Plant Growth Responses for Smart Agriculture

Prospects and Applications

T. Girija, Nandini K., Parvathi M S, T. Girija, Nandini K., Parvathi M S

• Publisher: CRC Press
• Year: 2021
• Print ISBN: 9781032158099
• eBook ISBN: 9781000506198
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

Plant Physiology is a dynamic science which goes on adding knowledge to already characterized basic processes in plants. The past decade has witnessed an unprecedented progress in biological sciences with the advent of innovative technologies viz. recombinant DNA techniques, omics approaches and advanced phenotyping platforms. These tools have helped to redefine many of the already accepted facts of plant life. The present publication will give an insight into the lesser known signals that can influence plant growth and development. Knowledge of plant physiological processes provides the base for research in cognate disciplines such as crop improvement, crop production and crop protection. With the impetus for clean cultivation, information provided in the book can motivate researchers in developing environment-friendly and non-chemical means of improving crop production and activate the innate ability of the plant to enhance their field performance.  Note: T&F does not sell or distribute the hardback in India, Pakistan, Nepal, Bhutan, Bangladesh and Sri Lanka. This title is co-published with NIPA.

1Phenotypic Plasticity Concepts and Recent Advances

Girija T and Parvathi M S

Department of Plant Physiology, College of Horticulture

Kerala Agricultural University, Thrissur, Kerala

Introduction

Plasticity is a unique attribute by which the otherwise sessile plant species are capable of adjusting to environmental vagaries by changing their phenotypic and morphological characters. Any plant population will be able to survive only if it can respond to an extremely variable environment by becoming more plastic and more genetically variable. To achieve this, plants should be able to suitably change their morphology anatomy and physiology or any one of these parameters based on environmental changes so as to improve their adaptability and survival in the altered environment. When such changes are genetically heritable, then they lead to species evolution.

Plasticity helps plants to adapt to new environmental conditions, after migration to new geographical areas, by genetic assimilation of traits that can help to improve their performance under a new set of conditions. Understanding plasticity is important for predicting and managing the effect of climate change on native species as well as crop plants. Response of plants to modified environmental conditions is critical for their persistence.

Phenotypic plasticity has been defined as the ability of an individual genotype to produce different phenotypes when exposed to different environmental conditions (Pigliucci et al., 2006). This includes the ability of a plant to modify its development in response to environmental cues and also its ability to bring about changes in its metabolism which increases the chances of survival of an organism under a specific condition.

Variation of a species under different environmental conditions has been referred to as individual variability by Darwin, 1859. The term phenotypic polymorphism was coined by Mayr (1963) which helps to explain environmentally induced phenotypic variations and distinguish it from genetic polymorphism.

Types of plasticity

Phenotypic plasticity is seen at every stage of plant growth and development. During the initial stages of growth, we observe more of adaptive responses that decides the plant architecture while during developmental stages, signal responses are more pronounced. According to (Nicotra et al., 2010) phenotypic plasticity can be either long term or short-term. Long term plasticity is genetically controlled and heritable, which leads to evolution. Short term plasticity may be due to abiotic stress, herbivory or competition.

Physiological, morphological and anatomical plasticity can have different roles in enhancing plant adaptations.

Physiological plasticity ensures adjustment of gas exchange, light utilization and metabolic regulations that affect growth and development. This in turn enhances the capacity of species to colonize a new area and also acclimatize to adverse environments (Niinemets and Valladares, 2004; Zunzunegui et al., 2009).

Morphological and anatomical plasticity seem to have only secondary roles; they bring about modifications in resource acquisition, allocation and structural characters which improve plant adaptations. This also depends on age, placement of plant parts and physiological activity level which changes with time. Competitiveness of a new species in an environment depends on resource acquisition which alters with development and heritability of these traits (Harper, 1985).

Since plasticity is an adaptive mechanism that allows a plant to optimally respond to environmental heterogeneity, the development of phenotypic polymorphism may be either adaptive, non-adaptive (maladaptive) or neutral.

Adaptive plasticity: This is an advantage as it allows a genotype to have broader tolerance to environmental conditions and has higher fitness across multiple environments (Bradshaw, 1965; Baker, 1974; Pigliucci, 2001, 2005).

Non-adaptive plasticity: Many of the environmentally induced variations are non-adaptive. This occurs when compared to the ancestral phenotype, the fitness of the new environmentally induced phenotype has a reduced average fitness value, which is much lower or is further away from the adaptive peak in the new environment. This type of non-adaptive plasticity can itself lead to a cryptic evolution and produce a different population in a stressful environment. For example, under moisture stress conditions, plants may fail to grow to an optional height and produce few seeds (Kleunen and Fisher 2005; Grether, 2005). However, among these by chance a small number of genotypes may exhibit a beneficial plastic response to allow a few individuals to persist long enough to survive and reproduce in the new environment and pass on the new material or epigenetic effect leading to adaptive evolution. Hence, the non-adaptive character by itself can become an adaptive mechanism in the altered environment.

When the plant is unable to compensate for environmental stress and it leads to deleterious influence on the plant it is known as injurious plasticity. For example, in an arid environment, if the plant cannot maintain high water potential or if a plant produces less extensive rhizome systems in a more compact soil, in both cases growth is affected (Schmid and Bazzaz, 1990).

However, when there is no response of a species to environment vagaries, with no effect on fitness, then it is known as neutral plasticity (Alpert and Simms 2002; Callahan et al., 2005; Ghalambor et al., 2007).

Factors influencing phenotypic plasticity

A number of heterogeneous environmental factors can contribute to developmental changes in plants. When these changes occur over days, weeks, or months those plants that can alter certain features better under the new conditions is more likely to survive and reproduce.

Light

One of the expressions of plant phenotypic plasticity is the modification of leaf traits in different light environments. The most important leaf trait affected is specific leaf area (SLA-the ratio between leaf area and leaf dry weight; Gratani, 2014). A strong correlation exists between leaf thickness and light saturation rate of photosynthesis per unit leaf area (Dorn et al., 2000). Sun leaves have higher photosynthetic rate compared to shade leaves which is based on leaf lamina thickness per unit leaf area (McClendon and McMillen, 1982). Another important trait influenced by light is the anthocyanin pigmentation. Anthocyanins are produced in leaves in response to excess light, temperature and osmotic extremes, and serve as a reversible plastic mechanism for the protection of photosynthetic machinery. Growth of internodes and leaf angles are affected by both quantity and quality of light (Franklin and Whitelam, 2005)

Temperature

Plant species have an optimum range of temperature requirement for growth and development. When temperatures are higher or lower than normal, it may contribute to abnormal growth such as elongation of petiole and increased water loss leading to reduction in yield (Crawford et al., 2012). Temperature cues are important for floral evocation; hence flowering time is an important character that has shown to be under both environmental and genetic control. Changes in temperature triggers a chain of events which induces floral initiation and flowering, provided the plant has completed its juvenile stage. Due to climate change, such cues may not be reliable if they occur at the wrong time with respect to the lifecycle and ecology of a species. Induction of such environmental cues or signals which can elicit a response scheme might contribute to maladaptive plastic changes in plants.

Water

In addition to water, various other factors such as soil temperature, nutrients and pH affect root architecture of plants. Adaptation of roots to various environmental factors is very important in crop growth and yield. Morphological plasticity of root characters such as root tip diameter, gravitropism and rhizo-sheaths allow the plants to adapt to new situations which may also be useful for improving water use efficiency in crop species. Such plastic responses have been observed in Mesembryanthemum crystallinum, a native of Africa, Western Asia and Europe. The plant normally has a prostrate succulent nature and is covered with large glistening bladder cells or water vesicles. It is also commonly known as ice plant or crystalline ice plant. Bladder cells are enlarged epidermal cells. The main function of ‘bladder’ is to reserve water. Under normal condition, the plant has C₃ metabolism but when exposed to water or salt stress, it shifts from C₃ ...

Table of contents

• Cover Page
• Half-Title Page
• Title Page
• Copyright Page
• Dedication
• Foreword
• Preface
• Table of Contents
• Abbreviations
• 1. Phenotypic Plasticity: Concepts and Recent Advances
• 2. Plant Acoustic Responses: Concept and Significance
• 3. Spectral Manipulation of Plant Responses
• 4. Geomagnetic Responses in Plants
• 5. Electricity from Living Plants: Myth or Reality?
• 6. Plant Architecture: Evolution Diversity, Regulation and Scope
• 7. Plant Neurobiology: A Paradigm Shift in Plant Science