Effects Of Photoperiodism On Plants And Animals

 Photoperiodism is the response of plants and animals to the length of day and night. Photo means "light" and period means "duration". Although the specific mechanisms underlying the ability to measure day length differ between taxonomic units (taxa), individuals can somehow determine the time of year, the length of the daily photoperiod, and whether day lengths are increasing or decreasing. Organisms' ability to predict seasonal changes provides some advantages. Thus, environmental conditions are optimal for them, such as breeding in spring or summer to take advantage of warmer weather, producing flowers at the right time of year to attract pollinators (pollinators), camouflaging fur color against predators, or migrating to avoid harsher winter conditions. Most seasonal events are triggered by a photoperiod of a certain length. This specific photoperiod length is called the critical day length or critical photoperiod. The length of the critical photoperiod varies not only between species, but also between the same species at different latitudes.

Photoperiodism in Plants

Almost all plants are capable of photosynthesis, and photosynthesis is the key to the survival of these plants. Photosynthesis enables plants to produce sugar molecules that act as fuel and building materials. Plants also respond in other ways to light, and sometimes to certain wavelengths of light. These non-photosynthetic responses allow plants to adapt to their environment and optimize growth. Some types of seeds sprout only when they receive sufficient light (along with other signs of initiation). Some plants have ways of detecting whether they are in the shade of neighboring plants based on the quality of light they receive. So they can increase their upward growth to outdo their neighbors and get a larger share of sunlight.

Photoperiodism is the regulation of physiology or development in response to day length. Most flowering plants are capable of sensing changes in the season (i.e. the length of day and night) and blooming at the right time. To do this, they use photoreceptor (light sensitive) proteins called "phytochromes". Phytochromes contain chromophores. In plants, light is detected by special molecules called photoreceptors, which consist of a protein attached to a light-absorbing pigment called a chromophore. When the chromophore absorbs light, it causes a change in the shape of the protein, altering its activity and initiating a signaling pathway. The signaling pathway results in a response to the light cue, such as a change in gene expression, growth, or hormone production.

Some plant species require certain lengths of day or night (critical photoperiod) to flower, i.e. to enter the reproductive stage of their life cycle. The critical time may vary in different plants. Depending on the critical time, plants can be divided into the following three categories:

1-Long Day Crops

Long-day plants bloom when the day length is above a certain threshold or when the days get longer. Plants that fall into this category are also called "short night plants." They require more than the critical light period (usually 14-16 hours) for flowering. The light period is very critical in long day plants. Extending the light period or short exposure to light during the dark period increases flowering in these plants. Where a day length is too short, long day plants are generally not found. Spinach, radish, mallow, lettuce, chickpea, rye, dill, barley, sugar beet, wheat are long-day crops.

2-Short Day Plants

Short-day plants bloom when the day length is below a certain threshold or when the days get shorter. They do not bloom when the day is long and the night is short. Plants in this category are also called “long night plants”. They require less than the critical light period (approximately 8-10 hours) and a continuous dark period (approximately 14-16 hours) to bloom. The dark period is critical for short day plants and should be continuous. These plants will not bloom if the dark period is briefly interrupted by light. Short day plants are not usually found in areas where the day length is very long. Plants such as soybeans, tobacco, millet, rice, strawberries, hemp, potatoes, spurges, chrysanthemums are short-day plants.

3-Day Neutral Plants

Not all plants are short-day or long-day plants. Some plants are day neutral plants. These plants do not meet the critical time constraint, the flowering is not dependent on the day length. In other words, they are unprivileged plants that are neutral to the length of the day or night. Plants such as tomatoes, sunflowers, peas, roses and yellow pine are day neutral plants.

Scientists use the concept of photoperiodism to classify and locate plants.

Photoperiodism in Animals

affects their hibernation and also their sexual behavior. For example, the frequency with which the canary bird sings or sings depends on the length of the day. Variations in day length, while probably not of direct significance to most animals, provide the most accurate indication of the time of year, thus allowing individuals to Allows them to predict seasonal conditions.

Photoperiodism Effect in Insects

Diapause (a state similar to hibernation, inactive period) in insects is directly related to the photoperiod. Pupae of Apatele rumicis (a moth variety) enter diapause in photoperiods of less than 15 hours, but skip this pause at a photoperiod of 16 hours.

Photoperiodism Effect in Birds

It has been found that the gonads of birds become active with increasing luminosity in summer and regress during shorter periods of illumination in winter. After the breeding season, the gonads of the birds studied to date have been found to regress spontaneously. This is the refractory period, in which light cannot induce gonadal activity, and its duration is regulated by day length. Short days hasten the end of the refractory period; long days make it longer. After the refractory period is complete, advanced stages begin in late autumn and winter. During this period, birds become fat, migrate, and their reproductive organs increase in size. This process can be accelerated by exposing the bird to a long day photoperiod. Completion of the following period brings the birds to the breeding stage. There is a similar photoperiodic response in cyprinid fish.

Photoperiodism Effect in Mammals

Seasonal photoperiodism cycles affect the reproductive cycles of many mammals, such as white-tailed deer and flying squirrels. For example, the flying squirrel has two breeding peaks in the Northeastern United States, the first in early spring, usually in April, and the second in late summer, usually in August.

Some species (sheep, goats, deer) are known as "short-day breeders" because their breeding season occurs mainly during the shorter days (summer and autumn).

Some species (hamster, mink) are known as "long day breeders". The gestation period in these animals is relatively short (1-2 months), mating, pregnancy and lactation occur on long days in late spring and early summer. In hamsters, the testicles are small on short days (i.e. winter) but grow significantly on long days. The duration of the critical photoperiod in hamsters is 12.5 hours. When the photoperiod falls below this, the testicles shrink in size and sperm production stops. When the duration of the photoperiod is longer than 12.5 hours, the testicles enlarge in size. The critical day length of female hamsters is similar so that the reproductive cycles of both sexes overlap. Although horses have long gestation periods, they are included in the group of those who breed during the long day. They breed in late winter or spring, and their offspring are usually born in the spring.

Melatonin is a hormone produced by the pineal gland and is related to day length. Melatonin inhibits reproduction by blocking prolactin, a gonad-stimulating hormone. Suppression of prolactin causes gonad regression. Melatonin is produced by a photoperiodically controlled cycle. Its precursor, serotonin, is converted to melatonin by a process involving the enzyme N-acetyltransferase (NAT). NAT has a loop with an amplitude suppressed by constant light but free running in constant darkness. Normally, NAT and melatonin are produced at night.

In mammals, photoperiodic information can even be passed on to developing fetuses in the womb, so that the summer or winter phenotype can begin to develop before birth. Thus, photoperiodic rodents born in the spring grow to adult size, enter puberty and begin to breed in 6-8 weeks, a sibling born in the fall does not grow or enter puberty for 4-5 months. Day length can be used as a definitive environmental factor to probe gene expression during phenotypic development in the laboratory.

Photoperiod and Immune Function

Short day lengths often elicit many immune responses in the laboratory. According to the theory of work in the laboratory, increased immunological defenses at short day lengths serve to counter the stressful effects of winter conditions, including reduced food availability and increased thermoregulatory demands.

Worldwide, resource availability and environmental conditions change predictably over the course of a year. Pathogens, food availability, and ambient temperatures all change seasonally. Therefore, organisms that thrive at different times of the year are likely to experience different environmental conditions. Studies examining the effects of birth season on immune function are relatively few but best documented in humans. It is possible to draw inferences about the immune system by examining epidemiological data for seasonal changes in immune-related disease states. For example, in industrialized countries, the environment early in life has a profound effect on health outcomes. Cytokine responses and asthma, allergy, Season of birth effects have been reported for numerous health conditions, including inflammatory bowel disease and multiple sclerosis. Although the direction and strength of these associations vary between the specific immunological component and the disease state under investigation, seasonal differences are still evident.

Photoperiod and Non-reproductive Behaviors

While many seasonal behaviors in photoperiodic mammals are specifically reproductively related, there are several behavioral traits independent of gonadal steroids, such as photoperiod-adjusted affective responses and aggression. Immunological, hormonal, and neural factors, all modulated by the photoperiod, combine to alter behavioral output. Emotional disorders are often considered maladaptive; however, photoperiodic changes in the effect may represent an adaptive strategy to conserve energy during energy bottlenecks encountered during the short days of winter. In addition, conservation of energy during the short days of winter may be the putative mechanism that drives photoperiodic modulation of aggression.

The photoperiod can modulate learning and memory, a potentially functional consequence of altered hippocampal morphology in addition to changes in social and affective behavior. Seasonal differences in spatial learning and memory have been reported in rodents, fox squirrels (Sciurus niger), deer mice (P. maniculatus), and white-footed mice.

Effects of Photoperiod in Early Life

In addition to seasonally variable phenotypic changes, photoperiod history may also influence the adult phenotype. Many adult diseases and disorders are affected by the season of birth. For example, in humans, the season of birth has been associated with a number of disorders and pathologies, including increased risk of various types of cancer, susceptibility to pulmonary fibrosis, metabolic disorders, and susceptibility to cardiovascular disease. In both the northern and southern hemispheres, short-day late pregnancy and childbirth are associated with increased prevalences of schizoaffective disorder, autism, and major depression in the adult population. Season of birth may also affect subtypes of affective disorders differently, as long sunrises are associated with an increased risk of deficiency subtype of schizophrenia and risk of completed suicide.

Antenatal photoperiod conditions can regulate adult emotional behaviors and interact with post-weaning photoperiod conditions to regulate expression of affective behaviors in adults. Hamsters exposed to short days early in life have increased anxiety and depressive responses as adults. In addition, exposure to shorter days in hamsters born with long days also increases anxiety and depressive-like behaviors, and exposure to shorter days before birth reinforces these differences in adulthood. The lasting behavioral effects of early life photoperiod experience are not limited to rodents. Season of birth effects in humans may reflect endocrine changes in hypothalamic-pituitary-adrenal axis sensitivity. In a population of patients suffering from unipolar major depressive disorder,