependent on the carbon substrate and concentration but was independent of the hydrogen ion and sodium ion concentration. Cell extracts of rod-shaped and pleomorphic cells contained enzymes required for sugar catabolism and gluconeogenesis. Variations in these enzyme profiles were correlated with the carbon source used and not with the conversion to the bacteroid-like morphology. Rod-shaped cells cultured on glucose or 10 mM succinate transported glucose and succinate; however, the pleomorphic cells behaved similarly to symbiotic bacteroids in that they lacked the ability to transport glucose and transported succinate at lower rates than did rod-shaped cells.     

Examining Plant Physiological Responses to Climate Change through an Evolutionary Lens

Integrating knowledge from physiological ecology, evolutionary biology, phylogenetics, and paleobiology provides novel insights into factors driving plant physiological responses to both past and future climate change.Since the Industrial Revolution began approximately 200 years ago, global atmospheric carbon dioxide concentration ([CO₂]) has increased from 270 to 401 µL L⁻¹, and average global temperatures have risen by 0.85°C, with the most pronounced effects occurring near the poles (IPCC, 2013). In addition, the last 30 years were the warmest decades in 1,400 years (PAGES 2k Consortium, 2013). By the end of this century, [CO₂] is expected to reach at least 700 µL L⁻¹, and global temperatures are projected to rise by 4°C or more based on greenhouse gas scenarios (IPCC, 2013). Precipitation regimes also are expected to shift on a regional scale as the hydrologic cycle intensifies, resulting in greater extremes in dry versus wet conditions (Medvigy and Beaulieu, 2012). Such changes already are having profound impacts on the physiological functioning of plants that scale up to influence interactions between plants and other organisms and ecosystems as a whole (Fig. 1). Shifts in climate also may alter selective pressures on plants and, therefore, have the potential to influence evolutionary processes. In some cases, evolutionary responses can occur as rapidly as only a few generations (Ward et al., 2000; Franks et al., 2007; Lau and Lennon, 2012), but there is still much to learn in this area, as pointed out by Franks et al. (2014). Such responses have the potential to alter ecological processes, including species interactions, via ecoevolutionary feedbacks (Shefferson and Salguero-Gómez, 2015). In this review, we discuss microevolutionary and macroevolutionary processes that can shape plant responses to climate change as well as direct physiological responses to climate change during the recent geologic past as recorded in the fossil record. We also present work that documents how plant physiological and evolutionary responses influence interactions with other organisms as an example of how climate change effects on plants can scale to influence higher order processes within ecosystems. Thus, this review combines findings in plant physiological ecology and evolutionary biology for a comprehensive view of plant responses to climate change, both past and present.Open in a separate windowFigure 1.A, Abiotic conditions directly affect plant physiological traits. Also, the probability that a given species persists with climate change (both in the past and future) is influenced by the degree of phenotypic plasticity in these traits, the ability of populations to migrate and track environmental conditions in space, and the potential for populations to evolve traits that are adaptive in the novel environment. Interactions between plants and other organisms also affect plant physiology, the strength of selection on plant traits, and the probability of persistence. Climate change alters species interactions via direct effects on plant antagonists and mutualists and via changes in plant traits that influence the dynamics of these interactions. B, Following an environmental perturbation (vertical dashed line), plant populations with low genetic and/or phenotypic variability are unlikely to persist (red line). Phenotypic plasticity can facilitate the tolerance of environmental change over the short term (blue line). Migration to a more favorable environment and/or the evolution of adaptive traits (including greater plasticity) can facilitate long-term responses to environmental change (orange line).Due to rapid climate change, plants have become increasingly exposed to novel environmental conditions that are outside of their physiological limits and beyond the range to which they are adapted (Ward and Kelly, 2004; Shaw and Etterson, 2012). Plant migration may not keep pace with the unprecedented rate of current climate change (Loarie et al., 2009); therefore, rapid evolutionary responses may be the major process by which plants persist in the future (Franks et al., 2007; Alberto et al., 2013). In addition, although plants may have evolved physiological plasticity that produces a fitness advantage in novel environments, climate change may be so extreme as to push plants beyond tolerance ranges even in the most plastic of genotypes (Anderson et al., 2012).

ADVANCES

• Rapid climate change is disrupting long-standing patterns of natural selection on plant physiological traits. Microevolutionary responses to these changes can occur over time scales relevant to ecological processes.
• Emerging macroevolutionary analyses using large, time-calibrated phylogenies provide insight into evolutionary changes in plant physiology and species diversification rates following past climate change events.
• Past conditions, such as low [CO₂] during glacial cycles, likely produced lingering adaptations that could limit plant physiological responses to current and future climate change.
• Climate change can affect plant traits, fitness, and survival indirectly via shifts in biotic interactions. The ecoevolutionary consequences of altered species interactions can be as important as the direct effects of climate change on plant physiology.

Understanding the potential for evolutionary responses at the physiological level is a key challenge that must be met in order to improve predictions of plant response to climate change. A focus on physiology is critical because these processes scale from individual to ecosystem levels. For example, [CO₂] rise and climate change that alter photosynthetic rates may shift plant growth rates, overall productivity, and resource use (Ainsworth and Rogers, 2007; Norby and Donald, 2011; Medeiros and Ward, 2013). Other physiological responses to altered climate include increasing leaf sugars with elevated [CO₂], which may influence major life history traits such as flowering time and fitness via sugar-sensing mechanisms (Springer et al., 2008; Wahl et al., 2013). At higher scales, shifts in source/sink relationships of photosynthate can influence seedling survival, whole-plant growth, competitive ability within the broader plant community, symbiotic interactions, and fitness. Therefore, the potential for physiological functioning to evolve in response to climate change will be a key indicator of plant resiliency (or lack thereof) in future environments. Defining physiological components that correlate with fitness, particularly in newly emerging environments, will allow us to identify candidate processes that may be under strong selection in future environments and to predict the composition and functioning of future plant populations and communities (Kimball et al., 2012).It is clear that long-term changes in the environment spanning millions of years of plant evolution have shaped the major physiological pathways that are present in modern plants (Edwards et al., 2010; Sage et al., 2012), and these pathways will determine the range of physiological tolerances for the response to novel environments of the future. In addition, relatively recent conditions in the geologic record have shaped selective pressures on plant physiology (Ward et al., 2000) and may influence the ability of plants to respond to future conditions. For example, the peak of the last glacial period (20,000 years ago) represents a fascinating time when low [CO₂] (180–200 µL L⁻¹) likely constrained the physiological functioning of C₃ plants. During that period, [CO₂] was among the lowest values that occurred during the evolution of land plants (Berner, 2006). Modern C₃ annuals grown at glacial [CO₂] exhibit an average 50% reduction in photosynthesis and growth as well as high levels of mortality and reproductive failure relative to plants grown at modern [CO₂] (Polley et al., 1993; Dippery et al., 1995; Sage and Coleman, 2001; Ward and Kelly, 2004). Thus, this period likely imposed strong selective pressures on plants, as evidenced directly by artificial selection experiments (Ward et al., 2000) and in the recent geologic record (Gerhart and Ward, 2010).A series of key questions have now emerged. (1) How will plants evolve in response to rapid climate change? (2) How will evolutionary history and species interactions influence this evolutionary trajectory? (3) How have past responses to climate change in the geologic record influenced current and potentially future responses to a rapidly changing environment? To address these questions, we report on emerging concepts in the broad field of evolutionary physiology, paying specific attention to processes ranging from microevolution to macroevolution, the influence of species interactions on these processes, and insights from paleobiology (where we provide new findings). This review is not intended to cover all of the current ground-breaking work in this area but rather to provide an overview of how a multitude of approaches can influence our overall understanding of how plant physiological evolution has altered past ecosystems as well as those that will emerge during the Anthropocene Epoch.     

Paenibacillus polymyxa Invades Plant Roots and Forms Biofilms

Paenibacillus polymyxa is a plant growth-promoting rhizobacterium with a broad host range, but so far the use of this organism as a biocontrol agent has not been very efficient. In previous work we showed that this bacterium protects Arabidopsis thaliana against pathogens and abiotic stress (S. Timmusk and E. G. H. Wagner, Mol. Plant-Microbe Interact. 12:951-959, 1999; S. Timmusk, P. van West, N. A. R. Gow, and E. G. H. Wagner, p. 1-28, in Mechanism of action of the plant growth promoting bacterium Paenibacillus polymyxa, 2003). Here, we studied colonization of plant roots by a natural isolate of P. polymyxa which had been tagged with a plasmid-borne gfp gene. Fluorescence microscopy and electron scanning microscopy indicated that the bacteria colonized predominantly the root tip, where they formed biofilms. Accumulation of bacteria was observed in the intercellular spaces outside the vascular cylinder. Systemic spreading did not occur, as indicated by the absence of bacteria in aerial tissues. Studies were performed in both a gnotobiotic system and a soil system. The fact that similar observations were made in both systems suggests that colonization by this bacterium can be studied in a more defined system. Problems associated with green fluorescent protein tagging of natural isolates and deleterious effects of the plant growth-promoting bacteria are discussed.