Showing papers in "Brazilian Journal of Plant Physiology in 2007"

Ecophysiology of coffee growth and production

Abstract: After oil, coffee is the most valuable traded commodity worldwide. In this review we highlighted some aspects of coffee growth and development in addition to focusing our attention on recent advances on the (eco)physiology of production in both Coffea arabica and C. canephora, which together account for 99% of the world coffee bean production. This review is organized into sections dealing with (i) climatic factors and environmental requirements, (ii) root and shoot growth, (iii) blossoming synchronisation, fruiting and cup quality, (iv) competition between vegetative and reproductive growth and branch die-back, (v) photosynthesis and crop yield, (vi) physiological components of crop yield, (vii) shading and agroforestry systems, and (viii) high-density plantings.

Use of physiological parameters as fast tools to screen for drought tolerance in sugarcane

Abstract: Drought is one of the major limitations to plant productivity worldwide. Identifying suitable screening tools and quantifiable traits would facilitate the crop improvement process for drought tolerance. In the present study, we evaluated the ability of four relatively physiological parameters (variable-to-maximum chlorophyll a fluorescence ratio, F v/F m; estimated leaf chlorophyll content via SPAD index; leaf temperature, LT; and, leaf relative water content, RWC) to distinguish between drought tolerant and susceptible sugarcane genotypes subjected to a 90-d drought cycle. Eight field-grown genotypes were studied. By 45 d after the onset of treatments, the F v/F m, SPAD index and RWC of drought-stressed plants had declined significantly in all genotypes compared to values at the onset of well-watered treatments. However, the reductions were more severe in leaves of susceptible genotypes. Under drought stress, the tolerant genotypes as a group, maintained higher F v/F m (8%), SPAD index (15%), and RWC (16%) than susceptible genotypes. In general, LT of drought-stressed plants was higher (~4oC) than that of well-watered plants but the relative increase was greater among drought susceptible genotypes. Under drought stress, LT of tolerant genotypes was on average 2.2oC lower than that of susceptible genotypes. The results are consistent with the tolerant-susceptible classification of these genotypes and indicate that these tools can be reliable in screening for drought tolerance, with F v/F m, SPAD index and LT having the added advantage of being nondestructive and easily and quickly assessed.

Physiology of citrus fruiting

Abstract: Citrus is the main fruit tree crop in the world and therefore has a tremendous economical, social and cultural impact in our society. In recent years, our knowledge on plant reproductive biology has increased considerably mostly because of the work developed in model plants. However, the information generated in these species cannot always be applied to citrus, predominantly because citrus is a perennial tree crop that exhibits a very peculiar and unusual reproductive biology. Regulation of fruit growth and development in citrus is an intricate phenomenon depending upon many internal and external factors that may operate both sequentially and simultaneously. The elements and mechanisms whereby endogenous and environmental stimuli affect fruit growth are being interpreted and this knowledge may help to provide tools that allow optimizing production and fruit with enhanced nutritional value, the ultimate goal of the Citrus Industry. This article will review the progress that has taken place in the physiology of citrus fruiting during recent years and present the current status of major research topics in this area.

Ecophysiology of the cacao tree

Abstract: Cacao, one of the world's most important perennial crops, is almost exclusively explored for chocolate manufacturing. Most cacao varieties belong to three groups: Criollo, Forastero and Trinitario that vary according to morphology, genetic and geographical origins. It is cropped under the shade of forest trees or as a monocrop without shade. Seedlings initially show an orthotropic growth with leaf emission relatively independent of climate. The maturity phase begins with the emission of plagiotropic branches that form the tree crown. At this stage environmental factors exert a large influence on plant development. Growth and development of cacao are highly dependent on temperature, which mainly affects vegetative growth, flowering and fruit development. Soil flooding decreases leaf area, stomatal conductance and photosynthetic rates in addition to inducing formation of lenticels and adventitious roots. For most genotypes drought resistance is associated with osmotic adjustment. Cacao produces caulescent flowers, which begin dehiscing in late afternoon and are completely open at the beginning of the following morning releasing pollen to a receptive stigma. Non pollinated flowers abscise 24-36 h after anthesis. The percentage of flowers setting pods is in the range 0.5 - 5%. The most important parameters determinants of yield are related to: (i) light interception, photosynthesis and capacity of photoassimilate distribution, (ii) maintenance respiration and (iii) pod morphology and seed fermentation, events that can be modified by abiotic factors. Cacao is a shade tolerant species, in which appropriate shading leads to relatively high photosynthetic rates, growth and seed yield. However, heavy shade reduces seed yield and increases incidence of diseases; in fact, cacao yields and light interception are tightly related when nutrient availability is not limiting. High production of non-shaded cacao requires high inputs in protection and nutrition of the crop. Annual radiation and rainfall during the dry season explains 70% of the variations in annual seed yields.

Ecophysiology of tea

Abstract: Tea [Camellia sinensis (L.) O. Kuntze] is one of the most important beverage crops in the world. The major tea-growing regions of the world are South-East Asia and Eastern Africa where it is grown across a wide range of altitudes up to 2200 m a.s.l.. This paper reviews the key physiological processes responsible for yield determination of tea and discusses how these processes are influenced by genotypic and environmental factors. Yield formation of tea is discussed in terms of assimilate supply through photosynthesis and formation of harvestable sinks (i.e. shoots). The photosynthetic apparatus and partial processes (i.e. light capture, electron transport and carboxylation) of tea show specific adaptations to shade. Consequently, maximum light-saturated photosynthetic rates of tea are below the average for C3 plants and photoinhibition occurs at high light intensities. These processes restrict the source capacity of tea. Tea yields are sink-limited as well because shoots are harvested before their maximum biomass is reached in order to maintain quality characters of made tea. In the absence of water deficits, rates of shoot initiation and extension are determined by air temperature and saturation vapour pressure deficit, with the former having positive and the latter having negative relationships with the above rates. During dry periods, when the soil water deficit exceeds a genotypically- and environmentally-determined threshold, rates of shoot initiation and extension are reduced with decreasing shoot water potential. Tea yields respond significantly to irrigation, a promising option to increase productivity during dry periods, which are experienced in many tea-growing regions.

Structure, organization, and functions of cellulose synthase complexes in higher plants

Abstract: Annually, plants produce about 180 billion tons of cellulose making it the largest reservoir of organic carbon on Earth. Cellulose is a linear homopolymer of b(1-4)-linked glucose residues. The coordinated synthesis of glucose chains is orchestrated by specific plasma membrane-bound cellulose synthase complexes (CelS). The CelS is postulated to be composed of approximately 36 cellulose synthase (CESA) subunits. The CelS synthesizes 36 glucose chains in close proximity before they are further organized into microfibrils that are further associated with other cell wall polymers. The 36 glucose chains in a microfibril are stabilized by intra- and inter-hydrogen bonding which confer great stability on microfibrils. Several elementary microfibrils come together to form macrofibrils. Many CESA isoforms appear to be involved in the cellulose biosynthetic process and at least three types of CESA isoforms appear to be necessary for the functional organization of CelS in higher plants.

Physiological characteristics of cassava tolerance to prolonged drought in the tropics: implications for breeding cultivars adapted to seasonally dry and semiarid environments

Abstract: The paper summarizes research conducted at International Center for Tropical Agriculture (CIAT) on responses of cassava to extended water shortages in the field aided by modern gas-exchange and water-relation techniques as well as biochemical assays. The aim of the research was to coordinate basic and applied aspects of crop physiology into a breeding strategy with a multidisciplinary approach. Several physiological characteristics/traits and mechanisms underpinning tolerance of cassava to drought were elucidated using a large number of genotypes from the CIAT core germplasm collection grown in various locations representing ecozones where cassava is cultivated. Most notable among these characteristics are the high photosynthetic capacity of cassava leaves in favorable environments and the maintenance of reasonable rates throughout prolonged water deficits, a crucial characteristic for high and sustainable productivity. Cassava possess a tight stomatal control over leaf gas exchange that reduces water losses when plants are subjected to soil water deficits as well as to high atmospheric evaporative demands, thus protecting leaves from severe dehydration. During prolonged water deficits, cassava reduces its canopy by shedding older leaves and forming smaller new leaves leading to less light interception, another adaptive trait to drought. Though root yield is reduced (but much less than the reduction in top growth) under water stress, the crop can recover when water becomes available by rapidly forming new canopy leaves with much higher photosynthetic rates compared to unstressed crops, thus compensating for yield losses with final yields approaching those in well-watered crops. Cassava can extract slowly water from deep soils, a characteristic of paramount importance in seasonally dry and semiarid environments where deeply stored water needs to be tapped. Screening large accessions under seasonally dry and semiarid environments showed that yield is significantly correlated with upper canopy leaf photosynthetic rates, and the association was attributed mainly to nonstomatal (anatomical/biochemical) factors. Parental materials with both high yields and photosynthetic rates were identified for incorporation into breeding and selection programs for cultivars adapted to prolonged drought coupled with high temperatures and dry air, conditions that might be further aggravated by global climate changes in tropical regions.

Environmental physiology of the bananas (Musa spp.)

Abstract: The bananas are thought to be particularly sensitive to changes in the environment. This review considers some historical and recent investigations into the response of the leaf, root and reproductive system to the environment. Monteith's analysis of the response of plants to intercepted radiation is appropriate for analyzing the productivity of bananas and plantains. The banana is sensitive to soil water deficits, and expanding tissues such as emerging leaves and growing fruit are among the first to be affected. As soil begins to dry, stomata close and leaves remain highly hydrated, probably through root pressure. Productivity is affected because of the early closure of stomata. We find the common belief that bananas use large amounts of water does not have a strong physiological basis. Improvements in water-use efficiency in irrigated plantations could come from a closer match between plant water use and the amount of water applied. We examine recent data on water-use efficiency of different banana cultivars and propose that agronomists, physiologists and breeders could quantify the amount of water available in each rain-fed environment and work towards directing more of that water through the plant. The banana is day neutral for floral induction, but photoperiods of less than 12 h are associated with a slowing in the rate of bunch initiation that is independent of temperature expressed as growing degree days. This may contribute to seasonal variations in banana flowering, even in more tropical environments with moderate temperatures.

Changes in the antioxidative enzyme activities and lipid peroxidation in wheat seedlings exposed to cadmium and lead stress

Abstract: Wheat seedlings were grown in presence of CdCl2 (0-200 µM) and Pb(NO3)2 (0-2000 µM) separately. The growth of metal-treated seedlings was significantly depressed. The activities of antioxidative enzymes namely superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (POX) were altered both in root and shoot tissues of 7-d-old seedlings. Under Cd stress, SOD activity in roots was undetectable even at the lowest Cd concentration (50 µM) whereas in shoots it declined sharply with increasing Cd levels. The activity of CAT declined to a greater extent in roots than in shoots. Even though the POX activity increased nine times in shoots, a decreasing trend was observed in root tissues due to Cd stress. Under Pb stress, the induction in SOD activity and decline in CAT activity were sharper in root tissues than in their shoot counterparts. The POX activity increased both in roots and shoots under Pb stress. Malondialdehyde concentration increased in both roots and shoots of Cd- and Pb-treated seedlings. The results suggest that metal toxicity was associated with oxidative stress. The decline in CAT activity may be the probable reason behind the Cd- and Pb-induced oxidative stress, since the alterations in SOD and POX activities showed different trends under these metal stresses.

Reproductive physiology of mango

Abstract: Mango flowering involves hormonal regulation of shoot initiation and induction events resulting in reproductive shoot formation. A balance or ratio of endogenously regulated phytohormones, thought to be auxin from leaves and cytokinins from roots, appears to govern the initiation cycle independently from inductive influences. Induction of reproductive or vegetative shoots is thought to be governed by the ratio of a temperature-regulated florigenic promoter and an age regulated vegetative promoter at the time of shoot initiation. Management of off-season flowering in mango trees is being accomplished in the tropics by successfully synchronizing shoot initiation through tip pruning and use of nitrate sprays coupled with management of the stem age to induce flowering such that it can be accomplished during any desired week of the year.

An overview of preharvest factors influencing mango fruit growth, quality and postharvest behaviour

Abstract: Mango, a tropical fruit of great economic importance, is generally harvested green and then commercialised after a period of storage. Unfortunately, the final quality of mango batches is highly heterogeneous, in fruit size as well as in gustatory quality and postharvest behaviour. A large amount of knowledge has been gathered on the effects of the maturity stage at harvest and postharvest conditions on the final quality of mango. Considerably less attention has been paid to the influence of environmental factors on mango growth, quality traits, and postharvest behaviour. In this paper, we provide a review of studies on mango showing how environmental factors influence the accumulation of water, structural and non-structural dry matter in the fruit during its development. These changes are discussed with respect to the evolution of quality attributes on the tree and after harvest. The preharvest factors presented here are light, temperature, carbon and water availabilities, which can be controlled by various cultural practices such as tree pruning, fruit thinning and irrigation management. We also discuss recent advances in modelling mango function on the tree according to environmental conditions that, combined with experimental studies, can improve our understanding of how these preharvest conditions affect mango growth and quality. (Resume d'auteur)

Stimulation of antioxidant system and lipid peroxidation by abiotic stresses in leaves of Momordica charantia

Abstract: The purpose of the present work was to evaluate both the antioxidant response system and oxidative stress in leaves from bitter gourd (Momordica charantia L) subjected to NaCl, UV-B and water stresses at three different stages of plant growth: pre-flowering, flowering and post-flowering. Except for peroxidase (POX), all enzyme activities including superoxide dismutase (SOD), catalase (CAT), polyphenol oxidase (PPO), glutathione reductase (GR), as well as concentrations of ascorbate (ASA), hydrogen peroxide (H2O2) and thiobarbituric acid reactive substances (TBARS) exhibited maximum values at the flowering stage under all three stresses. All the enzyme activities, SOD, CAT, POX, PPO, GR and the concentrations of ASA, H2O2 and TBARS were elevated under NaCl and UV-B stresses at all growth stages with the exception of H2O2 concentration at the post-flowering stage under UV-B radiation. Greater quantities of the inorganic ions Na+ and Cl- were accumulated at all growth stages under salt stress. Drought led to decreases in the concentrations of H2O2, ASA and activities of PPO and GR; conversely, it led to elevated concentrations of TBARS and activities of SOD, CAT, POX at all three stages in comparison with control values. The POX activity at the third stage was, however, reduced. The photosynthetic pigments decreased at all stages under all stresses. The chlorophyll stability index decreased under NaCl stress, accelerated only at the post-flowering stage under UV-B radiation and significantly increased at pre- and post-flowering stages under water stress. The protein concentration under NaCl stress decreased except at the pre-flowering stage and under UV-B and water stresses the protein concentration was higher than that of the control and NaCl treatment. It is suggested that M. charantia exhibits a protection mechanism against oxidative damage by maintaining a highly induced antioxidant system under all three stresses.

Cadmium toxicity causes oxidative stress and induces response of the antioxidant system in cucumber seedlings

Abstract: In this study, the effects of cadmium (Cd) on lipid peroxidation, electrolyte leakage, protein oxidation, ascorbate peroxidase (APX; E.C. 1.11.1.11), catalase (CAT; E.C. 1.11.1.6) and superoxide dismutase (SOD; E.C. 1.15.1.1) activities, and ascorbic acid, non-protein thiol groups and total soluble protein contents in cucumber seedlings (Cucumis sativus L.) were investigated. Seedlings were grown in vitro in an agar-solidified substrate containing four Cd levels as CdCl2 (0, 100, 400, and 1000 µmol L-1) for 10 d. The lowest Cd level decreased the malondialdehyde concentration. Electrolyte leakage increased only at 1000 µmol Cd L-1, whereas protein oxidation and total soluble protein content were enhanced at 400 and 1000 µmol Cd L-1. Activity of APX was inhibited while the activities of CAT and SOD were increased at all Cd concentrations. Ascorbic acid was enhanced at 400 and 1000 µmol Cd L-1 whereas non-protein thiol groups were increased at all Cd supplies. The results evidence the importance of the enzymatic and non-enzymatic antioxidant system in response to cadmium toxicity in cucumber seedlings.

Some aspects of citrus ecophysiology in subtropical climates: re-visiting photosynthesis under natural conditions

Abstract: Received: 14 November 2007; Accepted: 12 December 2007In this review we re-visit and discuss the current knowledge on ecophysiology of citrus trees, addressing the influenceof environmental conditions on citrus photosynthesis. Knowledge of physiological responses of citrus trees to theirsurrounding environment is essential in order to improve crop production and plant development, both beingconsequences of appropriate horticultural management in citrus orchards. In this context, citrus photosynthesis isaddressed as the primary source of carbon and energy for plant growth and development. The photosynthetic activityon both a daily and a seasonal scale is reviewed, taking into consideration the physiological aspects related to seasonalvariation of photochemical and biochemical activities, stomatal conductance and leaf water potential. These aspects aretreated for citrus plants growing in subtropical climates with varying environmental conditions, such as moderate tosevere drought during the winter season. In addition, the possible inhibitory/stimulatory effects of carbohydratemetabolism on citrus photosynthesis are discussed with regard to the source-sink relationship. Field experimentationthat enhances knowledge concerning citrus ecophysiology in subtropical climates is highlighted. Among interestingsubjects to be unraveled by future research, we may point out the effects of low temperatures on citrus photosynthesisand water relations, the nature of the relationship between leaf carbohydrate content and photosynthesis, and thesignificance of photosynthesis in different canopy layers and positions in relation to the total carbon gain in maturecitrus trees.

Ecophysiology of papaya: a review

Abstract: Papaya (Carica papaya L.) is a principal horticultural crop of tropical and subtropical regions. Knowledge of how papaya responds to environmental factors provides a scientific basis for the development of management strategies to optimize fruit yield and quality. A better understanding of genotypic responses to specific environmental factors will contribute to efficient agricultural zoning and papaya breeding programs. The objective of this review is to present current research knowledge related to the effect of environmental factors and their interaction with the photosynthetic process and whole-plant physiology. This review demonstrates that environmental factors such as light, wind, soil chemical and physical characteristics, temperature, soil water, relative humidity, and biotic factors such as mycorrhizal fungi and genotype profoundly affect the productivity and physiology of papaya. An understanding of the environmental factors and their interaction with physiological processes is extremely important for economically sustainable production in the nursery or in the field. With improved, science-based management, growers will optimize photosynthetic carbon assimilation and increase papaya fruit productivity and quality.

Ecophysiology of coconut palm under water stress

Abstract: Coconut palm is of great social and economic importance for millions of people in the tropics and subtropics. Drought is one of the main environmental factors that limit coconut productivity. In this review, physiological and morphological data are presented in an integrated perspective to provide a holistic view of the behavior of coconut trees facing water deficit under both field and controlled conditions. Great capacity to produce homorhizic roots capable of searching continuously for water and nutrients and high protoplasmic tolerance in leaves allows the coconut tree to endure water deficit. High membrane stability, osmoprotection, osmoregulation and enhanced activity of antioxidant enzymes are characteristics often found in leaves of drought-stressed coconut trees. Information on leaf gas exchange, leaf water potential, water-use efficiency and stomatal behavior was compiled highlighting the differences among cultivars and hybrids under water stress. Genotypic differences in physiological and morphological traits can largely explain the agronomic performance of field-grown coconut trees under drought conditions.

Physiology of cashew plants grown under adverse conditions

Abstract: The cashew (Anacardium occidentale L.) is an important crop for semi-arid agriculture and contributes to the social and economical development of several world regions, including the northeast of Brazil. In spite of its importance, very few studies aim to understand the effects of abiotic stresses on the development and yield of the cashew. This review covers the research on cashew ecophysiology, with emphasis on the effects of water and salt stress on its development, mineral nutrition and gas exchange processes. The results presented here were obtained at different plant growth stages and under different environmental conditions of soil and climate. The ecophysiological significance of this information is also discussed.

Tolerance and prospection of phytoremediator woody species of Cd, Pb, Cu and Cr

Abstract: High concentrations of Cd, Pb, Cu and Cr can cause harmful effects to the environment. These highly toxic pollutants constitute a risk for aquatic and terrestrial life. They are associated with diverse bioavailable geochemical fractions, like the water-soluble fraction and the exchangeable fraction, and non-available fractions like those associated with the crystalline net of clays and silica minerals. Depending upon their chemical and physical properties we can distinguish different mechanisms of metal toxicity in plants, such as production of reactive oxygen species from auto-oxidation, blocking and/or displacement of essential functional groups or metallic ions of biomolecules, changes in the permeability of cellular membranes, reactions of sulphydryl groups with cations, affinity for reactions with phosphate groups and active groups of ADP or ATP, substitution of essential ions, induction of chromosomal anomalies and decrease of the cellular division rate. However, some plant species have developed tolerance or resistance to these metals naturally. Such evolution of ecotypes is a classic example of local adaptation and microevolution, restricted to species with appropriate genetic variability. Phytoremediator woody species, with (i) high biomass production, (ii) a deep root system, (iii) high growth rate, (iv) high capacity to grow in impoverished soils, and (v) high capacity to allocate metals in the trunk, can be an alternative for the recovery of degraded soils due to excess of metallic elements. Phytoremediation using woody species presents advantageous characteristics as an economic and ecologically viable system, making it an appropriate, practical and successful technology.

Influence of iron on mineral status of two rice (Oryza sativa L.) cultivars

Abstract: Received: 02 April 2007; Returned for revision: 02 July 2007; Accepted: 14 August 2007Iron is an essential nutrient for plants. In aerobic conditions, Fe is highly unavailable for plant uptake, and Fe deficiencycan be severe in plants grown in calcareous soils. In waterlogged soils, however, Fe availability increases and can reachtoxic concentrations. Rice is an important staple crop worldwide and faces iron deficiency or excess, depending on thegrowth conditions. To contribute to the study of mechanisms involved in response to Fe deficiency and resistance to Feexcess, experiments were carried out with rice cultivars BR-IRGA 409 (I409, susceptible to Fe toxicity) and EPAGRI 108(E108, resistant to Fe toxicity) grown in culture solutions and submitted to Fe excess, control concentration ordeficiency (500, 6.5 or zero mg L

Effects of Zn and Cd accumulation on structural and physiological characteristics of barley plants

Abstract: The objectives of this study were to identify the structural changes caused by Zn and Cd accumulation in shoots and roots of barley (Hordeum vulgare) plants; and to correlate metal accumulation with anatomical, physiological and morphological changes. Potted plants were exposed to metal treatments of Zn and Cd for 19 and 16 d respectively. Leaves, stems and roots were harvested to identify structural changes and analyze metal accumulation. Barley effectively accumulated Zn (up to 11283 mg kg-1) and Cd (up to 584 mg kg-1) in the shoots. Microscopic structural changes, such as a decrease in intercellular spaces, breakdown of vascular bundles, and shrinkage of palisade and epidermal cells, occurred in leaves, stems and roots of plants treated with high concentrations of Zn. Zinc accumulation also resulted in a significant decrease in water content, fresh weight, dry weight and plant height. Cadmium only caused structural changes in roots at the higher concentrations. Barley plants were able to accumulate significant amounts of Zn and Cd without exhibiting symptoms of phytotoxicity when the metal concentrations were relatively low.

Effect of 28-homobrassinolide on growth, zinc metal uptake and antioxidative enzyme activities in Brassica juncea L. seedlings

Abstract: The present work was undertaken to study the effects of 28-homobrassinolide on growth, zinc metal uptake, antioxidative enzyme [guaiacol peroxidase (EC 1.11.1.7), catalase (EC 1.11.1.6), glutathione reductase (EC 1.6.4.2), ascorbate peroxidase (EC 1.11.1.11), superoxide dismutase (EC 1.15.1.1)] activities and protein content in 7-d-old seedlings of Brassica juncea L. treated with Zn metal at different concentrations. 28-homobrassinolide at 10-9 M concentration lowered Zn uptake and bioconcentration factor. Different concentrations of Zn-metal treatment alone decreased the enzyme activities and protein concentration of seedlings. However, pre-sowing treatments of 28homobrassinolide lowered the uptake of metal and enhanced the activities of enzymes and protein concentration of seedlings.

Ecophysiological factors underpinning productivity of Hevea brasiliensis

Abstract: High land productivity is a must for any commercial cultivation including Hevea brasiliensis (rubber). Also, the high demand for natural rubber has placed great pressure on expanding rubber cultivation to new and non-traditional areas. Understanding the ecophysiological principles behind the measures of productivity improvements is vital for wide application of these measures and to assess their sustainability. This review discusses the ecophysiological principles and tools used, along with the measures taken, to address productivity needs in terms of: genotype selection, determination of optimum planting density, and establishment of intercropping systems. Breeding for high yields and selection of suitable genotypes for different growing conditions are a top priority throughout the research history of rubber, however, early selection tools are necessary to reduce the time required for this process. As for any crop, photosynthesis drives the productivity of the rubber crop and, therefore, factors that govern and/or parameters that indicate the efficiency of photosynthetic productivity under field conditions could be used as tools in the selection of Hevea genotypes. Particularly for the early selection of genotypes in breeding programmes, mature crop characteristics which determine crop photosynthesis and productivity, should be linked to juvenile plant characteristics. The spatial and temporal efficiency by which plants acquire growth resources determines the overall productivity of the rubber crop, hence the optimum planting density and suitable crop combinations in intercropping systems. Changes in crop microclimate influence the efficiency of resource capture and thereby can be important for determining planting density and intercrops. Research needs regarding all the above aspects are also discussed.

Energetic flux and performance index in copaiba (Copaifera multijuga Hayne) and mahogany (Swietenia macrophylla King) seedlings grown under two irradiance environments

Abstract: Plant adaptation under conditions of limited irradiance can be investigated by their efficiency while using the available energy with a minimal thermodynamic energy loss. For this reason, we compared the energetic fluxes and the performance index (PIABS) in copaiba (Copaifera multijuga) and mahogany (Swietenia macrophyla) seedlings under both sunlight and shade. The experiment was carried out in Manaus (3o8'S, 59o52'W), Amazonas State, Brazil. The fluorescence transients were obtained in intact and healthy leaves using a Plant Efficiency Analyser (PEA) between 1200 h and 1300 h. Using the O-J-I-P test, the following parameters were calculated: 1) density of reaction centers per cross section (RC/CS), 2) maximum quantum yield for primary photochemistry of photosystem II (jPo), and 3) probability of energy excitation (Yo) or that of an absorbed photon (jEo) to move an electron further than quinone A, and 4) the performance index (PIABS). The highest PIABS was found in seedlings under shade for both species. Mahogany seedlings exhibited values of PIABS about three-fold and 14-fold higher than copaiba seedlings under shade and sunlight, respectively. For RC/CS, reaction centers were inactive under sunlight, 58% for mahogany and 78% for copaiba. The high irradiance induced a decrease of jPo in mahogany (36%) and in copaiba (69%) when compared to shaded seedlings. This likely was a result of need for excess energy dissipation under sunlight. In addition, it was verified that seedlings under sunlight presented a severe decrease in jEo, particularly in copaiba (23-fold), when compared to mahogany (9fold). Therefore, mahogany seedlings showed the highest performance in energy use under low and high irradiance, thus it may be proposed that mahogany presented lower entropy than copaiba seedlings, as demonstrated by the higher plasticity in the use of energy.

Physiological and oxidative stress responses of four potato clones to aluminum in nutrient solution

Abstract: Aluminum toxicity is a serious problem in Brazilian soils and selecting potato clones is an important strategy to produce this crop on these kinds of soils. Potato clones, Macaca, SMIC148-A, Dakota Rose, and Solanum microdontum, were grown in a nutrient solution (pH 4.0) with 0, 50, 100, 150 and 200 mg Al L-1. After 7 d, Al concentration in both root system and shoot of all clones increased linearly with increasing Al levels. Based on relative root growth, S. microdontum and SMIC148-A were considered Al-tolerant clones, whereas Macaca and Dakota Rose were considered Al-sensitive. Shoot growth in Macaca linearly decreased with increasing Al levels. Root H2O2 concentration in both Al-sensitive clones increased with increasing Al supply, whereas in Al-tolerant clones it either decreased (SMIC148-A) or demonstrated no alteration (S. microdontum). Shoot H2O2 concentration increased linearly in Macaca, whereas for Dakota Rose it showed a quadratic relationship with Al levels. On the other hand, shoot H2O2 concentration in the Al-tolerant clones either demonstrated no alteration (S. microdontum) or presented lower levels (SMIC148-A). Root catalase (CAT) activity in both Al-sensitive clones increased with increasing Al levels, whereas in Al-tolerant clones it either demonstrated no alteration (SMIC148-A) or presented lower levels (S. microdontum). Shoot CAT activity in the S. microdontum increased curvilinearly with increasing Al levels. In all potato clones, chlorophyll concentration showed a curvilinear response to Al supply, where in Al-sensitive clones it decreased upon addition of Al exceeding 100 mg L-1, but in SMIC148-A it increased at levels between approximately 100 and 150 mg L-1, and decreased in S. microdontum regardless of the Al level. Carotenoid concentrations in the Al-sensitive clones were linearly decreased with increasing Al levels. Aluminum supply caused root lipid peroxidation only in the Al-sensitive clones, whereas in the shoot it increased linearly in the Al-sensitive clones and in S. microdontum it only increased at around 50 mg L-1. Most of root protein oxidation was only observed in the Al-sensitive clones. However, shoot protein oxidation was increased with increasing Al levels for all potato clones. These results indicate that oxidative stress caused by Al in potato may harm several components of the cell, mainly in Al-sensitive clones.

Differential capacity of nitrogen assimilation between apical and basal leaf portions of a tank epiphytic bromeliad

Abstract: The leaf is the main organ of the vegetative body of tank epiphytic bromeliads, which may be subdivided into apical and basal parts. Little is known about the existence of morphological, anatomical or physiological differences between these two leaf portions. The objective of this study was to verify the existence of a differential capacity to assimilate nitrogen from urea between basal and apical leaf portions of Vriesea gigantea, a tank epiphytic bromeliad. Plants were cultivated in vitro in the presence of 5 mM urea for 15 days. During this period, the activities of the enzymes glutamine synthetase (GS, EC 6.3.1.2) and NADH-dependent glutamate dehydrogenase (NADH-GDH, EC 1.4.1.2) were quantified, as well as the densities of trichomes and stomata found at the leaf surface of both regions. The highest activities of GS and NADH-GDH were always detected at the top portion, and on the 3rd day of in vitro cultivation an increase in these activities was detected. An inverse correlation between number of trichomes and stomata in these two leaf portions was verified: the top region presented 30% less trichomes and twice as many stomata as the basal region. This suggests that the upper region of the leaf may be preferentially involved with the assimilation of nitrogen from urea via GS and NADH-GDH, whereas the basal region may be involved with its absorption. This is the first study to report that ammonium assimilation may take place preferentially in a specific portion of tank-forming bromeliad leaves.

Ecophysiology of tropical tree crops: an introduction

Abstract: In this special issue, ecophysiology of major tropical tree crops, considered here on a broader sense and including species such as banana, cashew, cassava, citrus, cocoa, coconut, coffee, mango, papaya, rubber, and tea, are examined. For most of these crops, photosynthesis is treated as a central process affecting growth and crop performance. The crop physiological responses to environmental factors such as water availability and temperature are highlighted. Several gaps in our database concerning ecophysiology of tropical tree crops are indicated, major advances are examined, and needs of further researches are delineated.

Photoacclimation in three species of freshwater red algae

Abstract: Tres especies de Rhodophyta continentais (Audouinella eugenea, A. hermannii e Compsopogon coeruleus) foram testadas em resposta a fotossintese, crescimento e concentracao de pigmento em dois niveis de irradiância (baixa irradiância, BI, 65 µmol m-2 s-1 e alta irradiância, AI, 300 µmol m-2 s-1) e dois periodos (curto periodo, CP, 4 d e longo periodo, LP, 28 d). Observaram-se maiores taxas de crescimento em BI, mas diferencas significativas foram encontradas apenas em A. hermannii. Observaram-se maiores valores de fotoinibicao em BI para as tres especies, consistentes com a dinâmica de fotoinbicao como um mecanismo fotoprotetor reversivel contra alta irradiância. Nas tres especies, verificou-se diminuicao induzida por luz no rendimento quântico efetivo, consistindo de forte queda de BI para AI. Aumentos rapidos de extincao nao-fotoquimica (NPQ) foram observados principalmente em BI, indicando dissipacao do excesso de energia pelos centros de reacao. Os resultados revelaram estrategias distintas de fotoaclimatacao para enfrentar altas irradiâncias: especies de Audouinella exibiram somente caracteristicas de algas adaptadas a sombra: aclimatacao por mudancas do tamanho das unidades dos fotossistemas (UF) sob LP e por numero de UF sob CP; valores maiores do parâmetro de fotoinibicao e NPQ e menores de rendimento quântico efetivo (RQE) em BI; maior capacidade de recuperacao de rendimento quântico potencial (RQP) em BI e sob CP; correlacao positiva altamente significante entre taxa relativa de transporte de eletrons (TTE) com NPQ. Compsopogon coeruleus apresentou caracteristicas de algas adaptadas ao sol: aclimatacao por mudancas no numero de UF sob LP e de tamanho de UF sob CP; maior capacidade de recuperacao de RQE; correlacao baixa ou nenhuma correlacao entre TTE e NPQ. Assim, estas caracteristicas indicam que C. coeruleus enfrenta altas irradiâncias mais eficientemente do que as especies de Audouinella.

Limitations to photosynthesis at different temperatures in the leaves of Citrus limon

Abstract: The response of CO2 assimilation rate (A) to the intercellular partial pressure of CO2 (Ci) was measured on intact lemon leaves over a range of temperatures (10 to 40oC). The A/Ci response shows how change in the leaf temperature alters the activity of ribulose-1,5-bisphosphate (RuBP) carboxylase-oxygenase (Rubisco) and RuBP regeneration via electron transport. The rate of A reached a maximum of 7.9 to 8.9 µmol m-2 s-1 between 25 and 30oC, while dark respiration (Rd) increased with temperature from 0.4 µmol m-2 s-1 at 10oC to 1.4 µmol m-2 s-1 at 40oC. The maximum rates of carboxylation (Vc,max) and the maximum rates of electron transport (Jmax) both increased over this temperature range from 7.5 to 142 µmol m-2 s-1 and from 23.5 to 152 µmol m-2 s-1, respectively. These temperature responses showed that A can be limited by either process depending on the leaf temperature, when Ci or stomatal conductance are not limiting. The decrease in A associated with higher temperatures is in part a response to the greater increase in the rate of oxygenation of RuBP compared with carboxylation and Rd at higher temperatures. Although A can in theory be limited at higher Ci by the rate of triose-phosphate utilization, this limitation was not evident in lemon leaves.

Alterations in leaf anatomy and physiology caused by the red mite (Oligonychus ilicis) in plants of Coffea arabica

Abstract: Three degrees of red mite infestation (Oligonychus ilicis McGregor) (Acari: Tetranychidae) were evaluated with regard to leaf anatomy, photosynthetic gas exchange and leaf ethylene production, in a commercial crop of approximately 12-year-old trees of Coffea arabica 'Catuai Vermelho'. As a complementary study, foliar anatomy was also evaluated in a recuperated crop of C. arabica 'Mundo Novo' that had presented a high degree of red mite infestation during the dry period of the prior growing season. The red mite-infested leaves were bronze-coloured, with intensity proportional to the degree of internal damage. On feeding, the red mite introduces its stylet in the adaxial epidermis and, as a result, chloroplasts are destroyed in the feeding area. The number of chlorophyll-free cells in the palisade parenchyma was proportional to the intensity of attack by red mites. The cells of the spongy parenchyma, localized below the feeding areas of the mites, did not show any alterations, having intact chloroplasts, with the exception of some leaves that suffered from intense attack. Net photosynthesis rate declined, but only in leaves under intense red mite attack, due to destruction of chloroplasts in the attacked cells. Nevertheless, transpiration and stomatal conductance were unaffected by red mite. The concentrations of ethylene produced by the leaves were similar regardless of three levels of attack, suggesting that red mite infestation does not lead to leaf abscission. In addition, anatomical studies of 'Mundo Novo' leaves of plants that visually recovered from red mite attack showed that, even with scars present, they continued attached on the plant.

Relationship between gibberellic acid and growth parameters in developing seed and pod of pigeon pea

Abstract: Changes in endogenous gibberellic acid (GA) levels were determined in developing seeds and pods of pigeon pea (Cajanus cajan). Antibodies against GA3 were raised in rabbits and indirect ELISA developed to estimate GA level. Two varieties, black seeded variety (V1) and B.D.N2 (V2), were selected on the basis of their seed index value. The pod length and number of seeds per pod were significantly different for the two varieties. Dry weight, water content (WC), rate of water accumulation, rate of dry matter accumulation (DMA), and GA content in pod and seed were all larger in V1 than in V2. In both varieties, higher GA content was observed during cell elongation and DMA phases, respective to their varietal differences in growth traits. Relationships between WC and rate of DMA, and WC and GA differed significantly between the two varieties. The results suggest a role of GA and WC in sink-size development in both varieties studied.