Long Day Plants

Long-day plants require more exposure to light in order to initiate flowering. Flowering is initiated when they are exposed to a period of light that is longer than the critical photoperiod.

Photoperiodism

Photoperiodism is the response of plants to varying periods of light and dark. Certain plants require a specific combination of light and dark periods to initiate flowering, with the relative duration of the light and dark periods being important for certain physiological reactions.

Garner and Allard first observed that daylight length was significant in photoperiodism. It was later discovered that it is the length of night that controls the photoperiodic response.

Leaves perceive the light and dark periods which, when receiving the correct amount of photoperiod, produces a hormone that triggers flowering. This hormone is transported to the shoot apices and induces flowering.

On the basis of the amount of dark and light periods required, the plants can be classified into three types:

  • Short-day plants
  • Long-day plants
  • Day-neutral plants

  1. Long Day Plants: They need to be exposed to light for a period longer than the critical period to make them flower.

  2. Short Day Plants: They require exposure to light for a period shorter than the critical period in order to induce flowering.

  3. Day-neutral Plants: Plants whose flowering does not depend on the photoperiod are referred to as day-neutral plants.

The critical photoperiod is different for different plants. Photoperiodism induces the formation of floral buds on shoots. The shoot apices get modified to the flowering apices at the time of flowering, but they do not perceive photoperiods. Photoperiods are perceived by leaves.

Many flowering plants detect seasonal changes in the photoperiod or night length through photoreceptor proteins, such as phytochromes or cryptochromes.

Phytochromes are sensitive to light in the red and far-red regions of the visible spectrum, while Cryptochromes are flavoproteins and sensitive to blue light and UV-A.

Other than flowering, photoperiodism also influences the seasonal growth in stems, roots and the fall of leaves.

Long Day Plants

Long-day plants require light way above the critical photoperiod to induce flowering, typically during the long days of early summer and late spring.

The obligate long day plants flower strictly only when the plant is exposed to the required photoperiod, whereas the facultative long day plants flower in any photoperiod, but flowering is faster under a certain photoperiod.

Examples of long day plants are as follows:

Long day obligate plants:

  • Carnation (Dianthus)
  • Oat (Avena)

Long Day Facultative Plants:

  • Wheat (Triticum aestivum)
  • Pea (Pisum sativum)

Short Day Plants

Short day plants require light below a critical photoperiod to induce flowering. They typically bloom during the seasons when days are shorter in length, such as during the summer or fall. A continuous period of darkness is necessary for flowering in short day plants.

The obligate short day plants flower exclusively when a certain dark period is provided, while facultative short day plants can flower in any photoperiod, but flowering tends to be faster when a certain dark period is present. The length of the dark period required for flowering can vary between different plants.

Examples of short day plants are as follows:

Short Day Obligate Plants:

  • Hyacinth Bean (Lablab purpureus)
  • African Marigold (Tagetes erecta)

Short-day Facultative Plants:

  • Cotton (Gossypium)
  • Soybeans (Glycine max)
  • Rice (Oryza)

Difference between Long Day and Short Day Plants

Long day plants (LDPs) require a long period of light exposure in order to flower, while short day plants (SDPs) require a short period of light exposure to flower. LDPs are typically found in higher latitudes, while SDPs are typically found in lower latitudes. The length of the day and the intensity of light will determine the type of plant that will grow.

| Long Day Plants |

| Short Day Plants | represents a table

Column 1 Column 2
A B
Column 1 Column 2
A B

| They flower when exposed to a period of light longer than the critical photoperiod.

They flower when they are exposed to a period of light shorter than the critical photoperiod. represents a table

Name Age
Bob 25
Name Age
Bob 25

| The length of the light period that is continuous is more critical.

| The uninterrupted dark period is more crucial.

Item Price
Apples $1.00
Item Price
Apples $1.00

If a flash of light interrupts the dark period, flowering is stimulated.

| They do not flower if a flash of light interrupts their dark period.

Name Age
John 30
Name Age
John 30

| Flowering is not inhibited even if the dark period interrupts the long period of light.

| If the long period of light is interrupted by a dark period, flowering is not stimulated. represents a table

Name Age
John 25
Name Age
John 25

| They typically bloom during late spring or early summer.

| They typically bloom during early spring or fall. represents a table

Column 1 Column 2
Value 1 Value 2
Column 1 Column 2
Value 1 Value 2

Gibberellic acid induces flowering.

Gibberellic acid generally does not induce flowering. represents a table cell

Name Age
John 32
Name Age
John 32
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