Photosynthetic pigments and optical properties of chloroplasts

The leaf of orchid is the main organ of photosynthesis, and chloroplast is an important organelle of photosynthesis, which contains a variety of pigments to adapt to the function of photosynthesis, and is also the main factor in the emergence of line art. Chinese orchids are mostly shade-tolerant plants with many and large chloroplasts, which can accept the maximum amount of light in low light.

General chloroplasts contain four pigments, namely, chlorophyll a, chlorophyll b, carotene and lutein. Chlorophyll a (C55H72O5N4Mg) is blue-green, chlorophyll b (C55H70O6N6Mg) is yellow-green, carotene (C40H56) is orange, and lutein (C40H56O2) is golden. The different proportions of these photosynthetic pigments in the leaves constitute the basis of the different arts of the orchid.

In addition to the above four pigments, the vacuoles of leaf cells also contain anthocyanins, pigments and so on. They exist mainly in petals, and anthocyanins are also found in some young or withered leaves. Because as one of the national orchid appreciation trends of color flower art, its different colors of flowers or red buds, yellow buds are determined by the content of anthocyanins and pigments.

Of the four pigments of chloroplasts, the main one that plays the role of photosynthesis is chlorophyll a, which converts absorbed light energy into chemical energy. The other three pigments can also absorb light energy, but the light energy they absorb must be transferred to chlorophyll a to work.

Among the optical properties of chlorophyll, the most important thing is that it can selectively absorb light energy and have fluorescence phenomenon.

By observing the absorption spectra of chlorophyll an and b, we can see that they have two largest absorption parts, one in red.

The light part; the other is in the blue-purple part. Chlorophyll does not absorb green light. The light that is strongly absorbed by chlorophyll is the most efficient light in photosynthesis. The absorption spectra of carotene and lutein show that they can only absorb blue-purple light, and the absorption range of blue-purple light is wider than that of chlorophyll. Therefore, the line art orchid should increase the light of blue and purple light.

The direct light of the sun contains more red light, and the scattered light contains more blue-purple light. In overcast days or shady places, or under the shade shed, orchid plants can use scattered light for photosynthesis, and carotenoids can absorb more blue-purple light. Transfer energy to chlorophyll a, so that plants can still carry out a certain intensity of photosynthesis under weak light. As the line magnolia contains more carrots, so the cultivation conditions should be a little shady, on the one hand, it can increase and absorb the blue-purple light of scattered light, and on the other hand, it can prevent direct red light from burning leaves. However, the light energy absorbed by carotenoids will eventually be transferred to chlorophyll for photosynthesis, so "Gaoyi" line orchids or "ghost buds" gradually die due to lack of chlorophyll nutrients. In addition to the advanced artistic development of "Jinyi" or "Baoyi", an important thing is that it maintains a certain amount of chlorophyll, which not only meets the appreciation requirements of art students, but also meets the physiological needs of orchid plants. therefore, these artistic orientations have always been the goal and mainstream of Yilan appreciation.

The formation and destruction of chlorophyll are closely related to light, temperature, mineral nutrition, water and oxygen.

Light is a necessary condition for the formation of chlorophyll. New plants growing in the dark are yellow and white and turn green soon after seeing light. This is the result of the conversion of prochlorophyll formed in the dark to chlorophyll in the right light. Therefore, the new buds of many "dragon roots" or colored peanuts are yellow pigment at the beginning, which is due to the lack of light time, the original chlorophyll is not transformed into chlorophyll, so these new buds will gradually return to green under light conditions. However, restricted by some conditions, the original chlorophyll synthesized by the plant can not be reduced to chlorophyll under light, and the plant can not grow up.

Too strong light can also lead to the destruction of chlorophyll, so the yellowish brown leaves of the blue plants cultivated in the shade shed are caused by this reason.

The formation of chlorophyll requires some mineral elements. Some components of chlorophyll, such as magnesium and nitrogen, apply a large amount of nitrogen fertilizer, which will make the leaf color dark green. Iron plays a catalytic role in the formation of chlorophyll, and copper and zinc are the activators of some enzymes in the process of chlorophyll formation. If the plant lacks these elements, it will lead to the symptom of green deficiency.

Most of the biosynthesis of chlorophyll involves enzymes. Temperature affects the activity of enzymes, which also affects the synthesis of chlorophyll. It can be referenced that the lowest temperature for chlorophyll formation is 2: 4 ℃, the optimum temperature is 26: 30 ℃, and the highest temperature is 40 ℃. When the temperature is low, the green is not dark, and the red and yellow is more bright. When the temperature decreases gradually, the speed of chlorophyll formation is less than the rate of destruction, chlorophyll gradually disappears, the color of lutein and carotene shows, and the leaves change to yellow or orange. Under the condition of low temperature, the new buds or low temperature for a long time, the color flowers such as "Taoji", "Yingji" and so on, are more colorful. Under the condition of high temperature, the design and color of "Yufei" is also more green. This is due to the low temperature, the synthesis of chlorophyll is less than the decomposition process, carotenoids appear, and more sugars in the body form anthocyanins. When the temperature is high, the effect will be reversed. The temperature in Japan and other places is relatively low, and the cultivation of line orchids and colored orchids are more obvious, which is also due to this effect. The cultivation of "imperial concubines" in Japan to produce more attractive colors is an obvious example.

Lack of water and oxygen, the formation of chlorophyll is inhibited, but also promote the decomposition of original chlorophyll. Therefore, the leaves generally show the phenomenon of yellowish brown and fade green during severe drought or waterlogging.

Therefore, the environmental conditions for the cultivation of magnolia should be lower temperature, higher shading, limited application of some mineral elements and scientific replenishment of water, so as to cultivate high-grade national orchid works of art. (Liu Zhongjian)