On the ecological and evolutionary significance OF BRANCH AND LEAF MORPHOLOGY IN aquatic Sphagnum (Sphagnaceae)

In aquatic environments difiusivity is low and CO₂ availability can limit plant growth. The hypothesis that natural selection has favored morphological features that reduce resistance to diffusion of CO₂ was tested using three phylogenetically independent species pairs from the genus Sphagnum (S. macrophyllum and 5. strictum; S. portoricense and S. papillosum; and S. trinitense and S. recurvum). The aquatic (former) and the nonaquatic (latter) species were grown submerged and emerged in a common garden and used for studies of form and function. Aquatic taxa all had similar morphological features that included larger, thinner branch leaves arranged at lower densities and photosynthetic cells more greatly exposed at the leaf surface. The relationship between observed branch and leaf morphology and boundary layer resistance in the S. trinitense–S. recurvum species pair was assessed by measuring diffusion and convection of ions onto nickel-plated models in a variable-speed electrochemical fluid tunnel. For all flow speeds and orientations, the aquatic S. trinitense model had thinner boundary layers than the nonaquatic S. recurvum model. Analysis of stable isotopes of carbon from the growth experiment corroborated results from the fluid-tunnel experiments. The aquatic taxa all had lower δ ¹³C values when grown submerged compared to their nonaquatic pair with the exception of the nonaquatic S. strictum, which was removed due to low growth rates. These results indicate that aquatic species did experience lower overall resistance to CO₂ uptake than nonaquatic taxa. Our observations suggest that aquatic habitats do select for morphological features that lower resistance to gas exchange.     

Geographical variation and genetic analysis of leaf shape inCrepis tectorum (Asteraceae)

Canonical variate analysis of plants raised in a uniform environment was used to study the pattern of geographical variation in leaf shape ofCrepis tectorum (Asteraceae). The diversity in leaf shape was much greater among populations confined to areas with exposed bedrock in the Baltic region than among weed populations scattered throughout Europe and Canada. A Ward's clustering linked outcrop populations from the archipelago of SW. Finland and the islands of Öland (Sweden) and Saaremaa (Estonia) due to the deeply lobed leaves characterizing these populations, while outcrop populations along the coast of E. Sweden were grouped due to their weakly lobed, narrow and dentate leaves. Most of the weed populations were grouped together but there was no tendency for the variation in this group to be related to habitat or geographical location. A mosaic of variation reflected in sharp (random) differentiation among local populations was superimposed on the large-scale ecogeographical pattern.—Crossing data indicated that most of the variation in degree of leaf dissection is governed by one major gene with deeply lobed leaves dominant over weakly lobed leaves. I suggest that the simple pattern of inheritance may have favoured rapid evolutionary changes in leaf shape, particularly in the Baltic area which emerged relatively late from the sea. Genetic correlations may have constrained the pattern of variation at higher taxonomic levels, since some of the trait associations detected in a segregating F₂ generation were also found at the among-population level.     

DIFFUSION RESISTANCE IN LEAVES AS RELATED TO THEIR STOMATAL ANATOMY AND MICRO-STRUCTURE

Transpiration from a plant leaf depends upon the water vapor pressure gradient between the substomatal cavity and the free air beyond the leaf. Transpiration also depends inversely on the resistance of the diffusion pathway through the substomatal cavity, stomate, and surface boundary layer. The value of the diffusion resistance is derived mathematically for Zebrina pendula, Medicago sativa, and Pinus resinosa. The vapor pressure gradient depends on the leaf temperature and therefore is related to the energy budget of the leaf. The exact solution of the diffusion equation is described and limiting examples discussed. The so-called “diameter law” is a special case which is distinctly limited in its application.     

Cotton genotypic variation in the photosynthetic response to irradiance

The photosynthetic response of 8 cotton (Gossypium hirsutum L.) genotypes to changing irradiance was investigated under field conditions during the 1998 through 2000 growing seasons. Equations developed to describe the response of net photosynthetic rate (P_N) to photosynthetic photon flux density (PPFD) demonstrated that, across all irradiances, the two okra leaf-type genotypes photosynthesized at a greater rate per unit leaf area than all of the six normal leaf-type genotypes. This superior photosynthetic performance of the okra leaf-type genotypes can be partially explained by their 13 % greater leaf chlorophyll content relative to that of the normal leaf-type genotypes. The 37 % reduction in leaf size brought upon by the okra leaf trait may have concentrated the amount of photosynthetic machinery per unit leaf area. Nevertheless, the lack of sufficient canopy leaf surface area suppressed the potential yield development that could accompany the higher P_N per unit leaf area.This revised version was published online in March 2005 with corrections to the page numbers.     

不同性状的棉花及其杂交F1代对棉铃虫的抗性

通过连续两年的田间试验,系统、全面地研究了棉花对棉铃虫(Helicoverpa armigera)的形态抗虫作用。研究结果表明：在小区试验条件下,以百株累积卵量、百株平均幼虫量及百株平均蕾铃受害量为考察指标,红叶可使危害减轻28.1%、31.45%和36.O%;鸡脚叶可使其下降19.0%、25.4%和28.4%;窄卷苞叶使其降低25.8%、32.9%和34.0%;光叶使各指标分别降低32.7%、35.1%和37.3%。高棉酚(油腺)抗性主要表现为对幼虫的抗生作用,使幼虫量下降了45.1%,使蕾铃受害量下降了51.4%。此外,研究还表明,两种抗虫性状的抗性效果有累加作用,鸡脚叶与红叶联合作用使三项指标分别下降达48.3%、55.2%和57.9%;红叶与窄卷苞叶则使危害减轻了52.7%、58.3%和60.6%;具有光叶与较密油腺两个抗虫性状的品种受害可减轻29.9%、54.9%和58.3%。将一些具有相对性状的品种进行杂交,其F₁有不同的抗虫表现。红叶、鸡脚叶和光叶品种与其对照杂交后的F1代因在不同程度上保持了抗虫性状故能表现出抗性,而窄卷苞叶品种与其对照杂交后F1代苞叶正常,则未能表现出抗性。因小区条件限制了无蜜腺抗性的表达,无蜜腺小区未表现出明显差异。     

Mapping and genomic targeting of the major leaf shape gene (L) in Upland cotton (Gossypium hirsutum L.)

Key message

A major leaf shape locus (L) was mapped with molecular markers and genomically targeted to a small region in the D-genome of cotton. By using expression analysis and candidate gene mapping, two LMI1 -like genes are identified as possible candidates for leaf shape trait in cotton.

Abstract

Leaf shape in cotton is an important trait that influences yield, flowering rates, disease resistance, lint trash, and the efficacy of foliar chemical application. The leaves of okra leaf cotton display a significantly enhanced lobing pattern, as well as ectopic outgrowths along the lobe margins when compared with normal leaf cotton. These phenotypes are the hallmark characteristics of mutations in various known modifiers of leaf shape that culminate in the mis/over-expression of Class I KNOX genes. To better understand the molecular and genetic processes underlying leaf shape in cotton, a normal leaf accession (PI607650) was crossed to an okra leaf breeding line (NC05AZ21). An F₂ population of 236 individuals confirmed the incompletely dominant single gene nature of the okra leaf shape trait in Gossypium hirsutum L. Molecular mapping with simple sequence repeat markers localized the leaf shape gene to 5.4 cM interval in the distal region of the short arm of chromosome 15. Orthologous mapping of the closely linked markers with the sequenced diploid D-genome (Gossypium raimondii) tentatively resolved the leaf shape locus to a small genomic region. RT-PCR-based expression analysis and candidate gene mapping indicated that the okra leaf shape gene (L ^o ) in cotton might be an upstream regulator of Class I KNOX genes. The linked molecular markers and delineated genomic region in the sequenced diploid D-genome will assist in the future high-resolution mapping and map-based cloning of the leaf shape gene in cotton.     

Drought‐introduced variability of mesophyll conductance in Gossypium and its relationship with leaf anatomy

Mesophyll conductance (g_m) is one of the major determinants of photosynthetic rate, for which it has an impact on crop yield. However, the regulatory mechanisms behind the decline in g_m of cotton (Gossypium. spp) by drought are unclear. An upland cotton (Gossypium hirsutum) genotype and a pima cotton (Gossypium barbadense) genotype were used to determine the gas exchange parameters, leaf anatomical structure as well as aquaporin and carbonic anhydrase gene expression under well‐watered and drought treatment conditions. In this study, the decrease of net photosynthetic rate (A_N) under drought conditions was related to a decline in g_m and in stomatal conductance (g_s). g_m and g_s coordinate with each other to ensure optimum state of CO₂ diffusion and achieve the balance of water and CO₂ demand in the process of photosynthesis. Meanwhile, mesophyll limitations to photosynthesis are equally important to the stomatal limitations. Considering g_m, its decline in cotton leaves under drought was mostly regulated by the chloroplast surface area exposed to leaf intercellular air spaces per leaf area (S_c/S) and might also be regulated by the expression of leaf CARBONIC ANHYDRASE (CA1). Meanwhile, cotton leaves can minimize the decrease in g_m under drought by maintaining cell wall thickness (T_cw). Our results indicated that modification of chloroplasts might be a target trait in future attempts to improve cotton drought tolerance.     

ARCHAEOPTERIS MACILENTA,ANATOMY AND MORPHOLOGY OF ITS FROND

The stem, rachides, and pinnae of Archaeopteris macilenta, formerly considered to be a fern of Devonian age, comprise a branch system in which the ultimate divisions heretofore referred to as pinnules are the leaves. The primary vascular system of the “frond” is a lobed siphonostele from which leaf traces arise in a spiral sequence. The anatomy of the “rachis” and of the “pinnae” is shown to be similar to that of the stem, Callixylon, which bore these “fronds.” Branching, epidermal pattern and stomates are described for the spirally arranged leaves (fertile pinnules). Attachment and dehiscence of sporangia as well as their stomates are reported. Archaeopteris is retained in the Class Progymnospermopsida which includes plants with gymnospermous anatomy and pteridophytic reproduction. It is suggested that Actinopodium, Svalbardia and Siderella are related closely to Archaeopteris and that this group of genera shows evolutionary stages in webbing of leaves and planation of branch systems. The opportunities for ontogenetic studies of the arborescent genus Archaeopteris are pointed out.     

Reduction of molecular gas diffusion through gaskets in leaf gas exchange cuvettes by leaf‐mediated pores

There is an ongoing debate on how to correct leaf gas exchange measurements for the unavoidable diffusion leakage that occurs when measurements are done in non‐ambient CO₂ concentrations. In this study, we present a theory on how the CO₂ diffusion gradient over the gasket is affected by leaf‐mediated pores (LMP) and how LMP reduce diffusive exchange across the gaskets. Recent discussions have so far neglected the processes in the quasi‐laminar boundary layer around the gasket. Counter intuitively, LMP reduce the leakage through gaskets, which can be explained by assuming that the boundary layer at the exterior of the cuvette is enriched with air from the inside of the cuvette. The effect can thus be reduced by reducing the boundary layer thickness. The theory clarifies conflicting results from earlier studies. We developed leaf adaptor frames that eliminate LMP during measurements on delicate plant material such as grass leaves with circular cross section, and the effectiveness is shown with respiration measurements on a harp of Deschampsia flexuosa leaves. We conclude that the best solution for measurements with portable photosynthesis systems is to avoid LMP rather than trying to correct for the effects.     

The influence of leaf size and shape on leaf thermal dynamics: does theory hold up under natural conditions?

Laboratory studies on artificial leaves suggest that leaf thermal dynamics are strongly influenced by the two‐dimensional size and shape of leaves and associated boundary layer thickness. Hot environments are therefore said to favour selection for small, narrow or dissected leaves. Empirical evidence from real leaves under field conditions is scant and traditionally based on point measurements that do not capture spatial variation in heat load. We used thermal imagery under field conditions to measure the leaf thermal time constant (τ) in summer and the leaf‐to‐air temperature difference (?T) and temperature range across laminae (T_range) during winter, autumn and summer for 68 Proteaceae species. We investigated the influence of leaf area and margin complexity relative to effective leaf width (w_e), the latter being a more direct indicator of boundary layer thickness. Normalized difference of margin complexity had no or weak effects on thermal dynamics, but w_e strongly predicted τ and ?T, whereas leaf area influenced T_range. Unlike artificial leaves, however, spatial temperature distribution in large leaves appeared to be governed largely by structural variation. Therefore, we agree that small size, specifically w_e, has adaptive value in hot environments but not with the idea that thermal regulation is the primary evolutionary driver of leaf dissection.     

Detection and relationships of cotton leaf curl virus and allied whitefly-transmitted geminiviruses occurring in Pakistan

A stock culture of cotton leaf curl virus from Pakistan (CLCuV-PK), was transmitted by whiteflies (Bemisia tabaci) to seven plant species, including French bean, okra, tobacco and tomato, and caused vein thickening and leaf curl symptoms. It was readily detected in triple antibody sandwich ELISA (TAS-ELIS A) by 11 out of 31 monoclonal antibodies raised against the particles of three other geminiviruses: African cassava mosaic, Indian cassava mosaic and okra leaf curl viruses. Reaction strength was enhanced when the tissue extraction fluid contained sodium sulphite. Minor variations in epitope profile were found among virus isolates from cotton (Gossypium hirsutum) collected from different districts in Pakistan over a 5-year period. These epitope profiles were distinguishable from that of cotton leaf curl virus from G. barbadense in southern India but indistinguishable from the profiles of viruses causing yellow vein disease of okra in India or Pakistan, or leaf curl of okra {Abelmoschus esculentus), Hibiscus tiliaceus, radish or sunflower in Pakistan, suggesting that these plants are putative natural hosts of CLCuV-PK. The viruses in cotton, and in okra with leaf curl or yellow vein symptoms, were also detected by PCR with three pairs of CLCuV-PK-specific primers. Five additional whitefly-transmitted geminiviruses were found among isolates from 11 other naturally-infected species in Pakistan, and were distinguished by their epitope profiles. These viruses were associated, respectively, with tobacco leaf curl, squash yellow blotch, tomato yellow leaf curl, watermelon leaf crinkle and soybean yellow mosaic diseases. The first four of these viruses were detected readily by PCR with geminivirus general primers but only weakly, if at all, with two pairs of CLCuV-PK-specific primers. Pakistani crops are infected with a range of distinguishable but relatively closely related whitefly-transmitted geminiviruses, some of which resemble those found in India.     

Diaheliotropic leaf movement enhances leaf photosynthetic capacity and photosynthetic light and nitrogen use efficiency via optimising nitrogen partitioning among photosynthetic components in cotton (Gossypium hirsutum L.)

• Phototropic leaf movement of plants is an effective mechanism for adapting to light conditions. Light is the major driver of plant photosynthesis. Leaf N is also an important limiting factor on leaf photosynthetic potential. Cotton (Gossypium hirsutum L.) exhibits diaheliotropic leaf movement. Here, we compared the long‐term photosynthetic acclimation of fixed leaves (restrained) and free leaves (allowed free movement) in cotton.
• The fixed leaves and free leaves were used for determination of PAR, leaf chlorophyll concentration, leaf N content and leaf gas exchange. The measurements were conducted under clear sky conditions at 0, 7, 15 and 30 days after treatment (DAT).
• The results showed that leaf N allocation and partitioning among different components of the photosynthetic apparatus were significantly affected by diaheliotropic leaf movement. Diaheliotropic leaf movement significantly increased light interception per unit leaf area, which in turn affected leaf mass per area (LMA), leaf N content (N_A) and leaf N allocation to photosynthesis (N_P). In addition, cotton leaves optimised leaf N allocation to the photosynthetic apparatus by adjusting leaf mass per area and N_A in response to optimal light interception.
• In the presence of diaheliotropic leaf movement, cotton leaves optimised their structural tissue and photosynthetic characteristics, such as LMA, N_A and leaf N allocation to photosynthesis, so that leaf photosynthetic capacity was maximised to improve the photosynthetic use efficiency of light and N under high light conditions.

     

Leaf Structure of Tobacco In Vitro Grown Plantlets as Affected by Saccharose and Irradiance

Tobacco plantlets were cultured in vitro under high (200 µmol m^–2 s^–1) or low (60 µmol m^–2 s^–1) irradiance with or without saccharose in the medium. Light microscopy and image analysis were used to evaluate the effect of these culture conditions on leaf anatomy. Addition of saccharose resulted in thicker leaves (all leaf layers) and larger mesophyll cells under both growth irradiances. Various irradiance affected leaf anatomy differently when plantlets had been cultivated in presence or absence of saccharose in the medium. While under high irradiance in presence of saccharose leaf thickness and number of chloroplasts per cell section were increased, plantlets grown under high irradiance in absence of saccharose had thinner leaves and less chloroplasts per cell section. The changes were more pronounced in palisade parenchyma layer.     

In vitro culture of callus tissues and cell suspensions from okra (Hibiscus esculentus L.) and cotton (gossypium hirsutum L.)

Summary Methods are described for starting and maintaining callus-tissue cultures of twoMalvaceae, okra (Hibiscus esculentus L.) and cotton (Gossypium hirsutum L.). Okra callus was slow to initiate, but once started it was easy to maintain, in contrast to cotton, which was difficult to initiate and grow. Different media were required to establish the two species. The inclusion of 5 mg per liter of ascorbic acid aided in reducing the formation of black pigments in cotton callus. Hypocotyls of sterile young okra seedlings and leaves of cotton plants were used to produce the callus tissue. Rapidly growing cell suspensions of okra and cotton were obtained in B5 medium.     

The After-effect of Wind on the Photosynthesis and Transpiration of Festuca arundinacea

The after-effect of wind on photosynthesis and transpiration of Festuca arundinacea Schreb, was determined. Following a period of exposure In a controlled environment wind tunnel the wind-treated plants showed reduced rates of photosynthesis when compared with the controls under standard conditions. Evaporation from paper model tillers was measured and the boundary layer resistance was shown to be low in all but very low wind speeds. Analysis of CO₂ and H₂O diffusion pathways indicated that mesophyll resistance in wind-treated plants was higher whilst leaf surface resistance was lower than in the controls. The high mesophyll resistance in the wind-treated plants was attributed to reduced water content.     

转大肠杆菌过氧化氢酶基因棉花的抗旱生理研究

以导入大肠杆菌过氧化氢酶基因KatE的T3代转基因棉花为供试材料,经卡那霉素检测和PCR鉴定,将筛选出的阳性转基因植株与对照棉花进行整个生育期的持续水分胁迫处理直至收获,比较材料间的生理生化指标的差异,鉴定转基因植株的耐旱能力。结果显示:(1)干旱胁迫持续至初蕾期时,转基因棉花与对照植株间各项抗旱生理指标差异均未达到显著水平。(2)水分胁迫持续至盛蕾和盛花期时,转基因棉花叶片相对含水量、光系统Ⅱ最大光化学效率(Fv/Fm)、CAT活性,以及叶片的净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)均显著或极显著高于对照植株,叶绿素含量也都明显高于对照植株。干旱胁迫持续至吐絮期时,转基因棉花的株高、果枝数和铃数均显著或极显著高于对照植株,且转基因棉花和对照的籽棉产量分别比正常灌溉处理降低57.5%和60.1%,全生育期的水分胁迫严重影响了棉花籽棉产量,但转基因棉花的籽棉产量仍显著高于对照。研究表明,在新疆石河子当地自然降水(干旱胁迫)条件下,转KatE基因棉花表现出了较好的生理和生长优势,KatE基因有助于提高棉花的抗旱性。     

Cotton genotypic variation in the photosynthetic response to irradiance

The photosynthetic response of 8 cotton (Gossypium hirsutum L.) genotypes to changing irradiance was investigated under field conditions during the 1998 through 2000 growing seasons. Equations developed to describe the response of net photosynthetic rate (P_N) to photosynthetic photon flux density (PPFD) demonstrated that, across all irradiances, the two okra leaf-type genotypes photosynthesized at a greater rate per unit leaf area than all of the six normal leaf-type genotypes. This superior photosynthetic performance of the okra leaf-type genotypes can be partially explained by their 13 % greater leaf chlorophyll content relative to that of the normal leaf-type genotypes. The 37 % reduction in leaf size brought upon by the okra leaf trait may have concentrated the amount of photosynthetic machinery per unit leaf area. Nevertheless, the lack of sufficient canopy leaf surface area suppressed the potential yield development that could accompany the higher P_N per unit leaf area.     

Mesophyll Resistance and Carboxylase Activity: A Comparison under Water Stress Conditions

The response of several leaf gas exchange parameters were monitored with decreasing leaf water potential in Phaseolus vulgaris L. leaflets. These included photosynthesis, transpiration, CO₂ compensation point, ribulose 1,5-diphosphate carboxylase activity, boundary layer plus stomatal, and mesophyll resistance to diffusion of CO₂. Mesophyll resistance was calculated under two assumptions: (a) the CO₂ concentration at the chloroplast was zero, and (b) it was equal to the CO₂ compensation point.