Volume 4 Special Issue 2 2010
PLANT NUTRITION and ABIOTIC STRESS TOLERANCE II
How to reference: Pandey N (2010) Role of Micronutrients in Reproductive Physiology of Plants. In: Anjum NA (Ed) Plant Nutrition and Abiotic Stress Tolerance II. Plant Stress 4 (Special Issue 2), 1-13
Naser A. Anjum
Aligarh Muslim University, India
Centre for Environmental and Marine Studies (CESAM) & Department of Chemistry, University of Aveiro, Portugal
CONTENTS AND ABSTRACTS
Nalini Pandey (India) Role of Micronutrients in Reproductive Physiology of Plants (pp 1-13)
Invited Review: Plant reproductive biology is a key developmental process and has a great impact on plant productivity. Reproduction in plant involves the interaction between the male and female gametophyte which depend on the sporophyte for their nutrient requirement. Till recently, it was thought that adequate supply of micronutrients (Fe, Mn, Cu, Zn, Mo and B) was required during the period of active vegetative growth. It has lately been shown that good vegetative growth of plants does not necessarily go hand in hand with a high seed yield. In a large number of crops even under conditions of moderate micronutrient deficiencies when biomass production is marginally reduced, the reproductive yield is severely decreased. This suggests a requirement of micronutrients for floral induction and reproductive development independent of the requirement for production of necessary assimilates. Sufficient evidence has emerged to show that the micronutrients, in particular Cu, Zn and B, are critically required for reproductive development and that their requirement is possibly higher than what can be met by retranslocation from the vegetative parts of the mother plants. Application of these micronutrients during an early stage of reproductive phase make substantial improvement in pollen fertility, pollen-stigma interaction, seed setting and seed quality. While there are numerous reports of response to micronutrient fertilization benefiting harvest yield of plants, information on involvement of the micronutrients in plant reproductive development is limited. In recent years the identification of a number of genes for the floral organs and specific transcription factors like the zinc-fingers has given new impetus to the role of micronutrients in transcriptional regulation of reproductive development. In this review the current status on the systematic studies on the role of micronutrients in reproductive biology of plants is discussed.
Jie He (Singapore) Mineral Nutrition of Aeroponically Grown Subtropical and Temperate Crops in the Tropics with Manipulation of Root-Zone Temperature at Different Growth Irradiances (pp 14-30)
Invited Review: Plant growth and productivity are often limited by high root-zone temperatures (RZT) which restricts the growth of subtropical and temperate crops in the tropics. High RZT temperature coupled with low growth irradiances during cloudy days which mainly lead to poor root development and thus causes negative impact on the mineral uptake and assimilation. However, certain subtropical and temperate crops have successfully been grown aeroponically in the tropics by simply cooling their roots while their aerial portions are subjected to hot fluctuating ambient temperatures. This review first discusses the effects of RZT and growth irradiance on root morphology and its biomass, the effect of RZT on uptake and transport of several macro nutrients such as N [nitrogen, mainly nitrate, (NO3−)], P (H2PO4−, phosphate), K (potassium) and Ca (calcium), and micro nutrient Fe (iron) under different growth irradiances. The impact of RZT and growth irradiance on the assimilation of NO3- (the form of N nutrient given to the aeroponically grown plants) and the site of NO3- assimilation are also addressed.
Amrit L. Singh, Ram S. Jat, Vidya Chaudhari, Himanshu Bariya, Seema J. Sharma (India) Toxicities and Tolerance of Mineral Elements Boron, Cobalt, Molybdenum and Nickel in Crop Plants (pp 31-56)
Invited Review: The minerals boron (B), cobalt (Co), molybdenum (Mo) and Nickel (Ni) are beneficial to plant in trace amounts, but excess levels of these cause toxicity limiting crop production. An attempt was made to review the phytotoxicity symptoms, effects on growth and physiology and tolerance and amelioration of these toxicities in crop plants. Though, chlorosis and necrosis of leaves are the common expression of toxicities of these minerals and except B the critical toxic concentration of Co, Mo and Ni in soil has been worked out only for a few crops, the toxicity responses of these minerals in soil and plant tissues vary considerably across the soils and crop genotypes. These toxicities reduce chlorophyll, affect cell metabolites and enzymes specially antioxidant and lipid peroxidation, alter nutrient transport and have negative effects on cellular functioning, these all result in reduced growth and yield. Existence of genetic variation among the crop genotypes highlight the differences in tolerance and scoring for toxicity symptoms and biomass at early growth stages can be considered as reliable criteria for screening for tolerance to toxicity. The Bo1 gene provides a major source of B toxicity tolerance. The restriction of uptake and transport and internal tolerance mechanisms are the two important criteria which plants employ to combat high external concentrations and hence tolerance could be attributed to the lower B, Co, Mo and Ni content of seed and lower uptake or accumulation of these in the root and shoot and high yield in toxic soils. Ameliorating high-mineral soils using soil amendments is expensive and extremely difficult. Use of tolerant crop genotypes, phytoremediation by tolerant crops, and inoculations of beneficial microorganisms are the solutions.
Raul Antonio Sperotto, Felipe Klein Ricachenevsky, Ricardo José Stein, Vinicius de Abreu Waldow, Janette Palma Fett (Brazil) Iron Stress in Plants: Dealing with Deprivation and Overload (pp 57-69)
Invited Review: Iron (Fe) is an essential nutrient for plants and one of the most abundant elements in soils. However, it is nearly inaccessible to plants because of its poor solubility in aerobic conditions at neutral or basic pH, resulting in much lower concentrations than required for the optimal growth of plants. However, when Fe is taken up in excess of cellular needs, it becomes highly toxic, since both Fe2+ and Fe3+ can act as catalysts in the formation of hydroxyl radicals, which are potent oxidizing agents that may damage DNA, proteins and lipids. Plants must be able to sense and respond to Fe stress in terms of both Fe-deprivation and Fe-overload. Depending on the level of severity, plants are unable to deal with such stress and undergo dramatic changes in cellular metabolism with a sequential dismantling of cellular structures, resulting in growth inhibition and ultimately plant death. Therefore, plants must tightly regulate Fe levels within the cell to ensure that Fe is present at adequate levels. Here, we describe recent progress made in understanding how Fe is sensed by plants, and how plants are affected by and try to deal with non-optimal Fe concentrations.
Kanwar L. Sahrawat (India) Reducing Iron Toxicity in Lowland Rice with Tolerant Genotypes and Plant Nutrition (pp 70-75)
Invited Mini-Review: Iron toxicity is a widespread nutrient disorder of lowland rice grown in tropical and sub-tropical regions of the world on acid sulfate soils, Ultisols and sandy soils with a low cation exchange capacity, moderate to high in acidity, high in easily reducible or active iron and low to moderately high in organic matter. The stress is caused by a high concentration of ferrous iron in soil solution. It is estimated that iron toxicity reduces lowland rice yields by 12-100%, depending on the iron tolerance of the genotype, intensity of the iron toxicity stress and soil fertility status. Iron toxicity can be reduced by using iron-tolerant rice genotypes and through soil, water and nutrient management practices. The objective of this paper is to critically assess the pertinent literature on the role of iron-tolerant rice genotypes and other plant nutrients in reducing iron toxicity in lowland rice. It is emphasized that research should provide knowledge that would be used for increasing lowland rice production and productivity on iron-toxic wetlands on a sustainable basis by integration of genetic tolerance to iron toxicity with soil, water and nutrient management.
Bhupinder Singh, Seva Nayak Dheeravathu, Kalidindi Usha (India) Micronutrient Deficiency: A Global Challenge and Physiological Approach to Improve Grain Productivity under Low Zinc Availability (pp 76-93)
Invited Review: Micronutrient deficiency in soils is a fast emerging phenomenon and a challenging abiotic stress in world agriculture. Most important micronutrients that the developing and developed world is concerned from point of view of sustaining grain productivity and malnutrition in human beings are iron and zinc. Biofortification of staple food crops with micronutrients by either breeding for higher uptake efficiency or fertilization can be an effective strategy to address widespread dietary deficiency in human populations. Cereal species greatly differ in their micronutrient efficiency (MiE), defined in this paper as the ability of a plant to grow and yield well under micronutrient deficiency. MiE generally has been attributed to the efficiency of acquisition of nutrients under conditions of their low soil availability rather than to its utilisation or (re)-translocation within a plant. A higher zinc and iron acquisition efficiency of genotypes could be attributed to either or all of the following; an efficient ionic metal uptake system, better root architecture i.e., long and fine roots with architecture favouring exploitation of micronutrients from larger soil volume, higher synthesis and release of metal mobilising phytosiderophore by the roots and uptake of Fe- and Zn-phytosiderophore complex. Seed Zn content has also been suggested to affect the respective MiE. Root morphology and characteristics and interaction between micronutrients and other ionic radicals have been implicated as determinants of MiE. This review attempts to examine critically the scanty and scattered reports available on status of micronutrient deficiency with special reference to Zn, globally; morphological, biochemical and physiological basis of regulation of MiE in cereals and approaches to improve MiE in terms of grain productivity and grain Fe and Zn vis-à-vis its bioavailability under conditions of poor micronutrient availability.
Girdhar K. Pandey, Akhilesh K. Yadav, Poonam Kanwar, Narendra Tuteja (India) Role of Calcium in Regulating Potassium-Sodium Homeostasis and Potassium as Nutrient Signal during Abiotic Stress Conditions (pp 94-103)
Invited Review: Calcium is a ubiquitous cation, which serves as a second messenger for numerous signals and confers specific cellular responses in eukaryotes. Recent studies have established a concept termed ‘Ca2+ signature’ that specifies Ca2+ changes triggered by each signal. However, it is very fascinating how this pervasive cation can translate an infinite number of stimuli into unique stimulus-dependent responses. Ca2+ is a fundamental component of nutrition signaling under stress condition. It interacts with various calcium sensors, which are directly involved in various molecular, biochemical and cellular changes occurring during the plant’s adaptation to nutritional stress. Recently, in calcium signaling in plants, the CBL-CIPK protein network has been implicated in phytohormone (ABA), abiotic stress and potassium nutrition signaling. This review will mainly focus on the functional relationship of calcium-mediated salt stress tolerance, potassium nutrition, and potassium-sodium homeostasis by involvement of the CBL-CIPK complex.
Ashraf M, Muhammad Afzal, Rashid Ahmad, Muhammad Aamer Maqsood, Sher Muhammad Shahzad, Ahsan Aziz, Naeem Akhtar (Pakistan) Silicon Management for Mitigating Abiotic Stress Effects in Plants (pp 104-114)
Invited Review: Abiotic stress factors including salinity, drought, heat, frost, lodging, shading and ion toxicities may adversely affect the crop productivity and quality. Increasing evidences suggest that adequate regulation of silicon (Si) may enable the plants to survive the stress environment in a wide variety of crops. Si, once absorbed by the xylem veins, is deposited in the cell wall of roots, reducing the apoplastic bypass flow, provides binding sites for salts and, thereby, reduces the uptake and translocation of salts from roots to shoots. Si deposition in the cell wall increases the rigidity of cell wall and reduces the loss of water through transpiration with a resultant decrease in salt uptake. An increase in internal storage of water within plant tissue, due to reduced transpiration, allows higher growth rate and consequently mitigating detrimental effects of abiotic stresses. Si stimulates antioxidant defense system which helps the plants to maintain the desired level of reactive oxygen species in stress environment. Plants grown in the presence of Si show an erect growth, minimizing the amount of shade and allowing better distribution of light within the canopy. Si can lower electrolyte leakage, promoting photosynthetic activity in plants grown in stress environment. Si can positively affect the activities of certain enzymes and decrease the injury caused by abiotic stress factors. Si reduces the toxicity of elements such as iron, aluminum, manganese and cadmium through reduced uptake, complexation or immobilization and compartmentation or homogenous distribution of metal ions within the plant. This review deals with the current knowledge of beneficial effects of Si with focuses being on possible mechanisms of minimizing abiotic stress effects on plant growth and development.
María Begoña Herrera-Rodríguez, Agustín González-Fontes, Jesús Rexach, Juan J. Camacho-Cristóbal, José M. Maldonado, María Teresa Navarro-Gochicoa (Spain) Role of Boron in Vascular Plants and Response Mechanisms to Boron Stresses (pp 115-122)
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Invited Review: To date, the primordial function of boron is its structural role in the cell wall through stabilization of molecules containing cis-diol groups (borate esters with apiose residues of rhamnogalacturonan II). Nonetheless, boron is a micronutrient also involved in a great variety of physiological processes in vascular plants. However the mechanisms underlying the various metabolic disorders caused by boron deficiency are indeed unknown. Recently it has been reported that boron deficiency and toxicity induce stress-responsive genes. In this contribution we review the mechanisms involved in boron uptake and distribution, the role of boron in vascular plants, the effects of boron deficiency and toxicity on them, as well as the interaction boron toxicity and salt stress. In addition, we discuss the most recent hypotheses proposed to explain how boron could exert its function in vascular plants from a mechanistic point of view. The importance of understanding the role of boron in plants as well as the response mechanisms to its deficiency and toxicity will allow us to improve the tolerance of crops to boron stresses.