DOCSLIB.ORG

Chloroplasts As Source and Target of Cellular Redox Regulation: a Discussion on Chloroplast Redox Signals in the Context of Plant Physiology

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Chloroplasts As Source and Target of Cellular Redox Regulation: a Discussion on Chloroplast Redox Signals in the Context of Plant Physiology Journal of Experimental Botany, Vol. 56, No. 416, pp. 1449–1462, June 2005 doi:10.1093/jxb/eri161 Advance Access publication 29 April, 2005 FOCUS PAPER Chloroplasts as source and target of cellular redox regulation: a discussion on chloroplast redox signals in the context of plant physiology Margarete Baier* and Karl-Josef Dietz Biochemistry and Physiology of Plants, University of Bielefeld, D-33501 Bielefeld, Germany Received 28 January 2005; Accepted 15 March 2005 Abstract Key words: Abscisic acid, antioxidants, chloroplast, gene expression, oxolipin, peroxiredoxin, photosynthesis, redox During the evolution of plants, chloroplasts have lost regulation, signalling, stress. the exclusive genetic control over redox regulation and antioxidant gene expression. Together with many other genes, all genes encoding antioxidant enzymes and enzymes involved in the biosynthesis of low molecular Introduction weight antioxidants were transferred to the nucleus. On the other hand, photosynthesis bears a high risk for In plants, photosynthesis generates redox intermediates photo-oxidative damage. Concomitantly, an intricate with extraordinarily negative redox potentials. Light-driven network for mutual regulation by anthero- and retro- electron transport transfers electrons from the acceptor site grade signals has emerged to co-ordinate the activities of photosystem I (Em < ÿ900 mV) to various acceptors of the different genetic and metabolic compartments. A including oxygen (Em = 815 mV; Blankenship, 2002). The major focus of recent research in chloroplast regula- redox intermediates cover an exceptionally wide range of tion addressed the mechanisms of redox sensing and mid-point redox potentials (Dietz, 2003) with a significant signal transmission, the identification of regulatory risk for electron transfer to oxygen and other appropriate targets, and the understanding of adaptation mech- targets. Among the best known examples for chloroplast anisms. In addition to redox signals communicated redox chemistry is the direct electron transfer from reduced through signalling cascades also used in pathogen ferredoxin to O2 in the so-called Mehler reaction (Mehler, and wounding responses, specific chloroplast signals 1951). The superoxide radicals formed can be quickly control nuclear gene expression. Signalling pathways converted into H2O2 and highly reactive hydroxyl radicals c are triggered by the redox state of the plastoquinone (HO ) (Elstner, 1990). Together with reactive oxygen pool, the thioredoxin system, and the acceptor avail- species (ROS) generated by other sources, they are a con- ability at photosystem I, in addition to control by tinuous threat to cellular constituents for uncontrolled oxolipins, tetrapyrroles, carbohydrates, and abscisic oxidation. acid. The signalling function is discussed in the con- In the context of (i) the physiologically bivalent oxygen text of regulatory circuitries that control the expression chemistry, (ii) the demand for reductive power, and (iii) the of antioxidant enzymes and redox modulators, demon- peril of excess photosynthetic electron pressure, chloro- strating the principal role of chloroplasts as the source plasts are prone to oxidative damage like no other organelle and target of redox regulation. (Foyer et al., 1997). Consequently, photosynthetic organ- isms have evolved defence mechanisms to control the redox poise of the electron transport chain and the redox envir- onment of the stroma. They range from the suppression of * To whom correspondence should be addressed. Fax: +49 (0)521 106 6039. E-mail: [email protected] Abbreviations: 2CPA, 2-Cys peroxiredoxin A; ABA, abscisic acid; DBMIB, 3-methyl-6-isopropyl-p-benzoquinone; DCMU, 3-(39,49-dichlorophenyl-)1,1- dimethyl urea; DOX, fatty acid dioxygenase; Em, mid-point potential; LOX, lipoxygenase; MAPK(K)(K), mitogen activated protein kinase (kinase) (kinase); NDH, NAD(P)H dehydrogenase; PET, photosynthetic electron transport; PQ, plastoquinone; Prx, peroxiredoxin; ROS, reactive oxygen species; Rubisco, ribulose-1,5-bisphosphate carboxylase oxygenase. ª The Author [2005]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: [email protected] 1450 Baier and Dietz ROS generation and avoidance of uncontrolled oxidation of essential biomolecules by accumulating high concentra- tions of low-molecular weight antioxidants to repair mech- anisms by reduction and de novo synthesis of damaged molecules. In the illuminated chloroplast, the reduction energy for the regeneration of oxidized metabolites is mainly taken from the photosynthetic electron transport (PET). Depending on the photo-oxidative strain, up to almost 100% of the photosynthetically transported elec- trons can be diverted into the antioxidant defence system (Asada, 2000). In the dark, when the strong reductive power of photosynthesis is missing, the redox environment of chloroplasts probably adjusts to redox potentials similar to those measured in the cytoplasm of heterotrophic cells (i.e. below ÿ300 mV to approximately ÿ240 mV; Dietz, 2003). Under these conditions, chloroplasts stabilize their redox poise by metabolization of starch and import of Fig. 1. The cytosolic antioxidant system shields the nucleus from chloro- plast ROS signals. Photosynthetic ROS signals and redox imbalances are reduction energy. buffered by cytosolic antioxidants. Whether they reach the nucleus Studies with various transgenic plant lines and mutants depends on the rates of ROS-formation and the strength of the cytosolic demonstrated the importance of a high antioxidant cap- antioxidant system. In contrast, a non-redox active second messenger can pass the cytosol without loss of function. acity as realized by low-molecular weight antioxidants (Pastori et al., 2003; Ball et al., 2004) and antioxidant enzymes (Willekens et al., 1997; Baier et al., 2000; may have additional functions, for example, as a metabolic Davletova et al., 2005). The antioxidant defence system re- intermediate. sponds to redox imbalances. The pool size of low molecu- lar weight antioxidants and the expression of chloroplast antioxidant enzymes increases if the photo-oxidative strain Redox coupling on the system is high (Foyer et al., 1997). Interestingly, oxidizing conditions correlate with a high reduction state, All redox active compounds together define the cellular since, as outlined above, excess electrons are transferred redox poise of a cell (Schafer and Buettner, 2001). In to O2 that, in turn, abstract electrons from organic targets. addition to the redox energetics defined by the mid-point This apparent contradiction (‘high reducing activity potentials and the concentrations of the various antioxi- results in oxidizing conditions’) will be important for dants, the redox state of a particular compound is under the understanding redox regulation, as for example in the control of kinetic constraints defining the reaction constants. peroxiredoxin function, in the context of photosynthesis Enzymes lower the kinetic barriers and couple redox pairs. (see below). However, all chloroplast antioxidant enzymes Recycling of oxidized intermediates, as well as regeneration and all enzymes involved in the biosynthesis of low- of the reductants, affect the redox state of specific redox molecular-weight antioxidants are nuclear encoded. The pairs (Dietz, 2003). Different drainage rates of electrons spatial separation of expression and function demands for from antioxidants and weak enzymatic linkages can un- signal transduction over the chloroplast envelope. Devia- couple the redox states of individual components of the tions from regular redox homeostasis can be sensed in the antioxidant network, as has been observed for ascorbate and chloroplast and transmitted to the nucleus by retrograde glutathione. While specific oxidation of the glutathione pool signalling cascades. Alternatively, redox imbalances in the took place in catalase-deficient barley (Willekens et al., chloroplast could be transmitted into the cytoplasm by 1997), reduced 2-Cys peroxiredoxin levels led preferen- metabolic coupling (Fig. 1). The sensor then resides in tially to the oxidation of the ascorbate pool in Arabidopsis the cytoplasm. Transmission of redox signals suffers thaliana (Baier et al., 2000). The favoured oxidation of from the drawback that cytoplasmic redox homeostasis glutathione in the catalase-lines is proposed to be caused by and antioxidant defence will strongly damp the spreading higher cytosolic dehydroascorbate reductase activity rather signal. than glutathione reductase activity, while the redox shift in Another terminology to be clarified is the distinction of the ascorbate pool in the peroxiredoxin antisense plants signalling and regulation. Both terms are used with a broad might be caused by insufficient dehydroascorbate reductase meaning here. Regulation describes any adjustment of activity in the chloroplasts (Noctor et al., 2000). For cellular activity, i.e. of enzymes or transcription factors, while redox homeostasis and redox metabolism, the nature of signalling refers to any transport of information from one a particular antioxidant employed in a specific detoxifica- site to another via a signalling molecule that, by itself, tion reaction and, within limits, the relative redox state of an Chloroplast redox regulation 1451 individual antioxidant may be of minor importance. How- Sensing the cellular redox poise ever, deviations from
Load more

Recommended publications
  • Plant Physiology General the Main Light Sensitive Pigment Able to Absorb Solar Energy in Both Plants and Algae Is
    Plant Physiology General the main light sensitive pigment able to absorb solar energy in both plants and algae is chlorophyll Photosynthesis this chlorophyll is contained with the chloroplasts probably the most characteristic “thing” that plants plants also have other “accessory pigments”: “do” is photosynthesis carotenoids – mainly yellow, orange almost all plants are autotrophs but usually their colors are masked by an abundance of !use energy from the sun to make sugar and chlorophyll other organic molecules out of simple fall colors are seen as a deciduous plant shuts down nutrients and chlorophyll is broken down and recycled leaving the colors of the other pigments photosynthesis requires carbon dioxide & water reds come from anthocyanins made to protect leaves as they recycle nutrients from the breakdown of chlorophyll CO2 enters through stomata or pores [Application] water is absorbed through roots researchers are studying the structure of the chloroplasts to light improve efficiency in the design of solar collectors CO2 + H2O sugar + O2 chlorophyll (glucose) today (2006) the most efficient solar cells capture only ~17% of solar energy that lands on them, while plant [photosynthesis converts water and carbon dioxide cell capture 30-40% to sugar and oxygen] !these sugars can then be broken down as needed for energy photosynthesis uses several chemical pigment to absorb the energy from sunlight Plants: Plant Physiology - General, Ziser, Lecture Notes, 2012.10 1 Plants: Plant Physiology - General, Ziser, Lecture Notes, 2012.10 2 Plant
    [Show full text]
  • BIL 161: Environment and Development: the Effects of Environmental Variables on Seed Germination
    BIL 161: Environment and Development: The Effects of Environmental Variables on Seed Germination The seed is more than just a plant waiting to happen. It is a complex marvel of evolution, a miniature life-support system that responds to environmental cues in order to give the embryo nestled within the best chance of survival. I. Characteristics and Classification of Plants Plants share synapomorphies that set them apart from other organisms. 1. true tissues (of types unique to plants) 2. waxy cuticle (to prevent desiccation) 3. stomates (microscopic gas exchange pores on the leaves) 4. apical meristems (permanent embryonic tissue for constant growth) 5. multicellular sex organs (male antheridia and female archegonia) 6. walled spores produced in structures called sporangia 7. embryo development inside the female parent 8. secondary metabolites (alkaloids, tannins, flavonoids, etc.) 9. heteromorphic alternation of generations The most primitive plants do not produce seeds at all, but rather release spores into the environment where they grow into a second life cycle stage, called the gametophyte. In seed plants, the life cycle is highly derived. Seed plants still make spores, but each spore grows into a gametophyte that is little more than a bit of tissue that gives rise to gametes. In the male parts of the plant, each spore develops into a sperm-producing male gametophyte known as pollen. In the female parts of the plant, meiosis occurs inside a structure known as the ovule, which will eventually give rise to the seed. Plants can broadly be classified as follows. A. Bryophytes – non-vascular plants (mosses, liverworts and hornworts) B.
    [Show full text]
  • Plant Physiology
    PLANT PHYSIOLOGY Vince Ördög Created by XMLmind XSL-FO Converter. PLANT PHYSIOLOGY Vince Ördög Publication date 2011 Created by XMLmind XSL-FO Converter. Table of Contents Cover .................................................................................................................................................. v 1. Preface ............................................................................................................................................ 1 2. Water and nutrients in plant ............................................................................................................ 2 1. Water balance of plant .......................................................................................................... 2 1.1. Water potential ......................................................................................................... 3 1.2. Absorption by roots .................................................................................................. 6 1.3. Transport through the xylem .................................................................................... 8 1.4. Transpiration ............................................................................................................. 9 1.5. Plant water status .................................................................................................... 11 1.6. Influence of extreme water supply .......................................................................... 12 2. Nutrient supply of plant .....................................................................................................
    [Show full text]
  • Plant Physiology and Biochemistry
    BSCBO- 303 B.Sc. III YEAR Plant Physiology and Biochemistry DEPARTMENT OF BOTANY SCHOOL OF SCIENCES UTTARAKHAND OPEN UNIVERSITY PLANT PHYSIOLOGY AND BIOCHEMISTRY BSCBO-303 Expert Committee Prof. J. C. Ghildiyal Prof. G.S. Rajwar Retired Principal Principal Government PG College Government PG College Karnprayag Augustmuni Prof. Lalit Tewari Dr. Hemant Kandpal Department of Botany School of Health Science DSB Campus, Uttarakhand Open University Kumaun University, Nainital Haldwani Dr. Pooja Juyal Department of Botany School of Sciences Uttarakhand Open University, Haldwani Board of Studies Prof. Y. S. Rawat Prof. C.M. Sharma Department of Botany Department of Botany DSB Campus, Kumoun University HNB Garhwal Central University, Nainital Srinagar Prof. R.C. Dubey Prof. P.D.Pant Head, Department of Botany Director I/C, School of Sciences Gurukul Kangri University Uttarakhand Open University Haridwar Haldwani Dr. Pooja Juyal Department of Botany School of Sciences Uttarakhand Open University, Haldwani Programme Coordinator Dr. Pooja Juyal Department of Botany School of Sciences Uttarakhand Open University Haldwani, Nainital UTTARAKHAND OPEN UNIVERSITY Page 1 PLANT PHYSIOLOGY AND BIOCHEMISTRY BSCBO-303 Unit Written By: Unit No. 1. Dr. Urmila Rana 1 & 2 Asst. Professor, Department of Botany, Pauri Campus, H.N.B. Garhwal University, Pauri, Uttarakhand 2. Dr. Shweta Kukreti 3 Asst. Professor, Department of Botany, Pauri Campus, H.N.B. Garhwal University, Pauri, Uttarakhand 3- Dr. Nishesh Sharma 4 Asst. Professor, Department of Biotechnology, Uttaranchal College of Applied and Life Science Uttaranchal University, Dehradun 4. Dr. Deepika Upadhyay 5 & 6 Asst. Professor, Department of Microbiology Chinmaya Degree College, BHEL, Haridwar 5- Dr. Manish Belwal 7 & 8 Asst Prof., Department of Botany Govt.
    [Show full text]
  • Introduction to Plant Physiology
    Chapter 1: Introduction to Plant Physiology Plant is source of food, fodder, fibers, clothing, shelter fuel, medicine, and oxygen. This all resources are the products of plant physiology. The basic and main process in plant, photosynthesis is responsible for the supply of all the above-mentioned resources. Figure 1: Different plant science areas studied under plant physiology. Definition: Plant physiology deals with the various metabolic process and pathways in plant. Practically it is heart of the botany, which study different functions performed by the plant. It deals with the study of organization and operation of all the physiological, biochemical and enzymological processes in plant. Importance of plant physiology: Plant metabolism is mainly anabolism and catabolism. Breaking and joining different biomolecules. Studying this aspect of plant provides the explanation the several question about the plant. Example: How plants utilize solar energy? SACP Dept. of Botany BO232 Plant Physiology How they obtain and distribute water and nutrients? How plants grow and develop? How they respond to the environment? How they produce flowers and seed? How seed germinate and form new plants? Answers of above questions helps to understand different process and acquired knowledge helps to improve productivity and yield of the crop. Need for the Study of Plant Physiology: • It is important branch of botany, understanding the plant physiology helps interlink other branches of botany. Understanding different physiological process such as Seed germination, Growth and development, Photosynthesis, Absorption of water and minerals, Ascent of sap, Translocation of solutes, Transpiration, Photorespiration, Respiration, Photoperiodism, Vernalization, Flowering, Ripening of fruits, Senescence and Death of plant gives huge knowledge and this knowledge finds wide application in every branch of botany.
    [Show full text]
  • 1 BOTANY, PLANT PHYSIOLOGY and PLANT GROWTH Lesson 9: PLANT NUTRITION Segment One – Nutrient Listing Plants Need 17 Elements
    BOTANY, PLANT PHYSIOLOGY AND PLANT GROWTH Lesson 9: PLANT NUTRITION Segment One – Nutrient Listing Plants need 17 elements for normal growth. Carbon, oxygen, and hydrogen are found in air and water. Nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur are found in the soil. The above nine elements are used in relatively large amounts by the plant and are called macronutrients. There are eight other elements that are used in much smaller amounts and are called micronutrients or trace elements. The micronutrients, which are found in the soil, are listed in the table below. All 17 elements, both macronutrients and micronutrients, are essential for plant growth. MACRONUTRIENTS Found in air and water carbon C oxygen O hydrogen H Primary Elements nitrogen N phosphorus P potassium K Secondary Elements calcium Ca magnesium Mg sulfur S MICRONUTRIENTS iron Fe manganese Mn copper Cu zinc Zn boron B molybdenum Mo chlorine Cl cobalt Co The terms primary, secondary, and micronutrients actually refer to the amount of these elements needed by the plants rather than their relative importance. All 17 elements are essential; this is an important concept when learning plant nutrition. The term “essential” means if even ONE nutrient is missing, you have a critical situation. The plant will stop growing, and will die eventually. Think of all 17 elements as a chain of 17 links; if you lose one link in the chain, it has no power. 1 Seldom do you need to be concerned about the supply of carbon, oxygen, and hydrogen, even though large amounts of each are used in plant growth and development.
    [Show full text]
  • Historical Review
    1 Historical Review INTRODUCTION This chapter presents a brief historical review of progress in the field of plant water relations because the authors feel that it is impossible to fully understand the present without some knowledge of the past. As the Danish philosopher Kierkegaarde wrote, "Life can only be understood backward, but it can only be lived forward," and this also is true of science. The present generation needs to be reminded that some generally accepted concepts have their origin in ideas of 17th or 18th century writers and although others were suggested many decades ago, they were neglected until recently. As might be expected, the importance of water to plant growth was recog- nized by prehistoric farmers because irrigation systems already existed in Egypt, Babylonia (modern Iraq), and China at the beginning of recorded history, and the first European explorers found extensive irrigation systems in both North and South America. However, irrigation was not used extensively in agriculture in the United States until after the middle of the 19th century and little research on plant water relations occurred until the 20th century. Early Research Although plant water relations appear to have been the first area of plant physiology to be studied, progress was slow from Aristotle who died in 322 B.C. to the middle of the 19th century. According to Aristotle, plants absorbed their food ready for use from the soil, and plant nutrition was controlled by a soul or vital principle that ailowed plants to absorb only those substances useful in 2 1. Historical Review growth. This idea only began to be questioned in the 17th century by Jung, van Helmont, Mariotte, and others, and it ~ersistedinto the 19th century.
    [Show full text]
  • Evolution of the Life Cycle in Land Plants
    Journal of Systematics and Evolution 50 (3): 171–194 (2012) doi: 10.1111/j.1759-6831.2012.00188.x Review Evolution of the life cycle in land plants ∗ 1Yin-Long QIU 1Alexander B. TAYLOR 2Hilary A. McMANUS 1(Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA) 2(Department of Biological Sciences, Le Moyne College, Syracuse, NY 13214, USA) Abstract All sexually reproducing eukaryotes have a life cycle consisting of a haploid and a diploid phase, marked by meiosis and syngamy (fertilization). Each phase is adapted to certain environmental conditions. In land plants, the recently reconstructed phylogeny indicates that the life cycle has evolved from a condition with a dominant free-living haploid gametophyte to one with a dominant free-living diploid sporophyte. The latter condition allows plants to produce more genotypic diversity by harnessing the diversity-generating power of meiosis and fertilization, and is selectively favored as more solar energy is fixed and fed into the biosystem on earth and the environment becomes more heterogeneous entropically. Liverworts occupy an important position for understanding the origin of the diploid generation in the life cycle of land plants. Hornworts and lycophytes represent critical extant transitional groups in the change from the gametophyte to the sporophyte as the independent free-living generation. Seed plants, with the most elaborate sporophyte and the most reduced gametophyte (except the megagametophyte in many gymnosperms), have the best developed sexual reproduction system that can be matched only by mammals among eukaryotes: an ancient and stable sex determination mechanism (heterospory) that enhances outcrossing, a highly bimodal and skewed distribution of sperm and egg numbers, a male-driven mutation system, female specialization in mutation selection and nourishment of the offspring, and well developed internal fertilization.
    [Show full text]
  • Department of Plant Sciences and Plant Pathology
    disease. Additional projects pertain projects involve soil-borne diseases Department of Graduate to biocontrol of plant diseases and of cereals, the genetic basis for Programs biocontrol of weeds using plant disease resistance in fi eld crops, Plant Sciences and Plant Pathology pathogens and/or their toxins. cereal leaf spots, virus diseases Master of Science Degrees of cereals and potatoes, bacterial Unique, hands-on study programs for students interested in landscape design, and the biology, genetics and biochemistry of plants Plant Sciences Option Doctor of diseases and the biochemistry and The department conducts research Philosophy Degrees molecular genetics of plant disease. programs in: cereal quality; Plant Sciences - Plant Additional current research projects cropping systems/specialty crops; Pathology Option pertain to the biocontrol of plant and molecular and conventional Many research projects are problem- diseases and the biocontrol of approaches to plant improvement. oriented and pertain to major weeds using plant pathogens and/or Faculty have expertise in plant pathological problems in the their toxins. Department research molecular genetics, plant breeding state. Currently active research projects employ modern molecular and genetics, cereal quality, biological and biotechnological cytogenetics, biochemistry, plant The department conducts techniques as well as traditional physiology and agronomy. research programs in: cereal plant pathology techniques. quality; cropping systems/ Plant Pathology Option specialty crops; molecular and Plant Sciences - Plant Most research projects in this option conventional approaches to Genetics Option are problem-oriented and pertain to plant improvement. Faculty The department offers advanced major plant pathological problems in have expertise in molecular study leading to a Ph.D. degree the state.
    [Show full text]
  • A Balance Between the Activities of Chloroplasts and Mitochondria Is Crucial for Optimal Plant Growth
    antioxidants Article A Balance between the Activities of Chloroplasts and Mitochondria Is Crucial for Optimal Plant Growth Zhou Xu 1 , Renshan Zhang 1 , Meijing Yang 1, Yee-Song Law 1 , Feng Sun 1 , Ngai Lung Hon 2, Sai Ming Ngai 2,3 and Boon Leong Lim 1,3,* 1 School of Biological Sciences, University of Hong Kong, Pokfulam, Hong Kong, China; [email protected] (Z.X.); [email protected] (R.Z.); [email protected] (M.Y.); [email protected] (Y.-S.L.); [email protected] (F.S.) 2 School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong, China; [email protected] (N.L.H.); [email protected] (S.M.N.) 3 State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, Hong Kong, China * Correspondence: [email protected]; Tel.: +852-22990826 Abstract: Energy metabolism in plant cells requires a balance between the activities of chloroplasts and mitochondria, as they are the producers and consumers of carbohydrates and reducing equiva- lents, respectively. Recently, we showed that the overexpression of Arabidopsis thaliana purple acid phosphatase 2 (AtPAP2), a phosphatase dually anchored on the outer membranes of chloroplasts and mitochondria, can boost the plant growth and seed yield of Arabidopsis thaliana by coordinating the activities of both organelles. However, when AtPAP2 is solely overexpressed in chloroplasts, the growth-promoting effects are less optimal, indicating that active mitochondria are required for dissipating excess reducing equivalents from chloroplasts to maintain the optimal growth of plants. It Citation: Xu, Z.; Zhang, R.; Yang, M.; is even more detrimental to plant productivity when AtPAP2 is solely overexpressed in mitochondria.
    [Show full text]
  • BOTANY, PLANT PHYSIOLOGY and PLANT GROWTH Lesson 8: ENVIRONMENTAL FACTORS
    BOTANY, PLANT PHYSIOLOGY AND PLANT GROWTH Lesson 8: ENVIRONMENTAL FACTORS The environment limits plant growth and distribution. If any one environmental factor is less than ideal, it will become a limiting factor in plant growth. Limiting factors are also responsible for the geography of plant distribution. For example, only plants adapted to limited amounts of water can live in deserts. Most plant problems are caused by environmental stress, either directly or indirectly. Therefore, it is important to understand the environmental aspects that affect plant growth. These factors are light, temperature, water, humidity and nutrition. In the subsequent lesson, we will discuss nutrition. Segment One - Effect of Light on Plant Growth Light has three principal characteristics that affect plant growth. These are light quantity, light quality and light duration. • Light quantity refers to the intensity or concentration of sunlight and varies with the season of the year. The maximum is present in the summer and the minimum in winter. The more sunlight a plant receives, up to a point, the better capacity it has to produce plant food through photosynthesis. As the sunlight quantity decreases, the photosynthetic process decreases. Light quantity can be decreased in a garden or greenhouse by using shadecloth above the plants. It can be increased by surrounding plants with reflective material, white backgrounds or supplemental lights. • Light quality refers to the color or wavelength reaching the plant surface. Sunlight can be broken up by a prism into respective colors of red, orange, yellow, green, blue, indigo and violet. On a rainy day, raindrops act as tiny prisms and break the sunlight into these colors, producing a rainbow.
    [Show full text]
  • Sybsc Botany II Sem-I Plant Physiology
    SYBSc Botany II Sem-I Plant Physiology Chapter-I: INTRODUCTION TO PLANT PHYSIOLOGY Introduction: Plant physiology is an interdisciplinary science. Its main aim is to get a complete and thorough Knowledge of all phenomenon occurring in plants. The Dictionary meaning of Plant physiology is the science of properties and function of plants as organism in normal condition. Definition- “Plant physiology is defined as the science which deals with the function of cells, tissues, organs of plants as a whole” The plant physiology is concerned with process and functions,the response of plant to change environment and the growth and development that result from response.plant process include ion absorption ,Sap movement ,photosynthesis ,respiration ,metabolism ,plant growth ,growth regulators ,process of flowering etc. plant structure, process and function are correlated which is basis of study of plant physiology. 1.1 Importance of Plant Physiology Plant metabolism mainly catabolism and anabolism is studied under plant physiology which is concerned with every aspects of plant life and provide explanation to several question about the plant.How the use solar energy ?How the obtained and distribute water and nutrients? How they produce flowers fruits and seed etc. Today it has become an important branch for conservation and protection of biodiversity, sustainable development, and and improvement in crops productivity under changing climatic condition. 1.2 Scope and Application of Plant Physiology The scope of plant physiology is well known and each and every aspect of plant and animal life it has vast scope and application in various disciplines of basic and applied science .is cover the studies right from gene level to organism level and concern with genotypic and phenotypic expression of plants.the fundamentals principals and laws of plant physiology are equally important and applicable to all unicellular and multicellular organism of either eukaryotic to prokaryotic nature.
    [Show full text]