Comparative ecophysiology of Encelia farinosa and Encelia frutescens

Summary Encelia farinosa and Encelia frutescens are drought-decidous shrubs whose distributions overlap throughout much of the Sonoran Desert. During hot and dry periods, leaves of E. farinosa utilize increased leaf reflectance to reduce leaf temperature, whereas leaves of E. frutescens have substantially higher leaf conductances and rely on increased transpirational cooling to reduce leaf temperature. E. farinosa is common on the dry slope microhabitats, whereas E. frutescens occurs only in wash microhabitats where greater soil moisture is available to provide the water necessary for transpirational cooling. E. farinosa tends not to persist in wash microhabitats because of its greater susceptibility to flashfloods. The consequences and significance of increased leaf reflectance versus increased transpirational cooling to leaf temperature regulation are discussed.     

INFLUENCE OF IRRADIATION,SOIL WATER POTENTIAL,AND LEAF TEMPERATURE ON LEAF MORPHOLOGY OF A DESERT BROADLEAF,ENCELIA FARINOSA GRAY (COMPOSITAE)

Laboratory experiments were performed to evaluate observed seasonal changes in leaf morphology of the desert perennial shrub, Encelia farinosa Gray. Plants were grown under low or high conditions of photosynthetically active irradiation, soil water potential (Ψ^soil), and leaf temperature (8 different experimental regimes). The relative growth rate, leaf water vapor conductance, leaf water potential, and leaf length were all greater for the high Ψ^soil regimes, the largest leaves occurring at low irradiation. High irradiation during growth led to thicker leaves with a higher internal to external leaf area ratio (A^mes/A); low Ψ^soil tended to increase A^mes/A somewhat. High irradiation also led to decreased absorptance to solar irradiation caused by increased pubescence. High leaf temperature during development resulted in slightly smaller, thicker leaves with higher A^mes/A. Thus, irradiation appeared to have its major influence on leaf thickness, A^mes/A, and absorptance, with a secondary effect on leaf length; Ψ^soil affected primarily leaf length, growth rate, and water status, and secondarily A^mes/A. Results are discussed with regard to recent ecophysiological studies on the observed seasonal changes in leaf morphology of E. farinosa.     

Leaf hairs: Effects on physiological activity and adaptive value to a desert shrub

Summary The effects of leaf hairs on photosynthesis, transpiration, and leaf energy balance were measured on the desert shrub Encelia farinosa in order to determine the adaptive significance of the hairs. The pubescence reduces leaf absorptance resulting in a reduced heat load, and as a consequence lower leaf temperatures and lower transpiration rates. In its native habitat where air temperatures often exceed 40° C, the optimum temperature for photosynthesis in E. farinosa occurs at 25° C, and at leaf temperatures above 35° C net photosynthesis declines precipitously. An advantage of leaf pubescence is that it allows a leaf temperature much lower than air temperature. As a result, leaf temperatures are near the temperature optimum for photosynthesis and high, potentially lethal leaf temperatures are avoided. However, there is a disadvantage associated with leaf pubescence. By reflecting quanta that might otherwise be used in photosynthesis, the presence of leaf hairs reduces the rate of photosynthesis. A tradeoff model was used to assess the overall advantage of possessing leaf hairs. In terms of the carbon gaining capacity of the leaf, the model predicted that for different environmental conditions different levels of leaf pubescence were optimal. In other words, under aird conditions and/or high air temperatures, leaves of E. farinosa would have a higher rate of photosynthesis by being pubescent than by not being pubescent. The predictions from this model agreed closely with observed patterns of leaf pubescence in the field.C.I.W.-D.P.B. Publication No. 613     

Intraspecific variation of drought adaptation in brittlebush: leaf pubescence and timing of leaf loss vary with rainfall

Reflective leaf pubescence of the desert shrub Encelia farinosa (brittlebrush) reduces leaf temperature and plant water loss, and is considered adaptive in xeric environments. Yet, little is known about intraspecific variation in this trait. Among three populations in the northern range of E. farinosa, which span a very broad precipitation gradient, both leaf absorptance variation and differences in the timing of drought-induced leaf loss were broadly associated with climatic variability. Where mean annual rainfall was greatest, drought-induced leaf loss was earliest, but these plants also had higher population-level mean leaf absorptance values. Higher absorptance increases the relative dependence on latent heat transfer (transpirational cooling), but it also provides greater instantaneous carbon assimilation. Plants at the driest site reached lower leaf absorptance values and maintained leaves longer into the drought period. Lower leaf absorptance reduces water consumption, and extended leaf longevity may buffer against the unpredictability of growing conditions experienced in the driest site. These observations are consistent with a trade-off scenario in which plants from wetter regions might trade off water conservation for higher instantaneous carbon gain, whereas plants from drier regions reduce water consumption and extend leaf longevity to maintain photosynthetic activity in the face of unpredictable growing conditions. Received: 2 April 1997 / Accepted: 11 August 1997     

Characteristics of Encelia species differing in leaf reflectance and transpiration rate under common garden conditions

Summary The performance of coastal and desert species of Encelia (Asteraceae) were evaluated through common garden growth observations. The obectives of the study were to evaluate the roles of leaf features, thought to be of adaptive value (increased leaf reflectance and/or transpirational cooling), on plant growth in the hot, arid, desert garden versus their impact on growth under cooler, relatively more moist coastal garden conditions. E. californica native to the coast of southern California and E. farinosa, and E. frutescens, interior desert species, were grown in common gardens at coastal (Irvine, California) and interior (Phoenix, Arizona) sites under both irrigated and natural conditions. Although all species survived in both gardens during the two and a half year study period, there were large differences in their sizes. In the desert garden, leaf conductance and leaf water potential were both lower than at the coastal site. E. californica shrubs were leafless much of the time under natural conditions in the desert garden and had the smallest size there as well. Under natural conditions, E. farinosa, with its reflective leaf surface, was able to maintain lower leaf temperatures and attained a large size than the other two species in the desert garden. The green-leaved species (E. californica and E. frutescens) were not able to maintain leaves into the drought periods in the desert garden, with the exception of the irrigated E. frutescens which did maintain its leaf area if provided with supplemental watering to maintain transpirational leaf cooling. In the coastal garden, all species survived and there were few clear differences in the physiological characteristics among the three species. E. californica, the coastal native, attained a larger size in the coastal garden when compared with either of the two desert species.     

Chlorophyll a fluorescence, enzyme and antioxidant analyses provide evidence for the operation of alternative electron sinks during leaf senescence in a stay-green mutant of Festuca pratensis

Mutation of the sid gene in Festuca pratensis prevents chlorophyll degradation. The senescing leaves retain their chlorophyll complement and stay green. Nevertheless, CO2 assimilation and ribulose-bisphosphate carboxylase/oxygenase content decline in both mutant and wild-type plants. Photosynthesis and chlorophyll a fluorescence measurements were performed in air and at low oxygen to prevent photorespiration. The maximum extractable activity of ribulose 1,5 bisphosphate carboxylase was higher in the senescent mutant leaves than in those of the wild-type control hut Mas much lower than that observed in the mature leaves of either genotype. The activation state of this enzyme was similar in mutant and wild-type lines at equivalent stages of development. Analysis of chlorophyll a fluorescence quenching with varying irradianco showed similar characteristics for mature leaves of the two genotypes. Genotypic variations in photosystem II (I'SII) efficiency were observed only in the senescent leaves. Photochemical quenching and the quantum efficiency of PSII were greater in the senescent mutant leaves than in (he wild type at a given irradiance. The calculated electron flux through PSII was substantially higher in the mutant with a greater proportion of electrons directed to photorespiration. Maximum catalytic activities of ascorbate peroxidase decreased in senescent compared to mature leaves of both genotypes, while glutathione reductase and monodehydroascorbate reductase were unchanged in both cases. Superoxide dismutase activity was approximately doubled and dehydroascorbate reductase activity was three times higher in senescent leaves compared with the mature leaves of both genotypes. In no case was there a difference in enzyme activities between mutant and wild type at equivalent growth stages. The pool of reduced ascorbate was similar in the mature leaves of the two genotypes, whereas it was significantly higher in the senescent leaves of the mutant compared with the wild type. Conversely, the hydrogen peroxide content was significantly higher in the mature leaves of the wild type than in those of the mutant, but in senescent leaves similar values were obtained. In leaves subjected to chilling stress the reduced ascorbate pool was higher in both mature and senescent leaves of the mutant than in their wild-type counterparts. Similarly, the hydrogen peroxide pool was significantly lower in both mature and senescent leaves of the mutant than in the wild type. We conclude that, in spite of deceased CO₂ assimilation, the mutant is capable of high rates of electron Slow. The high ascorbate/hydrogen peroxide ratio observed in the mutant, particularly at low temperatures, suggests that the senescent leaves are not subject to enhanced oxidative stress.     

Sensitivity to Abscisic Acid Modulates Positive Interactions between Arabidopsis thaliana Individuals

The ability of abscisic acid (ABA) to modulate positive interactions between Arabidopsis thaliana individuals under salinity stress was investigated using abi1-1 (insensitive to ABA), era1-2 (hypersensitive to ABA) mutant and wild type plants. The results showed that sensitivity to ABA affects relative interaction intensity (RII) between Arabidopsis thaliana individuals. The neighbor removal experiments also confirmed the role of phenotypic responses in linking plant-plant interactions and sensitivity to ABA. For abi1-1 mutants, the absolute value differences between neighbor removal and control of stem length, root length, leaf area, leaf thickness, flower density, above biomass/belowground biomass (A/U), photosynthetic rate, stomatal conductance, leaf water content and water-use efficiency were smaller than those of the wild type, while for era1-2 mutants, these absolute value differences were larger than those of the wild type. Thus, it is suggested that positive interactions between Arabidopsis thaliana individuals are at least partly modulated by different sensitivity to ABA through different physiological and phenotypic plasticity.     

Puzzle box,a tobacco line with flowers that mix floral and inflorescence characteristics

We characterized the development of a tobacco morphological mutant, puzzle box, previously obtained by selection for resistance to an inhibitor of an enzyme in the polyamine biosynthetic pathway. Puzzle box plants are shorter than wild type with smaller leaves and an irregular leaf plastochron. The diameter and shape of the puzzle box shoot apex are similar to wild type. In puzzle box plants, the terminal flower develops but not the cymose inflorescence. This flower has a variable phenotype with more than five sepals, five petals, and five stamens. The organs in the fourth whorl are produced by carpellike primordia and contain tissue biochemically similar to wild type transmitting tissue. These organs form a cylinder within which additional floral organs are produced. Some cultures of puzzle box buds and excised cylinders produce additional floral organs. The inflorescence and floral programs may be expressed together in puzzle box.     

Leaf catalase mRNA and catalase-protein levels in a high-catalase tobacco mutant with o(2)-resistant photosynthesis

Experiments were conducted with a tobacco (Nicotiana tabacum) mutant with 40 to 50% greater catalase activity than wild type that is associated with a novel form of O₂-resistant photosynthesis. The apparent K_m for H₂O₂ was the same in mutant and wild-type leaf extracts. Tobacco RNAs were hybridized with Nicotiana sylvestris catalase cDNA, and a threefold greater steady-state level of catalase mRNA was found in mutant leaves. Steady-state levels of ribulose-1,5-bisphosphate carboxylase small subunit mRNA were similar in mutant and wild type. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of partially purified catalase showed that the protein concentration in the band corresponding to catalase was higher in the mutant than in the wild type. Separation of leaf catalase proteins by isoelectric focusing revealed the presence of five major bands and one minor band of activity. The distribution of the catalase activity among these forms was similar in mutant and wild type, although the total activity was higher in the mutant in all five major bands. The results indicate that the enhanced catalase activity in mutant leaves is caused by an increase in synthesis of catalase protein and that this trait is mediated at the nucleic acid level.     

Regulation of Dark-Induced Stomatal Closure in <Emphasis Type="Italic">Arabidopsis</Emphasis> Dynamin-Like Protein 1E (<Emphasis Type="Italic">adl1e</Emphasis>) Mutant Leaves

Arabidopsis thaliana dynamin-like protein 1E (ADL1E) is known to regulate mitochondrial elongation. The adl1e mutant has no morphological phenotype, and the growth and photosynthetic activity of the mutant are similar to those of the wild type. Leaf O₂ uptake, which is supported by mitochondrial activity in the dark, is increased 1.7-fold by mutation in adl1e gene. The ATP content in the dark of guard and mesophyll cell protoplasts (GCPs and MCPs, respectively) was 2.5- to 4-fold higher in GCPs of the mutant and the wild type, and increased upon the addition of glucose in both genotypes. Oligomycin, an inhibitor of mitochondrial ATPase, suppressed ATP synthesis in both GCPs and MCPS isolated from adl1e plants, indicating that mutant had higher mitochondrial activity. The stomatal apertures of mutant and wild-type plants were then analyzed in vitro. In the light, the stomata of both genotypes showed similar patterns of opening. However, in the dark response, the stomata of the adl1e mutant closed faster than did those of the wild type. Oligomycin severely inhibited dark-induced stomatal closure in both cell types. The results suggest that stomatal closure in the dark is governed by cytosolic ATP concentration, which is stimulated by mitochondrial activity.     

Reduction in chlorophyll content without a corresponding reduction in photosynthesis and carbon assimilation enzymes in yellow-green oil yellow mutants of maize

The photosynthetic properties of a yellow lethal mutant, Oy/oy, and two yellow-green mutants of maize which are allelic (a homozygous recessive oy/oy and a heterozygous dominant Oy/+) were examined. Although Oy/oy had little or no chlorophyll or capacity for CO₂ fixation compared to normal siblings, it had 28% as much ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) activity, and from 40% to near normal activities of C₄ cycle enzymes.Both yellow-green mutants had only half as much chlorophyll per leaf area as normal green seedlings in greenhouse-grown plants in winter and spring. However, the absorbance of light by the mutants was relatively high, as their transmittance was only 5 to 8% greater than normal leaves. In winter-grown greenhouse plants, the activities of Rubisco and several C₄ cycle enzymes in the mutants were unaffected and similar to those of normal seedlings on a leaf area basis. After allowing for small differences in leaf absorbance, the light response curves for photosynthesis in the mutants were similar on a leaf area basis but much higher on a chlorophyll basis than those of the normal seedlings. In spring-grown greenhouse plants the enzyme activities and photosynthesis rates were about 30% lower per leaf area in the yellow-green mutant leaves compared to the wild type. The maximum carboxylation efficiency (measured under low CO₂ and 1000 mol quanta m^-2 s^-1) in the mutants and normal leaves was similar on a Rubisco protein basis. The results indicate that maize can undergo a 50% reduction in chlorophyll content without a corresponding reduction in enzymes of carbon assimilation, and still maintain a high capacity for photosynthesis.Abbreviations Chl chlorophyll - PEP phosphoenolypruvate - Rubisco ribulose-1,5-bisphosphate carboxylase oxygenase This research was supported by CSIRO and by USDA Competitive Grant 86-CRCR-1-2036.     

Changes in carbohydrate metabolism and assimilate export in starch-excess mutants of Arabidopsis

The aim of this work was to investigate the effects on carbohydrate metabolism of a reduction in the capacity to degrade leaf starch in Arabidopsis. The major roles of leaf starch are to provide carbon for sucrose synthesis, respiration and, in developing leaves, for biosynthesis and growth. Wild-type plants were compared with plants of a starch-excess mutant line (sex4) deficient in a chloroplastic isoform of endoamylase. This mutant has a reduced capacity for starch degradation, leading to an imbalance between starch synthesis and degradation and the gradual accretion of starch as the leaves age. During the night the conversion of starch into sucrose in the mutant is impaired; the leaves of the mutant contained less sucrose than those of the wild type and there was less movement of ¹⁴C-label from starch to sucrose in radio-labelling experiments. Furthermore, the rate of assimilate export to the roots during the night was reduced in the mutant compared with the wild type. During the day however, photosynthetic partitioning was altered in the mutant, with less photosynthate partitioned into starch and more into sugars. Although the sucrose content of the leaves of the mutant was similar to the wild type during the day, the rate of export of sucrose to the roots was increased more than two-fold. The changes in carbohydrate metabolism in the mutant leaves during the day compensate partly for its reduced capacity to synthesize sucrose from starch during the night.     

Intraspecific competitive effects on water relations,growth and reproduction in Encelia farinosa

Summary An experiment was conducted to assess the importance of intraspecific competition on water relations, growth and reproductive output in Encelia farinosa, a common deciduous-leaved shrub of the Sonoran Desert. Nearest neighbor analyses in monospecific stands indicated that plants exhibited a clumped distribution. Plant size and nearest neighbor distance were positively correlated, inferring intraspecific competition. Removal experiments monitored for two years indicated that plants now without neighbors had higher leaf water potentials, higher leaf conductances, and a greater leaf area than control plants. As a consequence, growth rates and reproductive output were significantly higher in plants without neighbors. These data strongly support the notion that warm desert plants with a contagious spatial distribution compete for water.     

Functional,histological and biomechanical characterization of wheat water‐mutant leaves

A wheat (Triticum turgidum subsp. durum) mutant, generated with sodium azide from wild‐type (WT) cv. ‘Trinakria’, differs in its water affinity of dry leaves, and was designated as a water‐mutant. Compared with the WT, water‐mutant leaves have lower rates of water uptake, while stomatal and cuticular transpiration do not differ. The nuclear magnetic resonance proton signals used for image reconstruction of leaf cross sections showed differences between these genotypes for the T₁ proton spin–density and the T₂ proton spin–spin relaxation time. Structural and histochemical analyses at midrib level showed that the water‐mutant has thinner leaves, with more and smaller cells per unit area of mesophyll and sclerenchyma, and has altered staining patterns of lignin and pectin‐like substances. Stress–strain curves to examine the rheological properties of the leaves showed a biphasic trend, which reveals that the tensile strength at break load and the elastic modulus of the second phase of the water‐mutant are significantly higher than for the WT. These data support the proposal of interrelationships among local biophysical properties of the leaf, the microscopic water structure, the rheological properties and the water flux rate across the leaf. This water‐mutant can be used for analysis of the genetic basis of these differences, and for identification of gene(s) that govern these traits.     

Mutants of Nicotiana plumbaginifolia with increased sensitivity to auxin.

Summary Two non-allelic, monogenic recessive mutations, ausl and aus2, have been isolated which result in auxin hypersensitivity in mutant Nicotiana plumbaginifolia plants. At relatively low concentrations of indole-3-acetic acid or 1-naphthaleneacetic acid, the elongation growth of mutant seedling hypocotyls is more inhibited than in the case of the wild type; at high auxin concentrations, mutant seedlings are killed. The leaves of mature mutant plants degenerate after a spray treatment with auxin that has only a mild, transient effect on the wild type. Seedling hypocotyls of ausl are more sensitive to l-tryptophan than those of the wild type but do not differ in their response to the d-isomer. The mutant is also more sensitive to ethylene and the ethylene precursor 1-aminocyclopropane-l-carboxylic acid, but not to either 6-benzyladenine or abscisic acid. Mutant seedlings display several distinct morphological characters: mild leaf epinasty, short primary root, increased root branching and no root hairs.     

拟南芥ABA敏感突变体asm1的分离与鉴定

以拟南芥(Arabidopsis thaliana)为研究材料,从T-DNA突变体库中筛选分离得到1株脱落酸(ABA)敏感突变体asm1(ABA sensitive mutant 1,asm1),在含有ABA的培养基中,与野生型相比,asm1突变体的根伸长明显受到抑制,且其种子萌发结果显示asm1对ABA同样表现出敏感特性。在生长发育方面,asm1突变体抽苔时间提前,植株矮化,并且荚果长度明显小于野生型。利用远红外成像系统分析发现,在干旱胁迫下asm1突变体叶面温度高于野生型;失水率分析显示突变体失水率降低以及水分散失减少。遗传学分析表明,asm1是单基因隐性突变且与一个T-DNA插入共分离;通过图位克隆成功获得候选基因ASM1。RT-PCR结果显示,在突变体中ASM1的表达受到抑制,并且能够调控多种ABA信号通路和胁迫应答基因的表达水平。研究结果表明,ASM1可能参与调控ABA信号转导并应答干旱胁迫。     

Mechanism for phenol tolerance in phenol-degrading Comamonas testosteroni strain

Comamonas testosteroni P15 and its mutant strain E23 can tolerate and utilize phenol as the sole source of carbon and energy at up to 15 mM and 20 mM, respectively. Compared to the wild type P15, mutant E23 showed higher values of K _s and K _i but a lower μ_max value, and had lower phenol hydroxylase and catechol 2,3-dioxygenase activities. Without phenol exposure, mutant E23 demonstrated a two-fold greater amount of cardiolipin than the wild type P15. Upon exposure to phenol, an increase in cardiolipin at the expense of phosphatidylethanolamine was observed in the wild type P15. However, there was no significant difference in major phospholipid contents between mutant E23 cells grown in the presence or absence of phenol. It was noted that the ratio of trans/cis fatty acids of phosphatidylethanolamine and cardiolipin in mutant E23 was 65–70% higher than that in the wild type P15. In the absence of phenol, the degree of saturation of cardiolipin in mutant E23 was 33% higher than that in wild type P15. In contrast to earlier findings, an increase in C16:1 9trans with a simultaneous decrease in C18:1 11cis instead of C16:1 9cis was observed in specific classes of phospholipids. Received: 30 July 1998 / Received last revision: 16 November 1998 / Accepted: 12 December 1998     

Extension-growth responses and expression of flavonoid biosynthesis genes in the Arabidopsis hy4 mutant

The hy4 mutant of Arabidopsis thaliana(L.) Heynh. was previously shown to be impaired in the suppression of hypocotyl extension specifically by blue light. We report here that hy4 is altered in a range of blue-light-mediated extension-growth responses in various organs in seedlings and mature plants: it shows greater length of bolted stems, increased petiole extension and increased leaf width and area in blue light compared to the wild type. The hy4 mutant shows decreased cotyledon expansion in both red and blue light compared to the wild type. Anthocyanin formation and the expression of several flavonoid biosynthesis genes is stimulated by blue light in the wild type but to a much lower extent in hy4. The results indicate that the HY4 gene product is concerned with the perception of blue light in a range of extension-growth and gene-expression responses in Arabidopsis.Abbreviations DFR dihydroflavonol reductase - CHS chalcone synthase - CHI chalcone isomerase We thank the UK Agricultural and Food Research Council for supporting this work through the award of a research grant to G.I.J. We are grateful to Robert Brown for excellent technical assistance and Drs B.W. Shirley (Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, USA), C.D. Silflow (Department of Genetics and Cell Biology, University of Minnesota, St. Paul, USA) and I.E. Somssich (Department of Biochemistry, Max-Planck-Institut, Köln, Germany) for providing plasmid DNA.     

GBSS‐BINDING PROTEIN,encoding a CBM48 domain‐containing protein,affects rice quality and yield

The percentage of amylose in the endosperm of rice (Oryza sativa) largely determines grain cooking and eating qualities. Granule‐bound starch synthase I (GBSSI) and GBSSII are responsible for amylose biosynthesis in the endosperm and leaf, respectively. Here, we identified OsGBP, a rice GBSS‐binding protein that interacted with GBSSI and GBSSII in vitro and in vivo. The total starch and amylose contents in osgbp mutants were significantly lower than those of wild type in leaves and grains, resulting in reduced grain weight and quality. The carbohydrate‐binding module 48 (CBM48) domain present in the C‐terminus of OsGBP is crucial for OsGBP binding to starch. In the osgbp mutant, the extent of GBSSI and GBSSII binding to starch in the leaf and endosperm was significantly lower than wild type. Our data suggest that OsGBP plays an important role in leaf and endosperm starch biosynthesis by mediating the binding of GBSS proteins to developing starch granules. This elucidation of the function of OsGBP enhances our understanding of the molecular basis of starch biosynthesis in rice and contributes information that can be potentially used for the genetic improvement of yield and grain quality.