Phototropic And Photomorphogenic Responses Biology Essay

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Photomorphogenesis: Its the light-triggered and non-directional plant development. It can result in complex form changes and its also accountable for flowering which is a example form of photomorphogenesis

The 1st step of phototropic & photomorphogenic responses is the perception of light. Photomorphogenetic events are known to be associated with red light perception of plants. Phototropic events are known to be linked to blue light perception of plants. Phytochrome is the hormone in all groups of plants and is found in two interconvertible types: Pf and Pfr. It is composed of two parts: a smaller chromophore, and a bigger apoprotein. Phytochromes also take part in numerous signaling pathways that ultimately culminate in gene expression. Some pathways also have G proteins or protein kinases. Even though phytochrome exists in cytoplasm, it comes into the nucleus to allow transcription of light response genes. When Pr is converted into Pfr, it's capable of entering the nucleus. Once it's in the nucleus, Pfr binds with proteins that form a "transcription complex" which ultimately results in the expression of light-regulated genes. This is known as protein-binding site of phytochrome, and it's critical for interaction with plenty transcription factors. In protein-kinase signaling pathways. When phytochrome converts to Pfr form, the protein kinase domain of the apoprotein may immediately phosphorylate a serine and amino terminus of the phytochrome. It could also phosphorylate another protein's serine that also contribute to light signaling. This triggers a signaling cascade that's capable of activating transcription factors and ultimately results in light-regulated genes' transcription.

Gravitropism: It's the plant's response to Earth's gravitational field. Auxin is the hormone involved in this.

Four steps that result in gravitatropic response

First the cell senses gravity

The cell senses gravity and then transduces a physiological signal from a mechanical signal

The physiological signal is next transduced both within the cell and externally to other cells

Differential cell elongation: impacts cells in up/down sides of root or the shoot.

Today's theory towards the 1st steps of gravity perception is that within shoots, gravity is sensed along the length of the stem in the endodermal cells that surround the vascular tissue, and signaling occurs near outer-epidermal cells. In the roots, the cap is the place of perception of gravity and the signal has to instigate differential elongation (and division) in the elongation zone.

Thigmotropism: It's the growth (directional) of plants or plant parts with regards to response to external contact (objects, animals, other plants). Auxin and ethylene are 2 hormones used in thigmotropism.

4 other recognized types of tropisms: phototropism, gravitropism, circadian rhythms, heliotropism


Dormancy: It's essentially a plant process responding to water/temperature/light.

An example of dormancy's "adaptivity" and ability to allow plants to survive harsh conditions often exists in temperate regions during winter. In such areas, scarcity of water and freezing temperatures plant growth very hard. Throughout winter, the deciduous buds and shrubs become dormant, and apical meristems are sufficiently protected due to their location inside enfolding scales. Several perennial herbs often remain underground and exist in the form of stout stems/roots that are packed with food. Dormancy often begins with leave dropping (deciduous trees do this in fall).


7 Major types of plant hormones: Cytokinins, Auxins, Gibberellins, Brassinosteroids, Ethylene, Oligosaccharins, Abscisic Acid





Promotes step elongation as well as growth; helps increasing plasticity for cell walls; creates adventitious roots; hinders leaf abscission; promotes cellular division

In apical meristems; other immature plant parts


Assists cell division stimulation; promotes development of chloroplasts; delays process of aging for leaves; promotes formation of buds

In root apical meristems; immature fruits


Helps allows stem elongation; stimulates production of enzymes in seeds that are germinating

Tips of roots and shoot; seeds


Same function as auxins and cytokinins; overlapping functions

Pollen; immature seeds; shoots; plant leaves


Assists pathogen defense of plants; helps reproductive development

Cell walls of plants


Controls leaves, flower, fruit abscission; promotes ripening of fruit

Several plant areas like fruits, shoots, apical meristems, leaf nodes, aging flowers, fruits that are ripening

Abscisic acid

Inhibits the growth of buds, has control over closure of stomata, can control seed dormancy, hinders hormonal effects in plants

Leaves, fruits, root caps, plant seeds

The acid growth hypothesis essentially depicts the auxin linking to cell wall expansion. It says that auxin triggers cells (that are responsive) to transport H+ ions from cytoplasm to space of cell wall. This whole process subsequently lowers the plant's pH and subsequently triggers enzymes that are capable of breaking the bonds between cell wall fibers. This hypothesis has been experimentally corroborated in several ways.

The environment influences flowering

Competence: It's essentially the ability to do something efficiently

Phase Change: it's the transition that happens in plants that wish to become competent to make response to external/internal signals that instigate formation of flower.

3 genetically regulated pathways to flowering that have been identified are temperature-dependent pathway, light-dependent pathway, and gibberellin-dependent pathway. Another one is autonomous pathway.

Photoperiodic Flowering Pathway: essentially a light signaling or "circadian rhythm" that decides plant life cycles.

Short-day Plants: Plants who are active throughout the day for minute intervals.

Long-day Plants: Plants who are active for nearly the whole day

Day-neutral Plants: plants who are active no matter day or night.

2 types of f molecules involved in day length perception are phytochromes and cryptochromes

Vernalization: IT happens during germination; its essentially the seed cooling for the purpose of speeding up flowering when its planted.

Carpels, petals, stamens, and sepals are the 4 floral organs formed at floral meristem.

Megaspore-derived female gametophyte exists within the "female" plants' ovules. It behaves like an embryo sac in plants that are flowering, and it produces egg cells for the purpose of fertilization. The ovule is home to female reproductive cells. It is made of integuments that compose the plants nucleus and plant's outer layer.


Structure of Flowers

Formation of Angiosperm Gametes

The microsporangium of plants ("male") produce pollen grains through microsporogensis. During this process, the diploid sporogenous cells produce 4 microspores. Thus occurs meiotic cell division takes place, and as a result, 4 microspores are made. These subsequently begin to produce pollen, which is essentially a male reproductive "spin-off". Pollen grains possess a polidy is half the parent cell's amount.

The embryo sac's formation in the flower's ovule is crucial for plant reproduction. Its triggered by pollen that's transported (by other organisms, wind, etc.) from male to female plant organ. The pollen then goes to the female ovule and begins to fertilize to the female eggs in the sac of the embryo. The embryo sac's cells' ploidy (after the eggs have fertilized) is now completely the same as the chromosome number as the parent cells contained.


Pollination: It's essentially a process where pollen goes from male plants to the female plant sex organ/cells. It is transferred in plant reproduction for the purpose of plants' sexual reproduction.

2 main types of flowering plants pollination are self-pollination and cross-pollination.

Self-pollination: it's essentially a process in which pollen goes from the anther to the same flower's stigma.


The fertilization process in plants is crucial for reproduction. The pollen starts out by entering the nuclei of the embryo sac of the female flower; this starts fertilization. The pollen is then taken by pollen tube to the ovule, in which it finds the eggs and therefore officially starts fertilization. Next the male pollen cells fertilize embryos that are found there. Because of meiotic cell division that happens in both egg and sperm cells (makes male pollen cells and embryos diploid) they become haploid within the embryo sac. When fertilization begins, cell division is fast and forms the structure into embryo. Once it is formed, it begins to grow into a seed and is maintained in dormancy until conditions that are favorable for germination of seeds comes about. This is fertilization in plants.

Endosperm is polyploidy; it is capable of having multiple varying numbers of sets of chromosomes. Majority of plants are normally triploid or diploid. The endosperm provides nutrition to seed the embryos. This nutrition is a lot of the times in starch form.

Seeds & Fruit

The angiosperm's integuments form the seed coat. 2 cotyldeons grow to bent shape in order to accommodate by the tightness of the seed. In some of the embryos, the shoot apical meristem is going to have already started a few leaf primordial. Early on in the angiosperm embryo's development, the embryo stops developing. In lots of plants theembryo development is halted right after the cotyledons and meristems differentiate. The integuments (the outer cell layers of the ovule) form into a more or less impermeable seed coat which closes over the seed with its stored food and dormant embryo.

Seeds are a crucial adaption.

Seeds maintain dormancy even when there are bad conditions and delay development until there are better conditions. If there are marginal conditions, plants can allow some seeds to germinate because some may survive while others can stay dormant

Seeds can have maximum protection to the new plant at its most weak and vulnerable point.

Seeds store food that lets the new plant grow and develop prior to the start of photosynthetic activity.

Seeds are adapted and ready for the purpose of dispersal; this allows plant genotypes to move into new habitats.

Food storage takes place in endosperm during the process of embryogenesis. The endosperm is the tissue that is made in the flowering plants' seeds that takes care o the plant during fertilization. It provides starch nutrition and provides proteins and oils to the seed that is still growing.

Seed: it's a plant's reproduction unit. Seeds can germinate and grow into adult plants.

Seeds are crucial for angiosperms. They cause angiosperms to maintain reproductive line. Seeds are crucial to living because they allow flexibility during germination of seeds. Ex. If a plant colony is entirely eliminated because of environmental causes, the reproductive line will survive due to seeds' dormancy. This essentially means that the seeds are capable of germinating whenever they want to (so long as there are suitable conditions). Thus angiosperms can continue to live no matter how harsh conditions are.

Fruit: they're products of seed-possessing and nutrient-possessing plants. They can be eaten and are meant to proliferate seeds into the habitat and environment for the purpose of extending plants' genetic lines.

8 types of fruit are:

Strawberry: they're red colored fruit that grow in climates that are rather temperature

Banana: they're yello fruit that grow in tropical climates. They're also C-shaped.

Apple: They're circular and red fruit that grow in temperate climates.

Grape: they're small fruits that can be green or purple. They're grown in temperature climates (especially around the Mediterranean sea)

Mango: Big yellow/orang colored. It has a "teardrop" shape. It's sometimes known as the "king of fruits". It's very sweet and grows in tropical climates.

Blueberry: They're small blue fruits that grow in temperature climates. They're full of antioxidants.

Watermelon: they're HUGE fruits with thick outer-skin (that is green and crisp), and soft red fruit inside. Watermelons grow in temperature and tropical climates alike. They're mainly water.