Why does the sunflower disk rotate with the sun?

Sunflower is positive because the morning sun shines on the young stem of sunflower, and the auxin content secreted by plants rises on the back of sunflower, which stimulates the cells on the back to elongate, and the stem will bend to the light source, thus slowly rotating to the sun.

After the sun went down, auxin was redistributed, and the sunflower slowly turned back to its original position and stood upright. In the morning, after the sun rose in the east, it began to "move" again. But once the disc is in full bloom, it no longer turns to the sun, but is fixed in the east.

Because the pollen of sunflower is afraid of high temperature, if the temperature is higher than 30℃, it will be burned and lose its vitality, while the disk of sunflower is fixed in the east, which can avoid direct sunlight at noon and reduce radiation.

The dish is exposed to sunlight in the early morning, which helps to dry the dew condensed at night and reduce the possibility of being attacked by germs; In the cold morning, the sun turns the sunflower tray into a warm nest, which can attract insects to stay there to help pollinate and reproduce. With the approaching of sunflower growth and maturity, the stem is no longer tender, the tissue structure tends to age, the auxin content secreted by plants decreases, the elongation and thickening of stem cells slow down, and the growth process basically ends.

At the same time, there is also a slow process due to inhibition. When the stems of sunflowers stand upright at night, most of the disks can still face the east in the morning, and the disks can be slowly fixed in the southeast.

Extended data:

Characteristics of sunflower

1, salt tolerance

Sunflower has strong salt tolerance, and when the soil salt content is 0.4%, the whole seedling can be produced. In bud stage, when the salt content of 0 ~ 5 cm and 5 ~ 1~5cm soil layer is 0.42% and 0.445% respectively, sunflower can still grow normally. Sunflower not only has strong saline-alkali tolerance, but also has salt absorption performance. According to laboratory tests, sunflower stems contain about 0.5% sodium chloride, which is one of the crops for biological alkali control in saline-alkali land.

2. Drought tolerance

Sunflowers have strong drought resistance. According to the test, after nearly 40 days of drought before and after flowering, the sunflower still grows normally when the soil moisture content is 8.8%, 15. 12% and 19.6% respectively.

3. Waterlogging tolerance

According to the verification, more than 90% of the plants have not died after growing for 40 days in the flooded state (50 cm water on the ground), and there are still gains. This is because the roots and stems of sunflower are well developed in ventilated tissues, and the ability to proliferate new roots after meeting water is quite strong. The increment of new roots in 5 days is equivalent to 2 1% of total roots.

References:

Baidu encyclopedia-sunflower